JP4774246B2 - Non-contact optical measurement method and apparatus for thermal glass body thickness using light dispersion - Google Patents

Description

  The present invention relates to an optical measurement method and apparatus for measuring the thickness of a thermal glass body without direct contact with the thermal glass body using light dispersion or chromatic aberration immediately after production when the thermal glass body is still hot.

  During the glass body manufacturing process, the glass body must maintain certain dimensions. Such dimensions are usually specified by the customer and this dimension must not exceed or fall below a predetermined tolerance limit.

  Currently, precise measurement of glass thickness is performed at the end of the cooling path. This is because if the measurement is performed at an earlier stage using a mechanical sensor, the glass surface is damaged, and contactless measurement with respect to hot glass does not work. Therefore, since the optical path is distorted by the heat of air generated by the hot glass, for example, laser triangulation cannot be performed. Measurement by ultrasonic measurement is also not possible because a coupling conductor is required between the glass and the ultrasonic source. White light interferometers cannot operate under severe manufacturing conditions. Measurements using a confocal microscope coupled with an autofocus system are also possible, but require a very high cost of several thousand euros for each measurement direction.

  However, detecting and removing defects in the production line as early as possible can reduce the production of defective products, so it is desirable to measure the glass thickness as early as possible.

  Manufacturing each product takes several hours before the product reaches the end of the cooling path, called the “cooling end”, and thus the measurement that needs to be corrected at the thermal end takes effect. If early measurement can be performed, it is very advantageous in manufacturing.

  An object of the present invention is to provide a glass body thickness measuring method and apparatus capable of measuring the thickness of a glass body with high accuracy in advance immediately after the production of the thermal glass body (in the “thermal termination portion”).

  These and other objects of the present invention will become more apparent in the following description and are achieved by the methods and apparatus defined in the claims.

The glass body thickness measurement method without contact with the glass body immediately after the glass body generation according to the present invention is a measurement method based on light dispersion or chromatic aberration, and a) on the glass body using a focusing device immediately after the glass body generation. Focusing a light beam from a multicolor light source;
b) guiding the reflected light from the glass body into the spectrometer when the light beam is focused on the glass body to obtain a spectrum of the reflected light;
c) Step of finding two wavelengths from the reflected light having a higher reflected light intensity than the other wavelengths in the spectrum obtained in step b) among the reflected light reflected from the front and rear surfaces of the glass body. When,
d) determining the thickness of the glass body in consideration of the refractive index of the glass body from the wavelength difference between the two wavelengths having high intensity;
e) maintaining the focusing device at a temperature of 120 ° C. or less during the measurement of the thickness;
f) It comprises the step of substantially blocking the heat radiation acting on the focusing device using at least one heat blocking filter.

  The method according to the present invention measures the layer thickness or layer spacing using a known light dispersion phenomenon that occurs during refraction by passage through a lens or diffractive material. In focusing white light, there is no single focus, but instead each color or wavelength has its own focal length or focus on the optical or beam axis. In other words, the focal point of each color is found at a point on the beam axis or optical axis. Since the generation of color fringes in a photograph is undesirable, the photographic technique uses several lenses made of different types of glass to remove chromatic aberration. Here, the term “chromatic aberration” refers to an optical phenomenon in which light of different wavelengths (that is, colors) is strongly refracted separately by a lens or a correction objective lens. Conversely, this action can be used to measure thickness. The length of the optical axis portion or beam axis portion where the individual focal points are found depends on the lens used and its material. When a lens having a focal range of 22 to 25 cm is used, it is possible to measure a glass thickness up to 3 cm. A polychromatic or white light beam is conducted through a glass fiber optic cable into a focusing device (measuring head or light pen), and in such a known manner from there into a glass body. Due to the optical colored image characteristics, different wavelengths are focused at different intervals from the optical instrument. If there is an interface (for example, a transition between air and glass) at the focal point of a wavelength, this wavelength is strongly reflected. That is, the reflected light intensity for that wavelength is maximized. All other wavelengths reflect back weaker, creating a weak diffuse background in the reflection spectrum. This reflected light passes through the focusing device and through the glass fiber optic cable and is conducted into the spectrometer. Therefore, the strongly reflected wavelength is detected as the maximum intensity wavelength in the spectrum.

