Closed loop optimal control enabled micro-force sensors

This paper presents a closed loop optimal control enabled force sensing technology in micromanipulation and microassembly. The developed micro-force sensor is based on a cantilevered beam structure with piezoelectric polyvinylidene fluoride (PVDF) actuating/sensing layers symmetrically bonded over its entire surfaces. In this type sensors, when an external load is applied, the deformed PVDF sensing layer detects the force signal and feed it through a linear quadratic regulator (LQR) optimal servoed controller to the PVDF actuating layer, as a result, a closed feedback loop can be formed when a balance force is generated by the actuating layer within the sensor to balance the externally applied load, making the moving tip of the highly sensitive sensor remain in its equilibrium position. Once balanced, the sensor stiffness is virtually improved, so that accurate motion control of the moving part of the sensor can be attained. Furthermore, the applied force can also be achieved from the balance force in real time. This closed loop optimal control enabled force sensors can greatly enlarge the dynamic range of the microforce sensor and will enhance manipulability during micromanipulation/microassembly when the sensor is mounted to the end-effector