CN116209874A

CN116209874A - Method and apparatus for measuring geometry of bent glass sheet

Info

Publication number: CN116209874A
Application number: CN202280004309.0A
Authority: CN
Inventors: T·尼尔森
Original assignee: Saint Gobain Glass France SAS
Current assignee: Saint Gobain Glass France SAS
Priority date: 2021-09-30
Filing date: 2022-09-07
Publication date: 2023-06-02
Also published as: WO2023052064A1

Abstract

A method for measuring the geometry of a bent glass sheet (1) at a temperature of at least 200 ℃, said glass sheet having a first side (I) and a second side (II), wherein a) will have a first wavelength (λ _M ) Is directed at a measurement point (P) on the first side (I) and the back-radiated radiation (B) is detected with a first detector (6), and the measured distance h, B) between the measurement point (P) and the laser (L) is determined to have a different wavelength (lambda) than the first wavelength (lambda) _M ) Is of the second wavelength (lambda) _R ) Is directed at a reference point (R) on a diffusely reflecting reference sample (5) having a known nominal distance f from the reference Laser (LR), and is detected by means of a second detector (7)Measuring the back reference radiation (BR) and determining a reference distance R, c) between a reference point (R) and a reference Laser (LR), determining a difference between the reference distance R and the target distance f, and subtracting the difference from the measured distance h, such that a corrected distance d, d) is obtained, steps a) to c) are performed for at least two measurement points and as many reference points, and determining the spatial position of the at least two measurement points from the at least two corrected distances.

Description

Method and apparatus for measuring geometry of bent glass sheet

Technical Field

The present invention relates to a method and apparatus for measuring the geometry of a bent glass sheet.

Background

In the field of vehicles, increasing demands are being placed on the geometry of the louvers. This relates in particular to the bending of the window pane, which may lead to undesired optical effects if the bending deviates from a specified value. These optical effects may be, for example, optical distortions when looking through the glazing panel or a distorted representation of a heads-up display.

Accordingly, there is a need for a method for accurately measuring the bending of bent glass sheets, which are suitable for industrial mass production. In particular, there is a need for such a measurement method that can be integrated into the glass bending methods commonly used in industry. The complex glass sheets are typically bent in a multi-stage bending process, including, for example, a gravity bending step (pre-bending) followed by a press bending step (final bending). For example only, reference should be made to EP1836136B1, FI912871A, US2004107729A1, EP0531152A2 and EP1371616A1. The multi-stage bending method may benefit from the measurement of bending between bending steps: the parameters of the subsequent bending step may be adapted to the achieved pre-bending in order to achieve a final bending with a reduced deviation from the specified bending value.

Laser methods for making pitch measurements are known, such as laser triangulation. In this case, the laser radiation reflected by the surface of the object to be measured is detected, wherein the distance is measured from the angle of the observation point. By measuring two or more points, the relative position and thus the geometry of the object can be deduced by such a method. Since no direct contact with the object is required, but the geometry measurement is carried out remotely, in principle this laser method can also be well integrated into the bending method. However, laser triangulation and similar methods are premised on diffuse reflection at the surface of the measurement object, which in the case of glass plates does not always occur to the required extent. Furthermore, bending of the glass sheet occurs partially at temperatures exceeding 500 ℃. When the measurement is performed in a hot atmosphere, turbulence in the furnace atmosphere causes inaccuracy in the measurement. This is caused by the temperature dependence of the refractive index of air.

US20100051817A1, EP0747664A2, EP3786576A1 and DE202020104634U1 disclose methods for measuring the geometry of bent glass sheets, wherein tin deposits, which occur in the case of float glass as a result of production, for example, are excited by means of laser radiation to fluoresce. The spatial position of the fluorescing surface or point is determined, from which the geometry of the glass sheet, in particular its curvature, can be deduced. These methods also suffer from measurement inaccuracies caused by the hot atmosphere in the glass bending furnace.

US2019302582A1 relates to a method and a measuring device for focusing and leveling for use in the field of photolithography.

US2008068620A1 relates to a method for measuring deflection of a glass sheet when bending the glass sheet on a ring (Ringform), wherein the method comprises setting up a stationary or fixed reference plane with respect to the ring and measuring the deflection at a measuring point of the glass sheet and using the measurement data to control the flow of the bending process, in particular heating of the glass sheet or suspension of the bending process.

Disclosure of Invention

The object on which the invention is based is to provide a method and a device for measuring the geometry of a bent glass sheet at elevated temperatures, which are suitable for industrial applications and which can be realized in a simple manner. In particular, the method should be simple to integrate into a multistage bending method.

The object of the invention is achieved according to the invention by a method according to claim 1. Preferred embodiments are known from the dependent claims.

The method according to the invention is used for measuring the geometry of a bent glass sheet. In this case, the expression "geometry" relates to the bending of the plate. Thus, it is also possible to speak of a measurement of bending, bending geometry (Kr mmungsggeometry), bending shape or curvature (Kr mmungsgrad). The glass sheet has a first side (I) and an opposite second side (II). The circumferential edge (side) of the panel extends between the first side and the second side.

The method according to the invention is particularly suitable for being carried out in hot atmosphere, i.e. at an ambient temperature of at least 200 ℃, preferably at a temperature present in a furnace or between two furnaces, as when glass is bent. These are temperatures of at least 300 ℃, preferably at least 400 ℃, very particularly preferably at least 500 ℃, such as for example about 650 ℃. A particular advantage of the method according to the invention is that the method can be used even at such high temperatures and provides accurate results. The process also works at lower temperatures. However, particular advantages are particularly pronounced at high temperatures.

In step a) of the method according to the invention, a first wavelength λ is provided _M The radiation of the measuring laser is directed at a measuring point on the first side (I) of the glass plate. The back radiation is then detected by the first detector. The measuring laser is a laser used for illuminating a measuring point to be determined on the first side of the glass plate. The first detector detects the back-radiated radiation as a position-dependent signal. From this, the measured distance h between the measuring point and the laser is determined by means of laser triangulation.

In step b), a second wavelength lambda is to be provided _R Is aligned with a reference point on a diffusely reflecting reference sample having a known position and the back-radiated reference radiation is detected with a second detector as spatially resolved reference signal. Since the position of the diffusely reflecting reference sample is known, the nominal spacing f between the reference laser and the reference point is alsoAre known. The reference distance r between the reference point and the reference laser is determined by means of triangulation.

The second wavelength is different from the first wavelength such that the radiation of the measurement laser back is also different from the reference radiation of the reference laser back. Thus, the radiation of the radiation back of the measuring point and the reference radiation of the radiation back of the reference point can be detected as differential signals in that two different wavelengths are detected. The reference laser is a laser used for irradiating the reference sample.

