Automated Storage System Research Articles

Order picking in an automatic warehouse: Solving online asymmetric TSPs

We report on a joint project with industry that had the aim to sequence transportation requests within an automatic storage system in such a way that the overall travel time is minimized. The manufacturing environment is such that scheduling decisions have to be made before all jobs are known. We have modeled this task as an online Asymmetric Traveling Salesman Problem (ATSP). Several heuristics for the online ATSP are compared computationally within a simulation environment to judge which should be used in practice. Compared to the priority rule used so far, the optimization package reduced the unloaded travel time by about 40%. Because of these significant savings our procedure was implemented as part of the control software for the stacker cranes of the storage systems.

Using the Median Distance to Compare Object Shapes in Content-BasedImage Retrieval

Turning Angles (TAs) representation is considered one of the most interesting methods for representing object shapes in content-based image retrieval systems. Nevertheless, the distance commonly used to measure the similarity between shapes represented by TAs, the Euclidean one, is generally too sensitive to small variations in shapes. In this paper we present a new distance between shapes represented by TA, namely the Median distance, specially devised to minimize the effects of small variations in shapes. Its analytical properties are discussed and experimental results are provided and compared with those obtained by applying traditional techniques based on Euclidean distance. The Median distance has been implemented in the Automatic Image Storage and Retrieval (AISR) system, which allows storage and content-based retrieval of 2D images.

Simulation modelling of a narrow aisle automated storage and retrieval system (AS/RS) serviced by rail-guided vehicles

A computer simulation model of an Automatic Storage and Retrieval System (AS/RS) consisting of 5 storage conveyors, 5 retrieval conveyors, 2 bi-directional conveyors, 2 order-picking stations, 7 narrow-aisle cranes and 9,310 storage locations, was created in ARENA TM version 1.1. Rail-guided vehicles move material to and from the storage racks. The computer simulation model of the AS/RS was used to examine the operational logic of the entire system in order to determine the operational deployment strategy that yields the optimal number of rail-guided vehicles (RGVs), the utilisation of the narrow-aisle crane and also the maximum throughput of the system. This paper reports on the results of running the simulation model. For example, increasing the capacity of the storage and retrieval conveyor from 1 to 2 effectively reduces the number of RGV deadlocks by about 94%. A change of the topology of the RGVs' from 1-zone to 2-zone yielded a slightly better part retrieval time and also a reduction in the optimal number of RGVs from 5 to 4. Under these conditions, the number of storages/retrievals is about 430. The maximum throughput of AS/RS is estimated to be about 33 items per hour. The best retrieval time per part is almost 1205 seconds. As it stands, the system could do with less retrieval stations and narrow-aisle cranes which are under-utilised.

Petri net modelling of buffers in automated manufacturing systems

This paper presents Petri net models of buffers and a methodology by which buffers can be included in a system without introducing deadlocks or overflows. The context is automated manufacturing. The buffers and models are classified as random order or order preserved (first-in-first-out or last-in-first-out), single-input-single-output or multiple-input-multiple-output, part type and/or space distinguishable or indistinguishable, and bounded or safe. Theoretical results for the development of Petri net models which include buffer modules are developed. This theory provides the conditions under which the system properties of boundedness, liveness, and reversibility are preserved. The results are illustrated through two manufacturing system examples: a multiple machine and multiple buffer production line and an automatic storage and retrieval system in the context of flexible manufacturing.

Picking strategies to the two‐carousel‐single‐server system in an automated warehouse

Abstract An automatic storage system comprised of two storage carousel conveyors and a retrieval apparatus integrated by computers has been considered in this paper. The order picking problem for such a two‐carousel‐single‐server system is presented here. The retrieval time is analyzed by a two‐stage solution procedure for the scheduling sequence of retrieving items from the system in order to satisfy an order requirement. The analytical results can be directly applied for the scheduling of the carousel storage system.

A framework for the exact evaluation of expected cycle times in automated storage systems with full-turnover item allocation and random service requests

We present a new framework for obtaining analytic expressions of the expected throughput rate in Automated Storage and Retrieval Systems (AS/RSs). The models developed consider generalized full-turnover item allocation policies and random storage and retrieval requests. Both single command and dual command operations are considered. A general expression for the expected cycle time in a single command class-based system is also developed. It is shown that some well known results are derived as special cases of our expression. These results provide for rapid performance evaluation of various operational policies in automated warehouses and in certain mass-storage information devices currently used by various computer systems. The potential for significant reductions in the expected cycle time is demonstrated in the case of full-turnover item allocation.

Optimal stock picking decisions in automatic storage and retrieval systems

Recent technological developments have brought on a revolution in the design and operation of warehousing systems. Automatic storage/retrieval systems (AS/RS) driven by embedded computers are becoming increasingly more prevalent. The increased use of AS/RS is creating the need for computerized control algorithms to support the scheduling and logistical decisions in such automated warehouses. In this research we explore the problem of deciding which storage locations to retrieve when confronted with a set of discrete orders for a given inventory item. In addition to the normal costs associated with the retrieval decision, this support introduces the cost of a location “breakdown” as a complicating factor in the retrieval decision. The problem is formulated as a type of mixed zero-one integer program. Computational results from a sample set of problems are reported.

Discrimination between steady-state enzyme kinetic functions: An improved flow assay device using Fourier deconvolution

A flow assay device for the study of steady-state enzyme kinetics is described. The apparatus employs a peristaltic pump and has a fluorimeter as the monitoring device. An automatic data storage and handling system is used. Theoretical considerations are made on the determination of the apparent initial velocity and flow-induced distortion of the initial velocity versus initial substrate concentration profile. Several analytical expressions useful in calculating the magnitudes of errors and for designing experiments are given. The distortion of output evident in this and in a previously described apparatus of a similar kind is removed by use of Fourier deconvolution using the response of the instrument to a δ function input. Some data obtained with rabbit muscle glyceraldehyde-3-phosphate dehydrogenase, which displays nonhyperbolic kinetics, are discussed and used as an illustration of the application of the method.

Project intrex: A general review

A comprehensive review of the experimental information storage and retrieval system developed by Project Intrex is presented, together with a description of major results and conclusions that were derived through use of the system. Salient features of the Intrex system included an augmented catalog stored in an online interactive computer in combination with full-text storage on microfiche. Guaranteed access to full text at remote locations was provided through use of an automatic fiche storage and retrieval system that was computer-controlled. Discussed in the paper are the details of the catalog structure, user experiments, economic studies and information-system networking.