Patent ID: 7080825
Filing Date: 2006-07-25
Classification: B66D

Abstract:
1. In a chain hoist having a casing with a bidirectional chain drive motor that has a rotary drive shaft housed therewithin, the improvement comprising: a position encoder located within said casing including a position sensor producing encoded electrical position signals in response to rotation of said drive shaft, and tracking circuitry located within said casing for receiving electrically encoded destination signals from a source located externally of said casing and for receiving said encoded position signals, and providing electrical encoded motor driving signals responsive to differences between said encoded position signals and said encoded destination signals, and wherein said motor driving signals accelerate rotation of said chain motor drive shaft starting from a stationary condition and decelerate rotation of said chain motor drive shaft as said differences between said encoded position signals and said encoded destination signals approach zero, further comprising: a chain drive output shaft, a slip clutch connected between said motor rotary drive shaft and said chain drive output shaft, a chain drive output encoder coupled to said chain drive output shaft and including a chain drive output sensor producing encoded electrical chain drive output signals in response to rotation of said chain drive output shaft, an encoder mismatch detection circuit coupled to receive said encoded electrical position signals and said encoded electrical chain drive output signals and to produce a brake actuating signal in response thereto, at least one motor brake for preventing rotation of said bidirectional chain drive motor, and a brake relay circuit for applying said motor brake in response to said brake actuating signal.