A STUDY OF THE UTILIZATION OF CAPACITY CONSTRAINED RESOURCES IN DRUM‐BUFFER‐ROPE SYSTEMS*

Goldratt, the originator of the Theory of Constraints (TOC), maintains that only the system's primary resource constraint(s) should be scheduled at 100% of capacity. All other resources should have excess capacity. This paper presents the results of a simulation experiment that studies how changes in the capacity utilization of a systems two most heavily utilized resources affect the performance of a drum‐buffer‐rope (DBR)scheduling system. The research demonstrates that 100% utilization of the primary constraint is not optimal. It also shows that DBR responds well to relatively low levels of increased capacity at the operations second most heavily utilized resource. This research also highlights several other issues related to capacity utilization that need further investigation.     

Performance of TOC based finite capacity material requirement planning system for a multi-stage assembly factory

This paper aims to develop a finite capacity material requirement planning (FCMRP) system based on TOC philosophy (TOC-MRP) for multi-stage assembly factory that has some bottleneck stations. The proposed TOC-MRP system tries to load and schedule operations on bottleneck stations in a manner that they are free of idle time and overtime. The schedules on non-bottleneck stations will be arranged until they are not conflicting with those on the bottleneck stations. The non-bottleneck stations are allowed to have idle time and overtime if necessary. To analyse whether TOC-MRP is effective, it is compared with a FCMRP method that does not adopt TOC philosophy. The experimental results reveal that the TOC-MRP outperforms the FCMRP without TOC philosophy.     

The impact of non-bottleneck variation in a manufacturing cell

Protective capacity is the 'extra' capacity placed at non-bottleneck resources to absorb random disruptions in planned levels of performance so that the bottleneck resource continues to be effectively utilized. A full factorial experiment with a simulation model was conducted to explore issues associated with the quantity and location of processing variance in a five-station manufacturing cell. The cell's performance was measured using both mean flow time ( MFT ) and bottleneck shiftiness ( SHIFT ) for 3 patterns of variance for the non-bottlenecks at 5 different levels of variation. In order to investigate the importance of the quantity of added capacity on the variation both a low level of protective capacity (10%) and a high level (50%) were considered. The results indicate that having the higher variation work centres close to the bottleneck provides reduced MFT and SHIFT . The performance measures improved at both the low and high setting of protective capacity.     

A TUTORIAL ON BOTTLENECK DYNAMICS: A HEURISTIC SCHEDULING METHODOLOGY

We give a tutorial on bottleneck dynamics. Bottleneck dynamics is a scheduling framework that uses approximate dual resource prices to make decentralized decisions. The basic idea is to establish a price for a resource as a function of the set of jobs that need to be processed by the resource. Tasks are then sequenced according to a cost/benefit ratio. Starting with one resource sequencing problems, we describe how priorities for jobs can be developed and how they translate into resource prices. We then describe how resource prices can be approximated in a multiresource situation and how lead times which are critical for these approximations can be accurately computed. We also describe a number of studies that have shown bottleneck dynamics to be an effective approach in several different problem areas.     

The effectiveness of input control based on aggregate versus bottleneck work loads

This study compares input control based on aggregate shop loads with that based on bottleneck resource loads. Two appropriate release mechanisms are developed and compared in flow and job shops that have various levels of a bottleneck constraint. Simulation results show that both the level of bottleneck and the flow pattern influence the effectiveness of the strategies. Release based on aggregate loads works well when shop loads are balanced or when there is a bottleneck but the flow is highly structured, as in a flow shop. Release based on bottleneck loads works best when flow patterns are less structured, as in a job shop.     

