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:
Oct. 23, 1990
Filed:
Jan. 31, 1989
Keith O Jurkowski, Waukesha, WI (US);
David C Wycoff, Elm Grove, WI (US);
Harnischfeger Corporation, Brookfield, WI (US);
Yaskawa Electric Mfg. Co. Ltd., Tokyo, JP;
Abstract
An adjustable frequency motor drive system for a hoist is disclosed in which the frequency of the power supply to the motor can be selectively varied and the speed of the motor will follow the varying frequency at a slip speed relative to the frequency. The slip speed of the motor may not exceed a value beyond which the motor can control the hoist load. Accordingly, a frequency value based on the frequency of the power supply to the motor is selected as the frequency which is not to be exceeded by the motor speed expressed as a frequency. Signals representative of the actual motor speed and the selected frequency value are compared and, if the signal representative of the motor speed exceeds the signal representative of the frequency value which is not to be exceeded, an output signal is produced which may be used to apply a brake which stops and holds the motor and hoist and thereby maintains the load suspended. A motor speed deviation time period may also be provided and the hoist brake not applied to the motor until the time period is exceeded.