Position/force modeling and analysis of a piezo-driven compliant micro-gripper considering the dynamic impacts of gripping objects

The compliant micro-gripper driven by piezo actuator has emerged as a representative end-effector in micro-manipulations. To achieve high performance gripping of tiny and fragile objects, the switched position/force modeling approach has been well explored for such systems. In the present work, we investigate a lever-bridge-lever type piezo-driven compliant micro-gripper and develop a new position/force model to describe both kineto-statics and dynamics of the micro-gripper, where the free motion and gripping motion states in the manipulation process are unified in the modeling approach. In particular, the impacts of gripping objects on the dynamic properties of the gripper (in gripping motion state) are incorporated by considering the gripping object as a spring-damper system with a characteristic length. With this, the dynamic model can better predict the position of the gripping jaw and the contact position of the object, as well as the force applied on the object, which also offers the capability to estimate the stiffness of unknown objects in manipulations. Various gripping experiments with soft and stiff objects of different dimensions are conducted, which demonstrate the effectiveness and accuracy of the proposed modeling approach.