U.S. patent application number 09/034481 was filed with the patent office on 2001-08-09 for flatness measurement system for metal strip.
This patent application is currently assigned to BETRIEBSFORSCHUNGSINSTITUT VDEH-INSTITUT FUR ANGEWANDTE FORSCHUNG GMBH. Invention is credited to DEGNER, MICHAEL, MULLER, ULRICH, PEUKER, GUSTAV, SONNENSCHEIN, DETLEF, THIEMANN, GERD, WINTER, DETLEF.
Application Number | 20010012388 09/034481 |
Document ID | / |
Family ID | 7822971 |
Filed Date | 2001-08-09 |
United States Patent
Application |
20010012388 |
Kind Code |
A1 |
MULLER, ULRICH ; et
al. |
August 9, 2001 |
FLATNESS MEASUREMENT SYSTEM FOR METAL STRIP
Abstract
The invention relates to a flatness measurement and control
system for metal strip, which makes it possible to obtain improved
strip or coil quality by a simple and effective measurement of
departures from flatness and to control the finishing parameters
through the evaluation of a line pattern on the strip surface or on
the end face of a coil as it is coiled.
Inventors: |
MULLER, ULRICH; (MONHEIM,
DE) ; PEUKER, GUSTAV; (MONCHENGLADBACH, DE) ;
SONNENSCHEIN, DETLEF; (ESSEN, DE) ; WINTER,
DETLEF; (MEINE, DE) ; DEGNER, MICHAEL;
(DORTMUND, DE) ; THIEMANN, GERD; (BOCHUM,
DE) |
Correspondence
Address: |
MERCHANT & GOULD
P O BOX 2903
MINNEAPOLIS
MN
55402-0903
US
|
Assignee: |
BETRIEBSFORSCHUNGSINSTITUT
VDEH-INSTITUT FUR ANGEWANDTE FORSCHUNG GMBH
DUSSELDORF
DE
|
Family ID: |
7822971 |
Appl. No.: |
09/034481 |
Filed: |
March 4, 1998 |
Current U.S.
Class: |
382/141 |
Current CPC
Class: |
B21B 37/54 20130101;
B21B 37/42 20130101; G01B 11/306 20130101; B21B 38/02 20130101;
B21B 37/44 20130101; B21B 37/76 20130101; B21B 38/04 20130101; B21B
38/006 20130101; B21B 45/0218 20130101 |
Class at
Publication: |
382/141 |
International
Class: |
G06K 009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 11, 1997 |
DE |
197 09 992.0 |
Claims
What is claimed is:
1. Method for measuring the flatness of metal strip or of the end
face of the coil when coiling strip, wherein a line pattern (2) is
produced on the measurement surface (4) by means of a projector and
is detected directly by a camera (5)
2. Method as claimed in claim 1, wherein the line pattern (2) is
compared by computer with a reference pattern after its detection
by the camera (5).
3. Method as claimed in claim 1 or claim 2, wherein the measured
values are used for control of a finishing train.
4. Rolling mill train comprising a finishing stand (6), a strip
cooling line (8), a coiler (7) and measuring means located before
and after the strip cooling line for measuring the strip flatness,
which is coupled with the means for controlling the finishing stand
(6), the strip cooling line (8) and the coiler (7).
5. Rolling mill train as claimed in claim 4, wherein the flatness
of the strip is detected in the run-out from the finishing line (6)
and evaluated for control of the last stands of the finishing
rolls, and the measured values of the flatness measurement are used
to modify the flatness after the strip cooling stage (8) and before
the coiler (7).
6. Rolling mill train as claimed in any one of claims 1 to 5
wherein, using the measured values detected after the strip cooling
line (8), a first secondary control loop (11) is produced which
permits the intended value for the cooling line (8) to be
adapted.
7. Rolling mill train as claimed in any one of claims 1 to 6
wherein, using the measured values detracted after the strip
cooling stage (8), a second secondary control loop (12) is produced
which permits the intended value for the coiler tension (7) to be
adapted.
Description
FIELD OF THE INVENTION
[0001] The invention relates to a flatness measurement and control
system for metal strip and for the end faces of the coil when
coiling strip.
