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.     

Performance Pay and Offshoring

In this paper, we construct a North–South general equilibrium model of offshoring, highlighting the nexus among endogenous effort‐based labor productivity and the structure of wages. Offshoring is modeled as international transfer of management practices and production techniques that allow Northern firms to design and implement performance compensation contracts. Performance–pay contracts address moral hazard issues stemming from production uncertainty and unobserved worker effort. We find that worker effort augments productivity and compensation of those workers assigned to more offshorable tasks. An increase in worker effort in the South, caused by a decline in offshoring costs, an increase in worker skill, or a decline in production uncertainty in the South, increases the range of offshored tasks and makes workers in the North and South better off. An increase in Southern labor force increases the range of offshored tasks, benefits workers in the North, and hurts workers in the South. International labor migration from low‐wage South to high‐wage North shrinks the range of offshored tasks, makes Northern workers worse off and Southern workers (emigrants and those left behind) better off. Higher worker effort in the North, caused by higher worker skills or lower degree of production uncertainty, decreases the range of offshored tasks and benefits workers in the North and South.     

Verifiable wage offers and recontracting: effect on wage and consumption profiles

This paper analyzes the effect of recontracting and matching verifiable wage offers on the intertemporal structure of contract wage and consumption profile for a two-period economy. A contract firm provides specific training for a worker during the first period, which increases his productivity if he stays in the second period, but the worker may quit to accept an alternative wage offer after a successful search. Wage offers are private to the worker but can be presented to the contract firm for matching. This paper shows that when capital markets are imperfect and wage offers are verifiable, the contract firm recontracts and matches any wage offers the worker receives up to the second-period productivity. The ex ante contract wage profile will be flat. Inefficient quits will be eliminated and there will be complete ex ante consumption smoothing. It is significant to note that the result of rising wage profile derived in numerous contract models is fragile with respect to assumptions on mechanism of interfirm labor mobility.     

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.     

Job mobility and careers in firms

This paper presents a theoretical model that combines employers learning about worker productivity, human capital acquisition, job-assignment and resolution of worker uncertainty regarding disutility of work from a job, to show how widely documented findings on both wage and promotion dynamics and turnover can be captured in a single set-up. Specifically we show how our model can capture results such as; probability of turnover decreases with labor market experience, wage changes during job changes is more in earlier periods, serial correlation in wages and probability of promotion increases in wages, amongst others.     

做好统计基础工作,服务科学发展

经济全球化环境下,各级政府、各界人士对统计信息的依赖程度日益突显。如何保障统计数据真实准确,是社会各方面都十分关注的问题。健全的统计制度、正确的统计方法、可靠的统计资料,是提高统计信息的可信度,提升统计工作的重要意义的保障。每位统计工作者应当以务实求真的态度对待本职工作,抓好统计基础工作,服务科学发展。     

区域自动气象观测站报警系统

中尺度自动气象观测站（以下简称自动站）报警系统通过采集分析自动站数据,在地图上直观地显示自动站各气象要素值;通过自动站数据分析自动站的运行状态,当出现自动站运行异常或出现重要天气现象时,以声音、颜色、文字等形式发出警报,以提醒用户注意自动站出现重要情况。同时,中尺度自动气象观测站报警系统提供了自动站数据的二次入库功能,对采集到的自动站数据进行分拆归类,存入标准数据库,以供数据二次开发利用,并在系统中集成了数据查询和基本统计对比功能。     

Overlapping operations in material requirements planning

Material requirements planning (MRP) is a planning and information system that has widespread application in discrete-parts manufacturing. The purpose of this article is to introduce ideas that can improve the flow of material through complex manufacturing systems operating under MRP, and that can increase the applicability of MRP within diverse manufacturing environments.MRP models the flow of material by assuming that items flow from work station to work station in the same batches that are used in production. That is, once work starts on a batch of a certain item at a certain work station, the entire batch will be produced before any part of the batch will be transported to the next work station on its routing plan. Clearly, efficiency can be increased if some parallelism can be introduced. The form of parallelism investigated here is overlapping operations.Overlapping operations occurs when the transportation of partial batches to a downstream work station is allowed while work proceeds to complete the batch at the upstream work station. The potential efficiencies to be gained are the following:

