JPH04332258A - Original reader - Google Patents

Abstract

PURPOSE:To produce the blurring on the image formation surface with a simple mechanism by deviating a focus and to remove moire by providing the reader with a means for changing focal distance of reflected light form a print matter. CONSTITUTION:When operation panel 1 inputs information that the original 1 is an offset printed matter, the CPU actuates the solenoid driving section to make the solenoid 13 insert a glass plate 12 having a predetermined thickness in the light path. Thus, the high frequency range component of a photo-image is removed, and as a result the same effect is obtained that a lens array 5 is moved, thereby generating a shade on the image-formation surface of image sensor 6. For gravure print such as photograph, insertion of a glass plate is stopped and the object is treated for photoelectric conversion at the best focus. Or, by rotating a pivotal section 24 via a driving motor gear and incling the glass plate 12 to the light axis in conformity with the magnification of zoom lens 20, thickness of the glass plate is substantially varied to make a shade at the focus. Furthermore, in the case or gravure print, the glass plate 12 is inclined in nearly parallel with the light axis to remove moire.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an original reading device for offset printed matter such as a scanner printer.

0002

2. Description of the Related Art The structure of a conventional example will be explained with reference to FIGS. 7 and 8. 7 and 8 are, for example, Japanese Patent Application Laid-Open No. 1-17
FIG. 4 is a front view showing a conventional document reading device disclosed in Japanese Patent No. 4160, and a diagram showing a lens array and its driving mechanism.

In FIG. 7, 1 is a document, 2 is a document table, and 3 is a document plate.
is a reading unit, 4 is an illumination lamp, 5 is a lens array,
Reference numeral 6 denotes a contact type image sensor composed of a plurality of photoelectric conversion elements such as photodiodes.

In FIG. 8, 7 is a drive motor, 8 is a worm gear, 9 is a gear, 10 is a height adjustment pin, and 11 is a ball, and the same ones are provided on the left and right sides of the lens array 5, respectively.

Next, the operation of the above-mentioned conventional example will be explained. Printing methods include gravure printing of photographs and offset printing using so-called halftone dot printing.When reading the original 1 printed using this offset printing, there is a difference between the screen pitch (halftone dot density) of the original 1 and the pixel pitch. Moiré may occur.

Conventionally, moiré has been removed by moving the lens array 5 in the optical path direction in accordance with the halftone dot density of the original 1 to shift the focal point by a predetermined amount to blur the image plane.

That is, the drive motor 7 is rotated, and the worm gear 8 moves the gear 9 and the height adjustment pin 10 in the horizontal direction. Then, the lens array 5 moves in the vertical direction along the tapered tip of the height adjustment pin 10 via the ball 11, and the focus of the lens array 5 shifts and the image plane becomes blurred by a predetermined amount. Become.

[0008]

SUMMARY OF THE INVENTION In the conventional document reading device as described above, since the lens array 5 is mechanically moved, the structure is complicated and the manufacturing cost is high. Furthermore, there is a problem in that movement control of the lens array 5 requires high precision of several tens of μm or less.

The present invention has been made in order to solve the above-mentioned problems, and provides a document reading device that can shift the focal point and blur the image plane using a simple mechanism, and can eliminate moiré. The purpose is to

0010

[Means for Solving the Problems] A document reading device according to the present invention is provided with the following means. [1] Optical means for condensing reflected light from offset printed matter. [2] An image sensor comprising a plurality of photoelectric conversion elements that convert the reflected light into electrical signals. [3] Focal length changing means for changing the focal length of reflected light passing through the optical means.

[0011]

[Operation] In the present invention, the reflected light from the offset printed matter is focused by the optical means. In addition, with an image sensor composed of multiple photoelectric conversion elements,
The reflected light is converted into an electrical signal. Further, the focal length changing means changes the focal length of the reflected light passing through the optical means.

0012

【Example】

Example 1. The configuration of Embodiment 1 of the present invention will be described with reference to FIGS. 1 and 2. FIG. 1 is a front view showing a first embodiment of the present invention, and the document 1 to image sensor 6 are completely the same as those of the conventional apparatus described above.

In FIG. 1, 12 is a glass plate, and 13 is a solenoid. In FIG. 2, 14 is an operation panel, 15 is a CPU (microcomputer), and 16 is a solenoid drive unit. Note that the surface of the glass plate 12 is coated with a reflective film to prevent reflection.

By the way, the optical means of the present invention is composed of the lens array 5 in the first embodiment of the present invention described above, and the focal length changing means of the present invention is composed of the glass plate 12, the solenoid 13, and the operating panel 14 in the first embodiment. , a CPU 15, and a solenoid drive section 16.

Next, the operation of the first embodiment described above will be explained with reference to FIGS. 3 and 4. FIG. 3 is a diagram showing the characteristics of blur when the position of the lens array 5 of Example 1 of the present invention is moved, and FIG. 4 is a diagram showing the relationship between the number of screen lines and the thickness of the glass plate determined from the characteristics in FIG. 3. It is. In FIG. 3, the horizontal axis shows the position (mm) of the lens array from the focal point, and the vertical axis shows the spatial frequency response (MTF). In FIG. 4, the horizontal axis represents the number of screen lines (lp/inch), and the vertical axis represents the thickness of the glass plate (mm). In addition, lp/inc
h is a unit representing the number of black and white line pairs (line pairs) per inch.

