Position control of articulated robots using frequency-shaped shaft torsional torque with low-rigidity couplings and double encoders

In this study, a position controller and an acceleration controller for an articulated robot are designed. The active joints of the robot are equipped with low-rigidity couplings to realize contact force control. The shaft torsional torque of these couplings is estimated using encoders installed on both the input and output shafts. This estimated torque is utilized to achieve target tracking and disturbance suppression. Herein, we compare three methods for utilizing the shaft torsional torque: the first method does not employ shaft torsional torque feedback (Comparison Method 1), second method applies a constant multiplier to the shaft torsional torque before feeding it back (Comparison Method 2), and third method feeds back frequency-shaped shaft torsional torque (Proposed Method). The simulation and experimental results validate the effectiveness of the proposed method.