JP3945648B2 - Image reading device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image reading apparatus that reads a sheet document, and more particularly to a technique for suppressing image density fluctuation.
[0002]
[Prior art]
FIG. 5 is a configuration diagram of a general image reading apparatus. The document conveyed from the upstream roller 1 passes through the contact glass 3 surface of the reading sensor 2 and passes through the downstream roller 4 and is discharged. On the contact glass 3 of the reading sensor 2 is a white pressure plate 5 having a function of white reference for shading correction and document pressing. Between the white pressure plate 5 and the surface of the contact glass 3 is thin paper. In many cases, a gap of about 0.3 mm is provided in consideration of the document conveyance performance conditions such as the above.
[0003]
Further, as a similar technique, the “image reading apparatus” of Patent Document 1 that reduces the burden of cleaning by the user, eliminates dirt on the shading member and the contact glass, and enables reading of a good shading correction signal and document information signal. "It has been known.
[0004]
[Patent Document 1]
Japanese Patent Laid-Open No. 2002-152474
[Problems to be solved by the invention]
However, when a contact sensor is used as the reading sensor, the output difference and waveform shape difference between the contact glass surface and the white pressure plate surface, which differ in height by 0.3 mm, are particularly large, resulting in density fluctuations on the image. Become.
[0006]
That is, when a shading correction operation for correcting the output of a read image is performed in an image reading apparatus that reads a sheet original, when a gap is provided between the white pressure plate for performing the shading correction and the contact glass, Since a difference occurs in the output waveform when the original is actually read, the reading density varies and density fluctuation (density unevenness) occurs in the image.
[0007]
6 (1) and 6 (2) are diagrams showing a conventional reading sensor output pattern. In the pattern 1 shown in (1), since the reading height of the white pressure plate is different, the ripple of the output waveform is different, and the image has a light and dark stripe pattern. The pattern 2 shown in (2) is a case where a difference occurs in the absolute output waveform shape, and the density unevenness occurs on the left and right as the image.
[0008]
An object of the present invention is to provide an image reading apparatus capable of eliminating (or reducing) a difference between an output waveform at the time of shading correction and an output waveform when an original is actually read, and suppressing density unevenness.
[0009]
[Means for Solving the Problems]
To achieve the above object, an invention according to claim 1, wherein, in the image reading apparatus for reading by the reading sensor sheet document is fed between the contact glass and the white pressure plate, at the time of document reading the white pressure plate The white pressure plate is moved away from the contact glass to a position where paper can be passed, and the white pressure plate is moved from the position where paper can be passed to a position in contact with the contact glass at the time of shading correction, and shading correction can be performed at an optimum position at the time of shading correction. And a contact / separation means for adjusting a position of the white pressure plate with respect to the contact glass .
[0010]
According to a second aspect of the present invention, in the image reading apparatus according to the first aspect, the contacting / separating means is constituted by an eccentric cam acting on the white pressure plate.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description, the same portions as those in the conventional example are denoted by the same reference numerals, and redundant description is omitted.
[0012]
FIG. 1 is a view showing a state where a contact glass and a white pressure plate are separated from each other in an image reading apparatus which is a reference example for explaining an embodiment of the present invention, and FIG. FIG.
[0013]
The white pressure plate 5 is provided so as to be movable up and down, and is in contact with one end of an arm 12 that swings around a fulcrum 11. A solenoid 13 and a spring 14 are locked to the other end of the arm 12 so as to face each other.
[0014]
When the solenoid 13 is off, the arm 12 is urged clockwise around the fulcrum 11 by the pulling force of the spring 14 to move the white pressure plate 5 upward. Therefore, in this state, a gap through which the sheet document can pass is secured between the contact glass 3 and the white pressure plate 5, and the sheet document is read in the state shown in FIG.
[0015]
At the time of shading correction, as shown in FIG. 2, when the solenoid 13 is turned on, the arm 12 that maintains the gap between the white pressure plate 5 and the contact glass 3 is pulled by the solenoid 13 and biased counterclockwise. The Then, the urging force of the arm 12 to the white pressure plate 5 is removed, and the white pressure plate 5 and the contact glass 3 are in close contact with each other.
[0016]
Thus, since the height of the original surface viewed from the reading sensor 2 and the height of the white pressure plate 5 are the same, the reading conditions by the reading sensor 2 can be matched when reading the sheet original and when correcting the shading.
[0017]
FIG. 3 is a view showing a state in which the contact glass and the white pressure plate are separated from each other in the image reading apparatus according to the embodiment of the present invention, and FIG. In the image reading apparatus according to the present embodiment, the eccentric cam 21 is made to act on the white pressure plate 5 that can move up and down.
[0018]
The optimal position (height from the contact glass surface) of the white pressure plate 5 at the time of shading correction varies depending on the conveyance condition difference of each machine and the difference of the reading sensor, and can be adjusted at the optimum position for each machine. Is desirable.
[0019]
In the present embodiment, the eccentric cam 21 is controlled by a stepping motor, and the white pressure plate 5 can be set at an optimal position to perform shading correction. The optimum position in this case refers to a position when a reference original is conveyed and read in a normal state, and the output and the shading output are most approximated.
[0020]
If this position is set at the time of shipment from the factory, normal shading correction is controlled to always be performed at the optimum position, and an optimum image is always obtained. Moreover, the optimum position setting for the shading correction is also effective for fluctuations over time, and by reviewing the settings, it is possible to cope with light source deterioration and conveyance condition fluctuations.
[0021]
【The invention's effect】
According to the present invention, when the original is read, the white pressure plate is moved away from the contact glass to a paper passing position, and when the shading correction is performed, the white pressure plate is moved from the paper passing position to a position in contact with the contact glass, In addition, by adjusting the position of the white pressure plate with respect to the contact glass so that shading correction can be performed at an optimum position during the shading correction, the reading conditions by the reading sensor can be set when reading a sheet document and during shading correction. It is possible to adjust the shading position of the white pressure plate and to adjust the shading position of the white pressure plate.
[Brief description of the drawings]
FIG. 1 is a diagram showing a state in which a contact glass and a white pressure plate are separated from each other in an image reading apparatus which is a reference example for explaining an embodiment of the present invention.
FIG. 2 is a view showing a state in which a contact glass and a white pressure plate are in contact with each other in a reference example.
FIG. 3 is a diagram showing a state in which the contact glass and the white pressure plate are separated from each other in the image reading apparatus according to the embodiment of the present invention.
FIG. 4 is a diagram showing a state of contact in the present embodiment as well.
FIG. 5 is a configuration diagram of a general image reading apparatus.
FIGS. 6A and 6B are diagrams showing a reading sensor output pattern of a conventional example. FIGS.
[Explanation of symbols]
2 Reading sensor 3 Contact glass 5 White pressure plate 21 Eccentric cam (contact / separation means)

Claims (2)

In an image reading device that reads a sheet document passed between a contact glass and a white pressure plate by a reading sensor,
When reading a document, the white pressure plate is moved away from the contact glass to a position where paper can be passed.When shading correction is performed, the white pressure plate is moved from the position where paper can be passed to a position in contact with the contact glass. An image reading apparatus comprising contact / separation means for adjusting a position of the white pressure plate with respect to the contact glass so that shading correction can be performed at any position . It said moving means, an image reading apparatus according to claim 1, characterized by being configured by the eccentric cam which acts on the white pressure plate.

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