[0016] Here, the original 1 of offset printing is 100
In the case of [lp/inch], an appropriate thickness of the glass plate 12 will be determined. The refractive index is about 1.52 and the thickness t
When inserting the glass plate 12 into the optical path as shown in FIG.
This shows the same effect as moving the image sensor 6 by t/1.52-t≈0.34t. Therefore, in order to produce the same blur as when the lens array 5 is moved by 0.4 mm as shown in FIG.
From this, the thickness t=0.4/0.34≈1.18 is determined. In this way, the case of other parameters [lp/inch] was obtained as shown in FIG.

[0017] The original 1 is output from the operation panel 14 at 100 lp/i.
If it is input that it is offset printing of nch, C
The PU 15 operates the solenoid drive section 16 to insert the glass plate 12 having a thickness of t into the optical path using the solenoid 13. In this case, the high-frequency components of the optical image are removed, and in other words, an effect equivalent to that of moving the lens array 5 causes blurring on the imaging plane of the image sensor 6, making it possible to remove moiré. Of course, in the case of gravure printing such as photographs, the glass plate 1 is
Stop the insertion of 2 and perform photoelectric conversion at the best focus.

Embodiment 1 of the present invention, as described above,
A glass plate 12 with a predetermined thickness t is configured to be put in and out of the optical path by a solenoid 13, and can be used by switching according to the type of original 1, so moiré can be removed when reading an offset printed original 1. It has the effect of being able to In addition, the mechanism is very simple and the precision is not too loose, which has the effect of lowering the manufacturing cost.

Example 2. A second embodiment of the invention will be described with reference to FIG. FIG. 5 is a front view showing a second embodiment of the present invention, in which the document 1 to illumination lamp 4 and image sensor 6 are completely the same as those in the first embodiment described above.

In FIG. 5, 12A is a glass plate whose thickness changes in the width direction or length direction, 17, 18, and 19 are mirrors, 20 is a zoom lens (imaging lens), 21 is a drive motor, and 22 is a The worm gear 23 is a gear. Note that the surface of the glass plate 12A is coated with a reflective film to prevent reflection.

By the way, the optical means of the present invention is composed of mirrors 17 to 19 and the zoom lens 20 in the second embodiment of the invention described above, and the focal length changing means of the present invention is composed of the glass plate 12A and the zoom lens 20 in the second embodiment. It is composed of a drive motor 21, a worm gear 22, a gear 23, etc.

In the second embodiment, the glass plate 12A is moved in accordance with the magnification of the zoom lens 20 and used in areas with different thicknesses. When reading the gravure printed original 1, the glass plate 12A is of course removed from the optical path.

Embodiment 2 of the present invention, as described above,
Since the glass plate 12A having a different thickness is used, moire can be removed in an optimal manner depending on the magnification of the zoom lens 20. In this second embodiment, when the lens has a fixed magnification, a glass plate 12 having a constant thickness may be used as in the first embodiment.

Example 3. A third embodiment of the present invention will be described with reference to FIG. FIG. 6 is a diagram schematically showing a third embodiment of the present invention, and except for a glass plate 12 having a constant thickness, a rotating support member 24 that supports this glass plate 12, and a gear (not shown) are those of the above-mentioned embodiment 2. is exactly the same.

In the third embodiment, as shown in FIG. 6, the rotation support member 24 is rotated via a drive motor and a gear, and the glass plate 12 is tilted with respect to the optical axis according to the magnification of the zoom lens 20. It is used with substantially different thicknesses. When reading a gravure-printed document 1, the glass plate 12 is tilted approximately parallel to the optical axis and removed from the optical path.

Embodiment 3 of the present invention, as described above,
Since the thickness is substantially changed by tilting the glass plate 12, which has a constant thickness, moire can be removed in an optimal state according to the magnification of the zoom lens 20. Note that the same effect can be obtained even if the glass plate 12A having a different thickness is used in Example 3.

[0027] In each of the above embodiments, a normal glass plate 1 is used.
Although the case where 2, 12A is used has been described, it goes without saying that any transparent material such as plastic will have similar effects.

[0028]

As described above, the present invention provides an image sensor comprising: an optical means for condensing reflected light from an offset printed matter; and a plurality of photoelectric conversion elements for converting the reflected light into electrical signals; Since the present invention includes a focal length changing means for changing the focal length of the reflected light passing through the optical means, it is possible to defocus with a simple mechanism, and it is possible to eliminate moiré.

[Brief explanation of drawings]

FIG. 1 is a front view showing Embodiment 1 of the present invention.

FIG. 2 is a diagram showing main parts of Example 1 of the present invention.

FIG. 3 is a diagram showing blur characteristics in Example 1 of the present invention.

FIG. 4 is a diagram showing the relationship between the number of screen lines and the thickness of the glass plate determined from the characteristics shown in FIG. 3;

FIG. 5 is a front view showing a second embodiment of the invention.

FIG. 6 is a diagram schematically showing a third embodiment of the present invention.

FIG. 7 is a front view showing a conventional document reading device.

FIG. 8 is a diagram showing a lens array and its driving mechanism of a conventional document reading device.

[Explanation of symbols]

1 Manuscript 2 Manuscript table 3 Reading unit 4. Lighting lamp 12, 12A Glass plate 13 Solenoid 14 Operation panel 15 CPU 16 Solenoid drive part

Claims (1)

[Claims] 1. An image sensor comprising an optical means for condensing reflected light from an offset printed matter, a plurality of photoelectric conversion elements for converting the reflected light into an electrical signal, and a focus of the reflected light passing through the optical means. A document reading device characterized by comprising a focal length changing means for changing a distance.