Imported: 17 Feb '17 | Published: 01 Aug '06

USPTO - Utility Patents

Provided are a method of generating a current trajectory for seek control of a hard disc drive and a seek control system using the same, the method including setting a current trajectory from harmonics of a sinusoidal wave; calculating a power consumed by a target device to be controlled using the current trajectory; and determining coefficients of the harmonics so as to minimize the power consumed by the device.

This application claims the priority of Korean Patent Application No. 2003-70047, filed on Oct. 8, 2003, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.

1. Field of the Invention

The present invention relates to a method of generating a current trajectory for seek control of a hard disc drive and a seek control system using the same, and more particularly, to a method of generating a current trajectory by which power is reduced during seek control of a hard disc drive, and a seek control system using the same.

2. Description of the Related Art

In general, a hard disc drive comprises a plurality of magnetic transducers that sense magnetic field of and/or magnetize a single rotating disc or each of a plurality of rotating discs, to write and/or read information to and/or from the disc. The information is typically formatted in a plurality of sectors placed in a ring-shaped track. The tracks are numbered across a surface of the disc. The track numbers being vertically similar to one another are called cylinders. Thus, each track is defined by a cylinder number.

In general, each transducer is integrated to a slider included in a head gimbal assembly (HGA). Each HGA is attached to an actuator. The actuator has a voice coil adjacent to a magnetic assembly, which also specifies a voice coil motor (VCM).

The hard disc drive also comprises a driving circuit for supplying a current to excite the VCM, and a controller. The excited VCM rotates the actuator and moves the magnetic transducers across the surface of the disc(s).

When information is written and/or read into and/or from the disc, the hard disc drive performs a seek routine for moving the magnetic transducers from one cylinder to another cylinder. During the seek routine, the VCM is excited by a current used to move the magnetic transducers to a position of a new cylinder from the surface of the disc. The controller performs a servo routine that guarantees the magnetic transducers to accurately move to a correct position of a cylinder at the center of a track.

Many studies on moving the magnetic transducers to a correct position within the shortest time during the seek routine have been made. However, a serious problem is power consumption of a hard disc drive mounted on a mobile device such as a camcorder or a MP3 player. Since a system in a mobile device is powered by a battery, the power consumption should be as small as possible. The power consumption can be reduced by scheduling operation or stop of a drive by an application program during execution of the application program, by driving a spindle motor, and by appropriately performing a seek control of the VCM.

As described above, the conventional seek control of the VCM has been focused on optimum time control, so as to minimize a track seek time. However, since an acceleration waveform is discontinuous, the optimum time control stimulates a high frequency mode of a mechanical system and increases undesired mechanical noise and vibration. Due to this problem, a seek controller using a soft acceleration waveform of a sinusoidal wave shape, instead of a square wave shape, has been used.

However, a hard disc employed in a mobile device should focus on reducing power consumption rather than on reducing seek time and noise. In particular, during a random file access, the amount of the power consumption during the seek control is not negligible. Accordingly, the hard disc drive used in the mobile device requires a control by which at least required seek time performance is maintained while power consumption is minimized.

The present invention provides a method of generating a current trajectory by which power consumption of a hard disc drive is minimized, and a seek control system for controlling a voice coil motor (VCM) using the same.

According to an aspect of the present invention, there is provided a method of generating a current trajectory, the method including setting a current trajectory from harmonics of a sinusoidal wave; calculating a power consumed by a target device to be controlled using the current trajectory; and determining coefficients of the harmonics so as to minimize the power consumed by the device.

According to another aspect of the present invention, there is provided a seek control system for driving an actuator in a hard disc drive, the system including a sinusoidal wave generator generating harmonics of a sinusoidal wave having predetermined coefficients; a trajectory generator generating trajectories of a position, a speed, and an acceleration of the actuator from the harmonics, so as to minimize a power consumed by the actuator; and a driving current supplying unit multiplying the position, speed, and acceleration trajectories of the actuator by predetermined coefficients, respectively, adding multiplication results, and outputting the addition results as a driving current for driving the actuator.

Hereinafter, an exemplary embodiment of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 illustrates a configuration of a hard disc drive. A hard disc drive **10** shown in FIG. 1 comprises at least one magnetic disc **12** rotated by a spindle motor **14**. The hard disc drive **10** further comprises a transducer **16** above a disc surface **18**.

The transducer **16** senses a magnetic field of and magnetizes each disc **12** to write and/or read information into and/or from the rotative disc **12**. Typically, the transducer **16** is coupled with the disc surface **18**. Even though a single transducer **16** is shown, it should be understood that the transducer **16** comprises a writing transducer for magnetizing the disc **12** and a reading transducer for sensing magnetic field of the disc **12**. The reading transducer is formed of magneto-resistive (MR) materials.

