文献翻译—关于自动化双货叉立体仓库系统

附件 1：外文资料翻译An Analysis Of Dual Shuttle Automated StorageAn Analysis Of Dual ShuttleAutomated Storage/Retrieval Systems Adhinarayan KeserlaBrett A. Peters August 1, 1994 This working paper is not to be copied, quoted, or cited without the permission of the authors. Address correspondence to Brett A. Peters, Dept. of Industrial Engineering, Texas A&M University, College Station, TX 77843-3131 or email to AbstractThis paper addresses the throughput improvement possible with the use of a dual shuttle automated storage and retrieval system. With the use of such a system, travel between time in a dual command cycle is virtually eliminated resulting in a large throughput improvement. The dual shuttle system is then extended to perform an equivalent of two dual commands in one cycle in a quadruple command mode (QC). A heuristic that sequences retrievals to minimize travel time in QC mode is developed. Monte Carlo simulation results are provided for evaluating the heuristics performance and show that it performs well, achieving large throughput improvements compared with that of the dual command cycle operating under the nearest neighbor retrieval sequencing heuristic. Keywords:Automated Storage/Retrieval Systems Design; Automated Storage/Retrieval Systems Operation; Material Handling Systems; Performance Modeling and Analysis IntroductionAutomated storage/retrieval systems (AS/RS) are widely used in warehousing and manufacturing applications. A typical unit load AS/RS consists of storage racks, S/R machines, link conveyors, and input/output (I/O) stations. An important system performance measure is the throughput capacity of the system. The throughput capacity for a single aisle is the inverse of the mean transaction time, which is the expected amount of time required for the S/R machine to store and/or retrieve a unit load. The service time for a transaction includes both S/R machine travel time and pickup/deposit time. This time typically depends on the configuration of the storage rack and the S/R machine specifications. Han et al. 2 improved the throughput capacity of the AS/RS through sequencing retrievals. Intelligently sequencing the retrievals can reduce unproductive travel between time when the S/R machine is traveling empty and thereby increase the throughput. They develop an expression for the maximum possible improvement in throughput if travel between is eliminated for an AS/RS that is throughput bound and operates in dual command mode. In essence, this means that if the S/R machine travels in a single command path but performs both a storage and a retrieval operation, the above throughput improvement could be obtained.In this paper, we analyze an alternative design of the S/R machine that has two shuttles instead of one as in a regular AS/RS. The new design eliminates the travel between the storage and retrieval points and performs both a storage and a retrieval at the point of retrieval, thereby achieving the maximum throughput increase calculated by Han et al. 3. The dual shuttle AS/RS is a new design aimed at improving S/R machine performance. most studies on AS/RS systems have been based on a single shuttle design. In our analysis of the dual shuttle AS/RS performance, we build upon these previous research results. Alternative S/R Machine DesignA typical unit-load AS/RS has an S/R machine operating in each aisle of the system. The S/R machine has a mast which is supported at the floor and the ceiling and travels horizontally within the aisle. Connected to this mast is a shuttle mechanism that carries the unit load and moves