• Reduced work-in-process inventory

• Reduced floor space requirements

• Reduced size of transfer vehicles

Additional costs may accrue through additional cost of transportation of partial batches and through additional costs of control.Some MRP software vendors provide the data processing capability for overlapping operations. However, the user is given little or no guidance on overlapping percentages or amounts. It is our intent to provide a simple, robust technique to MRP users who would like to overlap operations and gain some or all of the above efficiencies.An optimal lot-sizing technique is derived by considering a generic two work station segment of a manufacturing system. Under the assumptions of constant demand and identical production rates, a cost function that considers setup costs, inventory holding costs and transportation costs is derived. This cost function is minimized subject to the constraint that the production batch is an integer multiple of the transfer batch. We solve for the optimal production batch, the optimal transfer batch, and the integer number relating them. Solutions are obtained as closed form, easy to-evaluate formulas.By introducing more parallelism, overlapping operations can reduce lead time. However, this will not happen without modification of MRP logic to accommodate such reduced lead time. We derive a formula that shows how a significant lead time compression can easily be obtained and implemented in MRP.We consider an example to illustrate the application of the technique on typical data from the electronics industry. The outcome showed a cost savings of approximately 22.5% over the standard MRP approach.Overlapping operations allows the applicability of MRP to an increasing number of situations that are not modeled faithfully by conventional MRP logic. Three such situations that occur often are the following:

• Limited size of transfer vehicles dictate that several transfers should be planned.

• Lead time requirements prohibit nonoverlapped operations.

Our analysis suggests how to accommodate these difficult practical situations into MRP.Overlapping operations in material requirements planning provides an enhancement that allows wider applicability, shortened lead times, and lower total costs. It may be applied selectively to any two work stations where it is deemed appropriate. Due to the structure of the cost function, it is possible to make the transfer lot-sizing decisions independent of the production lot-sizing decisions. Therefore, significant improvements can be made through overlapping with minimum disruption to the existing MRP system machinery. It is our conviction that overlapping operations is an important concept that can and will impact MRP. We suggest the approach presented here as a systematic way to implement overlapping.     

Gas system failure rate

Gasunie buys and sells gas. This paper is about calculating the failure rate of the gas transport system of Gasunie in the Netherlands. The pipes in the network are connected at certain stations which may operate at degraded levels due to technical problems. The transport system, modelled as an optimization problem, needs to be checked for feasibility for every configuration of the degradation levels at all stations in order to see whether the system fails or not. The discrete probability distributions of the degradation levels at every station in the network are given. The number of possible combinations of degradation levels is huge and the computations for the feasibility of the gas network are computer-intensive. This paper presents a new algorithm for approximating this rate and it is parsimonious in actually checking for feasibility.     

LEADERSHIP DECISION-MAKING: AN EMPIRICAL TEST OF THE VROOM AND YETTON MODEL

Despite the common belief that greater worker participation in decision-making in industry will increase productivity and worker job satisfaction, the empirical evidence has been most contradictory. As a result, theories have been developed which now suggest that the degree of participation should depend on the particular problem or situation facing the leader. For the practising manager the problem has been the identification of the situation and the subsequent selection of an appropriate decision method. One answer to this problem is the Vroom and Yetton model which gives explicit directions to the leader as to how to categorize the problem and select the appropriate decision method. This paper describes our research to examine the external validity of this model. The sites chosen for the research were forty-seven owner-operated, small, non-unionized, franchised firms, where the leaders had the power and authority to effect organizational outcomes. On these various sites, there was relatively high similarity with regard to the technology employed, tasks performed, number of levels of hierarchy and the external environments. It was found that those leaders who were in high agreement with the Vroom and Yetton model had workers with higher productivity and higher satisfaction with supervision than those leaders who were in low agreement with the model. These findings give strong support for the Vroom and Yetton model. The implication of these findings on the training and selection of managers, and on further research, are discussed.     

Decomposing productivity patterns in a conditional convergence framework

In this study we examine regional data on per worker GDP, disaggregated at sectoral level, by focusing our interest on the role of differences in the sectoral composition of activities, and in productivity gaps that are uniform across sectors, in explaining the catching-up process, which is realized through physical and human capital as well as technological knowledge accumulation. Our objective is to investigate how much of the interregional inequality in aggregate productivity per worker is imputable to each component. A methodology for identifying and analyzing sources of inequality from a decomposed perspective is developed in the growth framework by combining a shift-share based technique and a SUR model specification for the conditional-convergence analysis. The proposed approach is employed to analyze aggregate interregional inequality of per worker productivity levels in Italy over the period 1970–2000. With respect to the existing empirical results, our approach provides a more comprehensive and detailed examination of the contribution of each identified component in explaining the regional productivity gaps in Italy. It is argued that region-specific productivity differentials, uniform across sectors, explain a quite large share of differences in productivity per worker. However, sectoral composition plays a non negligible role, although decreasing since the end of 1980s, and very different productivity patterns emerge within geographical areas.

