27.6 x
With
| A/D
. disk
unt of
at 0.5
le the
0 use
vice
tems
s the
array
1era,
are
ored
sors
nent
ina
ince
375
The on-line versions of the IMETRICS system series, the TP25x and TP65x systems (x denotes the number of cameras), use identical
cameras which are connected via a SCSI interface to a workstation. These systems can be used with either the notebook workstation
or the SPARCstation 20.
Typically, 2 to 6 cameras are used for one system although the hardware and software can be configured for even more cameras. The
cameras are synchronised and can be released from the workstation, from a wireless remote release or even from another test machine
via a TTL or other signal.
The systems of the TP250 and TP650 series are used to determine the 3D coordinates of targets for positioning (during building of
jigs), tracking and deformation analysis. In all of these application areas tremendous time savings have been achieved relative to
traditional industrial measurement systems. Another important factor for using digital 3D image metrology systems in these
applications is the high accuracy level which can be obtained. The systems are also immune to vibrations and movements of the
cameras. In addition, the systems can be operated with an optical touch probe, called a DigiPen. This device makes the systems into
transportable coordinate measuring machines with variable measurement volumes. Using DigiPens of different sizes the user can
rapidly digitize surfaces, measure and position items on jigs (or other structures) and measure geometric elements and points that need
not be visible from any of the cameras. Figure 2 shows the TP252 system with the cameras on either side of the workstation screen
and the DigiPen in use on a car door.
Figure 2. The TP252 system with the workstation screen, two cameras and a DigiPen in use on a car door.
3. OFF-LINE MEASUREMENTS
Practical accuracy requirements for off-line measurements start at relative accuracies of 1 part in 30 000. Many areas, such as in the
automotive and aerospace industries, require accuracies of 1 part in 100 000 or even higher. Examples from aerospace shall be used to
show some results achieved with off-line measurements.
Applications of 3D image metrology in aerospace include building jigs, verification of jigs, parts and substructures and measurement
of complete aircraft. One customer of IMETRIC uses the system to perform root and volume checks on built wings. This application
is ideally suited for digital photogrammetry. It is a repetitive task and requires the determination of the 3D coordinates of a
considerable number of points. The measurement consists of verifying the location and attitude of all stringers and other contact
planes with the fuselage at the root of a wing. This procedure was originally accomplished using gauges, taking up considerable
factory space and requiring several days. The introduction of industrial theodolite systems, such as ECDS from Leica, reduced the
measurement time to typically 10 man-hours for this task. The interruption of the production process was nevertheless too long. Thus
the measurements had to be performed during the night shift.
Using the IMETRICS systems the measurement time, i.e. the time taken to acquire the images, was reduced to less than 10 minutes.
This was made possible by special target adapters that are easy to place and remove. This target preparation (and removal) can be
performed while other personnel are still working on the wing. Furthermore, the images were downloaded directly on the job site.
After transferring the images from the PCMCIA disk onto the notebook workstation (which is performed by pressing one button in
the software), the images can immediately be checked. If no problems are detected in the images then the target adapters can be
removed. Figure 3 shows a prepared wing with adapters placed on the top of the surfaces to be checked and at reference locations.
IAPRS, Vol. 30, Part 5W1, ISPRS Intercommission Workshop "From Pixels to Sequences", Zurich, March 22-24 1995
