| During the assembly process of an aircraft,the countersunk rivets are usually used to connect the aircraft parts.The depth accuracy of countersinks has a direct impact on the quality of the connection,and thus has effects on the fatigue life and the aerodynamic shape of the aircraft.This paper studies the control technology of the countersink depth based on a robotic orbital drilling system independently developed by the Institute of Aeronautical Manufacturing Engineering of Zhejiang University.The major work and innovative points of the thesis are as follows:The research status of the orbital drilling technology is expounded,and the importance of countersinking depth accuracy in the countersinking as a downstream process of the orbital drilling is analyzed.Then the research status of countersinking depth control methods at home and abroad is introduced.And the main research content and framework of the paper are demonstrated.The structure components of the orbital drilling end effector and the automatic machining process are introduced.Based on this,the effects of on the nose structure of pressure foot,the deformation of the robot,the deformation of the workpiece,and the normal deviation on the countersink depth error in drilling are analyzed.The control methods of countersink depth are researched.The length gauge and linear grating scale in the end effector are used to compensate the feed of the tool for the position change of the pressure foot in real time,which reduces the countersink depth errors introduced by the deformation of the robot and workpiece.The laser displacement sensor installed around the pressure foot is used for normal error calculation and the normal correction,which reduces the countersink errors introduced by the error of the tool axis and normal.In order to verify the effectiveness of the proposed countersink depth control scheme,a test platform based on the robotic orbital drilling system is set up,and three groups of countersinking tests with different target countersink depths are designed.The test results show that the accuracy of the countersink depth can reach 0.04 mm after applying the proposed countersink depth scheme,and the quality of the hole is good,which meets the needs of the actual production.The traditional normal correction method has some limitations which could cause large normal errors and aborted normal correction process in certain cases.Considering that,a normal-adapted pressure foot is designed.The limit range of the normal correction is calculated using its structure parameters,and the tribological analysis of the spherical pair in the structure is performed.Finally,the thesis is summarized,and the future research is outlined. |
