| Assembly of aircraft components is a significant step in the process of aeroplane production,and drilling & riveting have a serious effect on the period of the aircraft assembly.Nowadays,with the assembly requirements of high-quality,high-effectiveness and low-cost,a method,which the industrial robots are applied in automatic drilling of aircraft parts,is continuously promoting.When industrial robots are used for automatic drilling,some problems,such as poor absolute positioning accuracy of industrial robots,alignment error between components and robots and unsuitable problem between theoretical contours and practical contours,are affecting the quality of drilling and other performances of the plane eventually.Aimed at these issues,this dissertation proposes two methods of off-line compensation based on Extreme Learning Machine algorithm for absolute positioning error of robot and on-line compensation method for robotic drilling error suitable for curved structure,and develops an on-line error compensation system.The main contributions of this thesis are as follows.1.The error variation of the absolute positioning error of industrial robots in the axial direction of the robot coordinate system is analyzed based on the spatial mesh sampling method,and the feasibility of modeling and compensating the positioning error is verified.2.Being based on the spatial mesh sampling,an off-line compensation method for robot absolute positioning error modeling based on Extreme Learning Machine algorithm is proposed and the number of hidden layer neurons is optimized for error model training.In addition,the error model is established by the number of different training sets in the same sampling space,and the compensating experiment based on the error model is conducted.The results show that the average positioning error,reaching 0.41 mm before compensation,are reduced to less than 0.20 mm after compensation.3.Aimed at the hand-eye relation problem for on-line compensation for robotic drilling,a new hand-eye relation,which represented as homographic relation between the vision image plane and the working plane,is proposed.And a simple calibration method is given.4.A on-line compensation method for robotic drilling error suitable for curved structure is proposed aimed at the problem of poor accuracy of automatic drilling.Four ranging sensors and a camera are used for information feedback to drive the robot to adjust its position and posture from the theoretical coordinates of the reference hole to the ideal position directly above the actual reference hole.The driving coordinates of the robot corresponding to the actual position of the reference hole are calculated through the hand-eye relationship.Then,according to the three-dimensional driving errors of a group of reference holes,the transformation matrix of the three-dimensional driving errors is calculated.Based on this,the compensating coordinates of the robots to be drilled in the vicinity of the reference holes are obtained,so as to compensate the positioning errors of the robots to be drilled..5.An on-line compensation system is programmed for the automatic drilling,which can achieve the communication between the computer,the camera,the range sensors and the robot.The complete experiment is conducted on an experimental aircraft component to verify the proposed method.The experimental results show that the drilling error,with average positioning error by 2.55 mm and 3.30°before compensation,are reduced to that the max positioning errors are less than 0.30 mm and 0.21°,which has verified the effectiveness of the proposed on-line compensation method. |
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