Imported: 17 Feb '17 | Published: 10 Jan '12

USPTO - Utility Patents

A position detecting device includes a position calculator that performs an optimization convergence calculation using an evaluation function that expresses an error between a measurement value and a theoretical value of magnetic field information of a detection target to calculate at least a position of the detection target; a storage unit that stores a final convergence result of the optimization convergence calculation performed by the position calculator; and a controller that determines whether a result of the optimization convergence calculation converges, suspends the optimization convergence calculation performed by the position calculator when the result does not converge, and performs, after a predetermined time has passed, a returning process of returning a state of the optimization convergence calculation to a converged state by causing the position calculator to perform the optimization convergence calculation based on the final convergence result.

This application is a continuation of PCT international application Ser. No. PCT/JP2008/067330 filed on Sep. 25, 2008 which designates the United States, incorporated herein by reference, and which claims the benefit of priority from Japanese Patent Application No. 2007-247922, filed on Sep. 25, 2007, incorporated herein by reference.

1. Field of the Invention

The present invention relates to a position detecting device that detects a position of a detection target based on a detection result of a magnetic field emitted from the detection target.

2. Description of the Related Art

In the technical field of endoscope, a capsule endoscope that can be introduced into a digestive canal of a subject, such as a patient, has conventionally been developed. The capsule endoscope is swallowed from a mouth of the subject to acquire images (hereinafter, occasionally referred to as “in-vivo images”) inside internal organs of the subject while moving in the digestive canal with peristaltic movements, and wirelessly transmits acquired in-vivo images to a receiving device located outside the subject. The capsule endoscope sequentially acquires in-vivo images of the subject since it is introduced into the digestive canal of the subject until it is naturally excreted from the subject.

Furthermore, a system that guides (that is, magnetically guides) a capsule endoscope introduced into a subject by a magnetic force has been proposed (see, for example, International Publication No. WO2005/112733 Pamphlet). In this system, an LC resonance circuit (hereinafter, “LC marker”), which uses a coil and a capacitor, and a magnet are incorporated in the capsule endoscope. The position of the capsule endoscope is detected based on a detection result of an induced magnetic field emitted from the LC marker. The magnetic field formed at the detected position is caused to act on the magnet in the capsule endoscope, thereby magnetically guiding the capsule endoscope in the subject.

A position detecting device that detects the position of a capsule endoscope generally detects, using a plurality of detection coils, an induced magnetic field emitted from an LC marker in the capsule endoscope due to application of an external magnetic field. The position detecting device calculates the position of the capsule endoscope based on a detection result of the induced magnetic field. The position detecting device sets an evaluation function that expresses an error between a field-strength detection value (a measurement value) of each detection coil and a field-strength theoretical value of each detection coil. This field-strength theoretical value is a field-strength value of an induced magnetic field theoretically detected by each detection coil from the LC marker in the capsule endoscope that is in a state of being directed to a provisional direction at a provisional position. The theoretical value is calculated in accordance with a predetermined operation expression. The position detecting device performs optimization convergence calculations based on such an evaluation function to calculate the provisional position and the provisional direction as the position information and direction information of the capsule endoscope. The provisional position and the provisional direction are values at which an error value in the optimization convergence calculation becomes equal to or less than a predetermined threshold (that is, converges). Such a position detecting device repeatedly performs the optimization convergence calculation by using a result of optimization convergence calculation, which is obtained when the error value in the optimization convergence calculation converges to a value equal to or less than a predetermined threshold, as a starting point of calculation for the next optimization convergence calculation. The position detecting device sequentially calculates the position information and direction information of the capsule endoscope.

A position detecting device according to an aspect of the present invention includes a position calculator that performs an optimization convergence calculation using an evaluation function that expresses an error between a measurement value and a theoretical value of magnetic field information of a detection target to calculate at least a position of the detection target; a storage unit that stores a final convergence result of the optimization convergence calculation performed by the position calculator; and a controller that determines whether a result of the optimization convergence calculation converges, suspends the optimization convergence calculation performed by the position calculator when the result does not converge, and performs, after a predetermined time has passed, a returning process of returning a state of the optimization convergence calculation to a converged state by causing the position calculator to perform the optimization convergence calculation based on the final convergence result.

A position detecting device according to another aspect of the present invention includes a position calculator that performs an optimization convergence calculation using an evaluation function that expresses an error between a measurement value and a theoretical value of magnetic field information of a detection target to calculate at least a position of the detection target; a threshold storage unit that stores a threshold concerning a measurement value of the magnetic field information; and a controller that compares the measurement value of the magnetic field information with the threshold to determine a difference between the measurement value of the magnetic field information and the threshold, permits, when the measurement value of the magnetic field information is equal to or larger than the threshold, the optimization convergence calculation performed by the position calculator, and prohibits, when the measurement value of the magnetic field information is smaller than the threshold, the optimization convergence calculation performed by the position calculator.

The above and other features, advantages and technical and industrial significance of this invention will be better understood by reading the following detailed description of presently preferred embodiments of the invention, when considered in connection with the accompanying drawings.

A position detecting device, which is the best mode for carrying out the present invention, is explained below. A position detecting device used for a capsule guiding system that magnetically guides a capsule endoscope (an example of a capsule medical device) that captures in-vivo images of a subject is exemplified as an example of a position detecting device according to the present invention. However, the present invention is not limited to this embodiment.

FIG. 1 is a block diagram schematically depicting a configuration example of a capsule guiding system **1** according to a first embodiment of the present invention. As shown in FIG. 1, the capsule guiding system **1** according to the first embodiment includes a capsule endoscope **2** that captures in-vivo images of a subject, a receiving device **3** that receives the in-vivo images from the capsule endoscope **2**, a magnetic guiding device **4** that magnetically guides the capsule endoscope **2** introduced into the subject, an image display device **9** that displays the in-vivo images and the like captured by the capsule endoscope **2** in the subject, and a position detecting device **10** that detects position and direction of the capsule endoscope **2** in the subject.

The capsule endoscope **2** is an example of a detection target whose position and direction are detected by the position detecting device **10**, and is a capsule medical device that acquires an in-vivo image of the subject. Specifically, the capsule endoscope **2** has an imaging function and a wireless communication function in a capsule-shaped casing, and is introduced in the digestive canal of a subject (not shown) such as a patient. The capsule endoscope **2** sequentially captures in-vivo images while moving in the digestive canal of the subject, and wirelessly transmits image signals including acquired in-vivo images sequentially to the receiving device **3** outside the subject. The capsule endoscope **2** includes in the capsule-shaped casing a magnet **2***a *for enabling magnetic guidance by the magnetic guiding device **4**, and a magnetic field generator **2***b *that generates a magnetic field to be used for a detecting process of a position and direction by the position detecting device **10**. The magnet **2***a *is realized by a magnetic body such as a permanent magnet or an electromagnet, and moves following the magnetic field formed by the magnetic guiding device **4**. The capsule endoscope **2** moves due to an action of the magnet **2***a*. As a result, the capsule endoscope **2** is magnetically guided by the magnetic guiding device **4**. The magnetic field generator **2***b *is realized by using a coil or the like, and generates the magnetic field outside the capsule endoscope **2**. The magnetic field generated by the magnetic field generator **2***b *is detected by a magnetic field detector **11** in the position detecting device **10** described later.

The receiving device **3** has a plurality of receiving antennas **3***a *to receive the in-vivo images of the subject from the capsule endoscope **2** via the receiving antenna **3***a*. Specifically, the receiving antennas **3***a *are distributed and arranged on a body surface of the subject, into the digestive canal of which the capsule endoscope **2** is introduced, to capture a radio signal from the capsule endoscope **2** moving (or magnetically guided) along the digestive canal. The receiving device **3** receives the radio signal from the capsule endoscope **2** via the receiving antenna **3***a *to perform a predetermined demodulation process with respect to the received radio signal, and extracts an image signal included in the radio signal. The image signal extracted by the receiving device **3** includes the in-vivo image captured by the capsule endoscope **2**. The receiving device **3** transmits the image signal of the in-vivo image to the image display device **9**.

The magnetic guiding device **4** magnetically guides the capsule endoscope **2** and includes a magnetic field generator **5** that generates the magnetic field for guiding the capsule endoscope **2** in the subject, a coil power source **6** that supplies electric current to a coil (an electromagnet) of the magnetic field generator **5**, an operating unit **7** that operates magnetic guidance of the capsule endoscope **2**, and a magnetic field controller **8** that controls strength and direction of the magnetic field generated by the magnetic field generator **5**.

The magnetic field generator **5** is realized by combining a plurality of electromagnets such as a Helmholtz coil, to generate a magnetic field capable of guiding the capsule endoscope **2** in the subject. Specifically, in the magnetic field generator **5**, a three-axis orthogonal coordinate system (hereinafter, “absolute coordinate system”) formed of orthogonal three axes (X-axis, Y-axis, and Z-axis) is defined, to generate a magnetic field of a desired strength, respectively, in respective axial directions (X-axis direction, Y-axis direction, and Z-axis direction) of the absolute coordinate system. The magnetic field generator **5** forms a three-dimensional magnetic field formed by the magnetic field in the respective axial directions of the absolute coordinate system inside a three-dimensional space A**0** of the absolute coordinate system (that is, inside a space surrounded by the electromagnets in the magnetic field generator **5**), and applies the magnetic field to the magnet **2***a *in the capsule endoscope **2** positioned in the subject (not shown) on a bed, which has moved into the three-dimensional space A**0**. The magnetic field generator **5** magnetically guides the capsule endoscope **2** by the magnetic field. The magnetic fields in the respective axial directions of the absolute coordinate system generated by the magnetic field generator **5** (that is, rotating magnetic field and gradient magnetic field) are controlled by the current supplied from the coil power source **6** (an energization amount from the coil power source **6**).

As described above, the absolute coordinate system can be the three-axis orthogonal coordinate system defined with respect to the magnetic field generator **5** (that is, fixed to the magnetic field generator **5**); however, the absolute coordinate system can be a three-axis orthogonal coordinate system fixed to the subject (not shown) incorporating the capsule endoscope **2** in the digestive canal, or a three-axis orthogonal coordinate system fixed to a bed (not shown) on which the subject lies.

The coil power source **6** supplies the current for generating the magnetic field that realizes the magnetic guidance of the capsule endoscope **2** in the subject to the magnetic field generator **5**. The coil power source **6** has a plurality of power sources corresponding to a plurality of coils (not shown) forming the magnetic field generator **5**, and respectively supplies alternating current to the coils in the magnetic field generator **5** under control of the magnetic field controller **8**, to generate the magnetic fields in the respective axial directions of the absolute coordinate system.

The operating unit **7** is realized by using an input device such as a lever and an input button. The operating unit **7** inputs instruction information for instructing the magnetic guidance of the capsule endoscope **2** to the magnetic field controller **8** in response to an input operation by a user such as a doctor or nurse.

The magnetic field controller **8** controls the energization amount of the coil power source **6** with respect to the magnetic field generator **5** based on the instruction information input by the operating unit **7**, and controls a magnetic-field generation operation of the magnetic field generator **5** that generates the three-dimensional magnetic field under control of the coil power source **6**. In this case, the magnetic field controller **8** acquires position and direction information including respective pieces of information of current position and current direction of the capsule endoscope **2** in the subject from a controller **16** of the position detecting device **10** described later, and determines the strength and direction of the magnetic field to be applied to the capsule endoscope **2** based on the acquired position and direction information. The magnetic field controller **8** causes the magnetic field generator **5** to generate the magnetic field having strength and direction for realizing the magnetic guidance of the capsule endoscope **2** instructed by the instruction information from the operating unit **7**, at a current position of the capsule endoscope **2** in the subject. As a result, the magnetic field controller **8** controls the magnetic guidance of the capsule endoscope **2** at a desired position or in a desired direction in the subject.

The magnetic field controller **8** stores the strength and direction of the magnetic field applied to the capsule endoscope **2** in the three-dimensional space A**0** (specifically, in the subject) by the magnetic field generator **5** at the time of controlling the magnetic guidance of the capsule endoscope **2** as field strength information and field direction information. When transmission is instructed from the image display device **9**, the magnetic field controller **8** transmits the field strength information, the field direction information, and the position and direction information acquired from the position detecting device **10** to the image display device **9**.

