Patent ID: 7419019

Claim:
A power-assist apparatus comprising: a bed having a frame extending therebelow and having a wheel rotatably mounted thereto so as to support the frame above an underlying surface; a drive wheel interconnected to said frame, said drive wheel movable between a first position which said drive wheel is positioned in spaced relationship to the underlying surface and a second position in which said drive wheel resiliently contacts the underlying surface; a control means cooperative with said drive wheel so as to move said drive wheel between said first position and said second position; a motor drivably connected to said drive wheel; and a support structure affixed to said frame of said bed, said motor affixed to said support structure, said drive wheel being rotatable relative to said support structure, said support structure comprising: a channel member affixed to a cross-member of said frame of said bed; a panel pivotally connected to said channel member, said motor and said drive wheel being supported beneath said panel; and an actuator means cooperative with said channel member and said panel, said actuator means for moving said panel and said drive wheel between said first and second positions, said actuator means comprising: a housing pivotally connected to one end of said channel member; and an actuator positioned in said housing, said actuator having a piston extending outwardly of said housing, said piston having an end opposite said housing received by a surface of said panel; and a spring extending between said housing and said surface of said panel so as to resiliently contact said surface of said panel, said piston being in slidable relationship to said surface of said panel, said spring resiliently urging said panel pivotally downwardly relative to said frame of said bed such that said drive wheel is in said second position, said piston generally being freely slidable through said surface of said panel, said piston comprising: a drive piston extending outwardly of housing; a support flange affixed to an end of said drive piston opposite said housing; and a pair of rods affixed to a side of said support flange opposite said drive piston, said pair of rods extending in generally parallel relationship to each other, said spring comprising a pair of springs extending respectively over and along said pair of rods.