Method of suppressing seek-excited vibration in a disk drive or similar servo system

• US 4,477,755 A
• Filed: 06/28/1982
• Issued: 10/16/1984
• Est. Priority Date: 06/28/1982
• Status: Expired due to Term

• Current Assignee: Storage Technologies Corporation (Oracle Corporation)
• Original Assignee: Storage Technologies Corporation (Oracle Corporation)
• Inventors: Rickert, David W.
• Primary Examiner(s): Truhe, J. V.
• Assistant Examiner(s): Keane, Patrick
• Application Number:
  US06/392,488
• Time in Patent Office: 841 Days
• Field of Search: 360/78, 364/553, 364/149-151, 318/561, 318/565, 318/611, 318/615, 318/620, 318/621, 318/671, 318/672, 318/687, 318/135, 318/128, 318/636, 318/601
• US Class Current: 318/611
• CPC Class Codes: G11B 21/083 on discs

Abstract

A disk drive control circuit designed to eliminate undesirable mechanical resonances that occassionally occur in the disk drive system as a result of a particular combination of seek commands. The control circuit uses an electrical model of the mechanical system in order to estimate or predict whether a particular seek command is likely to excite a mechanical resonance. The electrical model may be a filter network having frequency response characteristics similar to the mechanical system. The current used to drive a linear motor of the mechanical system is then applied to the filter network. The signal output from the filter network, which network effectively models the mechanical system, is thus representative of the mechanical response of the system upon performance of the seek operation. This signal output is monitored, and if it exceeds a predetermined threshold level, steps are taken to alter the system response so as to avoid exciting the mechanical resonance.

Claims

1. A disk drive control circuit for use with a disk drive that includes a rotatable disk and means for writing or reading information to or from selected locations of said disk, said write or read means including a mechanical system that selectively positions a head assembly so as to provide access to selected locations of said disk, said disk drive control circuit comprising:

an electrical circuit that comprises a model of said mechanical system;

means for exciting said electrical model circuit with a drive signal representative of the mechanical forces applied to said mechanical system in order to selectively position said head assembly, said electrical model circuit being adapted to provide a response signal that is representative of the displacement of said head assembly within said mechanical system;

alarm means for monitoring said response signal and generating an alarm signal whenever said response signal exceeds a predetermined threshold; and

control means responsive to said alarm signal for preventing the movement of said head assembly for a period of time;

whereby undesirable mechanical resonances associated with a particular sequence of head assembly positioning cycles can be stopped by selectively delaying the movement of said head assembly.

2. A disk drive control circuit as defined in claim 1 wherein the mechanical forces applied to said mechanical system are generated by a linear actuator that linearly moves a plunger in response to a drive current, said head assembly being mechanically coupled to said plunger, and further wherein said drive signal is derived from said drive current.

3. A disk drive control circuit as defined in claim 2 wherein said alarm means comprises a threshold detector circuit adapted to generate said alarm signal whenever said response signal, applied to a first input of said threshold detector circuit, has an amplitude that exceeds a reference voltage applied to a second input of said threshold detector circuit.

4. A disk drive control circuit as defined in claim 2 wherein said period of time during which the movement of said head assembly is prevented is a pre-determined fixed period of time.

5. A disk drive control circuit as defined in claim 2 wherein said period of time during which the movement of said head assembly is prevented is whatever time is required for said response signal to settle below said predetermined threshold.

6. An improved disk drive system comprising:

a base plate;

a disk rotatably mounted to said base plate, said disk having servo positioning data selectively placed thereon;

a head assembly slidably mounted to said base plate, said head assembly being adapted to read data from said disk;

linear positioning means for linearly positioning said head assembly along a radial axis of said disk in response to a drive signal, said linear positioning means comprising a linear actuator having a plunger that is linearly moved in response to a drive current, said drive signal comprising said drive current, and an input signal derived from said drive signal, said input signal comprising a voltage signal that is proportional to said drive current;

servo means coupled between said head assembly and said linear positioning means for generating said drive signal in response to a servo position command signal and servo positioning data read from said disk by said head assembly;

an electrical circuit coupled to said servo means, said electrical circuit comprising an electrical model of a mechanical system comprised of said head assembly slidably mounted to said base plate, said electrical circuit being adapted to receive said input signal derived from said drive signal and to generate a displacement signal in response to said input signal, the amplitude of said displacement signal representing an estimate of the relative linear displacement of said head assembly as a function of said drive signal, said electrical circuit model comprising a filter network having a frequency response characteristic approximately the same as the frequency response characteristic of said mechanical system for frequencies near the resonant frequency of said mechanical system, and wherein said electrical circuit model further comprises a pre-filter network coupled to said filter network, and a buffer circuit coupled to said pre-filter network, said buffer circuit being adapted to monitor said drive current and generate said input signal therefrom and to present said input signal to said pre-filter network, and further wherein said pre-filter network filters out frequencies contained within said input signal that are well below the resonant frequency of concern associated with said mechanical system; and

a control circuit responsive to said displacement signal for selectively controlling the response of said head assembly to said drive signal whenever said displacement signal exceeds a prescribed threshold;

whereby undesirable resonances associated with a particular sequence of head assembly linear movements can be minimized.

7. An improved disk drive system as defined in claim 6 wherein said buffer circuit, pre-filter network, and filter network are combined into a single, buffered, band-pass network.

8. A method for preventing undesirable mechanical resonances from being excited in a head assembly of a disk drive system as said head assembly seeks out, under servo control, addressed locations on said disk, said method comprising the steps of:

(a) modeling the mechanical system comprising said servo controlled head assembly with an electrical model circuit;

(b) exciting said electrical model circuit with a signal proportional to the force applied by said servo system to said head assembly, which force causes said assembly to seek out the addressed locations of said disk;

(c) monitoring the electrical response of said model circuit to the excitation of step (b), said response being representative of the mechanical response of said head assembly, said response being manifest by an output signal generated by said electrical model circuit; and

(d) controlling the movement of said servo controlled head assembly in response to said output signal so as to prevent undesirable mechanical resonances from occurring in the head assembly, said movement controlling step comprising delaying the start of the next seek operation until a perceived mechanical resonance, as sensed by monitoring said output signal, has sufficiently damped out.

9. A method as defined in claim 8 wherein the initialization of the next seek operation is delayed a fixed period of time whenever the amplitude of said electrical model output signal exceeds a prescribed threshold.