42 research outputs found
Scheduling Material Handling in Cross-Docking Terminals
RÉSUMÉ : La manutention au sein des plateformes de distribution est un problème d’ordonnancement. Le transport interne des produits doit en effet être synchronisé avec les arrivées et les départs des camions. Ce problème se retrouve dans toutes les plateformes de distribution où la manipulation des produits est effectuée manuellement par l’opérateur. Dans cette thèse, nous investiguons ce problème d’ordonnancement dans les plateformes de distribution. Nous mettons en relief les différentes facettes de ce problème et proposons une classification de ses différents sous problèmes. De manière générale, l'objectif est d'éviter les doubles manipulations (déplacer un produit d’un camion vers le stock, puis du stock vers un camion) qui doublent les coûts sans valeur ajoutée. Il faut minimiser ces doubles manipulations en orchestrant les transferts internes et la séquence de chargement/ déchargement des camions. Dans une première partie, nous analysons la structure du problème avec un modèle simplifié n’ayant qu’un quai de réception et un quai d’envois. Nous formalisons les décisions de manipulation interne et développons un algorithme optimal pour déterminer le meilleur plan de transfert de produits lorsque la séquence des camions est connue. Cet algorithme est utilisé comme fonction d’évaluation dans une recherche stochastique pour minimiser les doubles manipulations et optimisant les séquences de chargement/déchargement. Nous présentons ensuite un modèle de programmation linéaire en nombres entiers du problème général (ordonnancement des arrivées et départs de camions et transfert interne des produits). Nous proposons un algorithme de séparation et d’évaluation permettant une résolution efficace du problème. Nous proposons des structures de dominance et quelques inégalités valides permettant d’améliorer les performances de l’algorithme. Cette approche nous permet de résoudre à l’optimum en un temps raisonnable de très gros problèmes.
Dans une seconde partie, nous étendons ces modèles au problème général avec plusieurs quais. Nous nous intéressons d’abord au terminal de type satellite où l’ordonnancement des camions d’entrée est connu. Ces plateformes opèrent en deux mouvements différents : l’ordonnancement et chargement pour le transport de nuit et celui pour les livraisons matinales. Nous donnons une représentation mathématique qui permet de résoudre les problèmes de petite taille. Pour ceux de plus grandes ampleurs, nous utilisons une heuristique. Les résultats numériques montrent la validité de cette approche.
Finalement, nous généralisons le type de plateforme (les séquences d’arrivée et de départ sont à déterminer) et développons un nouveau modèle d’ordonnancement plus compact. Nous utilisons pour les grandes instances une recherche par voisinage. Nous mettons en place des voisinages originaux adaptés à ce type d’ordonnancement.
Mots clés: Transfert de produits, ordonnancement, plateforme de transbordement, recherche stochastique, programmation à nombres entiers, heuristiques, recherche du plus proche voisin.----------ABSTRACT : Material handling in cross-dock is a relevant class of scheduling problems in distribution centers in which inner transhipment decisions need to be considered in addition to the processing order of trucks. The problem has applications in distribution centers where operators manually perform internal transhipment. In this dissertation, we investigate the problem of material handling inside cross-docking terminals. The main component of the problem is presented, followed by a classification scheme to express its diversity. Moreover, double handling identifies the main source of deficiencies in transferring operations. The objective is to synchronize the trucks’ loading and unloading sequences with internal transferring decisions to minimize excessive product displacement inside the terminal. First, the problem is studied for a conceptual model of the platform with single receiving and shipping doors. We formalize decisions on internal transhipment and develop an algorithm to determine the best transferring plan with restricted orders on processing trucks. This algorithm is employed as an evaluation function in a stochastic search framework to ameliorate the order of processing trucks and reduce the cost of double handling. Then, a mixed integer linear programming formulation of the general problem is introduced. The proposed model determines the joint schedule between processing order of trucks at inbound and outbound doors with an internal transhipment plan. A path branching algorithm is proposed. We present several structural properties and some valid inequalities to enhance the performance of the algorithm. This method could solve fairly large instances within a reasonable time. Second, we extend the developed models and approaches to schedule material handling process for a real platform with multiple doors. In the first installment, we focus on the satellite cross-docks that have limitations on the processing order of trucks at inbound door. These platforms operate in two separate shifts: consolidating pickup freight for overnight shipments and processing received products for early morning deliveries. A mathematical formulation of the problem is presented that can solve small instances with commercial software. In addition, a sequential priority-based heuristic is introduced to tackle the large problems. Numerical results depict the stability of this approach. Finally, in the second instalment, we study the general model with no restriction on the arrival and departure pattern of trucks and formulate a new mathematical model. This model has considerably fewer variables and constraints than the previous one. Moreover, a variable neighborhood search heuristic is developed to tackle real life problems. This method consists of several operators incorporated in a search subroutine to find local optima and a perturbation operator to alter it. The developed method is adopted for three scenarios concerning limitations imposed by the network schedule. The analyzes demonstrate economical savings in the cost of material handling. Keywords: Material handling; scheduling; cross-dock; stochastic search; Integer programming; heuristic; variable neighborhood search