In step c), a difference between the reference pitch r and the nominal pitch f is determined. The differences are caused by disturbing influences of the environment, such as turbulence in the furnace atmosphere or vibrations of the chassis of the vehicle. The difference is thus subtracted from the measured spacing h, so that a corrected spacing d between the laser and the measurement point is obtained. The idea behind this approach is that turbulence in the furnace atmosphere affecting the radiated back radiation, e.g. due to the temperature dependence of the refractive index of the air, is the same for the reference point and the measurement point. Since the position of the reference sample is known, the measured pitch h can be corrected using the difference between the measured reference pitch r and the nominal pitch f.

In step d), steps a) to c) are performed for at least two measurement points and at least two reference points. The number of measurement points and reference points is the same. A corrected distance is then obtained for each measurement point. The spatial position of at least two measurement points is determined from the at least two corrected distances. The relative position of the at least two measurement points allows a statement regarding the bending geometry. Such a statement can already be made on the basis of two measurement points. By increasing the number of measurement points, a more accurate description of the plate geometry is possible.

The measured distance or the measured reference distance is determined by means of laser triangulation. This is a known method for distance determination at room temperature, the measurement principle of which has been published a number of times. For example, the measurement principles are described herein: laser triangulation A fundamental uncertainty in distance measurements, R.G. Dorsch, G.H ä Usler, J.M. Herrmann; applied Optics, vol.33, no. 7, 1306-1314. In this case, laser radiation is detected which is emitted back from the surface of the object to be measured, wherein the distance is measured from the angle of the observation point. By measuring two or more points, the relative positions of the points and thus the geometry of the object can be deduced by such a method.

The spacing in the sense of the present invention means the shortest distance between two points in space.

In the sense of the present invention, a point is understood to be a measuring point (laser spot ) of laser radiation focused according to an approximate point shape. The point is therefore not a point in the mathematical sense, but a plane which corresponds to the expansion of the punctiform focused laser radiation and is therefore associated with a focusing optical element (lens, in particular a spherical condenser lens). These illustrations apply to both the measurement and reference lasers.

The at least two measuring points in step d) may be discrete, i.e. spaced apart from each other, wherein no laser radiation impinges on the glass sheet between the measuring points. Two discrete measurement points may be illuminated simultaneously. That is, steps a) to c) are performed simultaneously for at least two measurement points. Alternatively, two discrete measurement points may be illuminated sequentially (i.e. sequentially).

It is also possible to use a single laser spot, wherein a relative movement occurs between the laser radiation and the glass plate such that the linear region of the first side is swept by the laser spot. A number of measurement points are then sequentially illuminated. Alternatively, however, it is also possible to irradiate a larger area at the same time, which area then comprises a large number of measuring points. Thus, in particular, a laser line, i.e. a linear radiation focus, can be used. Such a laser line can be understood as a number of adjacent measuring points. In other words, the laser line contains a large number of measurement points in the sense of the present invention. The described variant can be applied both to a measuring laser and to a reference laser. The same variants are preferably selected for the measuring laser as for the reference laser in order to achieve a correction of the spatially resolved signal and the number of reference points and the number of measuring points are identical.

In order to repeatedly perform step a), a plurality of measuring points on the glass surface are preferably measured using a plurality of different measuring lasers, respectively. For example, two measurement lasers having the same first wavelength may be used to measure two specific measurement points on the glass sheet. Alternatively, a single measuring laser is preferably used, which is focused onto a plurality of measuring points sequentially or simultaneously, as described above. Accordingly, in order to repeatedly perform step b), a plurality of different reference lasers are preferably used to measure a plurality of reference points on the reference sample, respectively. Alternatively, a single reference laser is preferably used, which is focused onto multiple reference points sequentially or simultaneously.

Steps a) and b) are performed as rapidly as possible (zeitnah), preferably simultaneously, so that the disturbing influence on the measuring point and on the reference point on the reference sample is the same. In case of very large time intervals, e.g. of more than 5 seconds, the influence of the environment on the measurement point and on the reference point may be different. The maximum time interval depends on the disturbing influence of the environment, which should be corrected. In the case of correction for vibrations of the chassis of the vehicle, the maximum time interval is, for example, related to the speed of the chassis.

The time interval between steps a) and b) is preferably less than 0.1 seconds, particularly preferably less than 0.01 seconds. Turbulence in the hot furnace atmosphere results in rapidly changing conditions such that the measurement and the reference measurement are performed as nearly simultaneously as possible.

The distance a between the measurement point on the glass plate and the reference point on the diffusely reflecting reference sample should preferably not be too large in order that the environmental conditions are as similar as possible so that a correction of the signal can be successfully performed. Distance a is the spatially shortest possible connection between the measurement point on the first side of the glass plate and the reference point. The distance a between the measurement point on the glass plate and the reference point on the diffuse reflection reference sample is preferably between 1 mm and 30 mm, preferably between 5 mm and 20 mm.

The term reference sample denotes a diffusely reflecting, i.e. for example white coloured, article. The article is preferably made of a thermally stable material. The article itself may have any geometric shape, such as a circle, rectangle, bar, or triangle. The article may be irradiated at a plurality of different locations (reference points). Multiple individual items may also be used so that reference points on different reference samples may also be used to correct for different measurement points. It is preferred to use reference samples that are irradiated at different reference points for repeated execution in step d).

The reference sample may be arranged stationary in position in the environment of the glass sheet, for example in a furnace, or for example directly on a movable carrier on which the glass sheet is transported. The arrangement on a carrier for the glass pane is particularly preferred, since in this case corrections are made simultaneously for undesired movements of the carrier.

Depending on the nature of the measurement laser and glass plate used, the radiation of the measurement laser is diffusely reflected at the first side of the glass plate, or the radiation of the measurement laser excites atoms on the first side to fluoresce, so that the back-radiated radiation is the emitted fluorescent radiation.

The method may be performed statically. This means an implementation in which the glass plate is positioned stationary during the measurement. The laser radiation can also be fixed in position on the glass pane. By stationary is meant that the laser radiation is not moved in the length or width direction of the glass sheet. At least two laser spots can be used for the measuring laser and/or the reference laser. Ideally, a large number of measuring points are distributed raster-wise over the glass plate in order to enable the bending profile to be measured as accurately as possible. The measuring points can be determined simultaneously with the divided radiation of a plurality of lasers or of a single laser, or sequentially, i.e. in succession, preferably with the same laser. Laser lines, which are understood to be laser radiation focused in a line-like manner, can also be used. The laser line preferably extends across the entire width of the glass sheet (or smaller laser lines using multiple lasers adjacent to each other so as to generally cover the entire width of the glass sheet). Preferably a plurality of spaced and parallel laser lines are used. Measurement with two or more laser spots results in two or more measured location points, measurement with one or more laser lines results in one or more linear curved profiles (profile lines, line profile) along the laser line(s). The reference laser and the measuring laser are preferably used in the same way. That is, if, for example, a laser line is used for the measurement laser, a laser line is also used for the reference laser.

