Research On Key Technologies Of Precisely Drilling For Aircraft Assembly Based On Parallel Posture Alignment Bracket

The accuracy of the hole position and the surface-normal accuracy have a great impact on the quality of the riveting.For hole position accuracy,large hole position error will change the load between the rivets and then affect the fatigue life of the structure.For surface-normal accuracy,if the surface-normal error is too large,the fatigue life of rivet will be reduced.Therefore,precisely drilling technology is of great significance to ensure the fatigue life of the aircraft.Bracket is widely used to fix the parts to be processed in aircraft automatic drilling.Bracket can be divided into fixed bracket,adjustable bracket,etc.The parallel posture alignment bracket(PPAB)based on positioner has the advantages of reconfigurability and flexibility,and has been applied in the field of aircraft assembly.To improve the positioning accuracy of the PPAB and reduce the influence of the positioning error of the PPAB on the operation accuracy of the drilling system,it is necessary to carry out the research on the precisely drilling technology based on the PPAB.A dynamic model for PPAB with redundant actuation is developed.To solve the coupling problem of posture parameters of PPAB with few degrees of freedom,the independent variables in the posture parameters are analyzed,then the mapping relationship between the posture parameters and the motion of each prismatic pair is established.Aiming at the problem that it is difficult for the existing dynamic model to solve the driving force accurately and quickly,based on the deformation coordination analysis of equivalent spatial position error,a dynamic model of the PPAB with redundant actuation is established.Based on the proposed dynamic model,the analytical analysis of the driving force of the active prismatic pair is performed,which improved the accuracy and efficiency of solution of the driving force.In addition,to solve the problem of driving parameters coupling of PPAB with redundant actuation,the independent variables in the driving parameters are analyzed.The mapping relationship between the driving parameters and the posture parameters of the moving platform is established,which lays a foundation for kinematic calibration,positioning error compensation,workspace analysis and path planning.A modeling method of posture-alignment error is proposed.In view of the problem that the existing error model has less identification amount and lower identification accuracy,the geometric error completeness analysis based on the error transfer equation is carried out to increase the identification types and improve the identificationa ccuracy of geometric error.Aiming at the problem that the deformation error caused by structural deformation affects the accuracy of geometric error identification and positioning error compensation,based on the proposed dynamic model,the deformation error caused by gravity,friction and support force at the spherical hinge is analyzed,which paves the way for geometric error identification and positioning error compensation.Based on the geometric error analysis and deformation error analysis,a posture-alignment error model is established.A positioning error compensation method based on correction of target position and posture is proposed.To solve the problem of commixture of position and posture error(PPE)caused by geometric error and PPE caused by structural deformation during error identification,an separation of PPE is performed,which improves the input precision of PPE in error model.Aiming at the problem that the geometric error coefficient matrix is changed by the regularization method resulting in low identification accuracy of geometric error,the geometric error coefficient matrix in posture-alignment error model is optimized to improve the identification accuracy.According to the problem that PPE is different in multi-posture space,compensation for PPE of PPAB is performed by correcting the target position and posture.For the problem of large workload of target position and posture correction during error compensation,batch correction of target position and posture of moving platform based on BP neural network is conducted,which improves the efficiency of positioning error compensation.A method of path planning for drilling based on position and posture optimization is proposed.Based on the anaysis of deformation error,the workspace of the drilling system is calculated.To improve the positioning accuracy of the PPAB,the GA-BP algorithm is used to optimize the position and posture of the moving platform.Based on the optimized position and posture,combined with the proposed dynamic model and positioning error compensation method,the path of drilling of the PPAB is planned by using quintic polynomial,so as to ensure that the PPAB can complete the posture alignment within the specified time,which improves the efficiency of automatic drilling.Based on the above mentioned key technology research,an automatic drillling system prototype based on PPAB is developed and relevant process verification is performed.The practice shows that the position and posture control method proposed can meet the requirements of precisely drilling,and has good engineering application value.