Study On Key Techniques Of Aircraft Intersection Holes Fine Boring Based On Industrial Robot

The aircraft intersection holes are key connecting parts in large aircraft components assembly.Their position accuracy has important influence on the interchangeability and coordination of aircraft parts and the assembly quality of the whole aircraft.To eliminate the accumulated error caused by the positioning and assembly deformation in assembly process,the intersection holes should be fine machined in aircraft assembly site.Traditional machine tools which are inflexible and require large installation space are difficult to be used in aircraft assembly site where there are too many assembly toolings and the working space is narrow.Therefore,in this dissertation,an aircraft intersection holes fine boring method based on industrial robot is proposed.For the problem that the robot has a low stiffness,a poor positioning accuracy,is easily subjected to vibration,some key techniques such as robot posture optimization,error compensation and vibration suppression are studied in depth,so as to ensure the position accuracy and machining quality of the intersection holes.The main work and innovation points are as follows:The impotance of the intersection holes and the development status of the processing technology are elaborated.The structure and machining process of the intersection holes fine boring system based on industrial robot are introduced.In order to make the robot move to intersection holes correctly,coordinate systems are constructed for the robotic boring system,and calibration methods of the tool coordinate system and workpiece coordinate system are proposed.Kinematics equations of the KUKA KR360-2 robot used in the system are established with the Denavit-Hartenberg method.On the basis of studying the robot stiffness model and its characteristics in depth,the strict linear relationship between the translational deformation and the external force acted on the robot is revealed.And a performance index which can be used to quantificationally evaluate the stiffness of the robot with a given posture is proposed.Due to its frame invariance,the index can be conveniently applied to evaluate the robot stiffness in different coordinate systems.By maximizing the index,for the general drilling situation(no interference,and no the 7th axis)and intersection hole boring situation(with interference,and with the 7th axis),different robot posture optimization models are established respectively and solved by the iterative IKP algorithm based on the Jacobian matrix.Experimental results achieved on the robot verify the correctness of the stiffness performance index,and application examples of the posture optimization method in a robotic drilling system and in a robotic boring system show its effectiveness.The robot pose error compensation technology based on the laser tracker is studied.For the situation that the robot end pose is difficult to measure due to its complicated structure and anomaly shape,a pose error compensation method based on the point sets fitting algorithm is proposed.By this method,the robot pose error can be calculated and compensated indirectly with the aid of assistant locating points.For the special situation of the robotic boring,an object-oriented pose error compensation method is proposed.By this method,the position error and orientation deviation of the boring tool can be calculated and compensated directly.In finish boring of aircraft intersection holes,the robot end tool can achieve a position accuracy of 0.05mm and an orientation accuracy of 0.05°with the introduced object-oriented pose error compensation method,which satisfies the accuracy requirement of the intersection holes on one large model aircraft in our country.After an in-depth study of the robotic boring characteristics and its stiffness performance,the mechanism of the vibration is revealed:The robot itself is the main part of the vibration and the type of the vibration is the forced vibration with a displacement feedback.When the robot vibrates,the tool path is an ellipsoid and the shape of the ellipsoid is closely related to the rotational frequency of the tool.Based on the results mentioned above,a vibration suppression method based on the pressure foot is proposed.With the fricitional force between the pressure foot and the workpiece counteracting the cutting force acted on the robot,the vibtation of the robot can be suppressed.Results of robotic boring experiment show that the analysis of the vibration mechanism is correct.And in fine boring of aircraft intersection holes,with the introduced vibration suppression method,the vibration of the robot can be suppressed effectively,the surface roughness of intersection holes achieves a grade of Ra0.8 and the dimentional accucacy is within H7 tolerance,which satisfy the machining quality requirements of the intersection holes on one large model aircraft in our country.Finally,the whole work in this dissertation is summarized,and the future work is discussed.