单向循环搬运系统交叉环布局优化问题研究

目的为了提高单环单向循环搬运系统的搬运量和系统效率,在单环单向循环搬运系统中增加交叉环且优化交叉环的布局(设置位置及数量)可以避免小车间不必要的等待时间,为搬运系统提供捷径,且提高搬运效率。方法构建系统的数学模型并对不同交叉环布局(设置位置及数量)进行理论分析,在2种基本调度算法下进行仿真实验优化。结果通过理论和仿真实验分析得出,2种基本调度算法下,交叉环设置为布局1时的系统干涉情况最小,但系统单位时间搬运量较少;交叉环设置为布局4时系统单位时间搬运量最大,但系统干涉增加。结论从减少能源消耗(干涉)的角度优化,交叉环应设置1条且设置在系统正中间位置,系统干涉时间最小,单位时间搬运量也最少;从单位时间搬运量最大的角度优化,应在每2个处理站点中间设置多条交叉环,单位时间搬运量最多,但系统干涉时间最大。     

交叉贮存环的检漏

一、引言交叉贮存环(ISABELLE)是由两个周长各为3.8公里的圆环所组成。在温度为4K的环中,超导磁体对加速到400兆电子伏的质子进行偏转和聚焦。由于所要求的压强很不相同,交叉贮存环有两个完全独立的真空系统。射束真空系统工作在1×10~(11)托的压强下,它使循环的质子束保持在一个非常洁净的环境中。在这个环中只采用离子泵和钛升华泵     

基于物流关系的BZGF厂厂区布局改进

以BZGF工厂厂区为研究对象,借鉴使用系统布置设计(SLP)方法,通过物料分析和工艺过程的分析,在工厂原有设施基础上设施之间的调整和组合优化来达到最终优化工厂布局的目的.优化目标是有效地利用空间,最大限度地减少物料搬运.以物料搬运量为评价标准,最终布置方案能够大大降低物料搬运量.属于比较典型的设施规划理论在实际问题中的灵活应用,对于设施规划方面的实践工作具有借鉴意义.     

考虑有限物流运输能力的智能车间AGV调度算法研究

以大批量生产模式智能车间为背景,针对单环布局下多自动导航小车 （AGV） 的调度问题进行研究。首先,对典型智能车间特点进行了分析,利用Plant Simulation仿真平台建立了基于实际生产场景的仿真模型;其次,提出了基于软时间窗的AGV调度规则和基于备选调度规则集的6个运行机制;最后,通过设计仿真实验对上述7个调度规则进行了分析和比较。实验结果表明,基于软时间窗AGV调度方法总体上表现更好。这为企业配置和调度AGV小车提供了决策支持。     

基于仿真的半导体自动物料搬运系统调度优化

利用Arena仿真软件对半导体制造中的Intrabay系统进行了仿真建模,根据关键因子和等待比例两个变量将系统状态分为三种情况,利用遗传算法与仿真模型结合来确定两个变量的阈值和三种系统状态下各自采用的调度规则,实现系统的动态调度。仿真实验表明,所确定的调度规则比使用静态调度最长等待时间规则获得了更好的性能指标。     

交叉绕制单模光纤环减小轴向磁场灵敏度

垂直光纤环面变化的轴向磁场会降低去偏陀螺的精度,因此提出减小轴向磁场灵敏度的新方法:用交叉绕法单模光纤环作为敏感环。与普通绕法相比,理想交叉绕法光纤环中的正反任一束光经过的路径可分为相等的两段,每段路径上产生的Faraday相位延迟大小相等、符号相反,整个路径上相互抵消,从而两束光不存在与磁场有关的Faraday非互易相位差。仿真结果表明,交叉环有很低的轴向磁场灵敏度,与轴向磁场灵敏度为23.4°/(h·mT)的普通环相比,其他参数相同、不对称度为1%的交叉二极子光纤环,轴向磁场灵敏度仅为0.23°/(h·mT)。     

