Optics: measuring and testing – By polarized light examination – With light attenuation
Reexamination Certificate
1999-11-29
2001-03-27
Kim, Robert H. (Department: 2877)
Optics: measuring and testing
By polarized light examination
With light attenuation
C356S370000, C356S237200
Reexamination Certificate
active
06208417
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to generally to inspection of irregularly or unsteadiness possibly appearing on the surface of objects, specimens and the like, and more specifically to a method and apparatus for detecting surface irregularity of objects, e.g., less conspicuous spots with imperceptible boundary scattered on an object surface, blot zones of differing density often present on the patternless homogeneous surface of a monolithic object, flaws on a patternless sheet-like specimen, and positional defects in an array of objects arranged at a predetermined pitch. Even more particularly, the instant invention is directed to a method and apparatus capable of examining stains or stain areas, minute flaws and crosswise defects of unclear boundary with no remarkable brightness differences, frequently appearing on the surface of various articles.
2. Description of the Prior Art
As is conventional, in the liquid crystal display hereinafter referred to as “LCD”, there occurs an occasion that the color filters thereof partially become bright or dark due mainly to the presence of dyeing stains. Likewise, spots of, e.g., differing density or thickness may be created in case of a monochromic patternless woven fabric attached to the ceiling of motor vehicles or a similar nonwoven fabric patch used as a drug carrier. This holds true for the shadow mask of a color cathode ray tube. Namely, electron beam penetration holes formed through the shadow mask may have irregular configuration or may be distributed in an erroneous spacing or pattern. In addition to the above, minute defects or alien matters are often found in a patternless film or an aluminum sheet for use in making beverage cans.
In accordance with the prior art approach, such a surface irregularly of object articles has been detected through the use of an inspection apparatus that includes a line sensor and an image processor associated therewith. The inspection apparatus is designed to find out surface defects by way of first scanning the surface of the object articles to obtain brightness information for each and every pixel and subsequently determining whether the respective brightness information falls within a permissible range.
As a more specific prior art example, the surface examination device shown in
FIG. 1
has been used to detect a stain
2
possibly present on a LCD color filter
1
. This device comprises a line sensor
10
, an image processor
11
and a display
12
wherein the image processor
11
is, in turn, provided with a plurality of brightness information adders
13
,
15
, a subtracter
14
and an evaluator
17
.
In order to detect the stain as a surface defect by means of the examination device noted above, the line sensor
10
takes a picture of the LCD color filter
1
to gain brightness information G
1
, G
2
, G
3
, - - - and Gn for the respective pixel
21
depicted in FIG.
2
. The brightness information may be graphically represented as in FIG.
3
(
a
) in which the ordinate indicates brightness with the abscissa pixel position. The rising ridge
23
sandwiched between a couple of broken lines
24
,
25
in the brightness information curve
22
corresponds to the stain on the LCD color filter
1
.
In the next step, it is necessary to select a given number of, e.g., seven pixels G
1
through G
7
, the brightness informations of which are summed by use of the first brightness information adder
13
to gain total brightness value a
1
. Similarly, the brightness informations for the successive pixels G
8
through G
14
are summed by use of the second brightness information adder
15
to gain total brightness value a
2
. The subtracter
14
comes to draw total value a
2
from total value a
1
in an effort to gain differential data N
4
. The evaluator
17
will then analyze the differential data N
4
to see whether it falls within a permissible range. If the data N
4
is determined to fall outside the permissible range, it should be recognized that there would exist a pixel or pixels of irregular brightness among the examined pixels.
In the subsequent step, another group of pixels G
2
through G
8
shifted rightward by one pixel pitch are selected to sum the brightness informations thereof by use of the first adder
13
, thus gaining total brightness value b
1
. In the same way, the brightness informations for the successive pixels G
9
through G
15
are summed up by use of the second adder
15
to gain total brightness value b
2
. The subtracter
14
comes to draw total b
2
from total value b
1
so as to gain differential data N
5
.
The above processing is repeatedly performed for the entire pixels with a view to obtaining their differential data. The display
12
plays a part in representing the resultant data in a readily understandable form. FIG.
3
(
b
) is a graphical representation of the differential data obtained through the foregoing process. It can be readily seen that the curve
25
of FIG.
3
(
b
) has a ridge and valley portion
26
sandwiched between the broken lines
24
,
25
, which is more conspicuous than the ridge
23
of the curve
22
shown in FIG.
3
(
a
). The same processing as set forth above can be executed in the y-axis direction as noted by an arrow
4
in
FIG. 1
in order to two-dimensionally highlight the stain or defect.
The prior art surface defect inspection device exemplified in the foregoing is, however, inherently disadvantageous in terms of the following four aspects.
(1) In case of examining surface defects of an object article with lattice-like pattern as shown in
FIG. 4
, e.g., LCD color filter
1
. The intersection point formed by a detection line
31
of the line sensor
10
and a lattice line
32
of the filter
1
may be erroneously recognized as a surface defect, if there exists a misalignment between the LCD color filter
1
and the detection line
31
of the line sensor
10
.
(2) Although it is possible to detect the linear stain
33
extending perpendicular to the detection line
31
of the line sensor
1
U as depicted in
FIG. 5
, this is not the case for the horizontally extending linear stain
34
which is parallel to the detection line
31
of the line sensor
10
as shown in FIG.
6
. The reason for the horizontally extending liner stain being undetectable is that there would occur no fluctuation between each of the brightness informations of the horizontal stain.
(3) Lastly, it is a frequent occasion that tiny alien matters or diminutive flaws
62
hereinafter referred to collectively as “miniature defects” may be borns by a sheet-like patternless film or an aluminum sheet for the manufacture of beverage cans, as is apparent from FIG.
7
. If the miniature defects
62
have a dimension of less than or slightly greater than the pixel size, it becomes hard to detect the miniature defects by way of solely determining whether the brightness informations for the respective pixel fall within or outside the prescribed range. For the “shading” or high frequency noise
71
would preclude convenient detection of the miniature defects
72
, as indicated in FIG.
8
.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a method for inspecting surface irregularity of object articles that makes it possible to detect not only low contrast specks out of an article surface but also miniature defects having a dimension of less than or slightly greater that the size of a sensor pixel. With this object in view, the invention provides a method of inspecting surface irregularity of an object article having a surface of uniform or regular brightness, which comprises the steps of:
gaining brightness informations for a plurality of two-dimensionally distributed pixels by taking a picture of the article surface;
finding stains on the article surface in response to each information obtained in the brightness information gaining step to produce a first output;
finding miniature defects smaller in size than a unit pixel in response to each information obtained in the brightness inform
Ichiba Kouzou
Itagaki Chuji
Itou Masahiro
Kim Robert H.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Toshiba Engineering Corporation
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