Position control apparatus and disk apparatus using the same

1. A position control apparatus that performs position control on an object using an actuator in accordance with a position of the object, comprising:

a digital control module configured to perform position control including disturbance adaptive control with a predetermined sampling period using a control constant, in accordance with a position error between a target position and a current position of the object; and

a table configured to store the control constant corresponding to one of values sin(ωT), cos(ωT), and sin(ωT/2), with ω representing an angular frequency of a disturbance, T representing the sampling period,

wherein the digital control module determines a control value of the actuator in accordance with the position error, calculates a value of one of estimated errors of sin(ωT), cos(ωT), and sin(ωT/2) according to an adaptive law from a signal based on the position error, multiplies the calculated estimated error by an adaptive gain in accordance with a value of the angular frequency ω, updates one of the values sin(ωT), cos(ωT), and sin(ωT/2), reads the corresponding control constant from the table based on the updated value, and updates the control constant, to perform the position control including the disturbance adaptive control.

2. The position control apparatus of claim 1 , wherein the digital control module performs the position control including the disturbance adaptive control by observer control.

3. The position control apparatus of claim 2 , wherein the digital control module calculates an estimated error from a state variable of the observer, an estimated gain, and an estimated position error, multiplies the estimated error by the adaptive gain, adds the estimated error to one of sin(ωT), cos(ωT), and sin(ωT/2), to update the one of sin(ωT), cos(ωT), and sin(ωT/2).

4. The position control apparatus of claim 2 , wherein the digital control module calculates an estimated error from a state variable of a current sample and a state variable of a next sample of the observer, multiplies the estimated error by the adaptive gain, adds the estimated error to one of sin(ωT), cos(ωT), and sin(ωT/2), to update the one of sin(ωT), cos(ωT), and sin(ωT/2).

5. The position control apparatus of claim 2 , wherein

the table stores a state estimating gain of the observer corresponding to the value of one of estimated errors of sin(ωT) cos(ωT), and sin(ωT/2), and

the digital control module updates the state estimating gain of the observer, as the control constant, by a state estimating gain read from the table.

6. The position control apparatus of claim 1 , wherein the digital control module clips the one of the calculated values sin(ωT), cos(ωT), and sin(ωT/2), so as to restrict the calculated value of the one of sin(ωT), cos(ωT), and sin(ωT/2) within a predetermined range.

7. The position control apparatus of claim 1 , wherein

the digital control module includes:

a control module configured to calculate the control value of the actuator in accordance with the position error; and

a disturbance adaptive control module configured to calculate the one of values sin(ωT), cos(ωT), and sin(ωT/2) according to the adaptive law, multiplies the calculated value by the adaptive gain to update the one of sin(ωT), cos(ωT), and sin(ωT/2), and calculates a disturbance adaptive control value using the control constant that is read from the table in accordance with the updated value, and

the actuator is driven with the control value of the control module and the disturbance adaptive control value.

8. The position control apparatus of claim 1 , wherein the digital control module multiplies the value of sin(ωT) by an adaptive gain that is proportional to cos(ωT).

9. The position control apparatus of claim 1 , wherein the digital control module multiplies the value of cos(ωT) by an adaptive gain that is proportional to sin(ωT).

10. The position control apparatus of claim 1 , wherein the digital control module multiplies the value of sin(ωT/2) by an adaptive gain that is proportional to cos(ωT/2).

11. A disk apparatus comprising:

a head configured to read information from a disk;

an actuator configured to move the head in a transverse direction of tracks of the disk;

a digital control module configured to perform position control including disturbance adaptive control with a predetermined sampling period using a control constant, in accordance with a position error between a target position and a current position of the object; and

a table configured to store the control constant corresponding to one of values sin(ωT), cos(ωT), and sin(ωT/2), with ω representing an angular frequency of a disturbance, T representing the sampling period,

wherein the digital control module determines a control value of the actuator in accordance with the position error, calculates a value of one of estimated errors of sin(ωT), cos(ωT) and sin(ωT/2) according to an adaptive law from a signal based on the position error, multiplies the calculated estimated error by an adaptive gain in accordance with a value of the angular frequency ω, updates one of the values sin(ωT), cos(ωT), and sin(ωT/2), reads the corresponding control constant from the table based on the updated value, and updates the control constant, to perform the position control including the disturbance adaptive control.

12. The disk apparatus of claim 11 , wherein the digital control module performs the position control including the disturbance adaptive control by observer control.

13. The disk apparatus of claim 12 , wherein the digital control module calculates an estimated error from a state variable of the observer, an estimated gain, and an estimated position error, multiplies the estimated error by the adaptive gain, adds the estimated error to one of sin(ωT), cos(ωT), and sin(ωT/2), to update the one of sin(ωT), cos(ωT), and sin(ωT/2).

14. The disk apparatus of claim 12 , wherein the digital control module calculates an estimated error from a state variable of a current sample and a state variable of a next sample of the observer, multiplies the estimated error by the adaptive gain, adds the estimated error to one of sin(ωT), cos(ωT), and sin(ωT/2), to update the one of sin(ωT), cos(ωT), and sin(ωT/2).

15. The disk apparatus of claim 12 , wherein

the table stores a state estimating gain of the observer corresponding to the value of one of estimated errors of sin(ωT) cos(ωT), and sin(ωT/2), and

the digital control module updates the state estimating gain of the observer, as the control constant, by a state estimating gain read from the table.

16. The disk apparatus of claim 11 , wherein the digital control module clips the one of the calculated values sin(ωT), cos(ωT) and sin(ωT/2), so as to restrict the calculated value of the one of sin(ωT), cos(ωT), and sin(ωT/2) within a predetermined range.

17. The disk apparatus of claim 11 , wherein

the digital control module includes:

a control module configured to calculate the control value of the actuator in accordance with the position error; and

a disturbance adaptive control module configured to calculate the one of values sin(ωT), cos(ωT), and sin(ωT/2) according to the adaptive law, multiplies the calculated value by the adaptive gain to update the one of sin(ωT), cos(ωT), and sin(ωT/2), and calculates a disturbance adaptive control value using the control constant that is read from the table in accordance with the updated value, and

the actuator is driven with the control value of the control module and the disturbance adaptive control value.

18. The position control apparatus of claim 11 , wherein the digital control module multiplies the value of sin(ωT) by an adaptive gain that is proportional to cos(ωT).

19. The position control apparatus of claim 11 , wherein the digital control module multiplies the value of cos(ωT) by an adaptive gain that is proportional to sin(ωT).

20. The position control apparatus of claim 11 , wherein the digital control module multiplies the value of sin(ωT/2) by an adaptive gain that is proportional to cos(ωT/2).