Dockboard utilizing a gas spring for counterbalancing

A dockboard to be mounted on a loading dock and adapted to bridge the gap between the dock and the bed of a carrier disposed in front of the dock, comprising a supporting structure, a ramp structure hinged at its rear edge to the supporting structure and movable between a generally horizontal cross traffic position and an upwardly inclined position, a gas spring assembly interconnecting the supporting structure and the ramp structure, said gas spring assembly including a closed cylinder pivotally connected to one of said structures and containing a compressible gas and containing a quantity of a liquid, a piston mounted for sliding movement within the cylinder, a piston rod connected to the piston and projecting through an end of the cylinder and pivotally connected to the other of said structures, orifice means disposed in said piston for permitting passage of said gas and said liquid through said piston as said piston moves within said cylinder, the differential in force acting against opposite faces of the piston through said fluid urging the piston rod to an extended position relative to the cylinder and thereby biasing the ramp structure to the upwardly inclined position, manually releasible uni-directional holddown means operably connected to the projecting end of said piston rod and movable between a locked position and a released position, said holddown means when in the locked position preventing extension of said piston rod but permitting free retraction of said piston rod, and said holddown means when in the released position permitting both free extension and retraction of said piston rod, and resilient means operably connected to the projecting end of said piston rod for permitting limited extension of said piston rod when said holddown means is in the locked position in order to accommodate variations in height between the dock and the bed of the carrier during the loading operation.

In a dockboard, a supporting structure, a ramp member 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 member about a hinge axis and movable between a downwardly hanging pendant position and an extended position, elevating means operably connecting the supporting structure and the ramp member for moving the ramp member to its upwardly inclined position, a gas spring assembly operably connected between the ramp member and the lip for counterbalancing a portion of the gravity produced moment of the lip about the hinge axis, a crank member mounted for pivotal movement about said hinge axis and engaged with the undersurface of the lip, said gas spring assembly including a cylinder pivotally connected to one of said members and containing a quantity of a compressible fluid and a quantity of a substantially incompressible fluid, a piston mounted for sliding movement within the cylinder, orifice means disposed in the piston whereby the fluids can pass through the piston on movement of said piston within the cylinder, a piston rod connected to the piston and extending outwardly of said cylinder and pivotally connected to the other of said members, the force differential on opposite faces of said piston acting to bias the piston rod to an extended position, the axis of said cylinder being in substantial alignment with the hinge axis when the lip is in the pendant position, means responsive to upward movement of the ramp member for moving the crank member downwardly and moving the axis of said cylinder to an undercenter position with respect to said hinge axis, whereby the biasing force of said gas spring assembly will act through said crank member to assist in moving the lip toward the extended position.

In a dockboard, a supporting structure, a ramp member 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 member on a hinge axis and movable between a downwardly hanging pendant position and an extended position, elevating means operably connected to the ramp member for moving the ramp member to its upwardly inclined position, an arm member engaged with the undersurface of the lip and mounted for movement with respect to said hinge axis, a gas spring assembly including a cylinder pivotally connected to one of said members and containing a quantity of a compressible gas, a piston mounted for sliding movement within the cylinder, orifice means disposed in the piston whereby the gas can pass through the piston on movement of said piston within the cylinder, a piston rod connected to the piston and extending outward of said cylinder and pivotally connected to the other of said members, the force differential on opposite faces of said piston acting to bias the piston rod to an extended position, the axis of said cylinder being arranged relative to the hinge axis when the lip is in the pendant position such that the biasing force of said gas spring assembly is substantially nullified, means for swinging the lip from the pendant position toward the extended position and for moving the axis of said cylinder to an undercenter position with respect to said hinge axis, whereby the biasing force of said gas spring assembly will act through said arm to assist in moving the lip toward the extended position.