Operation sequencing in an automated process planning system

One of the most difficult tasks we face in automated process planning is determination of operation sequencing. In this paper we present an approach to automatic generation of machining sequences in an object-oriented automated process planning system. Sequencing of machining operations is carried out in three phases of planning: initial planning, set-up planning, and final planning. The initial planning generates general plans including the required operations and machine cells. Two types of information are used at this stage, manufacturing process knowledge and component information, including features and associated dimensions, tolerances, surface finish, and material conditions. Based on process requirements decided in the initial planning, the set-up planning selects machines and fixtures, decides the clamping surfaces and feature accessibility, and sequences the set-ups. The final planning determines all the detailed sequences of operations based on the set-ups using the built-in manufacturing logic and heuristics. We introduce the set-up planning, the core of the planning system, to link the part model, initial planning and final detailed planning. The strategy has been implemented in an object-oriented process planning system. An example is provided to demonstrate the approach.     

A constraint-based operation sequencing for a knowledge-based process planning

Process planning is a decision-making process. Decisions on machining operations for a particular feature have to be made on various independent conditions such as which operation should be performed with which tools and under what cutting parameters. An integrated knowledge-based CAPP system called ProPlanner has been developed. The system has five modules namely information acquisition, feature recognition, machining operation planning and tool selection, set-up planning, and operation sequencing. Most process-planning systems do not produce alternative process plans. Usually, a fixed sequence created by a process plan is not necessarily the best possible sequence. Therefore, the aim should be to generate all possible operation sequences and use some optimality criteria to obtain the best sequence for the given operating environment. This paper presents an efficient heuristic algorithm, belongs to the system's operation sequencing module, for finding near-optimal operation sequences from all available process plans in a machining set-up. The costs of the various machining schemes are calculated and the machining scheme with the lowest cost is chosen. All feasible cutting tools are identified for each particular feature and the corresponding machining operations. This process is repeated for all the features in the machining set-up. All possible feature sequence combinations allowed by the current feature constraints are then generated. Appropriate cutting tools are identified and assigned to different operations. The feature sequence with the smallest number of tool changes is adopted.     

Virtual reality and hypermedia in learning to use a turning lathe

Abstract A Virtual reality environment with hypermedia was designed to help undergraduates understand the structure and functioning of a turning lathe. Study 1 was carried out with 30 novice students and Study 2 involved 24 students attending a machining course. These studies demonstrated that the virtual lathe can foster the comprehension of some core machining concepts. Further, the studies suggest that novice students benefit most from earlier free navigation of the virtual environment whereas expert students benefit from an analysis of the hypermedia.     

Computer graphics simulation of a CNC lathe

A software system for simulation of the machining operations of a computerized numerically-controlled lathe is described. The microcomputer-based, BASIC software reads part program instructions from a sequential file, analyzes each instruction for errors and provides printed output describing the machine commands called for by the instruction as well as graphic output for tool motions. In an educational environment, the system can be used as a substitute for the more expensive machine tool or as a diagnostic and preview tool prior to actual machining.     

Development of an expert system for optimizing natural gas pipeline operations

This paper presents an expert system as a decision support tool to optimize natural gas pipeline operations. A natural gas pipeline control system is a controlling system that involves many complicated operating processes. Since a dispatcher (who operates the system) might not be able to handle all of his or her tasks consistently, an expert system has been developed for optimizing the operations by providing consistent, fast and reliable decision support to the dispatcher. Consequently, inconsistency in the dispatcher's performance can be minimized. To build an expert system, the knowledge from an experienced dispatcher, who is familiar with the process in this controlling system is acquired and that knowledge has been implemented as rules in the knowledge base of the expert system. When this expert system has been validated by gas pipeline experts, it can help inexperienced dispatchers to operate the processes more effectively. The expert system is implemented on the real-time expert system shell G2 (trademark of Gensym Corp. of USA). The system also consists of a user interface that helps dispatchers visualize system conditions.     