基于活动方法的瓶颈模型与拥挤收费问题研究

Vickrey提出的基于出行的瓶颈模型以出行作为分析单位,没有考虑出行与活动之间的相互关联.本文对Vickrey的瓶颈模型进行了拓展,提出了基于活动的瓶颈模型来研究通勤者早晨上班出发时间决策问题,模型考虑了通勤者对出行负效用与活动效用之间的权衡.在基于活动的瓶颈模型的基础上,分别研究了常数和线性边际活动效用下瓶颈动态拥挤收费和阶梯收费问题,并与传统的瓶颈模型的解进行比较.结果表明,当活动的边际效用为线性函数时,瓶颈处最优动态收费曲线不再呈分段线性关系,而是分段二次曲线;与基于活动的瓶颈模型相比,传统的基于出行的瓶颈模型将高估瓶颈处的排队延误、阶梯收费水平,以及早高峰的开始和结束时间;基于出行的瓶颈模型和常数边际活动效用下的瓶颈模型导致的最优阶梯收费是最优动态收费最大值的一半,并且刚好消除瓶颈处排队延误的一半;与线性边际活动效用下的瓶颈模型相比较,两者低估了阶梯收费能消除的瓶颈排队,从而低估了阶梯收费的效率.     

An investigation of output flow control,bottleneck flow control and dynamic flow control mechanisms in various simple lines scenarios

Flow control mechanisms have been a topic of academic research for several years. With the growth of business-wide information systems such as enterprise resource planning and supply chain, better planning, scheduling and control of the business transformation process is required in order to achieve increased throughput, reduced inventories, shorter lead times and reduced tardiness. This research compares two new approaches to flow control, output flow control and bottleneck flow control to a real-time flow control system, dynamic flow control. Both output and bottleneck flow control mechanisms are much simpler to implement and manage than dynamic flow control in that they do not require continual feedback and rescheduling. Line characteristics, such as location of breakdowns with respect to the bottleneck, the location of the bottleneck when breakdowns occur, and the impact of variability of processing times on the performance measures (output, WIP level, lateness, and number of tardy jobs) for these three flow control mechanisms are compared. Both output and bottleneck flow control mechanisms perform favourably (particularly bottleneck) under different scenarios and warrant further study across a wider range of scenarios (mixed models, job shops, etc.).     

The Service Role of Outside Boards in High Tech Start‐ups: A Resource Dependency Perspective

Despite growing interest in the board of directors of entrepreneurial firms, the role of outside board members in high tech start‐ups has been largely neglected. This dearth of research is surprising since the high level of resource dependency these ventures face is likely to heighten the potential contribution outside board members can make. We argue that, for high tech start‐ups, the service role the board plays will be crucial in overcoming resource dependencies. In contrast to existing studies that tie the outside boards’ servicing role to board characteristics, we propose that greater attention needs to be paid to the resource profile of the venture. Building on resource dependency theory, we find that the extent to which the outside board members fulfil a service role is dependent on the initial human, financial and technological resource base of the entrepreneurial venture. Specifically, we find that ventures with less diversified teams, teams with lower levels of R&D experience and higher levels of financial experience and ventures earlier in the technological development process receive higher levels of support from the outside board.     

Up Then Down: Bid‐Price Trends in Revenue Management

In the classic revenue management (RM) problem of selling a fixed quantity of perishable inventories to price‐sensitive non‐strategic consumers over a finite horizon, the optimal pricing decision at any time depends on two important factors: consumer valuation and bid price. The former is determined exogenously by the demand side, while the latter is determined jointly by the inventory level on the supply side and the consumer valuations in the time remaining within the selling horizon. Because of the importance of bid prices in theory and practice of RM, this study aims to enhance the understanding of the intertemporal behavior of bid prices in dynamic RM environments. We provide a probabilistic characterization of the optimal policies from the perspective of bid‐price processes. We show that an optimal bid‐price process has an upward trend over time before the inventory level falls to one and then has a downward trend. This intertemporal up‐then‐down pattern of bid‐price processes is related to two fundamental static properties of the optimal bid prices: (i) At any given time, a lower inventory level yields a higher optimal bid price, which is referred to as the resource scarcity effect; (ii) Given any inventory level, the optimal bid price decreases with time; that is referred to as the resource perishability effect. The demonstrated upward trend implies that the optimal bid‐price process is mainly driven by the resource scarcity effect, while the downward trend implies that the bid‐price process is mainly driven by the resource perishability effect. We also demonstrate how optimal bid price and consumer valuation, as two competing forces, interact over time to drive the optimal‐price process. The results are also extended to the network RM problems.     

