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Frequently
Asked Questions |
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WHAT
IS 3D LASER SCANNING?
In essence, laser scanning is to 3D objects what photocopying is to 2D
objects. Laser Design's Surveyor family of 3D Laser Scanning Systems makes
use of a laser sensor that is mounted to a 3 - 6 axis computer controlled
positioning system or retrofitted to an existing CMM. We even have a
portable model that sits on a camera tripod.
An object that is to be scanned is placed on the bed of the
digitizer and our Scan Control software then drives the laser sensor above
the surface of the object. 3D coordinate locations which lie on the
surface of the object are recorded by the scanning system according to
scan density and pattern parameters set by the user. These XYZ coordinate
locations are stored in a file that can be converted to IGES or ASCII
formats for input into nearly any CAD/CAM system or specialized
point-cloud processing software on the market today.
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WHAT
IS THE PRINCIPLE BEHIND LASER SCANNING?
All of the Laser
Design's scanning systems utilize laser-triangulation based technology.
The heart of the technology is a dual camera probe which emits a diode
based laser beam from the center as shown in the picture. The beam is
split into a plane of laser light that comes out of the probe and shines
below on the surface of the object being scanned. Thus it forms a profile
on the surface of the part.
A
two-dimensional CCD (Charge Coupled Device) array similar to the one used
in a home video camera is mounted on either side of the probe. They reside
inside two identical optical sensors. The reflected light form the profile
on the surface of the object activates the pixels on the array inside one
of the two sensors. The reason for having two sensors instead of one is
that if for some reason the view of the profile on the surface of the
object is blocked for one sensor there is always the second sensor that
can pick up the same profile. The user can toggle between the two sensors
but only one is active at one time. |
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The shape of that
single "2D" profile is recorded by the digital CCD and
subsequently, based on the calibration and look up tables of the lasers, a
Z position is determined and stored for each pixel value by the software.
This location along with the machine axes positions are used to compute
the X,Y,Z coordinates of the points along that profile. Hundreds and
thousands of similar profiles are thus collected as the probe marches over
the object and the software stores this information into a database for
later retrieval. Each profile comes into the database as a single polyline
entity with points distributed along the length of the line. These
polylines are also displayed graphically on the computer screen as they
are gathered.
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WHAT ARE THE MAIN ADVANTAGES
OF LASER SCANNING?
The primary advantage of
laser scanning is that the process is non-contact, fast and results in
coordinate locations that lie directly on the surface of the scanned
object. This allows fragile parts to be measured and makes the scanned
coordinate locations especially useful to CAD/CAM systems where splining
or surfacing through true surface coordinates is desirable. The
laser's high resolution and thinner beam also permits scanning of highly
detailed objects where mechanical touch probes may be too large to
accomplish the task. Also, while many touch probe systems attempt to
compute true surface coordinates by sensing probe deflection, there are
certain geometries where probe deflection can be "fooled".
Finally,
once true surface coordinates have been collected for an object, a single
set of data can be used to generate roughing and finishing tool paths for
machining, feed CAD/CAM and analysis software, drive rapid prototyping
equipment, and allow "electronic archiving" of physical objects.
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WHICH
INDUSTRIES ARE ALREADY USING YOUR SYSTEMS?
We
have an installed base that includes nearly every industry imaginable.
Automotive, aerospace, consumer electronics, medical, railroad, sports
equipment, toy, jewelry and container manufacturers are all using our
systems and endorse the technology. Two military branches and a leading
manufacturer of space shuttle components also use our equipment. Companies
in countries all over the world including Japan, France, Italy, Korea,
Singapore, Spain, Brazil, China and India have also purchased systems and
recognize that laser scanning is here to stay and will continue to define
state-of-the-art manufacturing.
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HOW
ACCURATE IS IT?
The standard laser
resolutions offered by Laser Design are 0.0004" and 0.0008"
although we have built custom systems with lasers having a resolution as
fine as 0.00006". When considering any optically based measuring
systems, it is important to realize that there is a difference between the
terms resolution and accuracy. Resolution is simply the
smallest change in distance that the sensor is capable of detecting.
Accuracy, on the other hand, is a function of the optical qualities of the
object being scanned. If the object has a matte surface, then resolution
and accuracy will be nearly the same. If the object has a glossy surface
however, the laser spot may "shimmer" and dance slightly on the
CCD array. This shows up as "noise" in the laser data which can
be filtered and smoothed to a certain extent within Laser Design's
Surveyor Scan Control software. On the other hand if the surface has light
absorbing finish (too black) so it doesn't return enough light to the
sensors, the part can be sprayed with a variety of coating materials to
enhance the laser readability but as obvious doing that will add a little
coating material build-up on the part.
Naturally, the mechanical accuracy of the
positioning system also comes into play when discussing accuracy. Our Scan
Control software accepts feedback from optional linear scales and supports
the use of a laser interferometer to build compensation tables that
correct subtle mechanical inaccuracies inherent in any machine.
The
volumetric accuracy specifications in our literature are based upon our
ability to digitize a ball-bar oriented several ways within the work
envelope and have the measured length of the ball-bar vary by no more than
the stated accuracy of the machine. A ball-bar is defined by the American
Society of Mechanical Engineers (ASME) in their standards document, ASME
B89.1.12M-1990, as a rigid bar to which a precision tooling ball is
mounted on each end.
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HOW
FAST IS IT?
Much
like a 35MM camera, the laser has exposure settings that need to be
adjusted depending upon the nature of the object being scanned. In
general, dark colored objects require longer exposure settings than light
colored objects and longer exposure settings require the system to operate
at slower velocities if data integrity is to be maintained. The point
sampling distance requested by the user also affects scanning speeds. In
general, we have experienced "real world" scanning speeds of
3000 to 4000 points per second although some situations may require slower
scanning speeds and other situations may permit scanning at full scan rate
of the probe which is 14,400 points per second. In any case, laser
scanning tends to be much faster than a CMM and somewhat faster than
mechanical tracing systems.
