Return-to-dock level mechanism for a hydraulic dockboard

Abstract

A return-to-dock level mechanism for a power operated dockboard. The dockboard comprises a ramp which is hinged at its rear edge to the frame of the dockboard and a lip is hinged to the forward edge of the ramp. A ramp cylinder connects the frame and the ramp and acts to pivot the ramp upwardly between a downwardly extending below dock level position to an upwardly inclined position, while a lip cylinder interconnects the ramp and the lip and acts to pivot the lip from a downwardly handing pendant position to an extended position. The return-to-dock-level mechanism includes a pair of position actuated switches, such as mercury switches, which are connected in an electrical circuit with a timer and the pump of the hydraulic system. One of the switches is mounted on the ramp, while the other switch is mounted on the lip. When the ramp is below dock level with the lip extended, the ramp switch will be closed and the lip switch will be opened. As the lip falls from the extended position to the pendant position after a loading operation is completed, the lip switch will close, which energizes the timer and when the timer times out, the circuit to the pump is completed to operate the pump and supply fluid to the ramp cylinder to raise the ramp. When the ramp is elevated to a position slightly above dock level, the ramp switch will open to stop operation of the pump and the ramp will then descend by gravity to the horizontal cross traffic position.