An agent-based modeling approach to analyze the impact of warehouse congestion on cost and performance

This article discusses a novel agent-based modeling (ABM) approach to analyze the impact of warehouse congestion and presents results indicating the significant effect of congestion on cost and performance in various scenarios. In particular, the simulation represents the behaviors of the order pickers in a picker-to-part, low picking warehouse and focuses on representing the traffic and movements of the pickers. The key motivation for simulating this system is the lack of literature discussing models or simulations capable of representing the congestion component of order pickers, a component important in actual warehouse operations. The conceptual model of the simulation is described and justified using the Conceptual Model for Simulation Diagram? and the simulation is constructed using the simulation software AnyLogic®. The simulation is operationally validated via a series of experiments performed to test the simulation’s results against the expected dynamics of the system as described in (Tompkins et al. 2003). After operationally validating the simulation, key results are discussed and it is shown that the ABM simulation paradigm is capable of quantitatively capturing new and traditionally difficult to explore dynamics in warehouse operations, including components of congestion not considered in literature.     

带式烧结机台车执行牵引装置的力学分析与控制

通过分析带式烧结机台车执行牵引装置的星轮和台车的力学关系，建立了台车无叠肩起拱的力学模型，提出了无叠肩起拱带式烧结机的力控制方法。在对台车执行牵引装置进行力学计算和运动仿真的基础上，得到了新型60m^2带式烧结机的力控制阈值和力控制曲线。该新型烧结机生产线的现场试验表明，所建立的力学模型正确，计算和仿真可靠，提出的力控制方法能有效地解决台车的叠肩起拱问题。     

Analysis and optimisation of a network of closed-loop automobile assembly line using simulation

The work presented in this paper describes the development of a decision support system based on a discrete event simulation model. The model is aimed at a specific class of production lines with a four closed-loop network configuration of automobile assembly and preassembly lines connected by conveyors. The total number of pallets on the conveyors (which also act as intermediate buffers) remains constant, except for the fourth loop, which depends on the four-door car ratio implemented between the door disassembly and assembly stations of the car body. Some governing equations of the four closed loops are incompatible with the capacities of several intermediate buffers for certain values of the four-door car ratio. The simulation model can be used to assess the impact of variation in the length of the conveyors (hence, the size of the intermediate buffers) on the performance of the line. In addition, this paper also presents a proposal for the alteration of the length of the intermediate buffers that can maximise the performance of the production line and improve the availability of the manufacturing system for any value of four-door car ratio.     

Toward learning autonomous pallets by using fuzzy rules, applied in a Conwip system

Nowadays, material planning and control strategies are becoming continuously complex tasks spanning from individual plants to logistic networks. In fact, this is the consequence of increasing intricacy in product variants and their respective convolution in networks’ structures. Customers ask for specific products with individual characteristics that force companies for more clever performances by more flexibility. For doing so, the existing planning and control systems, which work based on central monitoring and controlling, show some limitations for organizing every operation on time or in the right time. Therefore, in the recent decade, a great attention is put on decentralized control and, to some extent, autonomy. This paper tries to investigate the possibility of combining this new research paradigm with existing strategies in production logistics, in order to improve material handling and control task according to material flow criteria. To show this, an exemplary plant after decoupling point out of a logistic network is considered for simulation and analysis. This combines Conwip system with learning autonomous pallets’ concept in a discrete event simulation model. Several decentralized control scenarios are experimented and compared together. Here, the learn methodology is brought to pallets based on fuzzy rules and advantage of closed loop systems.     

AQM controller design for networks supporting TCP vegas: a control theoretical approach

In this paper, a mathematical model and control theoretical framework for designing AQM controllers in networks supporting TCP Vegas is introduced. We have emphasized on a modified TCP Vegas algorithm that can respond to congestion signals through explicit congestion notification (ECN). The overall nonlinear delayed differential equations of the dynamics model of closed loop system have been derived based on TCP Vegas model. The model is then linearized to derive a transfer function representation between the packet marking probability and the bottleneck router queue length as the input and output of the modified TCP Vegas/AQM system. The model properties have been then examined especially for the case of single bottleneck homogeneous network which is closely investigated. Finally an AQM controller based on Coefficient Diagram Method (CDM) has been designed for the system and its performance has been compared with some other AQM controllers. CDM is a new indirect pole placement method that considers the speed, stability and robustness of the closed loop system in terms of time domain specifications. In order for synthesizing the simulation scenarios, our campus router traffic has been studied experimentally for a sample period of one hour and the corresponding parameters has been extracted. The simulation results are representative of good performance of developed TCP Vegas/AQM structure for different simulated scenarios.     

