Modeling and implementing of an automated warehouse via colored timed Petri nets

The automated warehouse considered here consists of a number of rack locations with three cranes, a narrow aisle shuttle, and several buffer stations with the roller. Based on analyzing of the behaviors of the active resources in the system, a modular and computerized model is presented via a colored timed Petri net approach, in which places are multicolored to simplify model and characterize control flow of the resources, and token colors are defined as the routes of storage/retrieval operations. In addition, an approach for realization of model via visual c++ is briefly given. These facts allow us to render an emulate system to simulate a discrete control application for on-line monitoring, dynamic dispatching control and off-line revising scheduler policies

Conceptual design for the Space Station Freedom fluid physics/dynamics facility

A study team at NASA's Lewis Research Center has been working on a definition study and conceptual design for a fluid physics and dynamics science facility that will be located in the Space Station Freedom's baseline U.S. Laboratory module. This modular, user-friendly facility, called the Fluid Physics/Dynamics Facility, will be available for use by industry, academic, and government research communities in the late 1990's. The Facility will support research experiments dealing with the study of fluid physics and dynamics phenomena. Because of the lack of gravity-induced convection, research into the mechanisms of fluids in the absence of gravity will help to provide a better understanding of the fundamentals of fluid processes. This document has been prepared as a final version of the handout for reviewers at the Fluid Physics/Dynamics Facility Assessment Workshop held at Lewis on January 24 and 25, 1990. It covers the background, current status, and future activities of the Lewis Project Study Team effort. It is a revised and updated version of a document entitled 'Status Report on the Conceptual Design for the Space Station Fluid Physics/Dynamics Facility', dated January 1990

Design and Control of Warehouse Order Picking: a literature review

Order picking has long been identified as the most labour-intensive and costly activity for almost every warehouse; the cost of order picking is estimated to be as much as 55% of the total warehouse operating expense. Any underperformance in order picking can lead to unsatisfactory service and high operational cost for its warehouse, and consequently for the whole supply chain. In order to operate efficiently, the orderpicking process needs to be robustly designed and optimally controlled. This paper gives a literature overview on typical decision problems in design and control of manual order-picking processes. We focus on optimal (internal) layout design, storage assignment methods, routing methods, order batching and zoning. The research in this area has grown rapidly recently. Still, combinations of the above areas have hardly been explored. Order-picking system developments in practice lead to promising new research directions.Order picking;Logistics;Warehouse Management

Optimal Storage Rack Design for a 3-dimensional Compact AS/RS

In this paper, we consider a newly-designed compact three-dimensional automated storage and retrieval system (AS/RS). The system consists of an automated crane taking care of movements in the horizontal and vertical direction. A gravity conveying mechanism takes care of the depth movement. Our research objective is to analyze the system performance and optimally dimension of the system. We estimate the crane’s expected travel time for single-command cycles. From the expected travel time, we calculate the optimal ratio between three dimensions that minimizes the travel time for a random storage strategy. In addition, we derive an approximate closed-form travel time expression for dual command cycles. Finally, we illustrate the findings of the study by a practical example.AS/RS;Warehousing;Order Picking;Travel Time Model;Compact Storage Rack Design

