Controller Design for Precision Motion of Pneumatic Artificial Muscle Systems

Pneumatic artificial muscles (PAMs) have been applied in bionic robots, welfare devices, and parallel manipulators, because they possess many advantages over traditional actuators, such as a high power-to-weight ratio, a high power-to-volume ratio, a high degree of safety, and stick-slip-free operation. However PAMs have disadvantages of significant nonlinearity, creep phenomenon, and hysteresis. These provide the low controllability and unfortunately limit the application of PAMs. Thus the precision motion control of PAMs is an important and unsolved problem. This research aims to clarify a practical controller design method to achieve the precision motion control for PAM systems. For precision motion control, a practical controller design procedure is discussed and determined in this paper. The controller structure was decided based on the analysis of general characteristics of PAM systems. The control elements are represented by input-output relationships which were investigated by measured open-loop responses of a linear motion mechanism with a pair of McKibben PAMs. The positioning and the tracking performances are reported and discussed. According to the experimental results, it is found that the proposed controller is able to provide a sub-micrometer order positioning and a precision tracking of the PAM mechanism at low speed.