Cross-training workers in Dual Resource Constrained systems with heterogeneous processing times

In this paper, we explore the effect of cross-training workers in Dual Resource Constrained (DRC) systems with machines having different mean processing times. By means of queuing and simulation analysis, we show that the detrimental effects of pooling (cross-training) previously found in single resource constrained (SRC) heterogeneous systems are also apparent in DRC heterogeneous systems. Fully cross-training workers in DRC heterogeneous systems is only beneficial if the differences between mean processing times are not too large, otherwise cross-training should be pursued within homogeneous subgroups of machines. Due to the limited machine availability, DRC systems are unable to use some of the potential assignment flexibility from cross-trained workers (pooled queues) that can be used in SRC systems. However, it appears that this restriction in the DRC system may even improve the system mean flow (waiting) time performance compared to the SRC system for relatively large differences in processing time. Finally, in fully flexible multiple server queuing systems, restricting the assignment flexibility by applying a decentral when-rule (i.e. a commonly used labour assignment rule in practice and research) instead of a central when-rule also seems to improve the mean flow time performance under processing time differences.     

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.     

基于分组差错控制的轨道交通ATS信号可靠组播技术研究

为解决轨道交通中ATS信号组播丢包问题,拟定一种基于分组差错控制的可靠组播传输协议。该协议不需要路由器的支持,在每个接收节点都定义一个申请重传权值列表,根据组播丢包情况,动态更新接收节点的权值列表,从而为接收节点选择最佳的重传请求处理节点,以提高数据重传效率。仿真实验表明：在多个分组中,将该文所提出的基于分组差错控制的可靠组播传输协议应用于轨道交通中ATS信号仿真系统中,与传统的可靠组播传输协议相比,能有效减少差错修复时延,并提高系统整体的吞吐率。     

On the choice of a production control system

This paper deals with a problem to develop ‘factory automation systems’ which harmonize companies’ needs with workers’ desires. Two kinds of indices and methods of survey are proposed on the basis of the ‘fusion system concept’. One is that of the state of workers’ desires which are based on the ‘stimulus-response model’, the other is that of situations where ‘factory automation’ is implemented in a workshop. The effects of ‘factory automation’ on workers’ desires are clarified in a study of Japanese manufacturing industries in 1983. As a result of this investigation, some problems can be pointed out which should be solved in the future to develop ‘factory automation systems’.     

A Review of the Dual Resource Constrained System Research

This paper reviews the recent dual resource constrained (DRC)system literature. The DRC system research has gained new significance through the emphasis being placed on cross-training by Just-In-Time (JIT) system advocates. Cross-training is the key to labor flexibility-one of the key issues in the DRC system research. This review covers over twenty-five articles about DRC systems and should be helpful in familiarizing potential DRC system researchers with the field. The DRC system research and results, categorized into design and operating decisions, are summarized and suggestions for future research are provided. A table which summarizes the characteristics of the DRC systems modeled, decision rules examined, statistical analysis methods employed, and the performance criteria used in each study is also provided. An appendix is used to highlight characteristics that are common to many of the models employed in the studies surveyed.     

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.     

Solving cell formation and task scheduling in cellular manufacturing system by discrete bacteria foraging algorithm

We consider a joint decision model of cell formation and task scheduling in cellular manufacturing system under dual-resource constrained (DRC) setting. On one hand, machines and workers are multi-functional and/or multi-skilled, and they are grouped into workstations and cells. On the other hand, there is a processing sequence among operations of the parts which needs to be dispatched to the desirable workstations for processing. Inter-cell movements of parts can reduce the processing times and the makespan but will increase the inter-cell material handling costs. The objective of the problem is to minimise the material handling costs as well as the fixed and operating costs of machines and workers. Due to the NP-hardness of the problem, we propose an efficient discrete bacteria foraging algorithm (DBFA) with elaborately designed solution representation and bacteria evolution operators to solve the proposed problem. We tested our algorithm using randomly generated instances with different sizes and settings by comparing with the original bacteria foraging algorithm and a genetic algorithm. Our results show that the proposed DBFA has better performance than the two compared algorithms with the same running time.     

Measurement and Analysis of Physical and Climatic Distribution Environment for Air Package Shipment

There has been a significant growth in the air package shipment business, which involves the multi‐modal movement of a package in transportation and material handling systems that encompass conveyors, carts, trucks, delivery vans and aircrafts of various sizes and shapes. This study was aimed at establishing the ‘air package shipment’ conditions experienced by packages transported by air under ‘normal conditions of transport’. Air package shipment data (temperature, humidity, pressure, shock and vibration) were collected for several domestic and international routes through instrumented packages. The collected data were supplemented by previous research to measure and quantify this multi‐modal shipping environment. This study also compared industry‐accepted American Society for Testing and Materials (ASTM) pre‐shipment test methods with the general requirements of package design qualification testing as outlined in 49 Code of Federal Regulations (CFR) Part 178, Subpart M. This review revealed that the design qualification testing for certain distribution‐related hazard elements is not currently representative of the normal conditions of air transport. The data gathered in this study were analysed to represent the current ‘normal conditions of transport’, i.e. beginning‐to‐end delivery of air packages. The study used the time spent by the package in each of the segments of transportation to determine a ‘single profile’ or ‘test’ that would represent the average and normal expected levels for each hazard element and would serve as the basis of a minimum level for performance testing to establish normal conditions of transport by air. The recommended test methods and levels can be easily adopted by existing distribution packaging testing labs globally. Copyright © 2015 John Wiley & Sons, Ltd.     