The image display device **9** displays various pieces of information such as in-vivo images of a subject captured by the capsule endoscope **2**, and has a configuration of a workstation or the like that fetches various pieces of information from the receiving device **3** and the magnetic guiding device **4**, and stores and displays the fetched various pieces of information. Specifically, the image display device **9** fetches in-vivo images and the like of the subject from the receiving device **3**, and fetches the field strength information, the field direction information, and the position and direction information from the magnetic field controller **8**. The image display device **9** displays the various pieces of information such as in-vivo images, field strength information, field direction information, and position and direction information on a screen. The user such as a doctor or nurse checks the various pieces of information displayed by the image display device **9** to observe inside of the organs of the subject and performs the magnetically guiding operation of the capsule endoscope **2** using the operating unit **7**.

The position detecting device **10** detects the position and direction of the capsule endoscope **2** in the subject positioned in the three-dimensional space A**0** of the absolute coordinate system. The position detecting device **10** includes the magnetic field detector **11** that detects the magnetic field emitted from the capsule endoscope **2**, a position calculator **13** that calculates the position and direction of the capsule endoscope **2** based on a magnetic-field detection result by the magnetic field detector **11**, an input unit **14** that input various pieces of information, a storage unit **15** that stores various pieces of information, and the controller **16** that controls respective components of the position detecting device **10**.

The magnetic field detector **11** has a plurality of detection coils **12** to detect the magnetic field generated by the magnetic field generator **2***b *incorporated in the capsule endoscope **2**. Specifically, the detection coils **12** are arranged, for example, in a matrix, and convert the magnetic field from the magnetic field generator **2***b *(an alternating magnetic field) to a voltage and respectively detect the voltage. The magnetic field detector **11** performs predetermined arithmetic processing using voltage detection values Vd_{1}, . . . , Vd_{n }(n is the number of arranged detection coils **12**) of the respective detection coils **12** and a proportionality coefficient, thereby acquiring field-strength detection values Bd_{1}, . . . , Bd_{n}, which are measurement values of the field strength acquired by the respective detection coils **12**. The magnetic field detector **11** transmits the field-strength detection values Bd_{1}, . . . , Bd_{n }as a magnetic-field detection result of the respective detection coils (an example of magnetic field information of a detection target).

The magnetic-field detection results of the respective detection coils **12** are used for calculation of the position and direction information of the capsule endoscope **2** in the three-dimensional space A**0** (more specifically, six variables in total of a position coordinate rc (x, y, z) of the capsule endoscope **2** and a magnetic dipole moment M (mx, my, mz) in the position coordinate rc (x, y, z)). Accordingly, it is desired that the number of arrangement of the detection coils is six or more.

The position calculator **13** functions as an arithmetic processor that calculates the position and direction of the capsule endoscope **2** in the three-dimensional space A**0** of the absolute coordinate system. Specifically, the position calculator **13** temporarily sets the position coordinate rc of the capsule endoscope **2** and the magnetic dipole moment M under control of the controller **16**, and calculates theoretical values of the magnetic-field detection results acquired by the respective detection coils **12** (hereinafter, “field-strength theoretical values”) by using the temporarily set position coordinate rc and magnetic dipole moment M. The position calculator **13** acquires the field-strength detection values Bd_{1}, . . . , Bd_{n }acquired by the respective detection coils **12** via the controller **16**. The position calculator **13** generates an evaluation function expressing an error between measurement values in the magnetic-field detection results of the respective detection coils **12** (that is, the field-strength detection values Bd_{1}, . . . , Bd_{n}) and the field-strength theoretical values, and performs optimization convergence calculation based on the generated evaluation function to thereby calculate the position and direction of the capsule endoscope **2**. In this case, the position calculator **13** calculates the position and direction information of the capsule endoscope **2** based on the temporary position coordinate rc and the temporary magnetic dipole moment M when an error value in the optimization convergence calculation is minimized. The position calculator **13** then transmits a result of the optimization convergence calculation when the error value is minimized, that is, the position and direction information of the capsule endoscope **2** to the controller **16**. In this case, the position calculator **13** transmits to the controller **16** information of a vector p (x, y, z, mx, my, mz) including the respective components of the position coordinate rc and the magnetic dipole moment M as vector components, as the position and direction information of the capsule endoscope **2**, which is a result of the optimization convergence calculation.

The input unit **14** is realized by using an input device such as a keyboard and a mouse, and inputs various pieces of information to the controller **16** in response to the input operation by the user such as a doctor or nurse. The various pieces of information input to the controller **16** by the input unit **14** includes, for example, the instruction information for instructing the controller **16** and the temporary position and direction information of the capsule endoscope **2**. The temporary position and direction information is initial values of the position coordinate rc and the magnetic dipole moment M required at the time of calculating the field-strength theoretical value by the position calculator **13**, and specifically, is a temporarily set value of the vector P (x, y, z, mx, my, mz).

The storage unit **15** is realized by using various storage media that rewritably store information such as a RAM, ERPROM, flash memory, or hard disk. The storage unit **15** stores various pieces of information instructed to be stored by the controller **16**, and transmits information instructed to be read by the controller **16** from the stored various pieces of information. Specifically, the storage unit **15** stores convergence result information **15***a *of the optimization convergence calculation and area information **15***b *relating to a detection space of the position detecting device **10**.

The convergence result information **15***a *is a convergence result of the optimization convergence calculation performed by the position calculator **13**, and includes at least the final convergence result (the latest convergence result in time series). The convergence result is a result of the optimization convergence calculation in which the error value in the optimization convergence calculation converges to a value equal to or less than a predetermined threshold, of the optimization convergence calculations performed by the position calculator **13**. The area information **15***b *is coordinate information for respectively specifying a determination area and an inside area to be set in the detection space of the position detecting device **10**. The detection space is a space in a range in which the position detecting device **10** can detect the position and direction of a detection target (for example, the capsule endoscope **2**) in the three-dimensional space A**0** of the absolute coordinate system. The determination area is an area set in the detection space of the position detecting device **10** and having high reliability of the convergence result (an error between the position and direction information based on the convergence result and the actual current position and current direction of the capsule endoscope **2** is small). The inside area is set in the determination area, taking position detection accuracy of the position detecting device **10** into consideration, and reliably accommodates the position variation range of the capsule endoscope **2** calculated by the optimization convergence calculation in the determination area.

The controller **16** controls the operation of the respective components (the magnetic field detector **11**, the position calculator **13**, the input unit **14**, and the storage unit **15**) of the position detecting device **10**, and also controls input and output of signals between the respective components. Specifically, the controller **16** controls information input from the magnetic field detector **11** based on the instruction information input by the input unit **14** and calculation of the position and direction information by the position calculator **13**, thereby controlling detection of the position and direction information of the capsule endoscope **2**, which is a detection target.

The controller **16** includes a convergence determining unit **16***a *that determines whether the result of the optimization convergence calculation performed by the position calculator **13** converges, an area determining unit **16***b *that determines a presence area of the capsule endoscope **2** in the three-dimensional space A**0**, and an update processor **16***c *that updates information such as a convergence result of the optimization convergence calculation.

The convergence determining unit **16***a *acquires the result of the optimization convergence calculation performed by the position calculator **13**, and determines whether the acquired result of the optimization convergence calculation converges. The controller **16** stores the result of the optimization convergence calculation determined to be in a converged state by the convergence determining unit **16***a *(that is, a convergence result) in the storage unit **15** as a part of the convergence result information **15***a*. The convergence result of the optimization convergence calculation includes, for example, the information of the vector p (x, y, z, mx, my, mz) including the respective vector components of the position coordinate rc of the capsule endoscope **2** and the magnetic dipole moment M.

The area determining unit **16***b *determines whether the position of the capsule endoscope **2** calculated by the optimization convergence calculation by the position calculator **13** is within the determination area, and also determines whether the position of the capsule endoscope **2** is within the inside area. The controller **16** sets the determination space of the position detecting device **10**, which is a space for detecting the position and direction of the capsule endoscope **2**, in the three-dimensional space A**0** of the absolute coordinate system, and sets the determination area in the set determination space. The controller **16** also sets the inside area in the determination area, taking the position detection accuracy of the position detecting device **10** into consideration. The area determining unit **16***b *determines whether the position of the capsule endoscope **2** indicated by the position and direction information (specifically, the vector p) is within the determination area or the inside area, based on the respective pieces of coordinate information and position and direction information of the determination area or the inside area. The controller **16** stores a plurality of coordinate information for defining the determination area and a plurality of pieces of coordinate information for defining the inside area in the storage unit **15** as a part of the area information **15***b. *

The update processor **16***c *updates the final convergence result of the optimization convergence calculation. Specifically, the update processor **16***c *designates the result of the optimization convergence calculation (the convergence result) determined to be in a converged state by the convergence determining unit **16***a *as the final convergence result at the present moment, and sequentially updates the acquired latest convergence result as the final convergence result, every time the convergence determining unit **16***a *determines that the optimization convergence calculation is in the converged state. The controller **16** stores the final convergence result defined by the update processor **16***c *in the storage unit **15** as a part of the convergence result information **15***a*. The update processor **16***c *expands the determination area as needed, and updates the expanded determination area as the final determination area.

An operation of the position detecting device **10** according to the first embodiment of the present invention is explained next. FIG. 2 is a flowchart exemplifying a process procedure performed by the controller **16** in the position detection device **10** according to the first embodiment. When the position detecting device **10** detects the position and direction information of the capsule endoscope **2** in a subject, the controller **16** controls the information input from the magnetic field detector **11** and various types of arithmetic processing performed by the position calculator **13**, to control detection of the position and direction information of the capsule endoscope **2**.

Specifically, as shown in FIG. 2, the controller **16** acquires initial position and direction information input by the input unit **14** (Step S**101**), and initializes the number of convergence calculations of the optimization convergence calculation performed by the position calculator **13** to zero (Step S**102**). The initial position and direction information is, for example, initial information temporarily set by referring to an initial position of the capsule endoscope **2** in the three-dimensional space A**0** (specifically, in a subject), and includes information of a temporary vector p. The controller **16** transmits the initial position and direction information to the position calculator **13**.

The controller **16** then acquires, from the magnetic field detector **11**, the field-strength detection values Bd_{1}, . . . , Bd_{n }acquired by the respective detection coils **12** (Step S**103**). At Step S**103**, the controller **16** acquires, a predetermined average number of times, the field-strength detection value for each of n detection coils **12**. The controller **16** performs, for each detection coil, a movement averaging process with respect to the field-strength detection values Bd_{1}, . . . , Bd_{n }each of which has been acquired the average number of times. The controller **16** can reduce, by the movement averaging process, position variation factors concerning the capsule endoscope **2** that are included in the field-strength detection values Bd_{1}, . . . , Bd_{n}. The controller **16** transmits the movement-averaged field-strength detection values Bd_{1}, . . . , Bd_{n }of the respective detection coils **12** to the position calculator **13**.

When performing the movement averaging process, the controller **16** can select the required number of field-strength detection values (for example, six or more) of the detection coils to be used for the optimization convergence calculation by the position calculator **13** from the respective field-strength detection values Bd_{1}, . . . , Bd_{n }of the n detection coils **12**, to perform the movement averaging process respectively for the selected field-strength detection values.

Subsequently, the controller **16** causes the position calculator **13** to calculate the field-strength theoretical value of each of the detection coils **12** corresponding to the field-strength detection values used for the optimization convergence calculation (Step S**104**). At Step S**104**, the controller **16** transmits the temporary vector p (x, y, z, mx, my, mz) representing the temporary position and direction information of the capsule endoscope **2** and the position coordinate rs_{i }(i is an integer of 1 to n) of each of the detection coils **12** to the position calculator **13**. When the number of convergence calculations performed by the position calculator **13** is the first, the temporary vector p indicates the initial position and direction information input at Step S**101**, and when the number of convergence calculations by the position calculator **13** is the second or thereafter, the temporary vector p indicates the final convergence result by the previous optimization convergence calculation. The position calculator **13** calculates the field-strength detection theoretical value of each of the detection coils **12** based on the temporary vector p and the position coordinate rs_{i }of the detection coil **12** under control of the controller **16**.

Specifically, the position calculator **13** temporarily sets the position coordinate rc (x, y, z) of the capsule endoscope **2** in the three-dimensional space A**0** and the magnetic dipole moment M (mx, my, mz) in the position coordinate, based on the temporary vector p acquired from the controller **16**. The position calculator **13** then calculates a distance vector r_{i }(xi-1, yi-y, zi-z) between the position coordinate rc (x, y, z) and the position coordinate rs_{i }(xi, yi, zi) of ith detection coil **12**. The ith is a number for specifying each of the detection coils **12** and i is an integer of 1 to n. The position calculator **13** calculates the field-strength theoretical value B_{i }by using the magnetic dipole moment M, the position coordinate rc, and the distance vector r_{i}. The field-strength theoretical value B_{i }is a theoretical value of the magnetic detection result when the ith detection coil **12** detects the magnetic field by the magnetic dipole moment M (specifically, the magnetic field generated by the magnetic field generator **2***b*), and is calculated based on the following equation (1). The position calculator **13** repeatedly performs arithmetic processing based on the equation (1) to calculate magnetic-field theoretical values B_{1}, . . . , B_{n }of 1st to nth detection coils **12**.

