Incremental encoder synchronous decode circuit

Claim 1

In a positioning system including an n-line incremental encoder connected to a servomotor of an object positioning servosystem and generating one line per cycle having four transitions per encoder line for a gray code in response to movement of an object in a preselected dimension, a counter for timing the movement of the object in the preselected dimension and a counter latch for connection to a system computer for determining the count for distance measurement, a synchronous decoder circuit comprising: (a) an analog-to-digital (AD logic level) converter having an in phase channel comparator and a quadrature channel comparator for connection to the incremental encoder for conditioning the signals thereof; (b) a signal synchronizing latch operatively connected to the AD converter in phase and quadrature channel comparators for receiving the latest conditioned encoder signals, said latch having a feedback circuit for feeding back the latest conditioned encoder signals to the latch where they are delayed for providing previous latched encoder signals together with the latest conditioned encoder signals; (c) a programmable decode read only memory (PROM) operatively connected to the synchronization latch for decoding the latest and previous encoded signals for determining direction, said PROM being programmed with a gray code; (d) a gating logic circuit operatively connected to the PROM for receiving clock enable signals and direction enable signals; and (e) a clock generator operatively connected to the in phase and quadrature channel comparators, synchronization latch and gating logic circuit for clocking the synchronous decode circuit, said clock for generating a plurality of counter clock pulses at a preselected frequency determined by the number of counter clocks generated per encoder line (scale factor), encoder lines per revolution and servosystem operating speed; whereby the in phase channel and quadrature channel signals, respectively, start low and high to provide a gray code for each cycle in a first direction and conversely for each cycle in a second direction for comparison with the gray code of the PROM for direction of movement determinations.