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:
Jun. 14, 1977
Filed:
Aug. 25, 1975
Lester A Price, Greenfield, WI (US);
James N Nash, New Berlin, WI (US);
Harnischfeger Corporation, West Milwaukee, WI (US);
Abstract
A hoist uses an alternating current three-phase variable speed reversible wound rotor motor to hoist and lower a load. An electromechanical brake and a tachometer generator are connected to the motor shaft. Controllable SCRs connected to the motor stator (primary) windings control motor direction and speed and motor braking in response to error signals resulting from comparison of reference signals from an operator's master control and feedback signals from the tachometer. During hoisting and lowering (when the electromechanical brake is released), direct current voltage derived from appropriate gating of the controllable SCRs is applied to the motor stator (primary) winding to effect direct current braking as required. This direct current flow is smoothed and rendered more effective by gating 'on' a free-wheeling SCR which is connected across two of the motor stator (primary) windings. Emergency dynamic braking means operative in the event of failure of the electromechanical brake while the motor and control are deenergized but supporting a suspended load applies a rectified feedback signal from the tachometer to produce a magnetic field in the motor stator (primary) windings. A bridge rectifier is connected between the motor rotor (secondary) and stator (primary) windings. It produces a direct current voltage from the induced alternating current voltage in the rotor (secondary) which in turn provides additional direct current excitation to he stator to achieve emergency braking and slow descent of the load.