vertically up and down the mast. The shuttle mechanism also transfers loads in and out of storage locations in the rack. Figure 1 provides an illustration of the single shuttle S/R machine. Figure 1. Single Shuttle S/R Machine Design A typical single shuttle AS/RS can perform a single command cycle or a dual command cycle. A single command cycle consists of either a storage or a retrieval. For a storage, the time consists of the time to pickup the load at the I/O point, travel to the storage point, deposit the load at that point, and return to the I/O point. The time for a retrieval is developed similarly. A dual command cycle involves both a storage and a retrieval in the same cycle. The cycle time involves the time to pickup the load at the I/O point, travel to the storage location, place the load in the rack, travel empty to the retrieval location, retrieve a load, return to the I/O point, and deposit the load at the I/O point. If we critically analyze the dual command cycle of the S/R machine (shown by the solid line in Figure 2), a potential open location for a future storage is created when a retrieval is performed. Furthermore, if both a retrieval and a storage are performed at the same point, the travel between time (TB) is eliminated, and the travel time will be equal to the single command travel time. With the existing AS/RS design, this mode of operation is not possible; therefore, an alternative to the S/R machine, a dual shuttle R/S machine, is proposed. Figure 2. Dual Command Travel Paths of S/R and R/S Machines R/S Machine OperationConsider an S/R machine with two shuttle mechanisms instead of one. This new S/R machine could now carry two loads simultaneously. Each shuttle mechanism could operate independently of the other, so that individual loads can still be stored and retrieved. An illustration of the dual shuttle S/R machine is shown in Figure 3. This new S/R machine would operate as described below. Figure 3. Dual Shuttle S/R Machine Design The S/R machine picks up the item to be stored from the I/O point, loads it into the first shuttle, and moves to the retrieval location. After reaching the retrieval location, the second shuttle is positioned to pickup the item to be retrieved. After retrieval, the S/R machine positions the first shuttle and deposits the load. The S/R machine then returns to the I/O point. The operation can easily be seen as a single command operation plus a small travel time for repositioning the S/R machine between the retrieval and storage (as well as the additional pickup and deposit time associated with the second load). Therefore, the S/R machine now operates as an R/S machine performing a retrieval first then a storage in a dual command cycle. Since the R/S machine has two shuttles, the position of the shuttles has a role in the operation of the system. With two shuttles, the R/S machine is able to perform a dual command cycle at one location in the rack. This operation is accomplished by first retrieving the load onto the empty shuttle, transferring the second shuttle into position, and storing the load into the empty location in the rack. However, the choice of shuttle configuration does not impact the analysis in this paper. To perform these operations, the R/S machine must move the second shuttle into position after the first shuttle has completed the retrieval. Due to the small distance involved, the R/S machine will use a slower creep speed for positioning, but this travel time is generally small. Furthermore, an amount of creep time is usually included in the pickup and deposit time to account for