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.     

TOC会计

主要介绍TOC的基本原理、TOC会计以及产品组合。     

基于约束理论的设施规划的改进

在市场经济环境下,生产设施规划改进是企业的一项持续不断的工作。本文提出运用约束理论的基本分析步骤,结合工艺流程图分析等手段来分析生产系统的约束因素,并寻求改善和解决方案。     

基于TOC和Petri网的业务流程重组方法

业务流程重组是企业根据市场和环境变化进行自身调整和完善,从而在竞争中取得优势的重要手段.通过Petri网建模可以对企业业务流程进行动态分析和控制,寻找制约企业盈利的最薄弱环节.在此基础上,应用约束理论(TOC)能够对业务流程中最薄弱的环节进行改进和重组,逐一消除制约环节,不断提升企业的竞争能力.在分析Petri网流程建模思路和约束理论基本原理的基础上,提出了基于Petri网和约束理论的业务流程重组方法,并进行了实证研究.     

An algorithm for optimizing joint products decision based on the Theory of Constraints

A particular decision-making process that is needed by most firms who produce joint products is the one requiring an assessment of desirability of further processing joint products beyond the split-off point. The purpose of this paper is to develop an algorithm for optimizing a joint products further processing decision under the theory of constraints. To fit the jointly produced characteristic of joint products and the sequential produced characteristic between each joint product and its further processing product, the algorithm is composed of seven steps. These steps consider every bottleneck resource to the decision-making process by computing a priority ratio to establish its priority sequence. According to the priority sequence of the most constrained resource, the initial master production schedule is developed. Then, the following steps find the best path to reach the optimal solution under the guidance of all bottleneck resources. Due to its accessibility and comprehensibility, the TOC-based algorithm developed by this paper is a practical tool for obtaining the optimal joint products further processing decision.     

基于约束理论的管理方法及其应用

简要系统地介绍了约束理论的基本原理，指出在企业管理的持续改进方面，其管理哲理和技术较之其他更具有普适性，并应用实例说明了这一点。     

Bi-level multi-objective mathematical model for job-shop scheduling: the application of Theory of Constraints

This study highlights a different systematic approach to the application of Theory of Constraints (TOC). The work describes the decisions involved in the implementation of TOC in a job-shop environment as a bi-level multi-objective mathematical model. On the first level, the decision is made by minimising idle time on the bottleneck to generate the initial schedule. The second level decision is to improve additional performance measurements by applying the multi-objective technique, while maintaining the bottleneck sequence obtained from the first level decision. Moreover, the concept of transfer lot is also adopted in this model to reduce the waiting time on each machine by allowing overlapped operations. The concept of transfer lot is applied as the constraint on earliest starting time for each job on each machine in the proposed mathematical model. Additionally, the machine set up time and product demands are also adopted to make the model practical to use in the real situation. The numerical examples for both single and multiple bottleneck cases are given to demonstrate how this approach works. The commercially available optimiser, the LINGO 10 software package, is used to solve the examples and the result shows how this approach works in practice.     

The impact of human consideration,schedule types and product mix on scheduling objectives for unpaced mixed-model assembly lines

There is an increasing awareness in scheduling research that human behaviour needs to be considered explicitly in scheduling models. Although most scheduling literature ignores human behaviour, especially sequence-dependent processing times form a good basis for explicit consideration. Hence, a processing time function is derived that considers the effects of learning, forgetting, fatigue and recovery. The necessity for explicit human consideration can be regarded as most urgent for unpaced highly-manual mixed-model assembly lines. Based on real data a simulation study is conducted to determine the effect of explicit human consideration while also taking into account the effects of different idealised schedule types and the product mix. The results strongly indicate that the product mix has a consistently high impact on scheduling objectives, the schedule type affects lower-level objectives like starving and blocking times to a greater extent than higher-level objectives like makespan and flow time, and that for certain objectives the height of the objective values and the relative favourability of schedule types depends on human consideration.     

基于价值工程的可适应性评价方法

可适应设计是为适应用户需求不断变化、降低资源消耗而提出的一种新的设计方法,对产品的可适应性进行评价是其关键技术之一.在分析可适应设计原则及实现途径的基础上,给出了一种基于价值工程的产品可适应性的评价方法.该方法将产品的资源消耗总量、产品性能以及用户的使用环境等因素综合考虑,将用户使用产品后获得的效益与在完成这一系列任务时所消耗的资源量的比值作为评价产品可适应性的指标.通过该方法,可以选择使用户在产品的全生命周期内资源消耗量最少的产品设计方案.最后,将该可适应性评价方法用于高效圆柱齿轮机床的设计中,验证了该方法的有效性.     

