Abstract: A plural column hoist mechanism in which the lifting slides are synchronized by a chain and safety devices are operative in the event of chain breakage. If the chain is slack, the hoist mechanism may be operated to effect upward travel of the lifting slides.

Abstract: A hoist mechanism for lifting a load includes a hollow support post, a threaded spindle rotatably mounted within the post, a traveling nut carried by the spindle for movement therealong during rotation of the spindle, a carriage engaged by the traveling nut to move along the spindle, and a motor for effecting rotation of the spindle. The post has a longitudinal opening aligned with the spindle having a width permitting the spindle to be moved laterally therethrough. The spindle is releasably connected to the motor drive shaft at one end and to a support bearing at the other end. Lift arms for supporting a load are connected to the carriage through the post opening. The hoist mechanism also includes a clutch mechanism providing a braking force during lowering and a safety switch assembly for terminating operation whenever the lift arms are blocked.

Abstract: A low friction traveling nut assembly carried on a threaded spindle for linear movement therealong in response to rotation of the spindle about its rotational axis includes a housing, a roller rotatably mounted within the housing by roller bearings, and a clutch mechanism which engages when the spindle is rotated in one direction relative to the traveling nut assembly to effect substantial sliding friction between the roller and a bearing surface reacting with the housing so that the traveling nut assembly is automatically braked to resist movement in one axial direction.