An Intelligent Computer-Aided Assembly Process Planning System

This paper presents an intelligent computer-aided assembly process planning system (ICAAPP) developed for generating an optimal assembly sequence for mechanical parts. The system employs a graph set technique for creating an assembly model. The set includes an attributed topological graph, an attachment constraint graph, a tolerance graph and a special process constraint graph. In the generation of assembly sequences for any product, the critical problems to be addressed include determining the base part, selection of subassemblies, defining all necessary constraints, and quantifying and solving these constraints. In the ICAAPP system, algorithms have been developed for the selection of the base part, defining of the subassemblies, and determination of the constraint values. A simple mechanical assembly is used to illustrate the feasibility of the proposed algorithms.     

A hierarchical approach to disassembly sequence planning for mechanical product

An important aspect of design for the life cycle is assessing the disassemblability of products. This paper presents a novel approach to automatic generation of disassembly sequence from hierarchical attributed liaison graph (HALG) representation of an assembly through recursively decomposing the assembly into subassemblies. In order to increase the planning efficiency, the HALG is built according to the knowledge in engineering, design and demanufacturing domains. In this method, the boundary representation (B-Rep) models are simplified by removing the hidden surfaces to reduce the computational complexity of disassembly planning. For each layer of HALG, the subassembly selection indices defined in terms of mobility, stability, and parallelism are proposed to evaluate the extracted tentative subassemblies and select the preferred subassemblies. To verify the validity and efficiency of the approach, a variety of assemblies including some complicated products are tested, and the corresponding results are presented.     

Assembly sequences merging based on assembly unit partitioning

Assembly sequence planning is a typical of combinatorial optimization problem which is difficult to be tackled when the number of parts of assembly becomes large. To reduce the searching space of assembly sequence planning of complex products, assembly sequences merging based on assembly unit partitioning is suggested. Assembly unit partitioning is presented to decompose the complex products into a group of assembly units containing a reduced number of parts or components, and the assembly design constraints and the assembly process constraints are comprehensively taken into account. The global optimal assembly sequences can be acquired through three steps. Firstly, the assembly units and decision graph of assembly unit are generated utilizing fuzzy analytical hierarchy process approach. Secondly, the optimal or near-optimal subsequences of assembly units can be obtained with current efficient methods of assembly sequence planning. Thirdly, under the assembly interference of assembly relations (geometrical constraints) of the whole products and the assembly precedence concluded by subsequences of assembly units, the assembly sequence merging is implemented to generate the global assembly sequences, and the optimal sequence is obtained through assembly sequences evaluation. The assembly constraints considered at the two previous steps is represented by the evaluation function. The effectiveness of the method is verified by an illustrative example and the results show that the searching space of assembly sequence merging of complex products is reduced remarkably and the optimal assembly sequence of the whole produces is obtained.     

计算机辅助装配顺序生成方法研究

装配顺序生成是装配设计自动化中的一个重要而复杂的问题。本文在分析现有装配模型的基础上，引入虚拟子装配体的概念，提出了装配层状关系模型，采用割集法和与／或图产生可行装配顺序，给出了二级圆柱齿轮减速器装配工艺规划的应用实例。     

机械产品非线性装配顺序规划研究

提出了用于机械产品非线性装配顺序规划的关系码矩阵模型，通过编码将所有的装配关系信息集成于一个简单矩阵中，用连接模式，即二进制数模板技术来识别装配时零件的几何约束。基于关系码矩阵模型给出了规划可行的装配顺序，检测装配过程中零件的稳定性及识别子装配的计算方法，使用遗传算法搜索并优化装配顺序，用复合表表示遗传算法中个体的装配顺序。最后，通过一个实例验证了该方法的有效性。     

基于子装配识别的产品拆卸序列生成研究

对含有较多零件的复杂产品拆卸方法作了讨论,提出了一种基于子装配识别的拆卸序列生成算法。根据装配连接图和干涉图识别出子装配体,然后将子装配体看作一个零件,采用装配经验知识与几何推理相结合的方法生成子装配体序列,最后以一个装配实例说明了算法的有效性。     

基于零件约束的装配规划技术研究

装配规划是虚拟装配中的关键技术。这里将装配序列的分层规划方法和拆卸法求解装配序列的方法相结合，在研究产品装配层次结构的基础上，以子装配体为研究对象，利用零件之间的装配约束信息求解零件的拆卸方向和顺序，进而实现产品的装配顺序和路径规划。     

Design automation and optimization of assembly sequences for complex mechanical systems

Assembly sequence design for a mechanical system can have significant impact on manufacturing cost and product quality. Traditionally, such a design process is largely based on experience and best practices, often ineffective and non-optimal as the system becomes complex. This paper proposes a new, systematic method for automatic assembly sequence design and optimization. Key elements include assembly modeling, sequence planning, locating scheme optimization, dimensional quality evaluation, and optimization. First, a directed graph and an assembly matrix are employed to describe the assembly relation of a system. Then, the feasible assembly sequences are generated through layered subassembly detection of adjacency matrices, filtered by engineering constraints. To evaluate quickly the assembly quality and compare the influences of different locating point schemes, a linear 3D variation propagation analysis model with deterministic locating principle is introduced. The optimal locating scheme is then selected using a genetic algorithm with the least variation propagation. Finally, the assembly dimensional quality for different sequences is evaluated and the optimal assembly sequences are achieved through genetic algorithms. A case of automotive body side assembly is presented to illustrate the whole methodology.     

