An Improved Four-Pin Gripper for Robust 2.5-D Form-Closure Grasp

The four-pin gripper is an ideal end-effector to achieve form-closure grasps, which is especially useful in scenarios where a stable grasp is necessary. In this article, we propose an improved parallel four-pin gripper design. Compared with the previous designs, the new design achieves more planar configurations while introducing only one more actuator, thus enlarging the possibility of the gripper to stably grasp. Based on the improved design, we extend the environment constraint-based form-closure grasping point search algorithm to find the optimal parameters for the improved four-pin gripper. Furthermore, we apply an inverse kinematics-based planning method to drive the gripper from any initial state to a form-closure state. The simulation and experiment demonstrate that, compared with the previous designs, the improved design can achieve stable grasping for a wider range of planar objects.