this required positioning. A second design characteristic is that additional clearance beyond the first and last row and column of the rack must be provided for overtravel of the R/S machine to accommodate both shuttle mechanisms. Throughput ImprovementTo estimate the throughput improvement by the dual shuttle system over existing designs, we use the expressions for single command and dual command cycle times developed by Bozer and White 1 and the tabulated values for the nearest neighbor heuristic from Han et al. 4. In developing the expressions, the authors in 1 and 4 made several assumptions. The same assumptions hold for the new design and include the following. 1. The rack is considered to be a continuous rectangular pick face where the I/O point is located at the lower left-hand corner of the rack. 2. The rack length and height, as well as the S/R machine velocity in the horizontal and vertical directions, are known. 3. The S/R machine travels simultaneously in the horizontal and vertical directions. In calculating the travel time, constant velocities are used for horizontal and vertical travel. Acceleration and deceleration effects are implicitly accounted for in either a reduced top speed or an increased pickup and deposit time. A creep speed is used for repositioning the dual shuttle. 4. Pickup and deposit times associated with load handling are assumed constant and, therefore, these could be easily added into the cycle time expressions. 5.The S/R machine operates either on a single or dual command basis, i.e., multiple stops in the aisle are not allowed. (This assumption is later relaxed for the new R/S machine to perform a quadruple command cycle.) 6. For the nearest neighbor heuristic, a block of n retrievals is available for sequencing and there are m initial open locations in the rack face. Dual Shuttle S/R SystemsThe new design of the S/R machine has two shuttles and therefore could be operated as a dual shuttle system: carrying two loads and depositing them, retrieving two loads, and returning to the I/O point to deliver them as shown in Figure 4. The above operation can be performed by storing and retrieving the loads at four different locations. Therefore, the travel time would consist of the time for a single command travel plus three travel between times. To more efficiently perform the 4 operations, a retrieval and storage performed at one location is interspersed with a dual command operation. This mode of operation, termed the quadruple command (QC) cycle, eliminates one travel between and is more efficient than the previous mode mentioned above (see Figure 5). The QC cycle can be performed with storages at randomized locations and retrievals processed in a first-come-first-served (FCFS) manner. However, by intelligently sequencing the retrieval list, the travel time in performing the four operations can be significantly reduced. This type of analysis was used by Han et al. 4 to improve the throughput of a single load AS/RS. In our paper, we build on the results of their analysis. The notation and the assumptions mentioned in section 2.2. still hold, except that multiple stops of the S/R machine are now allowed. Figure 4. S/R Machine Path Performing Four Operations At Four Locations. Figure 5. S/R Machine Path Performing Four Operations At Three Locations. ConclusionsThis paper performs an analysis of dual shuttle automated storage and retrieval systems. Several contributions have been made including the following. 1.Throughput improvements in the range of 40-45% can be obtained using the quadruple command cycle relative to dual command cycles with a single shuttle system. 