Release policies for assembly systems

We consider a production system consisting of several fabrication lines feeding an assembly machine. The machines in the fabrication lines and at assembly are assumed to have general processing time distributions. Releases to the system are governed by the kanban release mechanism. We first derive a heuristic for the throughput of this system by replacing the assembly system under kanban release by an equivalent system under CONWIP release and by making use of an approximation for the throughput of a CONWIP assembly system (Duenyas, 1992). Comparisons with simulation show that this heuristic is robust over a wide range of conditions.

We also address the issue of which release mechanism is more effective in obtaining a desired throughput level with the minimum possible work-in-process inventory level in the system. We present both analytical and simulation results to demonstrate that the CONWIP release policy seems to be a more effective release policy for assembly systems.     

Estimating the throughput of a cyclic assembly system

We consider a production system consisting of several fabrication lines feeding an assembly station. The machines in the fabrication lines and at assembly are assumed to have general processing time distributions. Releases to the system are governed by the CONWIP protocol. We model this system as an assembly-like queue and develop approximations for the throughput of the system. Comparisons with simulations show that this approximation is robust over a wide range of conditions. Finally, we observe that throughput tends to be higher when machines with higher mean processing times and/or higher variances are in fabrication rather than assembly.     

Simultaneous balancing and sequencing of mixed-model parallel two-sided assembly lines

Growing interests from customers in customised products and increasing competitions among peers necessitate companies to configure their manufacturing systems more effectively than ever before. We propose a new assembly line system configuration for companies that need intelligent solutions to satisfy customised demands on time with existing resources. A mixed-model parallel two-sided assembly line system is introduced based on the parallel two-sided assembly line system previously proposed in the literature. The mixed-model parallel two-sided assembly line balancing problem is illustrated with examples from the perspective of simultaneous balancing and sequencing. An agent-based ant colony optimisation algorithm is proposed to solve the problem. This algorithm is the first attempt in the literature to solve an assembly line balancing problem with an agent-based ant colony optimisation approach. The algorithm is illustrated with an example and its operational procedures and principles are explained and discussed.     

A simulation study of CONWIP assembly with multi-loop in mass production,multi-products and low volume and OKP environments

This paper studies the performance of constant work-in-process (CONWIP) assembly system with multi-loop in mass production, multi-products and low volume and one-of-a-kind production (OKP) environments using simulation. We propose five basic design patterns of CONWIP loop and develop eight control policies of CONWIP loop based on the design pattern for standard assembly system. The performance of developed loop policies is evaluated in three production environments. In particular, control policies of CONWIP loop in OKP environment provide a valuable reference for OKP shop floor controlling. A heuristic algorithm of searching work-in-process (WIP) upper bound, the deadlock phenomenon in CONWIP assembly system and suggestion are introduced specifically. The summary of CONWIP installation guidelines in the mixed assembly system can apply CONWIP theory to practise.     

Hybrid systems for planning and optimization of virtual assembly

Virtual assembly is the simulation of parts assembly processes by computer, analysing, evaluating and optimizing the feasibilities and procedures of assembly. It can thus avoid the potential problems and risks from designing to assembling. In this way, we can achieve the global optimization of the products and timely respond to the needs of the market. This paper presents a modelling framework for virtual assembly paths design and optimization of two objects on the basis of a class of hybrid system, which is applicable in many manufacturing environments. We propose an elementary hybrid machine containing time-driven and event-driven dynamics. We describe in detail a method of assembly paths design. The objective of optimization is evaluated in terms of time in the transition dynamics so as to make the problem more tractable. An explicit algorithm for deriving optimal assembly policies is developed. The optimal results indicate the feasibility and efficacy of the model and control algorithms.     

LOT SIZING IN ASSEMBLY SYSTEMS WITH RANDOM COMPONENT YIELDS

We investigate the problem of choosing optimal lot sizes in assembly systems when component manufacturing or procurement yields, and possibly assembly yields, are random. For a single-period setting, we analyze two models. The first has components with identical yield distributions and costs, random demand and an imperfect assembly stage. We analyze this two-stage problem, and highlight the implications of the results for the single-stage case where the final product is just a set of good components. The second model is a single-stage system where components have non-identical yield distributions and costs. We analyze a two-component system with known demand, identify conditions for concavity, and derive the optimality conditions.     

