WO2013034812A1

WO2013034812A1 - Method and device for measuring a distance from a reflecting surface

Info

Publication number: WO2013034812A1
Application number: PCT/FI2012/050872
Authority: WO
Inventors: Mikko SYRJÄLAHTI; Miikkael Niemi; Kai Niiranen
Original assignee: Oy Sparklike Ab
Priority date: 2011-09-09
Filing date: 2012-09-07
Publication date: 2013-03-14
Also published as: FI124603B; FI20115887L; FI20115887A0

Abstract

A device (100) for measuring a distance (h) from a reflecting surface (101), such as a surface of a glass, comprises two light sources (102, 103) for emitting light beams to incident into a reflection position/area (106), which is common for the both beams on the reflecting surface. The device also comprises a detector (104, 105) for determining the individual positions (d1, d2) of the light beams reflected from the reflecting surface (101) onto the detector surface (104, 105). The (h) distance from the reflecting surface is then determined based on the positions (d1, d2) of the two light beams at the detector surface by numerically solving a trigonometric function.

Description

METHOD AND DEVICE FOR MEASURING A DISTANCE FROM A REFLECTING SURFACE

TECHN ICAL FIELD OF THE INVENTION The invention relates to a device and method for measuring a distance from a reflecting surface. Especially the invention relates to detecting a flatness of the surface.

BACKG ROUND OF THE INVENTION In a glass making process the glass sheets are transported e.g. through a furnace typically on a horizontal roller conveyor. In the furnace the glass sheet is heated for next processing steps, such as for tempering, whereupon the sheet is heated above its annealing temperature (typically about to 500-800 °C) and then rapidly cooled down (typically about to 60- 70 °C) in order to hardening the surface of the glass. This creates internal stresses in the glass, whereafter if the glass is broken, it will break into many small pieces instead of simply cracking, making it far safer. In addition the tempered glass is much stronger than the regular glass. However, the heating, roller conveying or other processing may cause undesirable distortion or variation in the flatness of the glass surface, which must be determined during the process.

Few solutions are known from prior art to detect these variations in the flatness of the glass surface, such as US 4390277, where collimated, monochromatic light is directed to a movable reflective surface. The reflected light varies from the normal incidence angle by an amount determined by the slope of the surface being tested. Another document is US 5251 01 0, where two light beams are generated to the glass sheet with predetermined distance and stored second distances are used to the reflected light to determine the surface distortion on that portion of the glass sheet. Also different kinds of patterns are illuminated onto the surface and the distortions in the reflected patterns are then determined based on thage recognition methods. However some disadvantages are related to the known prior art solutions namely in order to determine and analyse contours or other illumination patterns, a special software and especially an expensive components, such as CCD cameras are needed, which make the arrangement quite complex and expensive overall. Also installation needs relatively large space since the separate unit for creating and detecting the images are needed. In addition in order to determine distances to the surface essentially perpendicular visual connection to the surface under measurement is needed and in particularly the prior art methods don't tolerate measured surface tilting.

SUMMARY OF THE INVENTION

An object of the invention is to alleviate and eliminate the problems relating to the known prior art. Especially the object of the invention is to provide an arrangement for measuring a distance from a reflecting surface even if the surface is somehow tilted or distorted and so that these distortions or variations in the flatness of the glass surface would not effects or change to the result.

The object of the invention can be achieved by the features of independent claims.

The invention relates to a device according to claim 1 . In addition the invention relates to an arrangement of claim 6, a method of claim 8 and a computer program product of claim 1 1 .

