Harnischfeger Corporation

James N Nash

Lawrence A Millonzi

Ronald W Morters

Lester A Price

A control system for regulating the torque and speed of an alternating current wound rotor motor used in the traverse drive of an overhead travelling crane comprises an SCR bank controlled by a firing circuit responsive to actuation of an operator-controlled induction master control. The control system further comprises means for deriving a torque signal indicative of instantaneous rotor torque, means for deriving a speed signal indicative of instantaneous rotor speed, and summing means for combining the torque signal, the speed signal, and a reference signal from the induction master control to provide an error signal which is used to operate the firing circuit to thereby control the power delivered by the SCR bank to the motor and insure that motor torque is constant for the speed selected. The means for deriving the speed signal measures the instantaneous frequency of the instantaneous current flow in the rotor (secondary).

Control system for regulating the speed of an electric motor including

A control system for regulating the torque and speed of an alternating current wound rotor motor used in the traverse drive of an overhead traveling crane comprises an SCR bank controlled by a firing circuit responsive to actuation of an operator-controlled induction master control. The control system further comprises means for deriving a torque signal indicative of instantaneous rotor torque, means for deriving a speed signal indicative of instantaneous rotor speed, and summing means for combining the torque signal, the speed signal, and a reference signal from the induction master control to provide an error signal which is used to operate the firing circuit to thereby control the power delivered by the SCR bank to the motor and insure that motor speed is constant. The means for deriving the torque signal comprises means for deriving a voltage signal indicative of the instantaneous line-to-neutral voltage across one of the motor stator windings; means for deriving a current signal indicative of the instantaneous current in a phase line to the motor stator winding; and multiplying means for multiplying the voltage and current signals to provide a wattage or torque signal which is proportional to the instantaneous torque being developed by the motor. The wattage supplied to the motor minus the wattage attributable to fixed motor loses is directly related to the torque delivered by the motor shaft. The means for deriving the speed signal measures the instantaneous frequency of the instantaneous current flow in the rotor (secondary).

Control system for regulating the torque and speed of an electric motor

A hoist uses an alternating current three-phase variable speed reversible wound rotor motor to hoist and lower a load. An electromechanical brake and a tachometer generator are connected to the motor shaft. Controllable SCRs connected to the motor stator (primary) windings control motor direction and speed and motor braking in response to error signals resulting from comparison of reference signals from an operator's master control and feedback signals from the tachometer. During hoisting and lowering (when the electromechanical brake is released), direct current voltage derived from appropriate gating of the controllable SCRs is applied to the motor stator (primary) winding to effect direct current braking as required. This direct current flow is smoothed and rendered more effective by gating 'on' a free-wheeling SCR which is connected across two of the motor stator (primary) windings. Emergency dynamic braking means operative in the event of failure of the electromechanical brake while the motor and control are deenergized but supporting a suspended load applies a rectified feedback signal from the tachometer to produce a magnetic field in the motor stator (primary) windings. A bridge rectifier is connected between the motor rotor (secondary) and stator (primary) windings. It produces a direct current voltage from the induced alternating current voltage in the rotor (secondary) which in turn provides additional direct current excitation to he stator to achieve emergency braking and slow descent of the load.

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New Berlin, WI, United States of America

James N Nash