Study On Correcting Method Of Hole Position For A Flexible Track Automatic Drilling System

In the field of aircraft assembly, the joints between the aircraft structural parts are usually dominated by mechanical joints. The drilling quality of fastener holes is of great importance for enhancing joint accuracy and extending the aircraft life and safety. In order to improve the quality and efficiency of aircraft assembly, automatic drilling equipment is used to enhance the accuracy and quality of the fastener holes. The development of automatic drilling equipment and technology has reached an advanced level abroad. Manual drilling method accounted for the most of proportion in China. However, it is time consuming, and the quality of fastener holes may be unstable due to human factors. Therefore, the use of automatic drilling equipment is inevitable for the manual drilling method cannot meet the high requirements of fastener holes quality and assembly efficiency.Firstly, the paper summarizes the development of automatic drilling technology in aircraft digital assembly. To meet the high drilling accuracy requirement of aerospace fuselage joining assembly, this paper introduces a flexible track automatic drilling system and the mechanical constructions, the functions of individual components, the software design, the hardware design, the calculation of nominal vector and the method of hole position correction.In order to calculate the normal vectors, the system measures the coordinates of four points in the area which will be drilled through four non-contact laser displacement sensors. One parallelogram can be formed. The normal vector of the hole which will be drilled can be replaced by the normal vector of the parallelogram. The end-effector can be adjusted in order to remove the angular deviation of the normal vector and the tool axis. Finally, the tool axis is perpendicular to the aircraft panels, which is of great importance for the fastener hole quality.The method of hole position correction is achieved through the following steps:Firstly, the normal vectors of reference holes can be calculated; Secondly, the tangent vectors will be computed according to the normal vectors and the coordinates of reference holes; Thirdly, the error of the reference holes can be obtained based on the vision measurement system. The hole position correction method using error data of reference holes is developed to enhance the drilling accuracy by interpolating the Coons surface, and then the position correction can be realized by adding error to the nominal coordinates of the holes which will be drilled.The normal vector calculation method and the hole position correction method have been tested on the cylinder models, and the result indicates that the calculation result of normal vector is almost equal to the nominal normal vector. And the hole position correction method accounting for the changing curvature of the panel shape are better than double linear interpolating method. The method can effectively meet the geometric accuracy requirement of aircraft panels.