Development of a 7-DOF manipulator actuated by straight-fiber-type pneumatic artificial muscle

In recent years, robots have penetrated the fields of nursing and housework. These robots are expected to work alongside humans and, therefore, must be secure, safe, and able to collaborate. Thus, robots actuators should be light, soft, and have operating characteristics similar to those of humans. In this regard, pneumatic rubber artificial muscles are of interest as actuators for these robots. However, the McKibben artificial muscle commonly used for this purpose have certain drawbacks. Instead, we developed a straight-fiber-type artificial muscle that surpasses the output and contraction ratio of the McKibben muscle. We also developed a seven degree of freedom manipulator actuated by straight-fiber-type artificial muscles. The main features of this manipulator are the differential gear mechanisms in the shoulder and elbow joints, and the pulley-in-pulley mechanism in the wrist joint. However, to make use these mechanisms, we had to address the issues present in existing manipulators. In addition, we carried out various calculations necessary to design a control system for this manipulator. We performed experiments to verify the performance of the manipulator and control system. We realized steady state position control of the manipulator. However, in the dynamic state, we observed an overshoot in the rise time of the step response and proposed a solution for this issue.