=Paper=
{{Paper
|id=Vol-2533/paper25
|storemode=property
|title=Technologies of 3D-prototyping of Objects
|pdfUrl=https://ceur-ws.org/Vol-2533/paper25.pdf
|volume=Vol-2533
|authors=Natalia Lotoshynska,Anatoliy Kovalchuk,Ludmila Mayik,Volodymyr Mayik,Christine Strauss,Nataliia Melnykova
|dblpUrl=https://dblp.org/rec/conf/dcsmart/LotoshynskaKMMS19
}}
==Technologies of 3D-prototyping of Objects==
https://ceur-ws.org/Vol-2533/paper25.pdf
Technologies of 3D-prototyping of Objects
Natalia Lotoshynska 1 [0000-0002-6618-0070], Anatoliy Kovalchuk 1 [0000-0001-5910-4734],
Ludmila Mayik 2 [0000-0001-8552-0942], Volodymyr Mayik 2 [0000-0002-6650-2703],
Christine Strauss 3 [0000-0003-0276-3610] and Nataliia Melnykova 1 [0000-0002-2114-3436]
1 Lviv Polytechnic National University, Lviv, Ukraine,
natlot@ukr.net, akm0519@gmail.com, melnykovanatalia@gmail.com
2 Ukrainian Academy of Printing, Lviv, Ukraine,
ludmila_maik@meta.ua
3
Department of Electronic Business, University of Vienna,
Vienna, Austria
christine.strauss@univie.ac.at
Abstract. The innovative trends of development of 3D modelling and printing
technologies have been analysed. The available methods of manufacturing
computer 3D models of real objects have been studied. Using the results of the
conducted research, the optimal technical characteristics of the component
devices and environments have been summed up, provided that the process of
creating 3D models is of high quality.
Keywords: 3D-technologies, 3D model, photogrammetry.
1 Introduction
The modern world is on the verge of scientific progress. Science and technology are
developing very fast and every day researchers are demonstrating new discoveries.
One of the scientific breakthroughs is the field of 3D technology, the level of progress
of which has increased significantly lately.
3D printing technology is already being used in a large number of areas of human
activity [1]. For example, medicine has developed the first 3D printers to print
orthopedics and surgery items, and new areas of application of these technologies
emerge every year, including the organ printing [2]. More often, this technology is
being used in industry. For example, the company Boing already uses 3D printing
technology to make and design their engines. Researchers at the University of
Southampton were able to produce a drone on a 3D printer. With the emergence of
new 3D printer capabilities and the use of a variety of materials, the prospect of using
3D technology is emerging in printing industry as well. For example, today there are
attempts to produce stamps for embossing and other technologies. By using 3D
printing technology, one can create an alternative to congreve stamping. Another
Copyright © 2019 for this paper by its authors. Use permitted under Creative Commons License
Attribution 4.0 International (CC BY 4.0)
2019 DCSMart Workshop.
interesting way is to use this printing technology in the design of printing products,
namely to create voluminous decor details for both covers and book blocks, such as
children's books. In addition, due to the fact that this technology now allows printing
of a layer of 0.1 mm thickness, it is possible to create voluminous illustrations in
books for people with visual problems [3].
Ukrainian and foreign scientists study the use of 3D technologies in various areas
of human activity. The publications of foreign scientists are devoted to the study of
the impact of 3D printing technology on innovative development. In particular, such
issues were studied by S. Bekhtold, A. Gurko, K. Jewell, B. Deporter, D. Mendis, D.
Kolesnikov, V. Smirnov, S. Tolkachev, B. Tokarev. There are works of domestic
scientists: H. Androschuk, A. Hrechko, D. Dubov, O. Kronda, S. Chernyshov, O.
Stefan and others [4]. However, the versatility and complexity of the problem requires
further scientific, technical and economic research, because 3D printing technology is
promising [5]. The main advantages are the creation of complex internal structures of
the object, the non-waste production, the ability to combine different materials, etc. It
allows one to reduce the time and cost of creating bulky products that is not always
possible or profitable to produce with other technologies [6, 7].
