Expert Enhanced Coloured Stochastic Petri Net and its application in assembly/disassembly

This article comprises of an Expert Enhanced Coloured Stochastic Petri Net (rule base system, or RBS) for modelling and analysing assembly/disassembly systems. RBSs are an Enhanced High-level Petri net extended with Close-World-Assumption (CWA). Traditional Petri nets can be used to model RBSs containing explicitly described knowledge. The main focus was is to facilitate and analyse the process planning activities of assembly/disassembly. The advantages of the new modelling approach were: (1) consideration of the non-desirable events, (2) occurrence of assembly/disassembly tasks with regard to colour of the tokens and utilization of probability concept to determine feasible steps, (3) establishing a relationship among components by means of arc labels, and (4) deeper insight into the assembly/disassembly process using high- and low-level petri nets.     

An approach for estimating the end-of-life product disassembly effort and cost

Disassembly is the process of physically separating a product into its parts or subassembly pieces. The overall economics of the disassembly process, and in particular the cost to disassemble, is still not well understood. In this paper our goal is to introduce a methodology that will support and facilitate the economic analysis of the disassembly activity. We present a multi-factor model to compute the disassembly effort index (DEI) score, which is representative of the total operating cost to disassemble a product. The DEI score can then be compared against the projected market value of the disassembled parts and subassemblies to get an economic measure. To develop the DEI model we surveyed a variety of commercial disassembly facilities. Based on these surveys we propose a multifactor weighted estimation scheme. The seven factors are (i) time, (ii) tools, (iii) fixture, (iv) access, (v) instruct, (vi) hazard, and (vii) force requirements. The DEI scale is defined in the 0 to 100 range. This range is assigned on a weighted basis to each of the seven factors. For each factor, an independent utility scale is formulated, using the assigned range as anchors. Using a conversion scale the DEI score is used to derive an estimate of disassembly cost and the disassembly return on investment. An example is presented.     

A comprehensive end-of-life strategy decision making approach to handle uncertainty in the product design stage

This study employs fuzzy logic to evaluate uncertain component end-of-life (EOL) options in the design stage. Determining EOL strategies during the product design stage can be complex. For example, EOL strategies for retired bicycle components are various and may change with geographic location. Thus, adopting fixed EOL strategies in the product design stage may not always be appropriate; the element of uncertainty should be considered. Limited research has examined uncertainty of EOL strategies during the design stage. Moreover, the evaluation of EOL strategies in a comprehensive manner has not been shown in a realistic case study. These facts motivate this investigation. Fourteen evaluation criteria are used to generate a comprehensive framework for assessing seven EOL strategies. The evaluation process generates the likelihood for each of these strategies by aggregating fuzzy set operations and a left–right fuzzy ranking method. Using SUMPRODUCT calculation for these weights/probabilities and input sustainability value (i.e., cost, environmental impact and labor time), expected values are derived to represent the sustainability values for each EOL strategy. A Technique-for-Order-of-Preference-by-Similarity-to-Ideal-Solution (TOPSIS) based method is employed to identify the appropriate EOL strategy for each component/product. A refrigerator is used as a case study to illustrate the methodology. This study addresses the uncertainty involved in identifying an EOL strategy for a specific product component during the design stage through the use of fuzzy logic. The method closes a gap in the current EOL strategy assessment criteria and introduces a comprehensive evaluation framework to capture multiple strategic perspectives by incorporating 14 key evaluation criteria.     

一种基于Petri网的网络服务兼容性分析方法

针对目前基于网络服务业务过程执行语言(BPEL)的网络服务合成方法缺乏网络服务的兼容性分析机制,不能保证基于网络服务技术的业务过程正确执行的问题,建立了一种能从形式化的角度描述网络服务的接口交互情况的基于Petri网的多元工作流组合网模型,提出了一种能更快地获得网络服务可用性结果的网络服务兼容性判断算法.最后,提出了基于该算法的原型系统架构.     

Disassembly sequence generation: A Petri net based heuristic approach

The generation of a set of optimal or near-optimal disassembly sequences is an important task associated with the study of disassembly planning. This task encapsulates actions at the required disassembly depth to reach maximum net revenue while satisfying economic constraints. The Petri net modelling, combined with heuristic search procedures developed in this study, offers an efficient procedure for disassembly sequence generation. The heuristic generates and searches a partial reachability graph to arrive at an optimal or near-optimal disassembly sequence based on the firing sequence of transitions of the Petri net model. The proposed methodology reduces the search space in two areas: (1) pruning the disassembly tree (DT) and, (2) selective tracking of the reachability graph. The efficacy of the proposed methodology is demonstrated by using two examples from the literature.     

A fuzzy logic based approach to reliability improvement estimation during product development

During early stages of product development process, a vast amount of knowledge and information is generated. However, most of it is subjective (imprecise) in nature and remains unutilized. This paper presents a formal structure for capturing this information and knowledge and utilizing it in reliability improvement estimation. The information is extracted as improvement indices from various design tools, experiments, and design review records and treated as fuzzy numbers or linguistic variables. Fuzzy reasoning method is used to combine and quantify the subjective information to map their impact on product reliability. The crisp output of the fuzzy reasoning process is treated as new evidence and incorporated into a Bayesian framework to update the reliability estimates. A case example is presented to demonstrate the proposed approach.     

