SYSTEM AND METHOD FOR OPTICAL MEASUREMENT ON A TRANSPARENT SHEET

Abstract

The invention relates to a system for measuring light transmission and/or light reflection properties of a transparent sample sheet, the system comprising a detection assembly and a control unit, wherein the detection assembly comprises an integrating sphere having a sample port, an illumination port, a detection port, an internal light source positioned at the illumination port, and a photodetector coupled to a spectrometer and positioned at the detection port; means to detect radiation coming either directly from the sample port or from the wall of the integrating sphere; an external light source axially aligned with the sample port; means to illuminate with the internal light source or with the external light source; a reference standard, and means to position it at and from the sample port. This system is relatively compact, and can advantageously be used at existing sheet production lines for process and quality control. The invention also relates to a method for measuring light transmission and/or light reflection properties of a transparent sample sheet that applies said system; and to processes of making a sheet, especially an AR-coated glass sheet, comprising said method.

Claims

1. A system for measuring light transmission and/or light reflection properties of a transparent sample sheet, the system comprising a detection assembly and a control unit, wherein the detection assembly comprises an integrating sphere having a sample port, an illumination port; a detection port; an internal light source positioned at the illumination port; a photodetector coupled to a spectrometer and positioned at the detection port; and means to detect radiation coming either directly from the sample port or from the wall of the integrating sphere or both directly from the sample port and from the wall of the integrating sphere; an external light source or a transmittance detector axially aligned with the sample port; means to illuminate either with the internal light source or with the external light source if present or with no light source; a reference standard, and means to position it at and from the sample port.

2. The system according to claim 1, wherein the integrating sphere has a diameter of about 160 to 300 mm and the sample port has a diameter of about 40 to 60 mm.

3. The system according to claim 1, wherein the internal and external light source each comprise a mechanical shutter as the means to illuminate with the internal light source or with the external light source or with no light source.

4. The system according to claim 1, wherein the integrating sphere contains only one photodetector and one spectrometer.

5. The system according to claim 1, wherein the system comprises the means to detect radiation coming both directly from the sample port and from the wall of the integrating sphere, wherein the means comprises one photodetectors and spectrometers for measuring radiation from the wall of the integrating sphere, and one photodetectors and spectrometers for measuring radiation from the integrating sphere reflected from the sample port; the system comprises the transmittance detector axially aligned with the sample port and no external light source; and the photodetectors being capable of during use to measure radiation from the wall, radiation reflected from the sample port and radiation transmitted via the sample port at the same time.

6. The system according to claim 1, wherein the integrating sphere comprises a movable baffle as means to detect radiation coming either directly from the sample port or from the wall of the integrating sphere.

7. The system according to claim 1, wherein each photodetector is provided with a collimator and a movable shutter for preventing radiation from the integrating sphere from reaching the photodetector.

8. The system according to claim 1, wherein the system further comprise a frame having at least two arms, between which arms the sample sheet can be positioned or transported to be measured, with a first arm of said frame carrying the integrating sphere and a second arm carrying the external light source.

9. The system according to claim 1, wherein the reference sample is a silicon wafer.

10. A method for measuring light transmission and/or reflection properties of a transparent sample sheet using the system according to claim 1, the method comprising the steps of a1) recording a spectrum using the external light source and without any sample at the sample port, a2) recording a spectrum using the external light source and with the sample sheet positioned at the sample port, a3) recording a spectrum using the internal light source and without any sample at the sample port, and a4) recording a spectrum using the internal light source and with the sample sheet positioned at the sample port; and/or the steps of b1) recording a spectrum of radiation directly reflected from the sample port using the internal light source and with a reference standard at the sample port, b2) recording a spectrum of radiation directly reflected from the sample port using the internal light source and with the sample sheet positioned at the sample port, b3) recording a spectrum of radiation reflected from the wall using the internal light source and without a sample at the sample port, and b4) recording a spectrum of radiation reflected from the wall using the internal light source and with the sample sheet positioned at the sample port; and a step of c) computing transmittance T and/or reflectance R from these spectra.

