Patent ID: 7424933

Claim:
A ladder hinge assembly comprising: a first ladder hinge plate defining a first plate opening and at least one first locking slot in communication therewith; a second ladder hinge plate defining a second plate opening and at least one second locking slot in communication therewith; a housing extending through the first and second plate openings, wherein the housing is associated with the first plate and the interior of the second plate opening bears against the exterior of the housing to provide a rotation axis for the plates, and wherein the second plate is operable to rotate relative to the first plate about the rotation axis to selectively align first and second locking slots; a key outside the housing operable to engage aligned slots to prevent relative rotation of the plates about the rotation axis when the key is engaged with the aligned slots; a manual rotation member operably coupled to the key to selectively disengage the key from at least one of the aligned slots by rotation of the member a predetermined amount from a rotation member resting position; and a biased piston inside the housing and operably associated with the key to bias the key into engagement with aligned slots of the plates; wherein the manual rotation member is operably associated with the piston to rotate the piston relative to the housing, the piston including a first bearing surface for operable contact with a second bearing surface of the housing when the manual rotation member is rotated, wherein at least one of the first and second bearing surfaces is a ramped surface and rotation of the manual rotation member is operable to cause rotational and translational relative movement of the piston and the housing.