Design, analysis and evaluation of a self-lockable constant-force compliant gripper

Maintaining a constant gripping force is a challenging problem when manipulating fragile objects with variations of sizes and stiffness. In this paper we develop a novel constant-force compliant gripper with clamp state locking capability, which is composed of the constant force module, the multi-stable module, the adjustment module and the actuator module. In particular, the symmetric compliant slider-crank mechanism is employed to maintain a constant force between the jaw and object. The multi-stable module with behaviors of snap-through and negative stiffness is designed to balance the interaction force from the constant force mechanism (CFM). With this, the gripping state, including the gripping force and the jaw position, can be locked during the gripping operations. Theoretical model of the constant-force compliant gripper is also established, where the force-displacement relationships is analyzed and verified by finite-element simulations. Experimental studies on an additive manufactured prototype are further conducted, which effectively validates the constant gripping force and force self-locking performance of the developed gripper.