Simulated annealing and ant colony optimization algorithms for the dynamic throughput maximization problem

In many industries, inspection data is determined to merely serve for verification and validation purposes. It is rarely used to directly enhance the product quality because of the lack of approaches and difficulties of doing so. Given that a batch of subassembly items have been inspected, it is sometimes more profitable to exploit the data of the measured features of the subassemblies in order to further reduce the variation in the final assemblies so the rolled yield throughput is maximized. This can be achieved by selectively and dynamically assembling the subassemblies so we can maximize the throughput of the final assemblies. In this paper, we introduce and solve the dynamic throughput maximization (DTM) problem. The problem is found to have grown substantially by increasing the size of the assembly (number of subassembly groups and number of items in each group). Therefore, we resort to five algorithms: simple greedy sorting algorithm, two simulated annealing (SA) algorithms and two ant colony optimization (ACO) algorithms. Numerical examples have been solved to compare the performances of the proposed algorithms. We found that our ACO algorithms generally outperform the other algorithms.     

Scheduling algorithms for an air conditioner manufacturing system composed of multiple parallel assembly lines

This paper focuses on a scheduling problem in a manufacturing system composed of multiple parallel assembly lines. There are multiple orders to be processed in this system, and each order is specified by the product type, the number of products to be processed, and the due date. Each product is composed of two types of subassemblies, one unit of an external subassembly and one or more units of an internal subassembly. In the system, the parallel assembly lines are not identical, and certain lines are designated for certain product types. We present heuristic algorithms for the scheduling problem with the objective of minimizing total tardiness of orders. For an evaluation of the performance of the suggested algorithms, computational experiments are performed on a number of problem instances and results show that the suggested algorithms work better than the method used in a real manufacturing system.     

面向三维CAD的装配顺序建模系统研究

研究了面向三维CAD模型的装配顺序建模的原理、步骤和方法,先归纳出常见子装配体特征,再根据这些特征进行人机交互分析以划分装配顺序;开发了基于开目三维CAD的几何模型信息和三维CAD装配仿真模块的装配顺序建模系统;给出了使用该系统实现装配顺序规划的实例。     

模块化机器人几何误差分析及参数辨识研究

为解决模块化机器人重构后误差的快速补偿问题,对模块化机器人几何误差来源进行分析,将其划分为模块参数误差和模块间装配参数误差.基于指数积公式和齐次变换对关节模块、连杆模块及模块间装配位姿进行数学描述,建立关节-连杆子装配体的实际运动学模型.给出一种基于精密球和外部测量的模块参数及模块间装配参数辨识方法,完成子装配体运动学...     

Control of an Assembly System with Processing Time and Subassembly-Type Uncertainty

We address the problem of controlling an assembly system in which the processing times as well as the types of subassemblies are stochastic. The quality (or performance) of the final part depends on the characteristics of the subassemblies to be assembled, which are not constant. Furthermore, the processing time of a subassembly is random. We analyze the trade-off between the increase in the potential value of parts gained by delaying the assembly operation and the inventory costs caused by this delay. We also consider the effects of processing time uncertainty. Our problem is motivated by the assembly of passive and active plates in flat panel display manufacturing. We formulate the optimal control problem as a Markov decision process. However, the optimal policy is very complex, and we therefore develop simple heuristic policies. We report the results of a simulation study that tests the performance of our heuristics. The computational results indicate that the heuristics are effective for a wide variety of cases.     

复杂产品装配的分层有向图建模方法

由于复杂产品零部件数量大,后续装配顺序规划难度较大.用传统的方法建模,容易造成割集数量随着零件数量的增长而呈爆炸式地增长.针对这种问题,提出利用装配单元划分的方法进行分层;在每层中,用嵌套式的有向图表示装配定位关系信息的分层有向图模型.研究了分层有向图模型的建立和表示方法,并以某型机翼翼盒为实例予以应用验证.     

