Optical Sensor-Embedded Pneumatic Artificial Muscle for Position and Force Estimation

This study presents the design of a pneumatic artificial muscle with integrated soft optical sensing for estimation of muscle contraction length and contraction force. Each optical sensor uses an light emitting diode (LED)-photodiode pair to measure the light reflected by a silicone diaphragm embedded in the muscle. One diaphragm is designed to respond primarily to changes in muscle pressure, whereas the other is designed to respond to changes in muscle length. Muscle sensors were calibrated by measuring muscle contraction force versus length for a range of fixed muscle pressures and then mapping optical sensor data to the corresponding length and force data. To evaluate sensorized muscle performance in a robotic system, two antagonistic muscle pairs were used to actuate a planar two-degree-of-freedom arm. In various static and dynamic tests, arm positions and forces were estimated from optical sensor measurements. Optical sensor estimates of static and dynamic end-effector position estimation yielded average errors of 1.3 and 1.1 cm, respectively. Optical sensor estimates of static and dynamic end-effector force yielded average total force errors of 0.16 and 0.12 N for maximum end-effector forces of 2.0 and 2.4 N, respectively.