However, it is also possible in the case of static execution to move the laser radiation of the measuring laser and/or the reference laser on the glass plate, in particular by means of a suitable laser scanning device, for example in the case of two tilting mirrors. A single laser spot can be used here, which is preferably moved over the entire length of the glass pane. This results in a measurement of the line profile. In an advantageous embodiment, a plurality of laser spots are used, which are distributed along a line over the width of the glass sheet. These measurement points are moved over the glass sheet, preferably along the entire length of the glass sheet. So that the line profiles of the curved geometry, which are spaced apart from one another, can be determined. The method may be performed with the laser line of one laser, which preferably covers the entire width of the glass sheet (or with the smaller laser lines of a plurality of lasers adjacent to each other so as to cover the entire width of the glass sheet as a whole). If the laser line is then moved across the entire glass sheet (perpendicular to its direction of extension), a continuous or quasi-continuous curved profile of the entire sheet can be created.

In the case of static execution, variants using fixed-position laser radiation have the following advantages: the variant is also possible without complex and possibly disturbing scanning devices. Whereas the variant with moving laser radiation has the following advantages: the variant allows accurate measurements to be obtained with a smaller number of lasers (or with less technical effort for dividing the laser radiation).

Instead of being carried out statically, the method can also be carried out as a continuous method, in which the glass sheet is moved under laser radiation. This is understood as a movement of the glass sheet, wherein the laser radiation preferably remains stationary (i.e. aligned to the same point or the same plane in space) so that the sheet surface is swept by the laser radiation. If the glass sheet is moved under laser radiation, the laser radiation is swept across the glass sheet along its entire length. Here, the length means a dimension in the moving direction (conveying direction) of the glass sheet. During the movement of the glass sheet under the laser radiation, the irradiated radiation of the radiation back and the irradiated reference radiation of the radiation back are detected by means of the first and second detectors, and the measured distance h and the reference distance r are determined, respectively. After correction of the measured distance h using the difference between the reference distance r and the target distance f, the spatial position of the irradiated region can be determined in a position-dependent manner along the region swept by the laser radiation. The possible designs of the laser radiation (laser focal point (s)) correspond here to those which are executed statically with moving laser radiation. Thus, a single laser spot (measuring contour line), a plurality of laser spots distributed along a line over the width of the glass sheet (measuring a plurality of parallel contour lines) or preferably a laser line extending over the entire width of the glass sheet (measuring a continuous or quasi-continuous entire curved contour) can be used for the measuring laser and the reference laser, respectively.

Even when the method is performed as a continuous method, a movable laser beam may be applied, for example, to measure a plurality of contour lines placed side by side with respect to the conveyance direction with the same laser, or to scan the laser beam during movement of the glass sheet perpendicular to the conveyance direction for measuring contour lines perpendicular to the conveyance direction (along the width of the sheet), whereby a continuous or quasi-continuous curved contour of the entire sheet can be obtained.

Implementation in a continuous process is preferred over static implementation because implementation in a continuous process can be integrated particularly well into industrial processes, especially into multi-stage bending processes, where the glass sheet is typically moved from a first bending station to a second bending station. If a continuous process should not be possible, for example because the glass sheet is shaken too strongly during transport, the transport can also be stopped and the process performed statically.

The measuring laser and/or the reference laser may be operated in a pulsed manner or in a continuous wave mode. Pulsed lasers are preferred because they can be obtained at low cost, especially in the UV-C range. In this case, a high pulse repetition frequency (pulse sequence frequency) should preferably be used in order to be able to achieve a rapid measurement. The pulse repetition frequency is for example at least 100 Hz, preferably at least 1 kHz.

The measuring laser and the reference laser are not limited to a specific manner of construction. For example, "tripled" (355 nm; sum frequency mixing of fundamental radiation with frequency-doubled radiation; third harmonic) or double frequency (266 nm; fourth harmonic; frequency doubling of second harmonic) Nd: YAG lasers, which are popular for industrial applications (fundamental radiation 1064 nm), may be used. Alternatively, a likewise popular Yb-YAG laser (base radiation 1030 nm) is suitable. However, other laser types may be used, such as diode lasers, excimer lasers, or dye lasers.

In the case of a continuous process, the movement speed of the glass sheet is preferably from 0.5 m/s to 5 m/s, particularly preferably from 1 m/s to 2 m/s. Such movement speeds are common in the case of industrial bending methods. If the method is performed statically with moving laser radiation, the movement speed (scanning speed) of the laser radiation is preferably 5 m/s to 20 m/s. So that geometry measurements can be performed with low time consumption.

The minimum spread of the focal points of the laser radiation of the measuring laser and the reference laser (i.e. the diameter of the laser spot or the line width of the laser line) is preferably 0.2 mm to 1 mm, particularly preferably 0.3 mm to 0.7 mm. This range is particularly advantageous in terms of radiation intensity and resolution.

The laser radiation is preferably directed substantially perpendicularly to the glass sheet. This means that the optical axis (i.e. the propagation direction of the laser radiation) runs parallel to the surface normal of the geometric center of the bent glass sheet. The first and second detectors are preferably arranged on the same side of the glass sheet, wherein the detection direction typically encloses an angle between 0 ° and 90 °, for example 20 ° to 70 °, with the surface normal of the geometric center. Perpendicular illumination is preferred because the bending geometry of the plate sometimes requires a special design of the focus arrangement, which can be achieved more simply in this case. This is especially the case in the case of using laser radiation with a linear focus (laser line).

The first detector and/or the second detector is preferably a photodiode, a photomultiplier or a spatially resolved photodetector, for example a CCD (charge-coupled device) sensor or a CMOS (complementary metal-oxide semiconductur (complementary metal oxide semiconductor)) sensor or a photodiode array. These detectors detect spatially resolved signals. The spatially resolved signal is used to determine the distance of the measurement point from the laser and/or detector by triangulation.

The geometry of the glass sheet can be determined in different ways by means of the radiation that is radiated back. In principle, the radiation of the at least one measuring laser can be focused onto the first side such that at least two measuring points are irradiated simultaneously. For example, a CCD or CMOS camera is used as the first detector. Accordingly, the radiation of the at least one reference laser may be focused onto the first side such that at least two reference points are irradiated simultaneously. For example using a second CCD or CMOS camera as the second detector or using the same camera that can detect the back radiation and the back reference radiation at the same time.

The respective camera records a spatially resolved signal for each measuring point and reference point, from which the distance between the measuring point and reference point and the camera/laser is determined by means of triangulation. The processor required for calculating the spacing is preferably integrated in the camera, but may also be integrated in a computer connected to the camera.