2.With the dual shuttle design, travel between is virtually eliminated for a dual command cycle. The dual shuttle system shows promise for situations requiring high throughput. The main disadvantage with the new design is the extra cost of the S/R machine. An economic evaluation is needed to determine if it is appropriate for a particular situation. However, based on throughput performance, the dual shuttle design appears promising. The concept of dual shuttle systems can also be extended to other material handling systems. Furthermore, research is needed to consider other storage strategies, such as class based storage policies, to examine their impact on throughput in conjunction with the dual shuttle design. This paper provides a framework for analyzing dual shuttle AS/RS, and it provides a foundation for other material handling research related to this concept. References1 Bozer, Y.A. and J.A. White, Travel-Time Models for Automated Storage/Retrieval Systems, IIE Transactions, Vol. 16 , No. 4, 1984, 329-338. 2 Elsayed, E.A. and O.I. Unal, Order Batching Algorithms and Travel Time Estimation for Automated Storage/Retrieval Systems, International Journal of Production Research, Vol. 27, No. 7, 1989, 1097-1114. 3 Han, M.H., L.F. McGinnis, J.S. Shieh, and J.A. White, On Sequencing Retrievals In An Automated Storage/Retrieval System, IIE Transactions, March 1987, 56-66. 关于自动化双货叉立体仓库系统 摘 要:本文主要探讨的是可以提高生产效率的双货叉立体仓库系统。通过使用该系统，可以缩短堆垛机在一个双任务流程中的运行时间，从而大大提高了仓库的工作效率。双货叉仓库系统相当于一个四任务指令模块（quadruple command mode 简称QC）中的双指令任务书流程。一个很有建设性的思想被提出来，即通过堆垛机按某一顺序运行可以缩短在一个（QC）中的运行时间，蒙地卡罗对此进行了模拟对比实验，实验结果证明确实提高了堆垛机的搬运效率，这就说明了这种方案的可行性。关键字:自动化立体仓库设计； 自动化立体仓库的控制；物流系统；功能模拟和分析绪 论自动化立体仓库被广泛地应用于仓储和制造设备当中。典型的单位货物装卸立体仓库由储藏架，堆垛机，自动运输小车，和入库/出库台组成。衡量一个立体仓库系统的优劣的主要标准是仓库系统的工作效率。立体仓库的工作效率与堆垛机运行一个工作流程所需的时间成反比，这个工作流程时间包括堆垛机装卸货物的时间，显然堆垛机装卸货物的时间在一定程度上取决于堆垛机和货架的具体结构和规格。Han et al.2通过立体仓库返回站点的排列提高了立体仓库的工作能力，合理的排列返回站点堆垛机能减少不必要的行程，从而缩短了时间，提高了效率。这样他们就提出了一种最大限度提高效率理论，即如果堆垛机在双指令模块流程中可以缩短运行时间那么这将最大程度的提高立体仓库的工作效率。也就是说，如果堆垛机运行的是单命令路线，却能完成存货和返回的动作，则工作效率的提高也就实现了。在论文中，我们分析了一种可供选择的堆垛机设计方法，这种设计出来的堆垛机与一般的堆垛机不同，在原来的基础增加了一个货叉，这种新颖设计的堆垛机拥有两个货叉，它在运作中可以缩短在货架到返回点之间的运行时间。这种设计方案符合 Han et al.所说的最大效率理论。双货叉堆垛机主要是针对如何提高堆垛机的工作能力这一问题所设计的一种新颖堆垛机。目前，立体仓库系统的研究是以单货叉堆垛机为主要对象。在本文关于双货叉堆垛机功能的分析也是建立有前人研究的基础上的。可供选择的堆垛机设计一个基本的单一装载立体仓库系统中，每一个货架巷道内都有一台可供操作的堆垛机，每台堆垛机有一根立柱被固定在天花板和地面之间，这根立柱可以在巷道内的水平位置移动。与立柱相连的是一个货叉机构，它可以载着货物沿着立柱上下移动，货叉也可以作相对于货格的水平取货和存货运动，其结构原理如图1 所示。一个基本的单货叉堆垛机立体仓库系统能够完成一个单指令作业流程也能完成一个双指令作业流程。一个单指令作业流程由存货和取货组成，对于一个存货过程所需时间包括堆垛机在入库处装载货物，行驶到目标货格，卸下货物，然后回到仓库入口处这一连串动作总共所需的时间。同样可以分析取货过程所需时间。一个双指令流程就是在同一个工作流程中完成存货和取货的操作。这个过程时间包括从入口处装货，运行到存货货格位置，把货放在货架上，空运行到取货货格位置，从货架上取下货物，回到仓库入口处，并卸下货物这一过程总共需要的时间。如果我们对堆垛机的双指令工作流程路线（如图 2 中实线所示）稍加分析就会发现，当在完成一个取货运作时，就暗示着可以进行下一个存货运作，而且，如果在同一地方可以进行存货和取货运作，那么运行时间将被缩短，这个运行时间相当于运行一个单指令流程所需的时间。就目前已存在的立体仓库设计，要实现这种操作是不可能的，因此，另外一种双货叉式的堆垛机就应运而生了。堆垛机的运作设想一台安装了两个货叉的堆垛机,这种新颖的堆垛机可以同时装载两件货物,为了两件货物分别能存库和出库,所以堆垛机的两个货叉机构能够相互独立运行,具体结构如图 3 所示,这种堆垛机的工作过程将在下文详细介绍。堆垛机从仓库入口处将要被储存的货物装载到第一个货叉平台上，然后向取货的位置移动.到达要取货的位置之后，第二个货叉台伸货格内取货，当取货的动作完成之后，堆垛机控制第一个货叉台卸货。堆垛机然后再回到入口处。这整个操作流程就像是一个单指令运作再加上一小段重新定位运行过程（即堆垛机第二个货叉平台装载和卸载过程） ，这样一来，其运作就像一台堆垛机完成先完成取货然后再存货的一个双任务命令。因为这种堆垛机有两个货叉平台，所以两个货叉的定位控制将是系统的一个很重要的功能。堆垛机用两个货叉可以在某个货架的同一位置完成一个存、取双任务指令，先在空货驻台上取下要出库的货物，再移动第二货叉到指定位置把货物放在空货格内。然而，货叉平台结构的选择与本文的讨论内容无关。为了实现上述操作，堆垛机的第二个货叉必须在第一个货叉完成取货动作之后才能进行定位操作。由于货叉的定位移动量是较小的，堆垛机采用的是低速爬行方式来实现货叉微小的定位移动量，在这个过程中所耗费的时间与堆垛机在装货卸货耗费的时间相比一般是微乎其微的。仓库设计的另外一个特点是第一排货格和最后一排货格的两端要留有位置余量，以便在堆垛机超程时给两个货叉平台留有运动余地。工作效率提高 为了估算正在设计的双货叉系统工作量的提高，我们引用 Bozer 和 White1提出的有关单任务和双任务指令所需时间理论和 Han et al.提出的最近有意义想法价值理论，这些理论家都作了种种设想，他们设想的共同部分就是我们要引用的内容