JPS57206297A - Torque detecting device for induction motor - Google Patents

Abstract

PURPOSE:To cut down the cost of production and unnecessitate a multiplying circuit by a method wherein the torque is detected by comparing the torque generated while in operation and the torque setting signal which changes inverse- proportionately to the fluctuation of source voltage. CONSTITUTION:The output of the torque detector 6, consisting of the secondary current detector with a coil 5 wound around the ?-shaped core 4 whereon the end ring of a rotor will be insertee lraving an interval in radial direction, is applied to a comparison circuit 20 through the intermediary of a rectifying circuit 7. On the other hand, the commercial AC power source, which will be applied to the primary of the motor is recitifed and its negative voltage is inputted to one end of an adding circuit 22 and positive voltage is inputted to the other end of the circuit 22 through the intermediary of a constant voltage circuit 23, the output is applied to a comparison circuit 20 as the reference voltage to be used for torque setting through a variable resistor 24, and the signal indicating whether or not the torque has reached the set point is outputted. As a result, an expensive multiplier is unnecessitated, and the torque can be detected accurately even when there exists changes in source voltage.