Optimizing the multiple constrained resources product mix problem using genetic algorithms

The theory of constraints (TOC) is s a management philosophy for maximizing throughput. Since its introduction, many have criticized it as being inefficient when multiple constrained resources exist. The application of the five steps contained in TOC have been criticized by some researchers on the grounds that the application of five steps of TOC to the product mix decision leads to implicit or unrealizable solutions when multiple resource constraints in a plant exist. This paper views TOC as a management philosophy and a genetic algorithm-based TOC procedure is presented for solving combinatorial problems encountered in practice which cannot be solved using linear-integer programming or similar techniques. For smaller size problems, the results of the proposed procedure are compared with results of optimal methods published in the literature. The results are encouraging and therefore support the use of the proposed approach in an industrial setting.     

Information technology in operations management: a theory-of-constraints approach

The theory of constraints (TOC) has recently gained much success in its application to industrial and service organizations. This paper applies the TOC principles to the management of information technology (IT) in the organization. The paper creates a four tiered model for the application of the TOC to IT, starting with TOC's throughput-driven business policy; on with the seven step resource management methodology; through the cost/utilization capital investment technique; and concluding with the drum-buffer-rope production activity procedure. We draw a framework and a methodology showing how IT can be more effective using the TOC way of management. In order to systematically explore the location of the organization's constraints we adapt to the TOC a synthesis of three established management frameworks: stakeholder analysis, the value chain and Boston Consulting Group's portfolio analysis model     

制约理论在管理会计中的应用一例

制约理论是当今美国和欧洲比较流行的一套管理哲理和持续改进方法。通过实际案例，根据Goldratt的5个关键步骤，找到系统的制约，利用开发和释放制约从而使系统的整体能力得以提高。     

Tabu search-based algorithm for the TOC product mix decision

The theory of constraints (TOC) is a management philosophy that maximizes profits in a manufacturing plant with a demonstrated bottleneck. The product mix decision is one application of TOC that involves determination of the quantity and the identification of each product to produce. However, the original TOC heuristic is considered to produce unrealizable solution when a manufacturing plant has multiple resource constraints. This paper presents a tabu search-based TOC product mix heuristic to identify optimal or near optimal product mix for small problem instances under conditions where the original TOC heuristic failed. The tabu search-based TOC product mix heuristic is further used to solve large problem instances typical of practical manufacturing scenario. The experimental results for small to medium size problem show that the tabu search-based TOC heuristic compares favourably with those of optimal methods. Large size problems for which optimal methods have not been established in terms of feasibility in computation times were also solved in reasonable times with good quality solutions, thus confirming that the proposed approach is appropriate for adoption by production planners for the product mix problem in the manufacturing industry.     

Comparing JIT,MRP and TOC,and embedding TOC into MRP

The traditional material requirements planning (MRP) system for planning and controlling production systems is being replaced more and more by just-in-time (JIT) and the theory of constraints (TOC). Because JIT and TOC share many elements with MRP and because MRP is very flexible, it is not difficult to make MRP behave like JIT or TOC. Consequently manufacturers with MRP systems need not dismantle them to implement JIT or TOC. A five-step technical procedure for embedding TOC into MRP is presented in this paper along with an illustrative example from a microelectronics plant. Next a simple production line is analysed using a Markov chain model to examine the types of improvements each approach makes and the effect of these improvements on the performance of the line. Performance measures are the mean and variance of the output, shortage, inventory level, and cycle time of the production line. Insights are developed into the reasons for the superior performance of JIT and TOC.     

TOC-based performance measures and five focusing steps in a job-shop manufacturing environment

Theory of constraints (TOC) views a company as a set of interdependent processes working in harmony to achieve the profit goal of the company as a whole, and thus it emphasizes total system performance over localized measures to guide operational decisions. This paper demonstrates the usefulness of employing TOCbased global performance measures to make operational-decisions (e.g. product mix, continuous improvement, inventory management, production planning and scheduling) to strengthen the internal supply chain in a relatively complex manufacturing environment, i.e. a job shop. An ARENA-based simulation model is presented and a number of scenarios are discussed that provide insights regarding the characteristic features of TOC, such as goals and necessary conditions, performance measures, five-focusing steps for continuous improvement, and drumbuffer-rope scheduling. These insights will assist managers in making important decisions regarding approaches to successful TOC implementations, and will provide academics with a broad range of future research opportunities.     

