The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Dec. 01, 1992
Filed:
Aug. 23, 1990
Michael D James, Franklin, WI (US);
Robert H Reuss, Milwaukee, WI (US);
Harnischfeger Corporation, Brookfield, WI (US);
Abstract
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.