Development of two types of 2-DOF wrist joint driven by pneumatic artificial muscles

The demand for robots engaged in human activities, such as nursing care and housework, is presently growing. In the vicinity of humans, these robots must operate taking into consideration the human safety. Therefore, the actuator in these robots needs to be soft, light, and powerful. To fulfill these demands, we adopted artificial muscles as actuators of the manipulator. However, the McKibben-type artificial muscle commonly used for this purpose is problematic; therefore, we developed a straight-fiber-type artificial muscle that surpasses the output of the McKibben-type. We also developed two types of wrist joint manipulator for the 7-degree-of-freedom (7-DOF) manipulator. In this paper, we compare and evaluate the performance of the two types of wrist joints. Moreover, we propose a control system for this manipulator regarding the joint angle and stiffness. We used the PI control method to control the joint angle, and the torque feedback control method to control the joint stiffness. Finally, we performed experiments to verify the control system.