工序分析法在投影仪装配线改善过程中的应用

将投影仪组装作业按照其先后逻辑顺序和作业目的,使用工序图符号对产品组装流程进行工序分析,识别出生产流程改善点.通过改变生产工艺来减少机体反光镜组件的库存,减少在制品库存来缩短停滞时间,改善生产线布局来消除多余搬运活动.通过实施改善方案,工序总数减少,在制品库存降低70%左右,投影仪加工周期大幅降低.     

Continuous time scheduling for sugarcane harvest logistics in Louisiana

Despite a growing global appetite for sugar as both a foodstuff and a fuel source, there exists limited literature that explores sugarcane operations. In this paper, we look at the scheduling harvest and logistics operations in the state of Louisiana in the United States. These operations account for significant portions of the total sugarcane production costs. We develop an integer programming model for coordinating harvest and transport of sugarcane. The model seeks to reduce vehicle waiting time at the mill by maximising the minimum gap between two successive arrivals at the mill. To help improve tractability, we introduce valid inequalities and optimality cuts. We also demonstrate how to adapt solutions from a previous discrete-time model. Our results show that arrivals can easily be coordinated to reduce truck waiting time at the mill.     

Cost optimization for series–parallel execution of a collection of intersecting operation sets

A collection of intersecting sets of operations is considered. These sets of operations are performed successively. The operations of each set are activated simultaneously. Operation durations can be modified. The cost of each operation decreases with the increase in operation duration. In contrast, the additional expenses for each set of operations are proportional to its time. The problem of selecting the durations of all operations that minimize the total cost under constraint on completion time for the whole collection of operation sets is studied. The mathematical model and method to solve this problem are presented. The proposed method is based on a combination of Lagrangian relaxation and dynamic programming. The results of numerical experiments that illustrate the performance of the proposed method are presented. This approach was used for optimization multi-spindle machines and machining lines, but the problem is common in engineering optimization and thus the techniques developed could be useful for other applications.     

EGS环境下的订单分配优化分析

将在线与店内顾客购物冲突引起的通道拥塞问题简化为排队等待时间优化问题,以订单在店内的最大等待时间最小化为目标,利用M|M|1排队系统建立了排队论优化模型.算例分析显示:在最优解中,该模型试图令所有的商店均达到工作载荷均衡,从而在配送预算范围内的任意时刻拥塞程度均可达到最小化.在敏感度分析中,最优等待时间与成本预算和总利用率两个变量密切相关,即当配送预算和总利用率达到某个特定值后,再次下降时,等待时间将分别发生显著增加和减少,这将对系统的绩效产生负面影响.     

Synchronized strategy to minimize vehicle dispatching time:a real example of steel industry

Time compression in supply chains is a crucial aspect involved in the integration of warehousing and transport operations in the manufacturing industries.Supply chain flows could be interrupted due to many sources of delays that lead to additional time in dispatching process and reduction in customer service level.The problem considered in this paper consists of long waiting times of loading vehicles inside the plant.This work presents a simulation-based study to minimize vehicle dispatching time in a steel wire plant.Value stream map is developed to present a system perspective of processes involved in the overall supply chain.Process activity mapping is completed to provide a step by step analysis of activities involved in the vehicle dispatch process.A simulation model is developed for the system and a new model is proposed to improve the delivery performance by minimizing vehicles' waiting time.     

A synchronized strategy to minimize vehicle dispatching time: a real example of steel industry

Time compression in supply chains is a crucial aspect involved in the integration of warehousing and transport operations in the manufacturing industries. Supply chain flows could be interrupted due to many sources of delays that lead to additional time in dispatching process and reduction in customer service level. The problem considered in this paper consists of long waiting times of loading vehicles inside the plant. This work presents a simulation-based study to minimize vehicle dispatching time in a steel wire plant. Value stream map is developed to present a system perspective of processes involved in the overall supply chain. Process activity mapping is completed to provide a step by step analysis of activities involved in the vehicle dispatch process. A simulation model is developed for the system and a new model is proposed to improve the delivery performance by minimizing vehicles’ waiting time.     