The controller **16** then causes the position calculator **13** to generate the evaluation function expressing an error between the magnetic-field detection value and the field-strength theoretical value of each of the detection coils **12** (Step S**105**), and causes the position calculator **13** to perform the optimization convergence calculation based on the generated evaluation function (Step S**106**). In this case, the position calculator **13** generates the evaluation function expressing an error (for example, a square error) between the magnetic-field detection values Bd_{1}, . . . , Bd_{n }and the field-strength theoretical values B_{1}, . . . , B_{n }of the respective detection coils **12** under control of the controller **16**. The evaluation function generated by the position calculator **13** is expressed by the following equation (2).

The position calculator **13** performs the optimization convergence calculation based on the evaluation function expressed by the equation (2) to calculate the position and direction of the capsule endoscope **2** under control of the controller **16**. In this case, the position calculator **13** calculates the vector p (x, y, z, mx, my, mz) including, as the vector component, the temporary position coordinate rc and the temporary magnetic dipole moment M when an error value in the optimization convergence calculation is minimized, as the position and direction information of the capsule endoscope **2**.

The controller **16** then determines whether the result of the optimization convergence calculation performed by the position calculator **13** converges (Step S**107**). At Step S**107**, the convergence determining unit **16***a *acquires the error value in the optimization convergence calculation from the position calculator **13**, and compares the error value with a predetermined threshold. When the error value is larger than the threshold, the convergence determining unit **16***a *determines that the result of the optimization convergence calculation has not converged (that is, in a diverged state).

When the result of the optimization convergence calculation performed by the position calculator has not converged (NO at Step S**107**), the controller **16** determines whether the number of executions of the optimization convergence calculation exceeds the predetermined number of convergence calculations (Step S**108**). When the number of executions of the optimization convergence calculation is equal to or less than the predetermined number of convergence calculations, that is, when the position calculator **13** has not performed the optimization convergence calculation for the specified number of convergence calculations (NO at Step S**108**), the controller **16** corrects the temporarily set position and direction information (Step S**109**). At Step S**109**, the controller **16** corrects respective variables (that is, vector components) of the temporary vector p representing the temporary position and direction information, and designates the corrected temporary vector p as a starting point of calculation for the next optimization convergence calculation. Thereafter, the controller **16** increments the number of convergence calculations performed by the position calculator **13** (Step S**110**), and returns to Step S**104** to repeat a process procedure at Step S**104** and subsequent steps.

At Step S**107**, when the error value in the optimization convergence calculation performed by the position calculator **13** is equal to or less than a predetermined threshold, the convergence determining unit **16***a *determines that the result of the optimization convergence calculation converges (that is, the error value in the optimization convergence calculation is in a converged state). When the result of the optimization convergence calculation converges (YES at Step S**107**), the controller **16** determines whether the result of the optimization convergence calculation converges in the determination area (Step S**111**).

At Step S**111**, the area determining unit **16***b *determines whether the position coordinate of the capsule endoscope **2** indicated by the vector p based on the convergence result of the optimization convergence calculation is within the determination area. When the position coordinate of the capsule endoscope **2** is within the determination area, the area determining unit **16***b *determines that the result of the optimization convergence calculation converges in the determination area. When the position coordinate is outside the determination area, the area determining unit **16***b *determines that the result of the optimization convergence calculation pseudo-converges outside the determination area (that is, the result of the optimization convergence calculation is in a diverged state). When the result of the optimization convergence calculation converges in the determination area (YES at Step S**111**), the controller **16** updates the final convergence information of the optimization convergence calculation performed by the position calculator **13** (Step S**112**). The final convergence information of the optimization convergence calculation includes the vector p based on the convergence result (position and direction information of the capsule endoscope **2**), the determination area at the time of acquiring the convergence result, and the like. When the result of the optimization convergence calculation has pseudo-converged outside the determination area, the controller **16** performs a returning process of returning the diverged state of the optimization convergence calculation to a converged state (Step S**113**).

The controller **16** determines whether the process is to be finished after performing Step S**112** or S**113** (Step S**114**). When the process is not finished (NO at Step S**114**), the controller **16** returns to Step S**102** and repeats the process procedure at Step S**102** and subsequent steps. For example, when the input unit **14** inputs instruction information instructing to finish the process, the controller **16** determines to finish the process (YES at Step S**114**), and the process is finished.

At Step S**108**, when the number of executions of the optimization convergence calculation exceeds the predetermined number of convergence calculations (YES at Step S**108**), the controller **16** proceeds to Step S**111** to repeat the process procedure at Step S**111** and subsequent steps. In this case, the convergence determining unit **16***a *determines that the result of the optimization convergence result has not converged (that is, the error value in the optimization convergence calculation is in a diverged state) based on a fact that the number of executions of the optimization convergence calculation exceeds the predetermined number of convergence calculations. Accordingly, the controller **16** determines that the result of the optimization convergence calculations has not converged in the determination area at Step S**111** (NO at Step S**111**), and proceeds to Step S**113** to repeat the process procedure at Step S**113** and subsequent steps.

An updating process of the final convergence information (Step S**112**) is explained next. FIG. 3 is a flowchart exemplifying a process procedure until the controller **16** in the position detecting device **10** according to the first embodiment completes the updating process of the final convergence information. As shown in FIG. 3, when the result of the optimization convergence calculation performed by the position calculator **13** converges in the determination area, the controller **16** further determines whether the position of the capsule endoscope **2** indicated by the vector p based on the convergence result of the optimization convergence calculation (hereinafter, “convergence point”) is in the inside area (Step S**201**). At Step S**201**, the area determining unit **16***b *reads a plurality of pieces of coordinate information (for example, eight corners of a cube) specifying the inside area from the area information **15***b *in the storage unit **15**, and determines whether the convergence point is in the inside area based on the read coordinate information of the inside area and the vector component of the vector p.

When the convergence point is in the inside area (YES at Step S**201**), the controller **16** maintains the determination area set outside the inside area (Step S**202**). That is, when the position coordinate of the capsule endoscope **2** calculated by the optimization convergence calculation is in the inside area, the controller **16** maintains the coordinate information of the determination area at the present moment, and does not change the determination area.

When the convergence point based on the convergence result of the optimization convergence calculation is outside the inside area (NO at Step S**201**), the controller **16** expands the determination area outside the inside area (Step S**203**), and updates the determination area (Step S**204**). At Steps S**203** and S**204**, the update processor **16***c *expands the determination area corresponding to the position detection accuracy (specifically, the position variation range of the convergence point of the capsule endoscope **2**) of the position detecting device **10**, and sets the determination area in which the position variation range of the convergence point is included in the area. The update processor **16***c *updates the expanded determination area as the final determination area. The coordinate information for defining the final determination area after the update is stored in the storage unit **15** as a part of the area information **15***b. *

The controller **16** having performed the process procedure at Step S**202** or S**204** updates the convergence result of the optimization convergence calculation for calculating the convergence point (specifically, the vector p representing the convergence point) as the final convergence result (Step S**205**), and returns to Step S**112**. The final convergence result after the update is stored in the storage unit **15** as a part of the convergence result information **15***a*. The vector p corresponding to the final convergence result is used as the starting point of calculation for the next optimization convergence calculation.

The returning process of a converged state of the optimization convergence calculation (Step S**113**) is explained next. FIG. 4 is a flowchart exemplifying a process procedure until the controller **16** in the position detecting device **10** according to the first embodiment completes the returning process to a converged state of the optimization convergence calculation.

As shown in FIG. 4, when the result of the optimization convergence calculation performed by the position calculator **13** does not converge in the determination area, the controller **16** newly acquires the field-strength detection values of the respective detection coils used for the optimization convergence calculation, to update the respective field-strength detection values to be used for the optimization convergence calculation (Step S**301**). When a predetermined time has not passed since acquisition of the field-strength detection values of the respective detection coils **12** at Step S**103** (NO at Step S**302**), the controller **16** repeats the process procedure at Step S**301**. The controller **16** repeats the process procedure at Steps S**301** and S**302** until the predetermined time passes, to suspend the arithmetic processing of the position calculator **13** such as optimization convergence calculation for a predetermined period of time.

When the result of the optimization convergence calculation diverges, it is possible that the field-strength detection values of the respective detection coils **12** used for the optimization convergence calculation have been adversely affected by a disturbance such as noise. The controller **16** suspends the arithmetic processing of the position calculator **13** for a predetermined time and invalidates, from older ones, the field-strength detection values of the respective detection coils **12**. The predetermined time may be a time corresponding to a multiplication value of the average number of times, which the field-strength detection value is detected for the movement averaging process, and a sampling time required for acquiring one field-strength detection value from the respective detection coils **12**. With this, the field-strength detection value that caused the divergence of the result of the optimization convergence calculation can be eliminated.

When such a predetermined time passes (YES at Step S**302**), the controller **16** reads the final convergence result of the position calculator **13** from the convergence result information **15***a *in the storage unit **15** (Step S**303**), and transmits the read final convergence result and the field-strength detection values of the respective detection coils **12** updated at Step S**301** (specifically, respective field-strength detection values subjected to the movement averaging process for each detection coil) to the position calculator **13**. The controller **16** causes the position calculator **13** to perform the optimization convergence calculation using the field-strength detection values of the respective detection coils **12** and the final convergence result (the vector p representing the final convergence point) (Step S**304**). The final convergence result used for the optimization convergence calculation at Step S**304** indicates a convergence point (the vector p) included in the determination area (for example, the determination area before being expanded by the update processor **16***c*).

At Step S**304**, the position calculator **13** temporarily sets the position coordinate re (x, y, z) of the capsule endoscope **2** and the magnetic dipole moment M (mx, my, mz) based on the vector p acquired as the final convergence result, and recalculates the field-strength theoretical values B_{1}, . . . , B_{n }based on the equation (1) by using the temporarily set position coordinate rc and magnetic dipole moment M (mx, my, mz). The position calculator **13** then generates the evaluation function (see the equation (2)) expressing an error between the recalculated field-strength theoretical values B_{1}, . . . , B_{n }and the field-strength detection values Bd_{1}, . . . , Bd_{n }reacquired at Steps S**301** and S**302**, and performs once the optimization convergence calculation based on the generated evaluation function. The position calculator **13** transmits a result of the optimization convergence calculation performed once to the controller **16**.

The controller **16** acquires the result of the optimization convergence calculation performed by the position calculator **13** at Step S**304**, to determine whether the acquired result of the optimization convergence calculation converges in the determination area (Step S**305**). At Step S**305**, the convergence determining unit **16***a *determines whether the error value in the one optimization convergence calculation converges to a value equal to or less than a predetermined threshold, and the area determining unit **16***b *determines whether the position of the capsule endoscope **2** indicated by the vector p calculated by the one optimization convergence calculation is in the determination area. When the result of the one optimization convergence calculation converges in the determination area (YES at Step S**305**), it means that the diverged state of the optimization convergence calculation performed by the position calculator **13** returns to a converged state, and the controller **16** returns to Step S**113**.

In contrast, when the result of the one optimization convergence calculation has not converged in the determination area (NO at Step S**305**), the controller **16** returns to Step S**301** to repeat the process procedure at Step S**301** and subsequent steps.

When the error value of the one optimization convergence calculation converges to a value equal to or less than the predetermined threshold, and the position of the capsule endoscope **2** indicated by the vector p calculated by the one optimization convergence calculation is in the determination area, the result of the one optimization convergence calculation is determined as having converged in the determination area. When the error value of the one optimization convergence calculation is larger than the predetermined threshold or the position of the capsule endoscope **2** indicated by the vector p calculated by the one optimization convergence calculation is outside the determination area, the result of the one optimization convergence calculation is determined as having not converged in the determination area.

