Non-contact Reverse Engineering Research Articles

Studies on the Numerical Control Programming for Multi-Axis Machining of Turbomolecular Pump Rotor

Turbomolecular pumps (TMPs), boasting advantageous high pumping rates, stability, and cleanliness, have been widely used in the semiconductor and photoelectric industries. In the aviation industry, the lightweight rotors of turbomolecular pumps can enhance the performance of generators. With technological advancements and increased industrial performance demands, various designs for turbomolecular pump rotors utilizing twisted and curved blade surfaces have been proposed. This increase in complexity runs parallel with machining difficulties. Contact and noncontact reverse engineering equipment was used to reconstruct a computer-aided design (CAD) model of turbomolecular pump rotors. The machining of thin and long blades, cutting tool arrangement, and toolpath was planned. Postprocessing was used to convert the toolpath into numerical control (NC) programming codes, which were combined with solid model cutting simulation software to verify the efficacy of the generated machining NC program for turbomolecular pump rotors. A five-axis horizontal machining center (CK type) with aluminum alloy AL6061-T6 was used to conduct actual machining tests measuring the efficiency of the machining methods. The rapid prototyping (RP) blocks can be creatively used as a jig and stuffed between the blades to suppress the chatter problem during processing, and the roughness of the surface of the blades can be reduced from 4.4 μm to 1.3 μm. The processed rotor can meet the flow test requirements, and the overall research can be used as a reference for the industry.

LASER AND MULTI-IMAGE REVERSE ENGINEERING SYSTEMS FOR ACCURATE 3D MODELLING OF COMPLEX CULTURAL ARTEFACTS

Abstract. The recent scientific and technical developments of reverse engineering methods and tools have broadened the possibilities of applications in the field of cultural heritage conservation. In this paper, two different non-contact reverse engineering systems were utilized for 3D data acquisition of a cultural heritage artefact. The object of interest is a 17th century wooden engraved ecclesiastical sanctuary ciborium. The requirement of the 3D model is to aid the art conservators for the preservation of the wooden material and the restoration of small damages and cracks in the engraved parts, thus requiring accuracy of the model in the order of sub-millimetre. In this work, a Faro Vantage laser tracker was employed along with the FARO Edge Arm. In addition, image-based modelling was also implemented with a large number of overlapping images acquired with a Canon EOS 6D camera and processed using the well-known Structure from Motion (SfM) method with an auto-calibration procedure. The digital data acquisition and processing procedures of the scanned geometry are described and compared to evaluate the performance of both systems in terms of data acquisition time, processing time, reconstruction precision and final model quality. Whilst models produced with laser scanning and image-based techniques is not a novel approach, the combination of laser tracking and photogrammetric data still presents limited documentation in the field of cultural artefact documentation mainly due to the extremely high cost of the laser tracking systems.

Effects of crown movement on periodontal biotype: a digital analysis.

Orthodontic treatment has important correlations with periodontal changes. Various mechanical and biological factors are involved in determining such changes, but anatomical and morphological variables, generally addressed as periodontal biotype, play a key role. In measurement of such modifications, digital and non-contact reverse engineering technologies may be of tremendous advantage. The aim of this study is to retrospectively evaluate, in a series of digitized dental casts, some of the parameters addressing periodontal biotype and correlate them to extent and direction of tooth movement. Pre- (T0) and post-treatment (T1) dental casts of 22 patients were scanned by 3Shape TRIOS 3® scanner. A number of variables (crown ratio, gingival margin position, gingival contour, papillae position, gingival scallop) were investigated and their variations calculated after digital measurements on single casts at T0 and T1, or after direct measurement (T1 vs T0) on the superimposition and alignment of digital models. Univariate and multivariate statistics were then performed. No significant correlation was detected between the sagittal or vertical movement of dental crown and displacement of the gingival margin. On the other hand, vestibular gingival contour resulted significantly altered by vestibular and extrusion movements. Further studies are needed to ascertain the differential effect of bone and soft tissue on such modifications. The relationship between orthodontic treatment and the periodontium overcomes the consideration of gingival recession and includes all the concepts of periodontal biotype with its characteristics. Digital technologies and non-contact reverse engineering techniques now available have the potential to allow a more precise definition of such a relationship.

Influence of thread shape and inclination on the biomechanical behaviour of plateau implant systems