压滤机新型电液控制系统的建模与仿真研究

基于对控制系统的建模方法,提出了面向液压系统数学模型的"灰箱"建模法.在对压滤机的液压控制系统重新设计的基础上,利用"灰箱"建模理论建立了液压系统的数学模型,运用Matlab中的Simulink软件包对该系统进行了动态特性数字仿真.实测和运行验证了改造后的液压系统工作可靠性与稳定性得到提高,为改善压滤机液压控制系统性能奠定了良好的基础.     

Simulation of NC machining based on the dexel model: A critical analysis

Simulation systems for NC machining that also provide an analysis and verification component are a powerful tool to detect errors in NC codes off-line, i.e. before the NC program is put onto the machine and before damage can happen. The modelling scheme used to represent the workpiece and its development during machining has a great influence on the behaviour and the efficiency of the whole system. Without a well-chosen modelling scheme a realistic simulation and, especially, analysis and verification of NC programs are not possible. Recently, at RISC-Linz, an NC simulation system, NC-SAVE, has been developed that is based on the dexel model. The dexel model is an instance of spatial enumeration techniques, so it is an approximation technique, which allows the user to specify the accuracy he needs. Practical experience with the system has shown that the dexel model allows an efficient dynamic update of the workpiece and provides many facilities for analysis operations. In this paper, we study the accuracy of this modelling scheme. More precisely, we give formulae that state, depending on the curvature of the objects to be modelled, which resolution to take for the model to achieve a certain (pre-specified) accuracy. We also consider the influence of Boolean operations on the accuracy of models. The question of the interdependence between accuracy and resolution of the model, and also the influence of various operations on the model is quite important, in order to choose the resolution of the model in such a way that tolerances are kept. It turns out that the encoding of an object has to be done quite carefully in order to guarantee a certain accuracy of the model and to ensure that analysis operations and comparisons of models work properly. The insights from the theoretical analysis of the dexel model are interpreted in terms of their influence on practical applications of the system NC-SAVE. A much better understanding of the importance of good choices for the resolution of the model and the number and the positions of the viewpoints is provided. It is not the intention of this paper to demonstrate the usefulness and the advantages of the system NC-SAVE. It is rather the goal of this paper to give a careful analysis of the accuracy of the modelling scheme used within NC-SAVE. Such an analysis, together with recommendations for the use of the system, improve the results of the simulation.     

An investigation of pallet design using alternative materials for cold room applications

This paper presents an investigation into the improvement of existing design and materials for pallets used in material handling applications. The objective was to develop a pallet design made from alternative materials such as composites of recycled corrugated paperboard and plywood for cold room lifting needs. Several new designs are proposed and analysed using the finite element method (FEM) and related information of weight, loading and safety conditions. Among these, five designs are recommended – one is made of plywood, two are made of corrugated paperboard, and two are made of specially constructed composite materials. The selection process aimed to ensure pallets were safe and stable and involved checking for maximum deflection while lifting and for catastrophe failure due to maximum stresses under Rankine’s theory of failure. We conclude that plywood, corrugated paperboard and a composite of the two materials can be utilised successfully to manufacture stable and strong pallets. Using FEM analysis and simulation studies on Pro/Mechanica FEM software, we were able to suggest several optimum designs with one-third the weight and all of the functionality of traditional pallets.     

Simulation of low rigidity part machining applied to thin-walled structures

The aim of this study is to evaluate the modelling of machining vibrations of thin-walled aluminium workpieces at high productivity rate. The use of numerical simulation is generally aimed at giving optimal cutting conditions for the precision and the surface finish needed. The proposed modelling includes all the ingredients needed for real productive machining of thin-walled parts. It has been tested with a specially designed machining test with high cutting engagement and taking into account all the phenomena involved in the dynamics of cutting. The system has been modelled using several simulation techniques. On the one hand, the milling process was modelled using a dynamic mechanistic model, with time domain simulation. On the other hand, the dynamic parameters of the system were obtained step by step by finite element analysis; thus the variation due to metal removal and the cutting edge position has been accurately taken into account. The results of the simulations were compared to those of the experiments; the discussion is based on the analysis of the cutting forces, the amplitude and the frequency of the vibrations evaluating the presence of chatter. The specific difficulties to perfect simulation of thin-walled workpiece chatter have been finely analysed.     

