Development of a rubber soft actuator driven with gas/liquid phase change

Soft rubber actuators are very useful in applications involving humans, such as in medicine and reflexology. Additionally, they are useful in industrial devices because of their softness. However, many soft rubber actuators are driven by pneumatic power, and the power source is usually bulky. This makes the application of soft rubber actuators difficult. In this study, we propose a novel small power source for soft rubber actuators, which uses the gas/liquid phase change phenomenon of the actuator working fluid. When fluids change their phase between liquid and vapor, a large volume change occurs. We assume that this volume change is sufficient to drive a single soft rubber actuator. We fabricated a prototype of an actuator comprised entirely of silicone rubber via a molding process. Using the first prototype, we confirmed that the actuator can be driven by the gas/liquid phase change of the actuator fluid. Then, we fabricated a second prototype that includes a cartridge heater inside its body. We applied an electronics coolant fluid to this actuator. From the results of several experiments, we confirmed that the actuator produced amaximumoutput force of 405 mN. When the actuator was driven by the gas/liquid phase change, its trajectory was almost the same as that when driven by air pressure. Hence, the proposed pressure source maintained the characteristics and advantages of the soft rubber actuator. We believe that a pressure source using the gas/liquid phase change phenomenon of a working fluid will mitigate the problems of the driving system of soft rubber actuators.