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

Automated Order Picking Systems and the Links between Design and Performance: A Systematic Literature Review

With new market developments and e-commerce, there is an increased use of and interest in automation for order picking. This paper presents a systematic review and content analysis of the literature. It has the purpose of understanding the relevant performance aspects for automated, or partly automated, OPSs and identifying the studied links between design and performance, i.e. identifying which combinations of design aspects and performance aspects have been studied in previous research. For this purpose, 74 papers were selected and reviewed. From the review, it is clear that there has been an increased number of papers dealing with the performance of automated, or partly automated, OPSs in recent years. Moreover, there are differences between the different OPS types, but, overall, the performance categories of throughput, lead time, and operational efficiency have received the most attention in the literature. The paper identifies links between design and performance that have been studied, as well as links that appear to be under-researched. For academics, this paper synthesises the current knowledge on the performance of automation in OPSs and identifies opportunities for future research. For practitioners, the paper provides knowledge that can support the decision-making process of automation in OPSs

Designing a cellular-based fully automated case picking system

Order picking (OP) is the most expensive and labor-intensive activity in warehouses. Some authors argue that OP might be responsible for up to 55% of the operating costs in a warehouse. This might be more important for companies that handle large volumes of fast-moving commodities. Full-case picking processes and mixed pallet building are expensive and complex activities. Companies are looking for technologies to improve their efficiency and to reduce the operating costs of non-value added activities in their warehouses and distribution centers (DCs). Nowadays, the designers of order picking systems face great challenges due to increasing labor costs, less space and more frequent small orders with short delivery times. Consequently, there are constant research efforts devoted to finding new innovative full-case picking solutions that reduce operating costs, generate higher productivity, optimize space utilization and enhance customer service levels. This dissertation presents a new fully automated case picking system (ACPS) called the Automated Cellular Case Picking System (ACCPS). The new system is characterized by the full and permanent accessibility of all stock keeping units (SKUs) in the system, which permits a strategic higher picking rate. This new system could be applied to different levels of automation within warehouses and DCs, and it is suitable for a wide range of warehouse automation requirements. The proposed design consists of storage cells with the same design and operating principle as the vertical indexing case elevator, installed on one conveyor to form a storage line. Several storage lines are connected by a distributing conveyor from the inlet side and by a collecting conveyor from the outlet side, to form an ACCPS use-case model. The concept of this new system is based on the A-Farm concept, in order to create a new innovative dispensing and buffering system for cases. ACCPS is a new concept for a full-case picking system that aims to provide better solutions for warehouses and DCs that deal with a high volume and low variety of products, which are handled in plastic crates or trays. ACCPS would be an efficient solution for many types of commodities such as (food, beverage, grocery, dairy, flowers, sausage, bakery and others). Optimizing picking processes, minimizing operating cost, and increasing efficiency are the most important aims of the new proposed design. This research investigates the layout, design, structure, costs, operating principles, cycle time, and throughput of the new system. A simple logic process was applied to create a mathematical model in order to calculate the expected average time of the order picking and the throughput of this new ACPS. A simulation model has been developed to aid in measuring the effectiveness of the ACCPS proposed design under real operating conditions. Two case studies have been used to evaluate the performance of the new system. Based on the real-time data of these two cases, many simulation scenarios were studied and analyzed in order to solve the storage assignment problem and to determine the best order picking strategy. Many optimization scenarios were simulated and analyzed in order to determine the optimum scenario. In order to evaluate the ACCPS performance, a comparison was made between ACCPS and an alternative system with the same features. The alternative system, which is the most competitive system compared to the ACCPS, is the Gantry Robot System (GRS). The costs, throughput, and required areas were chosen as the main criteria for comparison between the two systems. The comparison confirmed the benefits of the ACCPS in decreasing the operating costs, required area, energy consumption, and the picking time. ACCPS also increased the space utilization rate and the throughput. ACCPS provides