Models for the schedule optimization problem at a public transit terminal

This work deals with the proposal of some models for the schedule optimization problem for public transit networks. In particular, we consider the case of a transit terminal where passengers are supposed to split among different lines of a service, or even change mode of transportation in case of intermodal systems. Starting from a given schedule for the transit lines arriving at the terminal, the aim is to decide the optimal schedule for the output lines, in such a way to balance the operative costs of the service and the passenger waiting time at the transit terminal. We propose two different models for this problem, which present strong similarities with some well known combinatorial optimization models. Computational results are also presented, showing the suitability of the models to solve real case studies.     

Scheduling flexible flow lines with no in-process buffers

An heuristic algorithm is proposed for scheduling a flexible flow line with no intermediate buffers. The line is made up of several processing stages in series, where each stage has one or more identical parallel machines. In the line different part types can be manufactured simultaneously, each of which is processed by at most one machine in every stage. Intermediate queues of parts waiting between the stages for their next operations are not allowed. The problem objective is to minimize the makespan of the schedule for a set of part types selected for processing. The algorithm proposed is a part-by-part heuristic, in which during every iteration a complete processing schedule is determined for one part type selected for loading into the line. The selection of the part type and its complete schedule are based on the cumulative partial schedule obtained for all parts selected so far. The decisions in every iteration are made using a local optimization procedure aimed at minimizing total blocking and waiting time of the machines along the route of the selected part type. The efficiency of the algorithm is tested on several groups of random test problems     

An accelerated failure time model for investigating pedestrian crossing behavior and waiting times at signalized intersections

The waiting process is crucial to pedestrians in the street-crossing behavior. Once pedestrians terminate their waiting behavior during the red light period, they would cross against the red light and put themselves in danger. A joint hazard-based duration model is developed to investigate the effect of various covariates on pedestrian crossing behavior and to estimate pedestrian waiting times at signalized intersections. A total of 1181 pedestrians approaching the intersections during red light periods were observed in Beijing, China. Pedestrian crossing behaviors are classified into immediate crossing behavior and waiting behavior. The probability and effect of various covariates for pedestrians’ immediate crossing behavior are identified by a logit model. Four accelerated failure time duration models based on the exponential, Weibull, lognormal and log-logistic distributions are proposed to examine the significant risk factors affecting duration times for pedestrians’ waiting behavior. A joint duration model is developed to estimate pedestrian waiting times. Moreover, unobserved heterogeneity is considered in the proposed model. The results indicate that the Weibull AFT model with shared frailty is appropriate for modelling pedestrian waiting durations. Failure to account for heterogeneity would significantly underestimate the effects of covariates on waiting duration times. The proposed model provides a better understanding of pedestrian crossing behavior and more accurate estimation of pedestrian waiting times. It may be applicable in traffic system analysis in developing countries with high flow of mixed traffic.     

Computer-aided optimization of multi-pass turning operations for continuous forms on CNC lathes

The Computer Numerical Control (CNC) machine is one of the most effective production facilities used in manufacturing industry. Determining the optimal machining parameters is essential in the machining process planning since the machining parameters significantly affect production cost and quality of machined parts. Previous studies involving machining optimization of turning operations concentrated primarily on developing machining models for bar components. Machined parts on the CNC lathes, however, typically have continuous forms. In this study, we formulate an optimization model for turned parts with continuous forms. Also, a stochastic optimization method based on the simulated annealing algorithm and the pattern search is applied to solve this machining optimization problem. Finally, the applications of the developed machining model and the proposed optimization algorithm are established through the numerical examples.     