基于模糊聚类的产品合理子装配划分

将模糊数学中的一些概念和理论引入产品合理子装配的划分之中 ,提出了产品零件集合的直积空间上的模糊紧密度关系、模糊装配连接图、模糊装配矩阵、产品模糊聚类等概念 ,并给出了基于产品模糊聚类的产品合理子装配划分方法。     

A Novel Representation Scheme for Disassembly Sequence Planning

The representation of the disassembly sequence is a key issue in maintenance planning. It involves a highly constrained combinatory problem, which is coupled with varying start and end nodes. These start and end nodes are dependent upon the nature of a maintenance task. In this paper, different representation and modelling schemes for disassembly sequence planning are first reviewed. Then, a novel representation scheme for disassembly sequence, which is generic and can be used to represent both the geometrical and precedence constraints dynamically in product disassembly, is proposed. Based on such a representation scheme, the process for the determination of possible disassembly sequences can be simplified. By taking into consideration disassembly constraints, the optimal disassembly sequence in relation to the component to be maintained (target component) can be quickly derived. This is achieved by pruning the search space of disassembly sequences, grouping related components into subassemblies, and identifying free components to facilitate disassembly oper-ations. Subsequently, the optimal disassembly sequence in relation to the target component can be obtained using genetic algorithms. In this manner, the disassembly sequences for a complex product comprising a relatively large number of components can be derived within a short time. A case study is used to illustrate the effectiveness of the representation scheme. Comparisons are made using the same case study with the AND/OR graph representation and the Petri net approach for disassembly sequence planning. The results show that the proposed representation scheme is simpler and is more efficient than the rest. ID="A1" Correspondence and offprint requests to: Dr L. P. Khoo, School of Mechanical and Production Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798. E-mail: mlpkhoo@nyu.edu.sg     

基于质量特征产品装配顺序规划的逆向推理算法探究

在Petri网柔性装配系统装配顺序规划中引入装配质量要素,并以装配零件的装配自由度,装配作业后稳定性,装配零件配合精度对装配质量的影响作为基本因子,提出装配质量置信度概念,解决柔性装配系统装配规划中装配质量及其定量化问题。根据装配形成的产品在Petri网装配状态图中表示为一个最终库所的特点,应用改进B树模型,提出仅以变迁信息的产品装配顺序规划Petri网逆向推理算法,简化装配顺序规划推理过程,对于多个变迁均可生成最终成品的情况,亦给出装配顺序规划的解决方案,并以摩托车发动机的装配为例,证明该算法是可行的。     

一种基于子装配体识别的装配顺序生成

装配体表达为装配连接图，在识别子装配的基础上，给出了简化装配体装配顺序的确定方法。文中对子装配的识别原则和装配顺序、装配方向的确定等问题进行了详细的阐述。     

面向协同装配规划的装配单元规划方法

作为复杂产品装配规划的有效求解策略,协同装配规划将复杂产品的装配规划结构按照装配要求分解为简单的子装配规划结构,子装配规划结构的最优或次优装配序列采用成熟的装配规划方法求解,通过装配序列合并得到产品的整体装配序列。协同装配规划所要解决的首要问题是装配规划结构分解,针对这个问题,提出装配单元规划方法。首先从产品可装配性的角度分析了影响装配单元规划的装配设计和装配工艺约束,并对归类的部分装配约束进行量化;进而基于模糊层次分析法生成装配单元决策图,采用最小生成树算法生成候选装配单元。同时,建立装配关系干涉矩阵对候选装配单元进一步验证,生成装配过程中互不干涉的装配单元。以一款电动机装配体为例验证提出的方法,结果表明该方法是一种求解装配规划结构分解问题的有效方法。     

An effective integration approach toward assembly sequence planning and evaluation

An integration strategy for assembly sequence planning and sequence scheme evaluation is proposed. This strategy can be used to plan a reasonable assembly sequence, to optimize a sequence scheme, and to predict whether a collision will occur between the assembly tool and assembled components by considering factors like target components and assembly resources. A hybrid method is presented for assembly sequence modeling that combines human-computer interactive operations to manually build a hierarchical assembly sequence main model and a hybrid graph method to automatically generate sub-assembly sequence schemes of the main model. An optimization algorithm based on time-cost is introduced to handle a best candidate components selection. This relieves the problem of limited capability found when handling large size assembly models with traditional methods. The essential issues involved in system implementation are discussed as well; these include a representation method for the assembly consequence model, an optimization model of assembly sequence planning, and an object-oriented system architecture model employed with multi-agent technology for visually evaluating the assembling process. This system, KM computer-aided assembly process planning, KMCAAPP, has been developed on the basis of our previous work, KMCAD3; KMCAAPP uses the presented approach. KMCAAPP can be integrated with CAD model from KMCAD3D. A case study shows that the presented approach can use large CAD assembly models and delivers a feasible and effective way to integrate the assembly sequence planning process with scheme evaluation by visually evaluating the assembling process. This allows the identification of design errors in a timely manner and mitigates economic loss.