Disk drive employing data-based basis function expansion for tuning seek servo loop
View Patent ↗A method of tuning a seek operation of a disk drive is disclosed, the disk drive comprising a disk, an actuator arm, a head coupled to a distal end of the actuator arm, a voice coil motor (VCM) for rotating the actuator arm about a pivot, and a closed loop servo system for generating a VCM control signal applied to the VCM. A function h is applied to the closed loop servo system and a corresponding output g of the closed loop servo system is measured. A reference signal is generated in response to a summation of a plurality of the function h, wherein each of the plurality of the function h is shifted by an offset and scaled by a coefficient, and the coefficients are generated in response to the measured output g.
1. A method of tuning a seek operation of a disk drive, the disk drive comprising a disk, an actuator arm, a head coupled to a distal end of the actuator arm, a voice coil motor (VCM) for rotating the actuator arm about a pivot, and a closed loop servo system for generating a VCM control signal applied to the VCM, the method comprising:
applying an initial function h to the closed loop servo system and measuring a corresponding output g of the closed loop servo system; and
generating a reference signal in response to a summation of a plurality of functions, wherein:
each of the plurality of functions is shifted by an offset from the initial function h and scaled by a coefficient; and
the coefficients are generated in response to the measured output g.
2. The method as recited in claim 1 , wherein the coefficients are generated in response to a desired output Ydes of the VCM corresponding to a target seek profile.
3. The method as recited in claim 2 , wherein the coefficients are generated in response to a dual basis function generated using a discrete Fourier transform of the measured output g.
4. The method as recited in claim 3 , further comprising:
generating a difference between a measured output of the VCM and a desired output of the VCM; and
adapting the coefficients in response to the difference and the dual basis function.
5. The method as recited in claim 4 , further comprising:
saving the VCM control signal generated while adapting the coefficients; and
using the saved control signal as a feed-forward control signal.
6. The method as recited in claim 5 , further comprising adapting the reference signal using iterative learning control while applying the feed-forward control signal to the VCM.
7. The method as recited in claim 1 , further comprising adapting the coefficients in response to a difference between a measured output of the VCM and a desired output of the VCM.
8. A disk drive comprising a disk, an actuator arm, a head coupled to a distal end of the actuator arm, a voice coil motor (VCM) for rotating the actuator arm about a pivot, and control circuitry including a closed loop servo system for generating a VCM control signal applied to the VCM, the control circuitry operable to:
apply an initial function h to the closed loop servo system and measure a corresponding output g of the closed loop servo system; and
generate a reference signal in response to a summation of a plurality of functions, wherein:
each of the plurality of functions is shifted by an offset from the initial function h and scaled by a coefficient; and
the coefficients are generated in response to the measured output g.
9. The disk drive as recited in claim 8 , wherein the control circuitry is further operable to generate the coefficients in response to a desired output Ydes of the VCM corresponding to a target seek profile.
10. The disk drive as recited in claim 9 , wherein the control circuitry is further operable to generate the coefficients in response to a dual basis function generated using a discrete Fourier transform of the measured output g.
11. The disk drive as recited in claim 10 , wherein the control circuitry is further operable to:
generate a difference between a measured output of the VCM and a desired output of the VCM; and
adapt the coefficients in response to the difference and the dual basis function.
12. The disk drive as recited in claim 11 , wherein the control circuitry is further operable to:
save the VCM control signal generated while adapting the coefficients; and
use the saved control signal as a feed-forward control signal.
13. The disk drive as recited in claim 12 , wherein the control circuitry is further operable to adapt the reference signal using iterative learning control while applying the feed-forward control signal to the VCM.
14. The disk drive as recited in claim 8 , wherein the control circuitry is further operable to adapt the coefficients in response to a difference between a measured output of the VCM and a desired output of the VCM.