Improving the stiffness of mechanical layer jamming cable-driven soft actuators through design optimization and frame reinforcement

Soft cable-driven actuators offer flexibility and adaptability but often lack stiffness, limiting their application in tasks requiring high load capacity. A variable stiffness mechanism has been developed to change the stiffness as needed to increase the actuator’s applications further. The layer jamming structure combined with the soft actuator can be tuned to increase the actuator’s stiffness when needed. The mechanical layer jamming using the actuator body to activate the jamming state has been shown as a new method of changing the stiffness of the actuator. The actuator is designed to change stiffness by pulling the cable that is also used for actuator bending. However, it still has low stiffness when jamming, which still limits the applications of actuators. This study focuses on improving the cable-driven actuator’s design to increase stiffness through cable routing and sheet materials. In addition, frame reinforcement was applied to reduce the sheet separation in the mechanical layer jamming. The experiments in each condition of the actuator were conducted by adding an external load to the actuator tip in the bending posture and measuring the displacement of the actuator in order to verify the effectiveness of the design in improving stiffness. The results of experiments show that our approach can successfully increase stiffness and load capacity with variable stiffness capabilities. Moreover, we tested the actuator in the soft gripper application to hold the objects. The results show that the soft gripper can control stiffness and, in the jamming state, is able to grasp the object with 1500g successfully.