Rack Warehouse Research Articles

Fire‐Induced Collapse of Automated Rack‐Supported Warehouses

AbstractAutomated self‐supporting rack warehouses are becoming increasingly common in the international logistics sector. Their static and seismic design has been studied in the literature; however, the fire design still needs to be improved. Some Standards, such as the Eurocodes or Italian Fire Code, accept the collapse of rack warehouses during fires but require avoiding a progressive collapse or obtaining an implosive collapse regardless of any other active or passive fire protection systems. A hierarchy that guides the kinematics of collapse needs to be defined appropriately but without any Code going into further details. Moreover, the scientific literature focuses more on optimizing fire protection systems for racks, such as sprinklers, rather than preventing fire‐induced progressive collapse. Here, a case study is presented, which, using finite element modelling, provide a first robustness evaluation and highlights some possible aspects to be considered in the structural design to avoid a progressive collapse in the event of a fire. The analyses are performed using the LOCAFI method for localized fires and nonlinear dynamic finite element simulations.

A study of layout determination of mobile rack warehouse

<abstract> <p>Labor cost reduction and resourceful space utilization are essential for efficient warehouse operation. In these challenges, mobile rack technology can increase storage space by 75% or more. The mobile racking system is a system where racks are constructed on a mobile base and steered by rails on the floor. Driven by an electrical motor, the mobile base moves along the rails to open one or more access aisles. Moving rack technology eliminates aisle space between racks and increases storage space by synchronizing wheels or rails. Hence, companies can stock and access a high volume of products while enduring space-efficient. Minimizing the cost per pallet is especially critical for cooler and freezer facilities. However, there is no straightforward solution to determining the optimal layout of a mobile rack warehouse. When designing a mobile rack warehouse, you can increase storage space by a minimum of aisles, but it can reduce work efficiency at the same time. Therefore, it is necessary to determine the appropriate layout of mobile racks considering both work efficiency and space efficiency. This study proposes a practical layout of a mobile rack warehouse to harmonize work and space efficiency. To validate the model, we examine several numerical examples and analyze the warehouse area, the total amount of rack movement, and working hours. Depending on the operating cost, a different layout is suggested.</p> </abstract>

Swing JIB rack stacker crane

Introduction. Rack stacker cranes are the main hoisting and transport machine for maintenance of multi-level rack warehouses. The efficiency and profitability of the warehouse depends on their efficiency. The traditional design of a rack stacker crane includes a trolley that moves along the rails on the floor of a warehouse, a column mounted vertically on the trolley, along which a carriage with a load gripping device and a load rises. The disadvantages of the traditional crane design are the relatively large mass of the trolley, the need to move it along with the column in a horizontal direction when moving around the warehouse, the relatively high energy consumption and the need to strengthen the floor of the warehouse. The crane rail tracks on the floor of the warehouse must be cleared of objects falling from above, which is associated with stopping the operation of the crane and reducing productivity.Materials and Methods. The design of a stacker crane is related to the shape of its working space. In order to improve the stacker crane, its design was developed on the basis of a jib with a counterweight, which does not require rail crane tracks. The crane of the proposed design is capable of storage in the hangars of a semicircular shape. For two warehouses: traditional rectangular and semicircular shapes, a comparative analysis of the sums of geometric distances was performed when the load gripping device moved from the loading point to randomly selected target cells. As a comparison criterion, the sum of the Cartesian distances of the load gripping device movements between the warehouse loading point and the target points, randomly selected according to the law of uniform distribution, was used. Three types of crane operation cycles were studied – simple single, double and mixed.Results. Comparative diagrams of criterion values are given. It has been established that for all types of cycles studied, to the greatest extent when working on a single cycle, the use of a crane of the proposed design with the same storage capacity significantly reduces the total geometric distance that the load gripping device must pass.Discussion and conclusions. Reducing the sum of the geometric distances of movement of the load handling device of the new crane allows to conclude that the time spent on the movements that determine the productivity of the work performed by the crane, as well as the energy costs associated with them, can be significantly reduced. Reducing energy costs is possible by replacing the translational movement of a massive undercarriage with the rotational movement of a balanced jib of a relatively small mass at the crane of the proposed design. Time is not wasted on regular cleaning of the crane tracks, associated with stopping the crane. The number of friction pairs in the proposed design of the crane is reduced compared with the traditional one.

