Preliminary Demonstration of Steady-State Force Generation by High-Frequency Actuation of a High-Response Artificial Muscle Actuator Using Dimethyl Ether Combustion (HADEC)

This study focuses on the structure and actuation principle of biological muscles and attempts to develop a novel actuator that emulates their behavior. Pneumatic artificial muscle (PAM), particularly those of the McKibben type, have been widely utilized in assistive suits due to their lightweight design, flexibility, and high-power density. However, their reliance on compressed air results in delayed response, making them unsuitable for rapid actuation. To address this limitation, we developed a combustion-driven artificial muscle named HADEC (High-Response Artificial Muscle Actuator using Dimethyl Ether Combustion), which generates impulsive contraction force by injecting and igniting a dimethyl ether (DME)– air mixture inside the artificial muscle. Since HADEC is only capable of impulsive behavior, it has not yet been able to achieve steady-state force generation. In this study, inspired by the behavior of biological muscles, we propose and demonstrate a system in which three HADEC actuators are driven in a phase- shifted manner at a high frequency of 4.166 Hz (0.24 s cycle). Furthermore, to address the scalability issue inherent in PAMs—which require an increasing number of solenoid valves when used in multiples—we also propose a fluidic circuit architecture for HADEC that operates without the need for valves. The proposed configuration successfully achieves steady- state force generation. Experimental results show that an arm could be held within a range of 10°–20° for approximately 1.5 seconds, indicating that repeated high-frequency actuation of HADEC can emulate the behavior of biological muscles and serve as an effective approach for achieving continuous actuation.