Development of String Type Flexible Displacement Sensor to Measure the Movement of Robot and Human Body

An importance of wearable devices in the field of medical treatment such as nursing care and rehabilitation has been strongly recognized. Also, the development of the power assisted device has been done to support the nursing care work for the elderly. The purpose of our study is to develop a flexible displacement sensor and bending sensor which can measure the movement of human body, flexible actuator or flexible joint of the robot by mounting on the surface of them. The developed string type flexible displacement sensor (FDS for short) consists of two fixed electrodes, a slide electrode and a nylon string coated with carbon (NSCC for short). It works as a flexible potentiometer by sliding the slide electrode along NSCC. We confirmed that the proposed sensor worked well by carrying out the position control of a McKibben artificial muscle with the tested sensor. We also proposed the flexible bending sensor that can measure the bending angle for various bending directions such as the movement of flexible joint of robot. The sensor consists of four tested FDSs, a coil spring and two plastic covers. The NSCCs are installed through the coil spring. We investigated the relation between bending angle and output voltages from four FDSs both experimentally and theoretically. As a result, we confirmed that the proposed sensor can work well and the proposed analytical model can predict well the bending angle and bending direction.