1. Field of the Invention
The invention relates to a device and a method for detecting flaws in continuously produced float glass.
2. Description of the Prior Art
DE 196 43 017 C1 discloses a method for determining optical defects, in particular of the refractive power, in large-area panes of a transparent material such as glass, in which, by projecting a defined pattern onto the glass and imaging this pattern onto a camera, the image observed is evaluated. This is done by a light-dark sequence of the grid pattern being respectively imaged onto a number of adjacently arranged pixels of the camera and the number being an integer multiple of the light-dark sequence. The object of this invention is to specify a method with which optical defects in at least one dimension of a pane can be determined locally without any reference pattern. Flaws in a continuously proceeding fabrication process of float glass cannot be determined hereby.
A method and a device for determining the optical quality and for detecting defects of flat glass, in particular of float glass, or other optically transparent materials are described in DE 198 13 072 A1. In this case, a video camera substantially observes a lighting device through the glass, wherein the focus is located on the glass and the video camera generates signals on the basis of the quality of the glass and said signals are evaluated. Such a known method is intended to achieve the object of devising a method in which no dead zones are present and the intensity of deflection (refractive power) and the magnitude of the glass defect can be determined. In addition, a measurement of the nucleus of the defect in the glass is to be possible. This object is to be achieved in that use is made of a lighting device the color and/or intensity of which change in a defined manner from one outer edge to the other, further in that, in the fault-free state of the glass, the observation spot of the video camera is located approximately in the center of the lighting device, in that the lighting device is assigned two video signals u1, u2 depending on color and/or intensity, and in that a change in the intensity of the video signal u1, u2 is used to assess the quality of the glass.
Flaws in a continuously proceeding fabrication process of float glass can likewise not be determined by this method.
The device according to the invention and, respectively, the corresponding method are therefore based on the object of proposing a device and a method with which, during the running process of the production of a band of liquid glass, what is known as float glass, the formation of flaws, for example in the form of inclusions, bubbles or similar undesired phenomena, can be detected and monitored continuously.
This object is achieved by a device for detecting flaws in a continuously produced float glass band by checking a glass strip which extends perpendicularly to the conveying direction and is observed in transmitted light, having the following features:
The device according to the invention will be described in more detail below.
In detail:
The basic idea of the present invention is, firstly, by what are known as scanning sensors, for example in the form of line cameras, to monitor the flow of the float glass band continuously and, secondly, also to create the possibility of being able to re-adjust or replace the individual scanning sensors, in the event of a repair or partial failure, during this continuous monitoring operation.
By using this lifting apparatus 13, it is possible to raise the entire fastening bridge 3 for the repair of one or more scanning sensors 2 and/or the associated adjusting apparatus 14 and, by the respective target apparatus 16 that can be pivoted in, to adjust the respective scanning sensor 2 without the reference surface of an otherwise necessary flat glass 7. Although this necessitates a brief interruption to the detection of flaws, the procedure of adjusting a scanning sensor by the target apparatus 16 that can be pivoted in can be shortened so highly as compared with the prior art that continued running of the glass band can be economic. This is because, from an economic point of view, the temporary failure of the possibility of detecting flaws, as compared with the previously necessary complicated breaking off and melting of the glass band, may appear to be tolerable.
An additional lighting apparatus 4 is illustrated in section on the right-hand side of the maintenance bridge 10, analogous to a corresponding apparatus 4 on the left-hand side. This apparatus spans the entire width of the strip of flat glass, but its central part is not visible in this illustration. The function of this apparatus will be described later during the explanation of
In
These adjusting apparatuses 14 can not only be raised and lowered overall with the scanning sensors 2 by the lifting apparatus 13, but in addition each intrinsically has the possibility of being moved independently of one another in all 3 spatial coordinates.
Thus, it is firstly necessary that the scanning sensors 2 can move in the direction of the longitudinal extent of the fastening bridge 3, here designated as the X direction, for example, both in the positive and also in the negative X direction, in order to ensure gap-free combination of the images of all the scanning sensors 2 involved over the entire width of the glass strip to be checked. This means that, in this way, it is possible to ensure by control that an image of a scanning sensor 2 ends where the image of the adjacent scanning sensor 2 starts.
Furthermore, for the correct alignment of each individual scanning sensor 2, it is necessary that the center thereof is aligned accurately on the dividing line between the linear lighting means 20 (oscillating) and the lighting means 23 (constant lighting) (
Furthermore, in addition a possible displacement of an individual scanning sensor 2 in the vertical direction, that is to say the Z axis, is necessary for the case in which an individual scanning sensor 2 must be adjusted precisely by the target apparatus 16 described later.
As a particular refinement, provision is made that, in the case of the re-adjustment of an individual scanning sensor 2 during the running operation of the float glass production, a gap-free testing operation is maintained in that each scanning sensor 2 with its associated adjusting apparatus 14 has an associated second version of itself at the closest possible distance in the direction of the glass flow. This second version is used for the purpose of replacing the corresponding first version in functional terms during the adjustment or the complete replacement thereof For this purpose, depending on the physical conditions, it may be necessary in a particular refinement to provide the additional possibility of a slight tilting inclination in the second version, in order to cover the same region on the dividing line between the two lighting means 20 and 23. This is necessitated by the horizontal offset of the respective first version and of the second version of a scanning sensor 2 and the associated adjusting apparatus 14 of the latter.
