3-D DIGITIZERS -- COMPUTER GRAPHICS WORLD MAGAZINE JULY ISSUE 1992
3-D DIGITIZERS: THIS ARTICLE WAS SCANNED FROM COMPUTER GRAPHICS WORLD
MAGAZINE JULY ISSUE 1992 Three-dimensional objects of all shapes and sizes
surround us, yet only a only a small fraction are stored in digital form.
Threedimensional digitizers enable you to copy these objects into a
computer. The computer model usually requires editing, bu the work is minor
compared to creating the object from scratch. Engineers use 3D digitizers
for reverse engineering of mechanical parts. Manufacturing professionals
apply them to the creation of new patterns for molded tooling and investment
casting. Medical specialists use 3D digitizers to digitize bones andother
anatomy for the development of prostheses and implants. Video production
experts use them to capture difficult-to-create shapes for TV commercials
and a variety of special effects. The Cyberware 3D digitizer, for
example, has played an important role in creating the special effects for at
least three major motion picturesÑThe Abyss, RoboCop 2, and Termlnator 2.
Each of the movies featured at least one computergenerated charcter that was
created by scanning in the heads and facial expressions of real actors.
In the medical world, one of the more unique uses of a 3D digitizer
involves neurosurgeon Richard Bucholz of the St. Louis University Medical
Center, who uses a special version of the Pixsys Firefly Electro-Optical 3D
Digitizer as a visualization aid during brain surgery. The device he uses
is similar to the general-purpose digitizer, except the LEDs are mounted in
the handle of his forceps instead of on the tip of a probe. The system also
requires LEDs located on a ring device that screws to the patient's skull.
he LEDs on the ring enable the system to track any possible movement of the
patient's head. The location of the tip of the forceps shows up on a Silicon
Graphics computer display, and when merged with MRI, PET, and other data,
the system allows the srgeon to figure out, in real time, the position of
the forceps within the patient's head to within two millimeters. In the
engineering and manufacturing world, 3D digitizers are finding uses in all
kinds of applications. One hearing aid manufacturer, for example, uses a
Digibot 3D digitizer as part of an automated system that optimizes the size
of hearing aids The digitizer is used to scan in the plastic shell housing,
and then customized Digibotics software fits a mathematical representation
of the electronic components into the polygonal mesh of the shell. The
system calculates the smallest possible size for the shell, and then a
rotary saw mounted on the Digibo system automatically cuts the shell at the
precise location.Categorizing the Systems Three-dimensional digitizers
fall into two broad categories: probe and non-contact. Probe digitizers
require the user to manually touch the tip of a probe to an object. This
usually involves several hours of repetitive selections, depending on th
number of points required to adequately represent the object. Prices for
probe digitizers range from $3500 to $25,000, but they're less expensive
than non-contact laser devices. Laser digitizers, priced from $30,000 to
more than $265,000, use laser light to obtain x,y,z coordinates without
physically touching the object. Because they require less mechanical motion
and do not risk destructive contact, laser digitizers aremore automatic and
much faster than probe digitizers. Laser digitizers can be further
divided into two smaller subcategories: single point and plane of light.
Single-point systems illuminate a small spot of light on the object. They
capture one point at a time, typically by rotating the object. The esult is
a vertical stack of evenly spaced contours stored as a list of x,y,z
coordinates. Because of the added mechanical flexibility of moving a single
beam of light about an object, the single-point technique is an effective
and accurate solution o laser digitizing. However, this technique is slower
than the plane-of-light technique.Plane-of-light digitizing systems
illuminate a line of light on the object. They capture not just one point at
a time, but rather a string of points that represent the contour illuminated
by the plane of light. Consequently, they can capture points mre quickly
than single-point systems. In fact, they usually capture more points than
are necessary to accurately define the surface of the object. They also
typically measure points redundantly by producing overlapping grids of data.
As a result, fils grow very large and often require a reduction of points
using special point- filtering software. Laser digitizers work by
projecting laser light onto the surface of an object. The light is then
reflected back to one or more sensors. The path of light forms a triangle,
and the angle formed at the point of contact with the object is called
theprobing angle. The probing angle decreases as the laser source and
sensors are positioned closer to one another. The smaller the probing angle,
the better the digitizer can probe objects with deep concavities, undercuts,
and openings. A digitizer with a probing angle of 25 degrees can get into
areas unreachable by a digitizer with a probing angle of 40 degrees.
However, accuracy decreases as the size of the probing angle decreases.