The TOC-based algorithm for solving product mix problems

The five steps of the theory of constraints (TOC) emphasize exploiting constraints in order to increase the throughput of a system. The product mix decision is one application of the TOC five steps. However, these steps were considered to be implicit or incomplete, the criticism being that they result in deriving an infeasible solution when a plant has multiple resource constraints. This paper follows the essence of these five steps and presents an explicit algorithm to address the problem. When testing its effectiveness by using a dual-simplex method with bounded variables, this algorithm gives the same result in each iteration.     

Potential productivity: Concepts and application

This paper is concerned with the meaning and measurement of potential productivity. Potential productivity is the difference between the actual and most efficient (optimal) productivity level. A number of concepts of potential productivity are outlined and their managerial implications discussed. Measures based on operating and lost time, peak output levels, estimating a capacity production function and work study (percentage utilisation of labour) are compared for the envelope-making division of a UK manufacturing company.     

Value–value load diagram: a graphical tool for lean–green performance assessment

Integrated assessment of operational and environmental performance of the production system requires mapping of all the processes and activities in the form of their resource utilisation efficiency. Prior research indicates that most lean assessment tools and techniques have studied operational dimensions ignoring environmental aspect as a part of the assessment tool. Moreover, movement towards the greener production system has become a key strategic consideration for organisations to maintain a competitive edge and to remain as market winners. Continuous assessment in both, lean and green, dimensions is crucial in improving the overall performance through efficient utilisation of the available resources. In lean environment, value stream mapping (VSM) allows assessment of operational performance through identification of non-value adding activities in time units but fails to integrate inefficiencies related to material and energy utilisation. The tool-like material flow cost accounting (MFCA) is able to assess the environmental performance through physical and monetary evaluation of material flow within the production system. This paper presents, a novel tool, value–value load diagram (VVLD), for modelling and evaluating the operational (lean) and environmental (green) performance of the production system. VVLD graphically represents resource consumption, value addition and performance improvement opportunities within the production system by integrating VSM, MFCA and pinch analysis methodology. VVLD permits evaluation of the lean–green performance in terms of the eco-leanness index and also exposes the improvement opportunities by pinch point location. Some common generic scenarios for improvement in the eco-leanness index are demonstrated using VVLD. Application of VVLD along with the developed computer-based support system (CBSS) is demonstrated for a manufacturing SME in India, allowing the managers to evaluate and tune their processes for improved resource utilisation efficiency.     

Maximizing product mix profitability - what's the best analysis tool

This paper takes a look at product mix profitability and compares several alternative methodologies for selecting the optimal product mix. It is argued that the optimal product mix is not determined using traditional accounting methodologies and that dropping marginally profitable products based on the accounting rules will give you less than optimal profitability. This paper looks at two different ways for coming up with the optimal product mix: one using theory of constraints (TOC) and another using linear programming.     

Critical objective function values in linear sum assignment problems

The linear sum assignment problem has been well studied in combinatorial optimization. Because of the integrality property, it is a linear programming problem with a variety of efficient algorithms to solve it. In the given research, we present a reformulation of the linear sum assignment problem and a Lagrangian relaxation algorithm for its reformulation. An important characteristic of the new Lagrangian relaxation method is that the optimal Lagrangian multiplier yields a critical bottleneck value. Lagrangian relaxation has only one Lagrangian multiplier, which can only take on a limited number of values, making the search for the optimal multiplier easy. The interpretation of the optimal Lagrangian parameter is that its value is equal to the price that must be paid for all objects in the problem to be assigned.     

不对称信息下反恐阻止网络设计

当前，我国面临的恐怖主义威胁日益严峻。为防止境外恐怖分子潜入，政府可设计反恐阻止网络，通过在交通网络中有效地分配例如安检仪器、传感设备等阻断资源，来提前识别和拦截正在潜入的恐怖分子。特别地，考虑信息不对称情形，把阻断资源分为"公开"和"隐蔽"两种类型，并假设恐怖分子观察不到"隐蔽"阻断。主要研究政府应如何同时优化两类阻断方案，才能发挥信息优势，设置"陷阱"并降低袭击分析。首先，将该问题构造为双层规划模型，上层规划是关于政府的阻止网络设计问题，下层规划则是关于恐怖分子的袭击节点选择和入侵路径优化问题。随后，设计一类用改进遗传算法处理上层规划，并结合下层规划直接求解的混合算法。其中，改进体现于杂交算子和变异算子的设计。最后，结合喀什地区进行算例分析，并分析"隐蔽"阻断的作用机理。     

