Displacement amount detecting device

Abstract

A device which detects the amount of displacement of a movable member moved by a feed device, and which outputs pulse signals corresponding to the amount of such displacement. The displacement amount detecting device includes a reference pulse generator for generating a train of reference pulses at a predetermined frequency, a carrier counter which counts the reference pulses from the pulse generator and outputs carrier signals, a dummy counter which counts the reference pulses from the pulse generator and which outputs a dummy signal, a transducer which receives the carrier signals and which generates a phase modulation signal proportional to the amount of displacement, a phase comparator which compares the modulation signal with the dummy signal and which outputs a first gate signal while the phase of the modulation signal leads the phase of the dummy signal and a second gate signal while the phase of the modulation signal lags the phase of the dummy signal, and input and output gating circuitry resonsive to the first and second gate signals. The input gating circuitry interrupts transmission of the reference pulses to the carrier counter while receiving the first gate signal and interrupts transmission of the reference pulses to the dummy counter while receiving the second gate signal. Such interruption is continued until the phase of the modulation signal coincides with that of the dummy signal, so that the reference pulses output from the output gating circuitry during such interruption correspond to the displacement amount of the movable member.