Mechanism and impedance control of the ball universal joint robot driven by the pneumatic muscle actuator group

Pneumatic muscle actuator (PMA) is the research focus of bionic robot. Therefore, a triaxial-ball universal joint robot driven by the PMA group is designed. The kinematics of the robot is analysed. On the basis of its kinematics analysis, the position control strategy of the PMA group is proposed. Based on the kinematics analysis and the energy saving principle, the contact force control strategy of the PMA group is proposed. An impedance control scheme with inner position PID loop is designed for the PMA group. Results show that under position control only, the control accuracy is higher than impedance control and the steady-error is less than 0.3°, however, the contact force is out of control. Impedance control sacrifices a certain degree of position control accuracy but can realize compliant control of contact force.