ASRS sizing for recreating automotive assembly sequences

Since a mixed model assembly line's efficiency depends on the sequence of jobs moving down the line, manufacturers spend considerable effort optimizing the sequence of jobs entering the plant. In automotive assembly plants however, repair loops and parallel stations scramble the sequence before it reaches the final assembly stage. Many automotive assembly plants use an automatic storage and retrieval system to revamp the scrambled sequence before final assembly. One plant even goes so far as to reconstruct the original sequence by completely undoing the sequence scrambling. We derive a relationship between the sequence scrambling information, the variety of model-colour configurations, and the size of the automatic storage and retrieval system needed to reconstruct the initial sequence. We enunciate this new ASRS sizing problem actually facing industry, show how to model it, present a solution approach, and demonstrate the approach on actual sequence scrambling data from an automotive assembly plant.     

Throughput and average inventory in discrete balanced assembly systems

We consider an assembly system consisting of two input machines and an assembly machine, with finite buffers between each input machine and the assembly machine, where all machines operate at deterministic and equal rates, and input machines are subject to random failures. Under the assumption that probabilities of failure and repair are constant during each cycle time (i.e., failure times and repair times are geometric random variables), we derive the steady-state average throughput and inventories for the system.     

Order-oriented cooperative sequencing optimisation in multi-mix-model assembly lines

Order-oriented products assembly sequence among different assembly lines becomes a critical problem for mass customisation manufacturing systems. It significantly affects system productivity, delivery time, and manufacturing cost. In this paper, we propose a new approach to extend the traditional products sequencing from mixed model assembly line (MMAL) to multi-mixed model assembly lines (MMMALs) to obtain the optimal assembly sequence with the objectives of minimising consumption waviness of each material in the lines, assembly line setup cost, and lead-time. A multi-objective optimisation algorithm based on variable neighbourhood search methods (VNS) is developed. We perform an industrial case study in order to demonstrate the practicality and effectiveness of the proposed approach.     

Impact of work teams: a comparison study of assembly cells and assembly line for a variety of operating environments

This research compares assembly lines with different cellular, team working environments. Organization of an assembly system using cells requires worker flexibility where each worker is allowed to help his or her co-workers in the same cell and often to undertake a number of different tasks within the cell. We compare two different cellular systems with an unpaced, serial assembly line. The manufacturing systems are initially compared through an exploratory Markovian approach. Subsequently, the relative performance levels of the systems are examined across a variety of operating environments using simulation models. Operating environments vary based on shop size, setup times and processing time variances. The results indicate the general superiority of the cellular systems over the assembly line. However, some interesting observations are drawn for cases where the assembly line outperforms the cells. One of the cases is where workers realize substantial benefits in terms of performing their tasks in less time due to specialization on the tasks. The other scenario is where working in teams make the overall completion of the tasks more inefficient compared to working individually. Specific cross-over points are analyzed where the assembly lines start performing better than the assembly cells under these scenarios. The conclusions highlight guidelines for practicing managers on the most appropriate system under a given set of operating conditions.     

跨尺度微小型零件的测量与装配

针对跨尺度微小型零件的精密装配中显微视觉视场狭小与零件的特征尺寸跨度较大相矛盾的问题,研究了跨尺度零件的位姿检测技术,基于高、低倍显微视觉单元研制了自动装配系统,系统采用模块化体系结构及先看后动的装配控制模式.提出局部特征拼接法实现了跨尺度零件的定位测量,使用标定尺对系统坐标系之间的误差角进行了标定,采用参考基准法辅助对显微视觉单元切换后的装配基准进行定位.设计测试模板对系统测量精度进行了验证,结果显示高倍显微视觉单元的同轴度测量精度优于1.5 μm,平行度精度优于1μm.利用研制的装配系统进行了装配实验,实验结果表明,关键零件的装配精度满足工艺要求.该装配系统可稳定、可靠地完成跨尺度微小型零件的自动装配.     

An examination of routeing flexibility for small batch assembly of printed circuit boards

In this paper, we examine and quantify the effects of introducing new processing flexibility in the rapidly changing environment of printed circuit board (PCB) assembly. Specifically, we perform experiments designed to establish the benefits and determine the limitations associated with the introduction of routeing flexibility. We examine system behaviour as batch sizes are reduced in an environment characterized by moderate set-up requirements. We further demonstrate that the performance of flexible routeing policies in this environment is adversely affected by larger batch sizes and that the introduction of routeing flexibility leads to improved system performance in small batch assembly.     

船体分段模块装配工艺决策研究

针对船体装配工艺设计自动化程度低，影响船舶建造周期和建造质量等问题，设计了分段模块的装配单元决策系统，建立了分段模块装配信息模型，基于模糊数学理论，应用模糊聚类方法实现了分段模块装配工艺的自动编制．实例表明，该方法是合理的和可行的．应用该方法在较高的装配层次上实现了船体模块装配工艺的制定，为船舶模块化生产提供了有效的工具．     

Free-space optical module configuration using a guide-frame assembly method

A new assembly method is described for easy construction of optical modules consisting of guide frames, spacer frames, and a housing frame. This method is used to assemble a two-dimensional optical-fiber collimator and a digital discrete correlator, which are fundamental parts of free-space optical computing systems. We show that a multistage optical system can be constructed simply by stacking of several optical functional blocks. Moreover, these compact modules do not need a conventional optical bench, they are compact, and assembly time is reduced. We demonstrated by experiment that the accuracy of optical modules assembled with this method is within the specifications of the optical system.     

