Patent ID: 7090055

Claim:
A lift braking system comprising: a winder having a load supporting cable wound thereon; a threaded shaft; a torsion tube disposed about and threadably interengaged with said shaft such that said tube is moved longitudinally relative to said shaft when said tube is turned axially about said shaft; said tube being operably connected to said winder such that axial rotation is transmitted between said tube and said winder; said tube carrying a first brake component; a rotatable ratchet for supporting a complementary second brake component adjacent said first brake component; a pawl that cooperates with said ratchet for restricting rotation of said ratchet in a first direction and allowing rotation of said ratchet in an opposite second direction; and a motor for axially rotatably driving said shaft selectively in opposing directions for respectively raising and lowering the load; said tube being responsive to the load supported by the winder and deactivation of said motor for turning axially on said shaft to interengage said brake components and interlock said ratchet with said pawl, whereby rotation of said tube and said winder are restricted and the lift is held at a selected elevation; said motor operating in a first direction to turn said tube axially relative to said shaft such that said brake components are momentarily disengaged and said tube and winder allow the load to be lowered by the cable, said tube thereafter being responsive to the supported load for turning on said shaft and re-engaging the brake components so that rotation of the tube and winder and lowering of the lift are controlled; said motor operating in an opposite, second direction to turn said tube axially relative to said shaft such that said brake components are interengaged and said ratchet component disengages and rotates freely of said pawl, whereby said tube and winder rotate to wind cable onto said winder and elevate the lift.