Abstract: The disclosure involves a drive system having a control section, an adjustable frequency drive unit coupled to the control section, and first and second drive motors. The drive system is used with a material handling machine such as a light-duty crane on which any two of the hoist, bridge and trolley drives are rarely used simultaneously and in any event need not be used simultaneously. The drive unit is a scalar or flux vector (feedback-type) inverter and is the sole drive unit providing electrical power to the drive motors. Preferred control is by a pendant station or radio transmitter. Operating a pushbutton on the pendant station (or a paddle-like stick control on the transmitter) for a particular drive motor "locks out" operation of the other motors. Motors are operated on a first-come, first-served basis.

Abstract: The inventive method and machine are improvements in aspects of a material handling machine (such as an overhead travelling crane) having an electrically-powered traverse drive, e.g., a bridge drive. Such machine has (a) regenerative motor braking and (b) a manually-applied hydraulic brake, both for retarding the machine. The invention prevents the bridge drive motor from "driving through the brake" when the hydraulic brake is being applied to result in significant retarding torque. When the hydraulic brake is pedal-applied, an electrical contact closes at a predetermined hydraulic pressure and other devices, relays and the like, are actuated to modify operation of the controller and prevent "motoring" simultaneous with hydraulic braking. Regenerative braking is likely to be set for a retardation rate less than results from application of the hydraulic brake. The invention prevents the drive motor and hydraulic braking system from "fighting.

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.