Updating Inventories of Substitutable Resources in Response to Forecast Updates

We show simple yet optimal results to update the inventory/capacity levels, expected profit, fill rates, and service levels of substitutable resources in response to an updating of the mean demand forecasts for the resources. We find that a change in the mean demand of one resource does not affect the optimal inventory level of any other resource. The results are obtained for demands with location‐scale distribution, and for a revenue structure satisfying a triangle property such that the manager will always use the inventory of a resource to meet her own demand first before using it for substitution. The results for updating the performance measures also extend to managers who maintain non‐optimal inventory/capacity levels. Implications for procurement, sales and operational planning, and multi‐store operations are discussed.     

面向安全硬约束的煤矿生产物流效率优化研究

在保证安全生产前提下实现效率最大化是煤炭生产企业亟需解决的现实问题。本文结合煤矿生产物流系统的复杂性特征,首先从人员素质、机械装备、环境改善、安全管理、应急救援等方面确定了煤矿生产物流的安全投入指标,运用响应曲面法分析了安全指标与安全水平间的作用关系,确定了煤矿生产物流安全硬约束条件;然后以效率最大化为目标函数、安全目标和资源投入为约束条件,构建了煤矿生产物流效率优化模型;最后通过实例验证了模型的有效性及适用性,为安全生产前提下实现资源优化配置,提高煤矿生产物流效率提供了科学依据。     

Bounds of Relative Regret Limit in p‐Robust Supply Chain Network Design

This research studies the p‐robust supply chain network design with uncertain demand and cost scenarios. The optimal design integrates the supplier selection together with the facility location and capacity problem. We provide a new framework to obtain the relative regret limit, which is critical in the robust supply chain design but is assumed to be a known value in the existing literature. We obtain lower and upper bounds for relative regret limit and obtain a sequence of optimal solutions for series relative regret limits between the upper and lower bounds. An algorithm for p‐robust supply chain network design is provided. A series of numerical examples are designed to find the properties of the bottleneck scenarios. A scenario with low probability and a low optimal objective function value for the scenario has a greater chance of being a bottleneck. To focus only on the influence from the relative regret, we also introduce three separate new objective functions in p‐robust design. The proposed new theories and approaches provide a sequence of options for decision makers to reduce the marketing risks effectively in supply chain network design.     

基于MDE资源分时段与活动平移并行的均衡优化

本文以资源均方差作为衡量工程网络计划资源均衡性的评价函数,基于非关键活动资源可以分段使用的状态,提出了对非关键活动机动时间及其各个时段的资源强度同时动态并行调整的优化策略,以弥补非关键活动平移幅度因受时差的限制而对均衡效果产生的影响,并以此构建了网络计划资源均衡优化模型;并针对网络计划均衡优化模型是一多峰值的非线性优化函数的特点,对基于种群的全局搜索策略的差分进化算法进行了改进和进行全局最优解的寻优,以优化各个非关键活动起止时间,求出各个非关键活动最优的安排;最后,通过实例分析,并与其它算法进行了对比分析,验证明了所提出的均衡优化方法的优越性和实用性.     

危险品集成物流管理系统选址-选线模型研究

以路网的危险度瓶颈限制为切入点研究了一类危险品集成物流管理系统选址—选线问题,对应于路网危险度瓶颈限制引入安全费用非递减函数,并根据运输工具的安全配置等级构造该等级下的子网络,物流系统的选址—选线结果随着路网的调整而不断变化.危险品集成物流系统的管理存在多个目标,文中首先分析了成本、风险和风险公平性等优化目标,在说明了建模的假设条件后,建立了基于路网危险度瓶颈限制的危险品集成物流系统选址—选线的多目标模型,并根据模型给出了一种启发式算法,最后用一个算例对模型进行了数值演算.