Automaattisen varastointi- ja keruujärjestelmän ohjausperiaatteet

Automated storage and retrieval systems (AS/RS) are popular for storing semi-fast moving items in distribution centers. They are costly systems whose design involves many critical decisions, which affect the overall performance of the system. This work is focused on the crane control policies of a double-deep dual-shuttle AS/RS. The goal of the thesis is to find out how operating performance of a crane can be improved with storage location assignment, dwell-point positioning and request sequencing. Alternative control rules were developed based on AS/RS literature and tested against those implemented by the supplier of the system. The comparison was carried out with a discrete-event simulation tool, which was built as a part of the thesis. The system was simulated under two different workload scenarios and rack fill levels. The simulation results indicate that sequencing and cycle formation algorithms can have a significant effect on system throughput in periods of high utilization. The effect was found larger with the lower 70 % fill level. The linear programming sequencing algorithm developed in this thesis was found to reduce the average cycle time by 5.3 % compared to the algorithm used by the supplier. In the on-shift scenario, the optimal dwell point strategy could reduce the average crane response time by 10 % compared to the policy used by the supplier. However, this difference was not noticeable when the average request turnover time was used as a measure.Jakelukeskuksissa yleiset hyllystöhissijärjestelmät ovat kalliita investointeja. Niiden keräilytehoa voidaan osaltaan parantaa tehostamalla varastohissin ohjausmenetelmiä. Tämän diplomityön tutkimuksen kohteena on hyllystöhissijärjestelmä, jossa on tuplasyvät hyllyt sekä hissi, jolla on kahden laatikon kantokapasiteetti. Työn tavoitteena oli selvittää, miten järjestelmän suorituskykyä voidaan parantaa hyllypaikkojen allokoinnin, hissin odotuspaikan valinnan, sekä hissitehtävien sekvensoinnin avulla. Järjestelmätoimittajan ohjausperiaatteiden hyvyyttä arvioitiin vertaamalla niitä kirjallisuuden pohjalta kehitettyihin ohjausmenetelmiin. Ohjausten vertailu tehtiin simulointityökalulla, joka rakennettiin työn aikana. Testiskenaarioissa simuloitiin järjestelmää kahdessa eri kuormitustilanteessa ja kahdella eri täyttöasteella. Simulointitulosten perusteella sekvensointi- ja syklinmuodostusalgoritmeilla huomattiin olevan merkittävä vaikutus tilanteissa, joissa hissillä on tehtäväjonoja. Vaikutus oli suurempi matalammalla 70 % täyttöasteella. Työssä kehitetty sekalukuoptimointiin perustuva sekvensointialgoritmi lyhensi keskimääräistä sykliaikaa 5,3 % toimittajan käyttämään algoritmiin verrattuna. Matalan käyttöasteen skenaariossa optimaalisen odotuspaikan valinta lyhensi hissin liikkumisaikaa seuraavan tehtävään 10 %, mutta ero oli käytännössä olematon, kun mittarina käytettiin keskimääräistä aikaa tehtävän saapumisesta sen suorittamiseen

Robotized Warehouse Systems: Developments and Research Opportunities

Robotized handling systems are increasingly applied in distribution centers. They require little space, provide flexibility in managing varying demand requirements, and are able to work 24/7. This makes them particularly fit for e-commerce operations. This paper reviews new categories of robotized handling systems, such as the shuttle-based storage and retrieval systems, shuttle-based compact storage systems, and robotic mobile fulfillment systems. For each system, we categorize the literature in three groups: system analysis, design optimization, and operations planning and control. Our focus is to identify the research issue and OR modeling methodology adopted to analyze the problem. We find that many new robotic systems and applications have hardly been studied in academic literature, despite their increasing use in practice. Due to unique system features (such as autonomous control, networked and dynamic operation), new models and methods are needed to address the design and operational control challenges for such systems, in particular, for the integration of subsystems. Integrated robotized warehouse systems will form the next category of warehouses. All vital warehouse design, planning and control logic such as methods to design layout, storage and order picking system selection, storage slotting, order batching, picker routing, and picker to order assignment will have to be revisited for new robotized warehouses

Design & Modeling of a Single Machine Flow Rack As/rs

In this paper, we aim to introduce a new variation of the flow rack automated storage and retrieval system (AS/RS) using a single machine for storage and retrieval operations instead of two machines. Also, analytical expressions are derived for expected single and dual cycle times of the storage and retrieval machine. For that, randomized storage assignment, and Tchebychev travel are assumed. Two dwell point positions are investigated and compared to determine the best one. Finally an experimental validation using simulation is conducted to verify the quality of the developed

Optimal Zone Boundaries for Two-class-based Compact 3D AS/RS

Compact, multi-deep (3D), Automated Storage and Retrieval Systems (AS/RS) are becoming more common, due to new technologies, lower investment costs, time efficiency and compact size. Decision-making research on these systems is still in its infancy. We study a particular compact system with rotating conveyors for the depth movement and a Storage/Retrieval (S/R) machine for the horizontal and vertical movement of unit loads. We determine the optimal storage zone boundaries for such systems with two product classes: high and low turnover, by minimizing the expected Storage/Retrieval (S/R) machine travel time. We propose a mixed-integer nonlinear programming model to determine the zone boundaries. A decomposition algorithm and a one dimensional search scheme are developed to solve the model. The algorithm is complex, but the results are appealing since most of them are in closed-form and easy to apply to optimally layout the 3D AS/RS rack. The results are compared with those under random storage, and show that a significant reduction of the machine travel time can be obtained. Finally, a practical example is studied to demonstrate the use and validate our findings.AS/RS;Class-based storage;Order picking;Storage rack design;Travel time model