基于结构阻尼的机械结合部动力学模型研究

机械结合部的阻尼由连接界面之间的相对滑动产生,为结构阻尼,因此提出了一种基于结构阻尼的结合部动力学模型。该模型通过刚度和结构阻尼对机械结合部进行等效,模拟结合部的动力学特性。为了对模型进行验证,设计了一组试验进行研究。首先利用DASP系统对试验件进行模态试验,得到模态参数和模态振型,然后根据模态试验数据识别机械结合部动力学参数。基于新模型的有限元复特征值分析结果与模态试验分析结果误差较小,表明结合部动力学模型在设置适宜的参数时,能够模拟机械结合部的动力学特性,验证了模型的可行性。     

Dynamic rules for due-date assignment

This paper presents two new dynamic due-date assignment rules which utilize shop congestion information. The new rules estimate job flowtime based on a sampling of recently completed jobs. These rules are compared with other established flowtime estimate models on the criterion of due-date performance via computer simulation. To evaluate the robustness of the rules, an experimental design with three different queue sequencing heuristics and two different shop balance levels was used. The results of this investigation clearly indicate that flowtimes from recently completed jobs provide very useful information for establishing effective due-dates in a job shop environment. In addition it is shown how the use of particular sequencing rules greatly increases the precision of flowtime estimates.     

Sustainable operator assignment in an assembly line using genetic algorithm

This paper addresses the operator assignment in predefined workstations of an assembly line to get a sustainable result of fitness function of cycle time, total idle time and output where genetic algorithm is used as a solving tool. A proper operator assignment is important to get a sustainable balanced line. To improve the efficiency and meet the desired target output within the time limit, a balanced assembly line is a must. Real world lines consist of a large number of tasks and it is very time consuming and crucial to choose the most suitable operator for a particular workstation. In addition, it is very important to assign the suitable operator at the right place as his skill of operating machines finally reflects in productivity or in the cost of production. To verify better assignments of workers, a genetic algorithm is adopted here. A heuristic is proposed to find out the sustainable assignment of operators in the predefined workstations.     

A genetic algorithm-based approach to machine assignment problem

Over the last few decades, production scheduling problems have received much attention. Due to global competition, it is important to have a vigorous control on production costs while keeping a reasonable level of production capability and customer satisfaction. One of the most important factors that continuously impacts on production performance is machining flexibility, which can reduce the overall production lead-time, work-in-progress inventories, overall job lateness, etc. It is also vital to balance various quantitative aspects of this flexibility which is commonly regarded as a major strategic objective of many firms. However, this aspect has not been studied in a practical way related to the present manufacturing environment.

In this paper, an assignment and scheduling model is developed to study the impact of machining flexibility on production issues such as job lateness and machine utilisation. A genetic algorithm-based approach is developed to solve a generic machine assignment problem using standard benchmark problems and real industrial problems in China. Computational results suggest that machining flexibility can improve the overall production performance if the equilibrium state can be quantified between scheduling performance and capital investment. Then production planners can determine the investment plan in order to achieve a desired level of scheduling performance.     

A bottleneck assignment approach to the multiple container loading problem

The container loading problem addresses the question of how to store several three dimensional, rectangular items (e.g. boxes) in one or more containers in such a way that maximum use is made of the container space. The multiple container problem concentrates on the situation where the consignment to be loaded cannot be accommodated in a single container. To minimize the number of required containers the repeated application of a single container approach is often suggested in the literature. In contrast, in this paper an approach based on a set partitioning formulation of the problem is presented. Within this approach a single container algorithm is used to produce alternative loading patterns. This approach easily allows introducing additional aspects, e.g. separation of boxes or complete shipment of boxes.     

基于LOG-Zernike算子的快速图像测量

图像测量技术,一个很重要的方面就是图像的边缘检测定位,而边缘定位的准确与否又直接影响到测量的精度.常用的检测算法都是像素级的,对测量要求较高的场合无法满足要求.定位速度一直是边缘检测算法的一大瓶颈,本文正是在保证一定精度的前提下,研究了快速图像测量算法,即运用LOG算子先对工件进行快速边缘定位,在此基础上采用zernjke矩法将精度提高到亚像素级.为了得到实际的测量尺寸,应用块规进行了系统标定并进行了一系列测量实验,实验结果表明该方法定位精度接近于Zernike矩法,且算法的运行对间大约在1.5s左右.     