According to an embodiment of the invention a device for measuring a distance from a reflecting surface, such as a surface of a glass, like a tempered class, comprises two light sources, which are configured to emit light beams so that they (i.e. optical axes) incident into a reflection position or area, which is common for the both beams. The common reflection area means that the distance between the incident beams may vary, but is typically at the range of few millimetres to several centimetres. According to an embodiment it is assumed that the reflecting surface between the incident beams is essentially planar so no any winding or major distortion would exist between these two points. Thus it is to be noticed that that distance can be varied due to the assumption of the distortion. The device also comprises an optoelectronic detector for determining the individual positions (distances d₁ and d₂) of the light beams reflected from the reflecting surface on the detector surface. The detector is advantageously a line detector and fixedly arranged opposite to the reflective surface to be measured.

In addition the device comprises a data processing means for determining the distance h (equation (4) below) from the reflecting surface based on the measured positions (d_1t d₂) of the two light beams at the detector surface by numerically solving a trigonometric function. According to an embodiment said trigonometric function comprises three equations {(1), (2), (3) below) with three unknown parameters: x being a mean tilt angle of the reflective surface at the reflection position/area, and h₁ and h₂ being distances of the first and second light sources from the reflective surface. Said three equations are solved numerically when the positions {d d₂) of the two light beams at the detector surface are detected. Said three equations {(1), (2), (3)) are: tan(z) = ^ m i (1 )

. d₁ cos(y+2x)cos y+x)

1 sin(2y+2x)cos(x) '

. d₂ cos(y-2x)cos(y-x) _{/ λ} tin = ( )

sin(2y-2x)cos(x) ' wherein y is an angle on which the light beams is emitted into the reflective surface from the light sources and m is a distance between the light sources {y and m are known).

When the system of said three equations {(1), (2), (3)) above is solved the desired distance h can be determined from the equation (4): h = ^ (4)

One example of numerical solution for the system of above equations can be seen below. It is based on a goodness of fit procedure where h₁ and h₂ are given values around the solution of problem and the goodness of fit value is calculated for how well the system of equations hold. A couple of things has to be carefully considered before using this kind of numerical method:

1 ) Size of input (h_1t h₂) grid. The right solution must always locate inside the grid, otherwise the result is wrong,

2) Step of input (h_1t h₂) grid. This has meaning for the accuracy. For example, if the step is 1 0 μιη, the calculation accuracy is about 5 μιη. (This is because the solution is the average of h₁ and h₂), and

3) Speed. The advantage of this method is that it gives always a correct result (if the first (1 ) condition holds). It cannot converge into any local extremes, which has to be taken into account when using e.g. faster gradient-based algorithms. However, it is possible to speed up the computing by iterating with several sensibly selected grids of different size and steps. In addition, of course, the preliminary information about the varying range of h₁ and h₂ help.

m = 110000;

dl = 46000;

d2 = 45000;

y = 30 * pi/180; bestjil = 0;

best_h2 = 0;

best_x = 0;

best _goodness = 100000000000000000000000; hi s = 37000:10:40000;

h2_s = 38000:10:41000;

for hi = hl_s,

for h2 = h2_s,

x = atan((h2 - hi) / m);

hl_e = (dl * cos(y+2*x) * cos(y+x)) / (sin(2*y+2*x)*cos(x)); h2_e = (d2 * cos(y-2*x) * cos(y-x)) / (sin(2*y-2*x)*cos(x)); goodness = (hl-hl_e) 2 + (h2-h2_e) 2;

if (goodness < best_goodness)

best_goodness = goodness;

best_x = x;

best il = hi;

best_h2 = h2;

end

end h = (bestjil + bestjil )/l; According to an embodiment the light sources are arranged in the opposite site of the reflection position. In addition, according to an embodiment, the operation of the light sources may be pulsed and/or the emitted light beams may have different wavelengths, whereupon the detector may deduce the light source of the measured beam. The operation of the light sources as well as the detector is advantageously controlled by the data processing means.

However, according to an embodiment when the distance between the light sources and the surface to be measured is even broadly known (typically the range is only few centimetres), the positions of the reflected light beams of each light source on the detector is therefore also known sufficiently accurately. Thus the both (or all) light sources can be put on/off at the same time because the positions of the each reflected beams on the detector are substantially known beforehand. This fastens the measuring procedure relating to process where the operation of the light sources may be pulsed.

