Note: Descriptions are shown in the official language in which they were submitted.
I, ~Z~9~5
by
`:
, :
CALIBRATION METHOD
I This invention relates to a method and
apparatus for calibrating a sensor means for measuring
the dimension of an article, a method and apparatus for
measuring the dimension of the article as well as methods
and apparatus for aligning a sensor means and detecting
10 the location of an edge in an image of an object.
Quality control and yield optimism of
manufactured articles such as steer slabs requires the
monitoring of, for example, hot slab dimensions.
Traditionally, these dimensions are measured by a manual
15 technique using calipers. Thus technique requires the
7~ii
. - 3 -
slabs to be stationary, and mill personnel -to come
uncomfortably close to the hot material to perform the
measurements. It is therefore apparent that manual
techniques have many disadvantages.
Modern electronic technology has made possible
development of non-contact in line systems to measure the
dimensions of hot steel products. For example a method
of measuring the dimensions of a slab is disclosed in
US. Patent No. 4,271,477 issued to Gerald B. Williams.
10 In this patent sensors, such as in line cameras, are
utilized to detect the slab. The cameras are focused
onto the slab so that the images of the slab are formed
on diodes within the camera. By determining the number
of diodes which are illuminated within the camera with
15 the image of the slab the dimension of the slab can be
calculated by suitable processing circuitry.
In order to obtain an accurate measurement with
prior art methods it is necessary to ensure that the
feuded array in the camera is parallel to the slab
20 face being measured. If the array is not parallel to the
slab face being measured the conventional techniques- will
give incorrect measurement values for the various
dimensions of the slab due to perspective distortions.
Perspective distortions are distortions due to non-
25 linearity of relative displacements between object co-
ordinates in the object plane with respect to relative
displacements between corresponding image co-ordinates in
the image plane. It is extremely difficult to ensure
that the cameras are arranged with their outdid
30 arrays exactly parallel to the slab face being measured
and the object of this invention is to provide a
calibration method which overcomes the need to ensure
strict parallel arrangement of the array relative to the
slab face. Furthermore the present inventors have found
35 that in arranging the photo diode array exactly parallel
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'I to the slab face a large portion of the viewing range of
the camera is wasted. By tilting the array so that it is
not parallel to the slab face the camera can be moved
closer to the slab so that viewing range is not wasted
5 and the method according to the first aspect of the
invention will automatically compensate for any
distortions which are inherent when attempting to align
the array parallel to the slab face or when arranging the
array at an angle to the slab face so that viewing Lange
10 of a camera is not wasted.
The invention in a first aspect may therefore
be said to reside in a method of calibrating a sensor
means for use in measuring the dimension of an article by
arranging the sensor means so that it will detect the
15 article to be measured during a measurement step, the
method of calibrating the sensor comprising locating a
reference datum having at least five reference locations
so that the at least five reference locations can be
detected by the sensor means, at least three of the
20 reference locations falling in a straight line (as
defined herein) and at least two of the reference
locations falling in a second line paralleljto the said
straight line, said second line being spaced from the
straight line in the direction of an imaginary line
25 between the sensor means and the reference datum;
determining calibration values having regard to the image
locations of the reference locations in the sensor means
utilizing known displacements between reference locations
in the datum to take into account perspective distortions
30 due to the positional relationship between the sensor
means and the datum.
A straight line is defined herein to be a line
which is straight when viewed from all directions.
assay
" Since, according to the first aspect of the
invention, the sensor means is calibrated to compensate
for perspective distortions due to the positional
I.
relationship between the sensor means and the datum the
5 sensor means need only be arranged so that they view the
article to be measured and the determined calibration
values may be utilized in the calculation of the desired
dimension of the article to provide improved accuracy in
the measurement of that dimension.
The invention in the first aspect may also be
said to reside in a system for calibrating a sensor means
for use in measuring the dimension of an article,
comprising a reference datum having at least five
reference locations all of which can be detected by the
15 sensor means, at least three of the locations falling in
a straight line (as defined herein) and at least two of
the locations falling in a second line parallel to said
straight line, said second line being spaced from the
: straight line in the direction of an imaginary line
20 between the sensor means and the reference datum, said
sensor means in use detecting said reference locations,
and processing means for determining calibration values
: having regard to the image locations of the reference
locations in the sensor means utilizing the known
25 displacements between reference locations in the datum to
take into account perspective distortions due to the
positional relationship between the sensor means and the
datum.
