Note: Descriptions are shown in the official language in which they were submitted.
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TITLE: SURFACE INSPECTION DEVICE
BACKGROUND OF THE INVENTION
Field of the Invention
Thle present invention relates to surface inspection device.
Description of the Prior Art
In the modern industrial fields, substitution to manual
inspection for parts or the like by visual sense, is increasing
by setting up automatic inspection devices that utilize video
camera and electronic processors. As objects of inspection,
there are raw materials, plain material, half products, completed
products, etc., where various surface inspection devices that
detect the surface flaws such as differences in shape or
appearance, dimensions or defects, are proposed and practically
used.
The surface inspection devices for objects of the prior art,
irradiate illuminating light on the inspected object, catch the
transmission light or reflection light from the inspected object
by the video camera and convert the light to the image signal,
and detect the defect by process analysis of the image signal by
an electronic processor containing a computer or the like.
In this case, the image signal as caught by the video camera
is an analog signal, and in order to make the electronic
processing easy, conversion of the analog signal to the digital
signal by the use of A/D converter or the like is the general
practice. Further, if the entire data on gray scale which is the
light and shade of the image, is attempted to be processed, it
means that enormous data volume must be processed which makes the
device complicated, and long processing time are necessary that
make it impractical.
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Accordingly, the presently used inspection devices separate
the light and shade of an image into binary values by a threshold
value, by which the processing is simplized as practiced on the
majority of devices in practical use. Otherwise, the gray scale
is confined into few stages and digitized for processing on
devices as noted in some cases.
For instance, in the case that surface defects on the
inspected object are to be detected, various problems are
encountered. As to the inspected objects, there are variations
such as, metal plates, metal strips or glass, plastic containers,
paper or plastic rolled material, etc., and it is substantially
difficult to extract the defect only from the surface and detect
the same. That is to say that upon picking up the inspected
object by a video camera, not only will the defects be picked up
as variance of the light and shade but the base material surface
course roughness or subtle wrinkles that are not defects, as well
as slight trace of dirtiness will at the same time be picked up
as variance in the light and shade, which cannot be distinguished
from the defects.
Such surface coarseness, wrinkles or slight traces of dirty
can be said to be "noise" in the image for the video camera and
the detection of only the defects from among such noise in a
simple manner was a difficult problem.
Various methods are offered in order to resolve such
problems. As one effective means among such offers, there is
the method to divide the picture screen into many small zones,
measure the-differences of light and shade within each small zone
so that whenever there is a variance exceeding a preset value,
judgement that a defect exists there is made.
The portion with noise like variance of light and shade is
lall within each small zone, whereas the variance of lig~
shade is great within the zone where defects exist, so that it is
easy to segregate the defect from noise and make a judgement. It
is need:Less to say that the size of the zones for division may be
adequately determined based upon the size of the defect to be
detected.
However, although the method of defect detection by
division of the picture screen into many small zones is a very
effective means, because it is necessary to scan and make
judgements for each of the small zones across the entire picture
screen, a great processing time is required to make judgement of
the entire frame.
OBJECTS AND SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to
provide an improved surface inspection device which can obviate
the shortcomings encountered with the prior art.
According to an aspect of the present invention, there is
provided a surface inspection device in which an inspected object
is irradiated by a light source, transmission light or reflection
light therefrom is picked up by a video camera and an image
signal from the video camera is image-processed by an electronic
processor to thereby detect defects on the inspected object,
comprising:
a) an image signal extracting means for extracting from
among the image signals of the video camera, an image signal
whose contrast of light and shade exceeds a preset value;
b) an-A/D converter for converting said image signal into
digital signal;
c) a memory for storing said digital signal;
d) a histogram formation means for producing a histogram
.gnal of the entire digital signals in the horizontal. o~
vertical direction of the image;
e) a lowpass filter for producing a waveform signal by
removing high frequency components of said histogram signal;
f) a signal extracting means for extracting a part of said
waveform signal that exceeds a preset threshold value;
g) vertical or horizontal position setting means for
obtaining a center line of said extracted part of said waveform
signal in the vertical or horizontal direction of an image;
h) a window setting means for setting a small window on a
picture screen with a preset size that allows defect detection;
i) a window address setting means for scanning the memory
in which the digital signal is stored by said window in the
vertical direction in a manner that the center of said window
coincides with the center line of the image as obtained from the
extracted waveform signals in the vertical or horizontal
direction; and
j) a judging means for judging that there exists a defect
when said memory is scanned by said window, whenever there are
more digital signal counts exceeding a preset value in said
window, or whenever the areas of the digital signal clot in said
window is larger.