The back-radiated radiation of at least two measuring points can be detected simultaneously with the respective cameras. The position of at least two measuring points, in particular their relative position to one another, can thus be determined, which allows statements about the bending of the glass pane.

In the case of the method described above, the laser radiation is preferably directed substantially perpendicularly to the glass sheet, but this is not absolutely necessary. In principle, the laser radiation can impinge on the glass plate at any angle of 1 ° to 90 ° to the surface normal (at the geometric center of the glass plate). The decisive is the angle between the radiation of the laser (excitation light path) aligned to the first plate and the radiation detected back (detection light path). The larger the angle, the better the resolution of the measurement method. The angle between the excitation light path and the detection light path is preferably 10 ° to 170 °, and can be selected by the person skilled in the art according to the requirements and limitations in the application case.

The method described above can be performed statically, i.e. with a fixed-position glass sheet or in a continuous process. In the case of static execution, two or more measurement points (laser spots) separated from each other may be used, which illuminate the glass sheet simultaneously, or one or more laser lines may be used, which desirably extend over the entire length or width of the glass sheet. The laser radiation can also be moved over a stationary glass plate in order to obtain more accurate measurements. Thus, two or more measurement points separated from each other may be distributed across the width of the glass sheet (along a line extending along the width dimension of the sheet) and moved across the length of the glass sheet. A laser line may also be used that extends across the width of the glass sheet and is moved over the length of the glass sheet. By continuous measurement with a detector, a parallel line profile along the length of the glass sheet (in the case of separate measurement points) or a total profile in length and width dimensions (in the case of laser lines) is obtained. When performed in a continuous process, two or more measurement points separated from each other may likewise be distributed across the width of the glass sheet, or a laser line may be used. The observation corresponds to a static execution with moving laser radiation, wherein the relative movement is performed here by moving the glass plate under the stationary laser radiation. A continuous process is preferred because it can be advantageously integrated into industrial processes, particularly bending processes, where the glass sheet is typically moved between the various bending stations.

When performing with a relative movement between the plate and the laser radiation, the Dimension in the direction of movement is denoted by length and the Dimension perpendicular thereto is denoted by width. The terms length and width are interchangeable when performed purely statically.

In a first preferred embodiment, in step a), the radiation of the measuring laser having the first wavelength is reflected by a first side of the glass plate. In this case, the reflected radiation is detected as return radiation by means of a first detector. The measurement need not be in direct contact with the glass sheet, but rather is performed at a relatively large spacing and is suitable for use in a continuous process. This allows a good integration of the method into an industrial bending process.

In a second preferred embodiment, in step a), the fluorescent radiation emitted from the first side is detected as a back-radiated radiation. The glazing panels are typically manufactured in a popular float glass process. The glass melt is guided into a bath of liquid tin, where it hardens into a glass layer, which is then divided into glass panes. The corollary of this approach is that the two surfaces of the glass sheet are not identical. A distinction is made between the side of the tin bath in direct contact with the tin bath and the opposite atmospheric side. This distinction is based in particular on: tin atoms diffuse from the tin bath into the glass surface during hardening of the glass sheet. These tin residues can be excited to fluoresce and diffuse fluorescent radiation can be used to determine the relative positions of different measurement points on the glass surface and thereby determine the bending geometry of the glass sheet. In contrast to directly reflected laser radiation, fluorescent radiation is incoherent, so that no disturbing interference effects ("specle"), laser granulation (lasermanulation) are to be expected. The measurement need not be in direct contact with the glass sheet, but rather is performed at a relatively large spacing and is suitable for use in a continuous process. Thus, the method can be well integrated into an industrial bending method. These are great advantages of the present invention.

According to a second preferred embodiment, the glass sheet is a float glass sheet and the first side is the tin bath side of the float glass sheet and the second side is the atmospheric side of the float glass sheet. The surface of the plate that is in contact with the tin bath in the float process is referred to herein as the tin bath side. The surface opposite the side of the tin bath that is in contact with the surrounding atmosphere in the float process is referred to as the atmosphere side. The surrounding sides of the plate extend between the tin bath side and the atmosphere side.

According to a second embodiment, a bent float glass sheet is measured. For measuring the geometry, the radiation of the measuring laser is aligned or focused to a measuring point on the side of the tin bath. Thereby, the tin residues deposited on or diffused through the side of the tin bath below the plate surface are excited to fluoresce (laser-induced fluorescence). The measuring laser is suitably selected for this purpose. The emitted fluorescent radiation is radiation that radiates back from the measurement point and is detected by means of a first detector (photodetector).

The measuring laser must be suitable for fluorescence excitation of tin residues in or on the glass plate. In particular lasers whose radiation has a wavelength in the UV spectral range of up to 360 nm are suitable for this purpose. It is particularly preferred to use radiation in the UV range from 240 nm to 355 nm, very particularly preferably from 240 nm to 300 nm, in particular from 240 nm to 280 nm, in the UV-C range. At wavelengths in the mentioned range, the tin residues have sufficiently high fluorescence quantum yields that the fluorescence radiation can be used as a basis for geometry measurements. Although the fluorescence quantum yield of tin residues is higher at wavelengths less than 240 nm, interfering effects such as low lifetime of the components (komponen), ozone formation in the bending furnace, high absorption of float glass plates and the need for large and expensive excimer lasers can sometimes occur.

In this case, for example, green (490 nm to 575 nm, e.g. 532 nm) or red (635 nm-750 nm, e.g. 650 nm) reference lasers are suitable as reference lasers, since these are available at low cost.

In a preferred embodiment, the method according to the invention for taking geometry measurements is integrated into a multistage bending method. The method is performed here between two bending steps. The method is preferably performed as a continuous process during the conveyance of the glass sheet from the first bending station to the second bending station. The glass sheet can be placed directly on a conveyor system, for example a roller or belt conveyor system, or on a carrier mold which is moved on its side, for example by a roller, rail or belt conveyor system. The first bending step is performed in a first bending station and the second bending step is performed in a second bending station. For example, the first bending step may be gravity bending with which a pre-bending of the glass sheet is achieved, and the second bending step may be press bending and/or suction bending with which a final shape (final bending) of the sheet is achieved. Such multi-stage bending methods typically suffer from non-negligible dispersion in plate geometry (Streuung). The application of the method according to the invention between two bending steps has the following advantages: the degree of pre-bending can be determined. The parameters of the subsequent bending step (e.g. bending temperature or pressing pressure) are then preferably adapted according to the measured pre-bending in order to reduce deviations from the specified plate shape and dispersion of the finally bent plate.

