1,720,968 research outputs found
CARATTERIZZAZIONE MECCANICA, GEOMETRICA E FUNZIONALE DI DISPOSITIVI BIOMEDICALI
Full text linkAim of this work is to develop and to validate a structured methodology to investigate mechanical, geometric and functional aspects having a direct impact on the quality and safety of the dental prosthesis.
Dental technicians are liable for damages when prosthesis are used. It’s clear from a review of the normative technical documentation as well as of the technical-scientific literature, that safety requirements are not universally accepted and, thus, not yet adopted in the design phase of the prosthesis production. Therefore operators rely on good manufacturing practices more than in inspection and testing investigations. Moreover new methods and technologies are introduced in the production process of dental prosthesis, which have made it increasingly difficult to assess the impact of methodological issues on functional, quality and safety requirements.
For these aspects, with reference to technical standards and scientific background, eight type of test were developed that were submitted to a sample of dental laboratories. Tests concern structural properties, geometric precision and functional aspects of dental devices.
The proposed tests and the results of the experimental campaign are presented. The results allow assessing the suitability of the proposed method for the characterization of medical devices under study and on that basis, for the definition of quality and safety requirements to be adopted in the design phase and process control.Obiettivo del lavoro è sviluppare e validare metodologie che permettano di investigare in modo sistematico gli aspetti meccanici, geometrici e funzionali che hanno un impatto diretto sulle caratteristiche di qualità e sicurezza dei dispositivi biomedicali.
I fabbricanti del dispositivo medico sono i primi responsabili nel caso in cui si manifestassero dei danni arrecati all’utente durante il corretto utilizzo. Da un’analisi della normativa vigente e dalla letteratura tecnica-scientifica del settore è emerso che i requisiti di sicurezza non risultano accettati universalmente e quindi non sono adottati nella fase di progettazione delle protesi. Ciò fa si che gli operatori del settore si affidino alle buone pratiche di fabbricazione in sostituzione dei controlli e prove finalizzate a limitare i rischi di insuccesso. Inoltre l’introduzione di nuovi metodi e tecnologie nel processo produttivo dei dispositivi dentali aumenta le difficoltà nel valutare la ricaduta delle scelte metodologiche sul rispetto dei requisiti funzionali, di qualità e di sicurezza.
Per tale ragione, in riferimento alle norme vigenti e al background scientifico, otto tipologie di prove sono state sviluppate e sottoposte a laboratori odontotecnici. Le prove hanno riguardato la verifica strutturale dei dispositivi, il controllo della precisione geometrica e gli aspetti funzionali delle protesi in esercizio.
Nel seguito sono descritte le modalità di prova e presentati i risultati della campagna sperimentale effettuata. I risultati consentono di osservare come il metodo proposto sia adatto alla caratterizzazione dei dispositivi medici oggetto dello studio e che su tale base si può pervenire alla definizione di requisiti di qualità e sicurezza condivisi e pertanto utilizzabili in sede progettuale e di controllo di processo
Bite force and contact area evaluation in a physical-virtual environment
No full textAn integrated physical-virtual methodology for the in-vitro study of the occlusion is proposed. Both the contact area and the bite force are investigated in order to evaluate the functional characteristics of removable complete dentures and its relation to teeth morphology, position and orientation in the dental prosthesis and to relative position between antagonist teeth. The force is experimentally estimated by a 6-axis strain gauges sensor, while the contact areas are virtually identified by reverse engineering techniques.
The proposed method is aimed to assist the functional design of artificial teeth for removable complete as well as the prototyping phases of the prosthesis
Form errors estimation in free-form 2D and 3D geometries.
No full textThe aim of this work is to present a method for the verification of form tolerances in free-form geometries.
Method:
New free-form error parameters, in accordance with ISO GPS standards are defined. Geometrical errors in 2D e 3D geometries are calculated using a new fitting method consisting in an association operation where nominal profile/surface is resized (with an offset), located and oriented on the non-ideal geometry. Form tolerance is estimated using peak-to-valley deviation after the best fit.
Result:
Automatic algorithms are implemented to analyse 2D free-form profiles of moulds for ophthalmic lenses obtained with grinding and polishing operations and to analyse 3D free-form surfaces of an injection moulded lamp lens for automotive industry.
