An Innovative Photogrammetric System for 3D Digitization of Dental Models

This paper presents an innovative system for 3D reconstruction of a physical dental model. The innovative system is based on close-range photogrammetry and enables the projection of digital light texture on the objects surface. It is based on the application of mirrors that direct the digital light texture to the vertical surfaces of the physical model. In this way, high coverage of the object is achieved, and 3D reconstruction from one set of photographs is possible. 3D digitization, verification and comparison of the proposed methodology was performed on dental models that are characterized by extremely complex surfaces. It was performed by comparing the proposed approach with active stereovision, and the efficiency was evaluated in relation to the reference 3D model obtained by the structured light 3D scanner. The comparison of the results was performed on the basis of the mean deviation and standard deviation for the 3D model with combined teeth and for the 3D model with metal caps. The absolute mean deviations for the 3D model with combined teeth are 0.004-0.021 mm, with a standard deviation of 0.055-0.058 mm, and for the 3D model with metal caps absolute mean deviations are 0.015-0.033 mm, with a standard deviation of 0.095-0.113 mm, respectively. Absolute minimum values of mean deviation of 0.004 mm and standard deviations of 0.055 mm were obtained by 3D model with combined teeth,which was reconstructed by the proposed innovative approach. The obtained results indicate a higher accuracy of the innovative approach in relation to the use of a commercial 3D scanner that uses active stereovision principle

Multi-Criteria Evaluation of Design Complexity for Patient-Specific Bone Graft

With the rise of modern computer-aided technologies, their use in various different fields is becoming more and more apparent, but more profoundly in the field of medicine. The use of such technology enables the design of complex anatomical structures, often found in different areas of medicine. Maxillofacial and oral fields are becoming more and more popular with the use of such technologies, all leaning toward designing and fabrication of patient-specific implants from a biocompatible material. The level of complexity in personal graft design depends on criteria that describe the bone graft\u27s various properties. This research applies multi-criteria decision aiding in selection of patient-specific bone graft optimal design.Twelve different patient-specific bone-grafts designs have been evaluated by four decision makers who expressed their preferences with direct weighting and revised Simos procedure. Well known VIKOR method was used for multi-criteria decision aiding and the final results verified that the fully curved shape graft design is the least complex while the complex shape is the most demanding from the graft design perspective

The Influence of Vacuum Level on the Friction Force Acting on the Pneumatic Cylinder Sealing Ring

Presented in this paper are the results of measurement of friction force acting on the pneumatic cylinder sealing rings under high vacuum atmosphere. The investigations were conducted at relatively low levels of sliding speed of the sealing ring. Special device was constructed and implemented to facilitate this experiment. The results indicate the importance of the vacuum level on the friction force magnitude. Higher vacuum levels influence significant increase of friction force. Special phenomenon is the decreasing of friction force at higher sliding speeds of the sealing ring along the cylinder, under the constant vacuum level. Therefore, detailed examination of this phenomenon in the domain of high sliding speeds could yield interesting results

Relation between Kinetic Friction Coefficient and Angular Acceleration during Motion Initiated by Dynamic Impact Force

The paper presents theoretical and experimental analyses of the kinetic friction coefficient of a ball bearing in conditions of rotational motion initiated by dynamic impact force. A method has been developed and a measurement system allows the measurement of a kinetic coefficient of friction through the measurement of the angular acceleration. This paper considers the friction caused by rotational motion initiated by the force impact impulse. After the external force (impact impulse) stops acting, the motion continues, and the loaded bearing (i.e. the zone of the bearing in which the frictional resistance forces act) exhibits a broad spectrum of velocities, from the maximum value at the moment of motion initiation to the zero value when motion stops, where the whole measuring system acts as a rotary encoder. Experimental results indicate a high dependency between angular velocity and friction coefficient, similar to functional dependency. This paper proves that kinetic friction coefficient can be reliably measured using the measurements of angle change and angular velocity. Analysed method has high potential in the diagnostics of energy loss in the tribo-mechanical systems