A Review on Quantitative Approaches for Dock Door Assignment in Cross-Docking
Cross docking is a relatively new technique in supply chain operations. It offers limited storage time to maximize the efficiency of goods transshipment. Efficient operation of a cross docking system requires an appropriate coordination of inbound and outbound flows, accurate planning and dynamic scheduling. Â The planning strategies at cross docking terminals, which are receiving growing attention today, are the truck-to-door assignment and destination to door assignment problems. This paper provides a comprehensive literature review of quantitative approaches in dock door assignment problems of cross docking planning. The contributions of this paper are to identify the gap of knowledge in operational levels mainly in dock door assignment and to point out the future research direction in cross docking
Cross-Docking: A Proven LTL Technique to Help Suppliers Minimize Products\u27 Unit Costs Delivered to the Final Customers
This study aims at proposing a decision-support tool to reduce the total supply chain costs (TSCC) consisting of two separate and independent objective functions including total transportation costs (TTC) and total cross-docking operating cost (TCDC). The full-truckload (FT) transportation mode is assumed to handle supplier→customer product transportation; otherwise, a cross-docking terminal as an intermediate transshipment node is hired to handle the less-than-truckload (LTL) product transportation between the suppliers and customers. TTC model helps minimize the total transportation costs by maximization of the number of FT transportation and reduction of the total number of LTL. TCDC model tries to minimize total operating costs within a cross-docking terminal. Both sub-objective functions are formulated as binary mathematical programming models. The first objective function is a binary-linear programming model, and the second one is a binary-quadratic assignment problem (QAP) model. QAP is an NP-hard problem, and therefore, besides a complement enumeration method using ILOG CPLEX software, the Tabu search (TS) algorithm with four diversification methods is employed to solve larger size problems. The efficiency of the model is examined from two perspectives by comparing the output of two scenarios including; i.e., 1) when cross-docking is included in the supply chain and 2) when it is excluded. The first perspective is to compare the two scenarios’ outcomes from the total supply chain costs standpoint, and the second perspective is the comparison of the scenarios’ outcomes from the total supply chain costs standpoint. By addressing a numerical example, the results confirm that the present of cross-docking within a supply chain can significantly reduce total supply chain costs and total transportation costs
Heuristics for Truck Scheduling at Cross Docking Terminals
Cross-docking is a logistics management concept that has been gaining global recognition in less-than-truckload logistics industries and retail firms. In cross-docking terminals, shipments are unloaded from inbound trucks at strip doors, consolidated insider cross-docks according to their destinations, and then, loaded into outbound tucks at stack doors. The goal of cross-docking is to reduce inventory and order picking which are the two most costly functions of traditional warehousing management. The sequence in which the inbound and outbound trucks have to be processed at the cross-dock is crucial for improving the efficiency of cross-docking systems. In this thesis we introduce an integer programming formulation and apply four heuristic algorithms: a local search, a simulated annealing, a large neighborhood search and a beam search, to schedule the trucks in a cross-docking terminal so as to minimize the total operational time
Cross-docking: A systematic literature review
This paper identifies the major research concepts, techniques, and models covered in the cross-docking literature. A systematic literature review is conducted using the BibExcel bibliometric analysis and Gephi network analysis tools. A research focus parallelship network (RFPN) analysis and keyword co-occurrence network (KCON) analysis are used to identify the primary research themes. The RFPN results suggest that vehicle routing, inventory control, scheduling, warehousing, and distribution are most studied. Of the optimization and simulation techniques applied in cross-docking, linear and integer programming has received much attention. The paper informs researchers interested in investigating cross-docking through an integrated perspective of the research gaps in this domain. This paper systematically reviews the literature on cross-docking, identifies the major research areas, and provides a survey of the techniques and models adopted by researchers in the areas related to cross-docking
Application of Tabu Search to Scheduling Trucks in Multiple Doors Cross-Docking Systems
RÉSUMÉ : Cette recherche focus sur l’amélioration des cross-dockings en vue d’augmenter les niveaux de performance du service et de réduire les coûts. l’algorithme de la recherche avec tabous est étudiée pour trouver la séquence optimale d’entrée et sortie des remorques au cross-docking. L’objectif de cette recherche est de maximiser le nombre total de transferts directs entre le fournisseur et une destination finale commune de livraison. Dans les stratégies de distribution actuelles, l’objectif est de synchroniser les chaines du fabricant et du client. Le cross-docking implique de recevoir les produits d’un fournisseur pour plusieurs clients et d’occasionnellement consolider cela avec les produits d’autres fournisseurs pour des destinations finales de livraison communes.