A model is required for printing, and there are many ways of obtaining it today.
However, the two most popular ones are: manual modelling of objects in editing
programs and scanning of required objects using a 3D scanner with further processing
in the same editors. One way or another prevailed at different time. It depended on the
emergence of new digitalization technologies, visualization algorithms, and new
software that made it easier and more efficient to process 3D objects [7, 8].
Nowadays it is possible to say that scanning and modelling are equally popular, but
this equality is gradually diminishing, due to the constant improvement of 3D
scanning technology [8]. In addition, the average user does not have the skills of 3D
modelling; it requires a theoretical and practical knowledge base and experience.
Therefore, you can use the three-dimensional object scanning method to simplify the
task and save the time. The only problem is that creating a high-quality 3D model
requires the use of professional 3D scanners, the costs of which are quite high [8, 9].
However, it is possible to create a simple, budget analogue of a 3D scanner
independently. Using this kind of 3D modelling one cannot expect very high quality
and accuracy, but if the details are not critical, then budget 3D scanning can be a
solution. In order to maximize the quality of a scanned model and successful
prototyping, it is important to pay attention to the specifications and compliance of
the scanner components, to control all the important factors.
Another breakthrough in computer modelling is the development of 3D models
with the help of still photographs using a digital camera or any phone camera to
capture real-world objects as fully textured 3D models. This method is ideally suited
for objects of complex shapes, when you need photographic similarity to the object,
as well as for creating 3D models of people with minimal material and time costs.
The main objective of this work was to research 3D printing technologies and
available methods of making computer 3D models of real objects. Based on the
research, various prototyping methods have been implemented and physical objects
have been subsequently obtained using 3D printing technology.
2 Technologies of 3D-prototyping of objects
2.1 Creating a virtual model by 3D contactless scanning method and its
physical prototype by 3D printing technology
The contactless scanning method has been selected for the implementation of the
work. Contactless scanners have two types of scanning: passive and active. An active
3D scanner has been selected that has the ability to generate its wave signal:
directional light, laser, sound, infrared. The principle behind this method is based on
measuring the distance from the scanner to the points of the scanning object using the
triangulation method. The emitter and the detector (camera) are at different levels,
and the beam is projected at a certain angle relatively to the detector. Thus, a triangle
is formed, the basis of which is the emitter and the camera, and the vertex is the point
on the object surface. One can calculate the angle between the projected and reflected
beams by shifting the reflection from this point, which is formed on the camera
sensor, and one can calculate the distance to the point of the object, knowing the angle
and the length of the base.
The main software is DAVID Laserscanner application [10], which allows one to
scan and digitize objects using a manual laser module, a calibration angle, and a
camera. The application generates 3D data in real time and displays it on a computer
screen. There are different versions of the application that are suitable for different
scanning technologies. There is DAVID Laserscanner Starter Kit available, which
includes: four-dimensional calibration sheets, panels for sheet fastening, a high-
resolution Logitech C615 webcam, a camera stand, a red laser (650 nm) with variable
focus and battery, and necessary software.
Stages of creating a virtual model by 3D scanning method and its physical
prototype by 3D printing technology:
1. Preparing the object for scanning. Scanning technologies have their
restrictions. Usually, these restrictions apply to scanning objects, because optical
technologies do not support the processing of transparent, mirror and shiny objects.
This is because the wave (in this case, a laser line) must be reflected from the object
so that the camera can capture it, process the information about the distance and
construct the object on a computer.
2. Camera calibration. The camera is calibrated using special calibration sheets at
90 degrees to each other. The type of such sheets depends on the software used for
scanning. DAVID Laserscanner 3.4.0.3008 is used, and templates of calibration
surfaces in PDF and CDR ready-to-print file formats are available. The sheet size is
selected based on the size of the scanned object. The height of the scanned object
should be 1.5-2 times smaller than the height of the calibration angle.
