Stiffness properties analysis and enhancement in robotic drilling application

Low stiffness and special stiffness properties limit the application of industrial robots in sophisticated manufacturing. The subject of the paper is to investigate the influence of robot stiffness properties on machining quality in drilling application. It is found that unidirectional thrust force could induce three-directional deformation of robot which will directly lead to hole defects during drilling procedure. Firstly, starting from the special characteristics of the robot, the key role of the preload pressing force is pointed out. Equivalent stiffness model under pre-load pressing force is established and stiffness promotion coefficient is defined to evaluate the effects of pressing force quantitatively. The matching criterion of robot drilling posture and thrust force is proposed, and the optimized value of pressing force can be predicted under the condition of stable machining. Limitation on hole diameter and roundness of robot drilling is evaluated too. By applying pre-load pressing force, the stiffness of robot drilling plane is markedly improved, and the drilling stability and hole diameter accuracy are also enhanced. Finally, the proposed method is verified by drilling experiments.