An integrated approach to the facilities and material handling system design

The facility layout problem involves the optimal location of manufacturing facilities into a workshop. The classical approach to the layout design is carried out in two separate steps: the first step is the construction of the block layout, i.e. the location of the departments into the workshop, and the second step is the design of the material handling system. The separate optimization of these two aspects of the problem leads to solutions that can be far from the total optimum. In this paper, an integrated approach to the facilities and material handling system design is proposed. Referring to a physical model, named the bay structure , and to a unidirectional AGV system, a genetic approach is proposed to individuate the locations of the departments, the positions of the pickup/delivery stations and the direction of the flow-path. The minimization of material handling cost is adopted as optimality criterion.     

Robustness of state-dependent queues and material handling systems

In many factory settings, performance modeling and optimisation of material handling systems (MHS) is a complex problem. State-dependent queueing models are effective and robust tools to capture this traffic congestion. The integration of state-dependent models of the material handling elements and finite queueing models of work stations is demonstrated. An important property of the state-dependent models when used to model the material handling elements is that they appear to be insensitive to the input distribution. Numerous topological network design (TND) problems and experiments are presented to show the effectiveness of state-dependent queueing models for TND/MHS design.     

The segmented bidirectional single-loop topology for material flow systems

This paper introduces the segmented bidirectional single-loop (SBSL) flow topology for carrier-based material handling systems. This configuration is based on a single-loop flow-path structure that is divided into non-overlapping segments, each containing a single carrier operating in a bidirectional mode. The design procedure comprises a 0 - 1 mixed-integer formulation to determine the single-loop including the pickup and delivery station location. The second stage is a segmentation procedure to determine the non-overlapping segments in the loop. Finally the performance of the SBSL is evaluated by means of simulation.     

智能制造系统AGV小车及缓冲区容量仿真优化

具有MHS(material handling system)的智能制造系统AGV(automated guided vehicle)小车及缓冲区最大容量配置优化,属于典型的非线性整数规划问题。由于约束无法用封闭形式表达,因此较难获得问题的精确解。为此,本文提出了仿真优化的方法以获得问题的近似解。首先,对AGV小车及缓冲区最大容量配置优化问题进行了描述;其次,基于Em plant平台建立了具有MHS的智能制造系统仿真模型;然后,基于不同的优化目标,提出了3种仿真优化方法;最后,通过仿真试验对上述3种方法进行了分析与比较。分析表明,本文提出的方法及优化结果,可为企业配置AGV小车及缓冲区最大容量提供决策支持。     

Advances in discrete material handling system design

The paper presents an outline of the research done in the area of facility layout and discrete material handling system design. The objective of this paper is to observe the trend in the literature in the area of manufacturing system design and predict the direction of future research in this area. The paper attempts to link the areas of facility layout design and material flow network design. A methodology for solving the integrated design problem is presented. An algorithm which aids in solving the combined pick-up/drop-off point location and material handling flowpath problem is outlined.     

A policy of picking up parcels for express courier service in dynamic environments

As a particular logistics service, the express courier service has seen considerable growth recently, which resulted in an unprecedented fierce competition. Besides, the development of information and communication technologies has enabled express company to manage their service. With the purpose of improving service quality and operation efficiency for express company, we focus on the problem of intercity express courier routing in courier-triggered pickup service. A novel pickup policy for courier routing is proposed based on the idea of centrality measures and the nearest-neighbour (NN) policy by considering the un-serviced customer requests as a globally coupled network. This policy enables to dispatch the idle courier to the more central request location, which allows the courier to easily serve the neighbouring requests around the central request location, thus securing both global and local performance. We also propose a simple prototype of real-time fleet management system where the proposed pickup policy is embedded into it. To evaluate the efficiency and practicability of the pickup policy, we conduct comprehensive computational experiments to generate various testing scenarios; moreover, two widely used dispatching policies – NN and first-come-first-served (FCFS) – are considered as the benchmark policy. Results show that the proposed pickup policy significantly outperforms the NN and FCFS policies in terms of waiting time and total service time.     