When applied in a bending method, the heat radiation of the bending furnace may interfere with the measurement. In an advantageous embodiment, an optical filter is therefore used for detecting fluorescent radiation by means of the first detector, which filter blocks radiation of a longer wavelength than its filtering edges. This filtering edge of the optical filter is preferably at most 600 nm, particularly preferably 500 nm to 600 nm. Thus, when detecting fluorescent radiation on the tin side of the float glass sheet, the fluorescence of the tin residues is mostly transmitted and the heat radiation of the usual bending furnaces is filtered out to a large extent. In the detection of the reflected radiation as a return radiation, a suitable bandpass filter or high-pass filter is likewise preferably used, which is tuned to the laser used and passes its wavelength. An optical filter is arranged in the optical path of the first detector between the glass plate and the first detector such that radiation recorded by the first detector first travels through the filter. A high-pass filter or a band-pass filter may be used as the optical filter. The high pass filter has a filtering edge in which longer wave radiation is blocked and shorter wave radiation is transmitted. The band-pass filter additionally has a further filter edge at shorter wavelengths, wherein shorter-wave radiation is blocked. The band-pass filter can thus only pass radiation in the wavelength range between the two filter edges. Instead of a band pass filter, a combination of a high pass filter and a low pass filter may also be used. If the first detector is sensitive only in the relevant spectral range and insensitive to interfering radiation, no optical filter may be required. In particular, the photodiodes can be designed in this way.

The bending method for a component part of a composite panel, such as a windshield, is sometimes performed such that two single panels, which should be connected to each other later, are bent identically simultaneously while being superposed. The shape of the veneer should thus be particularly well coordinated with each other. An advantage of the invention is that the measuring method can also be applied to two superimposed glass sheets and its geometry can be measured simultaneously.

When carried out according to the second embodiment, the excitation laser radiation passes through the plate and can excite fluorescence on both tin bath sides. The tin bath sides of the two plates preferably face away from one another.

When performed according to the first embodiment, the reflection of the radiation of the measuring laser may be detected at a powdered separating agent located on a first side of one of the two superimposed glass plates between the two glass plates.

The invention also includes a bending method having at least the following method steps:

1. pre-bending the glass sheet in a first bending step

2. The geometry of the glass sheet is measured using the method according to the invention,

3. the glass sheet is bent in a second bending step, the parameters of which are preferably adapted to the measured pre-bending.

Other bending steps may optionally be performed before the first bending step or after the second bending step.

The invention further includes an apparatus for measuring the geometry of a bent glass sheet having a first side and a second side, the apparatus comprising

A measuring laser having a first wavelength, the radiation of which measuring laser can be directed at least two measuring points on a first side of the glass sheet,

a first detector aligned with at least two measurement points, said first detector being adapted to detect the back-radiated radiation,

a reference laser having a second wavelength, the second wavelength being different from the first wavelength, the radiation of the reference laser being capable of being aligned to at least two reference points on a diffusely reflecting reference sample having a known position,

a second detector aligned with the at least two reference points, the second detector being adapted to detect the back-radiated reference radiation,

-an evaluation unit adapted to determine the spatial position of at least two measurement points from the corrected spacing d of the at least two measurement points.

From the radiation detected by the first detector, a corresponding measured distance h between the corresponding measuring point and the laser is determined by means of triangulation. This is preferably performed in a first evaluation unit for performing the distance calculation, which is directly connected to the first detector. The detector is then connected to a processor, which directly calculates the measured distance h. Alternatively, the measured distance h may be determined in a separate first evaluation unit, such as in a computer connected downstream.

The evaluation unit is adapted to determine the spatial position of at least two measurement points. This means that the evaluation unit is configured such that it can carry out steps a) to d) of the method according to the invention.

Accordingly, the respective measured reference distance r between the respective reference point and the laser is determined by means of reference radiation back from the radiation detected by the second detector by triangulation. This is preferably performed in a second evaluation unit for performing the distance calculation, which is directly connected to the second detector. The detector is then connected to a processor which directly calculates the measured reference distance r. Alternatively, the measured reference distance r may be determined in a separate second evaluation unit, such as in a computer connected downstream.

The above-described embodiments in combination with the method according to the invention are correspondingly applicable to the device according to the invention.

Since the method is preferably performed as a continuous method, the apparatus preferably comprises means for moving the plate. The device is adapted to move the glass sheet under the laser radiation such that the glass sheet is preferably loaded with the laser radiation along its entire length (in the direction of movement).

The invention further comprises an apparatus for bending a glass sheet, the apparatus comprising

A first bending station is provided for the purpose of,

the device according to the invention for measuring the geometry of a glass sheet,

a second bending station which is arranged to bend the sheet material,

means for moving the glass sheet from the first bending station to the second bending station through the apparatus according to the invention, in particular continuously.

The movement device can be configured, for example, as a rail-type, roller-type or belt-type conveyor system. The glass sheet may be placed directly on a conveyor system (especially in the case of a roller or belt conveyor system) or on a carrier mold. The carrier mold is in particular configured as a so-called frame mold having a frame-like contact surface, on which the circumferential edge region of the glass pane is placed, without a large part of the glass pane being in direct contact with the carrier mold.

The glass sheet is preferably a float glass sheet and is preferably composed of soda lime glass as is common for glazing panels. The thickness of the glass sheet can be freely chosen according to the requirements of the individual case. Typical thicknesses lie in the range 1 mm to 20 mm, especially 1.5 mm to 5 mm.

The glazing panel is preferably used as a vehicle panel or as a component of such a vehicle panel, in particular as a windscreen, side, rear or roof panel of a motor vehicle or as a component of such a component (in the case of a composite panel). The glass pane is particularly preferably used as a wind deflector for vehicles, in particular motor vehicles, where particularly high demands are made on the optical quality. The method according to the invention is particularly advantageous here, since it enables glass sheets to be produced with particularly low-deviation bending geometries, thereby reducing disturbing optical effects, such as distortions.

Drawings

The invention is illustrated in more detail with reference to the figures and examples. The figures are schematic and not to the right scale. The drawings are not intended to limit the invention in any way. Wherein:

figure 1 shows a cross section through a glass plate during an embodiment of the method according to the invention,

figure 2 shows a schematic diagram of a measurement of a pitch by means of triangulation,

figure 3 shows a top view of a glass sheet in the case of different embodiments of the method according to the invention for measuring the geometry of the glass sheet,

figure 4 shows a graph of the fluorescence quantum yield of tin residues,

figure 5 shows the spectra of the fluorescent radiation of a float glass sheet and of the heat radiation of a bending furnace,

FIG. 6 shows a cross section through a bending device with an integrated measuring device according to the invention, an

Fig. 7 shows a schematic cross section through a float glass sheet.

