Similarity Analysis Between a Nonmodel-Based Disturbance Observer and a Time-Delayed Controller for Robot Manipulators in Cartesian Space

Disturbance observer (DOB) techniques are effective and practical methods for rejecting disturbances in motion control applications. Nonlinear DOBs that are based on dynamic models are employed to apply the robust control technique to robot manipulators to improve position tracking performances. Time-delayed control techniques are also effective methods for addressing uncertainties in robot manipulators. Recent research results have demonstrated that both schemes are robust in compensating for highly nonlinear uncertainties in robot dynamics. The objective of this paper is to demonstrate the structural equivalence between a nonlinear disturbance observer and a time-delayed controller (TDC) under the nonmodel-based control framework of robot manipulators. In addition, a Cartesian TDC for robot manipulators is implemented and its stability is analyzed. The effects on the tracking performance in terms of sampling times, inertia values, and torque constants of the Cartesian TDC are compared and analyzed for a robot manipulator that follows a circular trajectory by both numerical and empirical investigations.