According to another aspect of the invention, there is
provided a surface inspection device in which an inspected object
is irradiated by a light source, transmission light or reflection
light therefrom is picked up by a video camera and an image
signal from the video camera is image-processed by an electronic
processor to thereby detect defects on the inspected object,
comprising:
a) an image signal extracting means for extracting from
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Inong the image signals of the video camera, an image siynal
whose contrast of light and shade exceeds a preset value;
b) an A/D converter for converting said image signal into
digital signal;
c) a memory for storing said digital signal;
d) histogram formation means for producing histogram
signals of the entire digital signals in the horizontal and
vertical directions of the image;
e) lowpass filters for producing waveform signals by
removing high frequency components of said histogram signals;
f) signal extracting means for extracting a part of each of
said waveform signals that exceeds a preset threshold value;
g) vertical and horizontal position setting means for
obtaining center lines of said extracted parts of said waveform
signals in the vertical and horizontal directions of an image;
h) a window setting means for setting a small window on a
picture screen with a preset size that allows defect detection;
i) means for obtaining a position at which the vertical and
horizontal center lines provided from said waveform signals
intersect each other and making the center of said window
coincident with said intersecting position; and
j) a judging means for judging that there exists a defect
when said memory is scanned by said window, whenever there are
more digital signal counts exceeding a preset value in said
window, or whenever the areas of the digital signal clot in said
window is larger.
~ BRIEF DESCRIPTION OF THE DRAWINGS
A better understanding of the object, features and
advantages of the invention can be gained from a consideration of
the following detailed description of the preferred embodiments
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lereof, in conjunction with the figures of the accompanying
drawings, wherein:
Fig. 1 is a schematic diagram in order to explain the basic
theory of the present invention;
Fig. 2 and Fig. 3, which are respectively formed of Figs.
2A, 2B and Figs. 3A, 3B drawn on two sheets of drawings so as to
permit the use of a suitably large scale, are block diagrams that
respectively illustrate embodiments of the present invention; and
Fig. 4 is a schematic diagram in order to explain the
function of the embodiment on Fig. 3.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
An explanation of the present invention shall be made in
reference with the drawings. The basic theory of the present
invention shall be explained in reference with Figs. lA to lE.
In the present invention, in the picture screen of the video
camera on which the image of the surface of an object to be
inspected is displayed, its portion where there exists a change
of light and shade is converted into a digital signal.
In doing so, the analog signal of the portion of the picture
screen containing the variance of light and shade may be binary
valued by using a preset threshold value and then converted to
digital signal, or by processing the analog signal of the light
and shade variance portion in differentiation fashion to form a
waveform on the boarder of light and shade and then similarly
make it a digital signal. The digital signals over the entire
picture screen are stored in a memory.
Fig. lA shows the above digital signals as scattered in the
responsive areas of a memory that memori~es the digital signals
and corresponds to the picture screen of the video camera or
picture screen 1 shown by dots, Roughly spotted black dots 2
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thin the picture screen 1 are the converted signals of the
light and shade variances by coarseness or traces of slight
dirtiness that exist on the surface of the inspected object as
other than defects as above described which are the so called
noise that are obstacles in the defect judgements.
On the other hand, dense black dots 3 and 3A in the screen 1
are the digital signals responding to the flaws or defects that
are to be detected and many black dots are assembled here.
Fig. lB shows the digital signals on a single scanning line,
which is the line X - X' on picture screen 1, by which it is
obvious that the defect or noise cannot be segregated if the
digital signals are detected as they are. However, by dividing
the picture screen 1 into small zones as shown on Fig. lA (in
this case, the division is vertically 4, horizontally 6), and by
counting the number of black dots within each zone, it is
apparent that the noise and defect can be segregated and
discriminated.
