1,720,962 research outputs found
Development of a generalized extended harmonic solution for analyzing the combination of chatter suppression techniques in milling
Get PDFIn this paper a comprehensive and structured analysis of the stabilizing properties linked to the combination of different chatter suppression techniques in milling was carried out. Specifically, the spindle speed variation, the stiffness variation and the usage of tools with variable pitch and variable helixangles were considered.
For this purpose, a unique, general and efficient frequency domain formulation (extended harmonic solution) was developed. It is suitable for dealing with differential delayed equations characterized by multiple and distributed time dependent delays and time periodic dynamics. It was demonstrated that the developed solution converges to the reference cases, which were studied in literature through semi-discretization and its extensions. Moreover, by selecting a proper number of considered harmonics, the computation time was reduced of one order of magnitude, in the face of a slight reduction of accuracy with respect to time domain approaches.
The computed stability lobe diagrams demonstrated that the combination of multi-chatter suppression techniques allows exploiting the best features of each methodology. The simultaneous use of the spindle speed variation and the stiffness variation was studied for the first time. The absolute limit of stability increased up to 204%, much more than by adopting the techniques in a separate manner. If the enlargement of the stability region is considered as the reference target, the best results were granted by the combination of all the three strategies. Indeed, the improvement with respect to the use of only two techniques was at least 10%
Disassembler: Cloud-Based Solution for Optimized Cutting Tool Quality Control
No full textIn Industry 4.0, exploiting the useful life of components can be a competitive advantage for companies in terms of cost and efficiency. In this context, the Disassembler solution of the Horizon Europe project AIDEAS was born. Its main purpose is to create a tool for identifying the wear of industrial cutting tools. The authors propose a deterministic algorithm that supports near-real-time analysis even using nonindustrial cameras. The proposed solution enables validation of the wear status of cutting tools being machined in a non-invasive manner, avoiding wasting time, material and economic resources. The tool proposed by the authors is a client server solution with a Python backend that communicates with the frontend, developed in React, through Flask CORS. Using some photos of new tools as reference, the backend compares the test images, taken, or simply uploaded on the interface by an operator, with reference ones; then a report is generated, and the operator can read up the condition of the element
Artificial Neural Networks to Obtain the Machining Parameters for a Compliant Part in a Single Re-Machining Step
No full textIn contemporary manufacturing systems, the efficiency of the production line is crucial for maintaining competitiveness in the current market. Therefore, minimizing re-machining operations becomes imperative to optimize production, reduce costs, and utilize resources more effectively. This necessity is particularly apparent in machining processes involving sizable components that require numerous hours, and at times, even days to accomplish. This study employs two Artificial Neural Networks with one layer and different numbers of neurons to determine the required material removal quantities for the production of cast iron columns with different lengths. The algorithm was tested on a 3-axis CNC machine in a real industrial scenario in the company PAMA S.p.A., a member of the European AIDEAS project consortium. The goodness of the solution has been demonstrated by the high score value in the prediction of the removal parameters (score = 0.998) and confirmed by the experience of the production manager of the compan
Chatter indicator for linear time periodic systems
Get PDFLAUREA MAGISTRALEIl chatter rigenerativo è uno dei principali fattori limitanti per efficienza e qualità nella fresatura. Si tratta di un fenomeno complesso che può emergere rapidamente a seconda dei parametri di taglio, della dinamica della macchina, dell'utensile e della geometria del pezzo. Lo sviluppo di strategie per prevedere, rilevare, evitare e sopprimere il chatter è sempre stato importante. Sebbene i sistemi reali non potessero essere modellati come sistemi lineari tempo invarianti, i metodi per la previsione del chatter erano principalmente basati sull'assunzione che il sistema fosse invariante nel tempo. Questa assunzione semplificativa può portare a trascurare caratteristiche essenziali. La complessità della creazione di diagrammi di stabilità e la necessità di coinvolgere le incertezze che si verificano durante la lavorazione e le conseguenze del cambiamento delle dinamiche portano allo studio di algoritmi affidabili di rilevamento delle vibrazioni in tempo reale. Poiché questo lavoro si basa su una tecnica che mira a sopprimere le vibrazioni variando periodicamente la rigidità della macchina, il principale focus del progetto è stato lo sviluppo di un indicatore dalle vibrazioni in tempo reale in grado di separare la frequenza vibratoria di chatter dalle bande laterali vicino alla frequenza di passaggio dei denti generata a causa del cambiamento della dinamica. Pertanto, E’ stato inoltre sviluppato un altro algoritmo per monitorare la velocità del mandrino e lo stato di modulazione