Safety toe-sensor for lift table

Abstract

A lift table includes a toe sensor responsive to contact around the entire perimeter of the base. Multiple pressure switches are installed over two sides of the base and capped by an overlapping four-sided suspended guard. Multiple guides and springs of appropriate stiffness support the guard suspended over the base, so that any appreciable pressure exerted on the guard causes the compression of the springs and the direct application of pressure on an underlying switch which, in turn, de-energizes the mechanism controlling the descent of the platform. The pressure switches are incorporated into a control circuit that is activated only when the platform is descending. The platform may be sized to extend over the base enough to overlap the guard of the toe-sensor.

I claim:  
     
         1 . A lift table comprising: 
 a base, a load platform, and a vertically extendible means for raising and lowering the platform relative to the base; and    means for interrupting a descent of the platform in response to an object encroaching the base.    
     
     
         2 . The lift table of    claim 1   , wherein said means for interrupting a descent of the platform comprises a sensor mechanism affecting a perimeter of the base.  
     
     
         3 . The lift table of    claim 2   , wherein said sensor mechanism includes a sensor actuate by a guard mounted on said base.  
     
     
         4 . The lift table of    claim 3   , wherein said sensor comprises a pressure switch.  
     
     
         5 . The lift table of    claim 3   , wherein said sensor comprises a Hall-effect switch.  
     
     
         6 . The lift table of    claim 3   , wherein said sensor comprises an optic-electronic fiber switch.  
     
     
         7 . The lift table of    claim 2   , wherein said sensor mechanism includes a perimeter beam-switch.  
     
     
         8 . The lift table of    claim 7   , wherein said perimeter beam-switch comprises an infrared radiation emitter and a receiver.  
     
     
         9 . The lift table of    claim 7   , wherein said perimeter beam-switch comprises an ultrasound radiation emitter and a receiver.  
     
     
         10 . The lift table of    claim 2   , wherein said sensor mechanism includes a plurality of sensors mounted on said base of the table lift, and a guard adapted to activate at least one of the pressure switches when pressure is exerted on the guard.  
     
     
         11 . The lift table of    claim 10   , wherein said sensors comprise a pressure switch.  
     
     
         12 . The lift table of    claim 10   , wherein said sensors comprise a Hall-effect switch.  
     
     
         13 . The lift table of    claim 10   , wherein said sensors comprise an optic-electronic fiber switch.  
     
     
         14 . The lift table of    claim 10   , further comprising a plurality of springs between the base and the guard, such that the guard is suspended over the base.  
     
     
         15 . The lift table of    claim 10   , further comprising a valve actuated by any one of said sensors to close and hydraulically interrupt the descent of the platform when pressure is exerted on the guard.  
     
     
         16 . The lift table of    claim 14   , further comprising a valve actuated by any one of said sensors to close and hydraulically interrupt the descent of the platform when pressure is exerted on the guard.  
     
     
         17 . The lift table of    claim 16   , wherein said sensors comprise a pressure switch.  
     
     
         18 . The lift table of    claim 16   , wherein said sensors comprise a Hall-effect switch.  
     
     
         19 . The lift table of    claim 16   , wherein said sensors comprise an optic-electronic fiber switch.