  In the case of a transparent glass body, there are always two intensity maximum points. This is because reflection occurs on the outside or rear side of the glass body (side far from the measuring head) and on the inside or front side (side closest to the measuring head). The wall thickness can be determined directly from the simple difference between the spaced apart targets in the spectrum, taking into account the refractive index of the glass to be measured. Measuring devices based on the principle of chromatic aberration described above are widely known. As such a measuring device, for example, a device of Precite Optronic GmbH of Rodgau, Germany, trade name CHR150E is available. Measurement is measured, analyzed, computerized and / or signaled using a computer. More than a thousand measurements per second can be processed. Since the measurement frequency is high in this way, it is easy to determine the average value, and it is possible to increase the measurement accuracy.

For example, the wall thickness of a glass body such as a glass tube, the thickness of a glass rod, or the thickness of a glass plate formed in a flat glass manufacturing plant is measured as early as possible after the glass body is formed. For this purpose, the glass body usually has a glass viscosity of 10 ^6.6 Pa. s. This is performed when the final shape is reached corresponding to a temperature equal to or lower than the softening temperature (softening point). Of course, the glass shrinks more naturally as it cools from this temperature to room temperature. The dimension measured in the hot glass state does not match the final dimension and decreases corresponding to the shrinkage. However, this reduction is not a problem because the temperature of the glass body being measured is known and the coefficient of thermal expansion of the glass body is also known.

  In order to reduce the heat load on the focusing device, the focusing device is maintained at a temperature below 120 ° C. by cooling. Furthermore, the influence of thermal radiation on the focusing device is blocked by providing a heat blocking filter in the beam path between the hot glass and the focusing device. Thermal barrier filters are known and are used in many projectors, projectors, beamers, and the like. These filters have the characteristic of allowing visible light to pass through without difficulty but impermeable to infrared rays (thermal radiation). Thermal barrier filters operate according to two different principles. The first principle is the reflection principle and the second is the absorption principle. When the heat blocking filter operates according to the reflection principle, the side of the heat blocking filter facing the radiation source is provided with an IR reflective coating such as gold, platinum, or a reflective layer packet (interference filter). . The absorptive heat blocking filter is made of glass containing a suitable doping component that absorbs sufficient infrared radiation. Since the latter filter is naturally heated and therefore must be cooled, a reflective heat blocking filter capable of reflecting infrared rays up to 98% is first placed in the beam path to block it. The remaining infrared light that has passed through the infrared filter is absorbed using a subsequent absorption type heat blocking filter. Many suitable filters that operate using both of the above filter principles are commercially available.

  In order to avoid aging effects on the focusing device, it is advantageous to maintain the temperature of the focusing device in a temperature range of 20-100 ° C. Also, in order to obtain good measurement accuracy, the temperature fluctuation of the focusing device should not exceed ± 10 ° C. from the set value. This method is suitable for the measurement of glass thickness in glasses with temperatures up to 1200 ° C. A preferred glass temperature for measuring the glass body dimensions is in the range of 200-1000 ° C.

  In the case of tube measurements, it is advantageous to take measurements at the center, i.e. at the position where the measurement beam impinges on the glass surface at an angle of 90 degrees, in other words at the position where the measurement beam passes through the axis of the tube.

  When the measurement beam is decentered and deviates from the center and collides with the tube system, an angle error occurs, and the thickness of the tube inner wall is different from the tube outer wall, resulting in an inaccurate thickness, resulting in a decrease in measurement accuracy. The smaller the tube diameter, the greater the error due to the off-center measurement beam. Generally speaking, in the case of a tube system having a diameter of about 10-20 mm and a wall thickness of about 0.4-1 mm, the actual thickness value can be obtained by moving about 0.5-1 mm laterally. An error of about 2 μm occurs. It is therefore very important that the measurement beam is always directed to the center of the tube. If the measurement beam deviates from the center, not only does the measurement error occur, but the light beam is directed toward the glass surface that is not at an angle of 90 °, and not all of the light beam is reflected. Also decreases. When the measurement head is moved across the tube axis until the reflected wavelength intensity with the higher maximum reaches that maximum, the measurement beam is centered with respect to the tube system. This adjustment can be done manually, but it is also possible to automate this adjustment to control the sensor using the adjustment motor and the corresponding computer program to take the optimum position during operation.

  An apparatus for carrying out the method for measuring a hot glass body thickness according to the present invention also forms part of the present invention.

An apparatus for measuring a thermal glass body thickness according to the present invention comprises:
A polychromatic white light beam light source;
A focusing device for focusing the light beam onto a glass body;
A spectrum analyzer for analyzing reflected light reflected from the glass body when the light beam is focused on the glass body;
A double-walled housing with the focusing device disposed therein and having an inlet and an outlet for cooling liquid;
An observation port through which the light beam and the reflected light pass;
It is composed of at least one heat blocking filter.

