基于马尔可夫过程的混流装配线缓冲区容量研究

为研究混流装配线缓冲区容量,基于马尔可夫过程原理,建立了通用的混流装配线模型,分析了模型中工作站和缓冲区状态,绘制了工作站与缓冲区的状态图,建立了状态转移矩阵,分析了工作站与缓冲区在不同状态下装配线正常运转的概率,推导出了装配线可用度与缓冲区容量之间的关系。用可用度计算公式分析混流装配线缓冲区设置对提高装配线可用度的影响,并以两级系统为例计算缓冲区容量,分析了缓冲区容量与可用度、费用之间的关系。     

可重组制造系统缓冲区容量的优化研究

为了确定可重组制造系统中的缓冲区容量,通过分析机床工作状态、生产需求量等因素对缓冲区容量的影响,建立了缓冲区状态数学模型.在此基础上,提出了缓冲区容量、机床可用度和任务需求率之间的函数关系.以满足生产任务为前提,将重组后加工域缓冲区容量最小化作为优化目标.通过粒子群优化算法,利用非可微精确罚函数法处理约束条件,采用可变惯性权重平衡搜索,以求得各工序间缓冲区容量.最后结合仿真实例,探讨了该生产线重组后系统缓冲区容量的最优配置.     

可重构制造系统多态可靠性建模与分析

针对利用传统方法建立多状态系统可靠性模型引起的组合爆炸问题,提出一种基于随机过程方法和改进的通用产生函数法(Universal generating function,UGF)的含中间缓冲区的可重构制造系统(Reconfigurable manufacturing system,RMS)多态可靠性建模方法。利用随机过程方法建立存在非相邻状态转移的可重构机床(Reconfigurable machine tool,RMT)的马尔科夫模型,求解机床各理论稳态概率;定义中间缓冲区状态,并通过分析中间缓冲区对机床可用度的影响,得到中间缓冲区可用度和机床各状态的实际稳态概率;结合RMS和RMT性能多态性的特点,对UGF进行改进。在此基础上,表示设备层和系统层的发生函数,建立多零件族可修RMS的多态可靠性模型,并对系统的各项性能指标进行分析。以双零件族四工序非串行缸盖机加工系统为例,验证该模型与分析方法的有效性。     

基于可用度评价的混联生产线缓冲区配置优化

为快速有效地分配缓冲区容量,提高混联生产线的可用度和生产率,提出了一种基于可用度评价的缓冲区分配方法。在考虑混联生产线特性的同时,通过分析设备状态与缓冲区状态之间的转化规律,将缓冲区进行等效处理,以获得等效设备的可用度;结合通用发生函数(UGF)法,建立混联生产线的可用度与缓冲区容量关系的数学模型,以整线可用度最大为目标,利用遗传算法(GA)求解得到最优的缓冲区配置策略。多个生产线实例缓冲区优化分配结果表明,基于可用度评价的缓冲区分配方法能够在有效解决缓冲区配置问题的同时,明显减少生产线的平均在制品数量。     

考虑设备多状态的缸盖生产线性能分析与优化

为实现发动机缸盖生产线的性能提升和成本管控,提出一种考虑设备多状态的发动机缸盖生产线性能分析与缓冲区配置优化方法。首先,采用马尔可夫模型揭示设备多状态与缓冲区库存的变化规律,建立了生产线可用度与缓冲区容量的耦合模型。其次,构建了以生产线可用度和缓冲区配置成本为目标的多目标优化模型,并采用NSGA-Ⅱ算法求解优化模型。最后,通过案例证明所提方法能提高缸盖生产线的生产性能并降低缓存区配置成本。     

基于Petri网的非串行制造系统的可靠性分析

对带有中间缓冲区的非串行系统深入研究其可靠性问题,建立基于广义随机Petri网的可靠性模型,着重考虑出现的装配、拆分以及按不同比例进行装配或拆分的加工工序,其中间缓冲区可用度对机器可用度的影响,在此模型基础上,采用缓冲区可用度定理,对中间缓冲区和机器本身的状态转移概率分别分类求解,计算出相应的缓冲区可用度和等效机器可用度;同时通过功能可靠度指标,对整个加工任务车间的可靠性进行总体评价,从时间量和产品量因子出发,来衡量由于生产率的不平衡以及中间缓冲区的库存太小,引起生产流程中传输道的阻塞和缺料,进而造成的相关工件的加工时间延迟等问题。以三台机床和两个待加工工件的加工装配单元为例,验证该模型与分析方法的有效性。     

柔性装配线缓冲区设计

针对柔性装配线缓冲区设计问题,采用数学方法与仿真方法相结合,设计出合理的缓冲区。利用e M-Plant软件进行仿真,找出柔性装配线的瓶颈工位位置;再利用装配线可用度与缓冲区容量之间的关系;设置满足要求的最小缓冲区容量;通过e M-Plant软件仿真,验证缓冲区设计的合理性。     