Measuring machine and product mix flexibilities of a manufacturing system

This paper provides a brief discussion on flexibility concepts in manufacturing. It emphasizes that flexibility measurements in a manufacturing system should be studied under dynamically changing environments rather than static ones. The approaches for assessing two major flexibility types, machine flexibility and product mix flexibility response, are presented. The machine flexibility model is based on machine-operation efficiency. The product mix flexibility response model is based on the difference between products in terms of tooling requirements, the number of operations that a machine can perform and the efficiency of different machines.     

An empirical study of impacts of production mix,product route efficiencies on operations performance and profitability: a reverse logistics approach

This research studies the impact of two reverse logistics business strategies on profitability of the firm through operations management (OM). The study is employed on scrap steel industry. The first strategy is production mix efficiency (PME), which is involved in the process of producing goods. The second strategy is product route efficiency (PRE), which engages in the transportation of goods. Our finding indicates that OM alone does not have a positive impact on profitability. However, the two strategies have a positive effect on profitability, which provides a potential answer to firms trying to improve profitability.     

Non-discrete ant colony optimisation (NdACO) to optimise the development cycle time and cost in overlapped product development

In order to expedite the process of introducing a product to market, organisations have shifted their paradigm towards concurrent engineering. This involves the simultaneous execution of successive activities on the basis of information available in rudimentary form. For this, cross-functional teams sporadically communicate to exchange available updated information at the cost of augmented time and money. Therefore, the aim of this paper is to present a model-based methodology to estimate the optimal amount of overlapping and communication policy with a view to minimising the product development cycle time at the lowest additional cost. In the first step of the methodology, an objective function comprising the cycle time and the cost of the complete project is formulated mathematically. To reach the optimal solution, a novel meta-heuristic, non-discrete ant colony optimisation, is proposed. The algorithm derives its governing traits from the traditional ant algorithms over a discrete domain, but has been modified to search results in a continuous search space. The salient feature of the proposed meta-heuristic is that it utilises the weighted sum of numerous probability distribution functions (PDFs) to represent the long-term pheromone information. This paper utilises a novel approach for pheromone maintenance to adequately update the PDFs after each tour by the ants. The performance of the proposed algorithm has been tested on a hypothetical illustrative example of mobile phones and its robustness has been authenticated against variants of particle swarm optimisation.     

Identification of the to-be-improved product features based on online reviews for product redesign

Acquisition of customer needs usually serves as the basis for the identification of to-be-improved features for the product redesign process. However, the customer's true needs tend to be non-obvious and are difficult to extract from the data source like interviews or market survey. In the era of Big Data, with the advances in e-commerce, the customer's online review has become one of the most important data source to reveal the insight of customer's preference. In this paper, an online-review-based approach is introduced to identify the to-be-improved product features. The product features and corresponding opinions are extracted and reduced based on the semantic similarity. A structured preference model based on the semantic orientation analysis is constructed. A redesign index is subsequently introduced to measure the priority of redesign for each feature, and a target feature selection model is created to identify the to-be-improved features from candidate features considering engineering cost, redesign lead time and technical risk. A case study for smartphones is developed to demonstrate the effectiveness of the developed approach. In the future study, the online reviews may be combined with the traditional survey data to provide a more effective and reliable identification on the to-be-improved product features.     

Process plan selection based on product mix and production volume

Most shops currently maintain a single process plan for each part type manufactured by the shop even when multiple process plans are feasible to produce the part. The use of a static process plan for a part regardless of the product mix and volume robs the shop of production flexibility and efficiency. In this paper, given that multiple process plans for a part exist, a method to determine the best process plan to implement for a part type in a given production scenario defined by a known product mix and volume is addressed. The method selects a set of process plans to implement based on minimizing total material handling and machining time for the part mix and volume. The problem is modelled mathematically and solved using a heuristic algorithm. Experimental results to describe the performance of the algorithm are presented for different production scenarios, problem sizes, and solution strategies.     