高精度多环片自动装配控制技术

为了实现对微小环片零件的自动化装配,搭建了自动装配系统.通过4根直线导向轴与4个直线轴承来提高系统的导向精度和刚度.采用直线导轨进行各装配作业模块之间的切换,保证了微小环片零件的自动装配与取出.在环片的装配方向上,螺旋升降机和光栅尺实现环片的位置精度控制.在Lab VIEW编程环境中,采用分层软件架构和模块化控制思想,避免了不必要的数据循环检测与丢失,能够达到环片组件的装配精度要求.控制系统分为系统初始化模块、参数设置模块、装配模块和取出模块,自动装配系统通过各个模块间的相互交流配合完成装配任务.采用本文中自动装配系统装配环片的实验结果表明,环片零件装配的最大位置误差为26μm,垂直度误差为17μm,平均装配时间为75 s/片,可满足环片组件所需的精度要求.     

基于规则和仿真的多机并行作业车间生产调度研究

资源分派和能力分派是作业车间生产调度中的重要问题,路径选择规则和分派规则是解决上述问题的有效途径。采用基于规则的仿真研究多机并行作业车间资源分派和能力分派问题,分析工件加工时间、到达率以及机器加工速率对调度结果的影响,以平均完工时间、平均延迟交货率以及平均资源利用率为评价指标,通过对4种路径选择规则和6种分派规则的仿真试验,确定不同性能指标下最佳的调度规则。仿真研究表明:调度规则的选用取决于车间资源配置和调度目标,应避免仅凭借经验或偏好选择规则的调度方法。     

含不一致任务重量的同型熔炼炉批调度优化

为求解含不一致任务重量的同型熔炼炉批调度问题,建立了最小化最大任务完工时间优化模型,设计了一种混合粒子群算法（HPSO）。算法使用随机生成的任务序列作为粒子,采用批首次匹配（BFF）规则对任务序列分批,最长加工时间（LPT）规则将批分配到批处理机,并提出了一种最小完工时间差（MCD）规则对LPT调度结果进行优化;为避免早熟,算法引入交叉和变异操作搜索最优解。通过仿真实验与SA、GA算法对比,实验结果表明算法具有良好的性能。     

DP600双相钢单向拉伸的交叉颈缩现象与有限元分析

目的探究DP600双相钢单向拉伸时交叉颈缩现象的产生原因。方法在单轴拉伸实验的基础上,利用ABAQUS有限元软件对拉伸过程进行模拟,对交叉颈缩区域进行应力、应变分析。结果即将发生断裂时刻,试样标距内中心位置应力达到最大值,临近中心位置两侧由于"局部卸载"而出现应力大幅减小的情况。结论试样标距内两侧距离中心越远的位置,越接近于单轴应力状态。DP600板材裂纹萌生时,与断裂发生部位越接近,其应力状态与平面应变状态越相似,沿着颈缩线方向基本没有应变产生,材料主要由颈缩线区域的板材厚向减薄颈缩线加宽补偿垂直于颈缩线方向上的拉伸。     

Novel slack-based robust scheduling rule for a semiconductor manufacturing system with uncertain processing time

The NP-hard scheduling problems of semiconductor manufacturing systems (SMSs) are further complicated by stochastic uncertainties. Reactive scheduling is a common dynamic scheduling approach where the scheduling scheme is refreshed in response to real-time uncertainties. The scheduling scheme is overly sensitive to the emergence of uncertainties because the optimization of performance (such as minimum make-span) and the system robustness cannot be achieved simultaneously by conventional reactive scheduling methods. To improve the robustness of the scheduling scheme, we propose a novel slack-based robust scheduling rule (SR) based on the analysis of robustness measurement for SMS with uncertain processing time. The decision in the SR is made in real time given the robustness. The proposed SR is verified under different scenarios, and the results are compared with the existing heuristic rules. Simulation results show that the proposed SR can effectively improve the robustness of the scheduling scheme with a slight performance loss.     