基于约束的生产系统再造及评价方法

在分析生产系统再造原理的基础上,将约束理论引入生产系统再造过程,提出基于约束的企业生产系统再造方法。这一方法的特点是依据约束理论思想进行约束流程的判别和确定,围绕现有生产系统约束进行再造设计。这一方法还基于约束理论的系统评价指标建立了生产系统再造评价指标,从而实现对再造效果动态评价。     

负荷型对偶单元授权卡片交叠循环系统性能仿真

负荷型对偶单元授权卡片交叠循环(load-based paired-cell overlapping loops of cards with authorization,LB-POLCA)是一类面向非重复性制造车间的新型物料控制系统,用于实现车间内加工资源的负荷均衡和在制物料的有效流转。现有研究已经验证了LB-POLCA系统的有效性,但其大多忽视了物料之间存在的装配关联性,即装配工序只有在其所需物料齐套之后才能开工,此时系统控制的核心需求是实现关联物料的加工进度协同。鉴于此,本文针对一类带装配约束的一般流水车间,首先给出相适应的LB-POLCA系统运行机制及其涉及的卡片获取规则、负荷计算方法和作业分派规则等关键控制参量;然后基于Plant Simulation平台构建一般化的仿真模型,并通过大量实验揭示出不同装配关联度和不同系统控制参量组合下的系统性能变化。     

Theory of constraint methodology where the constraint is the business model

This paper addresses the issue of business model (BM) management and its relationship to the theory of constraints (TOC). Coman and Ronen (Coman, A. and Ronen,B., 2007. Managing strategic and tactical constraints in the hi-tech industry. International Journal of Production Research, 38(7), 1631–1639) have extended TOC methodology to include the alignment of the organisation's competencies with the business arena's strategic constraints. The aim of this paper is to take TOC one step further and to combine it with the business models theory. Business models have become important value creators due to the proliferation of new and innovative business models (i.e. new ways of creating value). New firms with new business models are threatening and replacing established companies and conventional ways of doing business. Among these are the music, publishing, books, retail, airline and many other industries. This paper argues that in the wake of the World Wide Web, contract manufacturing and globalisation it not enough to manage the firms (internal, external or strategic) constraints. In addition, the management of the firm's BM as a potential constraint is a key factor in the modern management theory.     

Revolutionizing supply chain management the theory of constraints way: a case study

This research describes in detail an application of theory of constraints (TOC) and its resulting benefits on the supply chain performance of India's largest lock manufacturing company over a period of seven years. Using TOC's thinking process, the core constraints that had limited the company's performance in the areas of production, distribution, supply group and projects were identified and eliminated. TOC's unique approach helped the company achieve a significant reduction in its finished goods, raw material and work-in-process inventories at various levels across the supply chain. The stock-outs and excess in the distribution system nearly disappeared. The existing lead times saw a drastic reduction while the availability of items increased to nearly 100% despite significant decrease in inventory levels in the supply chain. The inventory turns of the distributors and retailers more than tripled and their profitability increased significantly. The overall sales of the company grew nearly three times during the six years post TOC implementation. TOC's holistic approach helped the company to double its profits and improve its cash position during the Great Recession.     

