Cross-training policies and team performance

Labour flexibility is an important issue in the design and development of teams. By means of an analytical study this paper investigates the impact of cross-training on team performance. Four cross-training policies are distinguished and compared according to their effects on important performance measures, such as the load of the bottleneck worker and the number of newly used qualifications seen in various situations. These measures indicate a team's effectiveness and efficiency. Furthermore, they are related to psychological, social and organizational aspects of team functioning. A task assignment heuristic serves as a tool for comparing the cross-training policies. This is applied in an experimental study in which the team situation varies with respect to the cross-training policy, the level of absenteeism, and the variation in the mix of orders. It is shown that a worker-oriented cross-training policy, which attempts to spread multi-functionality evenly among employees, performs well. This policy offers the opportunity to shift work among employees to keep the load of the bottleneck worker low. The required coordination effort for allocating workers to tasks is also relatively low. In line with previous research, this study shows a diminishing positive effect of expanding the level of labour flexibility. The coordination effort required to apply additional flexibility appears to increase linearly with the amount of additional cross-training. The diminishing positive effect and the linearly increasing coordination effort suggest that managers should critically consider the level of labour flexibility in worker teams.     

Impact of lean interventions on time buffer reduction in a hospital setting

This paper focuses on performance changes stemming from a series of lean interventions in a medical laboratory. This research is one of the first to link a series of lean interventions and performance over time. In a mixed-method case study, six years of patient-related throughput data, retrieved from a laboratory computer database, are analysed. Three distinct periods with significant differences in throughput time performance can be distinguished. Semi-structured interviews were held to investigate the lean interventions preceding the performance changes. Given the long-term nature of the study, the event history calendar method was applied to enhance the respondents’ recall and reliability. A single lean intervention, among the hundreds that took place, was supposed to cause the main reduction in throughput times. It concentrated on improving process flow through the removal of batching, a source of artificial variability. A later major intervention, the introduction of flow-focused machinery, had mixed effects and initial performance gains were not sustained. The results show that ongoing series of interventions do not always lead to ongoing performance improvements in terms of throughput times but support theories emphasising the importance of variability reduction.     

Performance comparison of virtual cellular manufacturing with functional and cellular layouts in DRC settings

This study investigates the performance of virtual cellular manufacturing (VCM) systems, comparing them with functional layouts (FL) and traditional, physical cellular layout (CL), in a dual-resource-constrained (DRC) system context. VCM systems employ logical cells, retaining the process layouts of job shops. Part family-based scheduling rules are applied to exploit the benefits of group technology while retaining the flexibility and functional synergies of the job shop. Past studies of VCM have been based entirely on single-resource-constrained (SRC) systems, i.e. as purely machine-limited systems, assuming that resources such as labour and tooling do not restrict the output. However, given the fact that labour forms a second major constraining resource, and many of the advantages associated with cellular manufacturing are derived from labour flexibility, it becomes necessary to extend the research to DRC systems. In this study, we assume several levels of labour flexibility in all three systems, in addition to other relevant factors such as lot size, set-up reduction, and labour assignment rules. It is shown that VCM can outperform efficiently operated FL and CL in certain parameter ranges, as preliminary research has shown so far. However, it is shown that CL tends to outperform both VCM and FL in the parameter ranges customarily advocated for CL, namely, low lot sizes, adequate levels of set-up reduction, cross training of workers, and worker mobility within cells.     

Photorealistic real‐time rendering of spherical raindrops with hierarchical reflective and refractive maps

Synthesizing rainy images is a common challenge found in film, game engines, driving simulators, and architectural design. Simulating light transport through a raindrop's optical properties is a view‐dependent problem, and large quantities of raindrops are required to produce a plausible rainy scene. Accurate methods for rendering raindrops exist but are often off‐line techniques that are cost prohibitive for real‐time applications. Most real‐time solutions use textures to approximate the appearance of moving raindrops as streaks. These approaches produce plausible results but do not address the problem of temporal effects such as slow‐motion or paused simulations. In such conditions, streak‐based approximations are not suitable, and proper raindrop geometry should be considered. This paper describes a straight‐forward approach for rendering raindrops in such temporal conditions. The proposed technique consists of a preprocessing stage that generates a raindrop mask and a run‐time stage that renders raindrops as screen‐aligned billboards. The mask's contents are adjusted on the basis of the viewpoint, viewing direction, and raindrop position. The proposed method renders millions of raindrops at real‐time rates in current graphics hardware, making it suitable for applications that require high‐visual quality without compromising performance. Copyright © 2011 John Wiley & Sons, Ltd.     

