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MDT环境下RP数据处理与设备驱动程序的研发
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摘要
作为一种新兴的综合性制造技术,快速成形(Rapid Prototyping)技术以计算机辅助设计(CAD)和数控(NC)等多项使能技术为基础,并随着这些技术的发展而不断向前发展。目前,几乎所有的快速成形系统均采用STL文件作为数据交换接口。STL文件是CAD模型表面的三角化表示,无疑会造成精度损失。另外,现有快速成形系统的CAD模块、数据处理模块、监控加工模块三者彼此独立,使得快速成形的前处理过程相当繁琐。针对以上问题,本文基于MDT软件环境,在深入研究RP自适应分层方法的基础上,开发了RP数据处理及设备驱动程序,为实现CAD/CAPP/RP一体化奠定了基础。论文所做的主要工作如下:
     (1) 在综合考虑各种分层算法的基础上,提出了法线与面积综合判定法来确定分层厚度的CAD模型直接自适应分层算法:并针对同一模型对自适应分层和等厚分层进行了比较,结果发现:自适应分层在精度方面虽然与等厚分层基本相当,但是其层数可以显著减少,所以采用自适应分层可使成形效率显著提高。
     (2) 研究了MDT软件平台下CAD模型数据的内部表达方法,运用Autodesk公司提供的MDT二次开发工具ObjectARX和MDT API,实现了MDT模型的几何信息和拓扑信息提取,使自适应分层算法得以实现。
     (3) 通过对直接分层轮廓进行处理,实现了层片轮廓数据的提取、层片轮廓的重建、激光光斑的补偿,以及层片轮廓的填充和扫描路径的优化。
     (4) 从激光选择性烧结机理出发,建立了激光扫描功率与扫描速度之间的匹配规则,以实现在不同扫描速度下激光功率的自动匹配。
     (5) 针对SLS工艺,从理论上推导了振镜式扫描系统中振镜转角与X、Y坐标之间的关系,为CLI格式文件向PMAC运动程序的数据转化提供了理论依据。
     (6) 考虑SLS工艺特点,根据PMAC指令规则,实现了从标准CLI格式文件到PMAC运动程序的自动转化。同时,针对SLS工艺,设计了基于PMAC的控制系统方案。
     (7) 基于Windows操作系统,应用VC++6.0和ObjectARX对MDT6.0进行了二次开发,并对各模块进行了集成,形成了功能比较完善的基于MDT环境的RP应用软件。
     本课题的研究,对于提高RP制件精度、提高成形效率、实现CAD/CAPP/RP一体化具有重要的理论意义和实用价值。
As a kind of rising integrated technologies, Rapid Prototyping (RP) technology is rapidly developing with the development of various enabling technologies, such as Computer Aided Design (CAD) and Numerical Control (NC) etc. Nowadays, nearly all types of rapid prototyping systems commonly adopt STL file as their data exchange interface. The STL file is a triangularization representation of CAD model surface. Using it to represent CAD model will reduce the part precision. The existing RP-related software include a CAD module, a data processing module, and a monitoring and controlling module, which are independent of one another. Thus, the preprocessing procedure of RP is rather complicated. Aiming at the issues above, this thesis deals with the direct and adaptive slicing methods of CAD model, and develops the data processing and device driven system based on the Mechanical Desktop (MDT) software. The work of this thesis lays a solid foundation for the integration of CAD, CAPP and RP. The main work may be summ
    arized as follows:
    (1)After discussing all kinds of existing algorithms, this thesis presents a new kind of adaptive slicing algorithm that determines the slicing thickness by comprehensively considering the surface normal and the cross-sectional area. And for the same part, a comparison between the adaptive slicing and the equal-thickness slicing methods is performed. The results show that the adaptive slicing method can greatly improve the manufacturing efficiency in the equivalent precision. The adaptive slicing gains advantage over the equal-thickness slicing.
    (2)Based on a close research of the interior representation of CAD model in MDT, this thesis picks-up the interior topological and geometrical information of model expressed in the boundary representation (B-Rep) using the development tools of ObjectARX and MDT API offered by Autodesk Inc. The picking-up information makes it successful to implement the adaptive slicing method.
    (3)The direct slicing data are processed in order to accurately extract and reconstruct the data information of the 2D contours. Based on it, the radius compensation of laser beam spot, the filling contours and the optimization of the scanning paths are all implemented.
    
    
    (4)Based on the mechanism of SLS (Selected Laser Sintering), a matching rule between scanning velocity and laser power is established so as to realize the laser power matching in different scanning velocities.
    (5)Aiming at the SLS technology, the relationship between the rotation angle of mirror and X, Y coordinates of scanning point are derived theoretically, according to which the CLI file can be translated into PMAC instructors.
    (6)Considering the SLS technological characteristics and according to the PMAC instructor rules, the automatic conversion of the CLI file into the PMAC movement program is accomplished. In the meantime, a NC system scheme for rapid prototyping machine is designed for the SLS technology based on PMAC.
    (7)Based on the Windows operating system, all the functional modules above are developed and integrated with Visual C++ and ObjectARX in DMT 6.0 environment. This may be relatively good integration software for RP.
    The work of this thesis will be theoretically and practically beneficial to improving the part quality, boosting the forming efficiency and realizing the integration of CAD, CAPP and RP.
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