基于遗传算法的机器人自动化生产线缓冲区容量分配方法

研究一种机器人自动化生产线缓冲区容量分配问题的优化方法。生产系统的生产率与各工序可靠性、生产率及缓冲区容量密切相关。生产线缓冲区总量受限,须将此总量分配至各生产工序的缓冲区。采用连续型生产线模型,并使用近似和分解方法建立生产线可用度和缓冲区容量分配间的关系模型。提出在缓冲区总容量受限状态下,以生产线最大可用度为目标的优化策略。设计半父体比例交叉和单亲交叉型变异的遗传算法得到缓冲区容量分配的次优解,并将该方法应用于一种2平动自由度高速并联机械手为核心的输液软袋装箱码垛自动化生产线,得到该类生产线的缓冲区分配优化方案。多条机器人装箱码垛生产线运行结果表明,此方法是行之有效的。     

装配系统中缓冲区容量的研究

为了确定装配系统中的缓冲区容量,在建立缓冲区状态数学模型的基础上,根据随机过程的原理,提出了缓冲区被充满概率和缓冲区容量之间的函数关系.以缓冲区被充满概率最小化为目标,确定合理的缓冲区容量.最后给出一种递进算法,通过回归方程计算缓冲区对装配工位生产率的影响,逐步求出由多个工位组成的整个装配系统各个工位之间的缓冲区容量.     

基于排队网模型的流水车间缓冲区容量优化

针对订货型单类型工件多级流水车间缓冲区容量优化设置问题,在考虑各级工序节点之间耦合关系的前提下,基于连续时间Markov随机过程原理建立了多级流水车间的排队网节点状态模型,并根据缓冲区容量优化目标函数的特点,给出缓冲区容量和任务拒绝率之间的关系。基于该模型计算系统的关键性能指标,以任务拒绝率为约束条件,提出一种缓冲区容量优化的启发式优化算法。通过该算法计算算例及结果分析,最终确定了合理的缓冲区容量。     

A study of FMS part type selection approaches for short-term production planning

This research compares seven approaches from the literature to the selection of part types for simultaneous production over the next time horizon. A flexible approach to the selection of part types and the simultaneous determination of their mix ratios so as to balance aggregate machine workloads is presented. Constraints on tool magazine capacity are considered. Simulation studies are conducted on realistic, detailed models of flexible flow systems (FFSs) configured as pooled machines of equal sizes. The simulated settings are constructed to evaluate the impact of such factors as blocking, transportation, buffer utilizations, and fixture requirements and limitations of various types.One of the goals of this study is to encourage industry to relax, for those FMS types for which the procedure is appropriate, what is essentially an artificial constraint: that tool changing be isolated in time, to a period between batches. For other types of FMSs, batching may be appropriate.The results indicate that using the flexible approach enables the system to be more highly utilized. It is also observed that the batching approaches tend to require more fixtures of each type than the flexible approach. The system utilizations for the batching approaches seem to be more sensitive to restrictions on the number of fixtures of each type. Further research needs are also discussed.     

A robust scheduling of projects with time, cost, and quality considerations

CAM programs can generate cutting tool paths to be used by machining centres. Experience shows that CAM programmed feed rates are rarely achieved in practice during machining, especially when finishing free-form surfaces. These slower feed rates are due to the machines’ kinematic capabilities and behaviour of the numerical control (NC). To improve control over the machining process, applications need to be developed to predict the kinematic behaviour of the machines, taking the mechanical characteristics of the axes and NC capacities into account. Various models to simulate tool paths in linear and circular interpolation have been developed and are available in the literature. The present publication will first focus on the use of the polynomial model to simulate the behaviour of the machine when passing through transitions between programmed blocks with tangency discontinuities. Additional features are proposed to ensure enhancement of the match between the model and the machine’s behaviour. Analysis of machine behaviour shows that NCs do not always allow the axes to reach maximum performance levels, with an attendant loss in productivity. The present article proposes an optimisation procedure allowing control laws to be defined to reduce time spent in the transition. The contributions made by these optimised control laws are then evaluated, while impediments to their implementation are also considered.     

Machine cell formation for cellular manufacturing systems using an ant colony system approach

The aim of a cellular manufacturing system is to group parts that have similar processing needs into part families and machines that meet these needs into machine cells. This paper addresses the problem of grouping machines with the objective of minimizing the total cell load variation and the total intercellular moves. The parameters considered include demands for number of parts, routing sequences, processing time, machine capacities, and machine workload status. For grouping the machines, an ant colony system (ACS) approach is proposed. The computational procedure of the approach is explained with a numerical illustration. Large problems with up to 40 machines and 100 part types are tested and analyzed. The results of ACS are compared with the results obtained from a genetic algorithm (GA), and it is observed that its performance is better than that of GA.     

