Electricity: motive power systems – Positional servo systems
Reexamination Certificate
1999-05-03
2001-02-13
Ip, Paul (Department: 2837)
Electricity: motive power systems
Positional servo systems
C318S561000, C318S611000, C360S075000, C360S078040, C360S078050, C369S044250, C369S044290
Reexamination Certificate
active
06188191
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a servo system producing a signal for positioning one member having a resonant frequency f which varies with temperature, relative to another member and, more particularly to such a system which includes means for controlling responsiveness of the one member to temperature changes.
BACKGROUND OF THE INVENTION
A computer disk drive typically employs a servo system containing means to position a read/write head relative to a data-containing disk. The disk has data arranged in tracks which also contain a track following signal. When it is desired to move the read/write head to a new track, a broadband signal is applied to the positioning means to drive the read/write head to the desired track.
As the read/write head nears the desired track, a reverse polarity signal is applied to the positioning means, causing it to act like a brake and ideally stopping the read/write head over the desired track, centered over the track following signal. During this process, considerable but variable heat is generated. Furthermore the mechanical structure of the positioning means has a natural resonance at a frequency f, the value of which is a function of temperature. Thus frequency f may range from a low of f1 to a high of f2.
The prior art solution to the problem involved attenuating the broadband signal over the entire range of possible resonant frequencies, i.e., the creation of a notch in the frequency spectrum of the broadband signal. Any such attenuation also affects the broadband signal at frequencies away from the notch, and results in a less than ideal behavior. By widening the notch to account for the changes in frequency of the resonant mode due to temperature, this effect is increased. Further, as the depth of the notch is not constant with frequency (that is, every notch is more effective at some frequencies than others), the behavior of the system can change as temperature changes move the frequency of the resonant mode.
In summary, the problems with the prior art solution are (1) the notch needs to be wide to account for the change in frequency of the resonant mode with temperature, and (2) the behavior of the system can change as temperature changes move the frequency of the resonant mode.
Accordingly, it is an object of this invention to provide an improved method and apparatus for control of a read/write head positioning means under conditions of varying temperature.
SUMMARY OF THE INVENTION
A servo system for operating in a region of ambient temperature includes a first member, and a second member positionable relative to the first member. The system further includes a control loop producing a broadband frequency signal coupled to the second member for causing the second member to be positioned to a desired location relative to the first member. The second member has a natural resonant frequency f, which is a function of the ambient temperature.
The servo system provides a signal indicative of the temperature and the control loop includes means responsive to the temperature signal to attenuate the broadband frequency signal at frequency f.
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IBM Technical Disclosure Bulletin, vol. 32, No. 8B, Jan. 1990, pp. 346-347, “Automated Custom Tuning Servo System for Hard File Manufacturing”.
Frees Gregory Michael
Serrano Louis Joseph
International Business Machines - Corporation
Ip Paul
Ohlandt Greeley Ruggiero & Perle L.L.P.
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