The updating process (Step S**112**) of the final convergence information including the final convergence result of the optimization convergence calculation and the determination area and the returning process to a converged state (Step S**113**) are explained next in detail. FIG. 5 is a schematic diagram specifically explaining the updating process of the final convergence information of the optimization convergence calculation and the returning process to the converged state. In FIG. 5, positions P**0**, P**1**, and P**2** are positions of the capsule endoscope **2** sequentially calculated by the optimization convergence calculation performed by the position calculator **13**, where the position P**2** is a position coordinate calculated subsequent to the position P**1**, and the position P**0** is a convergence point calculated prior to the position P**1**.

As shown in FIG. 5, the controller **16** sets a determination area A**1** in the three-dimensional space in which the magnetic field detector **11** can normally detect the magnetic field by a plurality of the detection coils **12**, and sets an inside area A**2** in the determination area A**1** (for example, an area including a central part of the determination area A**1**), taking a position variation range A**3** of the capsule endoscope **2** into consideration. In this case, the inside area A**2** is an area capable of reliably accommodating the position variation range A**3** of the capsule endoscope **2** in the determination area A**1**. That is, the position of the capsule endoscope **2** in the inside area A**2** (for example, the position P**1**) is reliably accommodated in the determination area A**1** together with the position variation range A**3**. This means that there is little possibility that the position of the capsule endoscope **2** in the inside area A**2** cannot be detected suddenly.

The controller **16** determines whether the result of the optimization convergence calculation at the time of calculating the position P**1** of the capsule endoscope **2** converges in the determination area A**1**. In this case, the convergence determining unit **16***a *determines whether the error value in the optimization convergence calculation corresponding to the position P**1** converges to a value equal to or less than the predetermined threshold, and the area determining unit **16***b *determines whether the position P**1** is in the determination area A**1**. When the convergence determining unit **16***a *and the area determining unit **16***b *determine that the result of the optimization convergence calculation converges and the position P**1** is in the determination area A**1**, the controller **16** determines that the optimization convergence calculation corresponding to the position P**1** converges in the determination area A**1**, and acquires the position P**1** as the convergence point of the capsule endoscope **2**.

When the position P**1** is the convergence point in the determination area A**1**, the area determining unit **16***b *further determines whether the position P**1** is the convergence point in the inside area A**2**. When the position P**1** is the position coordinate in the inside area A**2** as shown in FIG. 5, the area determining unit **16***b *determines that the position P**1** is the convergence point in the inside area A**2**. In this case, the controller **16** maintains the determination area A**1**, and the update processor **16***c *updates the vector p (x, y, z, mx, my, mz) representing the position P**1** as the final convergence result.

When causing the position calculator **13** to calculate the position P**2** subsequent to the position P**1**, the controller **16** designates the final convergence result (the vector p) corresponding to the position P**1** as the starting point of calculation for the next optimization convergence calculation. The position calculator **13** temporarily sets the position coordinate rc of the capsule endoscope **2** and the magnetic dipole moment M by using the final convergence result corresponding to the position P**1**, to calculate the field-strength theoretical values B_{1}, . . . , B_{n}, based on the equation (1). The position calculator **13** generates the evaluation function (see the equation (2)) by using the calculated field-strength theoretical values B_{1}, . . . , B_{n }and the field-strength detection values Bd_{1}, . . . , Bd_{n}, of the respective detection coils **12**, and performs the optimization convergence calculation based on the generated evaluation function to calculate the vector p representing the position P**2** of the capsule endoscope **2**.

The controller **16** determines whether the result of the optimization convergence calculation converges in the determination area A**1** for the position P**2** of the capsule endoscope **2**, as in the case of the position P**1**. Specifically, when the convergence determining unit **16***a *determines that the result of the current optimization convergence calculation converges and the area determining unit **16***b *determines that the position P**2** is in the determination area A**1**, the controller **16** determines that the optimization convergence calculation corresponding to the position P**2** converges in the determination area A**1**, and acquires the position P**2** as the convergence point of the capsule endoscope **2**.

When the position P**2** is the convergence point in the determination area A**1**, the area determining unit **16***b *further determines whether the position P**2** is the convergence point in the inside area A**2**. The inside area A**2** is smaller than the determination area A**1** by at least the space corresponding to the position variation range of the capsule endoscope **2**, and is set inside of the determination area A**1** by the controller **16**. When the position P**2** is the position coordinate outside the inside area A**2** as shown in FIG. 5, the area determining unit **16***b *determines that the position P**2** is the convergence point outside the inside area A**2**. In this case, the update processor **16***c *expands the determination area A**1** to a determination area A**4** corresponding to the position variation range A**3** of the position P**2** (that is, sets the determination area A**4** acquired by expanding the determination area A**1** by the space corresponding to the position variation range A**3**), and updates the expanded determination area A**4** as the final determination area. In this case, the position variation range A**3** of the position P**2** is accommodated in the expanded determination area A**4**. The update processor **16***c *updates the vector p (x, y, z, mx, my, mz) representing the position P**2** as the final convergence result.

When the result of the optimization convergence calculation at the time of calculating the position P**1** of the capsule endoscope **2** does not converge in the determination area A**1**, the controller **16** invalidates, from older ones, the field-strength detection values of the respective detection coils **12** and suspends the arithmetic processing of the position calculator **13** until a predetermined time (a time corresponding to a multiplication value of the average number of times for the movement averaging process and the sampling time required for acquiring the field-strength detection value) passes. With this, the field-strength detection values corresponding to the number of times for movement averaging are updated for the respective detection coils **12**. When the position P**1** is not the convergence point, the controller **16** causes the position calculator **13** to perform the optimization convergence calculation, designating the final convergence result corresponding to the position P**0**, which is the latest convergence point of the convergence points of the position P**1** calculated previously as the starting point of calculation for the next optimization convergence calculation. The position P**0** corresponding to the final convergence result is the convergence point in the determination area A**1** before expansion.

The position calculator **13** performs the optimization convergence calculation designating the final convergence result (the vector p) corresponding to the position P**0** as the starting point of calculation under control of the controller **16** to calculate the vector p. When the optimization convergence calculation converges in the determination area, the controller **16** can return the result of the optimization convergence calculation, which has been a diverged state previously, to a converged state in a short period of time. The controller **16** causes the position calculator **13** to perform the optimization convergence calculation designating the convergence result of the optimization convergence calculation as the starting point of calculation for the next optimization convergence calculation.

In the first embodiment, as described above, the magnetic field from the magnetic field generator incorporated in a detection target such as a capsule endoscope is detected by the plurality of detection coils, and the optimization convergence calculation based on the evaluation function expressing an error between the measurement value (the detection value) in the respective magnetic-field detection results acquired by the detection coils and the theoretical value is performed by the arithmetic processor. It is determined whether the error value in the optimization convergence calculation performed by the arithmetic processor converges. When the error value in the optimization convergence calculation converges, the position and direction information of the detection target based on the convergence result of the optimization convergence calculation is calculated, and the convergence result is set as the starting point of calculation for the next optimization convergence calculation. When the error value in the optimization convergence calculation does not converge (diverges), arithmetic processing of the arithmetic processor such as optimization convergence calculation is suspended until a predetermined time passes, to acquire the measurement value in the respective magnetic-field detection results acquired by the detection coils again, and the optimization convergence calculation is restarted by the arithmetic processor, using the final convergence result acquired by the previous optimization convergence calculation as the starting point of calculation. Accordingly, the measurement value in the magnetic-field detection result adversely affected by a disturbance such as noise at the time of detecting the magnetic field generated from the magnetic field generator by the detection coils can be eliminated, and it is possible to prevent a case that the result of the optimization convergence calculation at the time of divergence of the error value (an uncertain arithmetic result) is used for the starting point of calculation for the next optimization convergence calculation. Accordingly, even if the error value in the optimization convergence calculation diverges, the convergence result of the optimization convergence calculation can be reliably used as the starting point of calculation for the next optimization convergence calculation. As a result, a position detecting device that can return a diverged state of the optimization convergence calculation to a converged state in a short period of time, when the error value in the optimization convergence calculation for calculating the position information and direction information of the detection target diverges, can be realized.

The determination area is set in the detection space of the position and direction of the detection target, and it is determined whether the position coordinate of the detection target based on the convergence result of the optimization convergence calculation is in the determination area. When the coordinate is in the determination area, the convergence result of the optimization convergence calculation, which has calculated the position coordinate in the determination area, is designated as the starting point of calculation for the next optimization convergence calculation. When the position coordinate is outside the determination area, it is determined that the optimization convergence calculation, which has calculated a position coordinate outside the determination area, is in a diverged state, and the arithmetic processing of the arithmetic processor such as optimization convergence calculation is suspended until a predetermined time passes, to acquire the measurement value in the respective magnetic-field detection results again, and the optimization convergence calculation is restarted by the arithmetic processor, using the final convergence result acquired by the previous optimization convergence calculation as the starting point of calculation. Accordingly, it is possible to prevent a case that an uncertain result of the optimization convergence calculation such as a result of the optimization convergence calculation when the error value pseudo-converges is used as the starting point of calculation for the next optimization convergence calculation, thereby enabling to calculate the position and direction of the detection target highly accurately, and the converged state of the optimization convergence calculation can be maintained easily.

Further, the inside area for accommodating the position variation range of the detection target is set in the determination area, and it is determined whether the position coordinate of the detection target based on the convergence result of the optimization convergence calculation is in the convergence determination stability. When the position coordinate is in the inside area, the current determination area is maintained. When the position coordinate is outside the determination area, the determination area is expanded corresponding to the position variation range of the detection target, and the expanded determination area is updated to the determination area at the time of performing the next optimization convergence calculation. Accordingly, the determination area can be easily expanded, matched with the detection accuracy of the position detecting device, thereby enabling to control a state such that the optimization convergence calculation in which the error value has actually converged is erroneously determined to be in a diverged state and prevent a case that the optimization convergence calculation frequently diverges. As a result, the processing time of arithmetic processing such as optimization convergence calculation for calculating the position and direction information of the detection target can be shortened.

A second embodiment of the present invention is explained next. In the first embodiment, the magnetic field formed by the magnetic field generator **2***b *incorporated in the capsule endoscope **2** as a detection target, is detected by the detection coils **12**. However, in the second embodiment, the magnetic field is applied to an LC marker incorporated in the capsule endoscope as the detection target, and a generated induced magnetic field of the LC marker is detected by the detection coils **12**.

FIG. 6 is a block diagram schematically depicting a configuration example of a capsule guiding system according to the second embodiment of the present invention. As shown in FIG. 6, a capsule guiding system **21** according to the second embodiment includes a capsule endoscope **22** instead of the capsule endoscope **2** of the capsule guiding system **1** according to the first embodiment, and includes a position detecting device **23** instead of the position detecting device **10**. The capsule endoscope **22** includes an LC marker **2***c *instead of the magnetic field generator **2***b*. The position detecting device **23** includes a drive coil group **24** that applies the magnetic field to the LC marker **2***c*, a coil selector **25** that selects a drive coil that generates the magnetic field from the drive coil group **24**, and a coil power source **26** that supplies electric current for generating the magnetic field to the drive coil group **24**, and includes a controller **27** instead of the controller **16**. Other configurations of the second embodiment are the same as those of the first embodiment, and like components are denoted by like reference numerals.

The capsule endoscope **22** is the same as the capsule endoscope **2** in the first embodiment except for including the LC marker **2***c *instead of the magnetic field generator **2***b*. The LC marker **2***c *emits an induced magnetic field due to an action of the magnetic field applied by the drive coil group **24** in the position detecting device **23**. Accordingly, there is a more suitable drive coil depending on the direction of the LC marker **2***c*. The induced magnetic field generated by the LC marker **2***c *is detected by the detection coils **12** in the magnetic field detector **11**. In this case, the field-strength detection values Bd_{1}, . . . , Bd_{n }of the induced magnetic field detected by the detection coils **12** in the magnetic field detector **11** are an example of the magnetic field information of the detection target and are acquired by the controller **27**.

The drive coil group **24** is realized by a plurality of magnetic-field generation coils (drive coils) that generates the magnetic field for detecting the position and direction information of the capsule endoscope **22** in a subject. The drive coil group **24** applies the magnetic field of strength and direction appropriate to the current position of the LC marker **2***c *in the three-dimensional space A**0** and a coil axis direction to the LC marker **2***c*, and causes the LC marker **2***c *to emit the induced magnetic field due to the action of the applied magnetic field.

The coil selector **25** functions as a switching unit of the drive coil, and selects one or more drive coils that generate the magnetic field from the drive coil group **24** under control of the controller **27**. The one or more drive coils selected by the coil selector **25** generate the magnetic field of the appropriate strength and direction as the magnetic field that penetrates the LC marker **2***c *in the coil axis direction at the current position of the LC marker **2***c *in the three-dimensional space A**0**.