A4 format has been selected and the sheets have been placed on pre-prepared
wooden panels connected at right angles. The angle of 90 degrees is required to
refract the laser line correctly, which will be projected onto the object that is located
in front of the angle. One also need to make sure that there is nothing glossy on the
surface to prevent unnecessary interference with scanning.
The camera should capture the calibration markers and the markers should be
clearly visible during the calibration process. The sheets indicate the length of the
Scale line to be measured and input into the application. If the calibration process is
successful, the application gives the corresponding message "Calibration successful"
and marks the markers with green crosses. After the calibration, it is important that
the camera does not changes its position.
3. Object scanning. A laser module is used for scanning by the selected method
that projects not a point, but a line. Two red lasers have been used: one purchased and
one created independently using a laser pointer and a scanner unit. The scanner unit is
an optical lens, which is a glass cylinder that captures a 90-degree laser beam and
refracts it to form a line. If necessary, the refraction angle can be calculated
depending on the lens diameter.
Logitech C270 webcam with autofocus has been used as the detector, a device that
calibrates and captures the laser reflection. The matrix resolution is 3MP. The matrix
type is CMOS. Video frame rate is 30 frames per second. The interface is USB 2.0.
The camera image should be very dark when scanning. To do this, it is necessary
to minimize the light in the scanning environment and change the corresponding
camera settings so that only the laser line is visible.
One must position the object so that it is in the corner, in front of the calibration
sheets. Calibration markers should remain unobstructed around the object. When the
scanning process is started and the camera captures the data, one sees the object in
different colours. This is a depth map (see Fig. 1). As it is known, the wavelength of
the red visible spectrum is the largest and the purple visible spectrum is the smallest.
Here, the object is coloured on the same principle: the parts closest to the camera are
purple, the farthest ones are red. Other colours have intermediate values.
Fig. 1. A camera image when scanning in a depth map mode
The object scanning should be carried out from different view directions. That is,
having processed one side of an object, it is necessary to store the received image,
turn an object and start scanning again. The more scanned sides you get, the better is
for creation of a further model. Scanned sides must overlap each other by parts. That
is, each next scan must contain a part of the previous one. It is needed for the next
stage of gluing a model together.
An angle between the area of laser light and the camera must not be too low,
otherwise the refraction of the line will be insufficient and the application will report
the following: Intersection of angle too low. There are also other messages concerning
errors: Laser line not detected (too short/too weak?) – when a laser line is too short, or
too weak, or it is absent at all. Laser line not detected on the left (right) side – if a
laser line is not detected on the left (right) side of calibrated angle. That is, a laser line
shifted aside, so it is not detected on both sides, or a line is not projected horizontally
but with a curve. It can also mean that an object overlap calibrated markers on the left
(on the right) and the camera cannot detect a laser. Therefore, it is necessary to pay
attention to this and to control the process of scanning.
4. Adjustment and merging of scanned parts to get a complete model.
Adjustment of scans is a process of setting scanned parts into corresponding places,
so to join them into an integral model. For this purpose, the applications DAVID
Laserscanner and Meshlab are used. Meshlab is an application to process unstructured
three-dimensional forms. The system is aimed at processing three-dimensional
models, obtained by 3D scanning, and has tools for editing, cleaning, correction,
verification, rendering, and converting of a processed model into a necessary format.
DAVID Laserscanner application performs scans cleaning from large unnecessary
elements and adjustment by automatic facilities, and scans, which the application is
not able to process itself, are adjusted manually in Meshlab. There is also possibility
of manual substitution in DAVID Laserscanner, but it is designed on the total manual
control, but Meshlab allows adjusting scans on intersection points (see Fig. 2).
Choose a part of the model already located on its place and add another one to it,
marking with points basic areas that coincide. Thus, accuracy of correct substitution
increases.
