Posture optimization in robotic machining based on comprehensive deformation index considering spindle weight and cutting force

Abstract

Industrial robot has been considered to be the most promising choice to replace traditional CNC machine tool due to its low cost, high flexibility, versatility and large workspace. However, insufficient stiffness of the robot often leads to deformations and vibrations during the machining process. To improve the machining performance of robot, a posture optimization method through controlling the functional redundancy of robot is proposed. First, considering the spindle weight-induced deformation and cutting force-induced deformation simultaneously, a comprehensive deformation index is proposed to evaluate the stiffness performance of robot posture along the robot milling trajectory. Then, ideal stiffness interval at each cutter location point is calculated by minimizing the proposed deformation index in consideration of the constraints of joint and joint velocity. Next, the kinematics performance index is taken as the optimization target, and the postures of the entire milling trajectory are optimized collaboratively within the ideal stiffness intervals. In order to approximate the global optimal solution, the genetic algorithm is used to solve the optimal robot posture. Finally, a series of simulations and experiments are carried out to verify the proposed index and robot trajectory optimization method, and the results show that the machining accuracy can be efficiently improved by the proposed method.