DIFFERENTIATING CIRCUIT FOR ENCODER OUTPUT SIGNAL

PURPOSE:To prevent miscounting and accurately detect the drift of position by setting or resetting the data state of a circuit according to the levels of a pulse signal at the time of system resetting. CONSTITUTION:When the input signal phiA from a rotary encoder is in 'H' level at the time of system resetting, the output of a NAND circuit 25 becomes active, FF circuits 21 and 22 being set. In a differentiating circuit 10, when the signal phiA changes from 'H' to 'L', the differentiating pulse P12 in clock- like synchronization with the output of a NAND circuit 24 is output. When the signal phiA is in the level of 'L' at the time of system resetting, the output of a NAND circuit 27 becomes active, the circuits 21 and 22 being reset. When system resetting is canceled and the signal phiA changes from 'L' to 'H', a differentiating pulse 11 is output to the output of the NAND circuit 23. In an encoder 12, the differentiating pulses P11, 12, 14 and 15 generated in the differentiating circuits 10 and 11 are composed, and the number of pulses is counted down(13).