Harnischfeger Corporation

Robert H Reuss

Herbert D Long, Jr

Michael D James

A gantry crane travelable along a pair of rails and having an overhead girder transverse to the direction of travel, first and second legs connected to the girder, a load carrying trolley movable along the girder to a first position adjacent the first leg and to a second position adjacent the second leg, first and second spaced apart motor drives mounted on one of the legs in engagement with one of the rails for moving the crane, and third and fourth spaced apart motor drives mounted on the other leg in engagement with the other rail for moving the crane. When the trolley is at the first position, the first and second drives are highly loaded and the third and fourth drives are lightly loaded. Thereby, the lightly loaded drives attempt to drive the second leg such that it leads the first leg and skews the crane. When the trolley is at the second position, the third and fourth drives are highly loaded and the first and second motor drives are lightly loaded. Consequently, the lightly loaded drives attempt to drive the first leg such that it leads the second leg and skews the crane. A power source is connected to the first and third drives and a power source is connected to the second and fourth drives. The power sources are responsive to the presence of the trolley at either its first or second position to provide a large portion of their electrical power to the highly loaded motor drives to prevent skew.

Traveling crane

A hoist drive for a double hoist carrying member having a hold hoist drum, a hold rope connected to the hold hoist drum and from which the carrying member is suspended, and a hold motor for rotating the hold hoist drum to raise and lower the carrying member. The hoist drive further includes a close hoist drum, a close rope connected to the close hoist drum and from which the carrying member is suspended, and a close motor for rotating the close hoist drum to raise and lower the carrying member. During raising of the carrying member, the hold and close motors are each supplied with a.c. power at different preselected frequencies. The hold and close motors each operate along a first pair of intersecting frequency to torque curves during a raising operation in which the hold motor curve is steeper than the close motor curve. During a lowering operation the hold and close motors operate along a second pair of intersecting frequency to torque curves in which the hold motor curve is also steeper than the close motor curve. Due to the intersection and relative slopes of the first pair and the second pair of curves, the speed of the hold motor follows the speed of the close motor during both raising and lowering operation and the motors operate at the intersection points of the pairs of curves and share the load during both raising and lowering operation.

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Milwaukee, WI, United States of America

Robert H Reuss