Fig. 2. Joining of scans on intersection points in Meshlab
Gluing of the model itself has been carried out using DAVID Laserscanner
application. The program merges the adjusted parts in one three-dimensional model,
interpolating places with breaks or sharp transitions. After that the model is
transformed in OBJ format and passes to the next stage – editing.
5. Processing, "cleaning" of a model. Almost in all cases, after scanning and
gluing, a model needs a processing stage. It is possible, at this stage, to remove holes,
smooth out a surface, simplify general structure or remove unnecessary elements. All
this is performed with 3D design software. For project fulfilment, the editor Blender
has been chosen, as it is on free access. Another advantage of Blender is that it is
adapted for 3D printing. There is a plugin to test a model for fitness to printing, as
well as possibility to import into STL and OBJ formats.
6. Preparation of a model to 3D printing. An object cannot be printed at once
after simulation. Every model that is sent to a 3D printer must pass over the
preparation stage. Preparation of a model was also performed with the application
Blender, using a special plugin, and transformed a model into a necessary format.
Program-slicers operate with the STL file format (stereolitography). Therefore, a
model for printing [11] must be stored just in this format.
7. 3D printing. On this stage, a model first passes over preparation with a
program-slicer, where it is split into layers that are formed during printing by a
material. Simplify3D application was used for printing of this model.
On the basis of the conducted researches, the following conclusions as to optimal
technical specifications of the scanner parts and scanning environment have been
made:
The minimum illumination in a room during scanning. This is essential,
especially, if not too powerful, and thus, not too bright laser is used. For a camera-
detector to recognize a projected laser line better, contrast conditions are required, so
that another part of an image remains dark (even black), that is to minimize
illumination in the room.
Webcam with resolution capability of 640х480 and noises compensation. A
required resolution capability is calculated depending on the size of an object. At
640х480 resolution capability, an object is set in such a way that covers
approximately 300х350 pixels. A pixel is one 3D dot. Thus, we obtain more than 100
thousand 3D dots, but just only on one side of an object. Therefore, 640x480 is a
sufficient resolution capability for ordinary objects scanning. Compensation of noises,
in fact, is more important feature for cameras.
Manual focus and quality lenses of a camera are also important characteristics.
It is possible to use cameras with autofocus, but it is more convenient to have a
manual focus. In this case, it is possible to adjust the camera to various environments.
As to lenses, it is sufficient to use glass instead of plastic lenses. It will improve the
outcome of scanning.
Laser with power of 5mW, and 30° or 60° module that generates a line. Power
of a laser, as it was already mentioned above, depends on the environment of
scanning. If a room is not dark enough, then a laser must be more powerful. This
condition is also required at dark objects scanning (black, is known, does not reflect,
but absorbs light). Laser scanning is also possible to perform using a laser pointer, i.e.
its projection will be in a form of a dot. However, a laser line instead of a laser dot is
used to speed up the process. It is achieved due to the scanner unit (cylindrical lens)
or the system of mechanical scanner unit (a mirror that turns around). The angle of the
module depends on an object that is scanned. In most cases, an angle must be not less
than 30 degrees, if the angle value is lower, then the line that is projected will be
undersized to cover an object.
A laser line must be as thin as possible, especially, if an object of scanning is of
small size. The thinner the line is, the less noises it produces that prevent successful
scanning. Thus, a model surface will be smoother and more detailed.
Sheets for calibration, must be located at an angle of exactly 90° and with
distinctly printed calibration markers.
Triangular angle (angular inclination of a laser in relation to an object) should
be about 30°. If to scan at a lower angle, then refraction of a laser line will be too little
to recognize the surface of a scanned object.
2.2 Research and creation of 3D model using photogrammetric method
For implementing the experimental part, a method of the camera rotation around the
object and the object rotation around its axis has been used, since this method is
suitable and does not require special expensive equipment. Sony Cyber-Shot DSC-
W290 camera was used for the study.
