Limit switch tripping mechanism for lifting jacks

Abstract

A lifting jack has its upward and downward traveling distance controlled by means of a limit switch. The lifting jack has a base, an upright outer member rigidly connected to the base and an upright inner member movable coaxially within the outer member. An up stop and an adjustable down stop are rigidly attached to and move with the inner member. An adjustable mount is mounted in a fixed position on the outer member, and the limit switch is mounted in fixed position on the mount. A guide shoe assembly is pivotally connected to the mount and is oriented generally perpendicular to the direction of travel of the inner member. A stop engaging member at one end of the guide is positioned to engage the up stop and the down stop, and an arm guiding portion at the opposite end engages and guides an actuating arm of the limit switch. In operation, the guide (and therefore the actuating arm of the limit switch) is biased by garter springs which hold it in a normal position riding on the inner member which is generally perpendicular to the direction of travel of the inner member of the jack. When the stop engaging member engages the down stop, the stop engaging member moves downward and the arm guiding portion and the actuating arm move upward, thereby causing the limit switch to change from its normal state. Similarly, when the stop engaging member engages the up stop, it moves upward and the arm guiding portion and the arm move downward to cause a change in the state of the limit switch.