Configuration analysis to support product redesign for end-of-life disassembly

End-of-life product disassembly is an important process that makes the parts of a product available for different material and part recycling processes at end of its useful life. However, the efficiency of the disassembly process greatly affects the economics of meeting the environmental goals set for the product. An important determinant of the efficiency of disassembly is the product configuration. Therefore, it is essential for the designer to assess these implications of the configuration while designing a product for end-of-life disassembly. In this paper, a formal model, called the Configuration-Value (CV) model, is proposed to evaluate and analyse the effect of configuration on disassembly. The model focuses on the rate of value extraction during the disassembly process. The model is used to identify the critical bottlenecks in the configuration, to help the designer to identify the design changes that need to be made to improve the product 'disassemblability'. An example is presented to demonstrate the application of the proposed model.     

Two FMS scheduling methods based on Petri nets: A global and a local approach

We are interested in the Flexible Manufacturing System (FMS) scheduling problem. Different methods have been explored to solve this problem and to master its combinatorial complexity, which is NP-hard in the general case. In this paper we will give two different scheduling methods based on Petri nets. The first one tends to solve the general scheduling problem (acyclic schedule) using the Constraint Programming method to avoid exhaustive search. The second method is a dedicated cyclic scheduling method. The aim is not to compare the methods' performances (computation time, results' quality) because they do not solve exactly the same problem, but to compare their application domains in terms of parts number.     

基于Petri网的系统评价和优化模型

采用层次Petri网的方法,模拟在存在多种不同长度标准的情况下轧制系统的生产过程,对不同长度参数下系统运行性能进行评价和参数优化。实验结果表明,在解决对CIMS运行中的性能评价和参数优化问题上,Petri网的方法相对于纯数学方法更为有效。     

A heuristic approach to the formulation of manufacturing strategy

In this paper an attempt is made to define and analyse the critical subsystems relationships within a manufacturing strategy. For this purpose the whole production function is described as a pressurized Venturi system in an effort to clarify complex input-output and control relationships within a typical batch manufacturing environment. The value of scheduling methods is also discussed with attention directed towards critical value added stages and throughput time in the manufacturing process.     

A solution approach to the disassembly line balancing problem in the presence of task failures

In this paper, we discuss the disassembly line balancing problem in the presence of task failures (DLBP-F). There are precedence relationships among disassembly tasks and the tasks must be completed within a given time, determined by the demand in a given period. However, if a task (or more than one task) cannot be performed because of some defect, some or all of the remaining tasks may be disabled due to the precedence relationships among tasks. This may result in various complications in the flow of workpieces on the disassembly line, e.g. early-leaving, self-skipping, skipping, disappearing and revisiting workpieces. We discuss these complications and highlight their effects on the disassembly line. The problem is to assign tasks to workstations such that the effect of the defective parts on the disassembly line is minimized. This paper presents a solution procedure to the DLBP-F. An example is provided to illustrate the approach.     

Quantitative evaluation of product disassembly for recycling

This paper presents a method for evaluating the ease-of-disassembly of products. Its primary use is in designing products for recycling, but it also facilitates consideration of servicing and maintenance, and making environmentally-related decisions. The method is developed and discussed in the context of relatively small products that can be disassembled by a seated person using hand-held tools. The evaluation procedure is centered around a spreadsheet-like chart and uses a catalog of task difficulty scores. The scores were derived from work-measurement analyses of standard disassembly tasks, and provide a means of identifying weaknesses in the design and comparing alternatives quantitatively. The structure of the evaluation chart and the derivation of difficulty scores are explained, followed by a demonstration of analyzing a computer central processing unit. The limitations of the method and future extensions are outlined.     

基于Petri网和语义网络的虚拟维修过程建模与应用

针对当前虚拟维修过程中模型庞大,维修流程不可反复,部件间关系描述混乱等问题,论文提出一种Petri网和语义网络结合的过程建模方法——TJ(Training Join)网。TJ网上层利用语义网络对部件进行层次结构分解和资源规范聚类,实现子部件间逻辑互联;下层运用Petri网的变迁和触发规则提炼出Petri网元素模型,提高模型的通用性和建模效率。同时模型中的状态收集模块可实现部件属性状态间信息共享。最后,以虚拟维修平台中飞机电子设备架的维护为例,验证了TJ网的有效性。     

