Design of a low-cost underactuated finger for positioning or pinching thin objects

Robotic grippers in industry are expected to have low degrees of freedom (DOFs) with cost and simplicity concerns. However, thin objects (e.g. mobile phone covers, shielding of IC chips) cannot be handled by traditional gripper fingers, since deformation may be caused. To solve this problem, a low-cost underactuated finger with a special four-bar linkage and a flexible joint is proposed in this paper. The special four-bar linkage is designed to obtain the desirable motion trail of the fingertip which is a quasi-horizontal line, while the flexible joints reduce the impact force and achieve compliant force control. In this paper, the design methodology of the four-bar linkage and the flexible joint is introduced, while the kinematic performance is analyzed. An experiment was conducted to verify the design and analysis. Results show that the proposed two DOFs underactuated finger can be applied on a robotic gripper to pinch or position thin objects. Finally, an example for its application is briefly explained to reinforce the concept.