Prolonging the lifetime of straight-fiber-type pneumatic rubber artificial muscle by shape consideration and material development

A pneumatic artificial muscle is an air pressure-activated rubber actuator. It is lightweight and high in power density compared to motorized actuators and fluid-powered cylinders. In addition, it shows high compatibility with the human body because it has good flexibility. The authors have developed a straight-fiber-type pneumatic artificial muscle (SF-ARM) with high output and contraction amounts compared to those of the widely used McKibben-type artificial muscle. Although the fatigue life of the McKibben type has been examined, similar studies have not yet been performed for SF-ARM. In this study, the extension of the lifetime of SF-ARM, development of high-deformation rubber material, and examination of the SF-ARM aspect ratio were performed. First, from deformation analysis by the finite element method, the target elongation value of the rubber material was determined and a suitable material was developed. Next, the fatigue life and contraction characteristics were measured by reducing the strain of the rubber material by changing the aspect ratio. The results showed a relationship between the lifetime and the shape of the artificial muscle. We demonstrate that the relationship between the lifetime and contraction force and ratio, according to the application, can be selected by manipulating the shape and the size of the SF-ARM.