用XML建造专家系统知识库

专家系统是一种基于知识的智能系统，主要包括知识库、数据库、推理机制、解释机制、人机接口和知识获取等功能模块。它的主要特征是，系统中有一个巨大的知识库，存贮某个领域的专门知识，有很多种技术管理知识库。随着网络技术的发展，XML已经成为重要的网络计算语言。文中就如何用XML建造专家系统的知识库以及其相关操作做了深入的探讨。     

用XML建造专家系统知识库

专家系统是一种基于知识的智能系统,主要包括知识库、数据库、推理机制、解释机制、人机接口和知识获取等功能模块。它的主要特征是,系统中有一个巨大的知识库,存贮某个领域的专门知识,有很多种技术管理知识库。随着网络技术的发展,XML已经成为重要的网络计算语言。文中就如何用XML建造专家系统的知识库以及其相关操作做了深入的探讨。     

Fuzzy-set-based approach for concurrent constraint set-up planning

Material removal processes are integral parts of many manufacturing systems. They are either primary machining processes or an important part of preparing toolings for subsequent forming and moulding processes. Manufacturing process planning identifies the type of material removal processes and the machining parameters, cutting tools and fixtures needed to generate the features on a part. Previous research in manufacturing process planning has concentrated mainly on the role of features, in the derivation of the associated process and fixture plans. Many computer-aided process planning (CAPP) and computer-aided fixture planning (CAFP) systems derive process and fixture plans from the features on a part, on the basis that these features are context-free. However, manufacturing operations are interdependent processes. In the author's computer-aided set-up planning (CASP) system, a different perspective is adopted. Feature relations form the core of the conceptual structure. These features relations, which are often imprecise, are used in deriving set-up plans. The feature relations, which may be due to geometrical constraints, tolerance requirements, etc., are modelled using fuzzy sets and fuzzy relations. This paper presents the various feature relations considered in the present system and proposes a practical planning algorithm for set-up planning.     

数控自动编程专家系统

本文简要地介绍了数控自动编程专家系统.其中包括:专家系统知识表示的形式;分层次的黑板结构;前向推理求解策略和相应的解释功能;系统针对不同类型的曲线组合,采用不同的独立的知识源(KS)进行处理.由于在知识的处理上采用编码技术,在前向推理求解策略中使用启发信息和“剪技”技术,提高了系统的时空效率.系统中的规划程序能自动规划切削路径.输出供数控车床使用的 NC 代码,并可在显示屏上进行图形显示和切削仿真.目前原型系统已经在 IBM-PC 和 Sun3/60计算机上利用FORTRAN 语言实现.     

复杂生产过程实时故障诊断专家系统

本文以高炉炼铁过程为例介绍了复杂生产过程故障检测实时专家系统（ＢＦＤＥＳ）。该系统综合运用了面向对象方法，知识编译，产生式及框架方法。提高高炉传感器的数据，ＢＦＤＥＳ系统可对高炉炉况作出实时判断，并可预测高炉运动的故障，该专家系统以实际在线运行表明，其性能良好并已取得显著的经济与社会效益。     

A Web-based process planning optimization system for distributed design

In this paper, a process planning module, which can optimize the selection of machining resources, determination of set-up plans and sequencing of machining operations to achieve optimized process plans, has been wrapped as services and deployed in the Internet to support distributed design and manufacturing analysis. The module includes four intelligent approaches, and a Tabu search-based approach is explained in this paper to illustrate the optimization process. A Web-based prototype system has been setup for users to carry out visualization-based manipulations and process planning of design models by invoking the services remotely. The Web-based system has been integrated with a distributed feature-based design system, and the latter can generate design models and re-represent them in an XML representation based on VRML and attributes of features to provide the input of the former. Through effective utilization of the Web and Java technologies, this system is independent of the operating system, scalable and service-oriented, and can be used by a geographically distributed design team to organize concurrent engineering design activities effectively.     

基于PLC技术的组合机床改造

作为PLC控制的应用实例,介绍用于缝纫机机壳加工的组合机床进行PLC控制改造。描述了组合机床运动状况及控制要求。对PLC控制设计及编程作了具体的阐述。     

Intelligent process-control system design

The use of expert systems has vast potential in an intelligent process-control system. In this paper, the issue of process-control system design using a knowledge-based approach is discussed. Expert-system techniques have been used for the design of controllers for process-control systems. The expert system is developed in conjunction with the successful application of a systematic design approach. Design knowledge has been represented using rules, facts and frames. The design process consists of a sequence of operations obtained by heuristics and experience in the design techniques.     

