WO2000063894B1

WO2000063894B1 - Dual stage servo controller

Info

Publication number: WO2000063894B1
Application number: PCT/US2000/010572
Authority: WO
Inventors: Travis E Ell
Original assignee: Seagate Technology Llc
Priority date: 1999-04-21
Filing date: 2000-04-20
Publication date: 2001-01-18
Also published as: JP2002542558A; GB2363248A; WO2000063894A2; KR20010111511A; WO2000063894A3; CN1357137A; GB0123529D0

Abstract

A servo controller (250) controls the servo system in a disc drive (110). A proportional integrator component (166) receives the target track signal indicative of a target track and a measured track signal indicative of actual or measured data head position. During seek mode, the proportional integrator (166) provides an output signal based on the measured track signal and the target track signal. A profile generator component (170) provides a profile signal based on the output signal from the proportional integrator (166). A coarse actuator (120) is driven based on the profile signal. A filter component (252) is coupled to the profile generator (170) and filters the profile signal to provide a filtered profile signal. The fine actuator (127) is driven based on the filtered profile signal.

Claims

- 27 -AMENDED CLAIMS[received by the International Bureau on 17 November 2000 (17.1 1.00); original claim 10 amended; remaining claims unchanged (3 pages)]

1. A servo controller controlling a servo system in a disc drive, the servo system having a coarse actuator and at least one fine actuator, the actuators being coupled to a data head to move the data head relative to a surface of a disc in the disc drive, the servo controller comprising: a proportional-integrator (PI) component receiving a target track signal, indicative of a target track, a measured track signal indicative of an actual head position, and an error signal indicative of a head position relative to the target track and providing a PI output signal which, during a seek mode, is based on the measured track signal and the target track signal and, during a settle mode, is based on the target track signal, the error signal and an integrated bias signal; a profile generator component providing a profile signal based on the PI output signal, the coarse actuator being driven based on the profile signal; and a filter component coupled to the profile generator and filtering the profile signal to provide a filtered profile signal having a reduced low corner frequency, the fine actuator being driven based on the filtered profile signal.

2. The servo controller of claim 1 and further comprising: a notch filter receiving a position error signal indicative of the difference between the head position and the target track and filtering notch frequencies to provide the error signal; and a differentiator component coupled to the notch filter, differentiating the error signal to provide a differentiator signal, the coarse actuator being driven based on a combination of the profile signal and the differentiator signal.

3. The servo controller of claim 2 wherein the filter component is configured to offset a gain associated with the differentiator through a movement frequency range.

4. The servo controller of claim 3 wherein the movement frequency range is less than approximately 20,000 radians per second.

5. The servo controller of claim 4 wherein the movement frequency range is approximately 7000 radians per second to approximately 12000 radians per second.

6. The servo controller of claim 1 wherein the fine actuator includes a fine actuator driver receiving the filtered profile signal and driving the fine actuator based on the filtered profile signal, the filter component including a clamping component configured to clamp a level of the filtered profile signal based on a saturation level of the fine actuator driver.

7. The servo controller of claim 3 wherein the differentiator has a slope of approximately 20 Decibels (dB) per decade in radians per second over the movement frequency range, and wherein the filter component has a slope of approximately -20 dB per decade in radians per second over the. movement frequency range.

8. The servo controller of claim 8 wherein the filter component comprises a lag network. - 29 -

9. A servo system controlling positioning of a data head relative to a disc surface on a disc in a disc drive, the servo system comprising: a coarse actuator coupled to the data head to move the data head;

a fine actuator coupled to the data head to move the data head relative to the coarse actuator; and a control system having a fine actuator control component and a coarse actuator control component wherein the fine and coarse actuator control components are configured such that, at a frequency at which both the fine and coarse actuator control components have approximately equal gains, a phase difference between outputs of the fine and coarse actuator control components is less than approximately 120 degrees, for track seek operations.

10. The servo system of claim 9 wherein the fine and coarse actuator control components are configured such that, at a frequency at which both the fine and coarse actuator control components have approximately equal gains, a phase difference between outputs of the fine and coarse actuator control components is less than approximately 120 degrees, for track settle operations.

- 30 -

Statement under Article 19(1)

This statement is being filed in response to the International Search Report sent on October 11, 2000. The International Search Report cited two X references against claims 1 and 9 in the present application. The two references were U.S. patent No. 5,883,749 (the Park reference) and European Patent Application No. EP 0 942 689 A2 (the Texas Instrument reference) . Applicant respectfully submits that the references do not teach or fairly suggest the elements found in claims 1 and 9.

Specifically, the Park reference neither teaches nor suggests a fine actuator. Instead, Park simply shows a voice coil motor.

While the Texas Instruments reference does show both a microactuator and a voice coil motor, it does not appear to show the profile generator or filter component set out in claim 1. Similarly, the Texas Instruments reference does not appear to make any mention of a phase difference between the outputs of the fine and coarse components, during track seek operations, at a frequency at which both the fine and coarse actuator control components have approximately equal gains. Therefore, the Texas Instruments reference does not appear to disclose the control system set out in independent claim 9.

Applicant thus submits that the claims, as written, are novel and define an inventive step over the references cited in