Development of soft variable stiffness actuator with tendon-driven layer jamming mechanism

As the development of soft exoskeleton is ac-tivated, soft actuators used for soft exoskeleton have also become an important part. To ensure the safety of people with disabilities, stiffness must be adjusted according to trauma and recovery of a specific patient, and mechanism with capable of appropriate rehabilitation exercise according to their muscle stiffness and muscle tension are needed. Therefore, this paper focused on the development of variable stiffness tendon-driven mechanism that can be potentially used in the soft actuator part of soft lower limb rehabilitation robot. This mechanism is characterized by being able to accurately derive the stiffness of various ranges with one soft actuator. Since the actuator with this characteristic will be used by attaching to the lower limb, difference in axial stiffness of jammed and unjammed states was measured. As a result of testing different materials, it can be seen that the jammed stiffness has a larger value than the unjammed stiffness in all cases, and among them Dragon Skin 30 has the largest stiffness gap at 0.883 N/mm. Moreover, the stiffness gap calculated through the methodology and measured through the experiment has a similar range with an error of 0.045 N/mm or less. Therefore, we can prove the effectiveness of the mechanism and the accuracy of the methodology. In addition, we believe that soft actuator with tendon-driven layer jamming mechanism will be helpful to people who need lower limb rehabilitation.