Hybrid genetic algorithm-based optimisation of the batch order picking in a dense mobile rack warehouse.

The utilization of a storage space can be considerably improved by using dense mobile racks. However, it is necessary to perform an optimisation study on the order picking to reduce the time cost as much as possible. According to the channel location information that needs to be sorted, the multiple orders are divided into different batches by using hierarchical clustering. On this basis, a mathematical model for the virtual order clusters formed in the batches is established to optimize the order cluster picking and rack position movement, with the minimum picking time as the objective. For this model, a hybrid genetic algorithm is designed, and the characteristics of the different examples and solution algorithms are further analysed to provide a reference for the solution of the order picking optimisation problem in a dense mobile rack warehouse.

Совершенствование складских транспортных устройств на воздушной подушке с наклонными питающими каналами

Introduction. The paper considers the question of the directions of mechanization and automation of rack warehouses logistics. The paper considers hovercraft transport devices operating in the storage area with inclined feeding channels. The displacement of the load center relative to the geometric center of the support surface is studied. It is noted how this affects the main characteristics of the studied devices. Problem Statement. Previous studies have proved the sufficient performance of non-powered hovercraft transport devices with inclined feed channels, their safety and efficiency in the transportation of piece goods, as well as the potential for mechanization and automation of transport and storage operations in rack warehouses. The task of this work is to present a scheme of mechanization for the storage area of a rack warehouse equipped with a transport device with inclined feeding channels. Theoretical Part. In rack warehouses designed for the storage of individual goods, the receiving, storing and sending operations are in most cases carried out using carrying and lifting machines. Stacker cranes are most common, but their use requires the creation of complex and expensive systems, i.e. significant capital and operating costs. The article considers the system of mechanization of a rack warehouse with the use of hovercraft vehicles with an off-center location of the cargo. In this case, the height of the airbag depends on the eccentricity of the load location. The points of application and the values of the resistance and traction forces, torques and friction forces that affect the total resistance are shown, which are typical for such a situation Conclusion. The results of the research allow us to state that in some cases, instead of traditional transport devices, the use of hovercraft transport devices with the inclined feed channels is effective in logistics enterprises.

High-density storage with mobile racks: Picker routing and product location

In response to the scarce space in many urban areas, high-density storage has become a widely discussed topic in warehousing research and practice. We investigate a storage setting where mobile racks are mounted on rails, so that a strong engine moves whole blocks of racks aside, opening an aisle and enabling access to a specific rack. Moving the heavy racks takes a considerable amount of time and, consequently, it strongly affects the total pick time. We formalise the resulting operational picker-routing problem, which aims at routing the picker such that as few aisles as possible need to be accessed and the total distance covered is minimal. Moreover, we address the interdependent tactical product-location problem, which deals with deciding on the storage locations of the items to be picked. We present suitable exact and heuristic solution procedures for both problems. In a comprehensive computational study, we apply these algorithms to explore the interdependencies between product location and picker routing, and derive recommendations as to suitable storage policies in a mobile rack warehouse.

Perbandingan Algoritma Simulated Annealing dan Harmony Search dalam Penerapan Picking Order Sequence

Implementation of mobile rack warehouse is commonly used in manufacturing industry because it can minimize the warehouse area used. Applying picking orders in taking of Stock Keeping Unit (SKU) on mobile rack warehouses could give fast loading order. This research aims to find out which algorithm is better in applying picking order sequence in mobile rack warehouse. The algorithm used is Simualted Annealing (SA) and Harmony Search (HS) algorithm. Both of these algorithms will be compared in terms of the gap with the shortest path method.The result shows that the HS algorithm produces a better solution than the SA algorithm with lower CPU time, but the convergence rate of HS is lower than that of SA.HS was able to produce a better solution than the shortest path method of 9 cases, while SA only 8 cases from 15 cases.

