Air balance hoist with load position indicator

An air balancing hoist comprising:

• a housing having an interior bore therein;
• a ball screw mounted in said housing to extend axially through said interior bore;
• a ball nut received over said ball screw;
• a drum spool fixed to one of said ball nut and ball screw to move axially therewith through a range of motion, the other of said ball screw and ball nut fixed to said housing;
• a cable attached to said drum spool so as to be wound thereon and unwound therefrom upon rotation of said drum reel in either axial direction;
• a movable element axially movable in said housing interior bore and sealed therein to define a pressure chamber on one side thereof, the other side drivingly engaging one end of said drum spool to create an axial force thereon when said chamber is pressurized;
• a source of regulated air pressure in communication with said chamber applying a pressure level sufficient to at least substantially balance an axial force exerted by said cable supporting a load acting through said ball screw and nut to generate an axial force on said drum spool acting oppositely to said axial force generated by said regulated air pressure acting in said chamber;
• an element mounted to said housing to be movable therein, said element having a portion located opposite one end of said drum spool;
• means yieldably urging said element against a relatively fixed stop, said element portion located so as to be engaged by said one end of said drum spool at a predetermined point in moving through said range of axial movement thereof and disengaged upon return movement thereof past said predetermined point;
• and,
• signal generating means changing states in response to said one end of said drum spool engaging said portion of said element by movement of said drum spool past said predetermined point in said range of axial movement to move said element away from said fixed stop against the force exerted by said means yieldably urging said element against said fixed stop, or to allow said force to again position said element against said fixed stop, said change of state indicating a load height position in a range corresponding to said drum spool axial location whereat said element is engaged and disengaged.