US 4,540,306 AGranted

Positioning joint for folding ladders

OwnerChien-Yuan Wanginventor

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Abstract

A joint having two joint members which are pivotable with respect to each other about a common axis is lockable in a series of predetermined angular positions by engaging a spring-biased pawl provided within one member in notches formed at the peripheral edge of the other member. In manually operating the joint, the forked release element and the handle pivotably connected with each other act as an operating lever in cooperation with the clawed, spring-loaded control means in controlling locking and unlocking of the joint. The claw like stop portion of the control means, when being pushed to one side within the slot having its length at least twice longer than the width of the notch by the release element in counter-clockwise direction, permits engagement of the pawl in the notches and, upon operation of the handle thereby disengaging the pawl from the notches, returns to rest position under its spring force in clockwise direction. In this position, the stop portion, by pressing against the back of the release element in blocking the pawl from falling back to the notches, effectively prevents engagement of the pawl in the notches to permit free pivoting of the joint.

A positioning joint used for folding ladders comprising:

a first joint member formed with a disk portion composed of a pair of spaced-apart, opposed circular plates from which extends a flat tubular portion having in opposite sides thereof two slots through which is slidably supported a spring-biased pawl operable by an operating lever pivotably connected to said tubular portion and having a release element;
a second joint member formed with a flat, hollow locking disk from which extends a tubular portion, said locking disk provided with a plurality of peripherally distributed notches engageable with said pawl and a control means for controlling opening and closing of said notches;
said first and second joint members being pivotably connected together by a common axial bolt passed through the centers of disk portion of the first joint member and the locking disk of the second joint member which is concentrically sandwiched between the plates of said disk portion;
and characterized in that one side of the hollow locking disk of the second joint member is formed adjacent the respective notches with a corresponding plurality of slots, the length of each slot being at least twice the width of said notches, the other side of said locking disk is formed with a long opening and said control means is pivotably rivetted by said axial bolt to one inner surface of one side of the locking disk;
wherein
said control means is formed with same number of claw arms relative to notches on the locking disk, the free ends of said arms are bent at right angles to the arms to form stop portions which protrude out through the slots of the locking disk;
a spring is provided secured one end to a hook portion being formed at the end of the claw projection which extends out from the control means and the other end to a hook-like projection being provided on the same side of the locking disk where said long opening is formed and into which said projection projects;
and said end portions, each protruding through a respective slot of the locking disk, act as an one-way stop means for the release element of the operating lever in disengaging the pawl when said release element is disposed in between the edge leading to said notch and the outer surface of said end portion whereby said pawl is prevented from falling back into the notch.

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Abstract

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