【正文】 selected precisely in a twodimension plane. Even though with the provision of the function to generate a pipeline through assigning the start and end point, it constrains the pipeline just by the means of setting the shortest length and least segments condition, so the result of the path isn’t practicable in engineering. It does not work well to create a pipeline satisfying certain constraints. Therefore, in this paper, based on UG developing objectoriented technology, the research develops the 3D pipe layout system catering to the users, makes up the deficiency of the pipe layout modules of UG, and realizes the function of the automation of laying pipe. 2. DESIGN OF PIPE LAYOUT SYSTEM Pipe layout system is consist of four modules that are the ponent library module, pipe laying module, constraint checking module and the result output module which are shown in Fig 1. The parameterized model is used for the pipe connecting and fixing and stored in the ponent library, such as plug, nut, Tconnector, etc. Pipe laying module is used to create the route path, set bend radius, show solid route model and then check the interference. If the interference exists, it adjusts the route path using route editing tools. On the term of the mach inability, manufacturability and heat distortion, the pipe has to meet certain constraints. If the checking result of the constraints on the pipe does not satisfy the requirements, adjustment is needed. At last, the output of the bending document report, through the result output module for the manufacturing of pipe bending machine, can be obtained. And the materials list shows the pipe laying information of the entire route. 3. COMPONENT LIBRARY There will be lots of standard connector used in pipe laying, as shown in Figure 2. If the similar connector has to redesign just for the size reason, it will waste lots of time and energy of engineer. By building 3D Parametric Modeling of the connector as shown in Fig 3, performing parametric analysis, creating parametric table, putting all kinds of information (including dimensions, materials, number and other attributes) [7] into the database, we can edit and manage the part family by operating on the database [8] and generate a new entity through size driven. So the connector template and parametric table set up the ponent library collaboratively. Fig. 1 Design of pipe layout system Fig. 2Architecture of ponent library Piping ponent library is posed by three layers: presentation layer, function layer and database layer. Show in Fig 2. Data layer consists of two parts: database and file system. Database is used to store information on the size, materials and etc. of the connector. File system is used to store the connector template. Function layer provides operations on ponent library, including adding, deletion, and searching template and so on. It can get the spare parts’ dimension information from part table, the template from file system and then create the instance of the CAD model for users. Display layer is the interface of UG from which the functions can be called to insert all kinds of standard pipe part into the workspace for pipe layout. Fig. 3 Pipe connector Fig. 4 Trend model of pipeline 4. PIPE LAYOUT The principle of pipe layout is to ensure the safety and reliability of the system, to make its structure pact, easy to maintain on the basis of meeting the need of design and operating. It is also required to satisfy the priority rule with the following path mode: the prior rule of laying pipe along the side of the engines, the prior rule of laying pipe in dense area, the prior rule of laying pipe parallel, the prior rule of laying thicken pipe and the rule of laying pipe axial and circumferential and etc. under the premise of meeting the design, using and technical requirements. To make the structure of pipe lay pact and easy to fix, laying the pipe axial and circumferential along the engine surface as close as possible, so better vibration characteristics and outline size can be obtained. The path isn’t the only way in threedimensional space. For the pipeline whose direction is axial or circumferential, according to the direction and coordinates of the initial path, Three basic pipeline trend modes are summarized (line segment on behalf of the starting path, rectangle on behalf of connectors, broken line is a black box which contains the middle section of the path). They are the abstraction for threedimensional elements in twodimensional plane. The head and tail section are involved with the connector. They have close relationship with the type and interface direction of the connector. The pipeline is divided into three segments, head segment, middle segment and tail segment, which are created separately to simplify the process of pipe layout. The first and tail segments are the creation of single pipeline. The middle segment is posed by several， polyclinic, each of which has three elements: start point, end point and several segments on the surface. The schematic of polyclinic in the threedimensional space and the projection of it in the twodimensional space are shown in Figure 5. As any pipeline of the engine is consist of a number of line segments, whose main parameters are the coordinates of the start and the end. Therefore, after finding out the coordinates of every control points, connecting with line, setting the bend radius, you can build a plete path. The create process of pipeline is shown in Figure 6. Fig. 5 Projection of middle pipe on twodimensional plane . PIPE LAYOUT MANUALLY This pipe layout method is used mainly for the pipeline which is arranged irregular. The process of manual pipe layout is to input the coordinates of every control points of the pipe, or select the control points using mouse and so on to pl