Abstract: Included herein is a system and method for controlling a velocity vector of an overhead crane. A motor is attached to the crane and is positioned to move the overhead crane and has an output vector including a rotational direction and a rotational speed. A variable frequency drive is positioned to transfer voltage and current at a frequency to the motor. A processing unit converts the output vector to an amount of voltage and current at a given frequency and can instruct the variable frequency drive to send a frequency to the motor at a frequency substantially equal to the frequency at which the motor is presently rotating. This creates a speed match for the motor reducing spikes during operation of the motor and substantially eliminates open circuit decay. A hydraulic brake operates in connection with the processing unit and the variable frequency drive to slow the crane without driving the motor into the brake.

Abstract: A crane with an anti-skewing device comprising a platform suspended under a bridge deck by two end truck assemblies supported by runways on a bridge. Each end truck assembly includes two sets of trolleys and an upper load bar interconnects the two sets of trolleys. A lower load bar is suspended from the upper load bar by a kingpin for rotation about a vertical axis. Hinge tubes support the platform on the suspension assembly for pivotal movement in a direction lengthwise of the platform. Each end truck assembly is driven by a variable speed motor. As skewing occurs a mechanical sensing mechanism senses relative movement between lower load bar and the upper load bar and provides a signal to an electronic circuit causing one or both of the motors associated with the end truck assembly on which the sensing mechanism is mounted to increase or decrease the speed of the motor and thereby correct the skew.