Displacement estimation of tap-water driven McKibben muscles

This paper is concerned with tap-water driven McKibben muscles, especially displacement estimation methods. The muscles can improve environmental friendliness of systems because water hydraulics has 100% oil-free characteristics. In addition, tap-water can remove driving sources such as compressors and hydraulic pumps. Thus the muscles are suitable actuators for rehabilitation systems. The proposed estimation method uses two flowmeters to estimate the muscle displacement from the volume of the muscle. It is reasonable for estimation because it is easily possible to implement and displacement - volumetric characteristics has no hysteresis and effects of load connected with the muscle. The validity of the method is confirmed by experiment with simple muscle control system. As a result, the displacement - volumetric characteristics can be expressed as second-order polynomial and the displacement can be estimated correctly. Finally displacement control with proposed estimation method is applied to the muscle system and then it is shown that the proposed method can compensate the effect of load and the estimated error is less than approximately 2 mm.