The coil power source **26** includes a plurality of power sources corresponding to the number of drive coils included in the drive coil group **24**, and supplies the alternating current to the one or more drive coils selected in the drive coil group **24** by the coil selector **25** under control of the controller **27**. In this case, the alternating current generated by the coil power source **26** is applied to the selected one or more drive coils of the drive coil group **24** via the coil selector **25**, and generates the magnetic field in the one or more drive coils.

The controller **27** controls the drive coil group **24**, the coil selector **25**, and the coil power source **26**. Specifically, the controller **27** causes the coil selector **25** to select one or more drive coils of the drive coil group **24**. The controller **27** controls the energization amount of the coil power source **26** with respect to the one or more drive coils selected by the coil selector **25**, and controls the magnetic-field generation operation of the drive coil group **24** through control of the energization amount. The controller **27** acquires field-strength detection values Bd_{1}, . . . , Bd_{n }of the induced magnetic field of the LC marker **2***c *detected by the detection coils **12** from the magnetic field detector **11**. The controller **27** calculates the respective field-strength theoretical values B_{1}, . . . , B_{n }of the induced magnetic field based on the equation (1) mentioned above, and causes the position calculator **13** to perform the optimization convergence calculation based on the evaluation function (see the equation (2)) expressing an error value between the respective field-strength detection values Bd_{1}, . . . , Bd_{n }and the respective field-strength theoretical values B_{1}, . . . , B_{n }of the induced magnetic field. The controller **27** controls the switching operation of the drive coil group **24** in addition to the control for suspending the arithmetic processing of the position calculator **13** until a predetermined time passes, in the returning process of returning the diverged state of the optimization convergence calculation to the converged state. Other functions of the controller **27** are the same as those of the controller **16** in the position detecting device **10** according to the first embodiment.

An operation of the position detecting device **23** according to the second embodiment of the present invention is explained next. When the position detecting device **23** detects the position and direction information of the capsule endoscope **22** in the subject, the controller **27** repeatedly performs the process procedure substantially the same as the process procedure (Steps S**101** to S**114**, see FIG. 2) of the controller **16** in the position detecting device **10** according to the first embodiment. In this case, the controller **27** performs control for switching the drive coil group **24** instead of the returning process to a converged state at Step S**113**, following the control for suspending the arithmetic processing of the position calculator **13**, to perform the returning process of returning the diverged state of the optimization convergence calculation to a converged state.

FIG. 7 is a flowchart of a process procedure until the controller **27** in the position detecting device **23** according to the second embodiment completes a returning process to a converged state of the optimization convergence calculation. As shown in FIG. 7, the controller **27** updates the respective field-strength detection values to be used for the optimization convergence calculation as at Steps S**301** and S**302** (see FIG. 4) (Step S**401**). When the predetermined time has not passed yet (NO at Step S**402**), the controller **27** repeats Steps S**401** and S**402** to thereby suspend the arithmetic processing of the position calculator **13** such as optimization convergence calculation for a predetermined time.

When the predetermined time passes (YES at Step S**402**), the controller **27** reads the final convergence result of the position calculator **13** from the convergence result information **15***a *in the storage unit **15** as at Steps S**303** and S**304** (see FIG. 4) (Step S**403**). The controller **27** then transmits the read final convergence result and the field-strength detection values of the respective detection coils **12** updated at Step S**401** to the position calculator **13**, and causes the position calculator **13** to perform the optimization convergence calculation using the field-strength detection values of the respective detection coils **12** and the final convergence result (the vector p representing the final convergence point) (Step S**404**). The controller **27** determines whether the result of the optimization convergence calculation performed by the position calculator **13** converges in the determination area as at Step S**305** (see FIG. 4) (Step S**405**).

When a result of the one optimization convergence calculation performed by the position calculator **13** at Step S**404** has not converged in the determination area (NO at Step S**405**), the controller **27** controls the coil selector **25** to switch one or more drive coils that generate the magnetic field in the drive coil group **24** (Step S**406**). At Step S**406**, the coil selector **25** switches one or more drive coils in the drive coil group **24** according to a predetermined sequence under control of the controller **27** to thereby sequentially apply the magnetic field to the LC marker **2***c *in the capsule endoscope **2** in different magnetization directions. In this case, the drive coil group **24** to be switched by the coil selector **25** sequentially applies, for example, the magnetic fields in the X-axis direction, Y-axis direction, and Z-axis direction of the absolute coordinate system to the LC marker **2***c. *

The controller **27** newly acquires the field-strength detection values Bd_{1}, . . . , Bd_{n }of the induced magnetic field emitted by the LC marker **2***c *due to the action of the magnetic field of one or more drive coils selected by the coil selector **25** at Step S**406**, to update the field-strength detection values of the respective detection coils to be used for the optimization convergence calculation (Step S**407**). The controller **27** returns to Step S**404** to repeat the process procedure at Step S**404** and subsequent steps.

When the result of the one optimization convergence calculation performed by the position calculator **13** at Step S**404** converges in the determination area (YES at Step S**405**), it means that the diverged state of the optimization convergence calculation performed by the position calculator **13** is returned to a converged state, and the controller **27** returns to Step S**113**.

In the second embodiment of the present invention, as described above, the magnetic field is applied to an LC marker incorporated in a detection target such as a capsule endoscope by one or more drive coils selected in the drive coil group, thereby generating the induced magnetic field from the LC marker. The generated induced magnetic field is detected by the detection coils, and the arithmetic processor performs the optimization convergence calculation based on the evaluation function expressing an error between the measurement values (detection values) in the respective magnetic-field detection results acquired by the detection coils and the theoretical values. When the error value in the optimization convergence calculation diverges, one or more drive coils to apply the magnetic field to the LC marker is sequentially switched in the drive coil group to sequentially apply the magnetic field in different directions to the LC marker, and reacquires the field-strength detection value of the guiding magnetic field from the LC marker. The arithmetic processor restarts the optimization convergence calculation using the final convergence result acquired by the optimization convergence calculation as the starting point of calculation. Other features of the seconded embodiment are the same as those of the first embodiment. Accordingly, the second embodiment can achieve the same operational effects as those of the first embodiment, and the converged state of the optimization convergence calculation can be easily maintained or returned even when the detection target performs a sudden direction change.

Because the magnetic field is applied to the LC marker incorporated in the detection target to generate the induced magnetic field from the LC marker, power consumption of the detection target (for example, a medical device such as a capsule endoscope) can be reduced.

A third embodiment of the present invention is explained next. In the second embodiment, the induced magnetic field of the LC marker **2***c *incorporated in the capsule endoscope **2** as a detection target is detected by the detection coils **12**. In the third embodiment, a detection coil that detects a magnetic field is incorporated in a capsule endoscope as a detection target, and the magnetic field generated by the drive coil group arranged outside the detection target is detected by the detection coil in the detection target, to acquire a magnetic-field detection result of the detection coil via the receiving device of the image signal.

FIG. 8 is a schematic block diagram of a configuration example of a capsule guiding system according to the third embodiment of the present invention. As shown in FIG. 8, a capsule guiding system **31** according to the third embodiment includes a capsule endoscope **32** instead of the capsule endoscope **22**, a receiving device **33** instead of the receiving device **3**, and a position detecting device **34** instead of the position detecting device **23** in the capsule guiding system **21** according to the second embodiment. The capsule endoscope **32** includes a detection coil **32***b *instead of the LC marker **2***c *to wirelessly transmit a field-strength detection value of the detection coil **32***b *and in-vivo images of a subject to the receiving device **33**. The position detecting device **34** includes drive coil groups **35***a *and **35***b *instead of the drive coil group **24**, a coil selector **36** instead of the coil selector **25**, a coil power source **37** instead of the coil power source **26**, and a controller **38** instead of the controller **27** in the position detecting device **23**. The position detecting device **34** does not include the magnetic field detector **11**. The position detecting device **34** acquires the field-strength detection value from the receiving device **33**. Other configurations of the third embodiment are the same as those of the second embodiment, and like components are denoted by like reference numerals.

The capsule endoscope **32** includes an imaging function and a wireless communication function in a capsule-shaped casing as in the capsule endoscope **22** according to the second embodiment, and is introduced into the organs of a subject to sequentially capture in-vivo images of the subject by using the imaging function. The capsule endoscope **32** includes the detection coil **32***b *instead of the LC marker **2***c *in the capsule-shaped casing. The detection coil **32***b *sequentially detects a plurality of magnetic fields generated by a plurality of drive coils of the external drive coil groups **35***a *and **35***b*. The capsule endoscope **32** wirelessly transmits the in-vivo images of the subject captured by the imaging function and the field-strength detection values Bd_{1}, . . . , Bd_{n }of the respective magnetic fields detected by the detection coil **32***b*. The field-strength detection values Bd_{1}, . . . , Bd_{n }detected by the detection coil **32***b *are an example of the magnetic field information of the detection target and are acquired by the controller **38** via the receiving device **33**.

The receiving device **33** receives an in-vivo image group of a subject and the field-strength detection values Bd_{1}, . . . , Bd_{n }acquired by the detection coil **32***b *wirelessly transmitted by the capsule endoscope **32**. Specifically, the receiving device **33** receives a radio signal from the capsule endoscope **32** via a plurality of the receiving antennas **3***a*, and performs a predetermined demodulation process with respect to the received radio signal to extract the in-vivo images and the field-strength detection values Bd_{i }(i is an integer of 1 to n) included in the radio signal. The receiving device **33** sequentially transmits image signals of the acquired in-vivo images to the image display device **9**, and sequentially transmits field strength signals indicating the acquired field-strength detection values Bd_{1 }to the controller **38**. As a result, the receiving device **33** transmits the in-vivo image group of the subject captured by the capsule endoscope **32** to the image display device **9**, and also transmits the field-strength detection values Bd_{1}, . . . , Bd_{n }acquired by the detection coil **32***b *in the capsule endoscope **32** to the controller **38**.

The drive coil groups **35***a *and **35***b *are realized by a plurality of drive coils that generates the magnetic field for detecting the position and direction information of the capsule endoscope **32** in a subject. The drive coil groups **35***a *and **35***b *form a plurality of magnetic fields to be applied to the capsule endoscope **32** in the three-dimensional space A**0**. The magnetic fields generated by the drive coil groups **35***a *and **35***b *are sequentially detected by the detection coil **32***b *in the capsule endoscope **32**. The field-strength detection results acquired by the detection coil **32***b *are used for calculation of the position and direction information of the capsule endoscope **32** in the three-dimensional space A**0** (specifically, six variables in total of the position coordinate rc (x, y, z) of the capsule endoscope **32** and the magnetic dipole moment M (mx, my, mz)). Accordingly, it is desired that the number of drive coils to be arranged included in the drive coil groups **35***a *and **35***b *that sequentially apply the magnetic field to the detection coil **32***b *is six or more with respect to one detection coil **32***b*, and it is more desirable that the number of drive coils to be arranged is seven or more, taking switching of the drive coil groups into consideration.

The coil selector **36** functions as a switching unit of the drive coils, and selects a combination of a plurality of (for example, six or more) drive coils that generate the magnetic field from the drive coil groups **35***a *and **35***b *under control of the controller **38**. The drive coils selected by the coil selector **36** generate a plurality of magnetic fields having strength and direction appropriate as the magnetic field penetrating the detection coil **32***b *in the coil axis direction, at the current position of the capsule endoscope **32** in the three-dimensional space A**0**.

The coil power source **37** has a plurality of power sources corresponding to the number of drive coils included in the drive coil groups **35***a *and **35***b*, and supplies the alternating current to the drive coils selected in the drive coil groups **35***a *and **35***b *by the coil selector **36** under control of the controller **38**. In this case, the alternating signal generated by the coil power source **37** is applied to the selected plurality of (for example, six or more) drive coils of the drive coil groups **35***a *and **35***b *via the coil selector **36** to generate the magnetic fields in the drive coils.