Application of Horizontal Barrier on a Rack to Reduce Fire Spread

적재밀도가 높으며 수직적인 적재형태를 가지는 랙크식 창고는 화재발생 시 그 피해가 매우 심각하다. 이에 미국,일본에서는 자국의 랙크식 창고 실정에 맞는 In-Rack 스프링클러 및 수평차단막 등을 적용하여 화재확산을 최소화하는데 노력하고 있으나 국내의 경우, 그와 관련한 연구 및 제도가 전무한 실정이다. 이에 본 연구에서는 발화위치 및수평차단막 설치간격에 따른 화재특성 확인을 위해 국내 랙크식 창고 실정을 반영한 표준랙크를 대상으로 축소모델화재시험을 수행하였다. 그 결과, 수평차단막의 설치간격을 밀접하게 또는 빈번하게 할수록 약 30%씩의 수직 화재확산 억제성능이 발휘되는 것을 확인하였다. 아울러 수평차단막을 경계로 상하부의 온도를 측정한 결과, 차단막이 설치된 경우가 그렇지 않은 경우에 비해 온도분포가 약 2∼4배 이상 높은 것으로 나타나 수평차단막의 설치가 In-Rack스프링클러의 조기 작동에 도움을 줄 것으로 판단된다.A rack warehouse with a vertically loading type and high loading density has severe risks and damage during its fire. Inthis regard, US and Japan strive to minimize the fire spread by applying in-rack sprinkler, horizontal barriers, etc. corresponding to their own rack warehouse but there is no study and policy in Korea. Therefore, a model scale fire test wascarried out targeting the standard rack incorporating the national rack warehouse in order to check fire characteristics inignition points and installation distances of horizontal barriers in this study. As a result of the test, vertical fire spread of about30% was inhibited by narrowing its installation distance from 2-layer to 1-layer in an ignition condition of the flue space. In addition, as a result of the measurement of the temperature in the upper and lower parts of the horizontal barrier, thetemperature distribution showed about 2~4 higher in a condition with an installation of the barrier than that in the conditionwithout the barrier. Consequently, it is likely that the horizontal barrier will help the initial operation of in-rack sprinkler.

Processing User Input in Tracking Problems using Model Predictive Control

Using the application of a container crane in a high rack warehouse, the problem class of tracking problems is introduced, where the system has to reach a possible time dependent reference value while maintaining stability and safety.These problems are a subclass of nonlinear model predictive control problems, and can be solved numerically as optimal control problems. Numerical results are given for the described application, as well as some considerations on reducing the computational time.

성능위주 소화설비 적용을 위한 표준랙크의 화재확산속도 평가

물품이 수직 집약적인 형태로 적재되는 랙크식 창고는 화재발생 시 화염의 급속한 상승으로 인해 그 피해가 매우 심각하다. 이에 ESFR 및 In-Rack 스프링클러, 수직 및 수평차단막 등, 다양한 소화설비 적용을 통해 화재확산 억제에 노력하고 있으나 랙크의 크기 및 적재밀도, 적재물품의 종류 등, 매우 다양한 구성조건으로 인해 적절한 소화설비 선정에 어려움이 있다. 이에 본 연구에서는 현장조사 및 설문조사 등을 통해 국내 랙크식 창고 실정을 반영한 표준랙크를 제작하였으며, 발화위치 조건에 따른 화재특성 확인을 위해 실규모화재시험을 수행하였다. 이를 통해 도출된 화재확산속도는 향후, 개발 및 적용 예정 소화설비들의 성능비교를 위한 기초자료로서 유용하게 활용될 것으로 기대한다. In case of fire, vertically and intensively loaded rack warehouses are faced with a severe status due to the rapid increase in fires. In this regard, there have been trials to prevent fires from spreading by applying fire extinguishing systems, such as ESFR and In-Rack Sprinklers, vertical and horizontal barriers, etc.; however, it is difficult to calculate and design proper fire extinguishing systems caused by various composition conditions, such as the size and loading density of the rack, types of loading commodities, etc. Therefore, in this study, a standard rack was manufactured, incorporating a rack warehouse in Korea by site investigations, surveys, etc. In addition, a full scale fire test was executed to check the fire characteristics depending on the conditions of the ignition points. As a result, the extracted fire spread speed is expected to be utilized as a reference for performance comparisons of the fire extinguishing systems to be developed and applied in the future.

