Importance

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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.' With the invention, the motor control unit is disabled at some predetermined pressure in the brake hydraulic line. Thereafter, the machine is retarded solely by application of the manually-operated brake until the machine reaches a very slow speed.

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First Claim