1,721,009 research outputs found
A hybrid heuristic algorithm for solving the Traveling Salesman Problem with Time Windows
No full textSeveral issues related to the logistics field can be recognized as applications of the renowned Traveling Salesman Problem with Time Windows (TSPTW); examples of these issues include, among others, instance planning deliveries, managing internal logistics, bank couriers, material handling, but also production scheduling. In the light of such numerous applications, in this paper a hybrid algorithm based on the Divide-And-Conquer (DAC) technique and the Biased Randomized heuristic Algorithm (BRA) for solving the mentioned problem is presented. The aim is to propose a flexible solution suitable for implementation in many contexts where the TSPTW is relevant, thus improving performance and key indicators. The quality and reliability of the tool are validated on several benchmark problems through a comparison with a different algorithm already proposed in literature. In the light of the simulations carried out, it turned out to be effective and efficient when dealing with problems similar to those that characterize real applications, even in terms of computational time efficiency
Allocation of items considering unit loads balancing and joint retrieving
No full textIn the last years, the diffusion of lean thinking had a big impact, not only in manufacturing, but in logistics too. Because of one-piece-flow production and the point of view on inventory that considers it as inefficiency, purchasing and shipping batches have become smaller and more varied, requiring to the suppliers more shipments per day, a shorter throughput time, and, in general, higher performances. To improve retrieving performance in automated warehouses, many routing and scheduling procedures are presented in literature, although retrieving can be speeded up starting from the input phase using a correct allocation policy. In this paper, we present a procedure inspired by Genetic Algorithm (GA) for allocation of items inside unit loads. The procedure considers two aspects that are hardly studied in literature, such as unit load weight balancing and market basket analysis aimed at closed allocation of items that are usually jointly retrieved. The first one is a physical necessity, especially required in the steel sector, where objects stocked are heavy. The second one improves the retrieving performance and it increases the possibility to satisfy more order lines with fewer travels. The algorithm proposed was tested using the digital twin of an existing warehouse and comparing the results with the current performances of the real system
Cycle time calculation of shuttle-lift-crane automated storage and retrieval system
No full textThis article deals with cycle time calculation of Automated Storage and Retrieval Systems (AS/RS). Cycle time has a high impact on the operating performance of an AS/RS, and its knowledge is essential, both at the operational and design level. The novelty of this work concerns the peculiar kind of system that is considered, as the focus is on the Shuttle-Lift-Crane AS/RS. This solution, common in the steel sector, is used to store bundles of long metal bars, which are automatically handled by cranes, lifts, and shuttles. The functioning of these machines, which can operate in parallel and independently, is stochastically modeled, and the probability distribution function of the cycle time is computed, both for single and dual command cycles. The model, assessed via discrete event simulation, ensures a high average accuracy of 96% and 98%, under single and dual command cycles, respectively
A survey of literature on automated storage and retrieval systems from 2009 to 2019
No full textThis paper provides a literature review on automated storage and retrieval systems based on the Scopus database. The last comprehensive literature review that analyses the subject in its entirety dates back to 2009 by Roodbergen and Vis. Since then, the scientific community has provided many new efficient solutions, most of which are collected in Scopus. All these new published solutions need to be classified and summarised; thus, for this paper, more than one thousand scientific publications were analysed in order to classify the proposed solutions, deliver new academic insights to the field, and provide clear guidelines for researchers and practitioner
A flexible operating tool to provide an efficient project's staffing and resource allocation
No full textResource allocation is paramount for the success of complex projects; many allocation and staffing models have been proposed in the literature, but none of them has found its way into practice yet. Hence, we propose a tool to provide an efficient project's staffing and resource allocation, with the goal to create cohesive teams, and an almost perfect matching among time/quality requirements and resources' skills. To achieve this objective, the tool makes use of a specific heuristic that reproduces the reasoning of the project manager, using logical rules based on sorting and prioritising criteria, both for tasks and resources. To validate the tool, we applied it to a comprehensive set of past projects, completed by a consultant company over the past five years. Solutions provided by our tool were assessed by a team of experienced project managers, and they were found superior to the ones originally implemented by the company
An operational framework for the definition of the supply chain strategies in ETO environments