Preferably the step of determining calibration
30 values comprises the step of forming equations, which
include the calibration values, indicative of the
displacement or an object coordinate from the projection
of a line perpendicular to a sensing array in the sensor
means related to its image coordinate, solving those
35 equations to determine the calibration values, storing
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,.
6 -
" the calibration values for use in an equation or
equations which give the dimension or dimensions of the
article taking into account the distortions. Preferably
the method of calibrating the sensor means also
5 determines scaling of displacements between image
coordinates as compared to displacement between
corresponding object coordinates and also determines
unknown relative displacements between the sensor means
and a further sensor means.
lo The first aspect of the invention may further
reside in a method of determining the dimension of an
article comprising arranging at least one sensor means to
detect the article when the article is in a measurement
position, locating a reference datum at the measurement
15 position so that it is detected by the sensor means to
calibrate the sensor means by determining calibration
equations, including calibration values, for compensating
for perspective distortion and displacement of the sensor
means from the datum, solving the calibration equations
20 to determine the calibration values, storing the
calibration values, removing the reference datum, and
then detecting said article with the sensor means to
obtain information concerning the article and calculating
the dimension or dimensions of the article by means of
25 measurement equation or equations which include the
calibration values and the information concerning the
article.
- Preferably one of the calibration values is
indicative of the displacement of a reference location in
30 the datum from the projection of a Wine perpendicular to
a sensor array in the sensor means related to its image
coordinate in the sensor array.
A further difficulty in measuring dimensions of
an elongate object such as a hot Ahab is that the hot
35 slab may exit a rolling mill and travel along a roll
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" table at a slight angle to the longitudinal axis of the
table. In order to correctly determine the width of the
slab it is therefore necessary to determine the skew
angle of the slab with respect to a known axis such as
5 the longitudinal axis of the table.
The method described above of calibrating the
sensor means to compensate for distortions due to
physical relationships, whilst overcoming significant
problems experienced in the prior art, will not
10 compensate for the possibility of inaccurate measurement
of at least one dimension of a slab due to the slab being
skew with respect to the longitudinal axis of a roll
table.
The object of a second aspect of the invention
; 15 is therefore to provide a method and apparatus for
accurately measuring the dimension of an elongate article
not withstanding the fact that it may be at an ankle with
respect to a predetermined axis.
The invention in a second aspect, may therefore
20 be said to reside in a method of measuring the dimension
of an elongate article comprising the steps of arranging
at least two sensor means to detect said article,
calibrating each said sensor means to compensate for
distortions due to the physical relationship between the
25 sensor means and the article, receiving information from
each said sensor means to determine if the elongate
article is at an angle to a predetermined axis and
utilizing said information to provide said dimension or
allow the dimension to be obtained therefrom.
The invention in the second aspect may also be
said to reside in a system for measuring the dimension of
an elongate article comprising at least two sensor means
to detect said article, processing means for calibrating
each said sensor means to compensate for perspective
35 distortions due to the physical relationship between each
.
, I.
I
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' sensor means and the article and for receiving
information from said sensor means to determine if the
elongate article is at Jan angle to a predetermined axis
for use in providing said dimension or allowing the
5 dimension to be obtained therefrom.
Preferably the elongate article is a slab and
the predetermined axis is the longitudinal axis of a slab
table on which the slab is supported.
Preferably two sensor means are arranged above
10 the plane in which the article skews, said sensor means
being displaced relative to one another, along the
predetermined axis, by a predetermined distance and the
skew angle of the article is determined from the distance
between the sensor means and the distance between each
15 sensor means and a central point of the slab along a line
perpendicular to the predetermined axis.
The invention also provides a reference datum
for use in calibrating sensor means to be used to measure
the dimensions of an article, said datum comprising a
20 support frame, said support frame supporting at least
five reference locations such that three reference
locations are arranged in a straight line which will be
transverse to an imaginary line between the reference
datum and the sensor means when the reference datum is in
25 use, and two of the reference locations being in a line
parallel to said straight line and spaced from said
straight line in the direction of said imaginary line.
