1,410 research outputs found
From 3D Models to 3D Prints: an Overview of the Processing Pipeline
Due to the wide diffusion of 3D printing technologies, geometric algorithms
for Additive Manufacturing are being invented at an impressive speed. Each
single step, in particular along the Process Planning pipeline, can now count
on dozens of methods that prepare the 3D model for fabrication, while analysing
and optimizing geometry and machine instructions for various objectives. This
report provides a classification of this huge state of the art, and elicits the
relation between each single algorithm and a list of desirable objectives
during Process Planning. The objectives themselves are listed and discussed,
along with possible needs for tradeoffs. Additive Manufacturing technologies
are broadly categorized to explicitly relate classes of devices and supported
features. Finally, this report offers an analysis of the state of the art while
discussing open and challenging problems from both an academic and an
industrial perspective.Comment: European Union (EU); Horizon 2020; H2020-FoF-2015; RIA - Research and
Innovation action; Grant agreement N. 68044
Virtual reality based creation of concept model designs for CAD systems
This work introduces a novel method to overcome most of the drawbacks in traditional methods for creating design models. The main innovation is the use of virtual tools to simulate the natural physical environment in which freeform. Design models are created by experienced designers. Namely, the model is created in a virtual environment by carving a work piece with tools that simulate NC milling cutters.
Algorithms have been developed to support the approach, in which the design model is created in a Virtual Reality (VR) environment and selection and manipulation of tools can be performed in the virtual space. The desianer\u27s hand movements generate the tool trajectories and they are obtained by recording the position and orientation of a hand mounted motion tracker. Swept volumes of virtual tools are generated from the geometry of the tool and its trajectories. Then Boolean operations are performed on the swept volumes and the initial virtual stock (work piece) to create the design model.
Algorithms have been developed as a part of this work to integrate the VR environment with a commercial CAD/CAM system in order to demonstrate the practical applications of the research results. The integrated system provides a much more efficient and easy-to-implement process of freeform model creation than employed in current CAD/CAM software. It could prove to be the prototype for the next-generation CAD/CAM system
Advanced Process Planning for Subtractive Rapid Prototyping
This paper presents process planning methods for Subtractive Rapid Prototyping, which deals with
multiple setup operations and the related issues of stock material management. Subtractive Rapid
Prototyping (SRP) borrows from additive rapid prototyping technologies by using 2½D layer based
toolpath processing; however, it is limited by tool accessibility. To counter the accessibility problem,
SRP systems (such as desktop milling machines) employ a rotary fourth axis to provide more complete
surface coverage. However, layer-based removal processing from different rotary positions can be
inefficient due to double-coverage of certain volumes. This paper presents a method that employs STL
models of the in-process stock material generated from slices of the part along the rotation axis. The
developed algorithms intend to improve the efficiency and reliability of these multiple layer-based
removal steps for rapid manufacturing.Mechanical Engineerin
Rolling Shutter Stereo
A huge fraction of cameras used nowadays is based on
CMOS sensors with a rolling shutter that exposes the image
line by line. For dynamic scenes/cameras this introduces
undesired effects like stretch, shear and wobble. It has been
shown earlier that rotational shake induced rolling shutter
effects in hand-held cell phone capture can be compensated
based on an estimate of the camera rotation. In contrast, we
analyse the case of significant camera motion, e.g. where
a bypassing streetlevel capture vehicle uses a rolling shutter
camera in a 3D reconstruction framework. The introduced
error is depth dependent and cannot be compensated
based on camera motion/rotation alone, invalidating also
rectification for stereo camera systems. On top, significant
lens distortion as often present in wide angle cameras intertwines
with rolling shutter effects as it changes the time
at which a certain 3D point is seen. We show that naive
3D reconstructions (assuming global shutter) will deliver
biased geometry already for very mild assumptions on vehicle
speed and resolution. We then develop rolling shutter
dense multiview stereo algorithms that solve for time of exposure
and depth at the same time, even in the presence of
lens distortion and perform an evaluation on ground truth
laser scan models as well as on real street-level data
A Method of Rendering CSG-Type Solids Using a Hybrid of Conventional Rendering Methods and Ray Tracing Techniques
This thesis describes a fast, efficient and innovative algorithm for producing shaded, still images of complex objects, built using constructive solid geometry ( CSG ) techniques. The algorithm uses a hybrid of conventional rendering methods and ray tracing techniques. A description of existing modelling and rendering methods is given in chapters 1, 2 and 3, with emphasis on the data structures and rendering techniques selected for incorporation in the hybrid method. Chapter 4 gives a general description of the hybrid method. This method processes data in the screen coordinate system and generates images in scan-line order. Scan lines are divided into spans (or segments) using the bounding rectangles of primitives calculated in screen coordinates. Conventional rendering methods and ray tracing techniques are used interchangeably along each scan-line. The method used is detennined by the number of primitives associated with a particular span. Conventional rendering methods are used when only one primitive is associated with a span, ray tracing techniques are used for hidden surface removal when two or more primitives are involved. In the latter case each pixel in the span is evaluated by accessing the polygon that is visible within each primitive associated with the span. The depth values (i. e. z-coordinates derived from the 3-dimensional definition) of the polygons involved are deduced for the pixel's position using linear interpolation. These values are used to determine the visible polygon. The CSG tree is accessed from the bottom upwards via an ordered index that enables the 'visible' primitives on any particular scan-line to be efficiently located. Within each primitive an ordered path through the data structure provides the polygons potentially visible on a particular scan-line. Lists of the active primitives and paths to potentially visible polygons are maintained throughout the rendering step and enable span coherence and scan-line coherence to be fully utilised. The results of tests with a range of typical objects and scenes are provided in chapter 5. These results show that the hybrid algorithm is significantly faster than full ray tracing algorithms
Impact of Heterogeneity on Production in Tidal Sandstone Reservoirs: Application to the Linnorm Field, Offshore Norway
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