The controller **38** controls the drive coil groups **35***a *and **35***b*, the coil selector **36**, and the coil power source **37**. Specifically, the controller **38** causes the coil selector **36** to select a plurality of drive coils in the drive coil groups **35***a *and **35***b*, and controls an energization amount of the coil power source **37** with respect to the drive coils (for example, six or more) selected by the coil selector **36** to thereby control a magnetic-field generation operation of the drive coil groups **35***a *and **35***b *through control of the energization amount. The controller **38** acquires the field-strength detection values Bd_{1}, . . . , Bd_{n }of a plurality of magnetic fields acquired by the detection coil **32***b *in the capsule endoscope **32** via the receiving device **33**. The controller **38** calculates the field-strength theoretical values B_{1}, . . . , B_{n }of the magnetic fields based on the equation (1), and causes the position calculator **13** to perform the optimization convergence calculation based on the evaluation function (see the equation (2)) expressing an error between the field-strength detection values Bd_{1}, . . . , Bd_{n }and the field-strength theoretical values B_{1}, . . . , B_{n }of the magnetic fields. Further, the controller **38** controls the switching operation of the coil selector **36** for sequentially switching a combination of the plurality of (for example, six or more) drive coils from the drive coil groups **35***a *and **35***b*, in addition to the control for suspending the arithmetic processing of the position calculator **13** until a predetermined time passes, in the returning process of returning the diverged state of the optimization convergence calculation to a converged state. Other functions of the controller **38** are the same as those of the controller **27** in the position detecting device **23** according to the second embodiment.

When the position detecting device **34** that includes the controller **38** detects the position and direction information of the capsule endoscope **32** in a subject, the controller **38** repeatedly performs the process procedure substantially the same as that of the controller **27** in the position detecting device **23** according to the second embodiment. In this case, the controller **38** controls the coil selector **36** to sequentially switch a combination of the plurality of (for example, six or more) drive coils in the drive coil groups **35***a *and **35***b *at Step S**406**.

In the third embodiment of the present invention, as described above, a detection coil that detects the magnetic field is incorporated in a detection target such as a capsule endoscope. A plurality of magnetic fields formed by the plurality of drive coils selected in the drive coils group outside the detection target is applied to the detection target to detect the magnetic fields by the detection coil in the detection target, and magnetic-field detection results of the detection coil are sequentially acquired via the receiving device that receives the in-vivo images of a subject. The arithmetic processor performs the optimization convergence calculation based on the evaluation function expressing an error between the acquired measurement values (detection values) in the respective magnetic-field detection results and the theoretical values. When the error value in the optimization convergence calculation diverges, the combination of the drive coils that generate the magnetic fields is sequentially switched in the drive coil group to reacquire the respective field-strength detection values of the detection coil in the subject. The arithmetic processor restarts the optimization convergence calculation by using the final convergence result acquired by the previous optimization convergence calculation as the starting point of calculation. Other processes of the third embodiment are the same as those in the second embodiment. Accordingly, the third embodiment can achieve the same operational effects as those in the second embodiment, and the converged state of the optimization convergence calculation can be gained more easily.

A fourth embodiment of the present invention is explained next. In the first embodiment, the optimization convergence calculation is performed by the position calculator **13** every time the field-strength detection values Bd_{1}, . . . , Bd_{n }of the respective detection coils **12** are acquired from the magnetic field detector **11**. In the fourth embodiment, one of the acquired field-strength detection values Bd_{1}, . . . , Bd_{n }is compared with a set threshold every time the field-strength detection values Bd_{1}, . . . , Bd_{n }of the respective detection coils **12** are acquired, and execution of the optimization convergence calculation is permitted or prohibited depending on a comparison result.

FIG. 9 is a schematic block diagram of a configuration example of a capsule guiding system according to the fourth embodiment of the present invention. As shown in FIG. 9, a capsule guiding system **41** according to the fourth embodiment includes a position detecting device **43** instead of the position detecting device **10** in the capsule guiding system **1** according to the first embodiment. The position detecting device **43** includes a controller **46** instead of the controller **16** in the position detecting device **10** according to the first embodiment, and also includes a threshold storage unit **45**. Other configurations of the fourth embodiment are the same as those of the second embodiment, and like components are denoted by like reference numerals.

The threshold storage unit **45** stores a threshold relating to the magnetic field information of the capsule endoscope **2**. Specifically, the threshold storage unit **45** stores a threshold relating to the field-strength measurement value of the magnetic field from the capsule endoscope **2** (more specifically, an alternating magnetic field from the magnetic field generator **2***b*) detected by the detection coils **12** in the magnetic field detector **11**, that is, the respective field-strength detection values Bd_{1}, . . . , Bd_{n}.

The threshold stored in the threshold storage unit **45** is calculated based on the field-strength measurement values by the respective detection coils in the magnetic field detector **11** at the time of arranging the magnetic field generator at the respective coordinate positions in the three-dimensional space A**0**. For example, a mesh is set with equal intervals in the three-dimensional space A**0**, and the magnetic field generator is arranged at respective points on the mesh. In this case, the direction of the magnetic field generator at the respective points can be set in a predetermined direction such as a predetermined vector direction represented by a vector component (1, 1, 1) in an XYZ coordinate system or respective directions specified when an XY plane, a YZ plane, and a ZX plane are rotated by a 45-degree pitch, or can be one finely assuming a plurality of directions. When the magnetic field generators are sequentially arranged at each point and in each direction, the magnetic field detector **11** detects the field strength by the detection coils **12** by position and direction of the magnetic field generator. That is, the magnetic field detector **11** acquires the field-strength detection values for the number of detection coils **12** for each magnetic field generator in an arbitrary position and direction in the three-dimensional space A**0**. The maximum value of the acquired field-strength detection values is sequentially recorded for each position and direction of the magnetic field generator. The minimum value is selected from the respective maximum values recorded for each position and direction of the magnetic field generator. Because the selected minimum value is the field strength of the magnetic field generator, it varies depending on a diameter or number of turns of the coil or a circuit to be connected. Therefore, the minimum value is multiplied by a coefficient relating to the diameter of the coil, the number of turns of the coil, and the circuit to be connected unique to the magnetic field generator **2***b *in the capsule endoscope **2**. Accordingly, the minimum value is converted to the field-strength detection value corresponding to the magnetic field generator **2***b*. The converted field-strength detection value is stored in the threshold storage unit **45** as the threshold relating to the magnetic field information of the capsule endoscope **2**.

The controller **46** has a control function for controlling an information writing operation and an information reading operation of the threshold storage unit **45** in addition to the control function of the controller **16** in the position detecting device **10** according to the first embodiment. The controller **46** includes the convergence determining unit **16***a*, the area determining unit **16***b*, and the update processor **16***c*, and also includes a level determining unit **46***d *and an output unit **46***e*. The controller **46** compares the measurement value of the magnetic field information of the capsule endoscope **2** in the three-dimensional space A**0** with the threshold in the threshold storage unit **45** to determine a difference between the measurement value of the magnetic field information and the threshold, and controls the optimization convergence calculation by the position calculator **13** based on a determination result. Specifically, when the measurement value of the magnetic field information is equal to or larger than the threshold, the controller **46** permits the optimization convergence calculation by the position calculator **13**. When the measurement value of the magnetic field information is smaller than the threshold, the controller prohibits the optimization convergence calculation by the position calculator **13**. Other functions included in the controller **46** are the same as those of the controller **16** in the position detecting device **10** according to the first embodiment.

The level determining unit **46***d *determines whether the measurement value of the magnetic field information related to the capsule endoscope **2** in the three-dimensional space A**0** is smaller than the threshold in the threshold storage unit **45**. Specifically, every time the level determining unit **46***d *acquires the field-strength detection values Bd_{1}, . . . , Bd_{n }acquired by the respective detection coils **12** from the magnetic field detector **11**, the level determining unit **46***d *reads the threshold from the threshold storage unit **45**. The level determining unit **46***d *compares the maximum value of the field-strength detection values Bd_{1}, . . . , Bd_{n }with the threshold to determine whether the maximum value is smaller than the threshold.

The output unit **46***e *outputs a control signal for suspending the optimization convergence calculation to the position calculator **13**. Specifically, when the level determining unit **46***d *determines that the measurement value of the magnetic field information related to the capsule endoscope **2** (that is, field-strength detection values Bd_{1}, . . . , Bd_{n}) is smaller than the threshold, the output unit **46***e *outputs the control signal for suspending the optimization convergence calculation to the position calculator **13** based on a determination result.

An operation of the position detecting device **43** according to the fourth embodiment of the present invention is explained next. FIG. 10 is a flowchart exemplifying a process procedure performed by the position detecting device when the optimization convergence calculation is permitted or prohibited depending on a comparison result between the field-strength detection value and the threshold. The operation of the position detecting device **43** according to the fourth embodiment is the same as that of the position detecting device **10** according to the first embodiment, except for the operation at the time of permitting or prohibiting the optimization convergence calculation depending on the comparison result between the field-strength detection value and the threshold. The operation of the position detecting device **43** at the time of permitting or prohibiting the optimization convergence calculation by the position calculator **13** depending on the comparison result between the field-strength detection values Bd_{1}, . . . , Bd_{n }acquired by the respective detection coils **12** and the preset threshold is explained below with reference to FIG. 10.

As shown in FIG. 10, the controller **46** in the position detecting device **43** according to the fourth embodiment acquires the field-strength detection values Bd_{1}, . . . , Bd_{n }of the respective detection coils **12** from the magnetic field detector **11** (Step S**501**) in the same manner as at Step S**103**, and holds the maximum detection value, which is the maximum value of the acquired field-strength detection values Bd_{1}, . . . , Bd_{n }(Step S**502**). In this case, the level determining unit **46***d *acquires and holds the maximum detection value of the acquired field-strength detection values Bd_{1}, . . . , Bd_{n}, every time the field-strength detection values Bd_{1}, . . . , Bd_{n }of the respective detection values **12** are acquired from the magnetic field detector **11**.

The controller **46** then reads the threshold from the threshold storage unit **45** (Step S**503**), and compares the read threshold with the maximum detection value held at Step S**502** (Step S**504**) to determine a difference between the maximum detection value and the threshold (Step S**505**). In this case, the level determining unit **46***d *reads the threshold from the threshold storage unit **45**, which is stored in the threshold storage unit **45** beforehand as the threshold of the measurement value of the magnetic field information related to the capsule endoscope **2**. Subsequently, the level determining unit **46***d *compares the read threshold with the maximum detection value held at Step S**502**, to determine whether the maximum detection value is smaller than the threshold.

When having determined that the maximum detection value is smaller than the threshold at Step S**505** (YES at Step S**505**), the controller **46** prohibits the optimization convergence calculation by the position calculator **13** (Step S**506**), and then returns to Step S**501** to repeat the process procedure at Step S**501** and subsequent steps.

At Steps S**505** and S**506**, the level determining unit **46***d *determines that the maximum detection value of the field-strength detection values Bd_{1}, . . . , Bd_{n }is smaller than the threshold as a result of a comparing process at Step S**504**. The output unit **46***e *generates a control signal for prohibiting execution of the optimization convergence calculation based on a determination result of the level determining unit **46***d*, and outputs the generated control signal to the position calculator **13**.

The threshold in the threshold storage unit **45** indicates the smallest value of the respective maximum values of the magnetic-field detection values detectable by position and direction in the three-dimensional space A**0**. Accordingly, when the maximum detection value of the field-strength detection values Bd_{1}, . . . , Bd_{n }acquired by the respective detection coils is smaller than the threshold, there is high possibility that the current position of the capsule endoscope **2** as a detection target is outside the three-dimensional space A**0**, at least outside the detection space of the position detecting device **43**. Based on this fact, when the maximum detection value is smaller than the threshold, the level determining unit **46***d *determines that the current state is not suitable for performing position calculation of the capsule endoscope **2**, and the output unit **46***e *outputs a control signal for prohibiting execution of the optimization convergence calculation to the position calculator **13**.

Upon reception of the control signal for prohibiting the execution, the position calculator **13** suspends the optimization convergence calculation at Step S**106** shown in FIG. 2. As a result, the position calculator **13** does not need to perform useless optimization convergence calculations having high possibility of reaching the diverged state, in a state with the capsule endoscope **2** as a detection target being not present in the three-dimensional space A**0** (not present at least in the detection space of the position detecting device **43**).

In practice, the level of an acquisition signal of the field-strength detection values Bd_{1}, . . . , Bd_{n }can drift due to a peripheral temperature or the like of the capsule endoscope **2**. Therefore, it is desired that the threshold prestored in the threshold storage unit **45** is set to a value slightly larger than a calculated value, taking the drift of the signal level of the field-strength detection values Bd_{1}, . . . , Bd_{n }into consideration.

When having determined that the maximum detection value is not smaller than the threshold, that is, equal to or larger than the threshold at Step S**505** (NO at Step S**505**), the controller **46** permits the optimization convergence calculation by the position calculator **13** (Step S**507**), and returns to Step S**501** to repeat the process procedure at Step S**501** and subsequent steps.

