US 4,085,818 AGranted

Plastic ladder and safety device

OwnerWilliam E. Swagerinventor

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Abstract

A safety clamping device for use by climbers, combined with a fiber reinforced plastic rail upon which the clamp ultimately slides or grips. The clamping device has a pivotally mounted plate therein having a triggering arm extending outward for being engaged by a rope or chain, having one end carried by the belt mounted about the waist of the climber and the other being fastened to the triggering arm so that the climber slidably carries the clamping device upon the rail as he moves downward and upward on the ladder to which the rail is fastened. An inner end of the plate of the clamp is cam shaped and which is biased by a spring against the rail, but which, as supported by the climber, offsets the gripping by the cam so that the clamp easily slides with the climber as he ascends or descends the ladder, but ultimately grips the rail if the climber descends or falls rapidly, firmly engaging the rail to tightly clamp thereagainst as a safety device.

Claims13

Dependent claims

In combination, a step-ladder having an elongated fiber reinforced plastic rail having a clamp sliding surface shaped to receive a safety clamp, a web extending from and supporting said sliding surface and a base supporting said web and said surface providing clear and free sliding support of said clamp on said surface, a safety clamp sized and shaped to surround and to engage and slide on said rail, said safety clamp having a clamping portion comprising a wide smooth cam-shaped surface evenly bearing in its width against the correspondingly shaped and smooth sliding surface of said rail, said cam surface being alternately positioned to slide easily with said clamp or to bear against and firmly grip the surface of said plastic rail frictionally in a position of clamped engagement therewith, a trigger arm extending from said clamping portion engageable by a rope or chain carried by a climber for easy pull on said trigger arm and clamp to slide said clamp upward or downward on said rail in ascending or descending movement of said climber on said ladder, means above said cam surface biasing said clamping portion into a clamping engagement of said rail, said pull offsetting said bias sufficient to allow easy sliding movement of said clamp in normal upward or downward movement of the climber, said clamping portion being actuated into firmly clamped engagement with the surface of said rail by rapid downward pull of said rope or chain upon said trigger arm.

A safety clamp for use by climbers having a body portion shaped to engage and slide upon the curved surface of a rail;

said rail having a correspondingly curved plastic sliding surface supported by a web to provide full sliding movement of a clamp on said rail surface, and a base for mounting said rail to a ladder a wide clamping plate having an inner cam shaped surface curved to mate with the curvature of said rail surface, said plate being pivotally mounted in said body to bear against and grip the curved plastic surface of said rail and resilient means above said cam surface biasing said clamping plate and cam against said rail surface;
said clamping plate having a trigger arm extending laterally from said plate, for connecting to an end of a chain or rope mounted about the body of a climber, the weight of said clamp supported by said trigger arm and rope or chain in movement of the climber pivotally pressing said plate against said biasing means to release said clamp from gripping engagement from said rail surface whereby the clamp is carried slidingly upward or downward along said rail with the movement of said climber, and with rapid pull downward on said chain or rope, pivotally moving said cam portion of said plate into firm gripping engagement with said rail surface.

Dependencies are inferred from the claim text.