a new technique for automating the full-case picking process (CPP) that contributes greatly to decreasing total operating cost by minimizing labor requirements, space requirements, and potential errors, and increasing productivity and efficiency. The structure of ACCPS, which is based on individual modules, can further increase the flexibility and the adaptability of the system.Entwurf eines zellbasierten vollautomatischen Full-Case-Kommissioniersystems Der Kommissionierungsprozess (OP) wird als die höchst arbeitsintensive und kostenaufwändige Tätigkeit in den Lagern betrachtet. Einige Autoren behaupten, dass der Kommissionierungsprozess für bis zu 55 % aller Betriebskosten in einem Lager dafür verantwortlich sein könnte. Dies könnte möglicherweise wichtiger sein für Unternehmen, die große Volumina von schnell bewegenden Waren behandeln. Full-case-picking Prozesse und Mischpaletten von verschiedenen Produkten aufzubauen sind teure und komplexe Tätigkeiten. Firmen suchen nach Technologien, um ihre Leistungsfähigkeit zu verbessern und die Betriebskosten von zusätzlichen Tätigkeiten die keine Wertschöpfung erbringen in ihren Lagern und Distributionszentren (DCs) zu reduzieren. Heutzutage stehen die Designer der Kommissioniersysteme vor großen Herausforderungen, aufgrund der steigenden Arbeitskosten, weniger Platz und häufigere kleine Aufträge mit kurzen Lieferzeiten. Deshalb sind ständige Forschungsbemühungen gewidmet, um die Suche nach neuen innovativen Kommissionierlösungen für Stückgüter, die die Betriebskosten verringern, die Produktivität erhöhen, die Raumausnutzung optimieren und die Kundenservice verbessern. Diese Dissertation präsentiert ein neues vollautomatisiertes Kommissioniersystem für Stückgüter (ACPS), das als automatisiertes zelluläres Case-picking-system (ACCPS) bezeichnet wird. Das neue System zeichnet sich durch die vollständige und dauerhafte Zugänglichkeit aller Lagerhaltung Einheiten (SKUs) im System, das einen strategischen höheren Durchsatz des Kommissionierungsprozesses ermöglicht. Dieses neue System könnte auf verschiedene Niveaus der Automation innerhalb von Lagern und DCs angewandt werden, und ist für eine breite Reihe von Lagerautomationsvoraussetzungen passend. Das vorgeschlagene Design besteht aus Speicherzellen mit demselben Design und Betriebsprinzip wie der vertikale Senkrechtförderer für Stückgüter, der auf einem Förderband installiert ist, um eine Lagerungslinie zu bilden. Mehrere Lagerungslinien werden sich durch einen Verteilförderer von der Einlassseite und durch einen Sammelförderer von der Ausgangsseite verbunden, um ein ACCPS Use-Case-Modell zu bilden. Das Konzept dieses neuen Systems basiert auf dem Konzept des Schachtkommissionsystems (A-Farm), um ein neues innovatives System zum Zuführen und Puffern von Stückgütern zu schaffen. ACCPS ist ein neues Konzept für eine vollständiges Stückgütern Schachtkommissionsystem mit dem Ziel, bessere Lösungen für Lagern und DCs, die sich mit einer großen Menge und niedrigen Vielfalt von Produkten befassen, die in Kunststoffkisten oder Tablare behandelt werden zur Verfügung zu stellen. ACCPS würde eine effiziente Lösung für viele Typen von Waren wie (Nahrung, Getränk, Lebensmittel, Molkerei, Blumen, Wurst, Bäckerei und andere) sein. Optimierung der Kommissionierungsprozesse, Minimierung der Betriebskosten und Steigerung der Effizienz sind die wichtigsten Ziele des neuen vorgeschlagenen Designs. Diese Forschung untersucht Layout, Design, Struktur, Kosten, Betriebsprinzipien, Zykluszeit und Durchsatz des neuen Systems. Ein einfacher Logik-Prozess wurde angewendet, um ein mathematisches Modell zu erstellen, damit die erwartete durchschnittliche Zeit der Kommissionierung und der Durchsatz von dieser neuen ACPS zu berechnet werden. Ein Simulationsmodell wurde entwickelt, um bei der Messung der Effektivität des vorgeschlagenen Designs der ACCPS unter realen Betriebsbedingungen zu unterstützen. Zwei Fallstudien sind verwendet worden, um die Leistung des neuen Systems zu bewerten. Gestützt auf den Echtzeitdaten dieser zwei Fälle, viele Simulation Szenarien wurden untersucht und analysiert um das Problem der Lagerplatzzuweisung zu beheben und die beste Strategie für die Kommissionierung zu bestimmen. Viele Optimierung Szenarien wurden simuliert und analysiert um das optimale Szenario zu bestimmen. Im Hinblick auf die Bewertung der Leistung des ACCPSs, wurde ein Vergleich zwischen ACCPS und ein alternatives System mit denselben Eigenschaften durchgeführt. Das Gantry Robot System (GRS), ist das alternative System für das am meist konkurrenzfähige System im Vergleich zum ACCPS. Die Kosten, der Durchsatz und die erforderliche Fläche wurden als die Hauptkriterien zum Vergleich zwischen den beiden Systemen gewählt. Der Vergleich hat die Vorteile des ACCPSs im Verringern der Betriebskosten, der erforderlichen Fläche, des Energieverbrauchs und der Entnahmezeit (Pickzeit) bestätigt. ACCPS stellt eine neue Technik zur Verfügung, um die Full-case-picking Prozessen (CPP) zu automatisieren, die außerordentlich zum Verringern von Gesamtbetriebskosten durch die Minderung von Arbeitskräftebedarf, Platzbedarf und potenziellen Fehlern, und die Erhöhung der Produktivität und Leistungsfähigkeit beiträgt. Die Struktur von ACCPS, die auf individuellen Modulen basiert, kann weiter die Flexibilität und die Anpassungsfähigkeit des Systems vergrößern

