A cost-effective approach to stochastic line balancing with off-line repairs

The layout of production facilities is an important determinant of the productivity potential of a manufacturing enterprise. It is particularly important in the design of assembly lines where the objective is to assign tasks to work stations in such a way as to minimize total variable production costs.Early approaches to the line balancing problem assumed known constant task times and sought a line layout which would produce the desired output with the fewest number of work stations, which is equivalent to minimizing idle time. Studies have shown that task times are random variables, therefore the cost of task incompletion must be considered a part of total production cost. Incompletion cost will be the cost of repairing or completing tasks which cannot be completed within the cycle time after the item has reached the end of the assembly line.This paper describes a methodology for designing approximately minimum cost paced assembly lines under conditions of random task times and off-line repair of incompleted tasks. Task times are assumed to be normally distributed random variables with known means and variances. The methodology consists of heuristically identifying a large number of feasible balances for each of which total costs are computed. The line design with the lowest total is retained as the “best.”In order to evaluate candidate line layouts, a total cost model is developed. Total cost is the sum of normal operating cost—which is simply a function of the number of work stations—and the cost of repairing products containing incompleted tasks. Because this latter cost is a random variable for a given balance, the expected value is used to evaluate a candidate layout. The cost associated with one or more workers exceeding the cycle time is the product of the probability of this happening and the expected cost of off-line repair.The heuristic method for generating feasible balances builds work stations from continually updated lists of precedence satisfying tasks. Qualifying tasks are added to the station as long as the probability of the station exceeding the cycle time remains below a pre-specified threshold. The methodology requires systematically varying this threshold to permit a lowest total cost solution to emerge. The process of generating a large number of balances for a particular threshold is efficient. Evaluating the total costs of the resulting balances takes the majority of the computational time.An experiment was conducted in order to compare the above cost-effective methodology with a purely deterministic approach and a commonly used industrial approximation method for dealing with task time variability. The experiment applied the three methods to four problems from the literature under a variety of repair cost and time variance conditions. In 21 of the 24 cases studied, the stochastic method produced a lower cost balance than the two alternatives. In the remaining 3 cases, the deterministic method also found the lowest cost balance. The stochastic method saved an average of 22.5 percent in total operating cost over the deterministic method and 8.4 percent over the industrial method.The experiment clearly showed the need to explicitly consider task time variability in arriving at a line balance. The stochastic approach of this paper offers large potential savings with no risk of obtaining a less desirable balance and so should be considered for implementation whenever there is a variation in task times. Even for large-scale problems, the computational cost is infinitesimal in the context of assembly line balancing, where very small improvements in productivity can mean substantial increments to profitability.     

电动三轮车装配流水线的平衡分析与改进

在生产线平衡原理及改善方法的基础上,以电动三轮车装配流水线为研究对象,运用工作研究的方法分析工艺流程,测定流水线各工位的作业时间,找出瓶颈工位;运用"5W1H"提问技术和ECRS(取消、合并、重排、简化)原则对流水线进行分析与改进。通过对比分析,改进后该流水线大大节省了空间和人力,工位减少6个,工人减少11个,与此同时,平衡率提高27.6%。     

装配生产线平衡的改善

本文将精益生产有关理论运用在企业生产管理中,通过实例阐述了装配生产线平衡改善的基本原则和方法,并对装配生产线的平衡进行了分析和改善.     

基于FLEXSIM的某生产线物流仿真优化

通过收集某企业挖掘机装配流水线的工艺路线、工序设备处理率、生产节拍和生产线平衡等方面数据,利用FLEXSIM物流仿真软件构建装配流水线仿真模型,比较装配流水线优化前后指标,发现优化后的装配线具有生产节拍时间缩短、瓶颈工序缓解、生产线产能平衡等优点。     

基于时间和成本的加工装配线物流平衡方法

本文提出一种基于时间和成本的加工装配线上物流的规划方法，在对现有的生产装配线重新分配工件的同时保证最大效益的改善，执行花费／效益分析，同时该平衡方法借助于数据库和电子表格的联合应用，可以在短时间内完成。文中以哈锅阀门股份有限公司生产线的改造为例，详细介绍了该方法的使用。计算结果表明，这种物流平衡方法提供了企业一种效率高，费用低的现有加工装配线改造方法。     

