Concept design of a monolithic compliant series-elastic actuator with integrated position and two-level force sensing

Safe physical interaction is significant for the protection of the operated target during delicate micromanipulation tasks. This paper proposes the concept design of a series-elastic actuator mainly constructed by a fully compliant mechanism. It can reduce the transient contact force when the tip touches an object and monitor the interaction force in real time for safe handling. The rear end of the actuator is a flexible linear guide connected with a voice coil motor to offer a bidirectional displacement. The actuator's front end features a stiffness-switchable mechanism based on folding flexure beams, which provides two-level force buffering and sensing to accommodate varying degrees of contact status. Three strain gauges are integrated into the flexible beam of the mechanism, one of which is used for displacement sensing and the others for monitoring interactive force. After the structural design of the actuator, an analytical model is developed to assess its kinematic performance, which is further verified by finite-element simulation and experimental testing. The experimental results agree with the model and simulation, confirming the effectiveness and reliability of the actuator. The compliant actuator can be applied to some micromanipulation scenarios requiring precision positioning, contact, and interaction at the operating end.