装配序列规划问题的CSP模型及其符号OBDD求解技术

完全、正确的可行装配序列的表示和生成是装配序列评价、优化和选择的前提,为此建立了单调非线性装配意义下的可行装配序列规划问题的约束满足问题(CSP)模型,并给出了基于有序二叉决策图(OBDD)的符号求解算法.首先以装配联接图和移动向量函数为装配体模型,给出了装配联接图模型的共享二叉决策图(SBDD)表示、移动向量函数的OBDD表示,以及装配序列规划问题的CSP描述;然后将生成所有可行装配序列的问题转化为对CSP求解所有可能解的问题,利用回溯算法对CSP问题进行符号OBDD求解,得到了满足几何可行性约束的所有可行装配序列.最后通过装配体实验验证了基于CSP模型和OBDD推理的装配序列生成技术的正确性和可行性.     

一个基于知识的装配序列规划系统

本文提出一种基于知识的装配序列规划系统。该系统针对装配序列规划所涉及信息的纯几何描述和计算的复杂度等问题，采用领域知识推理，并结合适量几何计算的方法，求解装配序列规划问题。系统包括：任务理解，装配关系模型生成和序列规划三个组成部分。     

运用有向联接件知识求解装配序列规划

在分析联接件特征的基础上，提出了有向联接件的概念，建立基于联接件知识的零件表达式；运用有向联接件知识求解装配序列规划，实现了知识推理算法和几何约束推理算法的有机结合，有效地降低了装配规划的计算复杂度，保证规划所得装配序列的合理性和实用性．此外，还建立了装配体的自由空间图，可以解决非单调装配序列规划问题。     

基于图论和启发式搜索的装配序列规划算法

将装配序列规划中成熟的割集法和人工智能中启发式搜索方法相结合，提出一个高效的装配序列生成算法。此算法在启发函数的指导下，直接产生所需的最佳装配规划，避免了单独采用割集法产生装配AND／OR图而导致的组合爆炸的问题。同时省去了在选择装配规划时，对整个装配AND／OR图进行再次搜索。此算法与其它算法相比具有效率高、智能性强的特点。最后给出了一个实例。     

基于知识的装配前趋约束图的生成

装配前趋约束图的生成是装配规划的关键环节，也是其中最困难的一步.该文在讨论了几种装配前趋约束图生成方法的具体实现以及它们的优缺点之后，提出利用几何知识和装配经验知识相结合的方法，建立装配知识库/数据库，给出了几种在复杂度上可行的解决方法.最后给出结论，并简单地讨论了结合知识的数学算法的优越性，同时讨论了今后发展的方向.     

基于图的子装配识别与装配序列规划

本文基于图建立了装配模型,并提出了一种基于配合关联图的子装配识别和装配序列 规划方法．直接从配合关联图出发识别出围绕箱体、轴和螺纹联接等典型零件所形成的子装 配;对配合关联图进行了简化,完成了基于配合关联图的装配序列规划．     

面向装配序列规划的装配本体设计*

为提高装配序列规划的自动化程度,实现装配相关活动间信息的共享、重用和顺畅传递,实现装配序列规划系统与其它异构系统之间的无缝集成和互操作,将本体技术引入到装配建模中.针对装配序列规划建模需求,构建面向装配序列规划且基于装配对象的装配本体(OWL-ASP).OWL-ASP由Properties本体、AssemblyInfo本体和AssemblySeq本体组成,分别描述装配对象的装配属性、装配信息、装配顺序等.在OWL-ASP的基础上,利用语义Web规则语言刻画装配规则,形成统一的装配知识表示层次体系,实现对装配知识的严格刻画和自动推理.通过球阀装配的实例说明装配本体和装配规则的有效性.     