BACKGROUND AND PRIOR ART
[0002] The contact measurement usually used in cold strip mills is
only possible in the hot strip field at the expense of substantial
outlay on maintenance, because of the high strip temperature of
from about 1000.degree. C. Contact measurement on the end faces of
a coil being formed in a coiler is also not possible. It is
therefore difficult, if not completely impossible, to coil strip in
such a way that in the coil every turn lies exactly over the
preceding one so that flat end faces are obtained. And even in cold
strip mills efforts are made to avoid contact measurement, since
the mechanical measuring elements have only a limited life.
[0003] Strip flatness is therefore preferably measured without
contact. For example, it is known to measure departures from
flatness by means of spots of light projected on to the strip. The
position in space of the light spot produced on the surface of the
strip, preferably by means of a laser beam, is detected using a
range finder.
[0004] The two plane position coordinates of a particular point on
the surface are known from the position of the scanning or
illuminating beam relative to the surface of the strip. The height
coordinate of the point on the surface which is currently being
measured is detected by a position-sensitive sensor. The position
of the image point on the sensor varies simultaneously with the
height coordinate.
[0005] Using a large number of sources of radiation and sensors a
flatness image can be built up over the whole width of the strip
which is made up from the results of measurement of the spots of
light projected on the strip at particular distances apart.
Nevertheless, in this method the regions between the points of
light are not detected and in the case of continuous strip form
strip-shaped measurement gaps in which the flatness is not
determined. Moreover, this can result in measurement errors, for
example through wobbling or flattering of the strip being detected
by the measuring method as unevenness of the strip.
[0006] In the automobile industry it is known to measure relatively
small surfaces using the moir technique. In this method an
interference pattern is produced oil the surface of the object by
means of a light source. The interference pattern is detected using
a CCD (charge-coupled device) camera. The camera is arranged so
that an angle is formed between the light source, the surface and
the camera. By the use of a reference grid in the image plane a
so-called moir effect is obtained by superposition of the detected
pattern and the reference pattern. The height differences can be
determined quantitatively from the moir lines.
[0007] The moir technique provides more accurate measurement
results than measurement using spots of light, and moreover it
covers substantially the whole of the surface to be measured and
avoids the measurement gaps mentioned above. However, its use
involves problems, particularly in a hot strip mill.
[0008] To determine the height differences of the rolled strip a
complicated conversion of the pattern detected by the camera is
necessary. The height differences pictured as moir lines cannot be
converted into quantitative measured values in real time.
[0009] But in a rolling mill train rapid results are precisely what
is required from measurements, since otherwise it is hardly
possible to use the measurement for direct adjustment of the
rolling parameters so as to improve the flatness of the continuous
strip. Moreover for industrial application the fine interference
patterns are lacking in contrast and intensity.
[0010] In the case of conventional metal strip mill trains, in
which the strip flatness is measured by one of the above-mentioned
methods, departures from flatness are not measured from the cooling
line, and this can result in considerable loss in quality.
OBJECT OF THE INVENTION
[0011] The object of the invention is to provide a system which
allows strip quality to be improved by a simple and effective
measurement of the strip flatness and permits fine control of the
rolling and/or coiling parameters.
SUMMARY OF THE INVENTION
[0012] To this end, a line pattern is produced on the measurement
surface and/or on the end face of a coil being formed, the line
pattern is detected by a camera which can resolve the line pattern,
and the measurement data obtained are compared with a reference
measurement. By means of a process control computer the measurement
results are directly converted into control parameters for the
finishing train and the coiler and coordinated.
[0013] By measurement surface is to be understood here the surface
of the strip or, in the case of coiling, the end face of a coil
made up of a larger or smaller number of turns of the strip.
[0014] A projector produces by projection, for example through a
slide, a line pattern on the strip surface or the end face of the
coil corresponding to the resolution of the camera. For this
purpose the projector is mounted above the metal strip and projects
the line pattern on the surface of the metal strip at an angle to
the vertical, so that the lines preferably run transverse to the
strip surface and consequently take in the whole width of the
strip.
[0015] A CCD camera having a resolution of, for example, eight
pixels per line detects the lines running transversely across the
strip surface. In the event of absolute flatness of the strip a
uniform pattern of straight lines with constant line spacing is
formed.
[0016] Deviations of the strip surface from the ideal plane bring
about a change in the spacing between the lines in the region of
the unevenness. This change is recorded by the camera. It can be
converted by calculation in a simple manner into differences in
height by a comparison with an ideal pattern.
[0017] In a similar manner to the measurement of flatness on the
continuous strip, the flatness of the end faces during coiling can
be monitored and ensured by means of the measuring system of the
invention. The end face of the coil being formed in the coiler then
corresponds to the strip surface.
