Image analysis – Applications – Manufacturing or product inspection
Reexamination Certificate
2000-05-09
2002-09-03
Mehta, Bhavesh (Department: 2611)
Image analysis
Applications
Manufacturing or product inspection
C348S087000
Reexamination Certificate
active
06445813
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an inspecting system for inspecting a printed circuit board appearance, and in particular to an improvement of an image pickup section for use in the inspection system examining a component mounting condition on a printed circuit board.
2. Description of the Prior Art
Along with recent down-sizing trend of electronic machinery apparatuses, the down-sizing with high density in mounting of electronic components has progressed to such an extent that visual confirmation thereof in a manufacturing line process is substantially impossible, and therefore, an inspection apparatus for automatically inspecting a printed circuit board appearance in a manufacturing line process is more important. Accordingly, in the inspection apparatus for inspection of a printed circuit board appearance, it is an important requirement to realize both a low price and high speed performance together in the apparatus enabling the automatic inspection in a manufacturing line process. Conventionally, there was employed a two-dimensional area sensor type CCD camera capable of picking up about 512×480 pixels in one area pickup operation as an image pickup means in which images of an inspection object are picked up by repeating the two-dimensional movement of the CCD camera with stopping of the movement using an X-Y turn table.
In order to realize a high speed performance in inspection of an object, as compared with the conventional two-dimensional area sensor type CCD camera, a demand for employing a one-dimensional scanner linear sensor type CCD camera (hereinafter, referred to as a “line CCD camera”) is increased for use in the inspection apparatus, where the images of an object are picked up while the line CCD camera is linearly moved in one-dimension, thus eliminating the stopping time of the camera in movement to thereby realize a high speed inspection.
When a line CCD camera of a line sensor type is employed in the inspection apparatus for inspection of a printed circuit board appearance, because the line CCD camera has an image pickup width of several thousands pixels in one sensing line, the images in the lateral width of a printed circuit board can be collectively picked up by a one-line sensing operation of the line CCD camera. Therefore, the movement axes of the turn table for moving the CCD camera can be reduced by one axis as compared with the conventional inspection apparatus employing a two-dimensional area sensor type CCD camera, resulting in cost reduction of the apparatus.
However, in the case of employing a line CCD camera as an image pickup means in an inspection apparatus, because a positional control with high accuracy as well as a timing control with high accuracy in image pickup operation is essentially important, it is therefore required to drive the line CCD camera or the printed circuit board of the inspection object with use of a precision mechanism table for linear movement driven by a servo-motor, and the like, which causes an increase in cost of the apparatus.
A conventional inspection apparatus for inspection of a printed circuit board appearance using a line CCD camera of a line sensor type as an image pickup means is described below with reference to FIG.
7
and
FIGS. 8A-8B
.
Referring to
FIG. 7
, the inspection apparatus includes a servo-motor
12
for linearly moving a precision mechanism table
13
(hereinafter, referred to as a “table”) in one dimension. Placed on the table
13
, is a printed circuit board
1
having repeat patterns of chip elements and the like which the mounting condition thereof is an object to be inspected, and the placed printed circuit board is subjected to light scanning by means of a line CCD camera
3
to pick up images thereof. A camera control section
71
includes a camera controller unit
16
for generating an image pickup start timing signal S
1
and further includes a timer
17
for measuring a time of generation of the image pickup start timing signal.
The inspection apparatus further includes an image recognizing section
72
which is comprised of an image data memory
8
, an image recognizing unit
9
and a determination control unit
10
. Reference numeral
14
denotes a driver unit for driving the servo-motor
12
. The camera control section
71
, image recognizing section
72
and the driver unit
14
are operatively connected to a machine controller
73
for controlling a CRT display, key board and the like.
With respect to the above mentioned conventional inspection apparatus for inspection of a printed circuit board appearance employing a line CCD camera, the interaction between the components thereof and the operation of each component are described below.
In the first step, a printed circuit board
1
which is an object to be inspected is placed on the table
13
which is moved by the servo-motor
12
driven by the driver unit
14
.
In the next step, the table
13
is moved within a range under the image pickup sensing operation of the line CCD camera
3
at a constant speed in one direction (for example, in the direction shown by an arrow A), wherein an image pickup start timing signal S
1
is fed from the camera controller unit
16
to the line CCD camera
3
at predetermined time intervals measured by the timer
17
in the camera control section
71
. At each time in response to the feeding of the signal S
1
, the image recognizing section
72
receives an image signal S
2
of one line of pixels, i.e., one pixel×N pixels, from the line CCD camera
3
to be stored in the image memory
8
, where N denotes the number of the one-line pixels picked up by the line CCD camera.
Then, the output of the image memory
8
is fed to the image recognizing unit
9
in which the supplied image signal S
2
is subjected to recognition process to obtain high and low levels of the image picture signals in every cycle of the repeat patterns. Subsequently, in the final step, it is determined by the determination control unit
10
whether or not the printed circuit board appearance is good, namely, whether or not the mounting condition of elements on the printed circuit board is accurate. When a defect or difference in position exists in the printed circuit board appearance, there is generated an abnormal signal which is compared with a reference signal to indicate the existence of a defect or deviation.
By this arrangement, the line CCD camera
3
picks up the picture image of the printed circuit board
1
collectively every one line scanning with the lateral width thereof corresponding to the image pickup width of several thousand pixels of the line CCD camera. Therefore, the movement axes of the printed circuit board
1
with respect to the line CCD camera
3
can be reduced by one axis as compared to the old conventional inspection apparatus employing the two-dimensional area sensor type CCD camera, resulting in the cost reduction of the apparatus.
However, in the line sensor type inspection apparatus, the printed circuit board
1
is placed on the precision mechanism table
13
which is driven by the high precision servo-motor
12
, which causes an increase in the cost. This is because, when the image pictures of the printed circuit board are picked up using the line CCD camera
3
, the accuracy in position and timing of the image pickup starting operation, i.e., the accuracy in the time interval of the image pickup start timing signal S
1
greatly affect the quality of the resultant image picture to be obtained.
The influence of the accuracy in position and time interval of the image pickup start timing signal on the quality of the resultant image picture is described below with reference to
FIGS. 8A and 8B
.
FIG. 8A
shows an example of an image picture in the case where the image pickup start position with respect to the image pickup start timing signal is deviated from the accurate position. The deviation in the actual pickup position of an object al results in appearance as an elongation a
2
-
1
and a contraction a
2
-
2
on the resultan
Ikurumi Kazuhiro
Nakao Osamu
Okamoto Kenji
Tsujikawa Toshihiko
Tsujimura Masaharu
Matsushita Electric - Industrial Co., Ltd.
Mehta Bhavesh
Wenderoth , Lind & Ponack, L.L.P.
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