Therefore, developers of laser digitizers mus weigh accuracy against the
digitizer's ability to probe hard-to-reach areas.The difficulty of reaching
con-cavities and undercuts extends beyond the probing angle. If a bump on
the surface of a part obstructs the path of the light (light either coming
or going), the digitizer must be able to recognize the obstruction. If it
oesn't, the digitizer will miss this part of the surface. With the help
of intelligent software, coupled with adequate degrees of freedom between
the object and digitizer, certain developers have overcome this problem. In
these systems, the digitizer automatically probes the object from even angle
possile until it finds all of the points in the concavity. The only
restriction to this intelligent scanning technique is the probing angle. If
the angle is too large, it is impossible for the light to get in and back
out of the concavity. Still, even with these systems, it is difficult to
capture 100 percent of the surface of those objects containing holes and
deep concavities with small openings. Graphics editors and CAD tools are
available to patch and fix these missing surfaces Most laser digitizers
bundle a graphics editor and provide interfaces to CAD systems. For the
last several years, the major players in the 3D digitizer market were
Cyberware, Laser Design, Polhemus, and Science Accessories. Today, they
continue to dominate the market, but they are now sharing the field with
several newcomers, inclding Digibotics, Faro Technologies, Perceptron, and
Pixsys. All have shipped or plan to ship products this year.New Players
Enter the Market What these newcomers bring to the market is the ability
to mix clever probing techniques with proven technologies. That, combined
with aggressive pricing, may provide the appeal that's necessary to greatly
expand the market for 3D digitizers.Digibotics' Digibot system, for example,
combines laser technology and personal computing with speed and accuracy.
The use of a basic '386-based PC and Microsoft Windows, coupled with its
RS-232 serial interface and small size, makes it a true deskto peripheral.
Faro Technologies is targeting the lucrative AutoCAD market with its
Metrocom product. It is the only 3D digitizer company to offer a powerful
ADS interface to AutoCAD. The low price, reason able accuracy, and ability
to han dle a large work volume makes i an attractive choice for reverse en
gineering of large objects, such a~ automobile body parts. Perceptron
offers a produc called Lasar that blends a uniqu~ mix of laser and radar
technolog~ with a small size, portability, and a 126-feet ranging length.
The re sult is a digitizer that may open new markets in the theme park and
construction ndustries. The technology also has potential for machine vision
applications, such as robotic guidance and part inspection. The technology
may even make the product attractive to surgeons in the operating room.
While these new technologies are exciting and show impressive potential,
no company is yet poised to become the AutoCAD of the 3D digitizer industry.
The industry is still small, with less than 1000 general-purpose units
installed worldwide. Thatmeans the race to be the first company to produce a
machine that copies 3D objects as easily as a copy machine copies paper
documents is still wideopen. CGWHow Accurate is Accurate?Comparing
the accuracy of 3D digitizers can be confus-ing. The terms "accuracy,È
Çprecision," Çresolution," andÇrepeatability" are often misused,
misunderstood mislead-ing, or just plain omitted. A company may claim its
3Ddigitizer is accurate to +/- 0.010 inches. Yet it is usuallyimpossible to
achieve this accuracy all of the time, unlessyou are digitizing a very
simple shape, such as a sphere. Acomplex shape with holes and concavities,
such as an en-gine block, is a much better test of accuracy.Several factors
can affect the accuracy of laser digitiz-ers. If a part contains detail that
is smaller than thewidth of the laser beam, accuracy drops
significantly,since the beam hits and spreads over more than one sur-face.
Consequently, the detector is unable to accuratelylocate the center of the
beam. Corners and surfaces thatform sharp angles can cause a similar spread
of light.Some experts claim that the major source of error is thediameter of
the laser beam.Laser digitizers are also sensitive to shiny and
darksurfaces. Ideally, the object should be light in color, yetdull or flat.
If the surface is shiny, reflection can cause ashift in the location of the
point. If the surface is darkthe digitizer sensors cannot adequately see the
point. Us-ers of laser digitizers, therefore, often coat the surface ofthe
object with a white, water-soluble substance, such astempera paint, which
usually rinses clean from mostparts.Buyer confusion can also occur when
digitizer suppli-ers publish numbers related to the specific parts (for
ex-ample, linear rails and stepper motors) that make up thesystem. This can
be misleading. The precision of the sys-tem's mechanics does not reflect the
accuracy of the proc-ess. In fact, the precision of the mechanics is
usuallyalways better than the accuracy of the process.As for the term
"resolution," that refers to the densityof the points. If a digitizer has a
maximum resolution of0.010 inch, this means the points are never spaced
closerthan 0.010 inches apart. It would be impossible for amachine to offer
O.OO9-inch accuracy if the maximumresolution is 0.010 inches. Therefore, a
well designed sys-tem will always have a resolution that is greater than
itsaccuracy.
