Flexible Sensor for McKibben Pneumatic Artificial Muscle Actuator

Abstract

The demand for flexible, lightweight McKibben pneumatic artificial muscles (McKibben actuators) has been increasing for power assistance equipment used for assisting and rehabilitating the elderly. To accurately control this equipment, the length of the actuator should be measured. However, the equipment becomes heavier and less flexible when a rigid sensor, such as a potentiometer or an encoder, is used. The sensor should be flexible in order to take advantage of the favorable properties of the McKibben actuator. The aim of this study is to measure the length of the actuator without loss of its advantages. We propose a method of estimating the length from the circumferential displacement, which can be measured by a sensor made of electroconductive, flexible rubber. Higher accuracy is obtained by measuring the circumferential displacement than by measuring the axial displacement using this sensor. The sensor’s flexibility enables us to accurately control the actuator without any loss of flexibility or increase in weight. Furthermore, the sensor does not require the attachment of any rigid fixtures. The accuracy of the estimate is successfully evaluated and the usefulness of the proposed method is verified through its application to a multi-link arm driven by the McKibben actuator.