基于粗糙集理论的计算机图像识别系统

为解决专家系统较难获取完备知识的瓶颈问题,设计了一种基于粗糙集理论的诊断系统。研究历史数据所形成的决策表,运用粗糙集理论进行约简,构建专家系统知识库模型。通过计算诊断规则粗糙度,确定诊断规则的置信程度。利用推理机,实现对知识库的动态维护。结合诊断的特点,建立基于粗糙集理论的专家诊断系统模型,快速准确地实现诊断的目标。实例表明,该专家诊断系统有效、实用,具有很好的学习能力。     

卫星接收故障诊断专家系统的研究

文章分析了卫星接收系统的故障机理,研究了基于故障树的专家系统推理机的实现,提出了一种卫星接收故障诊断专家系统的设计思想及实现方法。推理过程以正向推理技术为主,应用二叉搜索树建立故障树,采用产生式表示法表示事实知识和规则知识,应用数据库作为知识库,构造了卫星接收故障诊断专家系统,用于对实时卫星接收过程的故障判断,指导操作员排疑解难。     

基于Ontology的专家系统研究

针对当前专家系统领域知识语义表示不精确及推理效率低的问题,提出一种基于Ontology的专家系统框架。根据规则结构建立规则模式Ontology和动作Ontology,将用户推理条件作为模式子Ontology,设计出基于名称和实例的相似度计算及Clips推理机制的专家系统推理算法。结合高性能切削加工应用背景给出一个应用实例,应用结果表明,该系统能够明显提高推理效率和推理结果的语义表达。     

Using an expert system for design diagnosis and design synthesis

Abstract This paper describes the concepts which allow an expert system to be used for both design diagnosis and design synthesis. An example of the implementation of these concepts is presented in the domain of preliminary design of domestic kitchens in the expert system PREDIKT. PREDIKT carries out both design diagnosis and design synthesis using the same knowledge base and utilises an existing expert system shell which has forward- and backward-chaining capabilities. The significance of graphical interaction with expert systems in design domains is demonstrated.     

故障诊断专家系统中知识库组织和维护技术的研究

在开发化工过程实时故障诊断专家系统的基础上,本文讨论了知识库的组织和维护技术,对知识表示和知识库结构进行了详细介绍。在知识库维护方面,采用面向对象的方法描述领域知识,并实现知识获取和转换;对于知识校验,提出一种基于有向图的知识校验方法。以润滑油生产过程为例,讨论了系统的知识校验过程。本文讨论的技术和策略已应用于润滑油过程实时故障诊断专家系统。实际应用表明,该技术和策略保证了知识库和专家系统的稳定和高效率。     

用于柔性生产线方案设计的分层工艺规划方法

在建立面向对象工艺模型的基础上，提出用于柔性生产线方案设计的分层工艺规划方法，即特征工艺设计、零件装夹定位规划、特征排序规划、工步排序规划、工序聚合规划等5个层次．采用基于黑板的递阶式层次推理结构，实现了综合排序策略，完成了用于柔性生产线方案设计的CAPP系统开发。     

Implementation of knowledge maintenance modules in an expert system for fault diagnosis of chemical process operation

Based on the authors previous work of developing an expert system for fault diagnosis of chemical processes, this paper presents principles and approaches of the knowledge base maintenance in the expert system. Development and implementation of maintenance modules for the knowledge base in the expert system for fault diagnosis of fluid catalytic cracking unit (FCCU) are reported in detail. Algorithms are proposed for integrality verification of five inconsistencies among heuristic rules: contradiction, redundancy, subsumption, circulation, and reclusion. The modules ensure the knowledge base and the expert system to work stably and efficiently. DELPHI and SQL SERVER are adopted in developing the modules. Application in FCCU fault diagnosis expert system shows that the modules work rationally and efficiently with user-friendly interface, besides its strong interactive feature and better performance of the expert system. The modules have been in continuous use in the expert system of fault diagnosis of FCCU installation in a refinery for the last two years.