Image analysis – Applications – Document or print quality inspection
Reexamination Certificate
2000-02-02
2002-04-16
Chang, Jon (Department: 2623)
Image analysis
Applications
Document or print quality inspection
C348S092000, C250S559050
Reexamination Certificate
active
06373966
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a printing quality examining apparatus (an apparatus for examining printing quality) used for decision as to whether printing quality is good or bad.
In a conventional printing quality examination method, as shown in
FIG. 10
, image data of printing paper are successively read in order of k=1, . . . , k=n−1, k=n by means of a camera and the image data are averaged in time to obtain estimated value data. In
FIG. 10
, i, j and k are marks for defining coordinates for picture or pattern data on paper. The estimated value data is compared with a previously read reference data and when a difference therebetween exceeds a threshold value, pixels thereof are decided to be defective. A flow chart of this decision operation is shown in FIG.
11
.
In the conventional printing quality examination method shown in
FIGS. 10 and 11
, however, an estimated value data which is an average value of image data on current printing paper and image data on past printing paper is compared with the reference data in order to improve detection accuracy. Accordingly, once any defect occurs, estimated value data of normal pixels on several printing papers used subsequently to the occurrence of the defect are influenced by defective data in the past, so that the normal pixels are decided as defective pixels in error and consequently even satisfactory paper is discharged as defective paper.
Further,
FIG. 12
illustrates a printing quality examination apparatus used heretofore. This conventional printing quality examination apparatus is now described with reference to FIG.
12
. In
FIG. 12
, numeral
105
denotes a printing paper put on an impression cylinder A so that the printing paper is curved arcuatedly, numeral
114
a camera disposed in a detection unit, numeral
115
a xenon lamp disposed far from the detection unit, numeral
116
an optical fiber extended from the xenon lamp
115
, numeral
117
a light irradiating end formed at an end of the optical fiber
116
, and numeral
118
an optical axis of the light source. The camera
114
is disposed so that an optical axis of the camera is substantially vertical to the printing paper
105
and the light irradiating end
117
is disposed so that an optical axis of the light irradiating end
117
is oblique to the printing paper
105
.
The printing paper
105
is irradiated by light from the light irradiating end
117
, while image data on the printing paper
105
is taken in by the camera
114
and defective paper is detected from the image data on the printing paper
105
.
However, in the illumination apparatus of the conventional printing quality examination apparatus shown in
FIG. 12
, the printing paper
5
is illuminated by illumination light from the single light irradiating end
117
and accordingly the xenon lamp
115
having the high luminous intensity is required. Furthermore, since the xenon lamp
115
is disposed far from the detection unit and light from the xenon lamp is led to the detection unit through the optical fiber
116
, a manufacturing cost thereof is increased.
Further, a condensing lens or the like is used to feed the illumination light from the xenon lamp
115
to the optical fiber
116
effectively. The condensing lens or the like must be maintained for the optical deterioration and a great deal of labor is required therefor.
In addition, at a held end of the printing paper
105
on the impression cylinder A, when image data is taken in by the detection unit, an amount of light incident on the detection unit is varied due to fluttering of the paper, so that amendment of the illumination light amount is influenced greatly. More concrete description is given as follows.
When normal printing paper is irradiated by illumination light vertically and an illuminometer
119
is moved in parallel to the printing paper to measure the luminous intensity on the paper while the illuminometer is maintained vertically and in an equal distance to the printing paper as shown in
FIG. 13
, the luminous intensity on the paper is expressed by a curve named a substantially normal distribution and the distribution of the luminous intensity is maximized in the vicinity of the optical axis
120
of the illumination.
In the illumination apparatus of the conventional printing quality examination apparatus, as shown in
FIG. 14
, illumination light is incident along an incident axis
121
oblique to the vertical axis and passing through an incident point of illumination light and the light is reflected along an emitting axis
122
having the same angle in the opposite direction. Accordingly, the maximum point of the luminous intensity on the paper is offset on the side of the reflected light with respect to the vertical axis as shown by a curve of FIG.
14
.
FIG. 15
illustrates variation in the luminous intensity on the printing paper
105
due to a fluttering of paper occurring at the held end of the printing paper
105
on the impression cylinder A.
When fluttering of paper does not occur at the held end of the printing paper
105
, the distribution of the luminous intensity shown by solid line is obtained and the luminous intensity on the paper on the optical axis of the camera
114
is I
0
. The case where the held end of the paper is moved up is now considered. An amount of variation or movement is regarded to be able to be neglected as compared with a distance from the light irradiating end
117
and the camera
114
to the printing paper
105
and the printing paper
105
is assumed to be angularly moved or rotated about an intersection point
0
of the printing paper and the vertical line drawn from the camera
114
to the printing paper. The upward movement of the held end of the paper corresponds to the angular movement of the printing paper
105
in the counterclockwise direction by an angle &agr;.
At this time, the normal line extending from the intersecting point
0
vertically to the printing paper
105
is rotated by &agr; in the counterclockwise direction similarly. Further, the emitting axis of the reflected light is rotated by 2&agr; and the maximum point of the luminous intensity in the distribution of the luminous intensity on the printing paper
105
is also moved leftward as shown by broken line in FIG.
15
. Thus, an amount of light received by the camera
114
is varied from I
0
to I
1
. This corresponds to a variation in the amount of light received by the camera
114
due to fluttering of paper.
Further,
FIG. 16
schematically illustrates a circuit configuration of a conventional printing quality examination apparatus. In this case, an image of a printing paper having the luminous intensity on the surface thereof maintained constant by illumination light from an illuminating light source is taken in by a line camera of a detection unit
201
. The luminous intensity on the printing paper is maintained to be constant and decision as to whether the printing paper is good or bad is made as follows.
As shown in
FIG. 17
, an output signal from the detection unit
201
is reduced in substantially inverse proportion to a machine speed. The output signal from the detection unit
201
is supplied to an amplifier
202
of
FIG. 16
to be amplified and the amplified signal is supplied to an analog-to-digital (A/D) converter
203
to be converted to a digital signal. Thereafter, the digital signal is subjected to a correction process with respect to the machine speed and is held to be a fixed signal level as shown in FIG.
17
. Then, the digital signal is supplied to a comparison operation circuit
204
of
FIG. 16
to be compared with a previously taken-in reference image data. This operation result is supplied to a decision circuit
205
in which decision as to whether the printing paper is good or bad is made.
The decision result is supplied to the control and display unit
206
in which unsatisfactory paper is discharged and an alarm to an operator is displayed.
However, the printing quality examination apparatus shown in
FIGS. 16 and 17
Fujii Tomohiro
Kitahara Rieko
Tasaka Norifumi
Chang Jon
Mitsubishi Jukogyo Kabushiki Kaisha
Trop Pruner & Hu P.C.
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