Magnetic recording disk drive with multiple feedforward controllers for rotational vibration cancellation

• US 20070217052A1
• Filed: 03/17/2006
• Published: 09/20/2007
• Est. Priority Date: 03/17/2006
• Status: Active Grant

• Current Assignee: HGST Netherlands B.V. (Western Digital Corporation)
• Original Assignee: Hitachi Global Storage Technologies Netherlands BV (Western Digital Corporation)
• Inventors: White, Matthew, Semba, Tetsuo, Tzou, Kevin
• Granted Patent: US 7,375,916 B2
• Time in Patent Office: Days
• US Class Current: 360/75
• CPC Class Codes: G11B 19/04 Arrangements for preventing, inhibiting, or warning against double recording on the same blank or against other recording or reproducing malfunctions

Abstract

A disk drive has multiple feedforward controllers for handling external disturbances, such as rotational vibration (RV), that have different external disturbance frequency spectra. Each feedforward controller is designed to be optimal for a canceling a specific associated RV spectrum. The actual RV spectrum acting on the disk drive is determined and the proper feedforward controller is then selected and used to generate a compensation signal for canceling the RV. Each feedforward controller may be tested when the disk drive is experiencing the RV, and the resulting compensation signal and PES measured. The feedforward controller that produces the best external disturbance cancellation is then selected as the feedforward controller. A signal from a RV sensor may be used to detect the peak frequency of the actual RV spectrum. This detected peak frequency is then matched to a peak frequency in a plurality of peak frequencies in a lookup table, and the feedforward controller associated with the matching peak frequency is selected as the feedforward controller.

Claims

1. A method for operating a disk drive, the disk drive including (a) a rotatable magnetic recording disk having a plurality of concentric data tracks containing servo positioning information;

(b) a recording head movable across the disk, the head being capable of reading data and servo positioning information in the data tracks;

(c) an actuator for moving the head;

(d) a disturbance sensor for sensing external disturbances to the disk drive;

(e) a servo control processor responsive to a position error signal (PES) from the servo positioning information for generating an actuator control signal; and

(f) a plurality of feedforward controllers, each feedforward controller generating a compensation signal to be summed with the actuator control signal for substantially canceling an external disturbance having a predefined spectrum;

the processor-implemented method comprising;

determining which of said plurality of predefined disturbance spectra most closely matches the actual external disturbance acting on the disk drive;

selecting the feedforward controller associated with said determined predefined disturbance spectrum; and

summing the compensation signal from said selected feedforward controller with the actuator control signal.

2. The method of claim 1 wherein each predefined disturbance spectrum has an associated peak frequency and wherein determining which of said plurality of predefined disturbance spectra most closely matches the actual external disturbance comprises detecting the peak frequency of the disturbance sensor signal.

3. The method of claim 2 wherein detecting the peak frequency of the disturbance sensor signal comprises performing a discrete Fourier transform of the disturbance sensor signal.

4. The method of claim 2 wherein detecting the peak frequency of the disturbance sensor signal comprises measuring the output of the disturbance sensor signal from each of a plurality of bandpass filers associated with the plurality of predefined disturbance spectra, and wherein selecting the feedforward controller comprises selecting the feedforward controller associated with the bandpass filter having the largest output.

5. The method of claim 4 further comprising filtering the output of the disturbance sensor signal from each of a plurality of bandpass filers at a frequency corresponding to a resonant frequency induced by a non-rotational disturbance to the disk drive.

6. The method of claim 1 wherein there are N feedforward controllers and N associated predefined disturbance spectra;

wherein determining which of the N predefined disturbance spectra most closely matches the actual external disturbance comprises successively measuring the compensation signal from each of the N feedforward controllers in response to the actual disturbance and storing the N measured compensation signals; and

wherein selecting the feedforward controller comprises selecting the feedforward controller that generated the greatest compensation signal of the N stored compensation signals.

7. The method of claim 6 wherein measuring the compensation signal comprises calculating a statistical measurement from multiple compensation signal samples from each feedforward controller.

8. The method of claim 1 wherein there are N feedforward controllers and N associated predefined disturbance spectra;

wherein determining which of the N predefined disturbance spectra most closely matches the actual external disturbance comprises successively summing the compensation signal from each of the N feedforward controllers with the actuator control signal, measuring the PES in response to the actual disturbance for each of the N feedforward controllers and storing the N measured PES values; and

wherein selecting the feedforward controller comprises selecting the feedforward controller that resulted in the smallest of the N stored PES values.

9. The method of claim 8 wherein measuring the PES comprises calculating a statistical measurement from multiple PES samples for each feedforward controller.

