JP2003101782A - Image forming equipment and image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide image forming equipment which is so constituted that accurate images can be formed in a surface image and a back image of an original document by making output characteristics (e.g. γ characteristic, MTF characteristic) of two kinds of reading means approximate suitably to each other, and an image forming method. SOLUTION: In the image forming equipment provided with a first image reading means which reads an image of the front page of the original document during conveyance, and a second image reading means having a type different from the first reading means which reads an image of a second page of the original document during conveyance, a correcting means is installed which makes the output characteristics of at least one image reading means approximate to those of the other image reading means.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus and an image forming method such as a copying machine, a printer and a facsimile, and more particularly, an output from two reading means capable of reading both sides of a document being conveyed. Corrected to
The present invention relates to an image forming apparatus and an image forming method, in which there is no difference between images formed on the front and back of a transfer material such as plain paper.

[0002]

2. Description of the Related Art In an image forming apparatus such as a digital copying machine, a printer or a facsimile, image reading means is provided on both sides of a sheet-shaped document conveying path so that images on both sides of the sheet-shaped document to be conveyed can be displayed. A configuration is known in which reading is performed during one-time conveyance, and as a result, image formation is speeded up.

Specifically, for example, Japanese Patent Application Laid-Open No. 11-136.
As shown in FIG. 6 of Japanese Patent Application Laid-Open No. 444, a document feeding path provided in a document pressure plate portion that can be opened and closed with respect to a document table glass is substantially V-shaped.
The reading unit including the contact type image sensor is fixed at a position closer to the front side than the top of the substantially V-shape when viewed in the document transport direction, and the position corresponding to the top of the V-shape is formed. A back-up roller for changing the conveyance path is provided to read the back side image of the document with the contact image sensor, and includes a moving scanning optical system (reduction optical system) and an image sensor provided below the document table glass. The reading means reads the surface image of the original document held by the backup roller.

Then, the laser exposure unit is drive-controlled according to the read image data, an electrostatic charge latent image is formed on the photosensitive drum by dot exposure, and the electrostatic charge latent image is converted into a toner image. Images are formed by being transferred to both sides of the recording paper (transfer material).

[0005]

The above arrangement is very useful in achieving high speed image formation.

However, the reading output characteristics of the reading unit including the contact image sensor and the reading unit including the reduction optical system and the image sensor may not be similar to each other. For example, the same image on a document is read. There is an inherent problem that the two toner images formed based on the image data and finally formed on both sides of the transfer material are images having a difference in resolution and density.

Such a problem is caused by, for example, an image pickup device (synonymous with a charge-coupled device) forming a contact image sensor.
Hereinafter, also referred to as a line CCD), and a type, an element density, and the number of elements of the image pickup device (synonymous with a charge-coupled device; hereinafter also simply referred to as CCD) in a reading unit including a reduction optical system and an image pickup device. Alternatively, it may be due to a difference in opening area, a difference in light source, or the like.

The present invention has been made in view of the above problems, and an object thereof is to appropriately approximate the output characteristics (for example, γ characteristic and MTF characteristic) of two types of reading means and faithfully reproduce the front and back images of the original. It is to provide an image forming apparatus and an image forming method that are configured to form a sheet.

[0009]

The objects of the present invention can be achieved by the following constitutions.

(1) First image reading means for reading the image on the first side of the document being conveyed, and second image reading means for the document being conveyed.
In an image forming apparatus having a second image reading unit different from the first image reading unit for reading an image on a surface, correction for making output characteristics from at least one image reading unit close to output characteristics of the other reading unit An image forming apparatus comprising means.

(2) First image reading means for reading the image on the first side of the document being conveyed, and second image reading means for the document being conveyed.
A second image reading unit different from the first image reading unit for reading an image on a surface is corrected so that at least one of the second image reading unit and the output characteristic of the other image reading unit is approximated to include the corrected read output. Form a toner image according to one read output on the image carrier,
An image forming method, which comprises transferring the toner image to both surfaces of a transfer material.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION An example of an embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic diagram showing the structure of an image forming apparatus for forming an image by an electrophotographic method.

In the figure, reference numeral 1 denotes an image forming apparatus, which is provided with an automatic document feeder 2 which is shown in a simplified manner on an upper portion thereof.
The automatic document feeder 2 is constructed so that it can be raised and lowered with the back side of the figure as a fulcrum.

The automatic document feeder 2 has a document placing table 200 for placing a sheet-like document, and one document placed on the document placing table 200 under the control of image formation. Feeding roller 202 as a sheet feeding unit for feeding
And a plurality of pairs of conveyance rollers 204, 206, 2 provided on a conveyance path of a document formed by a guide plate (not shown).
08, 210, 212 and the conveying rollers 204 and 20
6, a first image reading unit 250 (hereinafter, referred to as a first image reading unit 250 including a contact type image sensor fixedly arranged in a first reading unit for reading one surface (hereinafter, also referred to as a first surface) of a document to be conveyed. And a document discharge tray 270 for storing a document discharged from the conveyance path after being read.