An effective heuristic for adaptive control of job sequences subject to variation in processing times

Variation in sequential task processing times is common in manufacturing systems. This type of disturbance challenges most scheduling methods since they cannot fundamentally change job sequences to adaptively control production performance as jobs enter the system because actual processing times, are not known in advance. Some research literature indicates that simple rules are more suitable than algorithmic scheduling methods for adaptive control. In this work, a ‘state space – average processing time’ (SS-APT) heuristic is proposed and compared to four most commonly used scheduling rules and two well-established heuristics based on Taillard’s benchmarks. It is shown that the adaptive control is made possible under variation in processing times given the flexibility and strong performance of the SS-APT heuristic, especially for work-in-process inventory control.     

Labour flexibility and assignment policies in a job shop having incommensurable objectives

This study evaluates operating policies for offering a near-perfect delivery performance for vital customers in dual resource-constrained (DRC) job shop environments. Prior studies have considered this problem in machine-limited settings, and shown that dispatching rules that help realise a near-perfect delivery performance for vital customers necessarily deteriorate delivery performance for other customers served by the shop. This study extends prior work, and considers additional tools that can be used by managers in DRC shops such as labour flexibility, and assignment rules that incorporate customer-based information to deploy workers to departments containing high-priority jobs. Results show that labour flexibility in conjunction with appropriate decision rules allows for enhanced delivery performance for both vital and normal priority customers. These results hold even under conditions where 80% of the shop's workload is compromised of high-priority orders.     

Effects of reduced pressure and vibration on haz‐mat packages for liquids

Eleven different bottle/closure systems used to package dangerous goods for transportation by air were tested for leakage. The bottles were filled with water and subjected to the combined effects of random vibration and external pressure equivalent to an altitude of 14000ft (4267m) for up to an hour. The bottles were placed in the vertical, horizontal and inverted orientations and observed for leaks. The differences in bottle weights before and after the tests were used to quantify leakage. The results show that of the 11 package types tested, six leaked when subjected to simulation of the air transport environment. Those systems utilizing ‘stretch tape’ around the closure did not leak. Copyright © 2006 John Wiley & Sons, Ltd.     

Improved design of CMS by considering operators decision-making styles

Cell formation is one of the oldest problems in cellular manufacturing systems (CMS) including assigning parts, machines and operators to cells. Cell manufacturing contains a number of cells where each cell is responsible for processing the family of similar parts. Another important aspect of cell formation is worker assignment to cells. Since operators work together in long periods, it is suggested to consider operators’ personal characteristics to increase their satisfaction and the productivity of system. This paper considers decision-making styles of operators (as an index of operator’s personal characteristics) and presents a new mathematical programming model for clustering parts, machines and workers simultaneously. The model includes two objectives; (1) minimization of intracellular movements and cell establishment costs, (2) minimization of decision-making style inconsistency among operators in each cell. The paper applies ε-constraint method for solving the problem and gathering non-dominated solutions such as Pareto optimal solutions. Furthermore, this paper uses common weighted multicriteria decision analysis (MCDA)-data envelopment analysis method to choose the best solution from the candidate Pareto optimal solutions that have been achieved by solving the mathematical model. A real case study is investigated to show the capability of the proposed model to design CMS in the assembly unit. The proposed design assists decision-makers to develop cellular systems with more operators’ satisfaction and productivity.     

Innovation and employee injury risk in automotive disassembly operations

Engineering innovations in car disassembly systems are studied for affects on system operators’ risk of repetitive strain injury (RSI). Objective instrumented measures of injury risk factors with synchronised video-based task analyses were used to examine changes in operators’ RSI risk during two cases of engineering innovation: (1) a shift in industrial model from traditional extracting saleable parts to line-based full material recovery, and (2) the prospective effects of a simulated ‘Lean’-inspired process improvement in the line system. Both cases of innovation showed significantly increased movement speeds and reduced muscular recovery opportunities, implying increased RSI risk. This case study reveals a mechanism by which innovation may increase RSI risks for operators. Managers responsible for engineering innovation should ensure their teams have the tools and mandate necessary to control injury hazards as part of the development and design process. These cases suggest how failure to manage RSI hazards in the innovation process may allow increases of injury risks that can compromise operational performance. This ‘innovation pitfall’ has implications for operator health and organisational sustainability. Alternative pathways are discussed.     

