Optics: measuring and testing – Inspection of flaws or impurities – Transparent or translucent material
Reexamination Certificate
2000-09-25
2001-08-14
Font, Frank G. (Department: 2877)
Optics: measuring and testing
Inspection of flaws or impurities
Transparent or translucent material
C356S239700, C356S239800
Reexamination Certificate
active
06275286
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a method of determining the optical quality of and detecting faults in flat glass and other optically transparent materials.
A method is known for determining the optical quality of flat glass, especially of float glass, wherein a video camera is arranged to monitor an illuminating device either through the glass or by observing the reflection of the illuminating device on the glass. In this case, the focus of the video camera is on the glass and the sheet, respectively. In the process, the video camera generates signals in dependence on the quality of the glass. These signals will subsequently be evaluated.
FIG. 1
illustrates a method according to the state of the art. A video camera
1
or cell camera is provided to monitor, through a glass sheet
2
, an illuminating device
3
having a dark field arranged thereon.
In case of a faultless material of the glass
2
, the camera
1
will view the dark field
4
. In case of a fault, the optical effect of the glass
2
will distort and/or deflect the field of view of the camera
1
. If this effect is so large that the field of view of the camera
1
is caused to shift partially or wholly into the bright field
5
, the video signal will undergo corresponding changes.
The dark field
4
must always be sufficiently large to prevent the field of view of the camera
1
from being shifted into the bright field
5
also due to vibration or bending (e.g. under the influence of temperature). For this purpose, the sensitivity of the system is limited by dead zones.
As long as the field of view deflected by a fault is located in the borderline region between the dark field
4
and the bright field
5
, the amplitude of the error signal is dependent on the amount of the deflection. Since, however, the amplitude is also influenced by contamination of the sheet
2
under testing, a determination of the amount of the deflection is rendered impossible.
Faults in the glass usually have a core (bubble, inclusion). Since the core of a glass fault will primarily absorb light, a measuring of the core is possible only within the bright field
5
. In the dark field
4
, no measurement of the core is possible.
SUMMARY OF THE INVENTION
It is an object of the invention to provided a method wherein no dead zones exist and wherein the extent of the deflection (refractive power) and the size of the glass fault can be detected. Further, a possibility is to be provided to measure the cores of the faults in the glass.
According to the invention, the above object is achieved using illuminating devices whose color and/or intensity is changed in a defined manner from one outer edge to the other one, the observation spot of the video camera in the faultless condition of the glass is located substantially in the middle of the illuminating device, the illuminating device has assigned thereto two video signals U
1
,U
2
according to color and/or intensity and a change of intensity of the video signals U
1
,U
2
is used for evaluating the quality of the glass.
An advantageous variant is characterized in that the illuminating device comprises illuminating halves of different colors and that the video camera includes at least one color chip, with the video signals U
1
,U
2
assigned respectively to one color.
Thus, the illuminating device comprises two colored halves (e.g. red/green). The video camera includes a color chip, with the video signals U
1
,U
2
assigned to the two colors.
In the faultless condition of the sheet, the observation spot is located substantially in the middle of the illumination. The two voltages are substantially equal to each other. When, however, the observation spot is deflected or distorted due to optical deformation, one of the two voltages U
1
,U
2
will be increased while the other one will be decreased.
Connecting of the two voltages to
Upos
=
U
1
-
U
2
U
1
+
U
2
results in the voltage Upos, with its amplitude depending exclusively on the position of the observation spot of the camera. Alternatively, it is possible to use only the difference between the two video signals as a measure of the deflection and the position, respectively, of the observation spot.
In the above arrangement, no dead zones exist.
The amplitude of Upos is a measure of the strength of a deflection because of a fault.
A disturbance by contamination influences both of the voltages and is eliminated in the above term.
By application of
U
h
=U
1
+U
2
,
a bright field is realized. By evaluating only negative signals of U
h
, it is made possible to measure the core of the fault.
In the above described method, the enlargement of the illuminating spot through the depth of focus of the camera is utilized for the measurement of the positional change. In case of small apertures and large depths of focus, use can be made of graduated-density color filters.
U
1
and U
2
can be obtained also from a synchronous switching of the two illumination halves. To that end, the illumination is switched for each scan. U
1
and U
2
will then always be the video signals from the current scan and from the previous one. The illumination color can be chosen at random, and the camera used can be a BW camera.
In the evaluation, contamination is completely suppressed whereas deflections are maintained virtually unchanged.
REFERENCES:
patent: 5691811 (1997-11-01), Kibira
Droste Josef
Haubold Wolfgang
Paneff Edmund
Diller, Ramik & Wigh
Font Frank G.
Lasor AG
Stafira Michael P.
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