• Nonlinear Robust Internal loop Compensator (NRIC)
    • Description
      • 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. 
    • Features
      • 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    
    • Experiment 1
Moving 3rd to 6th joints in a sinusoidal motion. Using CTC only (top), CTC with NRIC (bottom)
    • Experiment 2
Moving only joint4 in a sinusoidal motion. Figure shows position of joint4 (top), joint5 (middle), and joint6 (bottom)