JPS6439523A - Magnetic displacement detecting device - Google Patents

Abstract

PURPOSE:To enable absolute displacement detection with high resolution even in a range exceeding the pitch of magnetic scales by providing a couple of read heads for each magnetic scale array, exciting each couple of heads by common signal sources, and utilizing the phase difference of signals between the couples. CONSTITUTION:The couples of read heads 24A and 24B, and 24C and 24D are arranged at a specific interval corresponding to the magnetic scales which differ in scale pitch, and excited by signal sources 30 and 40, commonly. The magnetic scales and read heads are moved relatively and then the couples of heads output 90 deg. out-of-phase signals e1 and e2, and f1 and f2, phase- modulated signals e3 and f3 are outputted through mixing circuits 26e and 26f and BPFs 27e and 27f as the signals between couples corresponding to the magnetic scales, and their phase angles are theta1 and theta2. A phase comparing circuit 52 generates signals (h) and (i) which go up to high level only between the rising zero-cross points of a reference signal (g) and the signals e3 and f3. Counted values c1 and c2 of clock pulses CP from an oscillator 42 which are pressed through AND gates 54H and 54I during the period correspond to a phase angle theta1 and a phase difference theta1-theta2.