A strategy to determine DEM parameters for spherical and non-spherical particles

In Discrete element method (DEM) simulations the choice of appropriate contact parameters is significant to obtain reasonable results. Particularly, for the determination of DEM parameters for non-spherical particles a general straightforward procedure is not available. Therefore, in a first step of the investigation here, methods to obtain the friction and restitution coefficients experimentally for single particles [Polyoxymethylene (POM) spheres and quartz gravel] will be introduced. In the following, these predetermined DEM coefficients are used as initial values for the adjustment of bulk simulations to respective experiments. In the DEM simulations, the quartz gravel particles are represented by non-spherical particles approximated by clustered spheres. The best fit approximation of the non-spherical particles is performed automatically by a genetic algorithm. In order to optimize the sliding and rolling friction coefficients for DEM simulations, the static and dynamic angle of repose are determined from granular piles obtained by slump tests and rotating drum experiments, respectively. Additionally, a vibrating plate is used to obtain the dynamic bed height which is mainly influenced by the coefficient of restitution. The adjustment of the results of the bulk simulations to the experiments is conducted automatically by an optimization tool based on a genetic algorithm. The obtained contact parameters are later used to perform batch-screening DEM simulations and lead to accurate results. This underlines the applicability of the in parts automated strategy to obtain DEM parameters for particulate processes like screening.     

应用Petri网改进基于故障树的诊断方法

故障树是表示故障发生和故障传播关系的一种逻辑模型,基于故障树诊断方法的广泛应用由于实际故障树分析过程的ＮＰ困难问题而受到妨碍。而Ｐｅｔｉｒ网是一种特殊的有向网,适合于描述故障的传播关系。本文提出了两种基于Ｐｅｔｒｉ网的改进方法,与下行法相比,用该方法寻找最小割集和最小路集能有效地节省上计算时间,提高推理速度和效率;最后还应用Ｐｉｔｒｉ网的状态方程分析方法提出了基于Ｐｅｔｒｉ网的故障监测和诊断方法。     

Modelling and planning of the disassembly processes using an enhanced expert Petri net

A sound disassembly Petri net model for the effective planning of disassembly processes and tasks is outlined. Owing to the unmanageable complexity associated with modelling of the disassembly processes and tasks, it becomes essential to have a more powerful Petri net model developed by incorporating the concepts of expert system, knowledge representation techniques, etc. Disassembly task planning at high and low levels can easily be represented by proposed high- and low-level expert Petri net. An algorithmic approach is also suggested for evaluating the end-of-life values of a product. These values are used to determine an optimal disassembly sequence and it is incorporated in the expert disassembly Petri net. A proposed expert enhanced high-level coloured disassembly Petri net is empowered to express such details vividly. The application of the proposed expert enhanced high-level coloured disassembly Petri net model is demonstrated through the sample disassembly of a flashlight.     

基于规则对象Petri网的柔性制造系统建模

针对FMS建模中存在的问题，通过分析FMS的组成和活动特点，提出了规则对象Petri网的建模方法。该方法集中了Petri网和面向对象技术的优点，并融系统决策规则子模型中。利用规则对象Petri网，建立了FMS的资源对象模型、动态行为模型和调度决策模型，为设计、分析和调度控制提供了有效的工具。     

Modelling,control and simulation of an IC wafer fabrication system: A generalized stochastic coloured timed Petri Net approach

This study presents a generalized stochastic coloured timed Petri net(GSCTPN) to model an IC wafer fabrication system. According to the GSCTPN, it models the dynamic behaviours of the IC fabrication system, such as loading, reentrant processing, unloading and machine failure. Furthermore, modular and synthesis techniques are used to construct a large and complex system model. The two major sub-models are the Process-Flow Model and the Transportation Model. The Transportation Model incorporates a simple motion-planning rule and a collision avoidance strategy to solve the variable speed and traffic jam problems of vehicles. This work also describes a simulation based performance analysis and schedule adjustment. To demonstrate the promise of the proposed work, this study makes actual Taiwanese IC wafer fabrication systems the target plant layout for implementation.     

一种确定超滤在线反冲洗周期的新方法

采用离散数据分析方法-斜率变点分析法对无反冲洗条件下超滤短期运行时的膜通量进行分析,得出起滤膜污染过程中的"临界时间",从而在理论上指导超滤运行过程中的最佳在线反冲洗周期;随后对超滤在不同反冲洗周期运行的过程进行试验验证,结果发现最佳反冲洗周期与超滤"临界时间"保持一致,实验结果支持了这种确定在线反冲洗周期的方法,该方法对超滤的实际应用具有一定意义.     

A multi-model approach to determine early manufacturing parameters for small-data-set prediction

Constructing an accurate prediction model from a small training data set is an important but difficult task in the field of forecasting. This is because when the data size is small, the incomplete data may mean that the model produced cannot sufficiently represent the true data structure or cause the model training to be overfitted. To address this issue, this paper presents an approach that combines multiple prediction models to extract data information in multiple facets. In the multi-model approach, a compromise weight method is proposed to determine the relative reliability of each of the prediction model. The methods used include multiple regression, artificial neural network, and support vector machines for regression. A thin-film transistor liquid crystal display manufacturing case study is used to illustrate the details of this research. The empirical results not only show that the proposed multi-model can reduce the manufacturing variation and increase the production yield, but also can propose a robust and reliable parameter interval to the online engineers in the early manufacturing stage.