Development of Smart Inner Diameter Sensor for Position Control of Mckibben Artificial Muscle

Due to the ageing and the decreasing birth rate in Japanese society, an important problem of providing nursing care for the elderly has occurred. Therefore, it is strongly desired to develop a wearable actuator to use in nursing care or rehabilitation. The purpose of this study is to develop a high-power flexible actuator with a displacement sensor which can be used in supporting a bathing. In our previous study, we proposed and tested a rubber artificial muscle with the inner diameter sensor. The inner diameter sensor consists of two electric circuit boards with two photo reflectors. Two boards are bonded together to contract the inner diameter sensor. The sensor also has a doughnutshaped bulkhead to keep a seal. The sensor is inserted into the tube of the artificial muscle. The senor is set at the end of tube. This sensor can be expected to estimate the axial direction displacement of the rubber artificial muscle, because the relation between the inner diameter and the axial directional displacement of the muscle has a strong correlation. However, if the external bending force is applied to the end of the muscle, the inner diameter sensor cannot hold at the center position of the tube. Therefore, the sensor cannot measure the inner diameter exactly. In this study, the improvement of the inner diameter sensor was executed. The improved sensor has 4 photo reflectors on the two electric circuit boards to compensate the measuring error. The position control was also carried out by using the actuator with the built-in inner diameter sensor. As a result, the axial direction displacement of the muscle could be estimated well by the tested inner diameter sensor, and a relatively good position control performance was obtained.