- Nonlinear Robust Internal loop Compensator (NRIC)
- Robustness is a very classical issue in the robotics field.
- Disturbance observer (DOB) can be a good choice to improve the robustness of the system.
- However, cannot bring nonlinearity of the system into the formulation.
- To overcome this problem, NRIC is proposed.
- NRIC is attached to an existing controller and improves robustness of the system like DOB.
- NRIC makes an auxiliary input that compensates the diffence between the output from the real plant and that from the nominal model.
- An auxiliary input is designed in a nonlinear H-infinity optimal control framework and the resulting input is given as a simple PID form.
- NRIC can give additional robustness to a controller
- NRIC is easy to implement and it effectively brings nonlinearities of the system into the formulation successfully.
- NRIC can be applied to not only motion controllers but other controllers like impedance control.
7-DOF Schunk manipulator used in the experiments
Moving 3rd to 6th joints in a sinusoidal motion. Using CTC only (top), CTC with NRIC (bottom)
Moving only joint4 in a sinusoidal motion. Figure shows position of joint4 (top), joint5 (middle), and joint6 (bottom)