Patent ID: 7837674

Claim:
A set-up arm to support a robotic arm, the set-up arm comprising: a first set-up joint to couple to a support structure; a second set-up joint spaced apart from the first set-up joint, the second set-up joint to couple to a robotic arm to provide support thereto; a counter balancing link pivotally coupled to the first set-up joint at a first pivot point and to the second set-up joint at a second pivot point, the counter balancing link to balance out the force of load at the second set-up joint, the counter balancing link including a hollow housing having a cylindrical cavity with a first opening at a first end; a spring in the cylindrical cavity having a first end coupled to the hollow housing, the spring to provide a spring force to balance out the force of load at the second set-up joint; a plurality of pulleys including a first pulley rotatably coupled to the first set-up joint at the first pivot point between the counter balancing link and the first set-up joint, and one of a pair of pulleys rotatably coupled to the first setup joint and another one of the pair of pulleys rotatably coupled to the hollow housing; at least one cable under tension coupled to the setup arm and wrapped over the plurality of pulleys to couple to a second end of the spring; and wherein a linear distance between the pair of pulleys varies to change a cable path length in response to the pivoting of the counter balancing link with respect to the first set-up joint to modify the spring force and the tension in the at least one cable under tension to counter balance changes in moment and mechanical advantage.