A model for the minimum cost configuration problem in flexible manufacturing systems

This paper presents a mathematical programming model to help select equipment for a flexible manufacturing system, i.e., the selection of the types and numbers of CNC machines, washing stations, load/unload stations, transportation vehicles, and pallets. The objective is to minimize equipment costs and work-in-process inventory cost, while fulfilling production requirements for an average period. Queueing aspects and part flow interactions are considered with the help of a Jacksonian-type closed queueing network model in order to evaluate the system's performance. Since the related decision problem of our model can be shown to be NP-complete, the proposed solution procedure is based on implicit enumeration. Four bounds are provided, two lower and two upper bounds. A tight lower bound is obtained by linearizing the model through the application of asymptotic bound analysis. Furthermore, asymptotic bound analysis allows the calculation of a lower bound for the number of pallets in the system. The first upper bound is given by the best feasible solution and the second is based on the anti-starshaped form of the throughput function.     

Simulating windows [window manufacturing]

Simulating a manufacturing operation often has surprising results. The author explains how a window manufacturer improved its processes. The production scheduling and operations management issues faced by a window manufacturer will be universally recognised by manufacturing engineers from all sectors. The processes may be different, but the end result - a quality product made in the shortest possible time and at the lowest cost - is the same. Simulation modelling is seen as a way of analysing dynamic systems that exhibit variability. Before experimental analysis of the simulation model can begin it is necessary to ensure that the model constructed provides a valid representation of the system. This process consists of verification and validation of the simulation model.     

The effects of machining process variables and tooling characterisation on the surface generation

The paper presents a novel approach for modelling and simulation of the surface generation in the machining process. The approach, by integrating a dynamic cutting force model, regenerative vibration model, machining system response model and tool profile model, models the complex surface generation process. Matlab Simulink is used to interactively perform the simulation in a user-friendly, effective and efficient manner. The effects of machining variables and tooling characteristics on the surface generation are investigated through simulations. CNC turning trials have been carried out to evaluate and validate the approach and simulations presented. The proposed approach contributes to comprehensive and better understanding of the machining system, and is promising for industrial applications with particular reference to the optimisation of the machining process based on the product/component surface functionality requirements.     

Finite element based model predictive control for active vibration suppression of a one-link flexible manipulator

This paper presents a unique approach for active vibration control of a one-link flexible manipulator. The method combines a finite element model of the manipulator and an advanced model predictive controller to suppress vibration at its tip. This hybrid methodology improves significantly over the standard application of a predictive controller for vibration control. The finite element model used in place of standard modelling in the control algorithm provides a more accurate prediction of dynamic behavior, resulting in enhanced control. Closed loop control experiments were performed using the flexible manipulator, instrumented with strain gauges and piezoelectric actuators. In all instances, experimental and simulation results demonstrate that the finite element based predictive controller provides improved active vibration suppression in comparison with using a standard predictive control strategy.     

An investigation of energy efficiency of a wheel loader with automated manual transmission

This paper describes an investigation of energy efficiency by applying an advanced powertrain system in a conventional wheel loader. A conventional powertrain of a wheel loader consists of an engine, torque converter and transmission. A torque converter in a conventional system generally causes a significant amount of energy loss, as determined by analyzing energy flow based on V-pattern working. To prevent energy loss in a torque converter, Automated manual transmission (AMT) was proposed and modeled in this paper as an advanced powertrain. A wheel loader based on AMT does not need to use a torque converter since the single clutch system is used between the engine and transmission with subsystems of engine controller, clutch actuator and controller. A simplified single clutch system and controller were constructed for V-pattern working of a wheel loader. Additionally, a PI-controller was used as a control algorithm for engine speed control to prevent energy loss while the clutch is not engaged. All simulation models have been constructed in the Matlab/ Simulink environment, and simulation studies were conducted by using a simulation model of a wheel loader with a driver model based on V-pattern working. Simulation results of the AMT-based wheel loader were analyzed by comparison with the results of the torque converter-based wheel loader, and the results show that the AMT-based wheel loader is more energy efficient than the conventional wheel loader.     

