Research On Assembly Quality Adaptive Control Method And System For Complex Mechanical Products Assembly Process

The overall performances of complex mechanical products are guaranteed by the design, manufacture and assembly. In order to ensure products reliability and stability in the service process, the products not only requires excellent design and manufacturing quality during product design and manufacturing, more important is to achieve the best overall performance on the basic of high precision, high stability and high efficiency assembly parts during product assembly. The flow of material, information and error is accompanied in the products assembly process. There are uncertain, nonlinear and dynamic interaction relationships among the quality control points. And the assembly defects will be propagated, accumulated and amplified with WIP (Work-in-process) to downstream process. So the products would be serious quality variations, and the defects of the assembly process will seriously affect the quality and cost of the final product.Thus, the assembly quality control not only meet the assembly processes specifications, and considering the relationships among the up and down stream processes and quality control points. To reduce quality variations and improve product quality stability and assembly efficiency, it is of great significance to achieve assembly quality adaptive control from the system-level in the complex mechanical product assembly process. The research object of this paper is complex mechanical product assembly process. In the background of digital, networked and intelligent production, considering the characteristics of complex mechanical product assembly process and quality control requirements, the goal of this paper is to realize assembly quality adaptive control and satisfy customers’ individual needs. Combining the idea of data analysis and model-driven, converting traditional product quality control into manufacturing process quality control, extending to non-dimensions quality characteristics from dimensions quality characteristics, transform the open-loop quality control into an adaptive closed-loop quality control, extending to the combination of qualitative and quantitative quality control form qualitative quality control, on the basis of researching the relationships between the quality control points, applying the methods of quality control points control threshold optimization and quality gate, finally the assembly quality adaptive control system is constructed. The proposed methods provide theoretical and technical support to improve the performance of complex mechanical product.The research contexts and innovations of this dissertation are as follows.1) On the basis of research on the characteristics of the product assembly process, the relevance model of between quality control points is built based on Copula theory. Quantitative expression relevance is realized by the model, which provides a basis for further explore the assembly quality adaptive control.2) Using the relevance model of between quality control points, the model for measuring the assembly stability is built based on mutual information theory. Then, from an assembly economy point of view, the model of assembly cost-control threshold is put forward. To meet the targets of assembly stability and economy, the stability and cost elements are converted into game decision-making body based on game theory. Finally, the optimization results are achieved.3) The model of assembly performance prediction is proposed based on PSO-BP neural network. Then, the technique of dynamic process capability analysis is researched. The assembly defect detection is explored based on machine vision. Finally, the method of assembly process quality gate control is generated based on expert knowledge system of layered reasoning.4) Considering the above-mentioned theoretical approaches, on the basis of Cyber-Physical System, an assembly quality adaptive control system for complex mechanical products is developed. The proposed system provides theoretical methods and technical support to realize high stability and high efficiency assembly in the mode of digital and networked production.