High-order joint-smooth trajectory planning method considering tool-orientation constraints and singularity avoidance for robot surface machining

Abstract

Compared with the traditional machine tools, robots are low-cost and flexible for the machining process. However, owing to the complex constraints in the operation space and the redundant degrees of freedom (DoFs), it is challenging to obtain a joint-smooth optimal trajectory for the robotic machining. This article develops a high-order smooth joint trajectory planning method for robot surface machining considering with the tool posture constraints (the collision avoidance and cutting angles limits) and the robot state limits (the singularity avoidance). In the proposed method, the whole trajectory of the tool posture is integrated by the optimized differential vector in steps. In every integrating step, the differential vector is optimized from the redundant DoFs with the combined and balanced optimization objective considering the joint-smooth requirements, tool orientation limits and robot state constraints. At the same time, the upper limit of the second-order differential is given to limit the change rate of the optimized differential vector and to smooth the generated trajectory further. As the drastic change of the feasible region and tool-tip path curve, the boundary of the feasible region should be smoothed in advance to compensate for the hysteresis of the numerical integration method. In the end, two cases of robot surface machining are provided to verify the method. In the experimental process, an UR-5 robot with Robot Operating System (ROS) controller is used and the complex curve is machined by the robot.