Measurements and comparison of saltation and pickup velocities in wind tunnel

This work presents experimental results of the pickup velocity measurements for variety of particulate solids. The experiments were carried out in a horizontal wind tunnel. The influence of three initial arrangements of particle(s) on pickup velocity was investigated. Particle(s) were placed either on the bottom surface of the tunnel or on the horizontal layer of particles or the heaps of particles with various heights were created in the wind tunnel. A high-speed video camera was used to visualize the particle entrainment. However, the pickup velocity was defined in a qualitative manner by extrapolating the carried weight of particles as a function of air velocity. Comparison between the saltation velocity in dilute phase flow and the pickup velocity, both measured in the horizontal wind tunnel, provide an insight and guideline how the minimum operating air velocity in a pneumatic conveying line could be defined and determined.Authors would like to thank Mr. Rhye Hamey and Mr. Milorad Djomlija for their valuable comments and proofreading.     

A multi-objective mixed-integer programming model for a multi-floor facility layout

We consider a multi-floor facility layout problem in which the overall length and width of the facility, the size and location of each department, the number and the location of elevators and the number of floors in the facility are all modelled as decision variables. We adapt a linear approximation scheme to represent the area of each department. We consider two objective functions in our model, namely minimising material handling and facility building costs, and propose a lexicographic ordering technique to handle multiple objectives. The numerical experiments show that the slack used in the lexicographic ordering approach has a significant impact on the optimal solution. The experiments also show that the material handling cost can be significantly reduced in a multi-floor facility compared with a single-floor facility.     

MOF‐Based Hierarchical Structures for Solar‐Thermal Clean Water Production

Solar‐thermal water evaporation, as a promising method for clean water production, has attracted increasing attention. However, solar water evaporators that exhibit both high water vapor generation ability and anti‐oil‐fouling ability have not been reported. Here, a unique metal–organic‐framework‐based hierarchical structure, referred to as MOF‐based hierarchical structure (MHS), is rationally designed and prepared, which simultaneously displays a high solar absorption and a superhydrophilic and underwater superoleophobic surface property. As a proof‐of‐concept application, a device prepared from the MHS can achieve a high solar‐thermal water evaporation rate of 1.50 kg m^?2 h^?1 under 1 sun illumination. Importantly, the MHS also possesses an excellent anti‐oil‐fouling property, ensuring its superior water evaporation performance even in oil‐contaminated water. The high solar‐thermal water evaporation rate and anti‐oil‐fouling property make the MHS a promising material for the solar‐thermal water production.     

Location Selection and Scheduling Optimization of Material Storage in Manufacturing Workshop

Based on improved immune algorithm, the location of material storage in manufacturing workshop is studied. Intelligent optimization algorithms include particle swarm optimization algorithm, genetic selection algorithm, simulated annealing algorithm, tabu search algorithm and so on. According to the non-linear constraints, the objective function is established to solve the minimum energy consumption of material distribution. The improved immune algorithm can solve the complex problem of manufacturing workshop, and the material storage location and scheduling scheme can be obtained by combining simulation software. Scheduling optimization involves material warehousing, sorting, loading and unloading, handling and so on. Using the one-to-one accurate distribution principle and MATLAB software to simulate and analyze, the location of material warehousing in manufacturing workshop is determined, and the material distribution and scheduling are studied.     

The value of the shortest loop covering all work centers in a manufacturing facility layout

In this study we develop mathematical models to design circular material flow systems. We first develop a tight formulation to find the shortest loop covering all work centers within a manufacturing facility layout. The shortest loop is an attractive solution for most types of conveyors and power-and-free systems, where the length of the flow path is the major driver of the total cost. We develop a primal as well as a dual graph formulation and discuss their one-to-one correspondence in node-edge as well as in connectivity constraints. Our solution times outperform other optimization models available for the facility layout shortest loop design problem. We then approach trip-based material handling, such as automated guided vehicle systems, where the total loaded and empty trip distance is the major driver of the total cost. The problem in these systems evolves into concurrent design of the loop, pickup and dropoff station, and the empty vehicle dispatching policies. On the foundation of the shortest loop model, we propose a decomposition heuristic for design of trip-based flow systems. Computational results indicate that the heuristic provides high quality and robust solutions.     

