Extremely constrained robotic milling posture active adjustment on curved surface: Divide and conquer strategy with index of generalized accumulative work

Abstract

Industrial robots have been widely used in many manufacturing scenarios, including curved surface with complicated geometric features, due to their flexible capability of posture adaptation and large machining range. This work utilizes the multi-solution feasible space characteristic of robot to construct a novel milling posture active adjustment model under multi-source heterogeneous constraints. Firstly, a generalized potential field is developed for dimensional unification, after analyzing the multi-source heterogeneous constraints from the robot ontology (macro-view) to the cutter-workpiece engagement (micro-view). In terms of the extremely constrained process requirements on the curved surface, a framework to solve the global posture planning in robotic milling process is proposed. For free-form surfaces with uneven curvature distribution, surface division is developed based on curvature similarity, under the premise of high-order continuity on subdivision boundary. A latent dynamic response model is established for active posture adjustment by introducing the imaginary potential torque. Significantly, generalized accumulative work is innovatively proposed as a global index for the intelligent optimization of milling posture in multi-solution feasible space. In comparison with the commercial planning result and the proposed active posture adjustment strategy, milling experiments are carried out on the complex parametric surface. Under the evaluation both in the distribution characterization (cell perspective) and eigenvalue quantization (string perspective), the milling results of the proposed strategy has improvement on four kinematic performance, and prominent breakthrough in machining precision by 12.12 % improvement. The active posture adjustment strategy for global optimization proposed in this work shows great application potential in the extremely constrained scenarios of robotic milling field, especially restricted working space, large machining range and high milling precision requirements.