11. A method for measuring light transmission and/or reflection properties of a transparent sample sheet using the system according to claim 1, the method comprising the steps of a1) recording a spectrum using the transmittance detector and the internal light source and without any sample at the sample port, a2) recording a spectrum using the transmittance detector and the internal light source and with the sample sheet positioned at the sample port, a3) recording a spectrum using the photodetector positioned at the detection port and the internal light source and without any sample at the sample port, and a4) recording a spectrum using the photodetector positioned at the detection port and the internal light source and with the sample sheet positioned at the sample port; and the steps of b1) recording a spectrum of radiation directly reflected from the sample port using the photodetector positioned at the detection port and the internal light source and with a reference standard at the sample port, b2) recording a spectrum of radiation directly reflected from the sample port using the photodetector positioned at the detection port and the internal light source and with the sample sheet positioned at the sample port, b3) recording a spectrum of radiation reflected from the wall using a photodetector and the internal light source and without a sample at the sample port, and b4) recording a spectrum of radiation reflected from the wall using a photodetector and the internal light source and with the sample sheet positioned at the sample port; and a step of c) computing transmittance T and/or reflectance R from these spectra.

12. The method according to claim 11, wherein the steps a2), a4) and b2) are carried out at the same time, preferably the measurement of steps a2), a4) and b2) is carried out at least 5 times for each sample sheet, more preferably the measurement are carried out at different positions of each sample sheet.

13. The method according to claim 10, wherein the steps a1) and a3) are carried out between sample sheet and the recorded spectra in steps a1) and a3) are used for computing transmittance T and/or reflectance R for multiple measurements of a2), a4) and/or b2).

14. The method according to claim 10, wherein the step b1) is carried out with a frequency of less than once every 10 sample sheets, preferably with a frequency of less than once every 30 sample sheets, more preferably with a frequency of less than once 100 sample sheets.

15. The method according to claim 10, using a system, wherein the shutter is movable between an open position where radiation may enter the photodetector from the integrating sphere and a closed position where the shutter blocks radiation from the integrating sphere, the method further comprising the step of measuring a dark signal from the photodetector with the shutter in the closed position and subtracting the dark signal when computing transmittance T and/or reflectance R, preferably the dark signal is measured at least one time for each photodetector for each sample sheet.

16. The method according to claim 8, wherein measuring is done at multiple positions on the sample sheet, by synchronously moving the integrating sphere and external light source transversely relative to the sample sheet, while maintaining alignment of integrating sphere and external light source, and of detection assembly and sample sheet.

17. A process of making an AR-coated transparent non-continuous sheet is made by steps of i) applying a liquid AR coating composition to the sheet; ii) drying and curing the applied coating composition; and iii) measuring light transmission and/or reflection properties of the coated sheet according to the method of claim 10; iv) adjusting step i) and/or step ii) based on the results of step iii) to result in a sheet having desired light transmission and/or reflection properties.

18. The process of claim 17 further comprising the step of a) applying a unique identifier to the sample sheet or reading a unique identifier of the sample sheet; and b) create a record of the light transmission and/or reflection properties of the coated sheet together with the unique identifier, and optionally add conditions of step i) and/or step ii) in the record.

19. Use of the system according to claim 1 for inline quality assurance in manufacturing of solar modules.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0107] FIG. 1 schematically illustrates an example of an optical measurement system according to the invention by a simplified cross-sectional side view representing relevant components of the system, in a position for measuring transmittance and reflectance on a sample sheet.

[0108] FIG. 2 schematically illustrates a system as in FIG. 1, but in a position for measuring transmittance and reflectance on a standard reference.

[0109] FIG. 3 schematically illustrates an alternative embodiment of the invention that comprises two photodetectors.

[0110] FIG. 4 schematically illustrates an alternative embodiment of the invention containing a transmittance detector and no external light source.

