US Patent 8215199 Parallel kinematic positioning system

A parallel kinematic positioning system 10 (PKPS 10) that is comprised of a stationary base plate (12) and an upper movable platform (28) to which is attached a workpiece or an instrument. Between the stationary base plate (12) and the upper movable platform (28) are positionally attached six strut assemblies (50). The six strut assemblies operate a hexapod that include in combination, a counterbalance subassembly (111), a servo motor subassembly (134), a bearing and encoder subassembly (156) and an electronics circuit (190). The combination accurately and repeatably positions the upper movable platform (28) within six degrees of freedom relative to the base plate (12).