基于自动化排布算法的工厂系统布局方法

智能制造将在未来制造业中扮演重要的角色,智能工厂作为智能制造的载体,对其作业单元进行智能排布与优化具有现实意义。考虑到在利用系统布局方法(SLP)排布的过程中,部分作业单元的确定规则比较模糊,受主观影响较大,当智能工厂中作业单元较多时,几乎无法利用SLP方法手工排布,因此提出了一种自动化排布算法。在算法的设计过程中给出了若干位置确定的启发式规则,并结合数学模型求解出最终作业单元的位置坐标。该算法的输入为各个作业单位对之间的综合关系,能够直接输出作业单元的位置相关图。本文对该算法进行了程序实现,并结合案例验证了排布结果的有效性和排布过程的敏捷性。     

带检测环节的制造单元布局优化

针对带检测环节的智能制造单元，考虑其具有随机性因素的特点，本文对其机器布局问题进行研究。首先对该智能制造单元的生产过程及特点进行分析，建立其机器布局优化问题的随机非线性整数规划的数学模型；然后建立该智能制造单元对应的仿真模型，对该优化问题进行求解；最后分析抽检率的变化对最优解造成的影响，并对该智能制造单元的性能指标进行方差分析，研究不同的布局方案和抽检率对系统性能的影响程度。研究成果为企业进行智能制造单元的机器布局提供决策依据。     

基于功能表面的机械产品布局关系表达

 布局模型是布局优化的关键，其完整性和先进性将直接影响整个布局优化的求解效率和可靠性．基于功能表面分解重构技术，建立了基于功能表面的装配模型和传动链表，由两者共同实现布局关系表达． 实例证明，该布局模型所表达的布局关系完整、明了，具有很好的通用性．     

自适应粒子群算法的制造单元集成布局方法

在考虑制造单元出入点具体位置与最短物流路径的情况下,对单元间布局两个环节的问题——确定单元在车间平面上的位置,确定出入点间最短物流路径——作了集成研究,避免分步研究导致的解空间缺失;基于割树策略建立了单元布局模型,设计了结构化编码的自适应粒子群算法,使车间平面形成整齐连续的布局;通过将车间平面布局转化成连通图,在算法中嵌入改进Dijkstra算法,量化了各单元出入点之间的最短物流距离;从而使布局结果更加符合生产实际。     

基于模型的区域物流配送系统规划研究

以经济区域的卷烟配送物流系统规划为背景,将整个区域划分为若干个配送单元,依据各配送单元的需求量、物流中心的建设投入和运行成本,并将物流中心的成本分为固定成本和变动成本,特别地将送货过程的车辆费用从变动成本中划分出来,建立了物流系统的运筹学模型,并通过模型求解获得该物流系统的优化布局方案.     

电机检修车间作业单位相关位置研究

本文以某机械制造公司电机检修车间设施布局为研究对象，详细分析车间布局的基本素，并对产品检修作业单位之间的物流关系和非物流关系进行了定性分析，得出，个层级的物流密切关系，从而得出产品检修作业单位位置相关图。     

基于遗传算法的飞机复合材料结构装配压紧力大小与布局的优化基于遗传算法的飞机复合材料结构装配压紧力大小与布局的优化

针对飞机复合材料结构装配时出现间隙的问题,考虑用压紧力消除间隙可能引起层合板产生损伤,提出了基于遗传算法的压紧力大小和布局的优化算法。结合有限元分析方法,考虑压紧机构之间的干涉问题,以复合材料分层损伤为约束条件,以间隙消除率为优化目标,建立了压紧力大小和布局的优化模型。以复合材料翼盒为例,建立基于内聚力单元的有限元模型,使用上述方法优化复合材料壁板上的压紧力大小和布局。将优化后得到的压紧力方案在有限元模型上进行验算,计算间隙消除率并分析应力应变状态和分层损伤情况。结果表明,优化后的方案能够在不使壁板产生分层损伤的前提下提高间隙消除率,并且能够使壁板的应力和应变分布趋于均匀。当装配间隙的初始值为0.2~0.8 mm时,优化后的方案使间隙消除率提高至77.4%~100%,比优化前的方案提高了19.2%~177.8%。      

直线型制造单元与设施集成布局方法研究

单元制造系统的布局对于提高系统的效率起着十分重要的作用。以最小化物料搬运距离和设施占地面积为目标,建立了一个单元制造系统布局的双目标优化模型,在该模型中单元间的系统布局、单元内设施的布局以及设施的摆放方向这几个问题都可以同时进行优化。通过设计特殊的编码方式和一种变尺度邻域解生成机制,提出了求解模型的模拟退火算法。算例表明算法所得布局方案在两个目标上都优于相比较的算法。     

