Measuring McKibben Actuator Shrinkage using Fiber Sensor

This paper focuses on sensing of McKibben actuator shrinkage using a fiber sensor. Control of McKibben actuators requires sensing their shrinkage without preventing their deformation. We applied electro-conductive yarn, with resistance related to its extensional strain, suggesting that measuring the resistance of the yarn can determine its length. The yarn is also bendable and light in weight, thus not preventing the deformation of a McKibben actuator. A fiber sensor consisting of these electro-conductive yarns was attached onto the membrane of a McKibben actuator to measure the distance between both ends of the sensor along the membrane. This paper describes a fiber sensor model that can calculate McKibben actuator shrinkage from the fiber sensor measurement. Based on the model, we investigated the arrangement of a fiber sensor so that the fiber extensional stress is within its allowable range. We then show a prototype of the fiber sensor that was utilized to measure McKibben actuator shrinkage. Experimentally, we found that the shrinkage of an actuator could be measured within 20 % error of its length.