  In a preferred embodiment of the device according to the invention, two elastic heat-resistant intervening rings are provided, and at least one heat-insulating filter is arranged between the rings. The two elastic heat-resistant intervening rings (19) are made of silicon rubber or fluorocarbon resin.

  In another preferred embodiment, a transparent window is arranged on the outside and front of the at least one heat barrier filter, the transparent window being made of a corrosion resistant material. The transparent window is made of corundum or fluorine-containing glass.

  The measuring device preferably includes a rinsing gas inlet disposed at a front portion of the transparent window and a through-opening portion for a light beam disposed at a predetermined interval from the housing in a beam transmission direction. A rinsing gas supply means including a radiation protection sheet is included.

  The objects, features and advantages of the present invention will be described in more detail using the preferred embodiments described below with reference to the accompanying drawings.

  FIG. 1 shows a measuring device. The light from the multicolor light source 1 is conducted to the focusing device 3 using the strand 2a of the glass fiber optical cable 2 composed of the glass fiber strands 2a and 2b. The light propagating from the focusing device is directed to the glass body 4 having the front surface 5 and the rear surface 6 to be measured. The focusing device 3 focuses light of different wavelengths from the light exit to different distances. The light of wavelength λ1 is focused on the front surface 5 of the glass body 4, while the light of wavelength λ2 is focused on the rear surface 6 of the glass body 4. The light reflected from the glass body 4 is transmitted to the spectrometer 7 through the strand 2 b of the glass fiber optical cable 2. Since the reflected light intensity from the front surface 5 is the strongest at the wavelength λ1 and the reflected light intensity from the rear surface 6 is the strongest at the wavelength λ2, these wavelengths can be detected by the spectrometer from the strongest intensity in the spectrum. . A digital signal processing unit 8 is connected to the spectrometer 7. The digital signal processing unit 8 displays the measured thickness or digitalizes and / or analogizes the measurement result according to a control signal that affects the manufacturing process.

  FIG. 2 shows the focusing device 3 provided in the housing. This focusing device 3 provided with a lens 10 is connected to a spectrum analysis unit 9 using a glass fiber optical cable 2. The focusing device 3 is disposed in a double-walled housing 11 provided with a coolant inlet 12 and a coolant outlet 13 for a coolant that normally uses water. The housing 11 can be provided with, for example, a spiral structure (not shown) or other means for producing a strong flow of the cooling liquid to cool the entire housing 11 uniformly. The housing 11 further includes an observation port 14 through which light from the focusing device 3 and light from the measurement object can pass. A cover 15 is provided on the rear surface of the housing 11, and the glass fiber optical cable 2 is guided to the outside through this cover. The focusing device 3 is fixed to the center of the housing above the observation port 14 using mounting means, for example, a fixing screw (not shown) protruding at an angle of 120 °. The interior of the housing 11 is protected from thermal radiation by an IR absorption filter 16 and an IR reflection filter. When the infrared load is small, only one IR filter can be used. Further, a transparent disk 18 is provided at the observation port 14 to prevent the reactive gas from acting on the filter windows 16 and 17. These filter windows 18 can be constructed using corundum. The windows 16, 17 and 18 are provided between the elastic intermediate ring 19 which has a function of sealing the housing from the outside air and correcting the stress between the housing 11 and the windows 16, 17 and 18 due to the difference in thermal expansion coefficient or temperature. Placed in. Silicon rubber and elastic fluorocarbon resins have been found to be suitable as materials for these rings 19. However, other materials can be used as long as they have the elasticity required for stress reduction and the necessary temperature stability. The housing 11 may further be provided with a radiation protection sheet 20 for preventing thermal radiation from reaching the housing directly. The radiation protection sheet 20 is arranged at a predetermined interval on the front surface of the object to be protected, like a normal radiation protection sheet. The radiation protection sheet 20 may be a metal sheet, but may include a material having low thermal conductivity such as a refractive oxide, or may be a porous sintered metal plate. The rinsing gas, particularly air, is guided through the tube 21 into the intervening space between the radiation protection sheet 20 and the housing 11, and a gaseous veil is generated at the front of the observation port 14 by the introduction of the rinsing gas. Generation of the gaseous veil prevents entry of reactive gas into the observation port 14 or generation of condensate from the vaporized glass component. When the rinsing gas is supplied, the filters 16, 17 and the window 18 are particularly well protected.