一种数控切削机床运行能耗状态在线判别方法

机床运行能耗状态由一系列的能耗状态节点和能耗过程构成。针对至今仍存在一些关键状态节点无法判别等问题,提出了一种数控机床运行能耗状态在线判别方法。该方法基于数控机床运行能耗状态和状态节点的系统分析,并综合机床功率信息和数控系统通信信息,提出关键节点状态与过程状态在线判别方法,解决了切削加工开始、完成等关键节点和精加工状态判别等难题,从而实现了数控机床全部运行能耗状态的在线判别。在FANUC数控机床上进行的案例研究验证了该方法的有效性和实用性。     

SIBS — a job shop simulation-based scheduler

The problem of finite capacity short-term scheduling in a modern CNC job shop is addressed. The application is an Israel Aircraft Industries (IAI) plant which is conceptually designed as a manufacturing cell. The cell contains six very large (bed length 451–452 inch) 3-head spindle, 5-axis CNC milling machines. A simulation-based scheduler based on SIMAN (a general purpose simulation package) is presented as the means for generating schedules. It is shown that shop performance measures such as lead times, throughput and machine utilizations are improved by an order of 30%, which represents a substantial saving due to the increased capacity of the manufacturing cell.     

Scheduling algorithms for a two-machine flexible manufacturing system

The flexible manufacturing system (FMS) considered in this paper is composed of two CNC machines working in series—a punching machine and a bending machine connected through rollers acting as a buffer system of finite capacity. The main difference between the present problem and the standard two-machine flow shop problem with finite intermediate capacity is precisely the buffer system, which in our problem consists of two stacks of parts supported by rollers: the first stack contains the output of the punching machine, while the second stack contains the input for the bending machine. When the second stack is empty, the first stack may be moved over. Furthermore, the capacity of each stack depends on the particular part type being processed.The FMS can manufacture a wide range of parts of different types. Processing times on the two machines are usually different so that an unbalance results in their total workload. Furthermore, whenever there is a change of the part type in production, the machines must be properly reset—that is, some tools need to be changed or repositioned.A second important difference between the present problem and the usual two-machine flow shop problem is the objective. Given a list ofp part types to be produced in known quantities, the problem considered here is how to sequence or alternate the production of the required part types so as to achieve various hierarchical targets: minimize the makespan (the total time needed to complete production) and, for instance, compress the idle periods of the machine with less workload into a few long enough intervals that could be utilized for maintenance or other reasons.Although Johnson's rule is optimal in some particular cases, the problem addressed in the paper isNP-hard in general: heuristic procedures are therefore provided.     

Constrained scheduling of the inspection activities on semiconductor wafers grouped in families with sequence-dependent set-up times

The scheduling of families of semiconductor wafers within the inspection department of a company producing electronic devices is considered in this paper. Changing the family of wafers to be inspected by an inspection machine requires a sequence-dependent set-up time; furthermore, due to the limited space availability of the inspection area, the available interoperational buffer capacity between the inspection machines is finite. The objective of the scheduling is the maximization of inspection department productivity, measured through the sequence makespan. A permutational flowshop group-scheduling problem (GSP) with sequence-dependent set-up times and limited interoperational buffer capacity has been taken into account. A benchmark of process scenarios considering different numbers of inspection machines wafers codes and families to be inspected has been generated. A Genetic Algorithm is here proposed as an efficient tool to solve the investigated problem. A comparison with a tabu search and a Nawaz, Enscore, and Ham procedure improving the currently available scheduler tool within the inspection department has been performed on the benchmark of problems. Finally, the influence on line productivity due to the finite interoperational buffer capacity is investigated.     

Production control in a failure-prone manufacturing network using discrete event simulation and automated response surface methodology

In this paper, a system consisting of a network of machines with random breakdown and repair times is considered. The machines in this system can be in one of four states: operational, in repair, starved, and blocked. Failure and repair times of the machines are exponentially distributed. Previous research on multi-machine failure-prone manufacturing systems (FPMS) has focused on systems consisting of machines in series or in parallel. This paper considers a network of machines with relationship constraints. Additionally, the system under study models work in process for multiple products, intermediate and final buffers and one type of final product. The demand rate for the final commodity is constant and unmet demand is either backlogged or lost. The objective of this control problem is to find the production rates and policies of the different machines so as to minimize the long run average inventory and backlog cost. The applied control policy is the hedging point policy that is determined by factors representing the level of buffer inventory for each machine. Obtaining analytical solutions is generally impossible for such complex systems. To simultaneously control the production rates of the machines we have therefore developed a method based on a combination of stochastic optimal control theory, discrete event simulation, experimental design and automated response surface methodology (RSM). The application of an automated RSM for Network FPMS is another contribution of this paper. The model can be extended easily to systems with age-dependent failure rates, a preventive repair maintenance policy and non-exponentially distributed up and down times.