No full textThis paper describes an operational methodology to support the project manager, in both proposal and management phases. The purpose of the proposed approach is to (i) estimate the criticality of the project both in terms of technical and management criticalities, (ii) identify the Business Partners (or suppliers) that it is most appropriate to involve in the project, (iii) estimate the expected direct and indirect costs of the project, and (iv) estimate the overall criticality of the project. In order to have an assessment of its validity and reliability, the proposed methodology is applied in a real project concerning the construction of an automated warehouse
Order picking: A comparison of heuristic and meta-heuristic approaches
No full textThis paper investigates the impact of several routing strategies on minimization of the travel-time for pickers in a manual warehouse. Many solutions have been proposed in literature over the last years, however, just a few authors really compare them on equal terms in order to carry out a proper comparison. In this work, three well-known heuristic strategies (i.e. S-Shape, Largest Gap, and Combined) are firstly compared to each other and then with two metaheuristic algorithms owning to swarm intelligence family (i.e. Ant Colony Optimization and Particle Swarm Optimization). Firstly, an empirical study has been made to find out the best setting for meta-heuristics’ parameters. Then, a discrete event simulation model has been developed by using both Python© and Cython© programming languages, and the analyzed strategies have been compared under several storage assignment policies
A dynamic operative framework for allocation in automated storage and retrieval systems
No full textTwo very important aspects in automated storage and retrieval systems (AS/RS) are productivity (or performance) and maintenance costs. In the literature, as in industry, it is very difficult to find a solution that guarantees satisfactory results in terms of both. Moreover, all the solutions that the scientific community has proposed are static, i.e., the system's behavior does not change as boundary conditions change. In this paper, we propose an innovative solution known as a dynamic operative framework (DOF), which allows the system to react to changes in operating conditions and guarantees good results in terms of productivity, with a consistent reduction in the distance that handling machines travel and a consequent reduction in maintenance and energy consumption costs. To test the proposed solution, we focused on the shuttle-lift crane AS/RS, a common configuration used to store bundles of long metal bars, and we compared the DOF with four benchmark policies that exploit a class-based reorganization of the stock performed during non-working shifts. Many simulation runs’ results indicated that the DOF ensures a throughput time aligned to that of the benchmarks, but without needing to reorganize the stock during nonworking shifts. In this way, it leads to consistent savings in terms of energy consumption and maintenance costs
RFID software-based shielding: Implementation of further approaches under varying surrounding conditions
No full textGiven the promising results obtained by the Software-Based Shielding (SBS) in our previous work entitled 'Software-based shielding for real-time inventory count in different store areas: a feasibility analysis in fashion retail', in this paper, we go into more detail by exploring the effect of certain surrounding aspects, such as (i) the partition wall, and (ii) the density of tags. We also propose alternative algorithms other than logistic regression analysed in the previous work -i.e., a heuristic algorithm, a Neural Network (NN), a Convolutional Neural Network (CNN), and the introduction of reference tags to enhance these approaches. The results show that the logistic regression and the CNN are the most accurate models. The choice between them might depend on the application context: the first is less reliable but much simpler to implement, while the second is a more complex and complete machine learning model. Concerning the environmental conditions, the density and disposition of RFID tags appear the aspects with the greatest impact
Software-based shielding for real-time inventory count in different store areas: A feasibility analysis in fashion retail
No full textRFID is an established technology and its implementation has been increasing steadily in different industries in the last decades. An important and relatively recent RFID breakthrough has been that of moving the level of tagging from pallet- or case-level, to item-level. This development has opened up a new set of use cases and benefits, especially in retail. One of these new use cases is the estimation of items' location by positioning and tracking the tags attached to them. This problem is often seen as a classification problem, especially when tags that are read at the retail store must be located either in the sales floor or in the backroom area. The typical approach to ease this classification consists of physically shielding the interested areas via hardware installations, although this solution is expensive and lacks flexibility. In this paper, we present a different solution, namely a software-based shielding approach, to address the classification problem. Our solution makes use of item-level RFID tags and is based on the well-known logistic regression. Whenever a reading session is performed by means of a handheld reader, the classification model estimates in real-time (i.e. within a few seconds) which tagged items are in the same area of the reader and which are not, with no need of any shielding hardware installation. According to the validation preliminary tests presented in this paper, in which we simulated a fashion retail store, the proposed approach has an overall average accuracy of 95.5%
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