Profit,productivity, and profit-sharing

This study is an investigation of the effect of profit-sharing on labor productivity. When monitoring labor performance is costly for management, a regular wage/salary contract is insufficient to induce profit-maximizing behavior from the worker. The authors demonstrate that when this profit-maximizing behavior can be induced only through profit-sharing, a linear profit-sharing program will increase productivity and the welfare of both management and labor. The benefit from profit-sharing is increasing up to the point where the utility of additional income is offset by the negative utility of extraordinary effort (working harder or providing higher quality work). The income effect, i.e., the change in negative utility of extraordinary effort given a change in income, can potentially either increase or decrease the point at which the income-effort tradeoff-reaches zero.     

The role of performance appraisals in motivating employees

Workers' rewards and career perspectives often depend on how their supervisors perceive their performance. However, evaluating a worker's performance is often difficult. We develop a model in which a worker is uncertain about his own performance and about his supervisor's ability to assess him. The supervisor gives the worker a performance appraisal aiming to affect both the worker's self‐perception and his own credibility in assessing the performance. We examine how performance appraisals affect the worker's future performance. Our model's predictions are consistent with empirical findings. Supervisors give, on average, “too” positive appraisals, and both positive and negative feedback can (de)motivate workers.     

Are we ‘sharing’ or ‘gig-ing’? A classification system for online platforms

There is a growing debate about the nature and extent of platform control over workers. Companies claim they are merely ‘matchmakers’ while labour advocates argue that these organisations exercise granular control over workers. Blending the fields of information science and labour relations, this article develops a classification system of sequential control to delineate between ‘high control’ and ‘low control’ platforms. In doing so, this article provides a theoretical method to distinguish ‘sharing’ versus ‘gig’ platforms and argues that worker autonomy—how platforms foreclose worker choice—can be used to understand platform control.     

拓宽选站思路 加快建站速度

文中从项目进度管理的角度,通过对基站选站的工作进行研究,针对选站工作提出选站的一些思路及解决方法。     

一次自动站运行故障解决方法探讨

对一次自动站运行故障解决方法、解决过程中遇到的问题进行阐述,得出地面测报业务人员在日常工作中应注意:按时进行自动站数据、台站参数备份;按时对自动站进行维护;实时对分钟及正点数据检查,加强学习提高自动站维护技能和计算机水平。并为出现同类型故障提供一种可参考的解决方法。     

地面最高温度人工站和自动站相差大的成因和处理方法

文章就玉林站地面最高温度值观测中出现的人工站观测与自动站观测的地面最高温度相差较大的成因进行了分析,提出了对基层台站具有实用价值的处理办法,对台站的实际工作有一定的借鉴意义。     

基于FTP的地基微波辐射计数据实时传输系统

本系统实现了地基微波辐射计单站与中心站的通信。将各个辐射计站点的观测资料、状态参数、定标数据和报警信息等数据实时上传至中心站计算机,方便中心站对管辖范围内的地基微波辐射计单站工作状态的控制,并对各站数据综合处理;同时各单站计算机也可以从中心站计算机中下载其他站点的数据信息,实现各单站计算机与中心站计算机之间的数据资源共享。在程序实现上,以VB6.0为开发平台,利用Microsoft Internet Transfer Control6.0等多种控件。文章给出了本数据传输系统的网络拓扑图、各模块的功能设置及实现功能使用的关键函数。主要功能包括:用户登录、文件存放路径设置、文件上传、文件下载。     

The Relationship Between Employee Fit Perceptions,Job Performance,and Retention: Implications of Perceived Fit

Meaningful work has become an increasingly important job outcome for individuals in recent years. Studies indicate that many employees lack experienced meaningfulness in their work and that organizations have not done a good job at creating meaningful and emotionally satisfying work experiences for employees. A person–job fit approach to meaningful work and employee retention is described that consists of matching individual self-concept with job tasks and behaviors. It is proposed that this self-concept–job fit will be strongly related to meaningful work. It is also proposed that meaningful work is related to important outcome variables valued by organizations, such as increased worker performance and employee retention. Path analysis supports the proposed relationships. Implications for human resource management activities and future research are discussed.