Detailed Description

Fig. 1 shows a cross section through a bent glass sheet 1 during the implementation of the method according to the invention. The radiation of the measuring laser L and the radiation of the reference laser LR are aligned as laser spots 2 to the first side I and the reference sample 5, respectively. The measuring laser L has a first wavelength lambda _M And the reference laser LR has a wavelength lambda from the first wavelength lambda _M A second, different wavelengthλ _R . The radiation of the measuring laser L is directed at the measuring point P and is radiated back therefrom as radiation B. The radiation B radiated back is fluorescent radiation emitted according to the properties of the glass plate and the wavelength of the laser L or radiation reflected at the first side. The back radiation B impinges on the first detector 6 and is detected there as a spatially resolved signal. The radiation of the reference laser LR is directed at a reference point R, which is located on the diffusely reflecting reference sample 5. The reference sample has a known position. The radiation of the reference laser LR is diffusely reflected at the reference sample as the back-radiated reference radiation BR. The back-radiated reference radiation BR is detected as spatially resolved reference signal with a second detector. In this case, the first detector and the second detector are CCD (charge-coupled device) color sensors that detect the back radiation B and the back reference radiation BR as separate signals. The CCD color sensor is connected to an evaluation unit for distance calculation, which determines a measured distance h between the measuring point and the laser and calculates a measured reference distance r between the reference point and the reference laser. This is done by known methods of laser triangulation. Correction is then made for the disturbing effects of the environment. For this purpose, the difference between the measured reference distance r and the known setpoint distance f is determined and subtracted from the measured distance h, so that a corrected distance d is obtained as d=h- (r-f).

The described steps are then repeated for a plurality of measurement points P and a plurality of reference points R. The number of measurement points P is the same number as the number of reference points R, respectively. The spatial position of the at least two measuring points can then be determined from the corrected distance d for the at least two measuring points by means of the evaluation unit.

The distance a between the measuring point P on the glass plate and the reference point R on the diffusely reflecting reference sample 5 is for example about 5 mm. Thereby ensuring similar environmental conditions for the measurement point and the reference point. It is thus ensured by means of the method according to the invention that turbulence in the furnace does not affect the measurement results.

For example, at least two measuring points can be irradiated simultaneously or can also be measured sequentially with the same laser L, which is aligned in turn with the two measuring points. Accordingly, a plurality of reference points are also illuminated, which are arranged either on the same reference sample or on a plurality of reference samples. For simplicity, the method is shown with only one measurement point. Increasing the number of laser spots 2 enables a more accurate determination of the bending geometry. An example of an arrangement of measurement points and reference points is shown in fig. 3.

The stationary glass pane 1 can be used statically (not only purely statically but also statically with moving laser radiation) or as a continuous process. In the case of stationary execution with moving laser radiation and execution with moving plates as a continuous method, it is sufficient for the measuring laser and the reference laser to be individual laser spots 2 which sweep the glass plate 1 and in this case determine a large number of measuring points along a line. The accuracy can be improved by a plurality of laser spots 2 (a plurality of measuring lines). The measurement laser and the reference laser are performed as identically as possible.

Fig. 2 schematically shows two measured distances h between two measuring points P1 and P2 and the measuring laser L, respectively ₁ And h ₂ Is determined by the above-described method. The measuring lasers are aligned with measuring points P1 and P2, the measuring points P1 and P2 are at different distances h from the lasers ₁ Or h ₂ . The first detector 6 is oriented such that it detects radiation that is radiated back from the measuring points P1 and P2 and detects said radiated back radiation as spatially resolved signals. The angle α or β at which the irradiated radiation impinges on the detector 6 is furthermore determined. The distance h can be determined from the angle and the known distance between the laser L and the detector 6 ₁ Or h ₂ . The distance thus measured is corrected by means of the parallel-executed measurement for the reference sample according to the method according to the invention.

Fig. 3 shows a top view of a glass pane 1 of a different embodiment of the method according to the invention. The embodiments differ in the way how the laser radiation is focused onto the glass plate 1.

In order to be able to make statements about the geometry, more precisely the curvature, of the glass sheet 1, the position of at least two measuring points on the sheet surface must be determined. The bending results from the positioning of these measurement points relative to each other. As described with respect to fig. 1, a corrected distance d is determined for at least two measuring points P1 and P2 by means of the method according to the invention. For this purpose, the measured distance h is determined from the back-radiated radiation of the measuring points P1 and P2. The measured distance h is corrected using the back-radiated radiation of at least two reference points R1 and R2 for which a reference distance is determined. These reference pitches are used to correct the measured pitches as described. The radiation back may be used to determine its origin using various methods described below. By analysing the corrected spacing d of the two measurement points on the surface of the plate, its relative positioning to each other can be determined. Comparing the relative positioning to the corresponding specified value allows statements about: to what extent the panel bends deviate from the specification (aufweicht). By increasing the number of measurement points, a more accurate and convincing measurement of curvature is possible.

At least two measurement points must be illuminated with a measurement laser. In the simplest case, this can be done with two mutually spaced laser spots 2 for measuring points P1 and P2 (fig. 3 a). This results in two mutually spaced starting points for the radiation back. Accordingly, the two laser spots 2 of the reference laser are aligned to one reference point R1 and R2, respectively, located near the measurement points P1 and P2. For each measurement point P1 and P2 this results in a back-radiated reference radiation starting point for the adjacent reference points R1 and R2. So that for each measuring point a value of the measured distance h is obtained, as well as a value of the reference distance r, which is necessary for the subsequent correction. If a large number of measuring points and corresponding reference points, each excited with a laser spot 2 and ideally distributed in a raster fashion over the plate surface (fig. 3 b), are used, a detailed analysis of the plate bending is derived from the individual measuring points.

Instead of the laser spot 2, a laser line 3 may also be used. The laser focus is focused here in the form of a line, which ideally extends over the entire width of the glass pane 1 (fig. 3 c). The laser line 3 may be understood as a superposition or alignment of a large number of measuring points or reference points, such that the laser line 3 contains at least two measuring points as required according to the invention. The resulting linear starting surface of the irradiated radiation can be evaluated in order to determine the spatial curvature of the starting surface. Along the laser line 3a contour line is derived. Both the measuring laser and the reference laser are focused in the form of lines. The measuring statement power can also be increased here by using a large number of laser lines 3 which ideally run parallel to one another and at uniform intervals from one another over the entire width of the glass pane 1 (fig. 3 d). A correspondingly large number of parallel contours are obtained from which the bending contour of the glass sheet 1 can be well determined.

The method according to the invention can be performed in different ways. On the one hand, the method can be performed statically, which is understood to be a measurement with a stationary glass plate 1. In this case, two variants can again be distinguished, namely, on the one hand, a measurement with stationary laser radiation (purely stationary) and a measurement in which the laser radiation is moved over the plate surface (stationary with moving laser radiation). But on the other hand the method can also be applied as a continuous method, wherein the laser radiation is stationary and the plate is moved under, i.e. relative to, the laser radiation such that the laser radiation is ideally swept across the glass plate 1 along the entire length of the glass plate 1. This enables a curved profile (krummmungspprofile) to be created along the area of the plate surface swept by the laser radiation.

