Design of a Durable Air-Muscle With Integrated Sensor for Soft Robotics

Soft robotics integrates compliant actuators and sensors that expand design possibilities beyond classic robotics based on rigid modular components. In particular, deformable elastomer-based actuators used in soft robots, such as air-muscles, offer the possibility of having large numbers of embedded degrees of freedom. However, air-muscles fatigue life and strain capability call for a tradeoff, limiting their practical use in demanding applications such as physical rehabilitation, medical robotics, and mobile robots. This paper presents the design of a durable high-strain air-muscle composed of a silicone tube and an axially elastic sleeve (radially rigid), which integrates a flexible Dielectric Elastomer (DE) position sensor. The uniformity of the sleeve, by opposition to usual braids, makes for a reinforcement without local stresses that cause membrane failure. Designed based on fatigue failure principles, this air-muscle withstands 145 000 cycles at 50 % elongation, which demonstrates its potential as a durable high-strain actuator. Performance maps of the air-muscle confirm good linearity between force, pressure and strain and demonstrate bi-directional force capability. Furthermore, the integration of a DE sensor allows for accurate position control of the air-muscle (0.17 mm), making the air-muscle/sensor unit a relevant building block for complex soft robotics systems. The all-polymer high-strain actuator/sensor unit proves to be accurate and durable as well as cost-effective, thus making it ideal for soft robotics applications requiring large numbers of actuators and integrated sensing.