外文翻译--关于自动化立体仓库使用双货叉问题的探讨

1、附录一 外文翻译an analysis of dual shuttle automated storage/retrieval systems brett a. peters august 1, 1994abstractthis 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 c

2、ommand 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 develope

3、d. 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 storag

4、e/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

5、 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 m

6、achine 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

7、 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 el

8、iminated 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 alt

9、ernative 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 calcul

10、ated 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 mac

11、hine 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 vert

12、ically 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

13、 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 s

14、imilarly. 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

15、, 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

16、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. du

17、al 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

18、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 move

19、s 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

20、 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

21、 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 retrievi

22、ng 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 shut

23、tle 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 t

24、o 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 over travel of the r/s machine to accommodate both shuttle mechanisms. throughput improvementto estimate the throughput impro

25、vement 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 sev

26、eral 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

27、 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

28、 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 mach

29、ine 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 th

30、ere 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 show

31、n 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

32、 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 randomi

33、zed 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 si

34、ngle 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 machi

35、ne 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 quadrupl

36、e 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

37、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 s

38、ystems. 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 ot

39、her material handling research related to this concept. 关于自动化立体仓库使用双货叉问题的探讨布雷特彼得斯 august 1, 1994摘要 本文通过在自动化立体仓库中运用双货叉设计，来提高立体仓库的吞吐量。由于这种系统运用，双指令系统的运行间的时间实际上被消除了，并且吞吐量得到了很大的提高。双货叉系统后来被延伸到执行一个相等的一个周期内执行双指令在四倍指令模式中。一个启发式的检索排序减少了运行时间，使得qc模式得到了发展。蒙特卡罗仿真的结果被用来评价启发式算法的性能，并且显示它表现出色，吞吐量得到了很大的提高相比于双指令周期下最近邻的检

40、索序列启发。关键字：自动化立体仓库，物料运输系统1.引言自动化立体仓库被广泛地应用于仓储及生产应用中，自动化立体仓库中一个典型的货物装载系统是由堆垛机、连接输送带，输入/输出部分组成。系统一个重要的指标是系统的吞吐能力。对于单通道系统的货物吞吐能力值得是堆垛机往返的平均时间，在这个所预期的时间里要求堆垛机储存一个或取出一个货物。整个服务的时间包括堆垛机行进的时间和货物存放的时间。这个时间通常决定于货架的结构和堆垛机的规格。一些人通过对检索进行排序来提高立体仓库的吞吐能力，对检索进行明智的而排序可以减少因堆垛机执行空运行而消耗的时间，从而提高吞吐能力。他们制定了一个表达式，为了最大限度的提高系统

41、的吞吐量，通过减少系统的运行时间，如果吞吐量和操作都执行双命令模式。本质上，这意味着堆垛机在一个命令的指挥下可以同时完成一个存储和一个取货任务，这样吞吐量的提高就可以实现了。在这篇论文里，我们设计了一个有两个货叉的堆垛机，而不是通常立体仓库中的一个。这种新的设计可以减少存储和取货的运行时间，在一个运行过程中可以执行一个存储和一个取货任务，从而最大限度的提高了吞吐量。在立体仓库中使用的双货叉技术是为了提高堆垛机的性能而设计的一个新技术。大多数对自动化立体仓库的研究还是基于单货叉技术。我们也是基于以前的研究成果来设计双货叉的性能。2.替代堆垛机设计典型的立体仓库货物装载系统是由每一个通道上的堆垛机

42、进行操作，这种堆垛机有一个大的柱子支撑在地面和天花板之间，在水平过道上行进。连接在这个柱子上的是一副货叉可以沿着柱子上下的搬运货物，货叉也可以搬运货物进出货架上的储存位置。一个典型的单货叉系统可以执行一个或两个指令周期，一个指令周期包括一个存储过程或者一个取货过程。对于一个存储过程的时间包括从出入货台拾取货物，再将货物运到存储位置，将货物存放到存储位置，再返回到出入货台。取货过程的时间与上面类似。一个双指令周期包括存储和取货两个任务在一个周期内，这个周期的时间包括堆垛机在出入货台拾起货物，运行至货位，将货物存入货位，再运行至一个取货的货位，将货物取出，返回出入货台，将货物放在出入货台上。如果我们准确的分析双指令周期的堆垛机，当一个取货的任务被执行后，一个潜在的空位置可以用于将来的存储，如果一个存货和一个取货任务同时都被执行，堆垛机的运行时间就被减少了，运行时间相当于单指令运行时间。基于目前的立体仓库设计，这种操作模式是不可能的。因此，一个可共选择的方案，双货叉堆垛机方案被提出来了。3.取存堆垛机的操作由于这种堆垛机采用双货叉而不是单货叉，这种新的堆垛机可以同时携带两个货物。每一个货叉可以独立与另一个来进行操作，所以单一的货物可以被存放也可以被取出。新的堆垛机系统将在下面进行描述。堆垛机从出入货台拾起一个要被存放的货物，将它