装配序列规划中拆卸方向的确定

以产品为出发点进行拆卸判断,以拆卸顺序的逆生成装配序列是装配序列规划中常用的方法,而拆卸方向的确定量是其关键的一步,而将拆卸方向简化为与坐标轴平行的方向不能产生完备的可行装配顺序集,在分析装配过程的特点基础上,提出一种根据装配约束关系用球面几何计算拆卸方向和方法,首先,利用球面几何的方法求解局部拆卸方向集,取局部方向集所对应的球面多边形的形心为局部拆卸方向;然后,利用投影的方法测试此局部拆卸方向是否为全局拆卸方向,文中提出的方法可以方便地用于工程实践中。     

虚拟环境中面向装配设计的数据场景图研究

作为虚拟环境中的数据结构，场景图的构建是虚拟现实技术领域的重要研究问题之一。针对虚拟装配设计系统的要求，讨论现有商业VR软件在开发虚拟装配设计时存在的限制，提出一个基于场景图的多层次虚拟装配设计模型VAM．在现有VR软件和VAM的基础上，说明了虚拟装配设计时的路径规划、序列生成、零件之间的约束关系等的表示和应用。     

基于图论和蚁群算法的虚拟装配序列规划研究

为了解决复杂装配体装配序列生成与优化问题,首先建立装配体的有向关联图,生成对应的关联矩阵.在运用蚁群算法求解满足最小装配代价的装配序列解的过程中,通过改进信息素更新策略,更新局部和全局信息素,指导蚁群快速寻找全局最优解;同时引入信息素挥发系数自适应调节机制,避免了求解过程陷入局部最优.最后通过实例验证了算法的有效性.     

基于深度邻域搜索PSO 算法的装配序列优化问题

针对产品结构特征建立几何约束矩阵, 以最大化满足几何约束条件装配次数和最小化装配方向改变次数为目标, 研究产品装配序列优化问题. 利用值变换的粒子位置和速度更新规则, 基于具有随机性启发式算法产生初始种群, 提出一种带有深度邻域搜索改进策略的粒子群算法解决装配序列问题. 通过装配实例验证了所提出算法的性能并对装配序列质量进行了评价, 所得结果表明了该算法在解决装配序列优化问题上的有效性与稳定性.

     

Reasoning algebraically about loops

We show how to formalise different kinds of loop constructs within the refinement calculus, and how to use this formalisation to derive general transformation rules for loop constructs. The emphasis is on using algebraic methods for reasoning about equivalence and refinement of loop constructs, rather than operational ways of reasoning about loops in terms of their execution sequences. We apply the algebraic reasoning techniques to derive a collection of transformation rules for action systems and for guarded loops. These include transformation rules that have been found important in practical program derivations: data refinement and atomicity refinement of action systems; and merging, reordering, and data refinement of loops with stuttering transitions. Received: 11 February 1998 / 18 March 1999     

基于子图同构与事例匹配的装配体局部结构相似性分析

基于事例推理是解决面向装配的设计和装配工艺规划问题的有效方法,装配体检索是应用此方法的关键步骤.为此提出一种基于子图同构与事例匹配的装配体局部结构相似性分析方法.该方法将装配体零件间的装配关系用属性邻接图来表示,通过对装配体中联结关系的定性分类及装配体属性邻接图预处理规则的定义,利用Ullmann算法匹配出相似的装配体图(子图)结构,并给出了装配体局部结构相似度计算公式.最后通过实例验证了文中方法的有效性.     

Disparate attributes algorithm for semantic assembly design rule management

To expedite a semantic product design environment, the relevant minimal set of design rules could optimally be distilled from the given disparate design rules. However, in disparate design rules, some attributes are frequently unused in other design rules. Treating all the attributes in all the rules increases reasoning complexity. In the situation of incomplete information, treating the attributes, which may be relevant to some rules and not to others, as “missing” ones is found to cause reasoning problems. In this paper, we present a new algorithm, i.e. the disparate attributes algorithm, for managing semantic assembly design rules. The proposed disparate attributes algorithm by identifying “inapplicable” information extends a rough set approach for managing semantic assembly design rules with systematic selection of various minimal sets of rules. To validate the disparate attributes algorithm, the approach is tested with multiple realistic assembly design cases.     

