Optimization of Robot Posture and Workpiece Setup in Robotic Milling With Stiffness Threshold

Industrial robot provides a promising alternative in freeform surface milling. However, due to its low stiffness, it is difficult to guarantee the machining quality. While existing research considers mainly the influence of robot posture on stiffness, the workpiece setup's influence is equally important. In this article, to ensure the overall workpiece's robot stiffness meets the requirement of stiffness threshold in robotic milling, a method for simultaneously optimizing the robot posture and the workpiece setup is proposed. First, to evaluate the robot stiffness during machining, this article presents a new stiffness index considering the robot's rotational deformation. And then, an optimization model is established to optimize both the robot redundancy and the workpiece setup, considering the constraints of joint limitation, singularity-free and collision-free. Moreover, for complex freeform surfaces, to obtain the minimum number of posture changes of the robot and workpiece under the premise of meeting the limit of stiffness threshold, this article constructs a minimum set covering problem, which is solved by a clustering algorithm and a greedy algorithm. Finally, simulations and experimental studies are conducted to validate the effectiveness of the proposed robot stiffness index and the proposed optimization method, showing that the robot stiffness is improved during a milling process of the entire workpiece.