Split Hopkinson pressure bar multiple reloading and modeling of a 316 L stainless steel metallic hollow sphere structure

The high strain rate (600 s⁻¹) compression deformation of a 316 L metallic hollow sphere (MHS) structure (density: 500 kg m⁻³; average outer hollow sphere diameter: 2 mm and wall thickness: 45 μm) was determined both numerically and experimentally. The experimental compressive stress–strain behavior at high strain rates until about large strains was obtained with multiple reloading tests using a large-diameter compression type aluminum Split Hopkinson Pressure Bar (SHPB) test apparatus. The multiple reloading of MHS samples in SHPB was analyzed with a 3D finite element model using the commercial explicit finite element code LS-DYNA. The tested MHS samples showed increased crushing stress values, when the strain rate increased from quasi-static (0.8 × 10⁻⁴ s⁻¹) to high strain rate (600 s⁻¹). Experimentally and numerically deformed sections of MHS samples tested showed very similar crushing characteristics; plastic hinge formation, the indentation of the spheres at the contact regions and sphere wall buckling at intermediate strains. The extent of micro-inertial effects was further predicted with the strain rate insensitive cell wall material model and with the strain rate sensitive behavior of MHS structure similar to that of the cell wall material. Based on the predictions, the strain rate sensitivity of the studied 316 L MHS sample was attributed to the strain rate sensitivity of the cell wall material and the micro-inertia.     

交互式三维纸盒包装CAD中分层对象拾取的研究

在交互式三维包装纸盒CAD中,需要以对象的拾取为基础来对每个纸盒基本构成对象进行操作。给出满足三维包装纸盒交互设计的数据结构和对于面、面内线段、面内点3个层次对象的拾取方法,并开发了交互式三维包装纸盒CAD系统。实践证明,此方法可以很好地实现层次对象的拾取,满足系统对各种交互操作的需要。     

A Monte Carlo simulation based heuristic procedure for solving dynamic line layout problems for facilities using conventional material handling devices

A simple procedure is proposed to identify line layout solutions when a production facility with work centres of unequal size uses conventional material handling devices and operates under stochastic demand scenarios. The procedure uses Monte Carlo simulation (MCS) to empirically search for robust solutions defined as those that simultaneously meet minimum material handling cost performance levels across all demand scenarios. The results reported in this study suggest that ‘robust’ line layout solutions can be identified using a modest volume of random sampling. The procedure and results are demonstrated through a series of sample problems.     

A Stock Location Rule For A Low Level Picker-To-Part System

This paper deals with the problem of assigning warehouse space to inventory items in a low level picker-to-part system. Recognizing the importance of weights in material handling activities in warehouse, a linear programming model is developed with the objective of minimizing the workload required for order picking operations. It is proved that the stock location rule proposed in this paper generates an optimal solution for the model. Compared with the well known cube-per-order index (COI) rule, it is shown that the proposed rule is substantially better from the view point of human safety with some sacrifice of throughput.     

大型钢筋混凝土长柱吊装的最优方案研究

为了解决电厂或工业厂房大型钢筋混凝土长柱吊装的施工难题,研究了其最优吊装方案的确定方法,并编制相应的计算机程序。针对拟定的双机双绳系统,建立了长柱内力分析的数学模型,选择吊点位置作为设计变量,以长柱吊装过程中弯矩最小作为目标函数,采用惩罚策略处理约束条件,以“网格法”和“遗传算法”对绳索系统的吊点位置进行了优化求解。通过对长柱在各种拟定绳系最优吊点下的内力比较,确定了最优的绳系方案。最后给出了一个算例说明方法的正确性和有效性。算例结果表明,通过优选绳系形式、吊点位置、绳长等参数,能使最大弯矩峰值下降30%左右。     

Modeling for flexible manufacturing systems with an FMS blocking mechanism and a BDSM job routing