In a preferred embodiment of the invention will
be illustrated in conjunction with the measurement of
30 dimensions of a hot slab produced in a steel mill with
reference to the accompanying drawings in which:-
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Figure 1 shows a schematic view of a system for
measuring dimensions of a hot slab;
Figure 2 shows viewing geometry of two of the
cameras used in Figure i;
Figure 3 is a plan view of a slab skew
measurement arrangement;
Figure 4 is a view of camera viewing geometry
and illustrates a comparison between viewing geometry of
a parallel array and a tilted array;
Figure 5 issue end view of reference datum in
the form of a calibration frame on a roll table;
Figure PA is a side view of the frame of Figure
I;
Figure 6 is a diagram of viewing geometry seen
15 by one of the cameras when viewing the calibration frame of Figure 5 and PA;
Figure 7 is a view of camera viewing geometry
used in calibrating the camera;
Figure 8 is a view of camera viewing geometry
20 for two cameras used in calibrating the cameras;
Figure 9 is a plan view of a skew calibration
arrangement;
Figure 10 is a diagram showing a degraded and
ideal image response of a slab edge;
Figure 11 is a block diagram of a processing
system;
Figure 12 is a flow chart of a main control
program;
Figure 13 is a view of a camera alignment
: 30 system; and
Figure 14 is a side view of the system of
Figure 13.
With reference to Figure 1 three cameras
numbered 1 to 3 are shown arranged around a hot slab.
35 The cameras are interconnected with a microprocessor
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.,
" system 12~ Cameras 1 and 2 are arranged to enable the
thickness and the width of the hot slab 10 to be
determined Camera number 3 is provided to enable
compensation for any skew of the slab 10 on a roll table.
5 The cameras 1 to 3 are preferably line scan cameras which
consist of a normal camera lens which focuses an image of
an object onto a linear array of photo diodes. The image
received by the photo diodes therefore represents only a
single line or a narrow band of the object in view.
The photo diodes produce an electrical signal
proportional to the intensity of incident light.
Additional electronics within the camera samples the
signal produced by each photo diode serially and produces
an electrical (video) signal varying in time. This
15 latter signal is therefore a facsimile of the image
intensity varying along the length of the array.
The cameras are all aligned so that their lines
of view are across the appropriate slab face and
perpendicular to the direction of travel of the slab.
The apparent width of a slab face as determined
from the location of the slab edge images senses my each
of the cameras is dependent on both the true width of the
face and its distance from the camera. Therefore to
measure the sectional dimensions of a slab it is
25 necessary to determine the distances from each camera to
the slab faces. This is achieved by taking simultaneous
measurements from the two cameras viewing the top and
side faces of the slab in the same plane. The dimensions
are obtained by solving the following simultaneous
30 equations which are derived from Figure 2 below. Note
that the distances do and dye are not the nominal focal
lengths of the lenses, but are the distance from the
principal point of the lens to the array.
Sue
. T = (X -Al) (m -ml ) (i)
do
W = ( YE Ye ) ( my -ml )
(ii,
y
X = ( YE Ye ) ( mm-mlX )
(iii)
dye
10 Ye = (X -Al) (m ml )
(iv)
do
Slabs lying skew on the roll table will cause
an error in the width measurement of the slab because the
15 viewing line of camera 2 will no longer be parallel to
the width dimension. The skew does not affect the
thickness dimension of the slab. The relationship
I; : between the true width W and the apparent width W' for a
skew angle is:
W = W' cost (v)
Determination of the amount of skew and hence
: correction of the apparent slab width is achieved by
employing a third camera which views the top face at a
known distance from camera 2 as illustrated in Figure 3.
25 The skew angle is defined by the following expression.
Em and Em hue the distances along the camera viewing
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,.
lines between the middle of the top face to camera 2 and
3 respectively. Ed is the displacement between cameras 2
and 3.
tan = Em Em
( vi )
The above equations (i) to (vim are valid only
if the camera arrays are aligned parallel to the slab
faces in view. This would require a critical alignment
10 of the cameras which is difficult to achieve in practice.
In addition, such an alignment would not necessarily make
the best use of the available measuring range of the
cameras. For example, if the array of camera 1 was
aligned parallel to the side face of the slab and located
15 at a height of 50mm above the bottom of the slab, to
avoid viewing the top or bottom faces when locating the
edges of the thinnest slab of loom, its total viewing
range would need to be 500mm in order to view a maximum
thickness slab of 300mm. This wasted viewing range and
20 hence loss of resolution is avoided by tilting and moving
the camera with the same lens closer to the slab face to
achieve a viewing range of 300mm as seen in Figure I
Any angle between the sensing array and the
face in view introduces a perspective error. The effect
25 of perspective is indicated by the dependence of the
apparent dimension of an image on its position on the
sensing array.
