Ladder hinge and multi-position locking mechanism therefor

An improved hinge for collapsible ladders, said hinge being of the type wherein first and second members each have a head portion and a ladder stringer-engaging portion, the first and second members being pivotally engaged for rotation about a pivot axis extending generally perpendicularly through said head portions and having respective first locking apertures which are radially spaced from the pivot axis and can be selectively aligned and mis-aligned by mutual rotation of said first and second member about the pivot axis, and at least one locking pin which is selectively translated through the locking apertures, when aligned, from an unlocked to a locked position thereby preventing mutual rotation of the first and second members, the improved hinge further comprising:

• a hub member having a longitudinal axis corresponding to the pivot axis and having a guide aperture defined therein about the longitudinal axis;
• a guide shaft disposed in the hub member for both axially slidable translation between extended and retracted positions along the longitudinal axis through the guide aperture and rotation about the longitudinal axis;
• a handle member securing together the guide shaft and a proximal end of the locking pin such that a distal end of the locking pin is translatable through the locking apertures when aligned;
• bias means for applying an axial bias force to the guide shaft to urge the guide shaft toward the retracted position;
• axial detent means responsive to the guide shaft being moved to its extended position for maintaining the guide shaft in the extended position in opposition to the bias force while permitting rotation of the guide shaft, the detent means comprising:
• a first detent bore defined through one of said hub member and said guide shaft and at least a first detent recess defined in the other of said hub member and said guide shaft such that said first detent bore and first recess are axially aligned when the guide shaft is in the extended position and are angularly aligned when the locking apertures in said first and second members are aligned;
• a first detent member disposed in the first detent bore and having a projecting portion configured to match the first detent recess;
• and
• first means disposed in the first detent bore for urging the projecting portion of the said first detent member radially toward the first detent recess;
• and
• wherein the distal end of the locking pin is spaced from at least the first member in the extended position of the guide shaft and is snapped into abutment with the first member through the locking aperture in the second member upon disengagement of the detent means by rotation of the shaft.