Estimation of Contraction Force from the Volume of Isothermalized Pneumatics Artifical Rubber Muscles

The applications of pneumatic artifi cial muscles (PARM) are increasing in the power assist and manipulator systems, since they have advantages such as high power weigh ratio and fl exibility. Usually, we have to measure the contract ratio of PARM using a displacement sensor installed near the actuator, which is not preferable from the aspect of preventing dust and water. In this paper, we propose a method of estimating contraction force from the volume change of the PARM, which makes it possible to have a sensor-less actuator. The air charged to and discharged from the PARM is measured by a quick response laminar fl ow meter. The volume of the PARM is estimated from the fl ow rate and the pressure measured by a pressure sensor. In order to estimate the contraction force accurately, thin copper wires are stuff ed in to the PARM to realize an almost isothermal condition during charge and discharge. The eff ectiveness of the proposed method is confi rmed experimentally.