Optimization-based parts-machines matching in flexible manufacturing systems

A new dynamic scheduling strategy, Parts-Machines Matching (PMM), is developed and tested in simulated flexible manufacturing systems. This strategy is aimed to achieve globally optimal matching between parts and machines by a semi-qualitative optimization algorithm, originally developed for the Stable Marriage Problem. Global and Partial implementations of PMM are presented and compared with other conventional part-flow rules. They are found to achieve better shop performance than conventional rules, in terms of system throughput, robustness against travel time uncertainties, and recovery from machine breakdowns. The prospect of bringing about system-wide optimization-based performance improvements into bidding schemes makes the proposed framework very significant.     

Order sequencing and capacity balancing in synchronous manufacturing

Synchronous manufacturing aims at achieving the benefits of intermittent production lines in production situations that operate without lines. Benefits such as short and constant throughput times and predictable capacity loading can be acquired through an appropriate design of the synchronous manufacturing system and its control system. The order release mechanism is an essential part of this control system. It determines the sequence in which orders are released to the shop floor. As orders may differ in the amount and distribution of their capacity requirements over subsequent production stages, total capacity load may vary over time. If the available capacity per period is not flexible, capacity balancing becomes an issue in the order release decision. In practice, heuristics or rules of thumb are used to solve this problem, but their effectiveness is questioned. This paper examines the effectiveness of some new heuristics that are based on insights from assembly system design and work load control, and compare their performance with an optimal solution approach. The approaches are evaluated in a rolling schedule environment, and under different levels of capacity fluctuations and problem sizes. The results show that the performance of the heuristic solutions deteriorates if capacity fluctuations between the stages increase. If we measure both the amount and frequency of shortages over a long period of time in a rolling schedule environment, a quite simple rule that only takes the available capacity during the first stage into account outperforms more intelligent rules.     

Scheduling at an auction logistics centre with physical internet

Auction logistics centre (ALC) performs transshipment operation on auction products from their inbound-from-supplier transporters to their outbound-to-client transporters with goods trading functions. Major third-party trading service providers have solved technological problems of dealing with millions of simultaneous biddings. But logistics that fulfils the massive and lumpy auction demands in the centre is still challengeable. The lack of process visibility and synchronised schedule has made the congestion on material flow, especially for the trolley loading and auction trading stages. Space resource is wasted and auction products deteriorate as holding time increases. This paper aims to provide a first demonstration of scheduling for auctions of perishable goods using Physical Internet (PI). PI-enabled scheduling is vital to facilitate the decision-making process while ensuring required throughput time with large trading volumes. A PI-ALC is created to automate the flow of information and enable the flexible implementation of scheduling. Following the hybrid flowshop classification, a timely operation scheduling model is developed. A heuristic-based solution approach is proposed to minimise either makespan or value loss using a set of dispatching rules. Simulation experiments show that the dispatching–picking mechanisms have statistically significant interaction impacts on both performance criteria. Decision-makers should strike a balance between minimising makespan and value loss based upon the growth in the frozen buffer size. Finally, the sensitivity analyses justify that schedulers can flexibly select dispatching rules under various demand patterns and operation time windows, as well as system configurations and trolley sizes.     

Adaptive subchannel allocation in multiuser multicarrier systems

The problem of multiuser scheduling in multicarrier (MC) systems under practical physical-layer constraints and implementations is considered. Subchannel allocation is an important resource assignment issue in multiuser MC systems. The multiuser scheduler is decoupled into a multiuser selector and a subchannel allocator, which result in a sub-optimum multiuser scheduler with significantly reduced computational complexity. Given an active user subset and a channel set, the multiuser scheduling problem then refers to the optimal subchannel allocation to maximise the instantaneous system throughput subject to certain fairness constraints. Efficient adaptive algorithms are developed for optimal subchannel allocation. The extension of the algorithms for tracking the time-varying optimum, which occurs in non-stationary environments, is also addressed. Simulation results are presented to demonstrate the performance of the proposed algorithms in terms of the throughput maximisation, the fast convergence, the excellent tracking capability in time-varying environments, the achievable throughput of the proposed multiuser scheduler as well as the long-term fairness     

