Patent ID: 7097145

Claim:
A counterbalance arm assembly comprising: a proximal hub formed to include a first proximal pivot axis extending therethrough, a second proximal pivot axis extending therethrough, and a third proximal pivot axis extending therethrough, said first, second and third proximal pivot axes being substantially mutually parallel, wherein the displacement between the first and third proximal pivot axes is adjustable, a distal hub having a first distal pivot axis extending therethrough and a second distal pivot axis extending therethrough, a first parallel link coupled at its proximal end for pivotal movement of the first parallel link relative to the proximal hub about the first proximal pivot axis and coupled at its distal end for pivotal movement of the first parallel link relative to the distal hub about the first distal pivot axis, a second parallel link coupled at its proximal end for pivotal movement of the second parallel link relative to the proximal hub about the second proximal pivot axis and coupled at its distal end for pivotal movement of the second parallel link relative to the distal hub about the second distal pivot axis, a spring coupled at its distal end to the second parallel link and at its proximal end to the second parallel link for longitudinal movement of the proximal end of the spring relative to the second link, a spring link coupled at its proximal end to the proximal hub for pivotal movement of the spring link about the third proximal axis, coupled at its distal end to the second parallel link for longitudinal movement of the distal end of the spring link relative to the second parallel link, and coupled at its distal end to the proximal end of the spring, wherein the proximal hub is formed to include an aperture extending radially from the first pivot axis and further comprising a pivot pin defining the third proximal pivot axis, said pin being slidably received in the aperture for movement of the pin radially with respect to the first proximal pivot axis, wherein a line intersecting the first and third proximal pivot axes is not colinear with and forms an angle with a line intersecting the first and second proximal pivot axes, wherein the first parallel link includes a longitudinal axis intersecting the first proximal and distal pivot axes, the second parallel link includes a longitudinal axis substantially parallel to the longitudinal axis of the first parallel link and intersecting the second proximal and distal pivot axes, the longitudinal axes of the first and second parallel links remain substantially parallel during movement of a device coupled thereto between a first elevation and a second elevation and the first longitudinal axis is between the second and third pivot axes.