基于案例的文化创意产品设计方法研究

针对文化产品的造型设计,将与产品造型相关的设计元素细分为功能、行为、文化、情感和构造法五个方面,结合基于案例的设计(case-based design,CBD)技术、遗传算法以及形状文法知识,建立文化创意产品设计概念原型系统并对文化创意产品进行引导设计。提出产品造型相关设计元素多目标优化模型,对用户需求进行匹配操作。提出文化产品造型设计方法模型,结合产品基因树交叉操作与形状文法知识,将现代类产品与文化器物类产品的设计元素进行交叉重组。通过对产品造型相关设计元素进行深入研究,并在文化创意产品设计概念原型系统中融入基于案例的设计技术、遗传算法和形状文法的知识,辅助设计师对文化产品进行创意设计。以小音箱为例,验证了该方法的可行性,为文化产品设计提供了一种有效方法。     

Heuristic solution to the product targeting problem based on mathematical programming

Maintaining customer lifetime longevity is a crucial issue for companies. One of the strategies for dealing with this issue is to offer different promotion campaigns. Planning these campaigns creates a problem: Which targeted products in the campaign should be offered to which customers in order to maximise profit? This problem becomes vitally important under the conditions of a limited budget and a lower bound on sales target of each product. It is also remarkable from the operational research perspective because of its NP-hardness. In this study, heuristic approaches to the product targeting problem based on mathematical programming are suggested. The proposed approaches principally determine the products to be included in a campaign using heuristic rules and then distribute these products to the customers optimally. Computational results confirm that these approaches generate superior solutions to the problem in comparison with existing methods in the literature. The effectiveness and efficiency of the approaches are also shown on very large-sized test problems generated in order to verify their potential for practical applications.     

Comparison between the fatigue response of hot and warm mix asphalts based on the dissipated energy approach

This study focused on the fatigue behaviour of warm mix asphalt (WMA) based on the dissipated energy (DE) approach. Two conventional binders consisting of 60/70 and 85/100 penetration-grade bitumens were used to prepare the control mix. WMA was prepared by incorporating 2% Sasobit by weight of bitumen. First, the basic properties of WMA containing optimum bitumen content were compared with those of control hot mix asphalt (HMA). The main laboratory programme included four-point flexural fatigue test that was accomplished at different strain levels of 250, 500, 750 and 1000 microstrain. The studied WMA had comparable Marshall stability and indirect tensile strength to those of control HMA. Furthermore, based on the resilient modulus test results, the temperature susceptibility of WMA was slightly more than that of the control mix. Fatigue lives of studied mixes were evaluated using the conventional fatigue curves that were developed based on the initial strain level. Comparison between these curves revealed the predominant fatigue behaviour of WMAs at different examined strain levels. The initial DE and the cumulative DE of WMAs were lower than those of HMAs. The latter issue justifies the predominant fatigue response of WMA. By considering the DE curve, the ratio of dissipated energy change (RDEC) was calculated. Afterward, the plateau value (PV) was determined using the moving average of fatigue data in the plateau stage of the RDEC curve. Finally, PV-based fatigue models were developed which could precisely estimate the fatigue life regardless of the mix type and testing condition.     

Optimisation of hot mix asphalt performance based on aggregate selection

Researchers over the last four decades have identified and demonstrated the effects of aggregate morphological properties (particularly shape, size distribution, angularity and texture) on the mechanical properties of hot mix asphalt (HMA). Rare studies, however, have clearly established the relationships between the aggregate properties and pavement performance. Therefore, they have not provided methods to optimise aggregate properties at the design stage to improve that performance. This study focuses on understanding the effects of aggregate gradation and type on moisture damage resistance of HMA and on pavement performance as indicated by stiffness and rutting. Results show that basalt aggregate achieves higher moisture susceptibility resistance and stiffness than limestone aggregate. Coarser gradation has the highest permanent deformation, while open gradation 2C provides the lowest moisture damage resistance. Furthermore, dense gradation 4C provides the lowest rutting and the highest stripping resistance. It is indicated that suitable selection of aggregate type and gradation can improve pavement performance and reduce the moisture damage problem of HMA.     

水产品新鲜度表征和评价方法研究综述

水产品的新鲜度是衡量水产品品质好坏的一项重要指标,直接影响水产品的销量、加工价值及消费者的食用安全。本文概述了水产品的腐败机理,较为全面地论述传统的水产品新鲜度评价方法和新型的新鲜度检测方法,对现有方法存在的问题作了概述,并对未来的研究发展趋势进行了展望。