  By using the method and apparatus according to the present invention, the wall thickness of the glass product (eg tube, rod, lens or flat glass) is at the end of heat after manufacture, i.e., immediately downstream of the roller in flat glass rolling, Further, in the production of a flat plate by the float method, measurement is directly performed with the highest accuracy for the first time in a float bath. By measuring the lens or lens blank before it is introduced into the cooling path in the test pass in the production of the lens or lens blank, it is possible to detect the wear of the press machine substantially earlier than currently possible. . By such measurement, it becomes possible to detect a defective product generated in the manufacturing process substantially earlier and more quickly, thereby improving the yield and quality of the product.

  In the above, the present invention has been embodied and explained as a method and apparatus for optically measuring the thickness of a thermal glass body without direct contact with the thermal glass body using light diffusion or chromatic aberration. Since various changes and modifications can be made to the present invention without departing from the spirit at all, the present invention is not intended to be limited to the details described above.

  Since the gist of the present invention does not require further analysis and is sufficiently disclosed by the above description, a third party can apply the latest knowledge to determine the general or specific aspects of the present invention from the standpoint of the prior art. It is possible to easily adapt the present invention to various applications without leaking the features that clearly constitute the essential features of this embodiment.

It is a schematic explanatory drawing of the measuring apparatus for enforcing the measuring method according to this invention. 1 is a schematic cross-sectional view of a focusing device comprising a cooling housing used in a measuring device according to the present invention.

Claims (14)

A glass body thickness measuring method for measuring the thickness of the glass body without direct contact with the glass body using light dispersion immediately after the production of the glass body comprising the following steps:
a) using a focusing device to focus a light beam from a multicolor light source onto a glass body immediately after manufacture;
b) guiding the reflected light from the glass body to a spectrometer to obtain a spectrum of the reflected light when the light beam is focused on the glass body;
c) A step of finding two wavelengths of reflected light in a spectrum having a reflected light intensity higher than other wavelengths in the spectrum obtained in step b) among the reflected light reflected from the front surface and the rear surface of the glass body, respectively. When,
d) determining the glass body thickness in consideration of the refractive index of the glass body from the wavelength difference between the two wavelengths with higher intensity;
e) maintaining the temperature of the converging device below 120 ° C. during the measurement of the thickness;
f) substantially blocking heat radiation acting on the focusing device using at least one heat blocking filter.   The method of claim 1, wherein the temperature of the focusing device is in the range of 20-100 ° C.   The method of claim 1, wherein the temperature of the focusing device is kept constant within an acceptable range of ± 10 ° C.   The method according to claim 1, wherein the measurement of the glass body thickness is performed when the temperature of the glass body is in a range of 200 to 1100 ° C.   The method further includes moving the focusing device transversely to the optical axis of the focusing device to maximize the higher intensity of the two wavelengths during the measurement of the glass body thickness. The method according to claim 1.   The method further comprises the step of generating a gaseous veil before the at least one heat-blocking filter to prevent entry of reactive gas or to prevent agglomeration from vaporized glass components. Item 2. The method according to Item 1. A polychromatic white light beam light source (1);
A focusing device (3) for focusing the light beam onto a glass body (4);
A spectrum analyzer (9) for analyzing reflected light from the glass body;
A double-walled housing (11) comprising an inlet (12) and an outlet (13) for cooling liquid and in which the focusing device (3) is disposed;
An observation port (14) through which the light beam and the reflected light pass;
The apparatus for measuring the thickness of a hot glass for carrying out the method according to claim 1, comprising at least one heat blocking filter.
  8. A device according to claim 7, characterized in that the at least one heat-insulating filter (17) is arranged between two elastic heat-resistant intervening rings (19).   9. Device according to claim 8, characterized in that the two elastic heat-resistant intervening rings (19) are made of silicon rubber or fluorocarbon.   8. The apparatus of claim 7, further comprising a transparent window (18) of corrosion resistant material disposed on the exterior and front of the at least one heat barrier filter.   11. The apparatus according to claim 10, wherein the transparent window is made of corundum or fluorine-containing glass.   8. The apparatus according to claim 7, further comprising a rinsing gas supply means comprising a rinsing gas inlet (21) arranged in front of the observation port (14).   The apparatus of claim 7, further comprising a radiation protection sheet (20) provided with a through opening for the light beam and spaced from the housing in a beam propagation direction. 14. The apparatus according to claim 13, further comprising a rinsing gas supply means comprising a rinsing gas inlet (21) disposed between the housing and the radiation protection sheet (20).

Images