Abstract: In an optical rotary encoder, a stationary plate having a zone plate and a rotary slit plate having slits are interposed between a light source and a light receiving element. A suitable radius of the innermost circle of the zone plate is selected so that the zone platess provide a sufficient convergence of light for reduction of silt interval (hence for improvement of the detection precision) with a distance between the stationary plate and the rotary slit plate maintained at a value permitting the fabrication of the encoder.

Abstract: A torque measuring device. The device comprises a mount base which is supported by a housing for swing motion around the axis of an output rotary shaft and for mounting an output rotary shaft-driving rotary machine thereon and whose center of gravity is located on the axis of a bearing assembly, a torque transmitting lever with its center of gravity located on the axis of its pivot for transmitting torque to a second lever, which second lever has a distal arm carrying thereon a moving coil disposed in a fixed magnetic field and is adapted to have a torque in the mount base transmitted thereto at its proximal point of action, and a position detector which detects the position of the moving coil and feeds its current output corresponding to a variation in the position of the moving coil back to the latter. This device is handy to carry.