Stiffness-oriented posture optimization in robotic machining applications

Industrial robots have been used in machining applications for their advantages such as their high flexibility and low cost. However, the relatively low stiffness of the robot can seriously affect its positioning accuracy and its machining quality. In this paper, a posture optimization method is presented, aiming at increasing the stiffness of the robot in machining applications. First, a performance index is proposed to evaluate the stiffness of the robot with a given posture after an in-depth study of the relationship between the translational displacement of the robot end effector and the force applied on it. The index is then demonstrated to be a frame invariant. By maximizing the index, a robot posture optimization model is further established and solved by a novel solution method based on the Jacobian matrix. Finally, experimental results achieved on a KUKA KR360-2 robot verify the correctness of the stiffness performance index, and the application of the posture optimization method in a robotic drilling system shows its effectiveness.