In
In the case of a flaw-free glass, the center of observation of each scanning sensor, for example a video camera, lies in the region of the boundary line of the lighting means 20 and the lighting means 23. In the event of a glass defect occurring, this observation center is displaced out of this central position as a result of refraction of light. As a result, at the location of the detected glass defect, different influences result on the output signal in the region of the relevant scanning sensor 2. From the change of two successive signals from a scanning sensor 2 and the additional information about the defect location and/or the position in the region of the relevant scanning sensor 2, in a novel way a resultant error signal can be obtained from the comparison of the measured values of two optical channels related to each other and can be fed to a circuit arrangement for fault detection and for further signal processing.
For more detailed explanation, in
The cooling apparatus 21 acts on the underside of the two light strips. A cover 22, which acts simultaneously as a light diffuser, forms the termination of the light strips opposite the underside of the glass band to be checked. As a special refinement of the device according to the invention, a second version of the above-described lighting means 20 and 23 can be provided, which, in terms of the position (parallel to the first version), correspond to the above-described second version of the adjusting apparatus 14 and the respective associated scanning sensor 2. In the event of a repair or the entire replacement of a lighting means unit or parts thereof, this additional arrangement ensures the undisturbed operation of the entire device according to the invention by an automatic changeover operation to this second version. The aforementioned additional tilting device on each adjusting apparatus 14 for the respective scanning sensor 2 is not necessary in this case, since the second version of an adjusting apparatus 14 is arranged directly above the center line of the second version of the lighting means 20 or 23. The respective second version, be it now the adjusting apparatus 14 or the lighting means 20 or 23, is arranged upstream of the first version in order to detect approaching flaws in advance and to supply them to further evaluation. It goes without saying that these second versions must likewise have corresponding, additional target devices 16 that can be pivoted in.
This target apparatus 16 has fixed marks in the form of simple lines and/or crossed lines of specific thickness and/or color, by which the respective sensor 2 can automatically be aligned in a desired reference position in accordance with a defined program.
Here, the appropriate scanning sensor 2 is raised to an extent which corresponds to the distance of the target apparatus 16 from the glass band. The adjusting apparatus 14 subsequently adjusts the relevant scanning sensor 2 in accordance with the optical predefinitions of the horizontal alignment of the target apparatus. After the adjustment of the scanning sensor has been carried out, the target apparatus 16 pivots back again and the scanning sensor is lowered again to its predetermined working height above the glass plate 7.
The additional lighting apparatus 4 has additional lighting means such as, for example, LEDs, UV lamps, quartz lamps, xenon lamps or helium lamps, which offer additional possibilities for determining undesired glass properties. These depend on the type of glass and the specific requirements on the glass mixture produced and thus the glass parameters or glass defects to be detected in each case.
In a particular refinement, an additional apparatus for measuring the glass thickness, for example by laser or ultrasound, assigned in position to each scanning sensor 2, can also be provided. With such an apparatus, the thickness of the glass band produced can additionally be detected and recorded during the production process, resolved in the transverse direction and longitudinal direction. These measured values can be used to monitor the production process of the float glass band.
In a particular refinement of the invention, provision can additionally be made that, at the same time as the detection of flaws in the float glass, a device for measuring and monitoring stresses in the glass band is provided. To this end, a method is proposed in which polarized light is sent into the glass band, wherein stresses that occur effect birefringence, and the emergent light beam is analyzed in order to determine the changes caused by the birefringence and thus the stresses occurring. These stresses are determined by sweeping continuously over the width of the glass band, registering the aforesaid changes of the birefringence type and simultaneously measuring the temperature at the relevant point swept over in each case. From the measured changes in the birefringence and the associated measured temperature at the respective measuring point, the permanent stress at the relevant measuring point and, as a whole, thus the entire width of the glass band can be determined. The continuous measurements of these stress variations in the width of the glass band supply important pointers to stresses in the float glass band in the longitudinal direction, which represent a high potential hazard to the entire fabrication.
The region subjected to the polarized light ray radiated in preferably has a diameter of less than 20 mm in this case. The temperature measurement can be carried out, for example, with an optical pyrometer. The control of the complex movement processes and the signal processing of the sensors used requires a specific control program.
What has been described above are preferred aspects of the present invention. It is of course not possible to describe every conceivable combination of components or methodologies for purposes of describing the present invention, but one of ordinary skill in the art will recognize that many further combinations and permutations of the present invention are possible. Accordingly, the present invention is intended to embrace all such alterations, combinations, modifications, and variations that fall within the spirit and scope of the appended claims.
Number | Date | Country | Kind |
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10 2010 046 433.3 | Sep 2010 | DE | national |
This application is a National Stage application of International Application No. PCT/DE2011/001772, filed on Sep. 21, 2011, which claims priority of German application Serial Number 10 2010 046 433.3, filed on Sep. 24, 2010, both of which are incorporated herein by reference in their entireties.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/DE11/01772 | 9/21/2011 | WO | 00 | 3/22/2013 |