At Steps S**505** and S**506**, the level determining unit **46***d *determines that the maximum detection value of the field-strength detection values Bd_{1}, . . . , Bd_{n }is equal to or larger than the threshold as a result of comparison at Step S**504**. In this case, the output unit **46***e *does not output the control signal mentioned above for prohibiting the execution to the position calculator **13**. As a result, the position calculator **13** is allowed to perform the optimization convergence calculation, and starts or continues the optimization convergence calculation at Step S**104** shown in FIG. 2.

The controller **46** can perform the process procedure at Steps S**501** to S**507** concurrently with the process procedure at Steps S**103** to S**106** shown in FIG. 2. Alternatively, the controller **46** can perform the process procedure at Steps S**501** to S**505** after performing Step S**102** can repeat the process procedure at Step S**104** and subsequent steps after performing Step S**506** or can repeat the process procedure at Step S**102** and subsequent steps, after performing Step S**507**.

A configuration of the capsule endoscope **2** as a detection target is explained next in detail. FIG. 11 is a schematic diagram of a configuration example of a capsule endoscope as a detection target. FIG. 12 is a schematic diagram of an example of a circuit configuration of a magnetic field generator incorporated in the capsule endoscope. An internal configuration of the capsule endoscope **2** is shown in FIG. 12.

As shown in FIG. 11, the capsule endoscope **2** includes a capsule-shaped casing **51** having a size introducible into organs of a subject such as a patient, and includes the magnet **2***a *and the magnetic field generator **2***b *in the capsule-shaped casing **51**. The capsule endoscope **2** also includes an imaging unit **53**, a signal processor **54**, a wireless transmitter **55**, an antenna coil **56**, and an endoscope battery **57** in the capsule-shaped casing **51**.

The imaging unit **53** is realized by using a light emitting unit such as an LED, a solid-state imaging element such as a CCD, and an optical system such as a condenser lens. The imaging unit **53** illuminates a subject through an optical dome of the capsule-shaped casing **51** and receives reflecting light from the illuminated subject to capture images of the subject (for example, in-vivo images of the subject).

The signal processor **54** acquires the image captured by the imaging unit **53**, and performs predetermined signal processing with respect to the acquired signal to generate an image signal including image data by the imaging unit **53**. The wireless transmitter **55** performs a predetermined communication process such as a modulation process on the image signal generated by the signal processor **54** to generate the radio signal including the image signal. The wireless transmitter **55** is connected to the antenna coil **56**, and transmits the generated radio signal to an external receiving device (not shown) via the antenna coil **56**.

The endoscope battery **57** is, for example, a button-shaped battery, and supplies driving power to the imaging unit **53**, the signal processor **54**, and the wireless transmitter **55**. The endoscope battery **57** needs only to supply the power required for the imaging unit **53**, the signal processor **54**, and the wireless transmitter **55** for a predetermined time or longer, and the number of endoscope batteries to be arranged is not particularly limited to two, and can be one or more.

As described above, the magnet **2***a *is an element to realize magnetic guidance of the capsule endoscope **2** by the magnetic guiding device **4**, and as shown in FIG. 11, is arranged at a rear end of the capsule-shaped casing **51**. Accordingly, the magnet **2***a *is arranged away from the antenna coil **56** as much as possible. As a result, deterioration of antenna characteristics of the antenna coil **56** is prevented. The magnet **2***a *is arranged such that a magnetization direction thereof is vertical to an opening direction of the antenna coil **56** to minimize such an occasion that the magnetic field generated by the magnet **2***a *passes the antenna coil **56**. A partition, which is a part of the capsule-shaped casing **51**, is provided between the magnet **2***a *and a battery dedicated to the magnetic field generator **2***b *(a battery **52***d *for a magnetic field generator) to maintain a predetermined gap therebetween. This is because a magnetic force of the magnet **2***a *is weakened by a magnetic body of the battery **52***d *for a magnetic field generator, thereby preventing a force acting on the capsule endoscope **2** from decreasing at the time of magnetic guidance. The rear end of the capsule-shaped casing **51** incorporating the magnet **2***a *is detachable so that the magnet **2***a *can be easily incorporated therein or detached therefrom.

The magnetic field generator **2***b *generates the magnetic field used for detecting the position and direction of the capsule endoscope **2**, and as shown in FIGS. 11 and 12, includes a resonance coil **52***a*, a resonance capacitor **52***b*, an oscillation driving circuit **52***c*, and the battery **52***d *for a magnetic field generator.

The battery **52***d *for a magnetic field generator is a single-purpose battery for the magnetic field generator **2***b*, and is realized by, for example, a button-shaped battery. The battery **52***d *for a magnetic field generator is arranged away from the antenna coil **56** as much as possible, thereby preventing deterioration of the antenna characteristics of the antenna coil **56**. Further, a part of the battery **52***d *for a magnetic field generator, which is incorporated in the capsule-shaped casing **51**, is detachable so that the battery **52***d *for a magnetic field generator can be easily replaced. The power generated by the battery **52***d *for a magnetic field generator is supplied to the oscillation driving circuit **52***c. *

The oscillation driving circuit **52***c *is configured by using a switching element **52***e *and a crystal resonance circuit **52***f *as shown in FIG. 12. When the power is supplied by the battery **52***d *for a magnetic field generator, the oscillation driving circuit **52***c *generates a signal by the crystal resonance circuit **52***f*, and outputs the generated signal to the resonance coil **52***a *and the resonance capacitor **52***b *via the switching element **52***e. *

The resonance coil **52***a *and the resonance capacitor **52***b *form the resonance circuit as shown in FIG. 12, and generates the magnetic field upon reception of the signal from the oscillation driving circuit **52***c*. The magnetic field generated by the resonance coil **52***a *and the resonance capacitor **52***b *is output outside of the capsule endoscope **2**, and then detected by the magnetic field detector **11**.

The battery **52***d *for a magnetic field generator needs only to supply power required for generating the magnetic field by the resonance coil **52***a *and the resonance capacitor **52***b *for a predetermined time or longer, and the number of batteries to be arranged is not particularly limited to two, and can be one or more. The magnetic field generator **2***b *can share the power of the endoscope battery **57**, and in this case, the battery **57** for a magnetic field generator does not need to be provided.

In the fourth embodiment of the present invention, as described above, the threshold of the measurement value of the magnetic field information related to the capsule endoscope in the three-dimensional space is stored beforehand in the threshold storage unit, and every time the magnetic field detector detects the strength of the magnetic field from the capsule endoscope, the field-strength detection value acquired by the magnetic field detector is compared with the threshold in the threshold storage unit to determine a difference between the field-strength detection value and the threshold. When the field-strength detection value is smaller than the threshold, the optimization convergence calculation by the position calculator is prohibited. When the field-strength detection value is equal to or larger than the threshold, the optimization convergence calculation by the position calculator is permitted. Other features of the fourth embodiment are the same as those in the first embodiment. Accordingly, the fourth embodiment can achieve the same operational effect as those of the first embodiment, and the optimization convergence calculation by the position calculator can be suspended in a state where there is no capsule endoscope in a space capable of detecting the position, thereby enabling to realize a position detecting device capable of reducing the power of the device consumed to perform the optimization convergence calculation.

Further, in a state where there is no capsule endoscope in a space capable of detecting the position, the optimization convergence calculation by the position calculator is not performed. Therefore, it is possible to prevent a case that the position calculation of the capsule endoscope having a large error is performed and the error value in the optimization convergence calculation diverges. Accordingly, the starting point of calculation having a large error is not set at the time of performing the next optimization convergence calculation. As a result, it is possible to prevent a case that the error value is diffused erroneously at the time of performing the normal optimization convergence calculation after the error value has converged.

In the third embodiment of the present invention described above, one detection coil **32***b *is incorporated in the capsule endoscope **32**. However, a plurality of detection coils can be incorporated in the capsule endoscope **32**. In this case, it is desired that a product of the number of drive coils to be arranged, which are included in the drive coil groups **35***a *and **35***b *that apply a plurality of magnetic fields to the plurality of detection coils, and the number of detection coils to be arranged is six or more.

In the first to fourth embodiments of the present invention described above, the position detecting device incorporated in the capsule guiding system that magnetically guides the capsule endoscope introduced into a subject to detect the position information of the capsule endoscope in the subject is exemplified. However, the position detecting device according to the present invention needs only to detect the position information by performing the optimization convergence calculation based on the evaluation function expressing an error between the measurement value and the theoretical value of the magnetic field information of a detection target, and is not particularly limited to the position detecting device combined with the capsule guiding system.

The detection target whose position information is detected by the position detecting device according to the present invention is not limited to a medical device such as the capsule endoscope described above. Further, the capsule medical device whose position information is detected as a detection target is not limited to the capsule endoscope, and can be a capsule pH-measuring device that measures pH in a living body, a capsule drug-administration device including a function of spraying or injecting a drug into a living body, or a capsule collecting device that collects a material in a living body.

In the second and third embodiments described above, the optimization convergence calculation by the position calculator **13** is performed every time the field-strength detection values Bd_{1}, . . . , Bd_{n }of the respective detection coils **12** are acquired from the magnetic field detector **11**. However, as in the fourth embodiment, the maximum value of the acquired field-strength detection values Bd_{1}, . . . , Bd_{n }is compared with the set threshold, every time the field-strength detection values Bd_{1}, . . . , Bd_{n }of the respective detection coils **12** are acquired, to permit or prohibit the optimization convergence calculation according to a comparison result. That is, the position detecting devices **23** and **34** according to the second and third embodiments can also include the threshold storage unit **45**, and the controllers **27** and **38** in the position detecting devices **23** and **34** can also include the level determining unit **46***d *and the output unit **46***e. *

In this case, the threshold storage unit **45** in the position detecting devices **23** and **34** according to the second and third embodiments stores a plurality of thresholds of the magnetic field information related to the capsule endoscope for each axial direction (an opening direction) of the magnetic-field generation coils included in the drive coil group. The controllers **27** and **38** select a threshold to be compared with the measurement value of the magnetic field information (that is, the maximum value of the field-strength detection values Bd_{1}, . . . , Bd_{n}) from the plurality of thresholds in the threshold storage unit **45**, corresponding to a magnetic-field generation coil, among the magnetic-field generation coils, that applies a magnetic field to the capsule endoscope.

In the controllers **27** and **38**, the level determining unit **46***d *identifies the magnetic-field generation coil being driven from the drive coil group based on the control signal with respect to the coil selector, and selects a threshold corresponding to the identified magnetic-field generation coil from the plurality of thresholds in the threshold storage unit **45**. The level determining unit **46***d *then reads the selected threshold from the threshold storage unit **45**, and as in the fourth embodiment, compares the threshold with the maximum detection value of the field-strength detection values Bd_{1}, . . . , Bd_{n}, to determine a difference between the maximum detection value and the threshold. As in the fourth embodiment, when the maximum detection value is smaller than the threshold, the output unit **46***e *needs only to output a control signal for prohibiting execution of calculation to the position calculator **13**.

Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.

1. A position detecting device comprising:

a position calculator that performs an optimization convergence calculation using an evaluation function that expresses an error between a measurement value and a theoretical value of magnetic field information of a detection target to calculate at least a position of the detection target as a convergence result;

a storage unit that stores a final convergence result of the optimization convergence calculation performed by the position calculator, wherein the final convergence result is the latest convergence result in a time series; and

a controller that

determines whether a convergence result of the optimization convergence calculation converges,

suspends the optimization convergence calculation performed by the position calculator when the convergence result does not converge, and

performs, after a predetermined time has passed, a returning process of returning a state of the optimization convergence calculation to a converged state by causing the position calculator to perform the optimization convergence calculation based on the final convergence result.

a position calculator that performs an optimization convergence calculation using an evaluation function that expresses an error between a measurement value and a theoretical value of magnetic field information of a detection target to calculate at least a position of the detection target as a convergence result;

a storage unit that stores a final convergence result of the optimization convergence calculation performed by the position calculator, wherein the final convergence result is the latest convergence result in a time series; and

a controller that

determines whether a convergence result of the optimization convergence calculation converges,

suspends the optimization convergence calculation performed by the position calculator when the convergence result does not converge, and

performs, after a predetermined time has passed, a returning process of returning a state of the optimization convergence calculation to a converged state by causing the position calculator to perform the optimization convergence calculation based on the final convergence result.

determines whether a convergence result of the optimization convergence calculation converges,

suspends the optimization convergence calculation performed by the position calculator when the convergence result does not converge, and

performs, after a predetermined time has passed, a returning process of returning a state of the optimization convergence calculation to a converged state by causing the position calculator to perform the optimization convergence calculation based on the final convergence result.