To overcome the problems associated with the
need to arrange the sensing arrays of the camera parallel
30 to the slab face in view the invention provides a
R2~
13 -
calibration technique to compensate for the effect of
perspective distortions introduced by the physical
relationship between the cameras and the slab.
With reference to Figure 5 and Figure PA
5 calibration frame 20 is provided which has a number of
reference points disposed thereon. Reference points 22
to 30 are arranged in a single plane so that they can be
viewed by one of the cameras arranged above the
calibration framer for example camera 2 in Figure l.
lo Reference points 32 to 40 are arranged so that they are
viewed by camera l in Figure l. The calibration frame 20
may include legs (not shown) for securely supporting the
calibration frame 20 on the roll table so that the
calibration frame is aligned perpendicular to the
15 direction of travel of a hot slab. The frame 20
comprises four planes which contain the reference points
20 to 40. Reference points 22 to 26 are arranged in one
plane and reference points 28 and 30 are arranged in
another plane for viewing by camera number 2 in Figure
20 and reference points 32 and 34 are arranged in one plane
and reference points 36 to 40 are arranged in a further
plane for viewing by camera number l in Figure l. The
first two mentioned planes are parallel to the top face
of a slab and the other two planes are parallel to the
25 side face of a slab.
The reference points are preferably in the form
of lights which are provided in housings so that they
direct light only towards the camera by which they are
intended to be viewed. The reference points 22, 24, 26,
30 28 and 30 should not be viewed by camera number l and the
other reference points should not be viewed by camera
number 2. Reference points preferably have a width of
about 3mm and are somewhat longer in length. The image
of the reference points therefore appear as very sharp
35 responses which approximate a normal distribution. The
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,.
center of the reference point image can therefore be
located by finding the mean of the distribution. As the
width of the distribution it spread over a number of
photo diode elements the-reference point center can be
5 located to an accuracy better than resolution of the
camera.
To calibrate cameras 1 and 2 the reference
frame is positioned in the viewing plane of these
cameras. The cameras are each adjusted to view five
10 illuminated reference points, three in the nearest and
two in the furthest planes. This viewing geometry is
illustrated in Figure 6.
The distance of an object coordinate Yip from
the projection of the line which is perpendicular to the
15 array is related to its image coordinate my by the
following expression.
Ox (mm mix
Yip
I; B A (mm-ml)
20 Where x - distance from the principal point of the
camera to the plane of measurement
(distance dimensions)
::
A = constant (array coordinate dimensions)
dependent on viewing perspective and is
zero when the array is parallel to the
plane of measurement
B = constant (array coordinate dimensions
squared) dependent on the distance from
the principal point to the array
Sue
- 15 -
.,
" R - scaling constant (array coordinate
dimensions)
mm = array coordinate corresponding to the
line drawn from the principal point of
the lens which intersects the array at
: right angles. This is nominally the
midpoint of -the array.
The above mentioned equation is derived in the
: following manner with reference to Figure 6 and 7.
. 10 Referring to Figure 7:
F = principal point of the lens
OFmm = line intersecting array at right
angles
Hump = line intersecting object plane at
:: 15 : : right angles
my = projection of~the:object coordinate
onto Thor
- :
OF: =: HF/Cos~ Jo x/cos~
x tan
AYE = OF tan
coy O
I; ; OX = OX coy s a
A = OX sin
: : : : :: :
;::: : : `: : :
:
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.. By - A tan ( + 0 ) = OX sin tan (I -t )
i OX + By = OX cost + OX sin tan (I Jo )
x tan
= [cost + sin Tony I)]
cost
tan mm mix m - my
Fmm d
Yip = Owe = distance to object coordinate Yip
from 0 in the object plane.
x.(mm-m.)
-> Yip = (cost + sin tan + 0 ))
duos
x(m.-m.~ 1
15 -I Yip m 1 At
dcos0(cos~ - Mimi sin )
d
Determination of the unknown quantities in
20 equation At is possible by observation of 5 reference
points in Figure 5 located in two parallel object planes
whose relative displacements are accurately known.
