Research On Technology Of Spatial Precise Positioning With Dual-machine Cooperativ Drilling And Riveting System

Automatic drilling and riveting machines are indispensable and very important for aircraft digital assembly as high-level manufacturing equipment.To improve the quality of automatic drilling and riveting for aircraft panels,it is the basis and premise for the automatic drilling and riveting machines with high positioning accuracy.Most traditional automatic drilling and riveting systems rely on the numerical controlled bracket or the flexible fixture,which restricts the panel size and the way of getting in and out of the station.It takes a long time for the panel to be hoisted and pre-installed on the fixture,which largely reduces the efficiency and floor-to-floor rate of the automatic drilling and riveting process.Therefore,a new horizontal automatic drilling and riveting machine has been developed in Zhejiang University which consists of two coordinated five-axis machine tool as a dual-machine system.Based on this application,this dissertation studies the spatial precise positioning technology in the coordinated workspace of dual-machine system,and focuses on some key techniques such as the associated kinematic modeling,the united kinematic calibration and the coordinated positioning error compensation,which aims to increase the machining accuracy of automatic drilling and riveting in aircraft panel assembly.The main work and innovation points of this dissertation are listed below:The importance and the development status of the automatic drilling and riveting technology in aircraft assembly is expounded.The structure layout and machining process of the newly developed automatic drilling riveting system for aircraft panel assembly are introduced.In order to realize the coordinated motion of dual-machine system precisely,necessary coordinate systems are defined firstly and the associated kinematic model of the dual-machine system are established.Besides,the constraint equation of the position and orientation of coordinated machines is given.And the coordinated workspace of the automatic drilling and riveting system is analyzed and described by the numerical methods.According to the cooperative working mode of dual machines in the automatic drilling and riveting system and the requirement of the drilling and riveting process,the positioning error of the dual-machine system is analyzed and the a kind of positioning accuracy evaluation index is put forward.The positioning error measuring method for the dual-machine system based on a laser tracker is proposed,and a new instrument composed of four gauges is designed for quick accuracy checking in the application.The kinematic parameters of the dual-machine system are defined,and a novel united kinematic calibration(UKC)method for the coordinated machines is proposed with the measured positioning error data.In this method,the optimization objective function representing the positioning accuracy of dual-machine system is established,and the number of measurement points,the initial values of parameters and convergence criteria are reasonably selected.Then,the kinematic parameters of the coordinated machines in the automatic drilling and riveting system are identified simultaneously by Levenberg-Marquardt method.To verify the effectiveness and the advantages of the proposed method,experiments have been conducted out on the developed dual-machine system including the tests compared with the traditional independent kinematic calibration(IKC)method.The coordinated positioning error prediction and compensation method for the dual-machine system is studied in depth.Firstly,based on the superposition and decomposition concept of motion,a new method for meshing the workspace of the dual-machine system is proposed.In this method,the coordinated workspace of dual machines is described as the superposition of the coordinated workspace of prismatic axes(CWP)and the coordinated workspace of revolute(CWR)axes.The method reduces the dimension of the coordinated workspace of the dual-machine system,which can avoid the curse of dimensionality to some degree and will be helpful to improve the efficiency for error compensation.Considering all static/quasi-static error sources such as the geometric-,gravity-and thermal-induced errors deteriorating the coordinated positioning accuracy of dual-machine system,an efficient error prediction model based on the multi-factors coupling is established which can predict the error at any desired temperature and spatial position and orientation in the coordinated workspace of dual machines.According to the driving and driven relationship of dual machines in the automatic drilling and riveting system,an error compensation strategy is presented to implement the coordinated positioning accuracy improvement.Hence,the automatic drilling and riveting system can realize the precise positioning in the coordinated workspace and improve the machining quality and assembly efficiency.To verify the effectiveness and the advantages of the proposed method,experiments have been performed on the developed dual-machine system which is compared with the traditional error compensation method based on meshing concept.Finally,the research work of the full text is summarized,and the contents for further research are prospected.