Efficient lightweight hoist with multiple-cable-size traction and safety

Abstract

This scaffold hoist uses a transmission mechanism whose output shafts are fastened to the hoist housing, and whose case rotates, carrying a sheave which impels the mechanism along the cable. The transmission mechanism is advantageously a quadrant drive for extremely high torque-to-weight ratio. The sheave has a peripheral groove, tapered and deep enough to seat a cable having any of three different diameters, at different depths in the groove. The cable wraps around three-fourths of the sheave. Around five-eighths of the sheave, a chain presses the cable into the groove. The chain rollers enter the groove deeply enough to engage even the smallest-diameter cables of interest, while clearing the sheave periphery. The chain side bars ride along the sides of the sheave, holding the chain and cable in position. A resettable overspeed brake uses a rotary cam that jams a cable of any of the three sizes, at correspondingly various cam angles. The cam is cocked out of contact with the cable, and immediately spring-driven against the cable when triggered by a centrifugal sensor. A backup block--which keeps the cable from retreating from the cam--slides away from the cable at an angle during resetting, to facilitate unjamming the cable by moderate force.