Advanced Storage and Retrieval Policies in Automated Warehouses

Warehouses are key components in supply chain. They facilitate the product flow from production to distribution. The performance of supply chains relies on the performance of warehouses and distribution centers. Being able to realize short order delivery lead times, in retail and ecommerce particularly, is important for warehouses. Efficient and responsive storage and retrieval operations can help in realizing a short order delivery lead time. Additionally, space scarcity has brought some companies to use high-density storage systems that increase space usage in the warehouse. In such storage systems, most of the available space is used for storing products, as little space is needed for transporting loads. However, the throughput capacity of high-density storage systems is typically low. New robotic and automated technologies help warehouses to increase their throughput and responsiveness. Warehouses adapting such technologies require customized storage and retrieval policies fit for automated operations. This thesis studies storage and retrieval policies in warehouses using several common and emerging automated technologies

On the performance of robotic parts-to-picker order picking systems

Order picking is the activity in which a number of items are retrieved from a warehousing system to satisfy a number of customer orders. Automating order picking systems has become a common response to the wide variety of products and components stored in today’s warehouses and the short delivery lead times requested by today’s customers. As a result, new technical solutions have reached the market, including robotic parts-to-picker order picking systems such as robot-based compact storage and retrieval systems (RCSRSs) and robotic mobile fulfilment systems (RMFSs).\ua0Despite the increased use of robotic parts-to-picker order picking systems, knowledge about how they perform in terms of throughput, order lead time, human factors, quality, flexibility, operational efficiency, and investment and operational costs needs to be further developed, as does knowledge about how their performance is affected by the order picking system’s design and context. Accordingly, the purpose of this thesis is to expand knowledge about the performance of robotic parts-to-picker order picking systems by investigating how their design and context influence their performance. \ua0The thesis is built upon three studies: a systematic literature review study focusing on automated order picking systems, a multiple-case study on RCSRSs, and a single-case study on RMFSs. First, the systematic literature review study on the performance of automated order picking systems provides an overview of literature on order picking systems to date, aspects of their performance, and how their performance relates to their design. Second, the multiple-case study sheds light on characteristics of the performance of RCSRSs and the relationships between their performance and design. Third and last, the single-case study affords insights on how the context of RMFSs affects their performance.\ua0The thesis contributes to practice by providing guidance to decision makers within industry in terms of the performance to expect of robotic parts-to-picker OPSs depending on their design and context. In turn, such knowledge can facilitate the selection and design of an OPS or else the redesign of a current system. At the same time, the thesis contributes to theory by providing a synthesis of literature addressing the performance of automated OPSs and by outlining the relationships between their design and performance

Order-picking workstations for automated warehouses

The FALCON (Flexible Automated Logistic CONcept) project aims at the development of a new generation of warehouses and distribution centers with a maximum degree of automation. As part of the FALCON project, this dissertation addresses the design and analysis of (automated) workstations in warehouses with an end-of-aisle order-picking system (OPS). Methods are proposed for architecting, quantifying performance, and controlling such a system. Four main topics are discussed in this dissertation. First, a modular architecture for an end-of-aisle OPS with remotely located workstations is presented. This architecture is structured into areas and operational layers. A hierarchical decentralized control structure is applied. A case of an industrial-scale distribution center is presented to demonstrate the applicability of the proposed architecture for performance analysis using the process algebra-based simulation language $\chi$ (Chi). Additionally, it is demonstrated how the architecture allows straightforward modification of the systems configurations, design parameters, and control heuristics. Second, a method to quantify the operational performance of order-picking workstations has been developed. The method is based on an aggregate modeling representation of the workstation using the EPT (Effective Process Time) concept. A workstation is considered in which a human picker is present to process one customer order at a time while products for multiple orders arrive simultaneously at the workstation. The EPT parameters are calculated from arrival and departure times of products using a sample path equation. Two model variants have been developed, namely for workstations with FCFS (First-Come-First-Serve) and for workstations with non-FCFS processing of products and orders. Both models have been validated using data from a real, operating workstation. The results show that the proposed aggregate modeling methodology gives good accuracy in predicting product and order flow time distributions. Third, the dissertation studies the design and control of an automated, remotely located order-picking workstation that is capable of processing multiple orders simultaneously. Products for multiple orders typically arrive out-of-sequence at the workstation as they are retrieved from dispersed locations in the storage area. The design problem concerns the structuring of product/order buffer lanes and the development of a mechanism that overcomes out-of-sequence arrivals of products. The control problem concerns the picking sequence at the workstation, as throughput deteriorates when a poor picking sequence is applied. An efficient control policy has been developed. Its performance is compared to a number of other picking policies including nearest-to-the-head, nearest neighbor, and dynamic programming. Subsequently, the resulting throughput and queue length distribution are evaluated under different settings. Insights for design considerations of such a system are summarized. Finally, the dissertation reflects on the findings from the proposed methods and uses them to come up with comprehensive design principles of end-of-aisle OPS with remotely located workstations. The various issues influencing the performance of such a system are highlighted. Moreover, the contribution of each proposed method with regards to these issues is delineated