Mathematical model for determining machining parameters in multipass turning operations with constraints

The paper presents a new mathematical programming model for optimizing process parameters and subdivisions of depth of cut in multipass turning operations. The model is a direct non-linear mathematical model that solves the optimization problem of multipass turning operations providing all decision variables (cutting speed, federate, depth cut, subdivision of depth of cut, number of passes) for both finishing and rough cutting in a single run. It relaxes restrictive assumptions related to depth of cut and other process parameters. In addition, the developed model eliminates the complexities encountered in existing methods. Illustrative examples from the literature are presented to test and compare the developed model against existing methods.     

液晶显示器外壳生产线平衡分析与改善

液晶显示器外壳生产线平衡分析与改善 针对苏州一个公司的液晶显示器外壳生产线平衡率不高的问题,通过程序分析,综合运用5W1H提问技术、ECRS原则等方法和工具,对其液晶显示器外壳生产线流程进行重新设计。结果表明,改善方案在等待时间、搬运时间和距离等方面有明显的改进。针对原流程中的瓶颈作业,通过运用Flexsim仿真软件进行分析,对比改进前和改进后各工位的作业时间、空闲时间及阻塞率等,讨论新方案的实施效果。最后对整个生产线改进效果进行预测,并对该公司液晶显示器外壳生产线改进提出实施建议。     

Optimum design of weaving structure of 3-D woven fabric composites by using genetic algorithms

This paper discusses the optimum design method of the weaving structure of three-dimensional (3-D) reinforced composites. We propose the design method which combines the genetic algorithms (GA) and the finite element analysis. GA is one of the optimization techniques for the combinatorial optimization problem. In the finite element analysis, we used the original structure model which can express the fiber arrangement state in the 3-D composites faithfully. In this study, the original weaving structure model is constructed by combining the basic structure which has the fiber bundle and the cubic grid of resin. From analysis results, in the small design region, we can obtain the optimum weaving structure. Moreover, we proposed a new genetic operation, to design the weaving structure at the larger design region. These operations aim to prevent the failure of the partial weaving structure in the analytical model as much as possible. From the analysis results, the optimum weaving structure is obtained at the large design region, similar to above results. Consequently, it seems that the proposed method enables the design of the optimum weaving structure in the 3-D composites.     

区间模型非概率可靠性指标的一维优化算法

证明了基于区间模型的非概率可靠性指标只可能存在于:标准化区间向量张成的凸域及其扩展空间中,通过原点和凸域顶点的有限条超射线与标准化失效面的某个交点处,从而极大地缩小了优化方法求取非概率可靠性指标的可行域,使放弃计算结果极易扩张的区间运算法则和计算量太大的高维寻优方法成为可能。提出了求取非概率可靠性指标的一维优化方法,讨论了一维优化方法搜索区间关于0对称且具有半径递减的特性,利用该特性明显提高一维优化算法的效率。     

An optimization based decision support system for integrated planning and scheduling on dedicated freight corridors

Empty wagon redistribution, train formation, routing and scheduling are complex problems for large railways, many of which currently have or are planning dedicated freight railway corridors (DFC). DFC operations due to their unique characteristics require research and new models for better operations planning. The rolling-stock, being expensive assets, need to be utilised in an optimal manner while meeting service quality levels. Motivated by Indian DFC, we present an integer programming formulation of the dynamic problem of empty distribution and train scheduling in DFC and discuss associated modelling issues. By unifying the separate problems into a single and dynamic model, we have developed a framework for more effective rolling stock utilisation. Based on this optimization model, an interactive decision support system is proposed for better decision-making on rolling-stock allocation and train scheduling. Extensive experiments and systematic analyses for a case of Indian DFC highlight the potentialities and effectiveness of the proposed DSS for DFC operations planning and management.     