The transducer **16** can be integrated to a slider **20**. The slider **20** has a structure in which an air bearing is generated between the transducer **16** and the disc surface **18**. The slider **20** is combined with a head gimbal assembly (HGA) **22**. The HGA **22** is attached to an actuator **24** having a voice coil **26**. The voice coil **26** of a voice coil motor (VCM) **30** is adjacent to a magnetic assembly **28**, which generates movement of the VCM **30**. A current supplied to the voice coil **26** generates a torque used to rotate the actuator at a center of a bearing assembly **32**. Due to rotation of the actuator **24**, the transducer **16** moves across the disc surface **18**.

In general, information is stored in a ring-shaped track **34** of the disc **12**. In general, each track **34** comprises a plurality of sectors. Each sector comprises a data field and an identification field. The identification field comprises a gray code for identifying a sector and a track (cylinder). The transducer **16** moves across the disc surface **18** to write and/or read information into and/or from another track.

Movements of the actuator **24** and the transducer **16** are performed by a controller (not shown). The controller moves the transducer **16** to a new track from a current track in accordance with a seek routine and a servo control routine. During the seek routine, the controller determines a seek distance between a first track and a second track, adjusts a seek time in response to a speed error between a calculated speed and a designed speed on the seek distance, and controls the actuator **24** to move the transducer **16** to the new track from the current track across the disc surface **18** using an acceleration trajectory.

Equations for the voltage and a motion required for driving the actuator **24** are as follows.

*L{dot over (i)}+K*_{e}{dot over (x)}+Ri=v

*{umlaut over (x)}+B{dot over (x)}=K*_{a}i (1)

Here, v, i, and x are a voltage, a current applied to the VCM **30**, and a position of the actuator **24**, respectively. Constants L, R, K_{e}, K_{a}, and B are inductance of the VCM **30**, a resistance of the VCM **30**, a constant on a counter electromotive force generated according to movement of the actuator **24**, an acceleration constant, and a friction coefficient of the actuator **24**, respectively.

During a seek operation, an averaged input power applied to the actuator **24** by an applied current and voltage is expressed by multiplication of a VCM voltage by a VCM current and is given by Equation 2.

Here, a constant T is a seek time.

Since the power consumed by the inductance is 0, the power consumed as heat by the resistance of the voice coil **26** is given by Equation 3.

The mechanical power applied to the actuator **24** is obtained using Equations 1 and 2 below.

The power consumption due to mechanical friction of the actuator **24** is obtained using the foregoing Equations below.

Thus, the total amount of power consumed is obtained using the foregoing Equations 3 and 5 below.

A current trajectory for minimizing the amount of power consumed can be obtained using Equation 6. To this end, the current trajectory is set as Equation 7 from harmonics of a sinusoidal wave.

Here, current coefficients I_{1}, I_{2}, . . . , I_{N }are unknown and are selected optimally, so as to minimize power consumption. To minimize power consumption, a friction coefficient of Equation 1 is assumed to be 0, and then an acceleration trajectory corresponding to Equation 7 is given by K_{a}i(t). In addition, speed and position trajectories are given by integrating and double integrating the acceleration trajectory as follows.

Thus, the current coefficients I_{1}, I_{2}, . . . , I_{N }are given by Equation 9 from a seek distance X_{s }given by the position trajectory of Equation 8 and a seek time t=T.

In the case of using the current trajectory of Equation 7, the amount of power consumed is given by Equation 10.

Thus, the problem of minimizing the power consumption comes to one of minimizing J(Y)=Y^{T}QY, for a matrix equation AY=b. Here, the square matrix Q, vector Y, vector A, and constant b are obtained using Equation 11.

Thus, a solution Y of the optimization problem, that is, the harmonic coefficients of the current trajectory are determined by Equation 12 in accordance with Ricatti Equation.

*Y=Q*^{−1}*A*^{T}(*AQ*^{−1}*A*^{T})^{−1}*b* (12)

Thus, when the friction coefficient B=0 and it is considered up to a secondary harmonic wave of the current trajectory, namely,

the current trajectory for minimizing power consumption is given by a waveform shown in FIG. 2. FIG. 2 shows a conventional sinusoidal wave current trajectory and a current trajectory generated according to an exemplary embodiment of the present invention. Referring to FIG. 2, the actuator **24** according to a control of the present invention reaches a peak value in a shorter time than in the prior art, and after reaching the peak value, the actuator **24** moves slow. The power consumed when the actuator **24** moves on the current trajectory according to the present invention is reduced by about 20% compared to the amount of power consumed when the actuator **24** moves on the conventional sinusoidal wave current trajectory.

FIG. 3 is a block diagram of a seek control system according to the present invention. The seek control system shown in FIG. 3 comprises a current generator **200**, an amplifier **210**, and an actuator **220**. The seek control system further comprises an estimator **230** which estimates the position, speed, and acceleration of the actuator **220** from position information output from the actuator **220**.

The current generator **200** generates a current for driving the actuator **220**, and the amplifier **210** amplifies the current generated by the current generator **200**. The actuator **220** is driven by the current amplified by the amplifier **210** and moves the transducer **16** of FIG. 1 to a desired position. The estimator **230** estimates the current position x_{e}(n) of the actuator **220**, speed v_{e}(n), and acceleration w_{e}(n) from the position information output from the actuator **220** and feeds back the estimated values to the current generator **200**.

