Reference position-detecting device for photoelectric encoder

Abstract

A reference position-detecting device for use with a photoelectric, incremental encoder which produces a sinusoidal signal in response to the movement of an index scale relative to a main scale. A pattern comprising bright portions and dark portions alternately arranged is formed on the main scale. A similar pattern is formed on the index scale. The device comprises a random pattern formed at some location of the main scale, a similar random pattern formed at some location of the index scale, optical devices for producing a signal indicative of a reference position, a first pulse generator for producing pulses in response to the signal above, second and third pulse generators for producing two kinds of pulses that are 90.degree. out-of-phase in response to the sinusoidal signal, a direction detector for detecting the direction of the movement of the index scale, an analog switch having non-inverting and inverting inputs, a counter for counting the count pulses from the switch, and a fourth pulse generator for resetting the counter on the leading or trailing edge of each count pulse during the presence of the pulses indicating the reference position.