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Abstract

The relative position of the armature and stator of a linear motor is controlled using the outputs of two optical transducers in phase quadrature from an optical graticule disposed along the length of the stator. An analog, velocity-indicating signal is derived from the output of the optical transducers. The optical transducers are digitized and cycle an up/down counter which produces an output of a ten-bit digital word representing the armature position. The outputs of the up/down counter are used as the ten higher order bits of the twelve-bit digital word representing the armature position which is compared by a comparator with a demanded armature position. The two lower order bits of the actual-position word are derived directly from the digitized outputs of the optical transducers to eliminate the effect of variation in the exact position at which the counter is reset to zero by a position-detecting switch. While the positional error is large, the motor is servoed in accordance with a predetermined velocity profile and, when the higher order bits of the position error word are zero, the circuitry switches over to a position-servo mode using as the actual position signal, the analog output of one of the optical transducers. The commutation of the motor coils is controlled in accordance with the seventh and eighth bits of the output of the up/down counter, the graticule spacing being chosen to equal the commutation spacing divided by two raised to an integral power.

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First Claim