According to an embodiment several measurements may be taken during a movement of the reflective surface (or relative movement of the measuring device and the reflective surface), whereupon the distance measurements of different points of the surface may be combined to determine a flatness of the reflective surface, or contour of at least one arch on the surface. According to an embodiment also the thickness of the glass sheet can be measured when the one beam of one light source reflects both from the first and second surfaces of the glass sheet and when the distances of these reflected beams emitted by said one light source are determined on the detector.

Still according to an embodiment a measuring table may be provided for receiving the glass sheet (or other object having a reflecting surface), where the measuring device for measuring the distance from the reflecting surface may be applied in connection with the measuring table. The object (like glass sheet) with the reflecting surface may lie on the measuring table essentially stationary and its surface is "scanned" by moving said measuring device. Furthermore according to an embodiment the measuring table may be hinged and configured to receive and fasten the object with the reflecting surface, whereupon the object can be tilted in vertical direction (upright position) around the hinge. The measuring device may also be applied in connection with the measuring table and again configured to "scan" the object tilted into the upright position (some standards requires the measurement taken in the upright position).

The reflecting surface described in this document may be e.g. at least partially reflecting surface, such as the surface of the glass sheet like a surface of a tempered glass panel, which is also at least partially transparent.

The present invention offers advantages over the known prior art. The use of two opposite light sources as is done in the invention makes possible to eliminate the effect of the tilt angle of the reflecting surface(s) to the measured distance(s). Also the use of an optoelectronic detector makes possible an accurate measurement of the mutual distances of the beams reflected from the reflecting surface(s) since from the intensity dispersion of the reflected beams, the determination of the intensity maximum can take place, which makes possible a very accurate distance determination. In addition the reflecting surface(s) moved past in a defined distance can be measured during their movement, without having to stop for this purpose so the measurements can be done in real-time. Connecting two or more devices parallel makes possible to cover wide area of surface to measure in real-time. Furthermore the device may be achieved very cost effective compared e.g. to contour devices using CCD-cameras. Also the installation of the device(s) is simple and fast and does not require heavy fitting stand. Extending the width of the measured area is easy just by adding a new parallel device.

BRIEF DESCRIPTION OF THE DRAWINGS

Next the invention will be described in greater detail with reference to exemplary embodiments in accordance with the accompanying drawings, in which:

Figure 1 A illustrates an exemplary device for measuring a distance from a reflecting surface according to an advantageous embodiment of the invention, Figure 1 B illustrates an exemplary device for measuring a distance from and thickness of a reflecting surface according to an advantageous embodiment of the invention,

Figure 2 illustrates an exemplary reflecting surface according to an advantageous embodiment of the invention,

Figure 3 illustrates an exemplary measuring principle for measuring a distance from a reflecting surface according to an advantageous embodiment of the invention,

Figure 4 illustrates an exemplary proofing concluding to the measuring principle for measuring a distance from a reflecting surface according to an advantageous embodiment of the invention, and

Figure 5 illustrates an exemplary measuring arrangement for measuring a distance from a reflecting surface according to an advantageous embodiment of the invention.

DETAILED DESCRI PTION

Figure 1 A illustrates an exemplary device 1 00 for measuring a distance h from a reflecting surface 1 01 according to an advantageous embodiment of the invention, where the device comprises two light sources 1 02, 1 03, which are configured to emit light beams 1 02a, 1 03a so that they (i.e. optical axes) incident into a reflection position or area 1 06, which is common for the both beams. The common reflection area means that the distance between the incident beams may vary (as is depicted in connection with Figure 2 by 1 06a, 1 06b, 1 06c), but is typically at the range of few millimetres to several centimetres (not limiting only to those). According to an embodiment it is assumed that the reflecting surface between the incident beams is essentially planar so no any winding or major distortion would exist between these two points. According to an embodiment the light sources 1 02, 1 03, 1 1 2, 1 1 3 are arranged in the opposite site of the reflection position 1 06. The device 1 00 also comprises an optoelectronic detector 1 04, 1 05 for determining the individual positions (see e.g. Figure 3 and 4 for distances d₁ and d₂) of the light beams 1 02b, 1 03b reflected from the reflecting surface on the detector surface. The detector is advantageously a line detector and fixedly arranged opposite to the reflective surface to be measured.

