Position control apparatus and disk apparatus using the same

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.