Improved Operational Space Control Framework for Compliant Motion of Robotic Manipulators

Abstract

This thesis studies effects of model uncertainties on the force-based operational space control formulation. Although this control framework works perfectly on simulation, its performance is significantly degraded in face of model uncertainties as will be shown experimentally in this thesis. Since the model plays an important role in the control framework, we first proposed a systematic procedure for identifying the robot dynamic model. To avoid the effects of the nonlinear joint friction, we suggested a simple and yet effective scheme to obtain a more accurate dynamic model. Experimental results on an actual industrial robot demonstrate the efficiency of our proposed procedure. Using the identified dynamic model, it is shown that model uncertainties can produce different effects depending on the control space. The analytical results also suggest that the control space need to be chosen carefully in order to minimise the effects of model uncertainties on control performance. This is also one of the main reasons of the poor performance of the force-based operational space control. The analyses raise a need of seeking for an alternative formulation to minimise the effects of model uncertainties while maintaining all the advantages of the force-based operational space control formulation. This is the main motivation for our proposed multi-rate operational space control structure. To justify the usefulness of the proposed control structure, intensive work on this control framework included stability analysis and real-time implementation on real industrial robot have been carried out. Real-time experimental results have shown a significant improvement in comparison to the conventional one. Since compliant motion control capability is one of the key features of enlarging the applications of robots in real life, the proposed multi-rate control structure has been studied in a real application, the grinding application in the last chapter. Experimental results in this chapter revealed some potential issues that need to be addressed in future research.