The distribution of the laser focus according to fig. 3a, 3b, 3c and 3d is suitable for purely static measurements (plate and laser focus position fixed). In the stationary execution with moving laser radiation and as a continuous method, one or more laser spots 2 or laser lines 3 may in turn be used. It is preferred to use for the measuring and reference lasers a plurality of laser spots 2 which are arranged along a line extending along the width of the glass plate 1 and which are ideally uniformly distributed (fig. 3 e). If the laser radiation is scanned along the length of the plate surface and the position of the plate surface in space is determined here continuously or quasi-continuously by the radiation radiated back, each laser spot 2 of the measuring laser results in a contour line along the length dimension (dimension in the direction of movement) of the glass plate 1 and each laser spot 2 of the reference laser results in a contour line along the length dimension, and can be used to correct the contour line of the measuring point. In principle, a single laser spot 2 for the measuring laser and a single laser spot 2 for the reference laser are sufficient, which single laser spot 2 for the measuring laser and single laser spot 2 for the reference laser then sweep over a linear region. This region can in turn be regarded as a superposition or alignment of a large number of measuring points, so that at least two measuring points required according to the invention are illuminated. The use of multiple laser spots 2 results in a more accurate measurement with multiple length profiles distributed over the plate width. It is also possible to use a laser line 3 for the measuring laser and the reference laser, respectively, which laser line 3 extends over the width of the glass pane 1 and sweeps over the length of the glass pane 1 (fig. 3 f). Whereby a continuous or quasi-continuous overall profile of the plate curvature is obtained. The relative movement of the laser radiation with respect to the glass pane 1 is illustrated in fig. 3e and 3f by the square arrow W. The relative movement can be achieved by moving the laser radiation over the stationary glass plate 1 (stationary execution with moving laser radiation) or by moving the glass plate 1 under the laser radiation (continuous process).

The laser spot 2 may be generated by focusing laser radiation by means of a spherically curved lens. The laser spot 2 is formed at the focal point of the lens (as long as the focal point (brennpkt) enters the lens in a collimated fashion). The laser line 3 may be generated by focusing laser radiation by means of a cylindrical lens, a Diffractive Optical Element (DOE) or a Holographic Optical Element (HOE). The laser line 3 is formed on the focal line of the lens. Instead of forming the radiation of a single laser as laser lines 3 extending over the entire plate width, it is equally possible to use a plurality of lasers which respectively produce laser lines 3 having smaller widths and to arrange these laser lines 3 adjacent to one another along the plate width, wherein the individual laser lines 3 are likewise oriented by means of an (an) plate width. Ideally, the laser lines 3 overlap one another in order to produce, in total, laser radiation which extends over the entire plate width. In principle, however, the laser lines 3 may also be spaced apart from one another. The planar profile of the plate bends (Scheibenkummung) at a distance from one another is then obtained.

Fig. 4 shows a graph of the fluorescence quantum yield of tin residue 4 (see fig. 7), plotted against the wavelength λ of the excitation radiation. The fluorescence quantum yield was measured at the tin bath side I of the float glass plate 1. Fluorescence excitation may occur at wavelengths less than about 360 nm. The quantum yield increases with decreasing wavelength, so that the same excitation intensity results in a more intensified fluorescence emission. In particular in the UV-C range of 100 nm to 280 nm, tin residues are excited efficiently to fluoresce. For example, a doubled Nd: YAG laser (266 nm) can be used for good fluorescence excitation. If it is desired to avoid too high excitation, for example in order to avoid fluorescence saturation, the excitation power can be reduced or operated at higher wavelengths (lower quantum yield).

Fig. 5 shows the spectrum of the heat radiation of an exemplary industrial bending furnace ("bending furnace spectrum") compared to the fluorescence spectrum of the tin bath side of the float glass plate 1 ("fluorescence spectrum"). Fluorescence spectra were recorded after excitation with a UV-C-LED having a nominal radiation wavelength of about 255 nm. It can be seen that the thermal radiation is significantly red shifted (rotverscheen) compared to the fluorescent radiation. Heat radiation starts at about 600 nm. In the case of the measurement according to the invention, the possible disturbing effects thereof can thus be filtered out in a simple manner, for example by using a high-pass filter with a filter edge (Filterkante) at approximately 550 nm in the detection beam path. The UV component, for example scattered excitation radiation, can also be filtered out by an additional low-pass filter. The combination of low-pass filter and high-pass filter can also be replaced by a corresponding band-pass filter. The selection of the reference laser is flexible because the back-radiated reference radiation always has a higher intensity than the back-radiated radiation of the measurement point, so that no filter is required here to inhibit interference caused by thermal background radiation.

Fig. 6 schematically shows a cross section through a bending device with an integrated device for measuring plate geometry according to the invention. The bending apparatus is provided for a two-stage bending method in which a float glass sheet 1 is pre-bent in a first bending chamber 12 and bent to a final shape in a second bending chamber 13. The float glass sheet is driven by means of a conveyor system 10, for example a roller conveyor system, into a first bending chamber 12 in such a way that it rests on a gravity bending mould 11 and is pre-bent there by means of gravity bending. The gravity bending mould 11 is then transported with the float glass sheet 1 from the first bending chamber 12 to the second bending chamber 13, where the float glass sheet is finally bent by press bending between an upper press bending mould 14 and a complementary lower mould, for example the gravity bending mould 11 or another mould to which the float glass sheet was previously handed over. The measuring device according to the invention is mounted between the first bending chamber 12 and the second bending chamber 13, with a measuring laser L and a first detector 6, and a high-pass filter 8 arranged upstream of the first detector 6 in order to filter out interfering thermal radiation. Furthermore, a diffusely reflecting reference sample 5 is arranged at the gravity bending mould 11. The reference laser LR irradiates the diffusely reflected reference sample 5 and the back-radiated reference radiation is detected by a second detector 7. The placement of the reference sample at the gravity bending mould 11 has the following advantages with respect to being placed at other locations, for example below the gravity bending mould: i.e. so that correction can also be made for the transport movement, since the reference sample undergoes the same movement as the bending die 11.

The bending geometry of the float glass sheet 1 can thus be determined after pre-bending when it is transported. Depending on the extent of the pre-bending, parameters of the press bending step, such as bending temperature or press pressure, may be adapted. Thus, deviations from a specified bending, which occur in the range of mass processing (Massenprozessen) according to scattering, can be reduced.

