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US 4,288,731 AGranted
Average value tachometer for a disc drive servo and the like
AssigneeSperry Corporation
InventorPatrick S. Lee
Life of this patent
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AssigneeSperry Corporation
InventorPatrick S. Lee
Estimating the term…
In a disc pack data storage system that has a plurality of discs and a plurality of heads for coaction with the discs, a tachometer for producing a signal indicative of the radial speed of the heads with respect to the discs. At least one of the disc surfaces is a servo surface and at least one of the heads is a servo head so that in response to radial movement of the servo head a triangular position signal is produced. Sampling pulses indicative of specific radial positions of the head are derived from the position signal so that the time required for the head to move between two positions represented by adjacent sampling pulses is inversely proportional to radial head speed. Control and computing circuitry measures the time between adjacent pulses by providing a clock pulse source and counting the number of clock pulses that occur between adjacent sampling pulses. There is circuitry for controlling the specific sampling pulses employed in accordance with radial head speed and the clock pulse source is frequency controlled to achieve accuracy at all radial speeds. A digital to analog converter converts the counted clock pulses to a voltage and amplifier circuitry derives from the voltage a speed signal indicative of radial speed. Circuitry active at very low speeds serves to combine with the speed signal a signal derived by integrating motor current so that an accurate tachometer signal is produced at all radial speeds.
A tachometer for a disc pack servo system comprising means for generating a triangular position signal in response to radial movement of a servo head with respect to a prerecorded servo track, said position signal having ascending and descending linear portions each of which has a slope representative of the rate of radial movement of the servo head, means responsive to the linear portion of said position signal for producing at least first, second and third sampling pulses on attainment of said position signal of respective first, second and third voltage levels, the difference between said voltage levels being equal and representing equal increments of radial movement of said servo head, a counter having a reset input connected to said sampling pulse producing means, said counter having a counting input and being constructed and arranged to terminate counting of pulses supplied to said counting input in response to receipt of a sampling pulse at said reset input, a clock pulse source producing a series of regularly recurring clock pulses connected to said counting input so that said counter produces a number N at its output which is representative of the time between adjacent said sampling pulses, a digital to analog converter having a digital input to which N is connected, said converter having a capacity N.sub.limit, a gain k and a reference voltage input and being constructed and arranged to produce an output equal to the product of k, (N/N.sub.limit) and the voltage connected to said reference input, a difference circuit having a first input connected to said converter output and a second input to which a reference voltage is connected, said difference circuit being constructed and arranged to produce a voltage proportional to the difference between the voltage applied to said first and second inputs, and feedback means for feeding back to the reference voltage input of said converter the output of said difference circuit so that the voltage at a circuit point between the output of said difference circuit and the reference input of said converter is inversely proportional to N and is indicative of average radial speed of said servo head.
Dependencies are inferred from the claim text.