Equivalence of resonance ratio and I-PD controllers in zero stiffness torque control for soft robot

Recently, a soft robot considering the contact of the human has attracted attention, and the zero stiffness torque control is required. Because a soft robot causes vibration at the load side, vibration suppression control of a soft robot is required. In this paper, the authors discuss position control and torque control of a soft robot by using a torsion torque sensor based on a resonance ratio control. Position control can be used to design parameters. However, torque control cannot be used to design parameters because the proportional gain Kp and resonance ratio gain Kr are not independent with regard to integral-proportional differential(I-PD) torque control. Therefore, in the case of torque control, resonance ratio control is equivalent to I-PD control.