For the research part, 3 objects, different in shape, texture, color and size had been
chosen beforehand. Based on the research, and considering all the mistakes, a
complete 3D model was created. The creation process can be divided into the
following stages:
1. Object preparation for the photography process.
Not all the objects can be displayed when creating a 3D model by overlaying
photos. It can be difficult to work with transparent, translucent, shiny, or mirror
objects, because the camera cannot catch their points clearly enough. In this case, it is
necessary to mask the surface with matt paint applied to the object. If the object is of
monochrome, little textured or plain, it will be difficult for the application to identify
which side the object was taken from. For this purpose it is necessary to apply special
signs (markers) for the subject of shooting (see Fig. 3), which will be further marked
in the application and numbered.
Fig. 3. Applying of the markers on the object
2. Preparation of the photographic zone.
To keep the photo sharp, you need to fix the digital camera with a tripod. Lighting
is one of the key factors for quality photography, so the next step is to create a light-
box. It has a white monochrome background and also mixes and scatters directional
light, which is formed by light fixtures, creating a drawing of the subject without any
shadow.
3. Camera calibration.
The camera should be positioned in such a way when the subject occupies the
largest possible area in the shot. When shooting small objects, it will be better to
make photos by the camera equipped with a macro lens that provides high image
clarity and detailing. In the absence of a macro lens, it is possible to use a lens with
the fixed focal length. The automatic white balance mode must be disabled before
shooting to ensure that it is the same in all shots.
It is also necessary to choose the mode – the aperture priority (A). Close the
aperture closer to the minimum value from f5.6 to f11 (depending on the subject) to
avoid loss of photo sharpness. The smaller is the aperture, the greater the depth of
area will be. Accordingly, the exposure will last more. ISO sensitivity is set to a
minimum value (50-100 ISO) to get the best possible picture quality.
4. Photo shooting.
The process of photo shooting can be performed in two modes:
It is performed by rotating the model (manually or using a special rotary table)
– such shooting is most convenient to perform in a light-box, where diffuse
light is required.
It is performed in such a way, when the photographer with the camera moves
around the model.
In both modes, photos are taken, approximately, after every 10 degrees, so at one
height nearly 30-36 shots are taken. In the case of complex models, photo shooting
should be repeated from a higher or lower position to fully cover the entire model.
5. Photo processing.
It is not recommended to cut photos, change their size [12] any resolution by any
editing program. At this point, extra points that are not relevant to the object are
masked. You can do this in Adobe Photoshop or in applications, in which a 3D model
can be created (such as PhotoScan).
6. Modeling a 3D object.
6.1. In PhotoScan application we load photos, select "Align Photos" from the
menu. The application finds common points of photos and determines such camera
parameters as status, orientation, focal length, distortion settings and more. At this
point, we obtain a sparse cloud of common points in the 3D space of the model and
data on the status and orientation of the cameras.
This result is used for visual evaluation of the photo alignment quality and further
creation of a 3D model based on a sparse point cloud. When you receive a point
cloud, you need to remove the extra points with the removal tool.
6.2. Now one needs to create a dense point cloud. To do this, we choose the menu
item "Create a dense point cloud". When this stage is complete, the contours of the
model are clearly visible and the extra points can be removed again.
6.3. Then we go to the model creation and select the menu item "Create Model".
As a result, we obtain a three-dimensional polygonal model describing the shape of
the object, based on a dense points cloud.
After making a model, sometimes it is necessary to edit it. In Photoscan application
it is possible to make such changes as removing of the isolated model components,
filling the holes, and so on.
The 3D model obtained by the scanning method usually has an excessive
polygonality. Polygonality reduction can be done with the help of Autodesk 3Ds Max.
When one switches to frame mode, in the application one can see an increase in the
number of vertices in the 3D model for several times. To do this, we call the
ProOptimiser modifier in the modifier stack.
Click on the Calculate button, and then the number of vertices in the model will be
calculated. Decrease them by a percentage where 100% is the current number of
vertices in the model. You must reduce the number of polygons until the shape of the
object is affected.