Scheduling in production,supply chain and Industry 4.0 systems by optimal control: fundamentals,state-of-the-art and applications

This paper presents a survey on the applications of optimal control to scheduling in production, supply chain and Industry 4.0 systems with a focus on the deterministic maximum principle. The first objective is to derive major contributions, application areas, limitations, as well as research and application recommendations for the future research. The second objective is to explain control engineering models in terms of industrial engineering and production management. To achieve these objectives, optimal control models, qualitative methods of performance analysis and computational methods for optimal control are considered. We provide a brief historic overview and clarify major mathematical fundamentals whereby the control engineering terms are brought into correspondence with industrial engineering and management. The survey allows the grouping of models with only terminal constraints with application to master production scheduling, models with hybrid terminal–logical constraints with applications to short term job and flow shop scheduling, and hybrid structural–terminal–logical constraints with applications to customised assembly systems such as Industry 4.0. Computational algorithms in state, control and adjoint variable spaces are discussed.     

Implementing theory of constraints in a traditional Japanese manufacturing environment: The case of Hitachi Tool Engineering

This research presents a case study of a virtual ‘textbook’ application of the theory of constraints (TOC) in a Japanese tool manufacturing company. Hitachi Tool Engineering uses state-of-the-art technology to design and manufacture cutting tools known as End-mills. The plant described in this study is a classic V-plant and exhibited all of the standard problems of a traditionally managed V-plant, existing within the unique framework of Japanese work culture. Plant management applied the five focusing steps and used the operations strategy tools, including drum-buffer-rope and buffer management, to improve the system. Following the approach recommended by Eli Goldratt, the thinking process tools of current reality tree and evaporating clouds were used to help identify and resolve problems when the implementation encountered major obstacles. While the implementation was a huge success, the devastating effect of a core problem being left unresolved is well documented. The implementation generated significant improvements in work-in-process inventory, production lead time, on-time delivery, productive capacity, inventory turnover, product quality, sales volume, and profitability. Moreover, management has extended the introduction of TOC to the non-manufacturing functions and TOC is becoming the common company culture that bridges four culturally diverse manufacturing plants.     

Assigning licenced technicians to maintenance tasks at aircraft maintenance base: a bi-objective approach and a Chinese airline application

Assigning technicians to maintenance tasks at an aircraft maintenance base is challenging and needs to consider technician licences, fairness and such operational constraints as hangar capacity and work shifts. We formulate the problem as a bi-objective optimisation model, which minimises total cost while simultaneously achieving fairness in workload allocation among different technicians. A tabu-based heuristic algorithm is developed to obtain Pareto efficient solutions. The algorithm is shown to be effective through comparison with CPLEX. A case study from a major Chinese airline demonstrates that our optimisation-based approach is applicable and beneficial to the practice. Managerial issues on maintenance workforce management are examined as well. The results show that training technicians and upgrading their licences may not be better off, and increasing the number of technicians has both favourable and unfavourable effects.     

Theory of constraints - A status report

The Theory of Constraints (TOC) was first applied to production scheduling. For many people this application is the only one TOC brings to mind. Over the past several years TOC has been applied to other areas such as performance measures, supply chains, marketing, sales and managing people. In this paper I review how TOC has been applied to these areas.     

Open shop scheduling problem with a multi-skills resource constraint: a genetic algorithm and an ant colony optimisation approach

The continuous evolution of manufacturing environments leads to a more efficient production process that controls an increasing number of parameters. Production resources usually represent an important constraint in a manufacturing activity, specially talking about the management of human resources and their skills. In order to study the impact of this subject, this paper considers an open shop scheduling problem based on a mechanical production workshop to minimise the total flow time including a multi-skill resource constraint. Then, we count with a number of workers that have a versatility to carry out different tasks, and according to their assignment a schedule is generated. In that way, we have formulated the problem as a linear as and a non-linear mathematical model which applies the classic scheduling constraints, adding some different resources constraints related to personnel staff competences and their availability to execute one task. In addition, we introduce a genetic algorithm and an ant colony optimisation (ACO) method to solve large size problems. Finally, the best method (ACO) has been used to solve a real industrial case that is presented at the end.     

