Electromechanically operated dockboard

Abstract

An electromechanically operated dockboard. The dockboard includes a ramp hinged at its rear edge to a supporting frame and the ramp is adapted to be moved from a generally horizontal cross traffic position to an upwardly inclined position by operation of a recirculating ball screw unit, which is connected between the frame and the ramp and is driven by a permanent magnet motor. A lip is hinged to the front edge of the ramp and can be pivoted from a pendant, downwardly hanging position to an extended position where it forms an extension to the ramp. Deactivation of the ball screw unit, after the ramp is elevated, causes the ramp to fall by gravity, and as the ramp descends, the lip is lifted to the extended position where it will engage the bed of the truck. During the descent of the ramp the ball screw unit is driven in a reverse direction and the permanent magnet motor serves as a brake to control the speed of descent.

I claim: 
     
       1. In a dockboard construction to be associated with a loading dock, a supporting structure mounted on the dock, a ramp structure hinged at its rear end to the supporting structure and disposed to pivot from a generally horizontal cross traffic position to an upwardly inclined position, a drive unit interconnecting the supporting structure and the ramp structure for pivoting the ramp from the cross traffic position to the upwardly inclined position, said drive unit including a screw member and a nut member connected with the screw member, a first of said members being connected to the supporting structure and the second of said members being connected to said ramp structure, .Iadd.a base, said first member being supported by the base, means for pivoting the base to the supporting structure, .Iaddend.and a motor operably connected to the drive unit and being capable of being driven in one direction by a power source to effect relative movement between said nut member and said screw member to thereby move the ramp from the horizontal position to the upwardly inclined position, and said motor being driven in the reverse direction as the ramp structure descends by gravity from the inclined position toward the horizontal position to provide a dynamic braking action to control the descent of the ramp structure. 
     
     
       2. The dockboard construction of claim 1, wherein said motor is operably connected to said first member. 
     
     
       3. The dockboard construction of claim 1, wherein said screw member is connected to said supporting structure and said nut member is connected to the ramp structure, said motor being operably connected to the screw member to rotate said screw member, said nut member being moved along said screw member on rotation of said screw member to thereby move the ramp structure to the inclined position. .[.4. The dockboard construction of claim 3, and including a base, said screw member being journalled for rotation on said base, and means for pivoting the base to the supporting 
     
     
        structure..]. 5. The dockboard construction of claim .[.4.]. 
     
     
        .Iadd.3.Iaddend., wherein said motor is supported by said base. 6. The dockboard construction of claim 1, wherein said second of the members is 
     
     
        connected to the forward end of the ramp structure. 7. The dockboard construction of claim 1, and including a lever connected to the rear end of the ramp structure, said second member being connected to the lever. 
     
     
           In a dockboard construction, a supporting structure, a ramp structure hinged at its rear end to the supporting structure and movable between a generally horizontal cross traffic position and an upwardly inclined position, a drive unit interconnecting the supporting structure and the ramp structure, said drive unit including a screw member having an external helical groove and also including a nut member having an internal helical groove, said drive member including a plurality of balls disposed within registering grooves in said screw member and said nut member, a first of said members being connected to the supporting structure and a second of said members being connected to the ramp structure, and a DC motor operably connected to the drive unit, operation of said motor in a first direction effecting relative movement between said nut member and said screw member in a first direction to thereby move the ramp structure from the cross traffic position to the upwardly inclined position, gravity descent of said ramp from the upwardly inclined position causing relative movement between said nut member and the screw member in the opposite direction to thereby drive the motor in an opposite direction, driving of the motor in an opposite direction producing a controlled descent of the 
     
     
        ramp structure. 9. The dockboard construction of claim 8, wherein said screw member is connected to the supporting structure and the nut member is connected to the ramp structure, said motor being operably connected to the screw member to rotate the screw member and thereby move said nut 
     
     
        member axially of said screw member. 10. The dockboard construction of claim 9, and including a base, said screw member being journalled for rotation on said base, and pivotal means for pivotally connecting the base 
     
     
        to the supporting structure. 11. The dockboard construction of claim 9, and including means associated with the drive unit and responsive to upward floating movement of the ramp caused by elevation of the level of a truck bed disposed in front of the dock for disconnecting the screw member 
     
     
        from the motor. 12. In a dockboard construction, a supporting structure, a ramp hinged at its rear edge to the supporting structure and movable between a generally horizontal cross traffic position and an upwardly inclined position, a lip hinged to the forward edge of the ramp and movable between a downwardly hanging pendant position and an extended position, a recirculating ball screw drive unit interconnecting the supporting structure and the ramp and including a base pivotally connected to the supporting structure, said drive unit also having a screw journalled for rotation with respect to the base and a nut engageable with said screw and movable along the length of said screw, said nut being connected to the ramp, and a DC permanent magnet motor operably connected to the screw to rotate the same, operation of the motor causing rotation of the screw in one direction to move the nut axially of the screw to thereby pivot the ramp from the cross traffic position to the upwardly inclined position, discontinuance of the operation of the motor causing the ramp to descend by gravity to move the nut axially of the screw and rotate the screw in the opposite direction, rotation of the screw in said opposite direction being transmitted to said motor to drive the motor in 
     
     
        an opposite direction and brake the descent of the ramp. 13. The dockboard construction of claim 12, and including a tubular member interconnecting the nut and said ramp, said tubular member being disposed radially outward 
     
     
        of said screw. 14. The dockboard construction of claim 12, wherein said nut has an internal helical groove and said screw has an external helical groove, and said drive unit includes a plurality of balls disposed in the 
     
     
        registering grooves of the nut and the screw. 15. The dockboard construction of claim 12, wherein said motor has a drive shaft and is mounted on the base, and said construction includes gear means 
     
     
        interconnecting the drive shaft of the motor and said screw. 16. The dockboard construction of claim 12, and including a connecting member interconnecting the nut and the ramp, said connecting member being 
     
     
        connected to the forward portion of the ramp. 17. The dockboard construction of claim 12, and including a lever connected to the rear end portion of the ramp, a connecting member interconnecting the nut and the lever, whereby movement of said nut in a rear-to-front direction will act to pivot the ramp from the cross traffic position to the upwardly inclined 
     
     
        position. 18. The dockboard construction of claim 12, wherein said motor has a drive shaft, and said construction includes clutch means having an engaged position wherein said drive shaft is operably connected to said screw and having a disengaged position, rapid upward movement of the ramp caused by elevation of the level of a truck bed disposed in front of the dock with the lip engaged with the truck bed acting to disengage said clutch means to prevent rotation of the screw from being transmitted to said motor.