in base alle specifiche frequenze di passaggio dei denti e alla possibile formazione di bande laterali.Regenerative chatter is one of the main limiting factors for efficiency and quality in milling. It is a complex phenomenon that can emerge rapidly depending on cutting parameters, dynamics of the machine, tool, and workpiece geometry. Developing strategies for predicting, detecting, avoiding, and suppressing chatter has always been important. Although real systems cannot be characterized as linear time-invariant systems, the methods for prediction of chatter were mainly based on time-invariant system assumption which simplifies the system and may result in neglecting essential features. The complexity of creating stability lobe diagrams and the need to involve the uncertainties occurring during the machining and the consequences of changing dynamics lead to the investigation of reliable real-time chatter detection algorithms. Since this work is based on a technique that aims to suppress the chatter by varying the machine stiffness periodically, a real-time chatter indicator that can separate the chatter frequency and the sidebands near tooth-passing frequency created due to the changing dynamics was the main focus. Therefore, another algorithm was developed for deciding the spindle speed and modulation status to specific tooth passing frequencies and possible sideband formation
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Chatter detection in linear time periodic systems with stiffness variation
No full textLAUREA MAGISTRALEIl chatter rigenerativo è una vibrazione autoeccitata causata dall'interazione utensile-pezzo durante la lavorazione. Può causare condizioni di taglio instabili con effetti dannosi che causano perdita di produttività e qualità, costi aggiuntivi, problemi di sicurezza, ecc. Per far fronte al chatter, in letteratura sono stati impiegati approcci di variazione di rigidità (SV) con diversi meccanismi di attuazione per la soppressione attiva del chatter nelle operazioni di tornitura, alesatura e fresatura. Durante la SV, la modulazione continua della rigidità altera la dinamica della macchina utensile introducendo caratteristiche lineari tempo-periodiche (LTP). Tuttavia, la maggior parte degli studi sul chatter in letteratura si basa su un'ipotesi di sistema lineare tempo-invariante (LTI) semplificata. Pertanto, è necessario un algoritmo generalizzato che copra sia le caratteristiche del sistema LTI che LTP per un ambiente industriale in continua evoluzione per una determinazione affidabile dello stato di taglio e il rilevamento del chatter all'inizio. In questo lavoro, un approccio di filtro adattivo già collaudato viene esteso alla dinamica LTP in termini di formazione di bande laterali attorno a frequenze periodiche e l'algoritmo di rilevamento del chatter basato sul filtro adattivo viene ampliato includendo l'estensione LTP e SV. I parametri del filtro vengono studiati per il segnale di accelerazione raccolto da un'operazione di fresatura di un pezzo ingombrante e confrontati con lo studio di riferimento, in cui viene proposto l'algoritmo del filtro adattivo. Dopo la separazione, il rapporto di varianza (VR) tra il segnale non periodico filtrato e il segnale originale viene calcolato come indicatore di chatter e le sue prestazioni vengono studiate per tre stati di taglio (stabile, chatter, soppressione del chatter con SV) a diversi casi di velocità del mandrino. Infine, le informazioni sulla frequenza vengono ottenute con i metodi del dominio tempo-frequenza (TF) per trovare la frequenza di chatter dominante. Il segnale non periodico filtrato viene scomposto con i metodi di decomposizione della modalità empirica (EMD), ensemble-EMD (EEMD) e decomposizione della modalità variazionale (VMD). Dopo la loro valutazione, le prestazioni di decomposizione di VMD in termini di localizzazione TF per le modalità sensibili con informazioni ricche di chatter risultano superiori alle altre. Grazie al filtro adattivo esteso, le informazioni provenienti da un'operazione di taglio possono essere elaborate per ogni lunghezza di dati di 0,5 secondi calcolata per l'indice di chatter ogni 0,3 secondi. Ciò consente di localizzare sia le informazioni di tempo che di frequenza in modo robusto per una determinazione tempestiva dello stato di taglio con e senza SV.Regenerative chatter is a self-excited vibration caused by tool-workpiece interaction in machining. It can result in unstable cutting conditions with detrimental effects causing loss of productivity and quality, additional costs, safety concerns, etc. To cope with chatter, stiffness variation (SV) approaches with different actuation mechanisms have been employed in the literature for active suppression of chatter in turning, boring, and milling operations. During SV, the continuous modulation in stiffness alters the machine tool dynamics by introducing linear time-periodic (LTP) characteristics. Nevertheless, most of the chatter studies in the literature are based on a simplified linear time-invariant (LTI) system assumption. Therefore, a generalized algorithm covering both LTI and LTP system features for an ever-changing industrial environment is needed for reliable cutting state determination and chatter detection on the onset. In this work, an already proven adaptive filter approach is extended to LTP dynamics in terms of sideband formation around periodic frequencies, and the chatter detection algorithm based on the adaptive filter is enlarged by including LTP extension and SV. The filter parameters are investigated for the collected acceleration signal from a