Hybrid Antagonistic System With Coiled Shape Memory Alloy and Twisted and Coiled Polymer Actuator for Lightweight Robotic Arm

Artificial muscles have been developed for various input power sources. Among them, thermally driven actuators can be easily actuated at a low voltage without an additional device using the Joule heating. Therefore, these actuators can be considered suitable for developing lightweight robots. Shape memory alloy or twisted and coiled actuators are typically used as both have the advantage of large specific power; however, their disadvantages include speed, hysteresis, and initial tension. In this letter, we developed a hybrid antagonistic system that alleviates the drawbacks of both actuators. Control methods for hysteresis are applied based on actuator models and controlling the cooling fan. The joint position control experiment was conducted, and the advantages of the two actuators could be utilized based on the results. Furthermore, a lightweight robot arm was developed using the hybrid system. By applying the hybrid system, the robotic arm could be fabricated with a light weight of about 1 kg and can move in 4 degrees of freedom. The robotic arm was possible to perform angle control of the elbow with the developed control algorithm. In addition, it was combined with a 3 degrees of freedom orthogonal joint to replace the role of the shoulder, and the robotic arm was able to demonstrate the motion of activities of daily living.