In addition the device 1 00 comprises a data processing means 1 07 for controlling the light sources as well as the detector. The data processing means 1 07 is also used for determining the distance h from the reflecting surface based on the measured positions {d d₂) of the two light beams at the detector surface by numerically solving a trigonometric function of three equations {(1), (2), (3)) described above and in connection with Figure 3. In addition the data processing means 1 07 may be configured to manage the operation of the light sources, such as pulsing them so that the light beams are emitted alternately from each of the light sources, whereupon the device has the knowledge from which light source the detected light beam was originated.

According to an embodiment several measurements may be taken during a movement 1 08 of the reflective surface, whereupon the distance measurements of different points of the surface may be combined e.g. by the data processing means to determine a flatness of the reflective surface, or contour of at least one arch on the surface.

Figure 1 B illustrates an exemplary device 1 00 for measuring both a distance h from and thickness t of a reflecting surface according to an advantageous embodiment of the invention. The thickness of the glass sheet can be determined e.g. by the data processing means 1 07 when the one beam of one light source reflects both from the first 1 01 a and second 1 01 b surfaces of the glass sheet 1 01 and when the distances h h₂ of these reflected beams emitted by said one light source are determined on the detector e.g. similarly as depicted in this document elsewhere. Thus the thickness of the glass sheet at the determination point 1 06 is t = h_b - h_a.

Figure 2 illustrates an exemplary reflecting surface 1 00 which may be winding or has different kinds of distortions or variations in the flatness. It is to be noted that the Figure 2 is only schematic and only for the purpose to understand the problems underlying in the glass manufacturing processes and measuring purposes of the invention. Thus as it is understood from the Figure 2 the "size" of the common reflection area 1 06 may vary depending on the distortions of the surface flatness to be determined. If the flatness of the surface is assumed to be very winding the distance between the incident beams is typically much smaller 1 06b that when the surface is assumed to be much planar 1 06a and especially 1 06c. The assumption is that the reflecting surface 1 06a, 1 06b, 1 06c between the incident beams is essentially planar so no any winding or major distortion would exist between these two points.

As an example the reflection position or area (so the distance of the beams) varies typically at the range of 1 -200 millimetres, more typically at the range of 5-1 00 millimetres and in most typically at the range of 1 0-50 millimetres millimetres. However, it is to be noted that these ranges are only as an example and the invention can be implemented naturally also for other ranges.

Figure 3 illustrates an exemplary measuring principle and method for measuring a distance h from a reflecting surface 1 01 according to an advantageous embodiment of the invention even though the reflective surface at the reflection position/area would be tilted (angle x). The distances of the reflected beams on the detector from the light sources are d d₂, y is an angle on which the light beams is emitted into the reflective surface from the light sources and m is a distance between the light sources {y and m are known, and d d₂ are determined by the detector). Based on the geometry and determined parameters a trigonometric function having the following three equations {(1), (2), (3)) can be solved numerically: tan(z) = ^ m i (1 )

. d₁ cos(y+2x)cos y+x)

1 sin(2y+2x)cos(x) '

. d₂ cos(y-2x)cos(y-x) _{/ λ} tin = ( )

sin(2y-2x)cos(x) ' When the system of said three equations {(1), (2), (3)) above is solved the desired distance h can be determined from the equation (4): h = (4).