MAGAZINE JULY ISSUE 1992 Three-dimensional objects of all shapes and sizes
surround us, yet only a only a small fraction are stored in digital form.
Threedimensional digitizers enable you to copy these objects into a
computer. The computer model usually requires editing, bu the work is minor
compared to creating the object from scratch. Engineers use 3D digitizers
for reverse engineering of mechanical parts. Manufacturing professionals
apply them to the creation of new patterns for molded tooling and investment
casting. Medical specialists use 3D digitizers to digitize bones andother
anatomy for the development of prostheses and implants. Video production
experts use them to capture difficult-to-create shapes for TV commercials
and a variety of special effects. The Cyberware 3D digitizer, for
example, has played an important role in creating the special effects for at
least three major motion picturesÑThe Abyss, RoboCop 2, and Termlnator 2.
Each of the movies featured at least one computergenerated charcter that was
created by scanning in the heads and facial expressions of real actors.
In the medical world, one of the more unique uses of a 3D digitizer
involves neurosurgeon Richard Bucholz of the St. Louis University Medical
Center, who uses a special version of the Pixsys Firefly Electro-Optical 3D
Digitizer as a visualization aid during brain surgery. The device he uses
is similar to the general-purpose digitizer, except the LEDs are mounted in
the handle of his forceps instead of on the tip of a probe. The system also
requires LEDs located on a ring device that screws to the patient's skull.
he LEDs on the ring enable the system to track any possible movement of the
patient's head. The location of the tip of the forceps shows up on a Silicon
Graphics computer display, and when merged with MRI, PET, and other data,
the system allows the srgeon to figure out, in real time, the position of
the forceps within the patient's head to within two millimeters. In the
engineering and manufacturing world, 3D digitizers are finding uses in all
kinds of applications. One hearing aid manufacturer, for example, uses a
Digibot 3D digitizer as part of an automated system that optimizes the size
of hearing aids The digitizer is used to scan in the plastic shell housing,
and then customized Digibotics software fits a mathematical representation
of the electronic components into the polygonal mesh of the shell. The
system calculates the smallest possible size for the shell, and then a
rotary saw mounted on the Digibo system automatically cuts the shell at the
precise location.Categorizing the Systems Three-dimensional digitizers
fall into two broad categories: probe and non-contact. Probe digitizers
require the user to manually touch the tip of a probe to an object. This
usually involves several hours of repetitive selections, depending on th
number of points required to adequately represent the object. Prices for
probe digitizers range from $3500 to $25,000, but they're less expensive
than non-contact laser devices. Laser digitizers, priced from $30,000 to
more than $265,000, use laser light to obtain x,y,z coordinates without
physically touching the object. Because they require less mechanical motion
and do not risk destructive contact, laser digitizers aremore automatic and
much faster than probe digitizers. Laser digitizers can be further
divided into two smaller subcategories: single point and plane of light.
Single-point systems illuminate a small spot of light on the object. They
capture one point at a time, typically by rotating the object. The esult is
a vertical stack of evenly spaced contours stored as a list of x,y,z
coordinates. Because of the added mechanical flexibility of moving a single
beam of light about an object, the single-point technique is an effective
and accurate solution o laser digitizing. However, this technique is slower
than the plane-of-light technique.Plane-of-light digitizing systems
illuminate a line of light on the object. They capture not just one point at
a time, but rather a string of points that represent the contour illuminated
by the plane of light. Consequently, they can capture points mre quickly
than single-point systems. In fact, they usually capture more points than
are necessary to accurately define the surface of the object. They also
typically measure points redundantly by producing overlapping grids of data.
As a result, fils grow very large and often require a reduction of points
using special point- filtering software. Laser digitizers work by
projecting laser light onto the surface of an object. The light is then
reflected back to one or more sensors. The path of light forms a triangle,
and the angle formed at the point of contact with the object is called
theprobing angle. The probing angle decreases as the laser source and
sensors are positioned closer to one another. The smaller the probing angle,
the better the digitizer can probe objects with deep concavities, undercuts,
and openings. A digitizer with a probing angle of 25 degrees can get into
areas unreachable by a digitizer with a probing angle of 40 degrees.
However, accuracy decreases as the size of the probing angle decreases.