多层级装配作业车间分批调度算法设计与分析

多层级装配作业车间调度是一类包含加工与装配的双阶段调度问题，装配产品具有不同的树状结构，且各层级的装配工序需要直属零部件完工方可执行。分批调度可以提高车间生产流动性，故而被运用在作业车间调度等领域。装配作业车间分批调度需要解决关联零部件及其下属子批的进度协同性问题，为此建立了多层级装配作业车间的分批优化调度模型，以最小化拖期成本与库存持有成本为优化目标。出于求解效率考虑，构建基于遗传算法与优先分派规则的混合求解算法以应对批量划分与排序两个子问题。最后，设计仿真实验验证分批调度算法的有效性，并分析评估在8种作业分派规则、3类分批策略下混合算法对于差异化产品结构的适应性。通过分析实验结果发现，等量分批策略可以在给定条件下有效提升混合算法的调度性能。     

考虑脑力负荷的模拟手工装配作业实验研究

目的为了减少员工装配作业时由于任务切换导致绩效下降的影响,探究员工在4种任务切换情境下手工装配作业的绩效表现与脑力负荷变化。方法采用复杂性与相似性(2×2)因素的交替任务切换范式,通过乐高模型装配,开展任务重复与任务切换的模拟手工装配作业实验。分析被试的行为绩效指标(错误率、反应时间(RT)、平均装配时间)和任务切换前后脑电(EEG)指标的变化及其差异。结果不同类型任务切换不会导致被切换任务错误率上升;复杂不相似任务切换时,切换任务错误率显著高于简单任务切换,反应时间显著高于另外3种任务切换;复杂相似任务切换时,脑力负荷处于平稳状态,其他3种均导致员工脑力负荷增大。结论 4类指标赋予相同权重情况下,任务切换类型的优选方案依次为复杂相似型、简单不相似型、简单相似型、复杂不相似型。     

Formalization of a process activity performance estimation approach using human competencies

In a changing environment, the human factor is a key element to ensure the survival of an enterprise. Hence, it is necessary to model and analyse the enterprise processes with regard to both human and material resources. A French approach to process performance and its relation to the competence concept are presented. Several studies in which competence is integrated in the estimation of process performance are presented, and the method developed is described. It integrates individual and collective competencies to estimate the performance of an activity. This is first achieved in a specific case, and then generalized and formalized for different viewpoints. Finally, some new studies in which the proposed method was used are pointed out.     

The task demands‐resources method: A new approach to human reliability analysis from a psychological perspective

This study proposes a new approach to human reliability analysis (HRA) by introducing the occupational stress model in human resources management. Most existing HRA methods are restricted to a given set of risk factors in the task context, which are often called performance shaping factors (PSFs), and they are built on the causal relationship between PSFs and human performance, with little concern for the psychological factors that drive human behavior. We argue that a well‐developed occupational stress model that incorporates comprehensive working conditions and focuses on psychological factors offers us a new perspective to evaluate human reliability. The proposed approach, namely, the task demands‐resources (TD‐R) method, considers that the PSFs, in the task context, can be categorized into two different groups: task demands and task resources. These two PSF groups can both motivate and stress the operators during the task, thereby influencing their performances. Based on the theoretical framework of the TD‐R method, we also designed a probabilistic model linking motivational intensity to human error probability (HEP) under different stress levels. A human reliability experiment has been conducted to validate the effectiveness and flexibility of the TD‐R method. The experiment results showed that the TD‐R method could produce a meaningful explanation for the operators' performances and provide a quantification result for HEP.     

A comprehensive VIKOR method for material selection

In engineering design, material alternatives evaluate according to different criteria depending on the objectives of the problem. Performance ratings for different criteria are measured by different units, but in the decision matrix in order to have a valid comparison all the elements must be dimensionless. However, a lot of normalization methods have been developed for cost and benefit criteria, not only there has not been enough attention for engineering design situations in which approaching the target values are desirable but also the available methods have shortcomings. A new version of VIKOR method, which covers all types of criteria with emphasize on compromise solution, is proposed in this paper. The proposed comprehensive version of VIKOR also overcomes the main error of traditional VIKOR by a simpler approach. Suggested method can enhance exactness of material selection results in different applications, especially in biomedical application where the implant materials should possess similar properties to those of human tissues. Five examples are included to illustrate and justify the suggested method.     

Modeling short- and long-term time-dependent nonlinear behavior of polyethylene

A new methodology for developing macromechanical constitutive formulations for time-dependent materials is presented in this article. In particular, two phenomenological constitutive models for polymer materials are illustrated, describing time-dependent and nonlinear mechanical behavior. In this new approach, short-term creep test data are used for modeling both short-term and long-term responses. The differential form of a model is used to simulate typical nonlinear viscoelastic polymeric behavior using a combination of springs and dashpots. Unified plasticity theory is then used to develop the second model, which is a nonlinear viscoplastic one. Least squares fitting is applied for the determination of material parameters for both models, based on experimental results. Due to practical constraints, experimental data are usually available for short-term time-frames. In the presented proposed formulation, the material parameters determined from short-term testing are used to obtain material parameter relationships for predicting the long-term material response. This is done by extending short-term information for longer time frames. Finally, theoretical and experimental results of tensile tests on polyethylene subjected to various load levels and test times are compared and discussed. Very good agreement of the modeling results with experimental data shows that the developed formulation provides a flexible and reliable framework for predicting load responses of polymers.     