Gestion des systèmes automatisés d'entreposage : simulation, optimisation et résultats empiriques

Les systèmes automatisés d'entreposage {Automated Storage and Retrieval Systems- AS/RS) sont considérés aujourd'hui comme une technologie de pointe dans le domaine de l'entreposage et de la distribution à haut débit. L'implantation d'un tel système représente un investissement corporatif majeur, il est donc attendu que son niveau de performance soit élevé. Ce niveau de performance, pour un environnement donné, est le résultat d'un ensemble de décisions relatives à la fois au design et au contrôle du système. Pour cette raison, tant aux niveaux industriel qu'académique, on cherche à développer des approches permettant de modéliser, concevoir et contrôler au mieux ces systèmes qui jouent un rôle critique dans les chaînes logistiques modernes. À cette fin, plusieurs approches issues de la recherche opérationnelle peuvent être appliquées. Cette thèse comporte quatre articles, présentant chacun un aspect distinct de l'étude des AS/RS. Nous présentons, dans le premier article, une revue de littérature traitant des approches de modélisation des AS/RS. L'étude met l'accent sur les hypothèses de modélisation employées dans les différents articles et qui ne sont pas toujours intuitives, ni même mentionnées. Cette réalité fait en sorte qu'il est parfois très difficile d'exploiter les résultats de recherches précédentes afin de les transposer dans un autre contexte. En plus d'isoler les hypothèses de modélisation, nous présentons une structure séparant les différentes questions de recherche en fonction des problèmes étudiés. Les résultats de cette revue prennent la forme d'une synthèse permettant d'associer, pour un problème donné, les études et résultats provenant de contextes similaires. Nous proposons dans le second article un modèle de simulation à événements discrets conçu pour étudier les AS/RS à charge unitaire. En prenant appui sur la programmation orientée-objet, le modèle a été conçu de manière à pouvoir aisément modéliser plusieurs configurations, comme par exemple les systèmes à plusieurs allées ou les AS/RS visant à gérer la collecte de petits items dans des contenants. Une description détaillée du moteur de simulation est donnée. C'est grâce à ce modèle que les chapitres subséquents ont pu voir le jour, en permettant l'étude empirique de ces systèmes hautement complexes et dynamiques. Dans le troisième article, nous présentons une étude sur le problème de gestion de l'espace dans les AS/RS. Ce problème consiste à définir, pour chaque localisation de stockage, le ou les produits pouvant y être stockés. Nous nous intéressons principalement à l'étude de l'entreposage par zones dont le nombre peut varier entre une seule zone et autant de zones qu'il y a de produits. La gestion de l'espace a suscité beaucoup d'intérêt scientifique vers la fin des années 70. Plusieurs modèles analytiques ont été formulés, résultant en certaines conclusions largement acceptées dans tous les milieux. Cependant, nous constatons que la validité de ces modèles analytiques repose sur certaines hypothèses restrictives. À l'aide du modèle de simulation présenté, nous montrons que ces conclusions ne tiennent plus lorsque nous nous transposons dans un contexte réaliste. Ce nouveau résultat nous amène à voir la gestion de l'espace en fonction des caractéristiques des produits entreposés. Dans le quatrième article, nous portons notre attention sur le problème de séquencement des requêtes dans un AS/RS. Le séquencement des requêtes consiste à définir l'ordre dans lequel les requêtes de stockage et de collecte seront complétées selon un horizon à durée déterminée, dans un objectif de minimisation du temps de cycle moyen. Cela revient à maximiser le rendement du système. Pour ce faire, nous proposons une adaptation des heuristiques de la littérature pour traiter le cas de séquencement dynamique, puis nous proposons une des premières formulations mathématiques au problème. Par la suite, nous évaluons les opérations du système à l'aide du modèle de simulation détaillé dans le deuxième article. Les résultats empiriques obtenus illustrent l'effet positif du séquencement sur la performance du système en plus de fournir une comparaison des différentes approches de séquencement étudiées. À travers ces quatre chapitres, nous démontrons que la simulation et l'optimisation des systèmes automatisés d'entreposage posent plusieurs défis. Nous avons présenté un modèle de simulation robuste qui a permis de faire avancer les connaissances dans le domaine de la gestion de l'espace et du séquencement des requêtes