10. A method for operating a disk drive, the disk drive including (a) a rotatable magnetic recording disk having a plurality of concentric data tracks containing servo positioning information;

(b) a recording head movable across the disk, the head being capable of reading data and servo positioning information in the data tracks;

(c) an actuator for moving the head;

(d) a rotational vibration (RV) sensor for sensing rotational vibration of the disk drive;

(e) a servo control processor responsive to a position error signal (PES) from the servo positioning information for generating an actuator control signal;

(f) memory associated with the processor; and

(g) N feedforward controllers stored in memory, each feedforward controller comprising a set of parameters for calculating a compensation signal to be summed with the actuator control signal for substantially canceling an RV having a predefined RV spectrum;

the processor-implemented method comprising;

determining which of N predefined RV spectra most closely matches the actual external RV acting on the disk drive;

selecting the feedforward controller associated with said determined predefined RV spectrum; and

summing the compensation signal from said selected feedforward controller with the actuator control signal.

11. The method of claim 10 wherein each predefined RV spectrum has an associated peak frequency and wherein determining which of N predefined RV spectra most closely matches the actual external RV comprises measuring the peak frequency of the RV sensor signal.

12. The method of claim 11 wherein measuring the peak frequency of the RV sensor signal comprises performing a discrete Fourier transform of the RV sensor signal.

13. The method of claim 11 wherein measuring the peak frequency of the RV sensor signal comprises measuring the output of the RV sensor signal from each of N plurality of bandpass filers associated with the N predefined RV spectra, and wherein selecting the feedforward controller comprises selecting the feedforward controller associated with the bandpass filter having the largest output.

14. The method of claim 10 wherein determining which of the N predefined RV spectra most closely matches the actual external RV comprises successively measuring the compensation signal from each of the N feedforward controllers in response to the actual RV and storing the N measured compensation signals;

and wherein selecting the feedforward controller comprises selecting the feedforward controller that generated the greatest compensation signal of the N stored compensation signals.

15. The method of claim 14 wherein measuring the compensation signal comprises calculating a statistical measurement from multiple compensation signal samples from each feedforward controller.

16. The method of claim 10 wherein determining which of the N predefined RV spectra most closely matches the actual external RV comprises successively summing the compensation signal from each of the N feedforward controllers with the actuator control signal, measuring the PES in response to the actual RV for each of the N feedforward controllers and storing the N measured PES values;

and wherein selecting the feedforward controller comprises selecting the feedforward controller that resulted in the smallest of the N stored PES values.

17. The method of claim 16 wherein measuring the PES comprises calculating a statistical measurement from multiple PES samples for each feedforward controller.

18. The method of claim 10 wherein summing the compensation signal from said selected feedforward controller with the actuator control signal comprises calculating the compensation signal from the stored parameter set associated with said selected feedforward controller.

19. A magnetic recording disk drive including (a) a rotatable magnetic recording disk having a plurality of concentric data tracks containing servo positioning information;

(b) a recording head movable across the disk, the head being capable of reading data and servo positioning information in the data tracks;

(c) a voice-coil-motor (VCM) for moving the head;

(d) a rotational vibration (RV) sensor for sensing rotational vibration of the disk drive;

(e) a servo control processor;

(f) memory associated with the processor;

(g) N feedforward controllers stored in memory, each feedforward controller comprising a set of parameters for calculating a compensation signal to be summed with the VCM control signal for substantially canceling an RV having a predefined RV spectrum; and

(f) a program of instructions stored in memory and readable by the processor for undertaking method acts comprising;

receiving a RV sensor signal from the RV sensor and a position error signal (PES) from the servo positioning information;

calculating a VCM control signal from the PES;

determining which of N predefined RV spectra most closely matches the actual external RV acting on the disk drive;

calculating a compensation signal from the stored parameter set for the feedforward controller associated with said determined predefined RV spectrum; and

summing the calculated compensation signal with the VCM control signal.

20. The disk drive of claim 19 wherein each predefined RV spectrum has an associated peak frequency and wherein determining which of N predefined RV spectra most closely matches the actual external RV comprises measuring the peak frequency of the RV sensor signal.

21. The disk drive of claim 19 wherein determining which of N predefined RV spectra most closely matches the actual external RV comprises successively measuring the compensation signal from each of the N feedforward controllers in response to the actual RV and storing the N measured compensation signals in memory;

and wherein calculating a compensation signal comprises calculating a compensation signal from the stored parameter set for the feedforward controller that generated the greatest compensation signal of the N stored compensation signals.

22. The method of claim 19 wherein determining which of N predefined RV spectra most closely matches the actual external RV comprises successively summing the compensation signal from each of the N feedforward controllers with the VCM control signal, measuring the PES in response to the actual RV for each of the N feedforward controllers and storing the N measured PES values;

and wherein calculating a compensation signal comprises calculating a compensation signal from the stored parameter set for the feedforward controller that resulted in the smallest of the N stored PES values.