Self-Sensing McKibben Artificial Muscles Embedded With Dielectric Elastomer Sensor

Abstract

Pneumatic artificial muscles (PAMs), also known as McKibben artificial muscles, are used in a variety of applications owing to its many positive features, such as simple and lightweight structure and high force to weight ratio. Sensing is essential to precisely control PAMs. Previous studies have proposed various embeddings of PAMs with sensors. However, these often require sophisticated fabrication processes and dedicated setups, which can cause production to be laborious and costly. This letter presents a method to create sensorized PAMs using a dielectric elastomer sensor (DES). In these self-sensing actuators, which we call PAM-DES, the sensor is consisting of a thin, highly compliant dielectric and conductive membranes, which allow the length of the actuator to be detected by reading the capacitance. The sensor directly wraps around the inner tube of the actuator. Therefore, the entire structure remains simple. This feature allows the fabrication of actuators to be relatively effortless and inexpensive. As a proof of concept, a PAM-DES with a length of 100 mm and diameter of 9 mm is fabricated. An analytical model is constructed to design and predict the sensor response. Characterization results show that the sensor properly detects actuator deformation, and low hysteresis and high robustness are observed. The prediction model shows good agreement with the experimental data. Furthermore, the presence of the sensor has almost no influence on the actuator performance. These results validate the concept and suggest that PAM-DES is a highly effective strategy to sensorize actuators of the same type.