EVSPSA: an elongated variable stiffness pneumatic soft actuator for rigid-soft coupling gripper

Soft grippers face limitations in load capacity due to the low stiffness of soft materials. This paper proposes an elongated variable stiffness pneumatic soft actuator (EVSPSA) to enhance the load capabilities of conventional soft actuators. The actuator employs a rigid-soft coupling method, comprising an elongation variable stiffness mechanism that features a soft rectangular variable stiffness chamber and rigid elongation parts at the upper and lower ends, as well as a rigid ring-sleeve that constrains a soft cylinder serving as the elongation chamber. The proposed EVSPSA maintains high elongation flexibility while also offering variable stiffness capability. Based on this, a two-finger rigidsoft coupling gripper with good grasping stability is developed. The gripper features inflatable contact chambers at the grasping end to increase the contact area with objects during grasping. The high flexibility and adjustable stiffness of the EVSPSA enable the gripper to grasp fragile objects of various shapes and weights non-destructively. Experimental results show that the EVSPSA exhibits good elongation performance and strong variable stiffness ability. The developed rigid-soft coupling gripper has a load capacity of 60.3 N when grasping objects with the maximum diameter, effectively improving load capacity and showing promise for industrial and agricultural fields.