Rule base reasoning in the knowledge-based mould design system

U članku se prikazuje parametarski, modularni, integrirani CAD/CAE sustav za konstruiranje kalupa, temeljen na značajkama. Predloženi sustav integrira Pro/E s izvorno razvijenim modulom za izračunavanje parametara injekcijskog prešanja, parametara kalupa i izbor kalupa. Sučelje koristi parametarske CAD/CAE značajke iz tipsko-orijentirane baze podataka, što doprinosi jednostavnijem procesu konstruiranja, uređivanja i izmjene podataka. S obzirom na prethodno istraživanje, članak prikazuje mogućnost modeliranja sustava primjenom pravila. U članku se još predstavlja popis inženjerskih metoda koje su se koristile za gradnju sustava zasnovanog na znanju, a metoda zaključivanja na osnovu pravila proizvodnje predstavlja se detaljnije.This paper describes knowledge-based oriented, parametric, modular, and feature-based integrated CAD/CAE system for mould design. The proposed system integrates Pro/E system with developed original module for calculation of parameters of injection moulding and mould design calculation and selection. The system interface uses parametric and CAD/CAE feature-based database to make the process of design, editing, and reviewing smoother. An example is provided to demonstrate our approach in rule-based representation. Also presented the lists of KBE techniques used for building the knowledge-based system and especially production rules reasoning

Model for analysis of environmental impacts of production processes in flooring industry based on LCA

Proizvodnja podnih obloga je, s aspekta utjecaja na okoliš, vrlo kompleksan proces zbog velikog broja utjecajnih parametara - različitih kemijskih emisija, neminovnosti otpada, većeg broja utjecajnih fizičkih veličina poput buke i vibracija, prašine i zračenja, zatim potrošnje energije, recikljivosti itd. Zanimanje za primjenu LCA u području proizvodnje podnih obloga traje već skoro dva desetljeća i postaje sve intenzivnije. Tijekom tog razdoblja evidentirani su različiti pristupi i pokušaji realizacije LCA u ovom širokom području. U ovom radu predstavljen je opći model za ocjenjivanje utjecaja na okoliš procesa proizvodnje podnih obloga zasnovan na LCA. Razvijeni model predstavlja doprinos unapređenju stanja u području i dodatni korak ka standardizaciji LCA analiza u području proizvodnje podnih obloga. Verifikacija je realizirana kroz studiju slučaja utemeljenog na realnom industrijskom postrojenju za proizvodnju PVC podnih obloga.The production of floor coverings, in terms of environmental impact, is a very complex process due to a large number of influential parameters – various chemical emissions, inevitability of waste, a great number of influential physical quantities such as noise and vibration, dust and radiation, energy consumption, recyclability, etc. Interest in the application of LCA within the production of floor coverings has been present for almost two decades and is intensely increasing. During this period different approaches and attempts of LCA implementation have been recorded in this broad field. This paper presents a general model for environmental impact assessment of the production process of floor coverings based on LCA. The developed model represents a contribution to the improvement and a further step towards the standardization of LCA analysis in this field of floor covering production. Verification has been carried out through a case study based on an industrial facility which produces PVC floor coverings

A Novel Method for Determination of Kinetic Friction Coefficient using Inclined Plane

Presented in this paper is the theoretical background for a novel method for determination of kinetic friction coefficient. The method is based on the equation of movement of a rigid body along an inclined plane and has not been previously discussed in literature. According to the theoretical results presented in this paper, mean kinetic friction coefficient can be determined based on the time it takes a rigid body to travel a distance along an inclined plane. Experimental results show that the mean kinetic friction coefficient increases with increasing mean sliding velocity, i.e. with decreasing sliding time. Increasing sliding velocity increases deviation of friction coefficients. This method also allows the determination of energy consumed due to friction along the travelled distance. Increasing mean kinetic friction coefficient and mean sliding velocity increases energy consumed due to friction. Practical calculation requires application of the distance law, which, in turn, requires accurate measurement of the sliding time and distance