A multi-objective procedure for labour assignments and grouping in capacitated cell formation problems

A hierarchical methodology for the design of manufacturing cells is proposed, which includes labour-grouping considerations in addition to partmachine grouping. It is empirically driven and designed for an interactive decision environment, with an emphasis on fast execution times. The method synthesizes the capabilities of neural network methods for rapid clustering of large partmachine data sets, with multi-objective optimization capabilities of mathematical programming. The procedure includes three phases. In Phase I, part families and associated machine types are identified through neural network methods. Phase II involves a prioritization of part families identified, along with adjustments to certain load-related parameters. Phase III involves interactive goal programming for regrouping machines and labour into cells. In machine grouping, factors such as capacity constraints, cell size restrictions, minimization of load imbalances, minimization of intercell movements of parts, minimization of new machines to be purchased, provision of flexibility, etc. are considered. In labour grouping, the functionally specialized labour pools are partitioned and regrouped into cells. Factors such as minimization of hiring and cross-training costs, ensuring balanced loads for workers, minimization of intercell movements of workers, providing adequate levels of labour flexibility, etc. are considered in a pragmatic manner.     

On the who-rule in Dual Resource Constrained (DRC) manufacturing systems

The who-rule is a labour allocation rule used in labour and machine-limited dual resource constrained (DRC) systems. A who-rule selects one worker out of several workers to be transferred to a work centre. By means of a practical instance, the paper shows that the who-rule plays a role in the daily practice of worker assignment. Previous simulation studies, however, either have not mentioned the who-rule or have treated it as a fixed factor. The present study will explore the need of including the who-rule in simulation studies. It will describe in detail at what decision moments the who-rule needs to be applied in simulation. Further, it will explore the flow time effects of applying different who-rules in several DRC systems where labour flexibility is limited and workers differ with respect to task proficiencies, the number of skills they possess and the loads of work centres for which they are responsible. As with other labour allocation rules, the impact of the who-rule depends on the specific DRC shop modelled. The paper will show that the average labour utilization, and the types and extent of worker differences, determine the impact of the who-rule on shop performance.     

Performance evaluation of family-based dispatching in small manufacturing cells

In many practical instances, the choice of whether to apply family-based dispatching or not can be decided per machine. The present paper explores the impact of the location of family-based dispatching, load variations between machines and routing of jobs on the flow time effect of family-based dispatching. These factors are explored in small manufacturing cells with and without labour constraints. An industrial case motivates the study. A simulation study is performed to assess the impact of these effects. The results show that shop-floor characteristics such as routing and load variation impact the decision where to locate family-based dispatching in manufacturing cells without labour constraints. By contrast, the effect of family-based dispatching is much less vulnerable to shop-floor characteristics in cells with labour constraints. Since workers are the bottleneck in these cells, it becomes less important at what machine the set-up time involving a worker is reduced. In general, there seems to be a trade-off between the positive effect of applying family-based dispatching at a (bottleneck) machine and the possible negative effect of the more irregular job arrivals at subsequent machines. The results further indicate that family-based dispatching is more advantageous in cells with labour constraints than in cells without labour constraints, when both types of manufacturing cells have comparable machine utilizations.     

Design of virtual manufacturing cells: a mathematical programming approach

In this paper, a new type of virtual cellular manufacturing (CM) system is considered, and a multi-objective design procedure is developed for designing such cells in real time. Retaining the functional layout, virtual cells are addressed as temporary groupings of machines, jobs and workers to realize the benefits of CM. The virtual cells are created periodically, for instance every week or every month, depending on changes in demand volumes and mix, as new jobs accumulate during a planning period. The procedure includes labor grouping considerations in addition to part-machine grouping. The procedure is based on interactive goal programming methods. Factors such as capacity constraints, cell size restrictions, minimization of load imbalances, minimization of inter-cell movements of parts, provision of flexibility, etc. are considered. In labor grouping, the functionally specialized labor pools are partitioned and regrouped into virtual cells. Factors such as ensuring balanced loads for workers, minimization of inter-cell movements of workers, providing adequate levels of labor flexibility, etc. are considered in a pragmatic manner.     

Planning for Waterway Renewal: Balancing Institutional Reproduction and Institutional Change

ABSTRACT

Modern waterway networks are ageing and need to be renewed, yet the institutional context in the waterway sector is averse to change because of path dependencies. Waterway renewal requires actors to navigate between institutional reproduction and change. Applying an innovative framework for analysing institutions in a case study of the Dutch national waterways, we mainly find instances of institutional reproduction, which turns waterway renewal into a technical and financial exercise. However, institutional change becomes increasingly evident through a new functional-relational path, suggesting that planning for waterway renewal also entails reconsidering novel waterway configurations and incorporating neighbouring spatial developments.     

Virtual manufacturing cells: A taxonomy of past research and identification of future research issues

This paper reviews prior research in the area of virtual manufacturing cells. A virtual manufacturing cell (VMC) is a group of resources that is dedicated to the manufacturing of a part family, though this grouping is not reflected in the physical structure of the manufacturing system. Distinguishing such groups in the production control system offers the possibility of achieving the advantages of cellular manufacturing in non-cellular manufacturing systems. The advantages may include improved flow performance, higher efficiency, simplified production control, and better quality. The paper reviews the previous publications on virtual manufacturing cells, to determine the methods and scope of present research. This results in a comprehensive framework which identifies the underlying principles of VMCs and classifies the different VMC concepts. It is shown that virtual manufacturing cells can significantly improve the performance of manufacturing systems. Based on the comprehensive review, many future research issues and high-impact research areas are also identified.