Discussion & Conclusion:
The comparison between results obtained using this approach and using traditional fitting methods shows differences on the fitting and errors parameters estimation. In particular in the traditional fitting there is a repartition of the size error contribution in the translation and form errors. The differences increase proportionally to the offset value estimated. The calculation of offset parameter allows the separation of size from geometric errors in free-form profiles/surfaces and the “true” form error estimation
Mechanical characterization of polyamide cellular structures fabricated using selective laser sintering technologies
No full textThe significantly growing use of Additive Manufacturing (AM) enables the fabrication of innovative parts,
characterized by lightness and good mechanical properties. The biomedical field takes great advantage of
these capabilities: in particular, the ability of producing porous or lattice structure-based parts allows to
obtain prostheses with human bone like stiffness, with a positive influence in patient’s lifestyle. The
knowledge of the mechanical behavior of materials used in AM and producible geometries is an essential
requirement to profit and improve this characteristic: in particular, recent studies focus on the
correlation between strength parameters and relative porosity of the part. In a previous work a set of
tensile tests have been performed on different types of specimens, reproducing a set of corresponding
emptying strategies, with different resulting porosity rates, and a linear predictive model has been
proposed. Aim of this work is to integrate the already acquired data, providing an interpretation on previous
results by numerical simulations: the influence of porosity rate on mechanical properties was
investigated by performing both global and local Finite Element Analyses, finding out an explanation
on inverse proportionality between material strength properties and porosity rate. The methodology
proved to be a profitable way in the optimization of lattice structures for Additive Manufacturing
A study on the material removal mechanisms in ball polishing
No full textThe manufacturing process of freeform glass components for precision optics is usually based on contour CNC grinding and polishing operations. To predict the geometrical precision of the production process, a correlation between the geometrical error and the process parameters is required. This is even more important in the polishing operation which is the final stage of the process.
In this work a model for material removal estimation in deterministic polishing of glass moulds is proposed and validated. The model is developed for CNC ball polishing of free-form surfaces, where the pad, made of a polyurethane layer superimposed to a rubber bulk, moves along a scanning path, in a suspension of cerium oxide. As many models in literature the removed material can be estimated by pressure and sliding velocity between polishing pad and workpiece. Adopting the Hertz theory these physical characteristics can be related to the CAD-CAM-CNC parameters, e.g. tool and workpiece shape, dimension and modulus of elasticity, feed rate, feed step, tool rotational speed and radial tool deformation.
The model validation was performed on ground glass flat samples polished with different process parameters, measuring the removed material by a contact probe profilometer. The developed model shows a satisfactory estimation of removal material as a function of the process parameters
La Precisione di Accoppiamento in Sottostrutture Fresate a Supporto Implantare
No full textLe terapie dentali implanto-protesiche che prevedono l’utilizzo di impianti osteo-integrati impongono
specifici requisiti sulla precisione di accoppiamento tra le strutture di supporto. Nel paziente edentulo
totale, tali requisiti risultano ancor più difficilmente conseguibili per la presenza contemporanea di più
impianti. I processi produttivi tradizionali, fino ad oggi ancora i più diffusi, non riescono a soddisfare
pienamente la domanda clinica di sovrastrutture ad accoppiamento passivo, in grado di preservare e
favorire i meccanismi di osteointegrazione mentre i nuovi processi CAD/CAM sembrano venire
incontro a questa esigenza primaria. Da qui l’esigenza di valutare e confrontare, mediante
l’individuazione di opportuni parametri geometrici, la precisione di fabbricazione di strutture
protesiche ottenute con differenti processi produttivi e materiali alternativi: leghe nobili, Co-Cr e Ti. I
risultati ottenuti per via sperimentale designano senza possibile dubbio il processo CAD/CAM come
l’unico in grado di consentire il raggiungimento di accoppiamenti passivi entro i limiti tecnologici
legati alle fasi ed alle attrezzature proprie del processo medesimo
Mechanical characterization of polyamide porous specimens for the evaluation of emptying strategies in Rapid Prototyping
No full textRapid-prototyping is usually considered as a powerful tool in geometric and functional optimization of a product. In such an approach, focus is exclusively on the real component, and not on the rapid prototype which represents it. This work takes part on a wider study which focuses on a rational, systematic approach in obtaining an ???optimized rapid prototype???, with particular regard to emptying strategies without loss of structural and geometric properties. In detail, a set of tensile tests have been performed on different types of specimen, which reproduce a set of corresponding emptying strategies: each type of specimen is characterized by a different percentage of porosity (40, 60 and 80%), obtained by the combination of particular values of two parameters: reticular structure and its density. As a result, the correlation between mechanical strength and geometric structure has been evaluated, allowing the identification of a profitable emptying strategy, in terms of cost and weight
- …
