An actuating device is taught for use with a robotic arm having a linear actuator which includes an actuated portion and a stationary portion with a tool device supported by the actuated portion. The actuating device includes a bracket attached to the stationary potion of the linear actuator with bracket presenting an engaging surface. There is a mechanical assembly for controlling rotation of parts acquired by the tool device which is attached to the actuated member of the linear actuator of the robotic arm. The mechanical assembly includes a displacement linkage member and a rotatable subassembly. The displacement linkage member contacts the engaging surface when the mechanical assembly is raised to a predetermined height through operation of the linear actuator portion. By raising the mechanical assembly above the predetermined height, the displacement linkage member is caused to drive rotation of the rotatable subassembly. A spring is provided to normally bias the displacement linkage member to a home position.