Managing strategic and tactical constraints in the hi-tech industry

This paper addresses the issue of constraint management in the hi-tech industry, from the vantage point of the theory of constraints (TOC). First, we argue that the hi-tech industry faces a market constraint in operations, and resource constraints in both research and development (R&D) and marketing and sales (M&S). We then make the distinction between strategic and tactical constraints, and build a methodology to identify and manage them.

While the TOC enables tactical treatment of the organization's internal resource constraints, we consider the prevailing constraint to be in the external business arena. In the short term, organizations apply the TOC methodology to increase their throughput, usually by focusing on the internal constraints. This is defined as tactical constraint management. In the long term, they navigate to position themselves in relation to the business arena's constraint. This is defined as strategic constraint management.

In the paper we address the strategic dilemma of where the constraints should be in the hi-tech industry and how to reposition them there. In so doing, we bear in mind the relatively high frequency at which the hi-tech industry constraints change their position, and provide examples of disruptive change.     

Optimizing the Hot Isostatic Pressing Process

A genetic algorithm (GA) is used to optimize the hot isostatic pressing (HIPing) process for beryllium powder. The GA evaluates a HIPing model with different processing schedules in an effort to minimize temperature, pressure, processing time, ramp rates, grain growth, and distance to target relative density. It is shown that this is a constrained, multiobjective, noisy, optimization problem to which the GA is able to evolve a large number of viable solutions. However, for the GA to work in such a large multidimensional search space, it is suggested that the constraints be treated as objectives and then penalize the Pareto ranking for each constraint violated. This approach is necessary because a large-dimensional objective space naturally results in most members being Pareto rank 1.     

TOC构造过程模型驱动产品创新设计

简要分析了产品冲突问题的约束理论(theory of constraints,TOC)思维流程,介绍了发明问题解决理论(theory of inventive problem solving,TRIZ)创新设计过程。描述了TOC中5个逻辑图表及其相互之间的关系。提出一种将TRIZ与TOC相结合的产品冲突问题解决过程构造模型的设计方法,利用所构造的产品当前实现树、逻辑图表和TRIZ的矛盾冲突解决矩阵来解决产品冲突问题。实例证明TRIZ与TOC相结合的方法用于驱动产品创新设计是切实可行的。     

Value enhancement in a dynamic environment—a constraint management expert system for the oil refinery industry

This paper analyses a case study of a dynamic expert system which was developed according to the theory of constraints (TOC) approach, and implemented at the Ashdod refinery of Oil Refineries Ltd in Israel, as part of an overall improvement process based on the focused management philosophy. The unique feature of the system is its ability to cope with dynamic bottlenecks typical of the continuous process industry, as well as frequent shifts from an external market constraint to internal capacity constraints. The paper examines the development and implementation stages, describes the expert system along with the new process control, and evaluates its impact. The system creates a dynamic, effective and immediate link between the production planning and the operation control, which enables the oil refinery to maximize its profits. During the first two years of its use, the system generated over $3 million of estimated benefits. Finally, we suggest practical implications to assist organizations in developing and utilizing similar applications, emphasizing knowledge gathering and maintenances, which are the major challenges facing expert systems projects.     

When less is better: Insights from the product mix dilemma from the Theory of Constraints perspective

Perhaps due to its origins in a production scheduling software called Optimised Production Technology (OPT), plus the idea of focusing on system constraints, many believe that the Theory of Constraints (TOC) has a vocation for optimal solutions. Those who assess TOC according to this perspective indicate that it guarantees an optimal solution only in certain circumstances. In opposition to this view and founded on a numeric example of a production mix problem, this paper shows, by means of TOC assumptions, why the TOC should not be compared to methods intended to seek optimal or the best solutions, but rather sufficiently good solutions, possible in non-deterministic environments. Moreover, we extend the range of relevant literature on product mix decision by introducing a heuristic based on the uniquely identified work that aims at achieving feasible solutions according to the TOC point of view. The heuristic proposed is tested on 100 production mix problems and the results are compared with the responses obtained with the use of Integer Linear Programming. The results show that the heuristic gives good results on average, but performance falls sharply in some situations.