Pneumatic artificial muscles embedded with dielectric elastomer sensor

We report on pneumatic artificial muscles (PAMs), also known as McKibben artificial muscles, that are integrated with a tubular dielectric elastomer sensor (DES). PAMs are usually composed of a rubber tube surrounded by a sleeve. When pressurized, the deformations of the rubber tube are conformed by the sleeve such that the actuator shrinks in the length direction and expands in the radial direction. To precisely control PAMs, a sensor is required to detect the deformations. DES is suitable for this purpose because it is highly compliant and thin, minimizing the influence on the configuration and performance of the actuators. In order to prove the concept, a sensorized PAM is fabricated by adhering a tubular DES onto the outside of the rubber tube, followed by placing the sleeve. A natural rubber tube with an outer diameter of 6 mm is employed. DES is made of an acrylic elastomer (3M, VHB4905) sandwiched between two compliant electrodes (Adhesives Research, ARcare 90366). When injecting air, the surface of the actuator increases therefore the capacitance of DES. This relationship enables the sensing of the actuator length by measuring the change in capacitance. We characterize the actuators in terms of capacitance as a function of the actuator displacement at different applied pressure.