[0018] The system in accordance with the invention makes possible a
rapid determination of the actual height differences of the strip
surface and in this way permits measurement of continuous lengths
of strip in real time. This has the advantage that the measurement
results permit the rolling parameters to be adapted immediately
after the appearance of an unevenness.
[0019] The invention makes possible a measurement which is
insensitive to spurious measurement results. Such spurious results
are obtained with conventional measuring systems for example as a
result of movement of the whole strip surface relative to the
height coordinate (flutterirg). Furthermore, the invention allows
the transverse arching of the strip to be determined. Conventional
measuring systems only measure the length of the strip fibres. In
addition the intensity and thickness of the measurement lines can
be adapted to meet different conditions. The problems of the fine,
low-intensity and low-contrast moir lines do not occur.
[0020] The system of the invention is particularly suitable for
making a measurement on the strip emerging from the finishing
stands combined with a measurement of the strip on the coiler. By
this arrangement variations in the flatness of the strip due to
cooling of the strip between the finishing stands and the coiler
can be detected and evaluated for flatness control.
[0021] The measurement data can be evaluated for control of the
finishing stands and of the coiler and for control of the coiling
line.
[0022] Measurement results which incorporate a departure from an
intended value bring about an immediate and interdependent
adaptation of the parameters for the finishing stands, the cooling
line and the coiler.
[0023] Besides its use for measurement of flatness in a finishing
train the system in accordance with the invention can also be used
in subsequent production lines, for example in the control of
stretch straightening devices and in pickling lines.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] The invention will now be described in more detail, by way
of example, with reference to an embodiment illustrated in the
drawings, in which:
[0025] FIG. 1 shows the production and detection of the measurement
lines on a length of strip;
[0026] FIG. 2 shows a projector and a camera arranged after a
finishing train;
[0027] FIG. 3 shows the projector and the camera arranged before a
coiler pit; and
[0028] FIG. 4 is a block diagram of the flatness control
system.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
[0029] Measurement lines 2 running transverse to tie strip 1 are
produced on the measurement or strip surface 4 using a projector
3.
[0030] The measuring arrangement is disposed in ore case in the
run-out from the finishing stands 6 and in the other case before
the coiler 7, on an instrument case 13. The CCD camera 5 is located
on the side of the instrument case nearer to the coiler 7, in a
water-cooled housing. The projector 3 is located on the side of the
instrument case remote from the coiler 7. To remove heat the
housing is cooled with air. The cooling of the projector 3 and of
the camera 5 is necessary to remove their intrinsic heat and the
radiant heat from the strip 1, which is at about 1000.degree.
C.
[0031] The camera 5 and the projector 3 are arranged in succession
relative to the direction of travel of the strip and are aimed at a
region of the strip located between them, on which the line pattern
is produced and sampled. The projector used may, for example, be a
xenon light source, which produces an easily readable line pattern
even on a hot slab.
[0032] Unevennesses on the strip surface 4 cause the measurement
lines 2 to follow an irregular course or to depart from geometric
straightness.
[0033] By means of a CCD camera 5 the measurement lines 2, and
consequently also the changes in their course caused by
unevennesses, are detected. After it has been detected the
measurement image is compared by computer with a previously
recorded reference pattern. The height differences and the
parameters for the control of the finishing train are derived
directly from the deviations.
[0034] A complete picture of the flatness of the strip 1 is thereby
obtained as it moves along in the direction of the arrow.
[0035] From the diagram of the flatness control system (FIG. 4) the
design in accordance with the invention can be seen. The hot strip
1 passes through the finishing rolls 6 and the strip cooling line 8
to the coiler 7 in the coiler pit. In the run-out from the
finishing rolls 6 the flatness of the hot strip is detected,
analysed and evaluated for control of the last stands of the
finishing rolls (roll bending aid tilting). This internal
flatness-control loop 9 is supplemented by an external
flatness-control loop 10. By a measurement of the strip flatness
after the strip cooling life 8 before the coiler 7 the external
flatness-control loop 10 is designed for adaptation of the intended
value of the internal control loop.
[0036] Using the measured values detected after the strip cooling
line a first secondary control loop 11 is also produced which
permits the intended value for the cooling line 8 to be adapted and
a second secondary control loop 12 which permits the intended value
for the coiler tension 7 to be adapted.
[0037] Altogether, the detection and control in accordance with the
invention can be used effectively to achieve a high strip
* * * * *