A cost evaluation method for dynamic line balancing

A procedure is presented for calculating stochastic costs, which include operator (labor) and inventory costs, associated with dynamic line balancing. Dynamic line balancing, unlike the traditional methods of assembly and production line balancing, assigns operators to one or more operations, where each operation has a predetermined processing time and is defined as a group of identical parallel stations. Operator costs and inventory costs are stochastic because they are functions of the assignment process employed in balancing the line, which may vary throughout the balancing period, and the required flow rate. Earlier studies focused on the calculation of the required number of stations and demonstrated why the initial and final inventories at the different operations are balanced.The cost minimization method developed in the article can be used to evaluate and compare the assignment of operators to stations for various assignment heuristics. Operator costs and inventory costs are the components of the cost function. The operator costs are based on the operations to which operators are assigned and are calculated for the entire work week regardless of whether an operator is given only a partial assignment which results in idle time. It is assumed that there is no variation in station speeds, no learning curve effect for operators' performance times, and no limit on the number of operators available for assignment. The costs associated with work-in-process inventories are computed on a “value added” basis. There is no charge for finished goods inventory after the last operation or raw material before the first operation.The conditions which must be examined before using the cost evaluation method are yield, input requirements, operator requirements, scheduling requirements and output requirements. Yield reflects the output of good units at any operation. The input requirement accounts for units discarded or in need of reworking. The operator requirements define the calculation of operator-hours per hour, set the minimum number of operators at an operation, and require that the work is completed. The scheduling requirements ensure that operators are either working or idle at all times, and that no operator is assigned to more than one operation at any time. The calculation of the output reflects the yield, station speed, and work assignments at the last operation on the line.An application of the cost evaluation method is discussed in the final section of the article. Using a simple heuristic to assign operators, the conditions for yield, inputs, operators, scheduling, and output are satisfied. The costs are then calculated for operators and inventories.In conclusion, the cost evaluation method for dynamic balancing enables a manager to compare the costs of assigning operators to work stations. Using this method to calculate the operator and inventory costs, a number of different heuristics for assigning operators in dynamic balancing can be evaluated and compared for various configurations of the production line. The least cost solution procedure then can be applied to a real manufacturing situation with similar characteristics.     

基于遗传算法的装配线平衡问题研究

文中针对装配线平衡问题,提出了一种基于可行作业序列的多种群遗传算法。该算法依据可行作业序列产生初始种群,并据此构造交叉、变异算子,以保证后代种群都是可行解;而且多种群的遗传算法,扩大了搜索的空间范围,所以可以有效的避免局部最优的情况发生,而且还能增强算法的运行效率。文章在最后,用实例进行了运行效果的验证。     

某减速器装配线平衡的精益改造研究

从装配线平衡和精益生产的概念出发,以某企业减速器装配生产线为实例,介绍了精益生产理论在改造装配线平衡问题上的应用。考虑装配生产现场,用鱼刺图分析了影响装配线平衡的各种制约因素,并系统的应用全员"5S"活动,制定标准作业时间,连续流改造以及团队互助协作等精益手段对原装配生产线进行改造。改造结果显示,装配线各工作站作业负荷趋于均衡,整体生产效率得以提高,改造效果明显。     

基于DELMIA的汽车装配线建模与仿真

汽车装配线直接决定了汽车生产的效率,因此,对汽车装配线进行建模与仿真,优化装配流程十分必要。基于DELMIA的DPM(Digital Process for Manufacturing)模块,对汽车装配线的装配序列规划、装配干涉以及装配路径规划进行研究,按规划的工艺流程对总装线进行模拟仿真,分析装配线的平衡率,通过仿真结果验证该装配线的可达性、可行性以及装配线的人因工效性。文中研究工作对优化及改善汽车装配过程,缩短工艺规划时间,实现汽车装配线的流水化具有一定指导意义和应用价值。     

工作研究在按摩椅组件装配方法改善中的应用

基于工作研究的原理和方法,对某健康产品有限公司按摩椅组件的装配方法进行了分析改善。首先对按摩椅组件的装配过程进行了流程程序分析,运用5W1H和ECRS方法,通过流程化改善减少了装配过程中的搬运和等待;其次对按摩椅组件的装配过程关键瓶颈工序进行了双手作业分析,通过合理摆放工具和物料,消除了作业浪费。通过对按摩椅组件装配过程的两次改善,装配产能提升了26.7%,单个工人的效率提高了42.9%。     