AN INTEGRATED APPROACH FOR DESIGN AND MANUFACTURE OF PLASTIC PRODUCTS

The aim of this paper is to present an integrated design procedure for plastic part development and manufacture. Reverse engineering (RE), re-engineering (ReE) and mold design have been incorporated to infuse agile characteristics in the proposed design and development process. The integration of RE and ReE presented in this paper accelerate the design process and provide information necessary for complete injection molding process of plastic parts. The purpose is to create a new object geometrically similar to the existing object. The new object must have better mechanical properties and more favorable geometry from the standpoint of mold ability. This paper also, describes a methodology for quality geometry check of the manufactured part that is need for verified the used integrated CAD/CAE technologies

Intelligent design and optimization of machining fixtures

U radu je predstavljen integralni sustav za projektiranje i optimizaciju konstrukcije naprava za strojnu obradu. Dio sustava za optimizaciju omogućuje, s jedne strane, određivanje optimalnih pozicija elemenata za baziranje i stezanje kako bi se postigla potrebna točnost i kvaliteta obrađene površine izratka, a s druge strane, generiranje konstrukcije naprava bez kolizija. Dio sustava za projektiranje osigurava izbor pojedinih elemenata naprava na osnovi prethodno definiranih produkcijskih pravila. Prilagođeni kriteriji izbora definirani su za elemente za baziranje, elemente za stezanje, elemente za vođenje alata, elemente za podešavanje položaja alata, elemente tijela naprava, elemente za povezivanje i nadogradne elemente. Sustav je baziran na geometrijskim karakteristikama i karakterističnim obilježjima djela, kao i dodatnim informacijama o obradi i informacijama iz tehnološkog procesa. Sustav je razvijan za operacije tokarenja, bušenja, glodanja i brušenja koje se izvode na rotacijskim i prizmatičnim radnim predmetima. U radu su djelomično prikazani izlazni rezultati razvijenog sustava. Na kraju rada dani su odgovarajući zaključci i istaknuti mogući pravci daljih istraživanja.This work presents an integral system for machining fixture layout design and optimization. The optimization module of this system allows determination of optimal positions of locating and clamping elements, which provides required accuracy and surface quality, while at the same time guarantees design of collision-free fixtures. The design module performs selection of required fixture elements based on a set of predefined production rules. Adequate criteria for the selection of fixture elements are defined for locating, clamping, tool guiding, and tool adjustment elements, as well as for fixture body elements, connecting elements and add-on elements. The system uses geometry and feature workpiece characteristics, as well as the additional machining, and process planning information. It has been developed to accommodate machining processes of turning, drilling, milling, and grinding of rotational and prismatic workpieces. A segment of output results is also shown. Finally, conclusions are presented with directions for future investigation

A comparative analysis of the corrosive effect of artificial saliva of variable pH on DMLS and cast Co-Cr-Mo dental alloy

Abstract: Dental alloys for direct metal laser sintering (DMLS) are available on the market today, but there is little scientific evidence reported on their characteristics. One of them is the release of ions, as an indicator of the corrosion characteristics of a dental alloy. Within this research, the difference in the elution of metals from DMLS and cast (CM) samples of Co-Cr-Mo dental alloy in saliva-like medium of three different pH was examined by inductively-coupled plasma mass spectrometry (ICP-MS). The obtained results show that the metal elution in artificial saliva from the DMLS alloy was lower than the elution from the CM alloy. The release of all investigated metal ions was influenced by the acidity, both from the DMLS and CM alloy, throughout the investigated period of 30 days. The change in acidity from a pH of 6.8 to a pH of 2.3 for the cast alloy led to a higher increase of the elution of Co, Cr and Mo from CM than from the DMLS alloy. The greatest release out of Co, Cr and Mo was for Co for both tested alloys. Further, the greatest release of all ions was measured at pH 2.3. In saliva of pH 2.3 and pH 4.5, the longer the investigated period, the higher the difference between the total metal ion release from the CM and DMLS alloys. Both alloys showed a safe level of elution according to the ISO definition in all investigated acidic environments