milling operation of a bulky workpiece and compared with the reference study, where the adaptive filter algorithm is proposed. After the separation, the variance ratio (VR) between the filtered non-periodic signal and the original signal is computed as a chatter indicator, and its performance is investigated for three cutting states (stable, chatter, chatter suppression with SV) at different spindle speed cases. Lastly, frequency information is obtained with the time-frequency (TF) domain methods to find the dominant chatter frequency. The filtered non-periodic signal is decomposed with empirical mode decomposition (EMD), ensemble-EMD (EEMD), and variational mode decomposition (VMD) methods. After their evaluation, the decomposition performance of VMD in terms of TF localization for the sensitive modes with chatter-rich information is found to be superior to the others. Thanks to the extended adaptive filter, the information coming from a cutting operation can be processed for each 0.5-second length of data computed for the chatter index at every 0.3 seconds. This makes it possible to localize both time and frequency information in a robust way for timely determination of the cutting state with and without SV
Chatter stability analysis of boring process equipped with Tuned Mass Damper through linear time periodic dynamics
Get PDFLAUREA MAGISTRALEIl fenomeno di instabilit`a rigenerativo, meglio conosciuto come Chatter rigenerativo, rappresenta
uno dei fattori pi`u limitanti nei processi di asportazione di truciolo. Tale fenomeno porta
ad una riduzione della produttivit`a, una riduzione della qualit`a del manufatto e un aumento
dell’usura dell’utensile e delle parti della macchina. Nel corso degli anni sono stati pubblicati
diversi studi atti a favorire lo sviluppo di strategie per sopprimere il Chatter ed estendere la
conoscenza del fenomeno.
L’obiettivo di questa Tesi, svolta in collaborazione con Pama S.P.A., `e studiare la stabilit`a di
una lavorazione di alesatura quando un Tuned Mass Damper `e installato sull’utensile e ruota
con esso. Il sistema in questione presenta caratteristiche asimmetriche dal punto di vista dinamico
e non `e modellabile attraverso la Dinamica Lineare Tempo Invariante. Per la prima volta,
il comportamento dinamico asimmetrico dell’utensile viene introdotto nel modello attraverso
la funzione di variazione della rigidezza, che consente di modulare la dinamica del sistema in
funzione della posizione dell’utensile stesso. L’ausilio della funzione di variazione della rigidezza
aggiunge un fattore di complessit`a al modello e richiede l’approccio ai sistemi Lineari Tempo
Periodici per studiare la stabilit`a del sistema. Il modello sviluppato `e stato applicato inizialmente
a tre diverse casistiche, e successivamente esteso alla condizione di taglio interrotto.
Il primo caso identifica l’analisi di stabilit`a di un processo di alesatura senza TMD, mediante
dinamica Lineare Tempo Invariante. Questo caso rappresenta lo stato dell’arte del processo di
alesatura e consente di definire il punto di partenza del lavoro svolto.
Il secondo caso identifica l’analisi di stabilit`a attraverso descrizione dinamica LTI, e sottolinea
come, questa modellazione della dinamica del sistema, non sia adatta a studiare la stabilit`a.
L’ultimo caso, il numero tre, descrive il processo attraverso la dinamica LTP e fornisce il miglior
compromesso in termini di stima della stabilit`a. Quest’ultimo caso `e stato esteso anche alle
condizioni di taglio interrotto.
I risultati ottenuti sono stati testati attraverso validazioni sperimentali e numeriche.Chatter is one of the most limiting factors in chip removal processes. This instability phenomenon
leads to a reduction in productivity, a reduction in quality, and an increase in the
wear of tool and machine parts. Over the years, different studies have been published which
led to the development of strategies to suppress Chatter and extend the know-how about the
phenomenon.
The goal of this Thesis, conducted in collaboration with Pama S.P.A., is to study the stability
of the Boring process when a Tuned Mass Damper is installed on a boring tool and rotates
with it. The system in question presents asymmetric characteristics from a dynamical point of
view, and cannot be modeled through Linear Time Invariant Dynamics. For the first time, the
asymmetric behaviour will be introduced in the model through the Stiffness Variation function,
which allows modulating the dynamics of the system in function of the position of the boring
tool. The aid of the Stiffness Variation function adds a factor of complexity to the model and
requires Linear Time Periodic laws to study the stability of the system.
The model developed was applied firstly to three different applications, and after was extended
to interrupted cutting conditions. The first case identifies the stability analysis of boring operation
without TMD through Linear Time Invariant dynamics. This case represents the state
of the art of boring process and allows to define the starting point of the work conducted.
The second case identifies the stability analysis of the boring process with TMD through LTI
dynamics and remarks the fact that, this dynamics description, does not model correctly the
process.
The last case, number three, describes the process through LTP dynamics and provides the
best compromise in terms of Chatter stability estimation. This last case was extended also to
interrupted cutting conditions.
All the results obtained were tested through experimental and numerical validations
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