When the surface is moving (or at least the surface and device are moving in relation to each other) the flatness of the surface in greater are can be determined by combining the results of plurality of measuring points. Figure 4 illustrates an exemplary proofing principle and method for concluding to the measuring principle for measuring a distance h from a reflecting surface 1 01 according to an advantageous embodiment of the invention. Following equations (5) and (6) can be constructed using the sine clause:

h v h v

sin(90°-x-y) sin(90°+x) cos(x+y) cos( (5) d v d

sin(2x+2y) sin(90°-2x-y) sin(2x+2y) cos(2x+y) (6)

The equation for h₁ (2) can be got from equations (5) and (6) by eliminating Again following equations (7) and (8) can be constructed using the sine clause:

v₂ v₂

sin(90°-y+x) sin(90°-x) cos(y-x) cos(x) (7) d₂ l>2 d₂ l>2

sin(2y-2x) sin(90°+2x-y) sin(2y-2x) cos(2x-y) (8)

The equation for h₂ (3) can be got from equations (7) and (8) by eliminating

Figure 5 illustrates an exemplary measuring arrangement 500 for measuring a distance from a reflecting surface 1 01 according to an advantageous embodiment of the invention, wherein the arrangement comprises typically on a horizontal roller conveyor 501 for transporting objects, like glass sheets, e.g. through a furnace 505. In the arrangement the measuring device 1 00 may be applied in connection with a stand 502a arranged typically over the conveyor, whereupon the object with the surface 1 01 to be measured is moved below the measuring device. According to an embodiment a measuring table 503 may be provided for receiving the glass sheet (or other object having a reflecting surface), where the measuring device 1 00 for measuring the distance from the reflecting surface 1 01 may be applied in connection 502b with the measuring table. The object (like glass sheet) with the reflecting surface may thus lie on the measuring table 503 essentially stationary and its surface is "scanned" by moving said measuring device 1 00, 502b over the surface 1 01 . Furthermore according to an embodiment the measuring table 504 may be hinged 506 and still configured to receive and fasten the object with the reflecting surface, whereupon the table with the object can be tilted in vertical direction (upright position) around the hinge 506. The measuring device 1 00, 502c may also be applied in connection with the measuring table and again configured to "scan" the object 1 01 tilted into the upright position (some standards requires the measurement taken in the upright position). It is to be noted that the measuring device may be configured to move along a measuring rails in relation to the surface to be measured.

The invention has been explained above with reference to the aforementioned embodiments, and several advantages of the invention have been demonstrated. It is clear that the invention is not only restricted to these embodiments, but comprises all possible embodiments within the concept and scope of the inventive thought and the following patent claims. Especially it is to be noted that the device may comprise plurality of light sources combined to determine the flatness of the surface in greater surface area. In addition the device may still comprise only one common line detector for all of the light sources or numbers of detectors. Again it is to be noted that number of devices may be combined to an arrangement to determine the flatness of the moving surface in real-time.

Furthermore at least part of the functionality of the device, such as functionality of data processing means, may be implemented by a computer program product, for example.

Claims

1 . A device (1 00) for measuring a distance (h) from a reflecting surface (1 01 ), such as a surface of a glass, characterized in that the device comprises

- two light sources (1 02, 1 03) the light beams (1 02a, 1 03a) of which are configured to incident into a reflection position/area (1 06) being common for the both beams on the reflecting surface,

- a detector (1 04, 1 05) for determining the individual positions (d_{l t} d₂) of the light beams (1 02b, 1 03b) reflected from the reflecting surface on the detector surface,

- a data processing means (1 07) for determining the distance (h) from the reflecting surface based on said positions (d_{l t} d₂) of the two light beams at the detector surface by numerically solving a trigonometric function.

2. The device according to a claim 1 , wherein said light sources (1 02, 1 03) are arranged in the opposite site of the reflection position (1 06) and wherein the detector (1 04, 1 05) is an optoelectronic detector, such as a line detector.

3. The device according to any of previous claims, wherein the operation of said light sources is pulsed and/or wherein the light sources are configured to emit light beams with different wavelength.