En résumé, l’approche examinée dans cette recherche donne une occasion significative pour l’amélioration des opérations au Cross-docking par la réduction du stockage des produits.----------ABSTRACT : Today’s supply chain management performance has been affected by continuously increasing pressure of market forces. The pressure of market includes demands on increased flow of products and throughput with less amount of storage, also customers demand for more products with lower operational costs and more value-added services provided to customers. Supply chain is responsible in cost reduction and service levels increase by providing transshipments across its members. However supply chain has to face fluctuations of demands with the short available lead times. Physical problem of warehouse limitations and also inventory costs and shipping affect the performance of supply chain. In today’s distribution strategies, the main goal is to provide a synchronization of customer chains and the suppliers. The objective is to reduce the inventory buffering between customers and suppliers. The idea of cross-docking is to receive different goods from a manufacturer for several end destinations and possibly consolidate the goods with other manufacturer’s items for common final customers; then ship them in the earliest possible time. The focus of this research effort is to improve cross-dock operations with the goal of increasing the service performance levels and reducing costs. Specifically, metaheuristics algorithm of Tabu search is investigated for finding optimal sequence of incoming and outgoing trailers at cross-docks. This thesis reviews available research literature on cross-dock operations. Tabu search for the truck scheduling problem is presented along with results. Tabu search algorithm is investigated for the truck scheduling problem in the multiple doors cross-docking with unknown incoming and outgoing sequences. The objective of this research is to maximize the total direct transfer of products from a supplier to common final delivery destinations. The algorithm is implemented in C++ and analyzed using different problem instances. The results gained from algorithm of Tabu search are compared with other iterative heuristic descent method. The results indicate that the Tabu search performs significantly better than the descent method for large problem instances. In general, the results present that a metaheuristic algorithm of Tabu search for multiple or single door cross-docking offers thelargest potential for improvement. In summary, the approach explored in this research offers significant opportunity to improve cross-dock operations through reducing storage of products
Integrating Dock-Door Assignment and Vehicle Routing in Cross-Docking
Cross-docking is a logistic strategy in which products arrive at terminals, are handled and then shipped to the corresponding destinations. Cross-docking consists of unloading products from inbound trucks and loading these products directly into outbound trucks with little or no storage in-between. Cross-docking aims to reduce or eliminate inventory by achieving an efficient synchronization of unloading trucks, material handling and loading trucks. This thesis introduces an integrated dock-door assignment and vehicle routing problem that consists of assigning a set of origin points to inbound doors at the cross-dock, consolidating commodities in-between inbound and outbound doors, and routing vehicles from outbound doors to destination points. The objective is to minimize the sum of the material handling cost at the cross-dock and the transportation cost for routing the commodities to their destinations. Five mixed integer programming formulations are presented and computationally compared. A column generation algorithm based on a set partitioning formulation is developed to obtain lower bounds on the optimal solution value. In addition, a heuristic algorithm is used to obtain upper bounds. Computational experiments are performed to assess the performance of the proposed MIP formulations and solution algorithms on a set of randomly generated instances
Models and Algorithms for Inbound and Outbound Truck to Door Scheduling
Cross-docking is a logistic strategy that facilitates rapid movement of consolidated products between suppliers and retailers within a supply chain. It is also a warehousing strategy that aims at reducing or eliminating storage and order picking, two of which are known to be major costly operations of any typical warehouse. This strategy has been used in the retailing, manufacturing, and automotive industries. In a cross-dock, goods are unloaded from incoming trucks, consolidated according to their destinations, and then, loaded into outgoing trucks with little or no storage in between.
In this thesis, we address an integrated cross-dock door assignment and truck scheduling problem in which the assignment and sequencing of incoming trucks to strip doors and outgoing trucks to stack doors is optimized to minimize the total time to process all trucks. We present a mixed integer programming formulation to model this problem and some valid inequalities to strengthen the formulation. We also present two metaheuristics to obtain high quality solutions in reasonable CPU times. These algorithms use a mix of composite dispatching rules, constructive heuristics, local search heuristics which are embedded into a greedy randomized adaptive search procedure (GRASP) and an iterated local search (ILS). Results of computational experiments are presented to assess the performance of the proposed algorithms, in comparison with a general purpose solver