Due date assignment in single machine with stochastic processing times

This paper considers two different due date assignment and sequencing problems in single machine where the processing times of jobs are random variables. The first problem is to minimise the maximum due date so that all jobs are stochastically on time. It is shown that sequencing the jobs in decreasing service level (DSL) order optimally solves the problem. The results are then extended for two special cases of flow shop problem. The other problem is to minimise a total cost function which is a linear combination of three penalties: penalty on job earliness, penalty on job tardiness, and penalty associated with long due date assignment. The assignment of a common due date and distinct due dates are investigated for this problem. It is shown that the optimal sequence for the case of common due date is V-shaped.     

Part assignment to electronic insertion machines: two machine case

Modern electronic circuit board production typically uses computerized insertion machines to insert electronic components into circuit boards in a flow shop type of production line. This paper studies the problem of assigning components to insertion machines with the aim of maximizing output. The paper initially examines the two machine assignment case, identifying requirements sufficient to ensure an optimal solution for two technological scenarios. Moreover, it is noted that the sequencing issue of different board types in a production cycle is immaterial, given large machine capacity. Solution procedures for this components assignment problem are described and tested on data obtained from a real life industrial setting. The resulting solutions are within 0-5% from optimality.     

FMS machine loading: A simulated annealing approach

In this paper the problem of FMS machine loading is considered with the objective of minimizing the system imbalance using a simulated annealing (SA) approach. New job sequences are generated with a proposed perturbation scheme named the 'modified insertion scheme' (MIS). These sequences are used in the proposed simulated annealing algorithm to arrive at a near global optimum solution. A new approach for temperature variation in the SA algorithm is also suggested in which temperature is assumed to be parabolic. The SA algorithm using the proposed MIS and the assumed temperature variation proved to be giving substantial improvement in system imbalance as against conventional sequences.     

Solving machine loading problems in a flexible manufacturing system using a genetic algorithm based heuristic approach

The machine-loading problem of a flexible manufacturing system (FMS) has been recognized as one of the most important planning problems. In this research, a Genetic Algorithm (GA) based heuristic is proposed to solve the machine loading problem of a random type FMS. The objective of the loading problems is to minimize the system unbalance and maximize the throughput, satisfying the technological constraints such as availability of machining time, and tool slots. The proposed GA-based heuristic determines the part type sequence and the operation-machine allocation that guarantee the optimal solution to the problem, rather than using fixed predetermined part sequencing rules. The efficiency of the proposed heuristic has been tested on ten sample problems and the results obtained have been compared with those of existing methods.     

Dynamic fracture under plane wave loading

A new plate impact experiment is presented for studying dynamic fracture processes that occur under sub-microsecond loading. The experiment is designed to provide comparatively straightforward interpretation within the framework of fracture mechanics. A disc containing a mid-plane, pre-fatigued, edge crack that has been propagated halfway across the diameter is impacted by a thin flyer plate of the same material. A compressive pulse propagates through the specimen and reflects from the rear surface as a step, tensile pulse with a duration of 1s. This plane wave loads the crack and causes initiation and propagation of the crack. The motion of the rear surface is monitored during this event using a laser interferometer system. The location of the crack front is mapped before and after the experiment using a focussed ultrasonic transducer.Experiments have been conducted on a hardened 4340 VAR steel at temperatures ranging from room temperature to — 100°C. Crack advance increases monotonically with increasing impact velocity and with decreasing temperature. Critical values of the stress intensity factorK _Ic are inferred from known elastodynamic solutions and the assumption that the measured crack advance occurs at a constant energy release rate. Fracture modes are characterized by means of scanning electron microscopy of the fracture surfaces.A finite difference method is used for numerical simulation of the experiments. The loading is modelled as that of a plane, square, tensile pulse impinging at normal incidence on a semi-infinite crack. Crack advance is assumed to initiate when the crack-tip stress intensity factor reaches the critical valueK _Ic. Crack velocities are prescribed corresponding to various fracture models. The predicted motion of the rear surface is found to be in good agreement with the measured motion when the crack velocity is taken to be a constant.