ObjectiveTo assess the influence of implant thread shape and inclination on the mechanical behaviour of bone-implant systems. The study assesses which factors influence the initial and full osseointegration stages. MethodsPoint clouds of the original implant were created using a non-contact reverse engineering technique. A 3D tessellated surface was created using Geomagic Studio® software. From cross-section curves, generated by intersecting the tessellated model and cutting-planes, a 3D parametric CAD model was created using SolidWorks® 2017. By the permutation of three thread shapes (rectangular, 30° trapezoidal, 45° trapezoidal) and three thread inclinations (0°, 3° or 6°), nine geometric configurations were obtained. Two different osseointegration stages were analysed: the initial osseointegration and a full osseointegration. In total, 18 different FE models were analysed and two load conditions were applied to each model. The mechanical behaviour of the models was analysed by Finite Element (FE) Analysis using ANSYS® v. 17.0. Static linear analyses were also carried out. ResultsANOVA was used to assess the influence of each factor. Models with a rectangular thread and 6° inclination provided the best results and reduced displacement in the initial osseointegration stages up to 4.58%. This configuration also reduced equivalent VM stress peaks up to 54%. The same effect was confirmed for the full osseointegration stage, where 6° inclination reduced stress peaks by up to 62%. SignificanceThe FE analysis confirmed the beneficial effect of thread inclination, reducing the displacement in immediate post-operative conditions and equivalent VM stress peaks. Thread shape does not significantly influence the mechanical behaviour of bone-implant systems but contributes to reducing stress peaks in the trabecular bone in both the initial and full osseointegration stages.

Non-contact Reverse Engineering Modeling for Additive Manufacturing of Down Scaled Cultural Artefacts

In recent years, reverse engineering has achieved a relevant role in the cultural heritage field. The availability of 3D digital models of artefacts opens the door to a new era of cultural heritage: virtual museum creation, artefact cataloguing, conservation, planning and simulation of restoration, monitoring of artefacts subjected to environmental degradation, virtual reconstruction of damaged or missing parts, reproduction of replicas, etc. In this paper, two different non-contact reverse engineering scanning systems were utilized for 3D data acquisition of a cultural heritage artefact. The digital data acquisition and processing procedures of the scanned geometry have been illustrated and compared to evaluate the performance of both systems in terms of data acquisition time, processing time, reconstruction precision and final model quality. Finally, additive manufacturing technologies were applied to reconstruct a down scaled copy of the artefact.

Virtual reconstruction and performance assessment of an eroded centrifugal pump impeller

Emphasis is placed on the performance of a two-stage pump equipped with an eroded impeller. Non-contact reverse engineering technique is utilized to acquire the point data constituting the three-dimensional geometrical model of the eroded impeller. With computational fluid dynamics, both the operation performance of the pump and flow patterns adjacent to the eroded blade surface are obtained. For comparison, the corresponding undamaged impeller is investigated as well. Preferable fidelity of the approach of constructing geometrical model of the damaged impeller is substantiated. The mechanism underlying performance degradation of the pump with the eroded impeller is evidenced. Local flow patterns near the eroded area are featured by explicit irregularity. Furthermore, between the defective and the undamaged pumps, disparity in positions where cavitation occurs is negligible.

Development and evaluation of a digital dental modeling method based on grating projection and reverse engineering software

Statement of problemFor reasons of convenience and economy, attempts have been made to transform traditional dental gypsum casts into 3-dimensional (3D) digital casts. Different scanning devices have been developed to generate digital casts; however, each has its own limitations and disadvantages. PurposeThe purpose of this study was to develop an advanced method for the 3D reproduction of dental casts by using a high-speed grating projection system and noncontact reverse engineering (RE) software and to evaluate the accuracy of the method. Material and methodsThe methods consisted of 3 main steps: the scanning and acquisition of 3D dental cast data with a high-resolution grating projection system, the reconstruction and measurement of digital casts with RE software, and the evaluation of the accuracy of this method using 20 dental gypsum casts. The common anatomic landmarks were measured directly on the gypsum casts with a Vernier caliper and on the 3D digital casts with the Geomagic software measurement tool. Data were statistically assessed with the t test. ResultsThe grating projection system had a rapid scanning speed, and smooth 3D dental casts were obtained. The mean differences between the gypsum and 3D measurements were approximately 0.05 mm, and no statistically significant differences were found between the 2 methods (P>.05), except for the measurements of the incisor tooth width and maxillary arch length. ConclusionsA method for the 3D reconstruction of dental casts was developed by using a grating projection system and RE software. The accuracy of the casts generated using the grating projection system was comparable with that of the gypsum casts.

A new method to assess the accuracy of a Cone Beam Computed Tomography scanner by using a non-contact reverse engineering technique

AimToday Cone Beam Computed Tomography (CBCT) has become an important image technique for dento-maxilla facial applications. In the paper a new method to assess the geometric accuracy of these systems was proposed. It uses a free form benchmark model and a non-contact Reverse Engineering (RE) system. MethodThe test geometry chosen for this study was designed in such a way that it simulated human spongy bone, cortical bone, gingiva and teeth and it composed of removable free form parts. It was acquired with a high-resolution laser scanner (D700 Scanner – 3Shape, Denmark). The reference 3D surface models obtained with the laser scanner was compared with the 3D models that were created from a CBCT system (Scanora 3D – Soderex, Finland) and from a traditional Multi-Slice Computed Tomography (MSCT) scanner (LightSpeed VCT 64 Slice – General Electric, USA) at different reconstruction settings, using an iterative closest point algorithm (ICP) in Geomagic® software. ResultsThe comparison between the different pairs of CAD models clearly shows that there is a good overlap between the models. ConclusionsAlthough the results obtained in this study could lead to increase the use of CBCT for an increasing number of dental procedures, the publication of the European Commission guidelines represents a baseline on which the clinicians should rely heavily when considering the use of CBCT in their practice. Clinical SignificanceThe results of this research show that the accuracy of CBCT 3D models is comparable to MSCT 3D models.