现代物流标准化与包装标准化

现代物流的构成要素是随着社会的不断发展而逐渐拓展和延伸的,而要保证整个现代物流"物质流动"的合理化、有序化、现代化、低成本,物流包装标准化是根本的途径和有效的保障.文中主要就包装与现代物流供应链各个环节之间的密切关系展开讨论,最终希望我国政府、行业、企业及每个企业员工都应树立加强包装标准化建设的意识,并通过一定的组织和技术标准保证我国物流产业在高起点上得以发展和壮大,以促使我国的物流产业尽快适应WTO的国际贸易的需求,加强我国企业和物流产业的国际竞争力.     

Inserting cost effectiveness to the ergonomic equation when considering practical solutions

From a practical point of view, the cost effectiveness of ergonomic solutions is often questioned. Many times managers omit ergonomic solutions because of their high cost. This paper introduces a way to implement cost effective ergonomic solutions by coupling computer-aided design and predetermined motion time systems. This is done by generating a comparison between the operation times and body motions used in existing and safer work situations. We demonstrate using two case studies how solutions may impact operation times and stress, to which workers are subjected, which may be expressed in relaxation allowances required for resting and recovery. The ‘final product’ which may interest management the most, the ergonomic recommendations, is presented in easy to understand figures and numbers, including time to return on investment on relevant ergonomic solutions, which becomes possible when suggested improvements to work-situations are translated to time and cost.     

Scheduling vehicles in automated transportation systems Algorithms and case study

One of the major planning issues in large scale automated transportation systems is so-called empty vehicle management, the timely supply of vehicles to terminals in order to reduce cargo waiting times. Motivated by a Dutch pilot project on an underground cargo transportation system using Automated Guided Vehicles (AGVs), we developed several rules and algorithms for empty vehicle management, varying from trivial First-Come, First-Served (FCFS) via look-ahead rules to integral planning. For our application, we focus on attaining customer service levels in the presence of varying order priorities, taking into account resource capacities and the relation to other planning decisions, such as terminal management. We show how the various rules are embedded in a framework for logistics control of automated transportation networks. Using simulation, the planning options are evaluated on their performance in terms of customer service levels, AGV requirements and empty travel distances. Based on our experiments, we conclude that look-ahead rules have significant advantages above FCFS. A more advanced so-called serial scheduling method outperforms the look-ahead rules if the peak demand quickly moves amongst routes in the system. Received: June 21, 2000 / Accepted: January 22, 2001     

Performance evaluation of cellular layouts: Extension to DRC system contexts

This study involves a comparison of the performance of functional layouts (FL) and cellular manufacturing (CM) systems in a dual-resource-constrained (DRC) system context. Past studies of FL and CM have been based mostly on single-resource-constrained (SRC) systems. Recent studies have included labour-related factors, but have assumed high labour flexibility levels, and shown the superiority of CM. In this study we assume more realistic levels of labour flexibility, and factors such as lot size, set-up reduction, labour assignment and transfer rule, and scheduling rules. The parameter range in which CM can outperform efficiently operated FL, in a DRC context, are indicated.     

Threshold-based method for elevating the system's constraint under theory of constraints

The principal tenet of theory of constraints (TOC) is that there is at least one constraint in each system that limits the ability of achieving higher levels of performance relative to its goal. Maximum utilisation of the constraint leads to maximum output of the system. However, activation of a non-constraint resource at 100% of its capacity does not increase output. Therefore, some resources are not fully utilised. In this paper, the authors use the left capacity of a non-constraint resource (NC) to elevate the system's constraint. It is assumed that the capacity-constrained resource (CCR) is a continuous time Markov process having a two-dimensional state space. The work in the NC is interruptible, allowing a worker in the NC to switch to CCR. The switch from NC to CCR would occur when the queue of waiting parts in the CCR becomes ‘too long’ and vice versa, when there are few parts in the CCR. Returning to the NC from the CCR may require some ‘re-orientation time’ on the part of the switched worker. The goal is to find the maximum output of CCR subject to the time-average number of workers in the NC must be greater than a pre-specified value.     

Modelling of an automated guided vehicle system (AG VS) in a just-in-time (JIT) environment

Like other production systems, just-in-time (JIT) systems need to address the issue of material transport between workstations such as those served by automated guided vehicles (AGVs). Unlike other production systems, however, the JIT philosophy imposes strict requirements on inventory levels and supply-demand protocols which render conventional AGV delivery strategies ineffective and counter-productive. This paper describes the modelling of an AGV system (AGVS) in a JIT environment in a way that is consistent with JIT principles. The influence of a ‘JIT perspective’ is emphasized throughout the model by introducing threshold values for both input and output queues, performance measures that emphasize lower inventories in addition to transport efficiency, and a new dispatching rule that implements better inventory and transport control. The dispatching rule is shown to perform better in a JIT environment than previously developed AGV dispatching rules in both transport and logistic criteria.