US Patent 7478786 Mechanical arm with spring counterbalance

A mechanical support arm for holding lamps, flat screen monitors or other equipment which comprises a base member and two links joined by pivoting joints and held in position by friction in the joints. The amount of friction required to hold the equipment in position is reduced by the use of spring-assisted counterbalances that compensate for the majority of the weight. The novel aspects of the invention include the design of the pivots, which are linked rings able to rotate about axles disposed at the pivot points, and the manner in which the springs are attached to the pivot points to reduce the amount of force that need be exerted on the arm to place the object being supported in the desired position.