Research On Virtual Machining Key Technologies In Networked Manufacturing System

With the development of knowledge economy and information technology, networkedmanufacturing is widely researched and applied. It is now becoming a new paradigm formanufacturing industry. Because product development activities are distributed innetworked manufacturing system (NMS), digital simulation tools, especially digitalmachining process simulation tools are required for rapid product development. Virtualmachining (VM) is the map of real machining in computer environment. On one hand, itassists designers to evaluate the machinability of a part based on simulation. On the otherhand, it can help process planner validate numerical control (NC) process and codes beforereal machining. Hence, the research of virtual machining key technologies in NMS is ofgreat importance in both theory and application.On the basis of the analysis of the characteristics and function requirements of virtualmachining system (VMS), a VMS architecture, which is composed of interface layer,function layer and data layer, is proposed. The key technologies for VMS are discussed andthus the research direction of the dissertation is determined.Virtual machining environment (VME) model is an important part of digital models inNMS, and it is also the basis of VMS. A hierarchical VME model is presented, which iscomposed of component layer, equipment layer and workshop layer. Component modelincludes a geometry model and a physics attribute simulation model. Component geometrymodel is made up of a display geometry model and an engineering semantic model, and itis independent of commercial CAD software. Equipment model consists of an equipmentconfiguration model and an equipment behavior control model. Environment modelincludes an environment configuration model and an environment behavior control model.The hierarchical VME model has the virtue of good expandability, full information andsupporting reconfiguration.Because the equipment in NMS is distributed and diverse, the NC code parser shouldbe all-purpose. Based on the analysis of NC code format, a general NC code processframework and a flow chart are proposed. The sub-program is processed on the basis ofcalling stack. This method can deal with the transfer of NC code location, the control ofNC sub-program calling number and the resume of calling conditions efficiently. The NCsystem customization method is designed to make the user set up the rules of a new NCsystem quickly and conveniently. The syntax is analyzed based on regular expression. Furthermore, the scheme of rule database is designed for general NC code processing.Visual machining process simulation is the core function of VM. Firstly, a workpiecesurface subdivision method and a method for solving swept volume surface of general toolare proposed. And then an optimized machining simulation algorithm based on triangularmesh model is put forward. For promoting the visual simulation speed of VM, an improvedregion partitioning algorithm is presented. The display surface is first divided into smallregions. Then the triangular facets are regrouped according to their covering regions.During machining simulation, since only the facets of modified regions need to be redrawn,each frame can be rendered in a short time. Three important aspects of the algorithm:triangular facet's region judgment, virtual scene components traverse and redraw regionjudgment are discussed in detail. The tests are done to demonstrate how the regiongranularity can affect the performance of the algorithm.Collision detection is a key technology for fully validating NC process and code. Ahybrid collision detection algorithm for VM is presented. The algorithm is made up of twoparts. One is an object space detection algorithm, the other is an image space detectionalgorithm. The object space algorithm prunes the non interference object pairs rapidly. Andthe image space algorithm judges the interference state between objects precisely. Firstly,the algorithm judges whether the graphics display hardware supports the visibility query. Ifthe function is supported, the algorithm based on visibility query is used. Otherwise, thealgorithm based on depth-stencil test is used. The performance of the algorithm is testedand the results show that the algorithm can enhance the efficiency of collision detectiongreatly.In the end, a virtual machining prototype system, which is a module of the networkedcollaborative design and manufacturing system e-CWS, is developed by COM techniques.Some application instances are introduced to validate the technologies of the dissertation.