Statistical Inference in Nonparametric Frontier Models: The State of the Art

Efficiency scores of firms are measured by their distance to an estimated production frontier. The economic literature proposes several nonparametric frontier estimators based on the idea of enveloping the data (FDH and DEA-type estimators). Many have claimed that FDH and DEA techniques are non-statistical, as opposed to econometric approaches where particular parametric expressions are posited to model the frontier. We can now define a statistical model allowing determination of the statistical properties of the nonparametric estimators in the multi-output and multi-input case. New results provide the asymptotic sampling distribution of the FDH estimator in a multivariate setting and of the DEA estimator in the bivariate case. Sampling distributions may also be approximated by bootstrap distributions in very general situations. Consequently, statistical inference based on DEA/FDH-type estimators is now possible. These techniques allow correction for the bias of the efficiency estimators and estimation of confidence intervals for the efficiency measures. This paper summarizes the results which are now available, and provides a brief guide to the existing literature. Emphasizing the role of hypotheses and inference, we show how the results can be used or adapted for practical purposes.     

HRM in dynamic environments: Exploitative,exploratory, and ambidextrous HR architectures

Abstract

The current economic crisis has brought to the fore the need for firms to deal with ambiguity and complexity. Hence, firms need a specific balance between exploration and exploitation in order to keep pace with varying and changing environmental conditions. Hitherto, there is limited research that has examined the nexus of HR architectures, ambidexterity, and environmental dynamics. In this conceptual paper we ask: How do HR architectures serve as a means of balancing exploitative and exploratory learning in different dynamic environments? We explain how exploratory, exploitative, and ambidextrous HR architectures with their embedded HRM systems on the business unit level enable organizations to meet different environmental requirements. Thus, firms in which heterogeneous demands for flexibility and for innovation co-exist need to develop internally differentiated HR architectures. In particular, we elucidate how critical the organization’s ability is to connect different HRM systems to create an ambidextrous HR architecture to find an appropriate balance between exploration and exploitation.     

产品拆卸线的影响因素及平衡问题研究

制造企业对废旧产品进行回收再利用,是节约资源和保护环境的有效方式。产品拆卸是实现废旧产品回收再利用的重要手段,是实现产品生命周期完整性与封闭性的必要环节。本文详尽分析了产品拆卸线的影响因素,并将产品拆卸线与产品装配线作了对比;然后针对产品拆卸线的平衡问题,构建了多目标优化模型。     

企业生产物流系统的建模与仿真

采用Petri网建立了某微型汽车厂总装车间的生产物流模型,并用VisualBasic语言对其生产线进行仿真。从而发现在生产不同的车型时,总装车间的三条流水线的节拍不一致,在生产空调车时,为了满足生产的平衡性,不仅要细化超工位装配的工序,而且需要对车间的人员安排进行调整。     

Data envelopment analysis with stochastic variations in data

The mathematical programming-based technique data envelopment analysis (DEA) has often treated data as being deterministic. In response to the criticism that in most applications there is error and random noise in the data, a number of mathematically elegant solutions to incorporating stochastic variations in data have been proposed. In this paper, we propose a chance-constrained formulation of DEA that allows random variations in the data. We study properties of the ensuing efficiency measure using a small sample in which multiple inputs and a single output are correlated, and are the result of a stochastic process. We replicate the analysis using Monte Carlo simulations and conclude that using simulations provides a more flexible and computationally less cumbersome approach to studying the effects of noise in the data. We suggest that, in keeping with the tradition of DEA, the simulation approach allows users to explicitly consider different data generating processes and allows for greater flexibility in implementing DEA under stochastic variations in data.     