In this case, it was reduced to 20% of the total number of vertices. A smaller
percentage showed the deformation of the object. For further work, it is recommended
to transfer the 3D model into Editable Poly.
6.4. The next menu item is Texture Creation. After processing, we get a finished
model that can be exported for viewing with Adobe Acrobat or Adobe Reader. It can
also be exported for further processing of the model in 3D .obj editors, in particular in
3Ds Max.
Another type of object texturing is working with Autodesk 3Ds Max application.
For this type, we pre-export the 3D model from PhotoScan in .obj format and a
texture by a separate .jpeg file. Next, we choose the type of Bitmap material into
which we upload a file with our previously stored texture and transfer it to the object.
7. Model correction. If necessary, clean the model in Autodesk 3Ds Max (see
Fig.4). In this case, due to the complex shape of the object, unnecessary polygons
were modeled. In EditPoly - Polygon mode, the selection tool picked unnecessary
polygons and removed them.
Fig.4. Correction of the 3D model
The result is the creation of a 3D model using a digital machine, which can be used
both electronically and to prepare the file for 3D printing. The photogrammetric
method was chosen for this. This method allows determining the spatial coordinates
of an object on its image, made from different angles. As a result of overlapping
photos in PhotoScan a three-dimensional model with the most realistic effect has been
created.
Based on the conducted researches, it has been concluded about the optimal
technical characteristics of the device and the conditions of photography:
No usage of transparent, translucent, shiny or mirror objects, or cover these
objects with matte paint and subsequently apply a texture to the software. In the
case of small textured objects, special marks must be affixed to them.
The object should be on a solid background.
It is necessary to provide a uniform diffusion illumination, with the help of a
photographic zone – lightbox, creating a shadowless image of the object. If the
subject is photoshoot in the natural conditions, it should be done in cloudy
weather.
To increase the sharpness of the photo, you need to lock the camera with the help
of a tripod. The object should occupy the largest possible area in the frame.
A camera with a macro lens or fixed focus lens.
Enable manual white balance mode. Set aperture priority (A). Close the aperture
closer to the minimum value, from f5.6 to f11 (depending on the subject).
Accordingly, the shutter speed will be longer. The ISO sensitivity is set to a
minimum value (50-108.0 ISO).
The object is photographed rotating every 10 degrees (30-36 shots). In the case of
complex models, repeat shooting from a higher or lower position to fully cover the
entire model.
It is not recommended to crop photos and resize them by any editor.
Reduce the polygonality of the object to about 20% of the total number of
vertices, depending on the model. Decrease the number of polygons until the
appearance of the object is affected.
3 Conclusion
3D printing technologies and available methods of making computer 3D models of
real objects have been researched. Different prototyping methods have been
implemented, and physical objects have been subsequently acquired by 3D printing.
The result is the development of 3D scanning hardware, which was the basis for
the development of a method of fixation of physical objects to further processing the
image in the 3D modeling software environment and 3D printing with a 3D printer.
For the project of 3D scanner development, the method of contactless active laser
scanning has been chosen. A linear laser module that is projected onto the object has
been used. Using a special calibration angle (the type of calibration angle is selected
in accordance with the scanning software), the webcam, which further captures the
reflected laser beams, is calibrated and the specialized DAVID-Laserscanner
application that calculates 3D coordinates from the intersection of the laser plane and
visible rays from the camera, a copy of the physical object in the form of a virtual
three-dimensional model is built.
Based on the conducted researches, the conclusions about the optimal technical
characteristics of the components of the scanner and the scanning environment are
made. A methodology for creating a 3D model using a digital device has been
developed, which can then be used both electronically and to prepare the file for 3D
printing. This method allows determining the spatial coordinates of an object by its
images taken from different angles. PhotoScan creates a three-dimensional model
with the most realistic effect.
Using the data of the conducted researches, it is concluded that the optimal
technical characteristics of the component devices and environments provide the
process of creating 3D models of the highest quality.
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