Synergistic Operation of a Thermo-Pneumatic Artificial Muscle With Embedded Shape Memory Alloy Springs

This study presents a novel synergistic actuator integrating thermo-pneumatic actuation and shape memory alloy (SMA) springs, achieving distinct operational modes with a single energy input. Conventional artificial muscles typically rely on a single actuation mechanism, limiting functionality. By combining thermo-pneumatic and SMA-based actuation, this actuator achieves cooperative, composite, and antagonistic modes without the use of a pneumatic pump. The cooperative mode utilizes the simultaneous actuation of both mechanisms to increase force and displacement output. The composite mode enables distinct actuation tasks, demonstrated through a soft robotic gripper capable of shape-adaptive grasping. The antagonistic mode exploits the opposing force generation of the two actuation sources by using a vacuum-based thermo-pneumatic actuator, facilitating bidirectional motions without additional bias mechanisms. Experimental evaluations confirmed improved force outputs and controllability under payload conditions with the actuator lifting payloads up to 20 kg. A thermodynamic model was combined with a quasi-static force model to predict the behavior of the actuator. The proposed actuator concept enables pumpless actuation of an actuation with two actuation sources using a single energy input and increases the performance of the actuator versus using a single actuation source while increasing the versatility of the actuator through its various modes of operation.