Sequencing of picking orders in mobile rack warehouses

A growing population and increasing real estate costs in many urbanized areas have made space for roomy warehouses with single-deep storage and wide aisles scarce and expensive. Mobile rack warehouses increase the space utilization by providing only a few open aisles at a time for accessing the racks. Whenever a stock keeping unit (SKU) is to be retrieved, neighboring racks mounted on rail tracks have to be moved aside by a strong engine, so that the adjacent aisle opens and the SKU can be accessed. As moving the heavy racks takes considerable time, the resulting waiting time determines large parts of the picking effort. It is, thus, advantageous to sequence picking orders, such that the last aisle visited for the preceding order is also the first aisle to enter when retrieving a subsequent picking order. We formalize the resulting picking order sequencing problem and present suited exact and heuristic solution procedures. These algorithms are tested in a comprehensive computational study and then applied to explore managerial aspects, such as the influence of the number of open aisles on the picking effort.

랙크 내 파렛트단위 적재물품의 화재특성에 관한 연구

A fire extinguishing system for a rack warehouse was recently designed, which only consider the gross area and number of stories. However, the design of such a system should take into account not only the planar structuree, but also the elevation perspectives due to its vertical structure. Moreover, the fire load of the commodities palletized on the racks should be considered, in order to design a performance-based fire safety system that is appropriate for these environmental conditions. For this reason, this study analyzed the fire characteristics of the commodities palletized on the racks (pallet + the commodities in a box unit + vinyl packing material), taking into consideration the results of a field investigation conducted in Korea, as well as the Hazard Classifications of Commodities used in other countries. Through this analysis, the heat release rate (HRR) and smoke production rate (SPR) were derived.

Fast and save container cranes as bilevel optimal control problems

For the use of container cranes in high rack warehouses, reference trajectories can be obtained from optimal control problems in order to control the swinging of the crane system during the fast movement and in order to reach an equilibrium position at the end of the trajectory. Safety requirements extend these problems to bilevel optimal control problems, where the existence of alternative stop trajectories has to be guaranteed. A method as to how these complex problems can be reduced to conventional optimal control problems, even under control and state constraints, is presented together with numerical examples.

Improving the productivity of order picking of a manual-pick and multi-level rack distribution warehouse through the implementation of class-based storage

Determining the proper storage locations for potentially thousands of products is one major task that faces the warehouse manager during the design of a new warehouse or the refurbishment of existing facility. There are many factors affects the storage assignment. For example, order picking method, size and layout of the storage system, material handling system, product characteristics, demand trends, turnover rates and space requirements. Selecting appropriate storage assignment policies (i.e. random, dedicated or class-based) and routing methods (i.e. transversal, return or combined) with regards to above factors is a possible solution to tackle this problem. However, the efficiency of these policies is interdependent. This paper aims to present a simulation study of a real case regarding storage assignment problem of a manual-pick and multi-level rack warehouse. Performance of the case is measured in terms of travel distance and order retrieval time. The results of the study indicate that the key to effective implementation of a storage assignment system is to match the types of warehouse storage system and the variety of items in the customer order. Also, the use of key performance indicator should clearly reflect the needs of the warehouse.

Optimal Control of long cable crane systems

AbstractCrane systems like overhead cranes used in high–rack warehouses are usually modeled as a multi body system with the cable modeled as a pendulum whose cable is regarded as linear. With cables around 40–50 meters long, it is possible that the description of the cable by a straight line is not sufficient anymore, because the cable is bended slightly. The shape of the cable is more like a curve than a straight line.A more suitable description could be achieved by a chain of piecewise linear links, which is again a multi body system and leads to a differential–algebraic system. Each of these links can be modeled again by a pendulum. Using the example of an overhead crane system used in high–rack warehouses, the conventional model with linearly connected trolley and load is compared to the new model with a piecewise linear connection between trolley and load.The optimal trajectories and controls for both models with respect to the same objective function are analyzed for different cable lengths, loads, transport distances and objective functions. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

自動車部品配送センターにおける自動倉庫システム(<特集>荷役・運搬機械)

自動車部品配送センターにおける自動倉庫システム(<特集>荷役・運搬機械)