A variable stiffness robotic gripper with soft revolute joint composed of double-network gel

This study introduces the design of a novel variable stiffness gripper mechanism featuring soft revolute joints inspired by the structure of a human finger, where a soft cartilage-like joint connects a rigid skeleton. The soft joint in this mechanism is composed of Double-Network gel (DN gel). Applying voltage across the soft joint allows for control over the ease of joint rotation, enabling variable stiffness of the gripper through voltage control across the soft DN gel joint. Further investigation was carried out to study the impact of finger stiffness under varying applied voltages and electrode surface areas. Utilizing DN gel joints facilitated achieving three independent degrees of freedom (DOF) motion of the finger using a single motor actuator. Different gripper configurations can thus be achieved through simultaneous control of the soft joint and actuator. Kinematic modeling and control mechanisms for the finger were developed and validated through experiments. Additionally, experiments were conducted to demonstrate the gripper's grasping capabilities across objects of different sizes and weights. The fabricated gripper demonstrated the capability to handle various objects with a diameter of 150 mm and a weight of 400 g.