[0111] In general, the figures as presented herein may not show all parts or components of a system according to the invention, and/or may not represent them to scale. Equivalents parts are indicated by the same numerals in these figures.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0112] The invention will be further illustrated by the following embodiments, without being limited thereto.

[0113] The system for measuring light transmission and/or light reflection properties of a transparent sample sheet as schematically and partly presented in FIG. 1 basically comprises a detection assembly and a control unit 10. The detection assembly comprises various components, which assembly can be mounted on e.g. a frame (not shown). The detection assembly includes an integrating sphere 1 of 180 mm diameter, which spherical hollow body was made using an Ultimaker 3D printer. The inner surface of the sphere and of other parts within the sphere are homogeneously coated with barium sulfate to result in even distribution of incident radiation throughout the sphere. The sphere has three circular openings in its wall, serving as a sample port 2, an illumination port, and a detection port. The sample port 2 has a diameter of 50 mm, such that an incident external light beam of about 40 mm will fully enter the integrating sphere, also passing through a scattering sample situated close to the port. Optionally, a flexible ring (not shown) is placed around the sample port on the outside of the sphere, forming a seal or bridge between sample to be measured and integrating sphere without actually contacting the sample sheet, and minimizing light from other sources entering the sphere. Internal light source 4, is positioned at the illumination port having a diameter of 38 mm. A photodetector coupled to a spectrometer, is positioned at the detection port of diameter 38 mm, such that the detector is directed to the sample port to detect radiation coming from the sample port, which can be empty (without a sample or reference material), or be covered by a sample sheet S or reference standard 9. The photodetector collects radiation, which is then sent to the coupled spectrophotometer to record intensity versus wavelength in the range of 380-1000 nm. The integrating sphere 1 further is provided with a movable baffle 8, as means for switching from detecting radiation coming from the sample port, or from the wall of the integrating sphere by masking out radiation directly from the sample port; see also FIG. 2. For such purpose baffle 8, which is also coated with barium sulfate, can be mechanically moved between two positions. The detection assembly further has an external light source 5, which is axially aligned along axis A with the sample port such that its collimated light beam of diameter 40 mm enters the sample port of the sphere 1. Both internal light source 4 and external light source 5 are provided with mechanical shutters 6 and 7, respectively, enabling illumination with either with the internal light source or with the external light source. This means that both light sources can be kept continuously on, rather than being switched on and off; to result in constant and stable radiation sources. The detection assembly further includes reference standard 9, which can be mechanically positioned at or from the sample port, to enable making quantitative measurements. The detection assembly is mounted on frame, having two arms such that a sample sheet S can be transported with transporting means (not shown) between the integrating sphere and external light source; transport direction being indicated with an arrow in FIG. 1. Both integrating sphere and external light source can be moved along the frame arms transversely relative to the sample sheet transport direction, while maintaining their relative alignment as well as distance and alignment relative to a sample sheet. The distance between sample sheet and integrating sphere is minimized, while securing both will not actually contact. In one way of using the measuring system in a process of the invention, the external light source is kept in a fixed position for transmission measurements along a virtual line path over moving sample sheet S and parallel to its transport direction when aligned with the integrating sphere; whereas the integrating sphere is moved transverse to the transport direction between the side edges of the sample sheet, thus making a virtual diagonal or zig-zag path over moving sample sheet S while making reflection measurements. In another embodiment of the invention, the external light source and the integrating sphere are moved synchronously transverse to the transport direction between the side edges of the sample sheet, thus making a virtual diagonal or zig-zag path over moving sample sheet S while making transmission and/or reflection measurements. The measuring system further comprises a control unit, which is configured to control operating and moving of the detection assembly and its components, and to acquire, store and process measurement information.