Job order releasing and throughput planning for multi-priority orders in wafer fabs

To meet the production target of multi-level (multiple priority rank) orders in wafer fabs, this paper uses a hierarchical framework based on a mathematical model, and without the assistance of any simulation tool, to build a production scheduling system to plan wafer lot releasing sequence and time. This system first applies capacity loading analysis to set up the batch policy for each level (rank) of orders. Next, the production cycle time of each product level is estimated with considerations of batching and loading factor. The cycle time is then used to derive system control parameters such as the most appropriate level of work in process (WIP) and the number of daily operations on the bottleneck workstation. Lastly, a Constant WIP mechanism is applied to establish a wafer release sequence table and a throughput timetable. The due date designation for each specific order can hence be confirmed. With the comparison with the result of simulation, it shows that under the designed system the performance and planning measures in the master production schedule can be drawn up quickly and accurately, and the system throughput target and due date satisfaction can be achieved. Overall, the proposed production scheduling system is both effective and practicable, and the planning results are supportive for good target planning and production activity control.     

Sequencing n Products Involving m Independent Jobs on m Machines

This article considers the problem of scheduling n products over m distinct machines. Every product consists of a set of jobs, each requiring a known processing time on a designated machine. There are no precedence constraints, and simultaneous processing of jobs requiring different machines within a product is allowed. The object of scheduling is to minimize a regular measure of performance associated with the products. It is shown that there exists an optimal schedule with the “no passing property.” Branch and bound routines are developed for finding the optimal solution for the two measures of performance: (1) total penalty cost; and (2) sum of product completion times. Comparisons between the optimal solution and solutions obtained using dispatching rules are given in the penalty cost case.     

A constraint-based perspective in resource constrained project scheduling

In this study, a new heuristic approach to the resource constrained project scheduling problem is introduced. This approach, which is called local constraint based analysis (LCBA), is more robust than the dispatching rules found in the literature, since it does not depend on an a priori insight as do the dispatching rules. LCBA consists of the application of local essential conditions which respect the current temporal and resource constraints to generate a necessary sequence of activities at a scheduling decision time point in a single-pass parallel scheduling algorithm. LCBA is a time efficient procedure due to the localized aspect with which the activities are handled. Only the activities which are schedulable at the current scheduling time are considered for the application of the essential conditions. LCBA is tested against well-known rules from the literature and some recently developed rules. This testing is done using a set of problems of a special design and also a set of optimally solved problems from a recent benchmark in the literature. It is observed that near optimal time efficient solutions are obtained by LCBA and the procedure's performance is considerably better than that of the dispatching rules.     

Effects of flexibility and scheduling decisions on the performance of an FMS: simulation modelling and analysis

This paper focuses on a simulation-based experimental study of the effects of routing flexibility, sequencing flexibility, and part sequencing rules on the performance of a typical FMS. Three routing flexibility levels, five sequencing flexibility levels, and four scheduling rules for part sequencing decision are considered for detailed investigation. The system work load characterised by the mean interarrival time of parts has been set at different levels. The performance of the FMS is evaluated using various measures related to flow time and tardiness of parts. The simulation results are subjected to statistical analysis. Multiple regression-based metamodels have been developed using the simulation results. The analyses of results reveal that deterioration in system performance can be minimised substantially by incorporating either routing flexibility or sequencing flexibility or both. However, the benefits of either of these flexibilities diminish at higher flexibility levels. When flexibility exists, part sequencing rules such as the earliest due date and earliest operation due date provide a better performance for all the measures.