Position Control of a Two-Degree-of-Freedom Parallel Robot Including Torsion Springs and Motor/Load-Side Encoders

In this paper, the position of a two-degree-of-freedom parallel robot with rotary motors is controlled. A low stiffness coupling is inserted between a motor output shaft and a link. The angle of the motor output shaft (motor-side angle) and the angle of the output shaft of the low-stiffness coupling (load-side angle) can be measured by encoders. A disturbance observer is utilized for disturbance compensation. A comparison is made between the case without shaft torsion torque feedback (the conventional method) and the case with shaft torsion torque feedback (the proposed method). The validity of the proposed method is verified using a simulation and experiment.