| 摘要 |
A servo system uses a position demand signal to drive a servo to position a transducer head over a specific track on a disc. The position demand signal is referenced to a tribit servo track on the disc. A tribit servo track demodulator circuit, similar to that taught by Mueller in U.S. Pat. No. 3,691,543, is used to compute a correction signal to be applied to the position demand signals used in the servo system. In the demodulator circuit (similar to the Mueller reference), first and second position indicating signals from the tribit servo track are processed on two parallel detection paths to compute an error signal. The invention improves the process by computing a first correction position demand signal from the error signal to position the transducer head over a null point proximate to the tribit servo track, and then switching the demodulator paths so the two position indicating signals are processed on the reverse demodulator paths to compute a second correction position demand signal to again position the transducer head over a second point where the transducer finds a null point proximate to the tribit servo track. The mean value of the first and second correction position demand signals is then computed and used in the servo system as a correction signal to be applied to position demand signals for movement of the head to other tracks on the disc. The mean value compensates for offset errors in the detection paths in establishing the tribit servo track location as a reference location.
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