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Résumé On présente un nouvel essai de choc sur plaque pour l'étude du processus de rupture dynamique qui se produit sous des charges inférieures à la micro-seconde. L'essai est conçu de manière à fournir une interprétation comparativement directe dans le cas de las mécanique de la rupture. L'essai consiste à soumettre à un choc un disque comportant une fissure du bord suivi un plan médian, préfatiguée et propagée sur la moitié du diamètre du disque, à l'aide d'une plaque mince mobile du même matériau. Une impulsion de compression se propage au travers de l'echantillon, se réfléchit sur la surface arrière comme sur un seuil, entraînant une impulsion de traction avec une durée d'une micro-seconde. Cette onde plane soumet la fissure à la sollicitation et provoque l'amorçage de la propagation de la fissure. On enregistre le mouvement de la surface arrière au cours du phénomène en utilisant un système d'interférométrie à laser. La localisation du front de fissure est tracée avant et après l'essai, en utilisant un transducteur ultrasonique focalisé.Des essais ont été conduits sur un acier 4340 Var durci, à des températures comprises entre la température ambiante et — 100°C. L'avancement de la fissure augmente de manière monotone avec les vitesses croissantes de choc et avec l'abaissement de la température. Des valeurs critiques des facteurs d'intensité de contrainteK _lc, sont déduites à partir des solutions élasto-dynamiques connues et de l'hypothése que l'avancement de la fissure mesurée se produit suivant une vitesse de relaxation en énergie constante. Les modes de rupture sont caractérisés au moyen de la microscopie électronique à balayage des surfaces de rupture.Une méthode finie différentielle est utilisée pour l'assimiliation numérique des essais. La mise en charge est modélisée comme celle d'une impulsion de traction plane et carrée agissant suivant une incidence normale sur une fissure semi-infinie. L'avancement de la fissure est supposé commencer lorsque le facteur d'intensité de contrainte à son extrémité atteint la valeur critiqueK _Ic. Les vitesses de fissuration sont établies en correspondance avec différents modèles de rupture. On trouve que le mouvement prévu de la surface arrière est en bon accord avec les mouvements mesurés, lorsque la vitesse de fissuration est considérée comme constante.

     

自适应多滤波器的高效卷积算子目标跟踪算法

针对单一滤波器难以适应复杂变化的目标跟踪环境的问题,本文在高效卷积算子目标跟踪算法的基础上,提出了自适应多滤波器的目标跟踪算法。该算法使用时空正则化滤波器、一致性检验滤波器和高效卷积算子算法中的相关滤波器分别与目标特征进行卷积,得到三个滤波检测得分。其中,时空正则化滤波器是通过将时间正则化引入相关滤波损失函数而得到;一致性检验滤波器是通过反向定位前几帧目标,比较反向与正向定位坐标的误差,只有误差小于阈值时才更新滤波器;选择峰值旁瓣比最大滤波检测得分,估计目标的位置。使用OTB-2015数据集和UAV123数据集对改进算法进行测试,实验结果表明,本文算法能够更好地适应跟踪过程中的复杂变化的环境,具有较高的精度和鲁棒性。     

Single-machine scheduling and common due date assignment with potential machine disruption

This paper studies a single-machine due date assignment and scheduling problem in a disruptive environment, where a machine disruption may occur at a particular time that will last for a period of time with a certain probability, and the job due dates are determined by the decision-maker using the popular common due date assignment method. The goal is to determine jointly the optimal job sequence and the common due date so as to minimise the expected value of an integrated cost function that includes the earliness, tardiness and due date assignment costs. We analyse the computational complexity status of various cases of the problem, and develop pseudo-polynomial-time solution algorithms, randomised adaptive search algorithms, and fully polynomial-time approximation schemes for them, if viable. Finally, we conduct extensive numerical testing to assess the performance of the proposed algorithms.     

迭代能量算子机械故障诊断研究

旋转机械元件的故障振动信号通常为多分量调幅调频信号,针对此类信号的故障特征提取问题,介绍一种基于迭代能量算子的机械故障诊断方法。首先阐述迭代能量算子对多分量信号的各分量信号进行幅值包络提取和平滑瞬时频率估计的基本原理;然后通过仿真试验给出与Hilbert-Huang变换的比较,表明该方法解调精度很高且速度较快;最后给出滚动轴承故障诊断实例,证明基于迭代能量算子的多分量调幅调频信号解调方法能有效地提取机械故障振动信号的故障特征。     

A note on single machine scheduling and due date assignment with general position-dependent processing times

This note considers single machine scheduling and due date assignment in which a job’s processing time depends on its position in a sequence. The objective functions include the cost of changing the due dates, the total cost of discarded jobs that cannot be completed by their due dates and the total earliness of the scheduled jobs. We analyse these problems with three different due date assignment methods. We provide a generic polynomial-time dynamic programming algorithm to solve the problems.     

Rescheduling parallel machines with stepwise increasing tardiness and machine assignment stability objectives

Nervousness in machine assignments during rescheduling can cause problems for the implementation of a scheduling system. This paper examines rescheduling due to the arrival of new jobs to the system. Parallel machine scheduling problems with stepwise increasing tardiness cost objectives, non-zero machine ready times, constraints that limit machine reassignments, and machine reassignment costs are considered. Simulation experiments and individual scheduling problems indicate that nervousness can be controlled at a low cost in some parallel machine scheduling environments. The rescheduling problems in the simulation are solved with a branch-and-price algorithm. Significant gains in schedule stability can be achieved by selecting the alternative optimal solution with the fewest machine reassignments.