Patent ID: 8167089

Claim:
A system for lifting a platform comprising: a platform including a frame; a plurality of upright members each having a plurality of equally spaced holes longitudinally aligned, each of said holes having an upper surface and a lower surface; each upright member having a corresponding hydraulic motor attached to said frame, and a corresponding pinion with an axis carried by said frame and driven by said corresponding hydraulic motor, each of the pinions having a plurality of equally spaced radially extending teeth, each tooth respectively including respectively opposing tabs supporting a respective roller journaled between the tabs over a journal bushing over a shaft, the roller offset from a center of the tabs so a back of the roller is located between opposing tabs of the tooth and a front of the roller is located between two adjacent teeth, said roller being freely rotatable about the shaft, said teeth capable of engaging said upright members wherein said teeth, each at said respective tabs and rollers, are capable of projecting into adjacent holes in said upright members wherein said front of the rollers can roll over said lower surfaces of said adjacent holes when said motors rotate said pinions in a direction to raise or lower said frame and platform; and wherein each respective motor being supplied fluid through a corresponding proportional control valve that directs and selectively restricts fluid flow to each corresponding motor, each motor having the corresponding pinion attached thereto, said proportional control valves having solenoids that move said control valves to control fluid flow to said corresponding motor, each solenoids being responsive to electric signals to initiate movement of said corresponding control valve, a level sensor for sensing an angle of said platform with respect to an horizontal orientation and providing said electric signals to actuate said solenoids to move said control valves connected to each motor so that each of said motors rotates the attached corresponding pinion at a rate to maintain each motor at an equal distance traveled along the upright member during raising or lowering of said platform, wherein if the platform is moving upwards, the fluid flow to the control valve of the motor on a higher end of the platform will be limited thus rotating the motor on the higher end slower, and wherein if the platform is moving downwards, the fluid flow to the control valve of the motor on a lower end of the platform will be limited thus rotating the motor on the lower end slower.