基于AMESim的电液伺服系统仿真与优化研究

AMESim是法国IMAGINE公司开发的高级工程系统仿真建模环境，为机械、液压、控制等工程系统提供一个较完善的综合仿真环境。目前该软件已广泛地被GM、Ford、LG、ZF、Bosch等公司采用，成为在汽车、液压和航空航天等研发部门的理想选择。文章首先介绍了AMESim软件的功能与特点，以典型的电液伺服控制系统为例，探讨了基于AMESim的液压系统建模与仿真的方法，研究了基于AMESim／DesignExploration模块和AMESim／matlab接口对AMESim仿真系统进行优化设计的方法，并给出了仿真与优化的结果。利用此方法，借助于AMESim所提供的多领域软件接口．可方便实现大型机电液一体化系统的联合仿真与优化研究．     

Deterministic fabrication of nanostructures for plasmonic lens by focused ion beam

Plasmonic lens is a key component in the development of sub-wavelength resolution optical system for bio-imaging and nanolithography applications. In order to develop a deterministic fabrication capability for nanostructures on plasmonic lens by using focused ion beam, this paper presents a highly robust and accurate surface topography model based on level set method. Sputtered atom distribution and angular dependence of sputter yield are calculated by Monte Carlo simulation programs SRIM/TRIM and TRIDYN, respectively. Redeposition effect is included in the physical model and successfully embedded into a topography simulation program by applying the level set method. The proposed model is validated and evaluated in the focused ion beam fabrication experiments. Simulation error of less than 7% is obtained. Two types of nanostructures for plasmonic lens were fabricated using the machining parameters approved by this simulation model. Simulation errors of 7 and 2?nm were found in a nanodots array and a spiral Bragg grating, respectively. The results clearly demonstrate the effectiveness of the modelling approach developed for deterministic fabrication of nanostructures.     

Finite-element and experimental analysis of dynamic behaviours of a micro-stamping tool system

As demands on the forming of micro-products increase, ensuring the high-quality design of machine–tool systems becomes increasingly more important. This is particularly due to a need to address smaller geometries and finer tolerance requirements, compared to those of conventional forming. Finite-element (FE) simulation of the dynamic behaviour of machines and tools is particularly useful for supporting design optimisation. Detailed finite-element modelling of stamping tool systems has, however, not been addressed previously. Difficulties tend to arise when many tool parts need to be considered in the modelling. In this paper, dynamic analysis of a micro-sheet-forming system driven by a linear motor is presented. Parameters that influence dynamic behaviours of the micro-stamping tool were investigated using the finite-element analysis and the results of experimental measurement. The findings provide useful information for the improvement of the design of micro-stamping tools as well as for the design of micro-forming-machine systems.     

Design of adaptive backstepping congestion controller for TCP networks with UDP flows based on minimax

The congestion control problem of TCP network systems with user datagram protocol (UDP) flows is investigated in this paper. A nonlinear TCP network model with strict-feedback structure is first established. The unknown UDP flow is regarded as the external disturbance, and the maximum UDP flow is calculated by using the minimax approach. And then, a congestion control algorithm is proposed by using the adaptive backstepping approach. Meanwhile, the adaptive law is employed to estimate the unknown link capacity. The design of the adaptive law is to introduce a parameter mapping mechanism to limit the parameter identification range to a specified interval, thereby improving the estimation efficiency of the parameters. Furthermore, a state-feedback congestion controller is presented to make sure that the output of the system tracks the desired queue. The simulation results show the superiority and feasibility of the proposed method.     

TYRE DYNAMICS MODELLING OF VEHICLE BASED ON SUPPORT VECTOR MACHINES

Various methods of tyre modelling are implemented from pure theoretical to empirical or semi-empirical models based on experimental results. A new way of representing tyre data obtained from measurements is presented via support vector machines (SVMs). The feasibility of applying SVMs to steady-state tyre modelling is investigated by comparison with three-layer backpropagation (BP) neural network at pure slip and combined slip. The results indicate SVMs outperform the BP neural network in modelling the tyre characteristics with better generalization performance. The SVMs-tyre is implemented in 8-DOF vehicle model for vehicle dynamics simulation by means of the PAC 2002 Magic Formula as reference. The SVMs-tyre can be a competitive and accurate method to model a tyre for vehicle dynamics simulation.     

塑料托盘在卷烟企业自动化立库中的应用与分析

通过对塑料托盘和木托盘两者优缺点的具体论述,论证了塑料托盘必将取代木托盘大规模使用.论文以某卷烟厂自动化立体高架库上所用塑料托盘的设计为例,针对塑料托盘在高架库上运行必须具备的条件和所受的制约,重点就承重、尺寸、防滑、变形量、刚性等方面进行具体分析和设计,设计后经过均载强度试验,证明完全能制造出适应自动化立体高架库标准要求的塑料托盘.实际应用中也证明塑料托盘在卷烟企业自动化立体高架库上的运行是可行的.