1、华东交通大学毕业设计 1 附录 A 英文原文 An Analysis of Dual Shuttle Automated Storage/Retrieval Systems An Analysis of Dual Shuttle Automated Storage/Retrieval Systems Adhinarayan Keserla Brett A. Peters Abstract: This paper addresses the throughput improvement possible with the use of a dual shuttle automated stora
2、ge 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
3、). 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 operati
4、ng 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 Introduction: Automated storage/retrieval systems (AS/RS) are widely used in
5、 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
6、 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 华东交通大学毕业设计 2 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 th
7、e 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 times when the S/R machine is traveling empty and thereby increase the throughpu
8、t. 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 storage and a re
9、trieval 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 storag
10、e and 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
11、 dual shuttle AS/RS performance, we build upon these previous research results. 1 Alternative S/R Machine Design A 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 wit
12、hin 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. Si
13、ngle 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 storage or retrieval. For storage, the time consists of the time to pickup the load at the I/O point, travel to the storage point, depo
14、sit the load at that point, and return to the I/O point. The time for retrieval is developed similarly. A dual command cycle involves both storage and 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
15、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 华东交通大学毕业设计 3 the solid line in Figure 2), a potential open location for a future storage is
16、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 possib
17、le； 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 2 R/S Machine Operations Consider an S/R machine with two shuttle mechanisms instead of one. This new S/R machine could now carry two loads simultane
18、ously. 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 T
19、he 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 shu
20、ttle 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 th
21、e 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
22、 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 no
23、t 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
24、 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. 3 Throughput Improvement To estimate the throughput improvement by the dual shuttle system over