The current generator **200** comprises a sinusoidal wave generator **201**, a trajectory generator **202**, a first adder **203**, a first coefficient multiplier **204**, a second adder **205**, a second coefficient multiplier **206**, a third coefficient multiplier **207**, and a third adder **208**.

The sinusoidal wave generator **201** generates harmonics of a sinusoidal wave, as defined as Equation 7. The coefficients of the harmonic waves are determined by Equation 12. The trajectory generator **202** generates trajectories of current position x*(n), speed v*(n), and acceleration w*(n), which are given by Equation 8, from the generated harmonics.

The first adder **203** subtracts an estimated position fed back from the estimator **230** from a position generated by the trajectory generator **202**. The first coefficient multiplier **204** multiplies an output of the first adder **203** by a first coefficient K_{p}. The second adder **205** adds speed output by the first coefficient multiplier **204** to speed output by the trajectory generator **202**, subtracts an estimated speed fed back from the estimator **230** from the added speed, and outputs a voltage V_{cmd}(n). The second coefficient multiplier **206** multiplies an output of the second adder **205** by a second coefficient. The third coefficient multiplier **207** multiplies an acceleration trajectory output from the trajectory generator **202** by a third coefficient M/K_{t}. The third adder **208** adds outputs of the second and third coefficient multipliers **206** and **207** to the estimated acceleration fed back from the estimator **230** and outputs a current i_{cmd}(n) for driving the actuator **220**.

Voltage and current trajectories output from the second adder **205** and the third adder **208**, respectively, are given by Equation 13.

The seek control system drives the actuator **220** while controlling the actuator **220** in a feed-forward type according to the voltage and current trajectories given by Equation 13.

As described above, a current trajectory is generated so as to minimize power consumption during a seek control of a hard disc employed in a mobile device. Therefore, the actuator can be driven with the power consumed during an identical time period more reduced.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the following claims.

1. A method of generating a current trajectory, the method comprising:

setting a current trajectory from harmonics of a sinusoidal wave;

calculating a power consumed by a target device to be controlled using the current trajectory; and

determining coefficients of the harmonics so as to minimize the power consumed by the device.

setting a current trajectory from harmonics of a sinusoidal wave;

calculating a power consumed by a target device to be controlled using the current trajectory; and

determining coefficients of the harmonics so as to minimize the power consumed by the device.

2. The method of claim 1, wherein the target device is an actuator driven by a voice coil motor in a hard disc drive.

3. The method of claim 1, wherein the power consumed in the actuator is power consumed as heat by a resistance of the voice coil motor and power consumed by mechanical friction of the actuator.

4. The method of claim 3, wherein the determining comprises:

obtaining a position, a speed, and an acceleration of the actuator according to the current trajectory and motion equations of the actuator;

obtaining power consumed according to the current trajectory for a predetermined seek distance and seek time; and

obtaining coefficients of the current trajectory using a predetermined optimization method of minimizing the power consumed.

obtaining a position, a speed, and an acceleration of the actuator according to the current trajectory and motion equations of the actuator;

obtaining power consumed according to the current trajectory for a predetermined seek distance and seek time; and

obtaining coefficients of the current trajectory using a predetermined optimization method of minimizing the power consumed.

5. A seek control system for driving an actuator in a hard disc drive, the system comprising:

a sinusoidal wave generator generating harmonics of a sinusoidal wave having predetermined coefficients;

a trajectory generator generating trajectories of a position, a speed, and an acceleration of the actuator from the harmonics, so as to minimize a power consumed by the actuator; and

a driving current supplying unit multiplying the position, speed, and acceleration trajectories of the actuator by predetermined coefficients, respectively, adding multiplication results, and outputting the addition results as a driving current for driving the actuator.

a sinusoidal wave generator generating harmonics of a sinusoidal wave having predetermined coefficients;

a trajectory generator generating trajectories of a position, a speed, and an acceleration of the actuator from the harmonics, so as to minimize a power consumed by the actuator; and

a driving current supplying unit multiplying the position, speed, and acceleration trajectories of the actuator by predetermined coefficients, respectively, adding multiplication results, and outputting the addition results as a driving current for driving the actuator.

6. The system of claim 5, further comprising an estimator estimating a current position, a speed, and an acceleration of the actuator from an output of the actuator and outputting estimated values to the driving current supplying unit.

7. The system of claim 6, wherein the driving current supplying unit adds the estimated position, speed, and acceleration of the actuator to a position, a speed, and an acceleration output from the trajectory generator, respectively.

8. The system of claim 5, wherein the trajectory generator determines a current trajectory, so as to minimize power consumed by the actuator and outputs the position, speed, and acceleration trajectories according to the determined current trajectory according to motion equations of the actuator.

9. The system of claim 8, wherein the trajectory generator determines the current trajectory using a predetermined optimization method, so as to minimize power consumed by the actuator when a motion friction coefficient of the actuator is set to 0.