Robert Christopher Lapota

US Patent:

53431340, Aug 30, 1994

Filed:

May 3, 1993

Appl. No.:

8/055744

Inventors:

David C. Wendt - Hubertus WI
Robert J. Lapota - Greenfield WI
Karl T. Flierl - Port Washington WI

Assignee:

Harnischfeger Corporation - Brookfield WI

International Classification:

H02P 318

US Classification:

318757

Abstract:

In an AC inverter drive connected to an AC induction motor on a material handling machine, the motor (which has a load holding brake and a pulse-emitting shaft encoder) moves a load in hoisting or lowering directions. A method for checking brake load-holding torque including the steps of decelerating the motor toward zero speed, setting the brake, applying "float" load-holding electrical power to the motor, changing the current flowing to the motor and checking for motor rotation by pulse-counting. Motor power is blocked if the number of counted pulses is less than a predetermined number or is increased if the number of counted pulses is greater than a predetermined number, the latter indicating that the brake is incapable of holding the load.

US Patent:

56252625, Apr 29, 1997

Filed:

Jan 3, 1996

Appl. No.:

8/582405

Inventors:

Robert J. Lapota - Greenfield WI

Assignee:

Harnischfeger Corporation - Milwaukee WI

International Classification:

H02P 550

US Classification:

318 71

Abstract:

A system having two or more A. C. motors driving the same load. The stator windings and rotors of both motors each conduct current having a vector representative of a magnitude and angular position of the current in the respective rotor and stator winding. Stator current sensors are provided for producing an indication of the magnitude of the stator current vector to each motor. Encoders are provided for sensing the rotating speed of each of the rotors from which can be calculated the angular position of the rotor load current vector with respect to the rotating stator flux current vector. A first torque control controls the magnitude of the stator current of a first one of the motors such that the stator flux current vector of the first motor and the rotor load current vector of the first motor are angularly separated by 90. degree. This angular relationship produces maximum torque at the rotating speed of the first motor. A second torque control receives an indication of the magnitude of the torque of the first motor from the first torque control.