bundle triangulation
23 um and an object
- and y-direction and
The results show a
directions and the z-
caused by the very
e sidewalls of the
accuracy is ten times
sy of the online CCD
odak DCS 460 is also
n of the system which
every twelve month.
ystem, the reference
sasured automatically
camera images with
sssing. The positions
, can be calculated
imaging optics. This
the basis for the later
jn of the shape in a
xterior orientation of
| with high precision.
rence marks on the
isured in each image.
portunity to test the
calibrations. In the
'arks are measured in
o the calibration are
the user can decide
ary or not. Calibration
ompletly | automatical
e the measuring and
ration are short it is
calibration at least
CEDURE
ed by methods from
sing which were used
tes of the bend points
ese threedimensional
comparison using a
ribed in several ways.
y in CAD systems a
e. The tube can be
with the theoretical
ction of two following
and endpoints of the
he polygon now the
be calculated. This
ice of two following
petween two following
angle calculated from
1e calculation of real
| between theoretical
ith tube diameter and
ina 1996
bending radius. Since all the necessary bending elements
can be calculated from the theoretical bend points, the
following description of the measuring principle is
reduced on the evaluation of theoretical bendpoints in
image and object space.
The measurement of a tube is performed in several
steps. First images of a tube from all cameras are frozen
in the computer. Then the contour of the tube is detected
automatically and measured precisely by contourline
reducing the contour to the centerline in every image.
Straight elements and curves are then extracted from the
measured tube contour. The intersection of straight
elements deliveres the position of the theoretical bend
points in the images (Figure 3). If a bend point can be
detected in at least two images, the 3-dimensional
theoretical bend points in object space can be calculated
by intersecting the imaging rays.
Fig. 3: Digital image with bend points
4.2 Optical gauge
In this mode of operation the theoretical bending
elements of a tube are measured and afterwords
compared to the data of a reference tube. Additionally the
coordinates of the bend points can be exported in a CAD
readable format like VDA-FS. In a menu the user can
adjust import parameters of the tube like approximate
diameter or adapter length. When starting the
measurement, the user is prompted to choose the
reference tube from the data base, to put the tube into
the measuring cell and to start the measurement. In
order to control a correct position of the tube in the
measuring cell the images of the different cameras can
be viewed on the video monitor. After the automatic
measurement of the tube a table shows which parts of
tube could be measured correct and complete. By
repositioning of the tube in the cell and a following
repeated measurement even difficult or large tubes can
be measured completely.
For the measurement of unknown tubes two different
ways can be selected. First, the CAD data of a similiar
tube exists in the database. This is often the case when
for example tubes which are bend from CAD data are
adjusted manually in the production process. In this case
the measurement runs automatically and similiar to the
57
optical gauge. Results of the measurement are then
imported to the database as mastertube data.
Second, if no information about shape and geometry of
the tube exists, the measured points have to be
confirmed by the user to ensure a complete
measurement and a correct sorting of the bend points.
For each type of tube to be compared in the optical
gauge the reference data are stored in a database. The
menu point allows to choose different database
functions, the input of data either manually by an editor
or by a CAD interface, to visualize tube shape graphically
and to rename or copy tubes.
5. TECHNICAL DATA
5.1 Measuring volume
The realized measuring volume is 2.500 mm x 1.000
mm x 700 mm. It is planed to realize two different types
of measuring cells. A compact small cell with a
measuring volume of about 1.500 x 1.000 x 700 mm and
a large cell with a measuring volume of about 4.000 x
1.200 x 700 mm.
5.2 Tube spectrum
In the optical tube measurement system tubes of
different shapes, diameters, materials and surface
properties can be measured. The following limitations
have to be considered: For tubes with small diameters or
tube ends with female screws, the tube ends have to be
signalized with special adapters. With top light
illumination only tubes with dark, nonspecular surfaces
can be measured. This limitation is not valid for
measuring cells with a light table on the ground plate. At
the time only bend points with bending angles larger then
five degrees can be measured precise and reliable.
Furthermore between two bend points a straight part of at
least 10 mm length must be visible, that means that no
bend points can be measured which go arc in arc.
5.3 Accuracy
Several tests with different types of tubes have shown
that the individual bend points can be measured with
accuracies better then 0.5 mm.
5.4 Measuring times
The time for a measurement depends on the length of the
tube and the number of the bend points to be measured.
But even for long and complicated tubes measuring
times below 1 minute can be reached.
6. INTEGRATION IN THE PRODUCTION LINE
The OLM is now integrated in the production line for an
automated process and quality control. Therefore the
OLM provides an interface to several different types of
bending machines. This interface consists of different
data structures depending on the manufacturer of the
bending machine. The measurement data can be send to
the bending machines either via a local area network or
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B5. Vienna 1996