Therefore, developers of laser digitizers mus weigh accuracy against the
digitizer's ability to probe hard-to-reach areas.The difficulty of reaching
con-cavities and undercuts extends beyond the probing angle. If a bump on
the surface of a part obstructs the path of the light (light either coming
or going), the digitizer must be able to recognize the obstruction. If it
oesn't, the digitizer will miss this part of the surface. With the help
of intelligent software, coupled with adequate degrees of freedom between
the object and digitizer, certain developers have overcome this problem. In
these systems, the digitizer automatically probes the object from even angle
possile until it finds all of the points in the concavity. The only
restriction to this intelligent scanning technique is the probing angle. If
the angle is too large, it is impossible for the light to get in and back
out of the concavity. Still, even with these systems, it is difficult to
capture 100 percent of the surface of those objects containing holes and
deep concavities with small openings. Graphics editors and CAD tools are
available to patch and fix these missing surfaces Most laser digitizers
bundle a graphics editor and provide interfaces to CAD systems. For the
last several years, the major players in the 3D digitizer market were
Cyberware, Laser Design, Polhemus, and Science Accessories. Today, they
continue to dominate the market, but they are now sharing the field with
several newcomers, inclding Digibotics, Faro Technologies, Perceptron, and
Pixsys. All have shipped or plan to ship products this year.New Players
Enter the Market What these newcomers bring to the market is the ability
to mix clever probing techniques with proven technologies. That, combined
with aggressive pricing, may provide the appeal that's necessary to greatly
expand the market for 3D digitizers.Digibotics' Digibot system, for example,
combines laser technology and personal computing with speed and accuracy.
The use of a basic '386-based PC and Microsoft Windows, coupled with its
RS-232 serial interface and small size, makes it a true deskto peripheral.
Faro Technologies is targeting the lucrative AutoCAD market with its
Metrocom product. It is the only 3D digitizer company to offer a powerful
ADS interface to AutoCAD. The low price, reason able accuracy, and ability
to han dle a large work volume makes i an attractive choice for reverse en
gineering of large objects, such a~ automobile body parts. Perceptron
offers a produc called Lasar that blends a uniqu~ mix of laser and radar
technolog~ with a small size, portability, and a 126-feet ranging length.
The re sult is a digitizer that may open new markets in the theme park and
construction ndustries. The technology also has potential for machine vision
applications, such as robotic guidance and part inspection. The technology
may even make the product attractive to surgeons in the operating room.
While these new technologies are exciting and show impressive potential,
no company is yet poised to become the AutoCAD of the 3D digitizer industry.
The industry is still small, with less than 1000 general-purpose units
installed worldwide. Thatmeans the race to be the first company to produce a
machine that copies 3D objects as easily as a copy machine copies paper
documents is still wideopen. CGWHow Accurate is Accurate?Comparing
the accuracy of 3D digitizers can be confus-ing. The terms "accuracy,È
Çprecision," Çresolution," andÇrepeatability" are often misused,
misunderstood mislead-ing, or just plain omitted. A company may claim its
3Ddigitizer is accurate to +/- 0.010 inches. Yet it is usuallyimpossible to
achieve this accuracy all of the time, unlessyou are digitizing a very
simple shape, such as a sphere. Acomplex shape with holes and concavities,
such as an en-gine block, is a much better test of accuracy.Several factors
can affect the accuracy of laser digitiz-ers. If a part contains detail that
is smaller than thewidth of the laser beam, accuracy drops
significantly,since the beam hits and spreads over more than one sur-face.
Consequently, the detector is unable to accuratelylocate the center of the
beam. Corners and surfaces thatform sharp angles can cause a similar spread
of light.Some experts claim that the major source of error is thediameter of
the laser beam.Laser digitizers are also sensitive to shiny and
darksurfaces. Ideally, the object should be light in color, yetdull or flat.
If the surface is shiny, reflection can cause ashift in the location of the
point. If the surface is darkthe digitizer sensors cannot adequately see the
point. Us-ers of laser digitizers, therefore, often coat the surface ofthe
object with a white, water-soluble substance, such astempera paint, which
usually rinses clean from mostparts.Buyer confusion can also occur when
digitizer suppli-ers publish numbers related to the specific parts (for
ex-ample, linear rails and stepper motors) that make up thesystem. This can
be misleading. The precision of the sys-tem's mechanics does not reflect the
accuracy of the proc-ess. In fact, the precision of the mechanics is
usuallyalways better than the accuracy of the process.As for the term
"resolution," that refers to the densityof the points. If a digitizer has a
maximum resolution of0.010 inch, this means the points are never spaced
closerthan 0.010 inches apart. It would be impossible for amachine to offer
O.OO9-inch accuracy if the maximumresolution is 0.010 inches. Therefore, a
well designed sys-tem will always have a resolution that is greater than
itsaccuracy.
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