Investigating scaling effects on virus capsid-like self-assembly using discrete event simulations

As self-assembled nanotechnology tackles increasingly complicated structures, biological self-assembly can teach us a great deal about the challenges of more complicated self-assemblies relative to the simpler systems accessible in current practice. The present study uses computer simulations of spherical assemblies inspired by virus capsids to understand the challenges artificial self-assembly systems will face as they approach biological levels of complexity. We quantify system complexity by two parameters-the total size of the completed structure in assembly monomers and the size of the first stable assembly nucleus. Simulations on a set of five model systems capturing a range of values for both parameters reveal several obstacles to extrapolating experience with simple systems to more complex ones. Assemblies of greater size result in total yields and assembly fidelities that are substantially more sensitive to the system parameters of intersubunit binding rates and to concentrations than are those of simpler assemblies. Larger nuclei partially mitigate these effects. Conversely, large assemblies have overall assembly rates with reduced sensitivity to system parameters, a feature that is also only partly mitigated by large nuclei. These changes can be partially understood by theoretical models based on nucleation processes, but such theory itself becomes less informative for the larger systems. We close with a consideration of mechanisms by which these obstacles may be overcome in actual viral systems.     

Fully automatic flexible assembly of an electromechanical timer group†

The article describes a fully automatic assembly system for a group of electromechanical timers. The layout of the flexible assembly system corresponds to the structure of the product: the most important components are motor assembly (line 1), drive gear assembly (line 2), bearing plate assembly (line 3), program dial assembly (line 4), final assembly (line 5). Already more than 60 timer variants are produced.     

AUTOMATED PROCESS PLANNING FOR PRINTED CIRCUIT CARD ASSEMBLY

Printed circuit card assemblies form the core of a vast array of contemporary manufactured products. The technologies for assembling printed circuit cards require a hierarchy of complex decisions for grouping card types and processes, staging components at assembly machines, arranging feeders, and sequencing placement operations. This paper is motivated by the largely unmet needs of industrial process planners for computer aids. Our objective is to develop a framework for the printed circuit card assembly process planning problem and to assess the current state of the research on appropriate models and solution methods. We first provide an overview of the essential elements of printed circuit card terminology, assembly technologies, and assembly system operations. Then we propose a decision hierarchy, survey the published literature, and identify needs for future research.     

产品可装配性评价系统建模及装配优化的研究

面向装配的设计(DFA)的研究和实践，对实施并行工程具有重要的意义，目前得到了广泛的重视。笔者依据将可装配性评价系统做为一个模块集成到整个虚拟装配支持系统中去的思路。从系统工程的观点出发，以装配单元为研究对象，提出并构造了可装配性评价的指标体系，建立了可装配性评价系统模型，并探讨了最优装配方式的求解策略和方法。     

可装卸式加油设备的管路系统装配设计研究

由于在不同装配空间的管路系统装配结构存在相似性和差异性,可装卸式加油设备的管路系统装配设计十分复杂．针对该问题,提出了基于谱系聚类法的管路系统装配空间聚类方法,使聚类后的每类装配空间能够通用多套已装配好的管路系统．通过定义类的典型装配空间及装配半径,使新设计的加油设备按其管路系统装配空间尺寸,迅速地找到符合要求的已装配好的管路系统．最后,以对一些典型的装配空间进行聚类及如何应用聚类结果为例,验证了该方法的有效性和合理性．     

Comparison of order-fulfilment performance in MTO and MTS systems with an inventory cost budget constraint

The make-to-order or make-to-stock decision is an important issue faced by firms in many industries. In the existing literature, optimisation models comparing the cost of making product to stock versus making it to order have been widely developed. Motivated by the problem faced by a machinery company, we examine the issue from a different perspective and formulate service-maximisation models with inventory cost budget constraints. We compare and analyse order-fulfilment performance measures for the two different production control systems. The goal is to identify the key influencing factors and devise a production strategy that maximises service performance subject to resource constraint. We show that the MTO production control system is preferred in the production system with low component values and long component processing times and high value and short lead time in the final assembly stage; while the MTS production control system is applicable to the production system with high component values and short component processing times and little value and long lead time in the final assembly stage.