US 5,210,473 A · System with delay timer for motor load equalization

Abstract

The invention is an improvement in an AC adjustable frequency load-moving system of the type having a control circuit providing a motor speed signal and using command ramps to control each of plural AC squirrel cage motors. The invention helps assure substantially equal load sharing by the motors. The improvement includes a dwell circuit which maintains the motor speed reference signal at a synchronizing value at least for a period of time denominated as the dwell time. This permits microprocessors--which may be running asynchronously--to both "read" the same value of motor speed signal even though such value may be read at slightly different instants. Separate inverter units monitor such signal and responsively generate synchronized command ramps to effect load sharing. The invention is suitable for use with a wide variety of plural-motor drive systems and has been found to be particularly suitable for use on crane hoist systems.

Claims16

Dependent claims

An improved system for equalizing motor load in an open loop open loop plural-motor drive of the type having a master switch for starting and imposing load on all motors simultaneously, a control circuit providing a motor speed signal and using command ramps to control each of plural AC motors, the improvement comprising:

delay circuit maintaining such signal at a voltage value for at least a delay time;
a separate inverter unit coupled to each motor, monitoring such signal and responsively generating synchronized command ramps,
whereby substantially equal motor speeds are maintained and the motors thereby share load substantially equally.

Dependencies are inferred from the claim text.

System with delay timer for motor load equalization

Life of this patent

System with delay timer for motor load equalization

Life of this patent

Abstract

Claims16