A two-phase heuristic algorithm for determining buffer sizes of production lines

In-process inventories are often used in many manufacturing systems to smooth and balance work flow. The buffer design problem of determining the best size of storage space between operations (or workstations) is one that has been approached in past and current research issues. Although past research attempted to apply traditional optimization methods to the buffer design problems, the applications revealed that some fundamental drawbacks were occurring due to the unique characteristics of the buffer design in the production lines. This paper addresses the unique characteristics involved in the buffer design, discusses drawbacks of traditional optimization methods applied, and finally presents an efficient two-phase heuristic method using a dimension reduction strategy and a buffer utilization-based beam search method, fn addition, numerical results show sensitivity analyses for the performance of the heuristic method with respect to parameters involved in the second phase of the method.     

Lotsizing in Multi-Item Multi- Machine Job Shops

A great many manufacturing facilities can be described as closed job shops which process multiple items through multiple work centers for stock or for assembly. The performance of these shops is strongly dependent on the batching policies employed for work in the shop. In particular, waiting time in queue and total manufacturing lead time for batches are functions of lotsizes. In turn these affect work-in-process costs, safety stock requirements, schedule performance and part coordination for assembly. The relationship between lot-sizing and shop performance is represented using a queueing network model which is then embedded in an optimization routine that searches for optimal lot sizes.     

Detection of an appropriate pharmaceutical company to get a suitable vaccine against COVID-19 with minimum cost under the quality control process

Some international pharmaceutical companies have succeeded in producing vaccines against COVID-19. Countries all over the world have aimed to obtain these vaccines with minimum cost. We consider a set of K-independent Markovian waiting lists. Each list contains a set of countries, where each one of them has an exponential service time and a Poisson arrival process. These companies differ in some characteristics such as the vaccine production cost and the speed of the required quantity delivery. We present a new detection model that helps in providing an appropriate decision to choose a suitable company. Moreover, the concept of balking and the retention of reneged countries is taken into consideration under the quality control process of each waiting list. Under steady state, we face an interesting and difficult discrete stochastic optimization problem. Its solution gives an optimal distribution of the searching effort, which is bounded by a known probability distribution. A simulation study has been derived to get the minimum value of the paid cost random values. The highest service rate, the total expected profit of each queuing system, and the optimum performance measures, which depend on this cost, have been obtained to show the effectiveness of this model.     

物料齐套时间不确定的多地总装作业前摄性调度

定制型生产线的总装环节具有工程项目式运作、在客户地开展手工装配、所需物料众多等特点,装配组在各个客户地往来调配需要差旅时间,而装配物料又难以如期齐套,容易导致人员和物料的相互等待,从而延长了此类生产线的交付周期。本文通过对总装作业进行前摄性考虑以减少等待浪费、缩短交期。首先建立不确定环境下多地总装作业前摄性调度数学模型,然后以质量鲁棒性和解的鲁棒性为优化目标,构建了结合缓冲时间插入策略和抽样仿真技术的非支配排序遗传算法NSGA-II求解问题,最后通过实际样例验证了算法的有效性。     

Reduced outpatient waiting times with improved appointment scheduling: a simulation modelling approach

Abstract. An outpatient department represents a complex system through which many patients with varying needs pass each day. An effective appointment system is a critical component in controlling patient waiting times within clinic sessions. Current waiting times are often unacceptable and place great stress on clinic staff. This paper describes the development and use of a detailed simulation model of an Ear, Nose and Throat (ENT) outpatient department. The simulation allows various appointment schedules to be examined and their effects on the clinic evaluated. The model has been used to identify a number of critical factors that influence patient waiting times and the build up of queues in the clinic. Alternative appointment schedules have been shown to drastically reduce patient waiting times, without the need for extra resources, and enable the department to move towards meeting the UK Government's Patient's Charter. RID="*" ID="*" The authors would like to express their thanks for the valuable support provided by the anonymous participants (outpatient department staff). Thanks also to Helen Gilby, Dr Arjan Shahani and Professor Valter de Senna for their useful comments and help during the research. Correspondence to: P.R. Harper