We consider a Flexible Manufacturing System (FMS) which is composed of a set of workstations, a common buffer and a Material Handling System (MHS). Each workstation includes a limited input buffer, several machines and a limited output buffer. The MHS consists of several carts moving jobs among the workstations according to the process paths required by the jobs. The carts treat blocked jobs in accordance with a new blocking mechanism, called the 'FMS blocking mechanism'. The function of the common buffer is to temporarily store blocked jobs. Such an FMS is formulated as an open queueing network, in which the MHS is modeled as a central station routing jobs to the workstations. In the model, the machines process jobs with an exponentially distributed processing time, and the carts route jobs to the workstations following a 'Blocking Depended Static Markov (BDSM) job routing' with an exponentially distributed routing time and treat blocked jobs in accordance with the FMS blocking mechanism. It is shown that the equilibrium state distribution of the model has a product-form solution. The blocking probabilities are obtained by computing a fixed point problem whose solution is revealed by an iterative algorithm. Moreover, it is shown that the throughputs of the workstations are independent of the spaces on the local buffers at the workstations. Several numerical examples are presented.     

Performance evaluation of a transportation-type bulk queue with generally distributed inter-arrival times

This paper is motivated by the performance evaluation of circulating vertical conveyor systems (CVCSs). CVCSs are bulk queues of transportation type. These material handling systems feature generally distributed inter-arrival times, which can be longer than the bulk service time. This leads to interdependencies between the number of arrivals in consecutive service intervals and the number of loads in the queue. We propose a new discrete-time approach for the steady-state analysis of such bulk service queues of transportation type with general arrival and service processes and finite server and limited queue capacities. The approach is based on a finite Markov chain that generates complete probability distributions for the key performance measures, including the queue length, waiting time and departing batch size. The proposed approach is exact in the cases of discrete-time slots, e.g. as in communication systems. We investigate the discretisation error that arises if the approach is used as an approximation for the continuous time using a numerical comparison to a discrete-event simulation. Moreover, we examine the impact of arrival stream variability on the system performance and compare the positive effects of a higher frequency of server visits with the effects arising from larger pickup capacities.     

A simulation study on the performance of task-determination rules and delivery-dispatching rules for multiple-load AGVs

In this paper, the control problem of multiple-load automated guided vehicles (AGVs) is studied. A control process that identifies four problems faced by multiple-load AGVs is proposed. The first problem is the task-determination problem, in which a multiple-load AGV determines whether its next task is a pickup task or a delivery task. The second problem is the delivery-dispatching problem, in which a multiple-load AGV determines which delivery point it should visit next if its next task is a delivery task. The third problem is the pickup-dispatching problem, in which a multiple-load AGV determines which pickup point it should visit next if its next task is a pickup task. Finally, the fourth problem is the load-selection problem, which requires a multiple-load AGV to determine which load it should pick up from the output queue of a pickup point. This paper focuses on the first and second problems. Different task-determination rules and delivery-dispatching rules are proposed for these two problems. For the problems that are not the main focus of this study, rules found in the literature or real systems are adopted in this study. The objective of this study is twofold. First, we need to understand how well the proposed rules will perform in different performance measures, e.g. the system's throughput and the mean lateness of parts. Second, we need to understand the mutual effects that different types of rules have on each other, so that the best combination of rules can be identified. Computer simulations were conducted to test the performance of the proposed rules. It is hoped the knowledge learned from this study can be beneficial to real multiple-load AGV systems similar to the one studied here.     

Injury patterns for occupants of small trucks

A limited number of studies have been completed on the factors contributing to accident-related injuries sustained by occupants of pickup trucks. The increasing number and changing pattern of use of light trucks necessitates the need to critically review this vehicle type with respect to contributing accident factors and associated injuries. This paper investigates the injury mechanisms of occupants of pickup trucks and the surfaces that the occupants contact in roadway accidents. Selection of cases from the Canadian vehicle database was based on the location of the vehicles' most severe impact deformation. The overall occupant injury severity was examined with respect to impact location, impact speed, and magnitude of occupant compartment intrusion. The results of the investigation illustrate the benefits of seat belt restraint use. In addition, identification of frequent injury contact surfaces establishes a reference for improved vehicle design initiatives and standards.