【作者】 周刚；

【导师】 潘晓弘； 邬义杰；

【作者基本信息】 浙江大学 ， 机械制造及自动化， 2008， 博士

【摘要】 随着产品数据交换的主流标准STEP(Standard for the Exchange of ProductData)向工场制造阶段延伸,逐渐形成新的标准ISO14649,即STEP-NC(STEP fornumerical controllers)。STEP-NC的出现打破了数字化制造过程中CAxs与CNC之间信息传输的瓶颈,使从设计到现场制造之间的信息双向高速传输成为可能,为集成制造技术的发展提供了基础。在此背景下,本文开展基于STEP-NC数控系统体系结构和若干关键技术的研究,为研发STEP-NC的数控系统提供方法和技术支持。分析了STEP-NC标准数据模型和开放式数控系统的体系结构,给出系统功能的需求分析及模型结构。分别建立基于非实时信息流、弱实时信息流和强实时信息流的STEP-NC数控系统的信息流模型。划分STEP-NC数控的层次结构为模型应用层、制造规划层和实时控制层。参考现有的数控系统拓扑结构,特别是基于PC的“软件型”数控系统结构模型,提出PC+嵌入式系统分层结构的标准型STEP-NC数控系统的体系结构。STEP-NC加工程序的信息提取是控制器获取信息的前提和基础。研究开发了基于STEP-NC数控加工程序信息提取系统。根据STEP信息共享和数据交换实现技术,采用基于SDAI(Standard Data Access Interface)原理的应用方法,构造节点、字典单元实体、实体结构树和加工程序结构树等数据结构。给出分步的实体实例信息提取过程模型——字典实体创建、节点实例创建、加工程序结构树创建和实体实例匹配。根据识别的实体实例数据进行特征信息的重构,包括制造特征重构、技术列表、执行流排序和资源特征列表及重构。曲面加工一直是数控加工的重要应用领域。由于STEP-NC数控系统对曲面和曲线加工的更为支持,能够有效提高加工效率和精度,本文研究了一种能够同时具有边界一致、基本符合二阶偏导数渐进变化和等参数要求的曲面刀具轨迹生成技术。该技术中一致的边界能够由用户指定,并适用于组合曲面刀具轨迹的生成。其中刀具轨迹的生成过程包括曲面离散、引导线生成、分段全局测地线生成和刀具轨迹生成。并在此基础上对一类带脊线曲面的刀具轨迹优化生成过程进行了初步研究。数控系统是工场级的实时系统,具有较高的实时性要求。传统数控系统一般采用精确定时为前提的实时调度机制。但是由于STEP-NC的引入,给数控系统带来的不仅仅是接口标准的改变和CAxs中功能模块简单移入。随着STEP-NC数控系统中功能的增强、功能模块数量的增加,各模块之间的计算量、实时性差异越来越大,并且某些模块的任务执行时间难以准确计算。由此对STEP-NC数控系统与实时相关的技术和方法提出了更高的要求。随着STEP-NC数控系统功能模块的复杂性和模块执行时间不确定性增加,不同模块实时性的要求差距增大。假设仍然采用以WCET(Worst-Case ExecuteTime,任务最长执行时间)计算等为基础的传统调度方式,STEP-NC数控系统的实时调度能力也将受到众多限制,系统的性能也将受到影响,在实现调度过程中也存在较大的困难。结合基于PC和嵌入式系统分层的标准型STEP-NC系统结构,认为在PC系统(也称上位系统)中的弱实时调度与传统数控实时调度存在较大的区别,分析PC系统中弱实时模块的时序约束,结合服务调度、优先级可变的模块耦合框架和调度机制,提出一种满足STEP-NC数控系统复杂模块结构要求的PC系统弱实时调度算法。STEP-NC数控系统中实时闭环制造是关于参数、策略规划和优化的过程,是数控系统采用STEP-NC后最显著的变化之一。分析了当前CAxs/CNC制造流程中实现基于特征信息的实时闭环制造所存在的困难。结合给定的STEP-NC数控系统体系结构,给出一种满足STEP-NC的数控系统实时闭环制造过程模型。针对以上研究内容,相应开发了基于STEP-NC数控加工程序信息提取实验原型系统和曲面刀具轨迹生成原型系统。加工程序信息提取系统能够识别STEP-NC加工程序,并能重构部分单特征的零件几何。刀具轨迹生成系统能够处理组合曲面的情况,并能对一类带脊线曲面进行刀具轨迹优化生成。更多还原