At the present invention, the histogram of the digital
signals (black dots) of each horizontal scanning line on picture
screen 1 is formed throughout the vertical direction on picture
screen 1. This histogram shows the distribution status of the
entire digital signals that appear in the horizontal direction on
picture screen 1. Fig. lC illustrates this histogram.
As the next step, the histogram as formed with the digital
signals and shown on Fig. lC is passed through a low pass filter
to remove the high frequency components thereof, and is
formulated into a waveform signal. Fig. lD, shows this waveform
signal of the converted digital signals.
In order to segregate the defects from the noise of dirty,
etc., the waveform signal as shown on Fig. lD is sliced by
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preset threshold value TH, find the position of the waveform
signal portion that exceeds the threshold value, and obtain a
center line CN in vertical direction for the image at this
position. In the case on Fig. lD, the portions of the waveform
signal that exceed the threshold value TH are 2 places, so that
the above center lines will be CN 1, CN 2. Further, the reason
that the histogram as formed by digital signals was shaped to the
waveform signal by the lowpass filter, was to make it easy to
obtain the center line of the digital signal clot. Also, it is
needless to say that the number of the center lines (CN) as
obtained as above becomes different dependent on the distribution
of the digital signals in the histogram and on the manner in
which the threshold value TH is set.
As shown on Fig. lE, the picture screen 1 of the memory that
memorizes digital signals is scanned by moving a preset small
zone window 6 along the center line (CN) in the direction from,
for example, the upper side to lower side and whenever there is
more digital signals than a preset number in window 6, or when
the area of the clot of digital signals in the window 6 is large,
a judgement that there is abnormality or a defect is made. The
window 6 is a single one with a preset size.
Fig. 2 is a block diagram that illustrates an embodiment
that practices the basic theory of the present invention. At the
example on Fig. 2, an image signal a rom a video camera 10 that
picks up an inspected object (not shown) is input to a
preamplifier 11. The preamplifier 11 supplies an amplified image
signal _ to-an image signal extractor 13 and synchronizing signal
separator 12. The image signal extractor 13 formulates a
extracted signal c by the image signal portion that exceeds a
preset threshold value TH1 set by a threshold value setting unit
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3A. The image signal extractor 13 is such as a comparator which
extracts the specific image signal c based on the threshold value
TH1. I'his extracted image signal c is input to an A/D converter
14 and is converted to a digital signal _. Such converted
digital signal d by the A/D converter 14 is input to a memory 16
through a fixed contact point X and a movable contact A of
conversion switch 15.
The synchronizing signal separator 12 consists of vertical
synchronizing signal separator 12v and horizontal synchronizing
signal separator 12h, which respectively separates a vertical
synchronizing signal _ and horizontal synchronizing signal h from
the amplified image signal _ that the video camera 10 has picked
up. These vertical and horizontal synchronizing signals _ and h
are input to an image address generator 17. The image address
generator 17 generates an address signal e. This address signal
e is input to memory 16 through a fixed contact X' and movable
contact A of conversion switch 15A to control the vertical and
horizontal addresses of memory 16 so that the digital signal d is
memorized in the memory 16 in synchronism with the image signal a
that the video camera 10 has caught.
On the other hand, the digital signal d that is output from
the A/D converter 14 is input to ~ horizontal histogram
formulator 18 to make a horizontal histogram signal f of digital
signal d 5refer to Fig. lC) which is then input to a lowpass
filter 19 to obtain a waveform signal g (refer to Fig. lD). At
the same time, the aforementioned vertical synchronizing signal
_and horizontal synchronizing signal h are input to the histogram
formulator 18 and lowpass filter 19 respectively in order to
accurately formulate the histogram signal f and waveform signal
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The waveform signal g is supplied to a signal extractor 20,
by which a signal i (see Fig. lD) exceeding a preset threshold
value TH2 set by a threshold value setter 20A is extracted from
the waveform signal _. This signal i is input to a vertical
position setter 21, so that the center point of this signal i in
the vertical direction of the image of the waveform signal g is
obtained. Also, to the vertical position setter 21, the vertical
synchronizing signal _ and the horizontal synchronizing signal
hare input, in order to control the vertical position setter 21
such that the center point is set at the correct position on the
picture screen and the vertical position signal ] is derived from
the setter 21.