4. The device according to any of previous claims, wherein the data processing means (1 07) is adapted to control the operation of the light sources (1 02, 1 03) and take several measurements during a relative movement (1 08) of the reflective surface and the device, and combine the distance measurements of different points of the surface to determine a flatness of the reflective surface.

5. The device according to any of previous claims, wherein the reflection position (1 06) the light beams (1 02a, 1 03a) incident is a common area (1 06) for the both beams, and wherein the device is configured to emit the light beams onto the common area so that the distance (1 06a, 1 06b, 1 06c) of the beams on the common area on the reflecting surface varies essentially at the range of 1 -200 millimetres, more essentially at the range of 5-1 00 millimetres and in most essentially at the range of 1 0-50 millimetres.

6. An arrangement (500) for measuring a distance (h) from a reflecting surface (1 01 ), such as a surface of a glass, characterized in that the arrangement comprises at least one device (100) of any of claims 1 -4 and a measuring table (503, 504) for receiving the object (101 ) with said reflecting surface for the measurement, wherein the table is either stationary or hinged (506) and thereby configured to be turned around the hinge into the upright position with said object.

7. The arrangement according to claim 6, wherein the arrangement comprises at least two devices (100) of any of claims 1 -4 functionally connected together, wherein the arrangement is configured to determine a flatness of the reflective surface (101 ) in real-time.

8. A method for measuring a distance (h) from a reflecting surface (101 ), such as a surface of a glass, characterized in that the method comprises steps of:

- emitting two light beams (102a, 103a) with two light sources (102, 103) into a reflection position/area (106) on the reflecting surface (101 ), where said light sources are arranged in the opposite site of the reflection position,

- determining by a detector (104, 105) the individual positions (d_{l t} d₂) of the light beams reflected (102b, 103b) from the reflecting surface on the detector surface, wherein the detector is an optoelectronic detector, such as a line detector

- determining by a data processing means (107) the distance (h) from the reflecting surface based on said positions (d_{l t} d₂) of the two light beams at the detector surface by numerically solving a trigonometric function.

9. The method according to claim 8, wherein the operation of said light sources is pulsed so that light beams are emitted alternately by said light sources and/or wherein the light sources are configured to emit light beams with different wavelength.

10. The method according to any of claims 8-9, wherein several measurements is taken during a movement (1 08) of the reflective surface and the distance measurements of different points of the surface is combined to determine a flatness of the reflective surface.

1 1 . A computer program product for measuring a distance (h) from a reflecting surface (101 ), such as a surface of a glass, characterized in that the computer program product comprises code means adapted to:

- operate two light sources (102, 103) to emit two light beams (102a, 103a) into a reflection position/area (106) on the reflecting surface,

- read an output of a detector (104, 105) detecting the individual positions (d_{l t} d₂) of the light beams (102b, 103b) reflected from the reflecting surface on the detector surface,

- determine the distance from the reflecting surface based on said positions (d_{l t} d₂) of the two light beams at the detector surface by numerically solving a trigonometric function,

when said computer program product is run at a data processing means.

12. Any of claims above, wherein said trigonometric function comprises three equations ((1), (2), (3)) with three unknown parameters x being a mean tilt angle of the reflective surface (101 ) at the reflection position/area (106), hj and h₂ being distances of the first and second light sources (102, 103) from the reflective surface, wherein said three equations are solved numerically when the positions (d_{l t} d₂) of the two light beams at the detector surface are detected, said three equations ((1), (2), (3)): tan(» = ^i (1 )

m

. d₁ cos(y+2x)cos y+x)

1 sin(2y+2x)cos(x) '

. d₂ cos(y-2x)cos(y-x) _{/ λ}

tin = ( )

sin(2y-2x)cos(x) ' wherein y is an angle on which the light beams is emitted into the reflective surface from the light sources and m is a distance between the light sources, after which the desired distance h is determined from the equation (4): h = (4).