【Abstract】 STEP(Standard for the Exchange of Product Data) has been the main standard in production data exchange. On such background, STEP has extended to NC(Numerical controller) machining in floor shop. A new ISO standard(ISO 14649) named STEP-NC was developed by vendors, user and academic institutes in word wide to provide a standard data interface model between CAxs(Computer Aid for X) and CNC. STEP-NC has broken the bottle-neck of information transfer between CAxs and CNC. In this thesis, a new standard type STEP-NC CNC architecture had been put forward, and some key technologys had been studied. The main research content included:STEP-NC data model and open NC architecture were introduced firstly. Then the system function model was put forward based on function requirement. Information stream model was structured succedently. And it was divided into three parts by real-time characteristic, there were non-real-time information, weak real-time information and strong real-time information. So the STEP-NC based NC system is divide three layers, there were model application layer, manufacture plan layer and real-time controller layer. By referencing existing NC system topology structure, especially the PC based soft type CNC, a two layers standard type STEP-NC NC architecture which combined PC system and embed system was put forward.STEP-NC machining program information extraction was the precondition and basic of controller development. A SDAI based STEP-NC machining program information extraction system was developed. The system includes two sects: data transfer and feature reconstruct. In the data transfer proceeding, there included dictionary data construct, entity instance construct, machining program tree construct and entity-instance match. In the feature reconstruct proceeding, four types feature need reconstruct. There were manufacture feature reconstructing, technology feature reconstructing, execute stream listing and resource reconstructing.Tool path generation on surface is the key technology of NC. A tool path generation algorithmic which can meet three demands simultaneously was put forward. Three demands included Arbitrary boundary conformed, change meeting second order PDEs rule and ISO-parameter. This algorithmic can apply on compound surface. In the tool path generation proceeding, surface was dispersed firstly, then generating lead lines on discrete surface by steady heat transferring principle, subsequently, global subsection geodesic lines was constructed base on lead lines and discrete surface using MMP algorithm. Then generate tool path on global subsection geodesic lines using iso-parameter method. There sever advance in which STEP-NC replaced G code as NC data model interface standard. It was not the simply function moving from CAxs to STEP-NC NC. By the some function and model were realized in STEP-NC NC controller, the system became complicated, Especially in real-time function and system dynamic stability. In the STEP-NC system, the real-time requirement in different models was widely. It will be unfitting the STEP-NC system demand if we used traditional real-time scheduling technology in NC. So real-time schedule method and closed loop real-time manufacture processing in STEP-NC NC system was considered.A real time scheduling mechanism meeting STEP-NC numerical control system is put forward. Because there were wide real-time requirement between different models, it was not suitable using precise timing technology, such as based on WCET(Worst-Case Execute Time). By analyzed PC OS(operation system) scheduling characteristic and STEP-NC NC model real-time reminding, a weak real-time scheduling method on PC base on integrate resource restriction was put forward. The method included real-time scheduling frame and algorithm. The frame was constructed by scheduling cell, scheduling serve and resource management. The scheduling algorithm met scheduling cell PRI alterable, serve application etc.Real-time close loop manufacture process included manufacture programming, strategy optimize. It was one of remarkable change in STEP-NC NC system compared with G code based NC. Current part manufacture process in CAxs and CNC was analyzed firstly. It is difficult in realizing closed loop between in CAxs and CNC for low interface standard-G code. But it is not exist when STEP-NC was used as NC data interface standard. So a Real-time close loop manufacture process model in STEP-NC NC system was put forward.The emergence of STEP-NC will influence NC manufacture technology and other technology such as e-manufacturing widely. STEP-NC NC system is the basic and important equipment, it is the new key part of the numerical manufacture process. The thesis was aim to develop the controller of STEP-NC and solve the some key technology.更多还原