Fig. 7 shows a cross section through a float glass plate 1. The float glass sheet 1 is composed of soda lime glass, for example having a thickness of 3 mm, and is manufactured in a float process. In this case, the glass melt is poured into a bath (Bad) consisting of liquid tin, where it is uniformly distributed and hardened. The surface of the formed float glass sheet 1 that is in direct contact with the tin bath is referred to as the tin bath side I, and the opposite surface is referred to as the atmosphere side II. Tin atoms can diffuse into the float glass plate 1 or adhere thereto during the float process via the tin bath side I. The tin bath side I is different from the atmosphere side II due to these remaining tin residues 4. The tin residue 4 can be excited to fluoresce, which is the basis of the second embodiment of the measuring method according to the invention.

List of reference numerals

1. Glass plate and float glass plate

2. Laser spot

3. Laser line

4. Tin residue

5. Reference sample

6. First detector

7. Second detector

8. Optical filter, high-pass filter, and band-pass filter

10. Conveyance system for glass sheet 1

11. Gravity bending die

12. A first bending chamber

13. A second bending chamber

14. Press bending die

L measuring laser

LR reference laser

B radiation of the first side

Radiation-back reference radiation of BR reference sample

Measurement Point on the first side of P

Reference point on reference sample

a distance between the measurement point and the reference point

h measured distance between measuring point and laser

f reference laser and known nominal spacing between reference points

reference spacing measured between reference laser and reference point

d corrected spacing between measurement point and laser

Direction of relative movement of W radiation S on float glass sheet 1

I first side of glass sheet 1, tin bath side of float glass sheet 1

The second side of the II glass plate 1, the atmosphere side of the float glass plate 1.

Claims

1. Method for measuring the geometry of a bent glass sheet (1) at a temperature of at least 200 ℃, the glass sheet having a first side (I) and a second side (II), wherein

a) Will have a first wavelength (lambda _M ) Is aligned with the measuring point (P) on the first side (I) and the back-radiated radiation (B) is detected by means of a first detector (6) and the measured distance h between the measuring point (P) and the laser (L) is determined,

b) Will have a different wavelength (lambda than the first wavelength (lambda) _M ) Is of the second wavelength (lambda) _R ) Is aligned with a reference point (R) on a diffusely reflecting reference sample (5) having a known nominal distance f from the reference Laser (LR), and the back-radiated reference radiation (BR) is detected by means of a second detector (7), and a reference distance R between the reference point (R) and the reference Laser (LR) is determined,

c) Determining a difference between the reference pitch r and the nominal pitch f, and subtracting the difference from the measured pitch h, so that a corrected pitch d is obtained,

d) Steps a) to c) are performed for at least two measurement points and as many reference points, and the spatial position of the at least two measurement points is determined from the at least two corrected distances.

2. The method according to claim 1, wherein the distance a between the measuring point (P) on the glass plate (1) and the reference point (R) on the diffuse reflecting reference sample (5) is between 1 mm and 30 mm, preferably between 5 mm and 20 mm.

3. The method according to claim 1 or 2, wherein the time interval between steps a) and b) is less than 0.1 seconds, preferably less than 0.01 seconds.

4. A method according to any one of claims 1 to 3, wherein in step a) the radiation of the measuring laser (L) is reflected by the first side (I) of the glass sheet and the reflected radiation is detected with the first detector (6) as a back-radiated radiation (B).

5. Method according to claim 4, wherein for detecting the reflected radiation by means of the first detector (6) an optical filter (8), in particular a band-pass filter, is used which is capable of passing the wavelength of the measuring laser (L).

6. A method according to any one of claims 1 to 3, wherein

-the glass sheet (1) is a float glass sheet (1) and the first side (I) is the tin bath side of the float glass sheet and the second side (II) is the atmospheric side of the float glass sheet (1),

-in step a), directing the radiation of the measuring laser (L) at a measuring point (P) on the side (I) of the tin bath, wherein tin residues are excited to fluoresce and the emitted fluorescent radiation is detected as back-radiated radiation (B) with a first detector (6), and

-the radiation of the measuring laser (L) has a wavelength in the UV spectral range of at most 360 nm, preferably 240 nm to 355 nm, very particularly preferably 240 nm to 300 nm.

7. Method according to claim 6, wherein for detecting the fluorescent radiation (B) by means of the first detector (6) an optical filter (8), in particular a high-pass filter (8) or a band-pass filter, is used having a filtering edge of at most 600 nm, preferably 500 nm to 600 nm, above which the radiation is blocked.

8. The method according to any one of claims 1 to 7, wherein the first detector (6) and/or the second detector (7) is a photodiode, a photomultiplier or a spatially resolved photodetector, such as a CCD or CMOS sensor or a photodiode array.

9. The method according to any one of claims 1 to 8, wherein the first detector (6) and the second detector (7) are identical.

10. Method according to any one of claims 1 to 9, wherein the radiation of the measuring laser (L) and the radiation of the reference Laser (LR) are focused in the form of at least two laser spots (2) or at least one laser spot (2) moving relative to the glass sheet (1), respectively, in order to illuminate the at least two measuring points (P) and the at least two reference points (R).

11. Method according to any one of claims 1 to 10, which is performed as a continuous method, wherein the glass sheet (1) is moved under the radiation of the measuring laser (L) and the reference Laser (LR) such that the radiation of the measuring laser (L) and the radiation of the reference Laser (LR) sweep the entire length of the glass sheet (1) in the direction of movement in order to determine the spatial position of the illuminated area as a function of position.

12. Method according to any one of claims 1 to 11, the method being performed between two bending steps of a multi-stage bending method, wherein parameters of the second bending step are preferably adapted to the measured geometry of the glass sheet (1).

13. An apparatus for measuring the geometry of a bent glass sheet (1) according to the method of claims 1 to 12, the apparatus comprising

-a measuring laser (L) whose radiation has a first wavelength (λ _M ) And the radiation of the measuring laser can be directed at least two measuring points (P) on the first side (I) of the glass plate (1),

-a reference Laser (LR) whose radiation has a different wavelength (λ) than the first wavelength (λ) _M ) Is of the second wavelength (lambda) _R ) And the radiation of the reference laser can be aligned to at least two reference points (R) on a diffusely reflecting reference sample (5),

a first detector (6) aligned with the at least two measuring points (P), the first detector being adapted to detect radiation radiated back from the at least two measuring points (P),

-a second detector (7) aligned with the at least two reference points (R), the second detector being adapted to detect radiation radiated back from the reference points (R),

-an evaluation unit adapted to determine the spatial position of the at least two measurement points (P) from the corrected distance d.

14. Apparatus according to claim 13, which is arranged between a first bending chamber (12) and a second bending chamber (13), and which has a transport system (10) for moving the glass sheet (1) from the first bending chamber (1) to the second bending chamber (13) by means of an apparatus for measuring the geometry.

15. The device according to claim 13 or 14, wherein the implementation unit is configured such that the implementation unit is capable of implementing steps a) to d) of the method according to the invention.