The known displacements Ye/ Yore and x and the
array coordinates ml to my allow the following three
25 equations to be formed.
Let Mom for convenience
Jo
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. 1.7
x M My .
y = 1 Allah)
duos ~(~ d ) ( do
----> my = Ml My - Allele)
_ _
does I - MlS~
x+ x My My
Ye = _ Allah)
does Loos (coy M4si~
:
Combining Allele and Allah) to eliminate Yin
coy 3~Ml 2M3 + My) sin ( 1 5 3 5 1 3
I: : d
Bin
Ados - = where A 1 3 5 Alluvia)
d
end B - 2MlE~5 - M3M5 -MlM3
375
8 -
Substituting At into At gives
Ax My i
Yip = ' ( )
sin coy Bohemia i
M. A
Yip = Ox . where K = _ _ Alluvia)
B-A My sin cost
and My = m -my
Equations Allah) and Alluvia) can now be
10 rewritten in terms of the constants AHAB and K as follows:
yule = OX! My
: By Awl) (BOHEMIA)
:
Ml My
I: 15 yule' K x E worry = - Alluvia)
Bawl BOHEMIA
: and
Ye Ox + I 2 My
I: : :
I : (BOHEMIA) (BOHEMIA)
I'
Sue
,
-- 19 --
My My
-I Ye = Ox + of where F = - Alluvia
(BOHEMIA) (BOHEMIA)
Jo
Solution of equations Alluvia) and Alluvia)
5 yields the following expressions for K and x.
K = EYE _ 2ylF
Alex)
-
EN a x
yule
10 I x = _ At
KEY
The expression or can be determined from
the expression for K given in equation Avow). However, K
has a dependence on the array coordinate mm which is
15 accurately known. mm is assumed to be the midpoint of
Thor for convenience in the above calculation. The
equation for the displacement between two points in the
object plane is given by an expression of the form of
equations Alluvia) and Alluvia. These expressions and
:
: equation At can be shown to be totally independent of
: : mm. the displacement of an object coordinate Ye from the
point of intersection of a line, drawn from an unknown
array coordinate my through the principal point, which
intersects the object plane at right angles is given by
25 the following expression which can be shown to be
independent of mm.
.
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, . .
yip = Ox j ] - P_ 1 where Mom
~B-AMj) (Bump)
M. -M
y. = Ox + P where P = P Alex)
up
(B-AMj) Bump
The value of the expression for P can be
determined from knowledge of the relative displacement of
; 2 reference points located in displaced object planes.
10 From Figure 6:
.
Yo-yo = Xx ¦ , + P] - K (x+ ox) ~,_~ +
L(B_AM1) (BOHEMIA)
15 -' P - - My Yo-yo Al(xll)
Q x Bawl (B-AM4)(B-AM4) Ox
To complete the:callbrat1on of the two cameras
: : l and 2 requires a calibration frame arrangement as
Jo illustrated in Figure 8. The known displacements Ye, Ye,
20 XD~and Yo-yo are substituted respectively for the terms Y
Ye, ox and Yo-yo in preceding equations to determine the
calibration constants A , By, Key, Xx and Pry for camera 1.
I; Similarity the known displacements Al, X2, YE and X14 are
: : substituted for the terms Ye/ Ye/ By and Yo-yo in the
: 25 preceding equations to determine the calibration
: constants Ax, By, Ox, My and Pox
:
.
, ....
s
. - 21 -
addition to these known displacements, the displacements
of the points in the planes facing one camera with
respect to -the planes at right angles Xc and Ye are also
known. A prerequisite for the measuring equations in the
5 following section is the determination of the relative
displacements between the two cameras XT and YE which are
represented by equations Alex) and Al(xiv) below. The
subscripts x and y denote horizontal and vertical
parameters respectively.
I lo
XT = Xc + Xx + Ox Y _ + Pox Axe)
( Bx-AxMlx )
lye
YE = Ye + Ye Key Xx Y Al(xiv)
(By-AyMly) _
The equations for the slab section dimensions
which are derived from equation Alluvia) in terms of the
array coordinates and displacements illustrated in Figure
2 are shown below.
My My
Thickness T - Key (XT-Xl) _ Al(xv)
( By~AyMly ) ( Bohemia )
975
- 22 -
Mix My -
Width W = Ox (YE Ye) - Al(xvi)
Jo (BX-AxMlx) ( x x 2x
The terms Al and Ye which are derived from
5 equation Alex) are given by the following expressions.