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IS
THE LASER SAFE?
The
Laser probes employed by our scanning systems use a diode based class II
laser. It has a very low power output with ratings at less than 1mW and a
670nm wavelength (visible red spectrum). It utilizes passive beam spreader
and has no moving parts. Class II lasers are still ocular hazard, but
viewing time in order to do the damage to the eye is significantly longer
than for instance for a class III laser.
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WHAT
SHAPES CAN I DIGITIZE?
In addition to XYZ positioning, Laser Design
supports computer controlled object rotation and laser orientation. This
allows scanning of virtually every side of a 3D object and eliminates the
traditional problem of scanning undercuts. Laser Design's Surveyor Scan
Control software includes powerful data manipulation tools which can blend
data from multiple views together into a single data set with the use of
tooling balls. Additionally
there are several other CAD/CAM packages available in the market today
that blend the data collected at different orientations into one complete
3D model using various powerful data matching algorithms.
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WHAT
ARE THE LIMITATIONS OF LASER SCANNING?
Although
used in a variety of inspection applications, laser scanning is not
intended to compete with the micron accuracies of some CMMs. As a rule,
CMMs are better suited to measure geometric parts where basic dimensions,
hole locations, diameters, flatness and roundness measurements are
required for accept/reject types of applications. Laser scanning tends to
be better suited for the measurement and inspection of contoured surfaces
and complex geometries which require massive amounts of data for their
accurate description and where doing this is impractical with the use of a
touch probe. Also laser scanning comes into play for picking fine features
that are inaccessible to a touch probe.
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IS LASER SCANNING
EASY TO DO?
Every
Laser Design's scanning system comes equipped with the Surveyor Scan
Control. Surveyor Scan Control is a menu and mouse driven software
that is used for driving the laser probe over the part with the aid
of a joystick as well as retrieving data and storing it on the hard
drive. It allows "programming" of the system so that the
laser probe mounted on a motion control system will follow a
"pre-defined path" in 3D space over the object being
scanned. Programming itself is totally "graphical" and no
"code" needs to be written. Though it is easy to use, some
prior experience with a 3D CAD/CAM package is desirable.
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HOW
IS THE DATA OBTAINED FROM LASER SCANNING USEFUL?
The
data acquired from laser scanning, can be used during the product
design phase to input physical models into CAD/CAM world, during the
manufacturing phase to generate tool paths for machining and also
during the quality assurance phase to verify dimensional accuracy of
the final product. For a detailed account of various applications
the laser scanned data is being used for, please go to
Service
Bureau Stories or Equipment
Stories.
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HOW DO I MANIPULATE LASER
SCANNED DATA?
There are several extremely powerful software packages available in
the market today that can import data from our systems and use it
for a desirable outcome. Laser Design Inc. proprietary software
Surveyor Scan Control can be used for data collection as well as
initial processing and clean up. Typically the raw data collected
from the system is de-spiked, filtered and smoothed depending upon
the quality of the data obtained and the application it is being
used for. A 3D model is then created either with software programs
like Geomagic Studio. The choice of the software to use greatly
varies depending on the application and other circumstances.
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WHAT
IS SURVEYOR SCAN CONTROL?
Surveyor Scan
Control is Laser Design Inc. proprietary software which comes with
all the Laser Design scanning systems. The two primary functions of
Surveyor Scan Control are to jog the machine in 3D space in order to
physically adjust the laser probe over the object that is being
scanned and to collect the data from the laser. (See Question 2
above). It organizes the 3D point coordinate information on each and
every point collected during scanning and stores this information in
a file on the hard drive. This file can be retrieved later for
editing. The same coordinate system is valid during data-editing as
in scanning.
The
scanning can be set-up using Surveyor Scan Control such that the
laser probe will follow a pre-defined path in 3D space while
scanning the part. The set up programming is entirely
"graphical" and no code needs to be written. Moreover,
Surveyor Scan Control has powerful macro capabilities also that
allow the user to automate the scanning process as well as store and
recall the scanning parameters in case the same or a similar part is
scanned again. For further information on Surveyor Scan Control,
read our
Spec
Sheet.
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WHAT
KIND OF TRAINING IS PROVIDED TO USE SURVEYOR SCAN CONTROL FOR
SCANNING?
Laser
Design offers Quick Start Training that prepares a new user for
using Surveyor Scan Control for scanning and data editing. Advanced
training is also provided for experienced users. For further
information and a training schedule, Click Here.
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WHAT
OTHER SOFTWARE PROGRAMS ARE USED IN ADDITION TO SURVEYOR SCAN
CONTROL FOR PROCESSING SCANNED DATA?
Laser Design offers
Geomagic software modules for processing the scanned data.
Geomagic
Qualify is a revolutionary software program for performing 3D
best-fit analysis of actual scan data to CAD nominal. Best-fit
registration is done either in space to minimize part deviation, or
directly to part datums. Once the registration is complete,
tolerance bandwidth is defined and results are displayed in a 3D,
color plot showing point deviation from nominal as color gradients.
At a glance, you will know the accept/reject status of the part.
Inspection results can finally be conveyed in a format that is
easily understood and communicated. Qualify also provides other
tools such as GD&T and point comparisons to cross sectional
data. These plots will display actual/nominal point deviation as
color "whisker plots" showing magnitude and directional
differences from nominal or you may measure on screen the actual
difference. Geomagic Studio provides surfacing capability for
creating a CAD model from the scan data.
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