Numerical Simulation of Elastic Behaviour and Failure Processes in Heterogeneous Material

A general numerical approach is developed to model the elastic behaviours and failure processes of heterogeneous materials. The heterogeneous material body is assumed composed of a large number of convex polygon lattices with different phases. These phases are locally isotropic and elastic-brittle with the different lattices displaying variable material parameters and a Weibull-type statistical distribution. When the effective strain exceeds a local fracture criterion, the full lattice exhibits failure uniformly, and this is modelled by assuming a very small Young modulus value. An auto-select loading method is employed to model the failure process. The proposed hybrid approach is applied to plane stress problems with fracture patterns and effective load-displacement curves presented to illustrate the full failure process.     

Determination of Thermal Properties in the Frequency Domain Based on a Non-integer Model: Application to a Sample of Concrete

A technique for determining thermophysical properties is proposed and applied to a sample of concrete by taking advantage of pseudo-random signals. Data are treated in the frequency domain. A new approach is developed for estimating the thermal impedance based on the formalism of non-integer order models. An experimental setup consisting of a heat flux and temperature sensor arranged in contact with a material assuming a semi-infinite boundary condition is studied. The theoretical expression for such a thermal impedance takes into account the thermal capacity of the sensor and the contact resistance and emphasizes fractional orders in the behavior model.     

Finite difference solution of steady state creep deformations in a short fiber composite in presence of fiber/matrix debonding

A finite difference technique is developed to predict the second stage creep displacement rates and stress analysis of a short fiber metal matrix composite subjecting to a constant axial load through a micromechanical approach. The technique is capable to take into account the presence of interfacial debonding as one of the main factors affecting the creep performance of short fiber composites. The exponential law is adopted to describe the matrix creep behavior. Also, a model for prediction of interfacial debonding at fiber/matrix interface is developed using a stress based method. The obtained results could greatly help to better understand the flow pattern of matrix material and the load transfer mechanism between fiber and matrix with and without the presence of interfacial debond. The predicted strain rate by the proposed approach exhibits good agreement with the experimental results.     

A Hybrid Probabilistic Model for Evaluating and Simulating Human Error in Industrial Emergency Conditions (HEIE)

Over the years, many techniques have been developed for human reliability analysis (HRA). The main weakness of traditional HRA approaches is the use of a simple classification scheme without a link to a model of cognition in terms of mental processes. The present work is an attempt in this direction through a particular hybrid probabilistic model. The human error in industrial emergency model aims to develop an integrated methodological approach useful in critical infrastructures during an emergency condition. The proposed method, starting from the integration of existing techniques, develops a very flexible tool, able to take into account the main external and internal factors responsible of human error in emergency conditions. The model is able to estimate the evolution of human behavior and error following the evolution of the emergency scenario. The final result is a simulation model that calculates the contextualized human error probability, through which it is possible to estimate a realistic and detailed scenario of the conditions during the emergency management.     

An exact penalty function method for optimising QAP formulation in facility layout problem

A quadratic assignment problem (QAP), which is a combinatorial optimisation problem, is developed to model the problem of locating facilities with material flows between them. The aim of solving the QAP formulation for a facility layout problem (FLP) is to increase a system’s operating efficiency by reducing material handling costs, which can be measured by interdepartmental distances and flows. The QAP-formulated FLP can be viewed as a discrete optimisation problem, where the quadratic objective function is optimised with respect to discrete decision variables subject to linear equality constraints. The conventional approach for solving this discrete optimisation problem is to use the linearisation of the quadratic objective function whereby additional discrete variables and constraints are introduced. The adoption of the linearisation process can result in a significantly increased number of variables and constraints; solving the resulting problem can therefore be challenging. In this paper, a new approach is introduced to solve this discrete optimisation problem. First, the discrete optimisation problem is transformed into an equivalent nonlinear optimisation problem involving only continuous decision variables by introducing quadratic inequality constraints. The number of variables, however, remains the same as the original problem. Then, an exact penalty function method is applied to convert this transformed continuous optimisation problem into an unconstrained continuous optimisation problem. An improved backtracking search algorithm is then developed to solve the unconstrained optimisation problem. Numerical computation results demonstrate the effectiveness of the proposed new approach.     

On advanced solution strategies to overcome locking effects in strong discontinuity approaches

This paper is concerned with the analysis of locking effects resulting from different orientations of micro‐defects and those of the corresponding macro‐defects. Based on a mixed‐mode material model embedded within the framework of the strong discontinuity approach (SDA), the described locking effect is illustrated by means of a crack analysis of a notched concrete beam. To overcome the deficiency of the proposed finite element model, the original SDA is modified and extended. For that purpose, two different advanced numerical formulations are developed: a rotating crack approach and a multiple crack approach. Restricting the governing equations to the material point level, a standard return‐mapping procedure is applied to the algorithmic formulations of both models. The applicability and the performance of the proposed numerical implementations are investigated by means of a re‐analysis of the two‐dimensional notched concrete beam. Copyright © 2005 John Wiley & Sons, Ltd.