Mix
Al KX(YT Ye) + Pox
( BX-AXMlX ) -
_
:~: Al T 1) Ox where Ox = Ox Mix x Al(xvii)
( Bx-AxMlx )
and _
M
Ye = Ky(XT~Xl) lye + pry
( By~AyMly )
:
l= (XT-Xl) My where Z = K Y Al(xviii)
: (BY~AYMlY)
Solution of equations Al(xvii) and Al(xviii)
yield the following expressions which are substituted
into equations Al(xv) and Al(xvi) to give the slab
dimensions.
.
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Al T y T
T Ye _ _ Al(xix)
x ( I- ~Z~cZy )
( XT ZXYT
5XT Al -- . Al ( xx )
Z ( 1 - Z Z
To calibrate the third camera, the same
calibration frame 20 is transposed from the first
: calibration position a distance ED corresponding to the
10 nominal longitudinal displacement between cameras 2 and
3. The frame is positioned such that its plane remains
perpendicular to the direction of travel of the slab and
there is no lateral displacement prom its previous
position. Camera 3 is adjusted to view the five
Jo 15 illuminated reference points in the two horizontal
planes.
; The calibration constants for camera 3 (A, By,
Kz, Pi and IT) are determined in a similar manner to
those for cameras 1 and 2. In addition to these
I:: 20 constants it lo necessary to determine the amount of
: lateral offset JO between cameras 2 and 3 as shown in
: Figure 9. JO is determined by finding the difference in
the lateral displacements of the two cameras with respect
; to camera I
The equation for the offset JO becomes:
:
I
, ...
- 24 -
Mlz
JO = Xc + Xx + Kz Zz + Pi IT (vii)
(By - AzMlz)
Where Xc = displacement of the first reference point from the side of the calibration frame
Xx displacement of camera 1 from the side of
the calibration frame
Zz = displacement of camera 3 from the top of
the calibration frame
Equation (vi) for the skew angle tangent
therefore becomes: ,
.
Z - X - X
tan (viii)
Z
d
Since in the preferred embodiment of the
invention the article being measured is a hot slab it is
not necessary to provide additional illumination.
However if a cold article is being measured additional
illumination such as conventional front or back lighting
- 20 or the like could be provided. Furthermore since the
temperature of hot slabs can vary between 900C and
1200C, the illumination Received by the camera can
change by a factor of more than 20. The preferred
embodiment of the invention may therefore compensate for
25 this by adjusting the camera exposure time. The
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micro processing circuitry 12 may adjust the clocking
frequency of the cameras to maximize the video signal
obtained without saturation.
The sharpness-of the edges of the slab images
5 obtained by the cameras is degraded by two factors. The
first of these is a defocusing effect which results from
changes in the object distance from the camera causing
shifting of the focused image plane. The range of
distance for which a lens maintains a suitably sharp
10 image is commonly referred to as its depth of field and
is dependent on the aperture setting.
The second factor influencing image edge
sharpness is caused by the radiation emitted from the
slab not being constant for the full width of a slab
15 face. The temperature of the slab reduces significantly
towards the edges of the face resulting in a gradual
reduction in intensity of the corresponding image.
The above effects can be summarized by Figure
10 where the ideal image of the slab edge would be a
20 step. However, as the higher frequency spatial
components are removed by defocusing or the overall
amplitude of the edge region is reduced by reduction in
temperature the location of the steepest gradient in the
edge region is unchanged. Therefore the preferred form
25 of the invention incorporates multi-level digitization of
the analog video signals from the cameras and
subsequent software processing by the microprocessor to
determine the location of steepest slope in the edge
region of the image.
The main processing unit 12 shown in Figure 11
incorporates an Intel 8085 microprocessor with associated
program memory, camera interface, analogue-to-digital
convertors (Adequacy), direct memory access (DAM) type
memories, serial interfaces, a front panel keyboard and
35 display, and power supplies. The camera video signal is
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26 --
digitized by the ADO and stored in memory via DAM. The
microprocessor processes this stored video data to
calculate the required dimensions which are displayed on
a front panel. This information is transmitted to a
5 remote display and a computer or other logging device via
a RS23~C standard serial communication link. The camera
interface includes camera clock control logic and digital
signal receivers which are used to control the timing of
digitization of the camera video signals. Operator
10 intervention of the processing system is achieved via a
front panel keyboard whereby other functions such as
calibration can be initiated. The calibration constants
are stored in non-volatile memory. Additional front
panel indication is provided to display any power supply
15 failure or camera over temperature alarms which are also
monitored by the microprocessor.