A comparison between customized clear and removable orthodontic appliances manufactured using RP and CNC techniques

ObjectivesAim of the research is to compare the orthodontic appliances fabricated by using rapid prototyping (RP) systems, in particular 3D printers, with those manufactured by using computer numerical control (CNC) milling machines.3D printing is today a well-accepted technology to fabricate orthodontic aligners by using the thermoforming process, instead the potential of CNC systems in dentistry have not yet been sufficiently explored. Materials and methodsOne patient, with mal-positioned maxillary central and lateral incisors, was initially selected. In the computer aided virtual planning was defined that, for the treatment, the patient needed to wear a series of 7 removable orthodontic appliances (ROA) over a duration of 21 weeks, with one appliance for every 3 weeks. A non-contact reverse engineering (RE) structured-light 3D scanner was used to create the 3D STL model of the impression of the patient's mouth.Numerical FEM simulations were performed varying the position of applied forces (discrete and continuous forces) on the same model, simulating, in this way, 3 models with slice thickness of 0.2mm, 0.1mm (RP staircase effect) and without slicing (ideal case). To define the areas of application of forces, two configuration “i” and “i−1” of the treatment were overlapped.6 patients to which for three steps (3rd, 4th and 5th step) were made to wear aligners fabricated starting from physical models by 3D printing (3DP-ROA) and afterwards, for the next steps (6th, 7th and 8th step), aligners fabricated starting from physical models by CNC milling machine (CNC-ROA), were selected. ResultsFor the 6 patients wearing the CNC-ROA, it was observed a best fitting of the aligner to the teeth and a more rapid teeth movement than the 3DP-ROA (2 weeks compared to 3 weeks for every appliance).FEM simulations showed a more uniform stress distribution for CNC-ROA than 3DP-ROA. ConclusionsIn this research, 6 different case studies and CAD-FEM simulations showed that, to fabricate an efficient clear and removable orthodontic aligner, it is necessary to consider a compromise of several factors. A lower staircase effect (lower layer thickness) and a higher physical prototype accuracy allow a better control of tooth movement.

Accuracy evaluation of surgical guides in implant dentistry by non-contact reverse engineering techniques

ObjectiveIn the paper laser scanning was used to evaluate, by indirect methods, the accuracy of computer-designed surgical guides in the oral implant supported rehabilitation of partially or completely edentulous patients. Materials and methodsFive implant supported rehabilitations for a total of twenty-three implants were carried out by computer-designed surgical guides, performed with the master model developed by muco-compressive and muco-static impressions. For all cases the surgical virtual planning, starting from 3D models obtained by dental scan DICOM data, was performed. The implants were inserted on the pre-surgical casts in the position defined in the virtual planning. These positions were acquired by three-dimensional optical laser scanning and compared with the laser scans of the intraoral impressions taken post-operatively. ResultsThe comparison between the post-surgical implant replica positions and the positions in the pre-operative cast, for the five patients, shows a maximum distance in the range 1.02–1.25mm, an average distance in the range 0.21–0.41mm and a standard deviation in the range 0.21–0.29mm. SignificanceThe results of this research demonstrate accurate transfer of implant replica position by virtual implant insertion into a pre-operative cast and a post-operative cast obtained from impressioning. In previous studies the evaluation of the implant positions have required a post-surgical CT scan. With the indirect methods by laser scanning technique, proposed in the paper, this extra radiation exposure of the patient can be eliminated.

A novel approach for a complete 3D tooth reconstruction using only 3D crown data

Current methods to produce 3-dimensional complete tooth (enamel, dentin and pulp) models involve conversion from tomographic data. In the paper a novel approach to obtain the complete 3D reconstruction of a tooth starting from the only 3D crown information is described. Using as reference models, five human posterior molars derived from micro-computed tomography (CT) data, specific computer aided design (CAD) modeling procedures were developed to create, in a simplified way, the surfaces of enamel, dentin and pulp of the teeth, starting from the data of a molar acquired by a non-contact reverse engineering (RE) system. To evaluate the simplified model, finite element method (FEM) simulations were performed and compared. The results from FEM analysis confirm the general validity of the proposed approach. This method allows to generate an efficient complete 3D reconstruction of teeth with a good approximation of the shape, due to the small number of parameters to adjust, and requires little interaction from the user. The described method can be successfully adopted to generate detailed 3D CAD models of teeth starting only from the crown data, acquired by non-contact RE systems (structured-light scanners, laser scanners or intra-oral laser scanners). It could be quickly implemented for other dental or biomechanical applications without the use of more expensive CT and micro-CT.