[0114] FIG. 1 shows the system of the invention during a method of measuring transmission and reflection properties of a glass sheet having an anti-reflective coating on one of its surfaces, while the sheet S passes the sample port 1 and is illuminated by external light source 5 to record detection signal 12 and spectrum 2 of the light transmitted by sheet S. For determining transmittance T of the sheet S three more measurements are needed in accordance with the measurement principle as described in the above: [0115] spectrum 1: detection signal I.sub.1 of external light source 5 with no sample at sample port 2; [0116] spectrum 3: detection signal I.sub.3 of internal light source 4 with no sample at sample port 2; [0117] spectrum 4: detection signal I.sub.4 of internal light source 4 with sample S at sample port 2.
In order to reduce total measuring time, and to enable more spectra are recorded on the moving sample sheet, spectra 1 and 3 may already have been recorded and stored in the control unit. The transmittance T of sample S is now calculated as T=(I.sub.2/I.sub.1)*(I.sub.3/I.sub.4).
For determining the reflectance R of sample sheet S similarly 4 spectra are recorded, but using only the internal light source 4: [0118] spectrum 5: detection signal I.sub.5 of internal light source 5 directly reflected from reference standard 9 with known reflectance R.sub.reference at sample port 2; [0119] spectrum 6: detection signal I.sub.6 of internal light source 5 directly reflected from sample sheet S at sample port 2; [0120] spectrum 7: detection signal I.sub.7 of internal light source 5 reflected from the wall with reference standard 9 at sample port 2; [0121] spectrum 8: detection signal 1.sub.8 of internal light source 5 reflected from the wall with sample sheet S at sample port 2.
As for measuring T, spectra 5 and 7 may be recorded at a different time than sample S. The reflectance R of sample S is now calculated as R=(I.sub.6/I.sub.5)*(I.sub.7/I.sub.8)*R.sub.reference.

[0122] In FIG. 2 the situation for recording reflectance spectrum 7 is represented, with baffle 8 positioned such that the photodetector 3 only measures light reflected via the wall of the integrating sphere.

[0123] FIG. 3 schematically illustrates an alternative embodiment of the invention, wherein 2 photodetectors and spectrometers 3a (also referred to as axial detector) and 3b are connected to the integrating sphere 1 at detection ports, to measure light reflected from the wall of sphere 1, or coming directly from the sample port 2, respectively. No switching baffle is needed in such embodiment.

[0124] FIG. 4 schematically illustrates an alternative embodiment of the invention, wherein two photodetectors and spectrometers 3a and 3b are connected to the integrating sphere 1 at detection ports. Photodetector 3a is also referred to as wall detector as it measures light reflected from the inner wall of the integrating sphere 1. Photodetector 3b is also referred to as reflectance detector as it measures light coming directly from the sample port 2. Because of the directional sensitivity of the photodetector (preferably enhanced by a collimator) photodetector 3b will therefore measure the light from integrating sphere reflected by the sample when the sample is placed at the sample port. Furthermore, a third photodetector and spectrometer 3c are arranged axially aligned (indicated by line A) with the sample port and opposite to the sample, S. Photodetector 3c is also referred to as transmittance detector as it measures coming from the integrating sphere through the sample or reference standard (if present). No switching baffle is needed in this embodiment. In FIG. 4, the light beam directed from the internal light source is also indicated. It is observed that the light beam from the internal light source does not fall directly on any of the detectors 3a and 3b, on the sample opening or on the part of the wall measured by the wall detector (also indicated in FIG. 4 opposite of wall detector 3a). After the first reflection of the light beam of the internal light source on the wall of the integrating, the light will be distributed to all parts of the wall and again further reflected to create what can be considered a homogenous light source evenly at all parts of the wall. Each of the detectors are preferably connected to a separate collimator 11 and movable shutter 12, which shutter is preferably arranged close to the collimator to allow for as short movement distance between open and closed position as possible. Such collimators and moveable shutters are also preferably arranged for detectors in other embodiments of the invention including the embodiments disclosed in FIGS. 1-3.

[0125] In FIG. 4, the detectors 3a and 3b are indicated as being arranged partially inside the integrating sphere. The detectors may also be arranged outside the wall for example connected via a connecting tube.