1,721,125 research outputs found
An approach for the robust design of a reconfigurable assembly cell with 7-axis robot
Full text linkThe increasing variety of products and the variability of the demand are pushing manufacturing companies in a challenging and competing environment. These trends affect many industrial sectors, including the automotive one, impacting the whole supply chain, including the production of spare parts. The automotive spare part’s market is aimed at providing replacing parts during the whole life cycle of cars. As the design of cars becomes more and more sophisticated, producing spare parts requires complex production processes, a wide range of different technologies and the need to cope with different materials. In this context, the design of assembly systems and proper management policies have a considerable importance for the competitiveness of spare parts suppliers. In this paper, a configuration approach is proposed, to select a robust design solution for a reconfigurable assembly cell. The solution consists of an initial configuration together with a set of alternative reconfiguration plans to cope with the intrinsic uncertainty of the spare part manufacturing requirements. An innovative reconfigurable assembly cell architecture is exploited, while robustness is pursued by minimising a function of the risk associated with investment and operational costs of the assembly cell. The viability of the proposed approach is demonstrated through the application to an industrial case
A scheduling approach for chemical vapour deposition processes in the production of semiconductors
Full text linkThe production of semiconductors for applications in microelectronics is operated through photo-lithographic and chemical processes whereof Chemical Vapor Deposition (CVD) technology is one of the most used. CVD processes need to operate in furnaces under controlled atmosphere and, every time the furnace is accessed from the external environment, a purging time is needed to restore the prescribed atmosphere. The optimisation of the utilisation of the furnaces depends on the sequencing of loading and unloading operations entailing the need to disturb the controlled atmosphere. We propose the use of a disaggregated time formulation based on step variables to model a scheduling problem aiming at identifying the optimal sequence of operations and supporting the definition of optimal dispatching policies
From Phonological Rules to the Person Case Constraint. Monovalent vs. Bivalent Features in Grammar
Full text linkIn phonology, segmental content has been predominantly represented in terms of binary features. Although binary features may provide an elegant description of some segmental contrasts, it is far from clear that speaker/hearer’s knowledge about segments is organized in a binary way, as we illustrated with specific reference to vocalic alternations (metaphony etc.). The debate about binarity in phonology has a potential parallel in morphosyntax. While syntactic categories (N, V, v, T etc.) are monovalent, a model like Distributed Morphology depends on standard generative phonology for a number of formal properties, including the adoption of binary features. Thus 1st and 2nd persons are [+participant] while 3rd person is the absence of such properties, namely [-participant]. We argue that this is not the most economical set of assumptions, specifically in the explanation of the syntactic generalization known as the Person Case Constraint (PCC). For both phonology and morphology, we show that the inherent richness of binary features leads to formal and conceptual problems, such as the fact that atomic segments or lexical items have as complex a feature matrix as non-atomic ones
An upper bound for the inter-exit time of two jobs in an m-machine flow shop
Full text linkThis paper addresses the class of permutation flow shop scheduling where jobs, after their completion, must be grouped in batches. This is a common scheme in industrial environments, where products undergo multiple process steps in different shops and, when completed, must be transported to customers or the next production step. A new optimisation criterion is used, the inter-exit time, i.e., the difference between the completion times of two jobs. An upper bound is proposed and demonstrated for a general permutation flow shop with m machines
La risposta europea all’emergenza da Covid-19
No full textQuesto capitolo mira a valutare se, e fino a che punto, la solidarietà abbia trovato concretizzazione nella risposta dell’Unione europea e dei suoi Stati membri durante l’emergenza da COVID-19, concentrandosi particolarmente sulla risposta all’emergenza in Italia (in quanto Stato membro maggiormente colpito, almeno in una fase iniziale). Lo studio si sviluppa in due parti. Nella prima ci si concentra sulla cooperazione tra Stati membri nel contesto della risposta europea all’epidemia. Si presenta dapprima la richiesta di assistenza inoltrata dall’Italia attraverso il Meccanismo unionale di protezione civile e si analizzano poi le risposte date dagli altri Stati membri. Questi, da un lato, si sono rifiutati di fornire assistenza per quasi un mese, in modo lecito ma poco solidale. E, dall’altro, hanno vietato per alcune settimane l’esportazione di materiale medico verso l’Italia, con azioni certamente non solidali e probabilmente illecite. La seconda parte dello studio affronta il contributo dato direttamente dalla Commissione alla gestione dell’emergenza, cioè la dimensione collettiva della solidarietà europea. La Commissione ha contribuito al coordinamento degli appalti per contromisure mediche, alla costituzione di scorte europee e, soprattutto, alla negoziazione con le società farmaceutiche dell’acquisto di vaccini contro il COVID-19. Nella conclusione si traggono le conseguenze della (scarsa) solidarietà dimostrata dagli Stati membri e degli interventi della Commissione
An Approximate Approach for the Verification of Process Plans with an Application to Reconfigurable Pallets
No full textThe manufacturing sector has to be able to manage high-variety and low-volumes per product, causing the adoption of a dedicated production system/cell to be unfeasible. In this context, reconfigurable pallets and flexible fixtures are enablers to manage product variety and volume variability. Namely, as a pallet is reconfigured, the associated part program needs to be verified to check for possible collisions between the tools and the new machining environment. An approach is proposed to verify the machinability of a pallet configuration given an existing part program. The approach grounds on an approximated collision check method exploiting a 3D representation of the machining environment (fixtures and parts). The approach is validated through an application to a realistic use case and the comparison with the results of a traditional collision check approach
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
- …