An application of design space for assembly process reasoning to utilize current assembly plant resources for new product family members

A successful and profitable product platform strategy requires both product family architecture and assembly process reasoning. New product family member production cost and time can be significantly reduced by utilizing available assembly resources, which can be achieved through systematic assembly process reasoning. A method to utilize existing assembly plant resources, during the development of new product family members, requires comparing feasible assembly processes with exiting assembly plants. The set of feasible assembly sequences for a product family member is modelled by developing an assembly sequence design space, which is combinatorial in nature, and applying constraints on the space. Models that capture effects of constraints on these spaces, explicitly represent feasible regions, and efficiently enumerate designs within this space are investigated. The feasible space is then searched to determine new product assembly sequence that will require minimum change in the current assembly plant. An automotive front structure family is utilized to demonstrate application of the assembly sequence space to perform assembly reasoning to increase exiting assembly plant resource utilization.     

A connector-based hierarchical approach to assembly sequence planning for mechanical assemblies

This paper presents an approach to find feasible and practical plans for mechanical assemblies based on a connector-based structure (CBS) hierarchy. The basic idea of the approach is to construct plans for an assembly (i.e. the root node of the CBS hierarchy) by systematically merging plans for primitive structures in the CBS hierarchy, while the plans for primitive structures are built using one of three methods: by reusing the existing plans, by retrieving the stored plans, and by geometric reasoning. The input to the approach consists of the assembly solid model, the connector-based relational model (CBRM) graph, the spatial constraint graphs, and the selected base part for the assembly, all of which are assumed to be generated previously in an interactive and/or automated way. Then, a CBS hierarchy for the assembly is automatically derived from the input CBRM by firstly establishing its functional model, which is constructed from the CBRM by decomposing the assembly or resulted part sets with respect to their connectors. Based on the CBS hierarchy, a set of assembly precedence diagrams representing good plans for the assembly are generated by merging plans for primitive structures systematically in a bottom-up manner. It can be proved that the proposed approach is both correct and complete. To verify the validness and efficiency of the approach, a variety of assemblies including some complicated products from industry are tested in the experimental CBHAP planner.     

Nested partitions method for assembly sequences merging

The severe competition in the market has driven enterprises to produce a wider variety of products to meet consumer’s need. However, frequent variation of product specification and more complexity of product cause the assembly sequence planning of product become more and more complicated. As a result, the issue of assembly sequence planning of complex product becomes a problem which is worthy of concern. In this study, a methodology for assembly sequence planning of complex components is presented, which consists of three phases: assembly-based modular design, assembly subsequences generation for each module and assembly sequences merging. Nested partitions (NP) method is used to merge assembly subsequences. Assembly sequences merging can make full use of subsequences information of modules and simplify assembly sequence planning of the complex products. A desk lamp is used as an example for implementation to validate the feasibility of this research.     

Multiple Adaptive Agents for Tactical Driving

Recent research in automated highway systems has ranged from low-level vision-based controllers to high-level route-guidance software. However, there is currently no system for tactical-level reasoning. Such a system should address tasks such as passing cars, making exits on time, and merging into a traffic stream. Many previous approaches have attempted to hand construct large rule-based systems which capture the interactions between multiple input sensors, dynamic and potentially conflicting subgoals, and changing roadway conditions. However, these systems are extremely difficult to design due to the large number of rules, the manual tuning of parameters within the rules, and the complex interactions between the rules. Our approach to this intermediate-level planning is a system which consists of a collection of autonomous agents, each of which specializes in a particular aspect of tactical driving. Each agent examines a subset of the intelligent vehicle's sensors and independently recommends driving decisions based on their local assessment of the tactical situation. This distributed framework allows different reasoning agents to be implemented using different algorithms.When using a collection of agents to solve a single task, it is vital to carefully consider the interactions between the agents. Since each reasoning object contains several internal parameters, manually finding values for these parameters while accounting for the agents' possible interactions is a tedious and error-prone task. In our system, these parameters, and the system's overall dependence on each agent, is automatically tuned using a novel evolutionary optimization strategy, termed Population-Based Incremental Learning (PBIL).Our system, which employs multiple automatically trained agents, can competently drive a vehicle, both in terms of the user-defined evaluation metric, and as measured by their behavior on several driving situations culled from real-life experience. In this article, we describe a method for multiple agent integration which is applied to the automated highway system domain. However, it also generalizes to many complex robotics tasks where multiple interacting modules must simultaneously be configured without individual module feedback.