2. The position detecting device according to claim 1, wherein the controller sets a determination area in a position detection space of the detection target to determine whether the position of the detection target is in the determination area, and performs the returning process when the position is outside the determination area, and

the storage unit stores, when the result of the optimization convergence calculation converges and the position of the detection target is in the determination area, the final convergence result of the optimization convergence calculation.

the storage unit stores, when the result of the optimization convergence calculation converges and the position of the detection target is in the determination area, the final convergence result of the optimization convergence calculation.

3. The position detecting device according to claim 2, wherein the controller sets, in the determination area, an inside area smaller than the determination area by at least a space corresponding to a position variation range of the detection target, determines whether the position of the detection target is in the inside area, expands the determination area by at least the space corresponding to a variation range of the detection target when the position of the detection target is outside the inside area, determines whether the position of the detection target is in the expanded determination area, and performs the returning process when the position of the detection target is outside the expanded determination area.

4. The position detecting device according to claim 1, further comprising:

a plurality of magnetic-field generation coils that are arranged around the detection target and apply a magnetic field to the detection target; and

a switching unit that selects from the magnetic-field generation coils at least one magnetic-field generation coil for generating the magnetic field,

wherein the detection target has a resonance circuit that resonates due to the magnetic field generated by the at least one magnetic-field generation coil to newly generate a resonance magnetic field, and

the controller performs, when a result of the optimization convergence calculation in the returning process does not converge, the returning process again after causing the switching unit to switch the magnetic-field generation coils.

a plurality of magnetic-field generation coils that are arranged around the detection target and apply a magnetic field to the detection target; and

a switching unit that selects from the magnetic-field generation coils at least one magnetic-field generation coil for generating the magnetic field,

wherein the detection target has a resonance circuit that resonates due to the magnetic field generated by the at least one magnetic-field generation coil to newly generate a resonance magnetic field, and

the controller performs, when a result of the optimization convergence calculation in the returning process does not converge, the returning process again after causing the switching unit to switch the magnetic-field generation coils.

5. The position detecting device according to claim 2, further comprising:

a plurality of magnetic-field generation coils that are arranged around the detection target and apply a magnetic field to the detection target; and

a switching unit that selects from the magnetic-field generation coils at least one magnetic-field generation coil for generating the magnetic field,

wherein the detection target has a resonance circuit that resonates due to the magnetic field generated by the at least one magnetic-field generation coil to newly generate a resonance magnetic field, and

the controller performs, when the position of the detection target calculated by the optimization convergence calculation in the returning process is outside the determination area, the returning process again after causing the switching unit to switch the magnetic-field generation coils.

the controller performs, when the position of the detection target calculated by the optimization convergence calculation in the returning process is outside the determination area, the returning process again after causing the switching unit to switch the magnetic-field generation coils.

6. The position detecting device according to claim 3, further comprising:
a plurality of magnetic-field generation coils that are arranged around the detection target and apply a magnetic field to the detection target; and
a switching unit that selects from the magnetic-field generation coils at least one magnetic-field generation coil for generating the magnetic field,
wherein the detection target has a resonance circuit that resonates due to the magnetic field generated by the at least one magnetic-field generation coil to newly generate a resonance magnetic field, and

the controller performs, when the position of the detection target calculated by the optimization convergence calculation in the returning process is outside the expanded determination area, the returning process again after causing the switching unit to switch the magnetic-field generation coils.

the controller performs, when the position of the detection target calculated by the optimization convergence calculation in the returning process is outside the expanded determination area, the returning process again after causing the switching unit to switch the magnetic-field generation coils.

7. The position detecting device according to claim 1, further comprising:
a plurality of magnetic-field generation coils that are arranged around the detection target and apply a magnetic field to the detection target; and
a switching unit that selects from the magnetic-field generation coils at least one magnetic-field generation coil for generating the magnetic field,

wherein the detection target has a magnetic field detector that detects the magnetic field generated by the at least one magnetic-field generation coil as the magnetic field information, and

the controller acquires the magnetic field information detected by the magnetic field detector, causes the position calculator to perform the optimization convergence calculation using the acquired magnetic field information, and performs, when a result of the optimization convergence calculation in the returning process does not converge, the returning process again after causing the switching unit to switch the magnetic-field generation coils.

wherein the detection target has a magnetic field detector that detects the magnetic field generated by the at least one magnetic-field generation coil as the magnetic field information, and

the controller acquires the magnetic field information detected by the magnetic field detector, causes the position calculator to perform the optimization convergence calculation using the acquired magnetic field information, and performs, when a result of the optimization convergence calculation in the returning process does not converge, the returning process again after causing the switching unit to switch the magnetic-field generation coils.

8. The position detecting device according to claim 2, further comprising:
a plurality of magnetic-field generation coils that are arranged around the detection target and apply a magnetic field to the detection target; and
a switching unit that selects from the magnetic-field generation coils at least one magnetic-field generation coil for generating the magnetic field,

wherein the detection target has a magnetic field detector that detects the magnetic field generated by the at least one magnetic-field generation coil as the magnetic field information, and

the controller acquires the magnetic field information detected by the magnetic field detector, causes the position calculator to perform the optimization convergence calculation using the acquired magnetic field information, and performs, when the position of the detection target calculated by the optimization convergence calculation in the returning process is outside the determination area, the returning process again after causing the switching unit to switch the magnetic-field generation coils.

the controller acquires the magnetic field information detected by the magnetic field detector, causes the position calculator to perform the optimization convergence calculation using the acquired magnetic field information, and performs, when the position of the detection target calculated by the optimization convergence calculation in the returning process is outside the determination area, the returning process again after causing the switching unit to switch the magnetic-field generation coils.

9. The position detecting device according to claim 3, further comprising:
a plurality of magnetic-field generation coils that are arranged around the detection target and apply a magnetic field to the detection target; and
a switching unit that selects from the magnetic-field generation coils at least one magnetic-field generation coil for generating the magnetic field,
wherein the detection target has a magnetic field detector that detects the magnetic field generated by the at least one magnetic-field generation coil as the magnetic field information, and

the controller acquires the magnetic field information detected by the magnetic field detector, causes the position calculator to perform the optimization convergence calculation using the acquired magnetic field information, and performs, when the position of the detection target calculated by the optimization convergence calculation in the returning process is outside the expanded determination area, the returning process again after causing the switching unit to switch the magnetic-field generation coils.

the controller acquires the magnetic field information detected by the magnetic field detector, causes the position calculator to perform the optimization convergence calculation using the acquired magnetic field information, and performs, when the position of the detection target calculated by the optimization convergence calculation in the returning process is outside the expanded determination area, the returning process again after causing the switching unit to switch the magnetic-field generation coils.

10. The position detecting device according to claim 1, wherein the controller comprises a convergence determining unit that determines whether a result of the optimization convergence calculation converges, and the controller suspends, when the convergence determining unit determines that the result of the optimization convergence calculation does not converge, the optimization convergence calculation performed by the position calculator, and performs the returning process after a predetermined time has passed.

11. The position detecting device according to claim 2, wherein the controller comprises an area determining unit that determines an area containing the position of the detection target calculated by the optimization convergence calculation,

the area determining unit determines whether the position of the detection target is in the determination area,

the controller performs, when the area determining unit determines that the position of the detection target is outside the determination area, the returning process, and

the storage unit stores, when a result of the optimization convergence calculation converges and the area determining unit determines that the position of the detection target is in the determination area, the final convergence result of the optimization convergence calculation.

the area determining unit determines whether the position of the detection target is in the determination area,

the controller performs, when the area determining unit determines that the position of the detection target is outside the determination area, the returning process, and

the storage unit stores, when a result of the optimization convergence calculation converges and the area determining unit determines that the position of the detection target is in the determination area, the final convergence result of the optimization convergence calculation.

12. The position detecting device according to claim 11, wherein the controller sets, in the determination area, an inside area smaller than the determination area by at least a space corresponding to a position variation range of the detection target,

the area determining unit determines whether the position of the detection target is in the inside area,

the controller expands the determination area by at least the space corresponding to a variation range of the detection target when the area determining unit determines that the position of the detection target is outside the inside area,

the area determining unit determines whether the position of the detection target is in the expanded determination area, and

the controller performs the returning process when the area determining unit determines that the position of the detection target is outside the expanded determination area.

the area determining unit determines whether the position of the detection target is in the inside area,

the controller expands the determination area by at least the space corresponding to a variation range of the detection target when the area determining unit determines that the position of the detection target is outside the inside area,

the area determining unit determines whether the position of the detection target is in the expanded determination area, and

the controller performs the returning process when the area determining unit determines that the position of the detection target is outside the expanded determination area.

13. A position detecting device comprising:

a position calculator that performs an optimization convergence calculation using an evaluation function that expresses an error between a measurement value and a theoretical value of magnetic field information of a detection target to calculate at least a position of the detection target;

a threshold storage unit that stores a threshold concerning a measurement value of the magnetic field information; and

a controller that compares the measurement value of the magnetic field information with the threshold to determine a difference between the measurement value of the magnetic field information and the threshold, permits, when the measurement value of the magnetic field information is equal to or larger than the threshold, the optimization convergence calculation performed by the position calculator, and prohibits, when the measurement value of the magnetic field information is smaller than the threshold, the optimization convergence calculation performed by the position calculator.

a position calculator that performs an optimization convergence calculation using an evaluation function that expresses an error between a measurement value and a theoretical value of magnetic field information of a detection target to calculate at least a position of the detection target;

a threshold storage unit that stores a threshold concerning a measurement value of the magnetic field information; and

a controller that compares the measurement value of the magnetic field information with the threshold to determine a difference between the measurement value of the magnetic field information and the threshold, permits, when the measurement value of the magnetic field information is equal to or larger than the threshold, the optimization convergence calculation performed by the position calculator, and prohibits, when the measurement value of the magnetic field information is smaller than the threshold, the optimization convergence calculation performed by the position calculator.

14. The position detecting device according to claim 13, wherein the controller comprises:

a level determining unit that determines whether the measurement value of the magnetic field information is smaller than the threshold; and

an output unit that outputs to the position calculator, when the level determining unit determines that the measurement value of the magnetic field information is smaller than the threshold, a control signal for suspending the optimization convergence calculation performed by the position calculator.

a level determining unit that determines whether the measurement value of the magnetic field information is smaller than the threshold; and

an output unit that outputs to the position calculator, when the level determining unit determines that the measurement value of the magnetic field information is smaller than the threshold, a control signal for suspending the optimization convergence calculation performed by the position calculator.

15. The position detecting device according to claim 13, further comprising a magnetic field detector that detects using a plurality of magnetic-field detection coils a magnetic field generated by the detection target and outputs each of detection results acquired by the magnetic-field detection coils to the controller as the measurement value of the magnetic field information.

16. The position detecting device according to claim 15, wherein the measurement value of the magnetic field information is a maximum value of the detection results acquired by the magnetic-field detection coils.

17. The position detecting device according to claim 15, further comprising:
a plurality of magnetic-field generation coils that are arranged around the detection target and apply a magnetic field to the detection target; and
a switching unit that selects from the magnetic-field generation coils at least one magnetic-field generation coil for generating the magnetic field,

wherein the detection target generates a resonance magnetic field upon reception of the magnetic field applied by the at least one magnetic-field generation coil, and

the magnetic field detector detects using the magnetic-field detection coils the resonance magnetic field generated by the detection target and outputs each of detection results of the resonance magnetic field acquired by the magnetic-field generation coils to the controller as the measurement values of the magnetic field information.

wherein the detection target generates a resonance magnetic field upon reception of the magnetic field applied by the at least one magnetic-field generation coil, and

the magnetic field detector detects using the magnetic-field detection coils the resonance magnetic field generated by the detection target and outputs each of detection results of the resonance magnetic field acquired by the magnetic-field generation coils to the controller as the measurement values of the magnetic field information.

18. The position detecting device according to claim 17, wherein the threshold storage unit stores a plurality of thresholds concerning the measurement values of the magnetic field information for each axial direction of the magnetic-field generation coils, and

the controller selects from the thresholds a threshold to be compared with the measurement value of the magnetic field information, the threshold corresponding to the magnetic-field generation coil, among the magnetic-field generation coils, that applies the magnetic field to the detection target.

the controller selects from the thresholds a threshold to be compared with the measurement value of the magnetic field information, the threshold corresponding to the magnetic-field generation coil, among the magnetic-field generation coils, that applies the magnetic field to the detection target.