The preferred embodiment of the invention may
also include hot metal detectors which are used by the
system to establish the position and direction of travel
20 of the hot slab on the roller table. For example two hot
metal detectors can be positioned on either side of the
camera 1 and 2 viewing plane so that the system will only
measure the section size of the swab excluding ends which
have not been scarfed.
The system software is approximately OK bytes
in length and is written in Intel 8085 Assembler
Language. It is structured into a number of modules
which are exercised as required by a main control
programmer which is automatically entered into after the
30 system is powered up. This programmer a flowchart of
which is shown in Figure 12 initiates the collection of
digitized video data from the cameras and processes this
information to calculate the slab dimensions. The system
2~975
- 27 -
software also contains other functions which can be
initiated from the front panel keyboard These functions
include:
- examine and modify system memory contents
- examine and modify system input-output ports
restart measuring tire. main control
programmer
- system hardware test
- calibrate cameras 1 and 2
- calibrate camera 3
- collect digitized video data
- copy video data into non-volatile memory
Another programmer which controls the operation
of the front panel or console keyboard and display also
15 permits a dynamic display of system memory contents to
assist in monitoring the system during trouble shooting.
When this facility is invoked the system continuously
updates the console display with the contents of a
selected memory location while the systems measuring.
20 The selected memory location can also be changed during
operation via the keyboard.
A serial communication link from the system to
a host computer has been provided to allow collection and
monitoring of sizing data. The system automatically
25 sends messages at the beginning and end of each slab, and
continuously sends new measurement results when
available. The also responds to control instructions
from the computer to send a status message, the last
measurement result or to reset after an error.
The preferred embodiment also proposes a method
of aligning the cameras 1, 2 and 3 so that they view the
reference points 22 to I on the calibration frame 20.
As shown in Figures 13 to 14 each of the cameras 1 to 3
975
- 28
(for example camera number 1) is provided with a laser
50. The laser 50 is arranged and fixed relative to the
camera so that the beam of light which spreads out in one
dimension from the laser 50 intersects with a -target,
5 such as the reference points on frame 20, corresponds to
the cameras field of view. The laser beam, therefore
gives a visual indication of where the line scan camera
is aimed. The beam may be spread by the use of electron
or acousto-optic scanners or a cylindrical lens, the last
10 being the simplest to implement.
In practice the laser 50 and camera 1 are
aligned prior to installation. To preserve this
alignment, brackets (not shown) holding them are locked
in position. The laser/camera assembly can then be
15 adjusted until the laser light falls on the desired
portion of a target. The camera will then be
automatically positioned correctly.
To initially align the laser 50 and the camera
1 the camera 1 is leveled and aimed at a suitable test
20 target 52 as shown in Figure 14. The target 52 is set to
the same height as the camera so that the field of view
is centralized. This is accomplished by monitoring the
video output of the camera. The target 52 is moved up
and down until it exits the cameras field of view. The
25 target is then positioned halfway between these exit
points. The laser 50 is turned on and is adjusted so its
beam lies on the center of the target. The laser camera
assembly is moved vertically so that the target moves in
and out of the cameras field of view. By monitoring the
30 video output and the laser line, a check can be made of
the coincidence of the target moving beyond both the
laser line and the cameras field of view. The assembly
is repositioned at a lesser distance from the target and
coincidence is again checked. Fine tuning of the laser
3~3~5
- 29
alignment may be necessary. This step is repeated for
other distances until coincidence occurs over the entire
operation distance.
This technique is suitable for any application
5 which uses a line scan camera without a view finder or
one with a view finder where its use is complicated by
mechanical constraints or poor locations. This aspect of
the invention therefore provides a simple and effective
manner of aligning the cameras, for example, to view the
10 reference points on the calibration frame 20.
Since modifications within the spirit and scope
of the invention may readily be effected by persons
skilled within the art, it is to be understood that this
application is not limited to the particular embodiment
15 described by way of example hereinabove.