In Fig. 2, 22 is a window setter which receives the vertical
and horizontal synchronizing signals _ and h and outputs window
setup signal k so that a small dimentioned window 6 with a size
that encloses the desired defect to be detected is setup. 23 is
a window address generator, which by receiving the vertical
position signal j, window setup signal k, vertical and horizontal
synchronizing signals _ and h, outputs such window address signal
1 that enables the window 6 at a given vertical scan position to
vertically scan the digital signal d as memorized in memory 16,
which address signal 1 is output to the other fixed contact Y' of
the conversion switch 15A. Switches 15 and 15A are interlocked,
fixed contact X and X' thereof are in signal intake mode to
memory 16, while the other fixed contacts Y and Y' thereof are in
judgement mode.
In this manner, switches 15 and 15A are placed in the signal
intake mode to the memory 16, and the entire image digital
signals d are stored in memory 16. Then, the switches 15 and 15A
are switched to judgement mode, and the window 6 is operated to
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an the screen 1 only in the setup vertical direction as shown
in Fig. lE, such result is judged by a judgement circuit 24 to
detect t:he defects 3, 3A.
The above explains an example case of function by seeking
the horizontal histogram, but it is apparent that by seeking the
vertical histogram in the place of horizontal histogram, and by
scanning the window horizontally, the same function and effects
can be obtained. In such case, the horizontal histogram
formulator 18 can be the vertical histogram formulator, and the
vertical position setter 21 can merely be changed to a horizontal
position setter so that the specific duplicated explanation
thereof shall be omitted.
Further, Fig. 3 is a block diagram of another embodiment of
the present invention. On Fig. 3 the same symbols as those of
Fig. 2 point to the same parts. The difference in Fig. 3 to Fig.
2 is that at the example on Fig. 3, a set of horizontal and
vertical histograms are simultaneously formulated.
For this reason, in the case of Fig. 3, a vertical histogram
formulator 18B, low pass filter l9B, signal extractor 20B and
threshold value setter 20C are installed together to the case of
Fig. 2.
The functional difference in the case of Fig. 3 compared to
the case of Fig. 2 is that on the embodiment of Fig. 3, the
vertical position setter 21 in case o$ Fig. 2 becomes a
horizontal and vertical position setter 21B that simultaneously
controls the horizontal position and the vertical position,
while the window address setter 23 generates a window address
signal to address the window 6 at the cross point of the
horizontal position and vertical position.
Fig. 4 illustrates this status, in which at crossing points
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_etween the vertical direction center lines CN1 and CN2 that are
obtained from the horizontal histogram and the horizontal
direction center lines CN3 and CN4 that are obtained from the
vertical histogram, the window 6 is consecutively setup thereby
carry out the judgement.
By this method, rather than scanning with the window,
judgement is made by simply moving the window consecutively to
the cross points so that it features a very short overall
judgement processing time.
As for the explanation of the other portions on Fig. 3, the
functions will be exactly the same to the case on Fig. 2 and
explanations therefore shall be omitted.
Also, although the functions of the present invention have
been made in reference to block diagrams, it is generally the
practice to carry out the present invention by computer
processings respectively, and it is apparent that anyone with
ordinary skill in the art can easily achieve such above mentioned
functions by software programming.
It also is not necessary to be bond by the rectangular shape
of the window, and depending upon the purpose it can be of a
special shape, and it is needless to say that freely arranged
setups by the detection purposes such as judgement processing
within the window can be by the count of the extract signal
numbers or the clot status or shape of the extracted signal as
the basis for judgement.
The present invention obviates such shortcomigs in the
processing time by the conventional methods, and enables an
extremely fast practice by a unique method of window processing
on the picture screen, and offers enormously huge merit by making
it possible to use this type of device on highspeed production
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ines. Further, it is not necessary to encounter complicated
compositions, but the device can be manufacted most conveniently.
It should be understood that the above description is
presented by way of example on the preferred embodiments of the
invention and it will be apparent that many modifications and
variations thereof could be effected by one with ordinary skilled
in the art without departing from the spirit and scope of the
novel concepts of the invention so that the scope of the
invention should be determined only by the appended claims.
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