Research And Design Of Aircraft Digital Assembly System Based On Mixed Tolerance Constraints

The essential process of aircraft digital assembly is measuring the actual posture of aircraft components through digital measuring equipment.Through the posture evaluation algorithm,the actual posture and the theoretical posture were compared to obtain the posture parameters.Then aircraft components were driven by the automated positioners,which move according to posture parameters,to reach the target posture.Aircraft digital assembly requires the distance error minimum and meet the tolerance constraints.The previous aircraft posture evaluation algorithm has less consideration of the following situations:(1)A posture with minimum distance error may not satisfy tolerance constraints;(2)The digital assembly based on the key features is less considered.In this paper,based on the application of digital assembly project of a certain type of aircraft wing components,an aircraft digital assembly method based on mixed tolerance constraints is proposed.In the first part of this paper,the research status of aircraft digital assembly at home and abroad was introduced and the principles,research concepts and practical methods of aircraft digital assembly technology were briefly explained.The second chapter takes the digital assembly project of a certain type of aircraft wing as an example and introduces the structural characteristics and assembly targets of the aircraft components.According to the ‘measurement assist assembly' concept,laser tracker was selected as the digital measurement equipment.The geometric relationship between the coordinates of the measurement points and the posture of wing components was expounded.The mathematical model of the target posture of wing components is derived,and the coaxiality measurement method of the ear hole and the axis based on the global least squares method are given.In the third chapter,the relationship between the three coordinate systems in the assembly system and the description of the rigid body posture in the global coordinate system was introduced.The posture evaluation model of the wing components in the global coordinate system was derived.A novel optimization model was proposed to obtain the optimal aircraft posture parameters under tolerance constraints.Tolerance constraints,which was transformed in-to a penalty function,was combined with the sum of distance errors as an objective function for optimization by using PSO for constrained optimization problems(PSO-COPs).Further improvement on the above algorithm,the maximum distance error of the aircraft feature points could be further reduced by using an improved PSO algorithm(IPSO),which was an iterative method by dynamically strengthening tolerance constraints.The simulation example and Monte Carlo simulation indicated that,com-pared with the singular value decomposition method(SVD)and the basic PSO algorithm,PSO-COPs and IPSO can better guarantee the accuracy of aircraft posture for assembly under tolerance constraints.In the fourth chapter,a set of digital assembly equipment solutions were proposed,including automated positioning system and threading system.The mechanical structure,working principle and function of automated positioners,ball-locking device,AGV,positioning jig,threading mechanism and turning mechanism was introduced in detail.In the fifth chapter,a digital assembly integrated control system for wing components based on the assembly of a certain aircraft wing component was designed.The composition and working principle of the control system are introduced in detail,including the positioner drive shaft control method,et al.HMI of control system was displayed.Experiments of positioners on positioning accuracy,relocation accuracy and load capacity was performed.Two optimization algorithms based on PSO and basic PSO were applied to the actual assembly cases of the mobilizable part and the fixed part.The experimental results were in accordance with the theory of the third chapter.The conclusion proved the effectiveness of the two optimization algorithms proposed in this paper.The sixth chapter summarized the full text and looked forward to the follow-up research work.