Abstract: A mechanical closed loop robotic arm end effector positioning system which produces a precision reference frame with an associated workpiece fixture or other robotic manipulator system is disclosed. The positioning system results in decoupling of end effector operation from gross movement inaccuracies or vibrations of the robotic arm, thus allowing less precise robots to perform high precision tasks. The system includes a wrist assembly which is mountable to the robotic arm near the arm's distal functional end. The wrist assembly has a compliant member and a first positioning member connected thereto. The first positioning member includes a first docking arrangement. A second positioning member associated with the workpiece fixture includes a second docking arrangement. The first and second docking arrangements are sized and positioned to engageably mate within the robotic arm's resolution when the robotic arm attains a target position relative to the workpiece fixture.