Direct teaching method for musculoskeletal robots driven by pneumatic artificial muscles

This paper presents a direct teaching method for musculoskeletal robots driven by pneumatic artificial muscles (PAMs). In order to reproduce motions which are directly taught by a human, it is necessary to reproduce the lengths of PAMs because they geometrically determine the posture assumed by the robot. However, it is difficult to measure the lengths of PAMs because mounting length sensors is space-consuming. Additionally, estimating lengths is also difficult because it is required to know the intrinsic parameters of PAMs which are extremely difficult to measure for each muscle. In order to overcome the above problems, the proposed method calculates the desired internal pressures or the desired axial tensions of the PAMs under a specific constraint, which forces PAM´s lengths in the reproducing phase to be similar to the lengths during the teaching phase. In this way, it is possible to reproduce the motion by controlling the internal pressures or the axial tensions instead of the lengths. The validity was confirmed through an experiment using a real musculoskeletal robot arm.