Some extensions of techniques to handle non-discretionary factors in data envelopment analysis

Data Envelopment Analysis (DEA) assumes, in most cases, that all inputs and outputs are controlled by the Decision Making Unit (DMU). Inputs and/or outputs that do not conform to this assumption are denoted in DEA asnon-discretionary (ND) factors. Banker and Morey [1986] formulated several variants of DEA models which incorporated ND with ordinary factors. This article extends the Banker and Morey approach for treating nondiscretionary factors in two ways. First, the model is extended to allow for thesimultaneous presence of ND factors in both the input and the output sets. Second, a generalization is offered which, for the first time, enables a quantitative evaluation ofpartially controlled factors. A numerical example is given to illustrate the different models.The editor for this paper was Wade D. Cook.     

Stochastic leader–follower DEA models for two-stage systems

Data envelopment analysis (DEA) is a non-parametric approach for measuring the relative efficiencies of peer decision making units (DMUs). In recent years, it has been widely used to evaluate two-stage systems under different organization mechanisms. This study modifies the conventional leader–follower DEA models for two-stage systems by considering the uncertainty of data. The dual deterministic linear models are first constructed from the stochastic CCR models under the assumption that all components of inputs, outputs, and intermediate products are related only with some basic stochastic factors, which follow continuous and symmetric distributions with nonnegative compact supports. The stochastic leader–follower DEA models are then developed for measuring the efficiencies of the two stages. The stochastic efficiency of the whole system can be uniquely decomposed into the product of the efficiencies of the two stages. Relationships between stochastic efficiencies from stochastic CCR and stochastic leader–follower DEA models are also discussed. An example of the commercial banks in China is considered using the proposed models under different risk levels.     

DEA-R: ratio-based comparative efficiency model, its mathematical relation to DEA and its use in applications

We propose a new mathematical model for efficiency analysis, which combines DEA methodology with an old idea—Ratio Analysis. Our model, called DEA-R, treats all possible ratios “output/input” as outputs within the standard DEA model. Although DEA and DEA-R generate different summary measures for efficiency, the two measures are comparable. Our mathematical and empirical comparisons establish the validity of DEA-R model in its own right. The key advantage of DEA-R over DEA is that it allows effective integration of the model with experts’ opinions via flexible restrictive conditions on individual “output/input” pairs.     

汽车发动机预装线装配平衡改进研究

为提高已经投产的汽车总装生产线的生产平衡率,研究发动机生产线生产平衡改进研究。以现有生产节拍和各个工位操作工时作为基础,运用生产线平衡的基本概念,对现有生产线进行优化。首先确定优化目标,通过工序同期化优化,减少生产岗位,从而提高部分岗位负荷,提高生产平衡率,为企业解决实际问题,节约人力、场地等资源。     

Currently practiced formulations for the assembly line balance problem

New formulations for the assembly line balance problem are proposed based on interviews and surveys of practicing engineers. These formulations are the basis for a model in goal programming form. A branch-and-bound algorithm is developed which can solve the model for an optimum solution. Computational studies show that computer run time is very modest for moderate size problems.Interviews and a survey of practicing engineers were used to develop a list of goals or constraints germane to the assembly line balance problem. These included minimizing working areas or employees, making sure tasks assigned to a station do not exceed the cycle time, and adhering to sequence constraints. These constraints are included in most traditional models. However, additional goals were mentioned. These included avoiding changes in workload assigned to a work area, adhering to layout requirements of the plant, making combinations of tasks interesting, avoiding the combination of physiologically demanding tasks, etc.The additional goals above are incorporated in a new formulation for the assembly line balance problem. This formulation is in goal programming form. The goal programming model attempts to minimize deviations from goals. If deviations are necessary, lowest ranked goals are violated first. The objective function of the model is based on an ordinal ranking of goals only. The survey mentioned above showed that engineers did not find it difficult to rank the importance of goals.The proposed goal programming model is a mixed integer linear program. Previous studies have shown that cutting plane and implicit enumeration techniques are inferior to branch-and-bound algorithms. A branch-and-bound method, called GoalOriented Algorithm for Line Balance (GOAL), is developed to solve the formulations proposed in the paper.GOAL was computationally tested with 50 problems. These problems varied in size from 4 to 35 tasks. One of the problems was an engine cradle assembly problem encountered by an automobile manufacturer. Computer run times appeared reasonable. For example, the engine cradle problem 35 tasks) required only 16.3 seconds CPU on the DEC PDF at California State University, Northridge. GOAL's execution time appeared linearly proportional to the number of tasks required for most problems.