Pneumatic artificial rubber muscles (PARMs) are lightweight and high-output soft actuators that generally require compressors and other peripheral devices, increasing system size and noise. To address these issues, gas-liquid phase-change actuators that do not require such devices have been studied. However, because their actuation depends on heat, response delay becomes a significant problem. In this study, the continuous-operation performance was investigated using an antagonistic actuation system composed of two PARMs. The results showed that increasing the driving frequency and force amplitude degraded the force-tracking performance and shortened the time required to reach the safety pressure limit. In addition, insufficient cooling during continuous operation caused increases in internal temperature and average pressure, thereby limiting the range of safe operation. These findings clarify the influence of heat on sustained antagonistic actuation and provide guidelines for improving the long-term stability of phase-change-based artificial muscles.
