Engineering is by no means a new concept...the basic idea and ingenious contraptions for
its application have been around for centuries, however emerging computer technologies are
now redefining and revolutionizing this age old discipline. For this research
project the term Reverse Engineering refers specifically to the creation of a copy or the
interpretation of a physical object as opposed to the reverse engineering of software,
materials, electronics, etc. In the broadest sense Reverse Engineering is the
utilization of manual or computer controlled devices to reproduce something in a tangible
form or a 3-D digital form. The process of Reverse Engineering an object through a
computer controlled device to obtain a 3-D digital model is commonly referred to as 3-D
digitizing or 3-D scanning. It's this particular aspect of Reverse Engineering that I have
focused on for this research.
Advances in 3-D
digital scanning technologies are beginning to redefine the logic of recreating an
existing part from scratch, even with a computer it can be compared to the copying of a
printed page by retyping it. In principle, 3-D scanning is similar to a number of
other technologies that quickly, accurately and cheaply record useful aspects of physical
reality. The unique aspect of 3-D scanning is that the 3-D digital representations
can be utilized in ways the original objects cannot. Digital representations
can be stored in, searched for, and retrieved from databases; transmitted electronically
over long distances; viewed on CRT's; used in computer simulations; manipulated and edited
in software programs; and used as templates for making electronic or physical copies.*
There are many different kinds of
digitizing technologies, ranging from manual touch-probe devices and coordinate-measuring
machines (CMM) to laser scanning systems, industrial CT scanners and medical x-ray
scanners that can obtain data from the interior of objects.* As with
everything each technology comes with its own set of strengths and limitations.
Almost all digitizing systems produce x,y,z coordinate data...the difficulty comes when
one tries to convert this data into a format that 3-D CAD software programs accept.
The difficulty of post processing scanned data is often underestimated...and contrary to
what many believe, it's a process that's anything but easy and automatic.
One of the main reasons for the difficulty
of working with 3-D digitized data is that CAD systems and 3-D digitizers define geometry
differently. In most CAD programs a straight line is defined by its start and end
points, while a digitizer places many points along these curves. For example,
an edge of a digitized model that's 3" long would contain not 2 but 150 points if the
resolution of the data is .02 "* To
make things even more difficult, the points rarely run in a straight line resulting in
somewhat jagged lines and this is not ideal for precision output. The ideal
situation would be to snap the points into a straight line but there aren't any Cad
packages that allow you to do this.* Simply put, CAD systems just weren't
designed to reposition clouds of point data. As advanced as this technology is it
still requires a highly skilled individual hours of post processing the point cloud data
into a functional and workable format.
Most 3-D digitizing systems are either a
non-contact device or one that uses a touch probe. Touch probes are the least
expensive, but they are manually operated. You must touch the object for every 3-D
point you want to produce. This makes it challenging and virtually impossible to
create 3-D computer models with high resolutions. Non-contact digitizing systems
are the only practical choice for high resolution scanning of mechanical parts. They
collect from 20 to more than 25,000 points per second and provide resolution of better
than .001-inch to .020-inch depending on the technology.* Laser digitizers have become the most popular
non-contact systems for most applications. They use a basic principle called
triangulation to determine the location of points in 3-D space. It works like
this: If light arrives on a surface from one direction, and if the light is seen
from another direction, the location of the point can be inferred.* This is how lasers and sensors work in harmony to create x /y/z
coordinates of points on the surface of an object.
Digitizing speed comes from the light
moving quickly across the surface as the sensors detect the location of the light.
The resolution comes from the distance between the points, which can be restricted by the
size of the illuminated area on the surface. Accuracy of the process comes from a
number of factors, including resolution, the system's optics and the proof of the
mechanical parts.* An object's characteristics can also impact
the accuracy of the data...dark or shiny surfaces will not be translated in 3-D digital
data as well as white, light gray or dull surfaces.
Making 3-D digitizing work is as much an
art as it is a science.* The scanning process itself requires expensive
equipment and an experienced operator let alone the expertise and patience needed to
endure the hours of post process editing needed to get an object from the scanning phase
to the finished 3-D digital model. Often it makes sense to use this technology but
sometimes it doesn't...so careful thought and selective decision making of the correct
scanning process should be exercised before taking on the inextricable challenges
associated with 3-D digitizing.
The colored asterix ( * ) within the above document represent footnotes. These footnotes, a
full bibliography of sources and a list of individuals who helped facilitate the
production of this research can be viewed on the credits page of this web site.