Displacement control system for hoist apparatus

Claim 1

Hoist apparatus for use in moving a load between relatively vertically movable locations, comprising: a winch having a load supporting cable connectable to the load, means for operating said winch to take up and play out said cable including slipping drive means adjustable to apply more or less torque to said winch to raise and lower said load, load position sensing means for sensing vertical movement of said load, reference position sensing means for sensing relative vertical movement of said locations, and control means for adjusting said slipping drive means operable by said load position sensing means and said reference position sensing means to cause said load to move vertically synchronously with the relative movement between said locations, said control means including means operable to cause said load to be moved between said locations, each said position sensing means including a body having an inlet chamber and an outlet chamber, a piston chamber communicating with said outlet chamber, a piston chamber communicating with said outlet chamber, piston means having a surface exposed to pressure in said piston chamber, actuator means for applying a force to said piston means in opposition to the force applied to said piston means by fluid pressure in said piston chamber, a pair of diaphragms defining an Exhaust chamber therebetween, one of said pair of diaphragms having an exhaust valve port leading from said outlet chamber to said exhaust chamber, a pilot pressure chamber, the other of said pair of diaphragms being exposed to pressure in said pilot pressure chamber, a passage having a flow restrictor therein leading from said inlet chamber to said pilot pressure chamber, a nozzle having a passage leading from said pilot pressure chamber to said piston chamber, a closure for said nozzle passage carried by said piston means and movable between positions opening and closing said nozzle passage upon movement of said piston means in opposite directions, and inlet and outlet valve means for controlling the direct flow of fluid from said inlet chamber to said outlet chamber and from said outlet chamber through said exhaust port in response to variations in the pressure in said pilot pressure chamber.