Electric hoist control and braking system
US3971971A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Nov 15, 1974 |
| Grant date | Jul 27, 1976 |
| Priority date | — |
| Expiry date | Nov 15, 1994 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH02P1/44
- WIPO fieldElectrical machinery, apparatus, energy
- WIPO sectorElectrical engineering
Abstract
The invention relates to control and braking systems for apparatus driven by single and polyphase alternating current induction motors. The system prevents destructive and dangerous overspeeding where the nature of the driven load is such that it can furnish sufficient torque to overdrive the apparatus in any one of several potential failure modes. A capacitor selected according to this invention is permanently connected across the motor winding such as to cause the drive motor to automatically develop retarding torque in the absence of power supplied thereto sufficient to restrict the overdrive speed to a value not appreciably exceeding the normal operating speed. The system also incorporates drive motors specifically designed with a predetermined value of starting torque appreciably less than that conventionally applied to similar apparatus for the specific purpose of limiting the load handling capability of the apparatus, thus preventing dangerous overloading. Numerous related benefits are attained through the aforementioned features, including improved controllability, improved holding brake life, and more reliable arresting of motion at limits of safe travel.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.