Optical type relative rotation measurement apparatus

Abstract

An optical rotary encoder is provided with a pair of corrective light-emitting and light-receiving elements in addition to a pair of light-emitting and light-receiving elements that are for producing an output in dependence upon the relative rotation of two slitted disks. A corrective reference voltage is produced from the output of the corrective light-emitting and light-receiving elements and an output conforming to the relative rotation is produced with the reference voltage serving as a threshold. If the amount of light produced by the light-emitting element decreases or if the amount of light reaching the light-receiving element is reduced due to a decrease in light transmission through the medium in which the encoder is used, the corrective reference voltage changes accordingly so that accurate output pulses conforming to the relative rotation are obtained at all times. Accordingly, in an arrangement where the rotary encoder is installed in the transfer system of an automobile to measure drive torque, drive shaft torsion, namely drive torque, can be measured accurately even if optical transmission through the transfer oil changes due to temperature or contamination or if the amount of light generated by the light-emitting element decreases.