Duo-block safety device

Claim 1

In a hoist system having a traveling block suspended on a cable driven by a power winding drum mounted on a bidirectional rotatable drive shaft, said drum having a clutch mounted on said shaft of said winding drum and a brake in braking relationship therewith, said brake and said clutch being simultaneously inversely actuated by valve means having a cam follower actuator, a safety apparatus for stopping at upper and lower limits the travel of said block, comprising: a gear reduction unit interconnected in driving relationship with said drive shaft having an output shaft rotating less than 360* in response to travel of said block between said upper and lower limits; a cam disc having a cam profile on the circumferential periphery thereof engaging said cam follower actuator of said valve means, said cam follower actuator being responsive to the rotative movement of the said cam disc; a pair of spaced-apart clutch plates coaxially mounted on said output shaft and rotatable in unison therewith, said cam disc being sandwiched between said clutch plates and rotatable by hand about said output shaft, said clutch plates being longitudinally movable relative to each other between engaged and disengaged positions; and means for longitudinally moving said clutch plates between said engaged and disengaged positions whereby in said engaged position said cam disc is fixedly engaged by said clutch plates to interconnect said cam disc to said output shaft for common rotation therewith and in said disengaged position said cam disc is rotatable by hand relative to said output shaft for adjusting the limits of travel of said block.