Other

Harnischfeger Corporation

David C. Wycoff

William a. Hipp

William A Hipp

David C Wycoff

A hoist having an alternating current induction motor for rotating the drum of the hoist and an adjustable frequency power supply connected to the motor has a first control connected to the adjustable frequency power supply for directing the power supply to provide power to the motor at a first voltage level at the initiation of a raising operation. A second control is also connected to the adjustable frequency power supply for directing the power supply to provide power to the motor at the initiation of a lowering operation at a second voltage level which is lower than the first voltage level. The voltage level supplied to the hoist at the initiation of a raising operation may comprise a voltage level which is increased by a raising o first voltage boost value above the voltage level that would be applied without the first voltage boost value. At the initiation of a raising operation, the first voltage level may include a first voltage boost value. At the initiation of a lowering operation, the second voltage level is increased by a lowering or second voltage boost value above the voltage level that would be applied without the second voltage boost value during lowering operation. However, the second voltage boost value is smaller than the first voltage boost value.

Method and apparatus for operating a hoist

A motor control method and apparatus for a hoist is disclosed in which a drive motor is connected to an adjustable frequency power supply in which the frequency of the power supplied to the motor can be selectively varied. At the initiation of a hoist operation, when the hoist brake is holding the motor and an object constituting a load on the motor stationary, power is supplied to the motor at a predetermined low frequency which is sufficient to provide load holding torque upon release of the brake. The actual current level of the power supplied to the motor is sensed at the initiation of the hoist operation and a signal representative of that current level is compared with a reference signal representative of a current level which is sufficient to provide the load holding torque. If the signal representative of the actual current level of the power supplied to the motor exceeds the reference signal, an output signal is provided which will result in the release of the hoist brake from its holding condition.

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Brookfield, WI, United States of America

William A Hipp