The contact-type image sensor 250 has a structure in which a line CCD having a size substantially the same as the width of the document in the main scanning direction, an LED array as a light source, and a rod lens array are integrated. The contact type image sensor in the embodiment uses a structure in which a CCD drive circuit is also integrated (see FIG. 2).

On the lower side of the automatic document feeder 2, the other surface of the document (hereinafter, also referred to as the second surface) is provided via a second reading section between the transport rollers 208 and 210.
A second image reading means 3 for reading the image is provided.

The second image reading means 3 is a different form from the first image reading means 250 and includes a reduction optical system and a CCD 350.

Specifically, the reduction optical system is a light source 351 composed of a halogen lamp, a first mirror 352 integrally formed with the light source, and a second mirror 353 integrally formed.
The third mirror 354 and the imaging lens 300 are the main elements.

Reference numeral 360 designates a reading window made of transparent glass provided in the second reading section, and reference numeral 370 designates a platen glass for placing a sheet-like original document or a thick original document such as a book for image formation. It has the same height as the window.

The first mirror 352 and the second and third mirrors 353 and 354 are fixed at the positions shown in the figure in a mode of reading a sheet-like document conveyed in the automatic document feeder 2, and the platen glass is used. In the mode of reading the original placed on the 370, the driving control is performed via the control means so as to move from the left side to the right side of the drawing along the platen glass 370 while keeping the optical path length.

The line CCD constituting the first image reading means 250 in the embodiment has 23 dots / m.
m (600 pixels per inch), CCD aperture area 4
2 μm ² , the CCD 350 constituting the second image reading means 3 has 23 dots / mm, and the opening area of the CCD is 7 μm ² .

In the above description, the first image reading means 250 in the automatic document feeder 2 and the second image reading means 3 provided below the automatic document feeder 2 and above the apparatus body are digital. It can be used as an image reading device in a copier, an image scanner, a printer, a facsimile, and the like.

The first image reading means 250 and the second image reading means 3 have different forms (structures) and different output characteristics from each other, so that there is no difference in image density or the like due to them. A correction means for bringing the output characteristics of each other close to each other is incorporated in the image processing circuit. The configuration for processing including the correction means will be described later.

An image writing unit 4 drives and controls the writing unit (writing device) according to the image information read by the first image reading unit 250 and the second image reading unit 3 to form an image on the photosensitive drum 500. Is a region for forming.

In other words, the image writing unit includes a writing unit including a semiconductor laser whose driving is controlled according to image information (image data) after the image processing and a polygon mirror for deflecting the laser light. Is provided, and in the writing process, the modulated laser light is reflected by the mirror 400.
The electrostatic charge latent image corresponding to the image data is formed on the photosensitive drum 500 by appropriately discharging the electric charge on the photosensitive drum 500 which has already been subjected to the charging process.

An image forming area 5 is provided with an image forming means, and the image forming means includes the photosensitive drum 500, a charging device 502 provided around the photosensitive drum 500, a developing device 504, a transfer device 506, and a separating device. It has a container 508 and a cleaning means 510.

Below the image forming area 5, there is a paper feeding area, and a plurality of paper feeding cassettes OA and OB accommodating a large number of transfer materials S and transfer images are formed on both sides of the transfer material. Reversing unit RU for sometimes reversing the transfer material
Is prepared.

Reference numeral 6 denotes a transport path for the transfer material S, and a large number of transport roller pairs (hereinafter, the transport roller pairs are simply referred to as transport rollers) are provided on the transport path.

For example, the above-mentioned paper feed cassettes OA and OB
A plurality of transport rollers 6 are provided on the transport path for moving the transfer material S sent from the second transport roller 620 toward the second paper feed roller 620.
10 is provided to guide the transfer material S having an image formed on one side thereof to the space formed under the paper feed cassette OB, and to convey the transfer material S to the reversing unit RU. A roller 630 is provided, and a plurality of transport rollers 650 are provided in the reversing unit RU.

A transfer material S after transfer is provided in the middle of the above-mentioned conveyance path.
Belt B for transporting the toner, a fixing device H for fixing an unfixed toner image on the transfer material S, and a switching member 67 for switching the transport path of the transfer material S after fixing.
0 is set.

Reference numeral 680 denotes a discharge roller for discharging the transfer material S to the outside of the apparatus, and 690 denotes a discharge portion connected to a discharge tray.

The process of forming an image on a transfer material by using the image forming apparatus having the above structure will be briefly described as follows.

The document image sent into the automatic document feeder by the feeding roller 202 is the first image reading means 2
The respective surfaces can be read by 50 and the second image reading means 3.

The read image information is subjected to analog / digital conversion, subjected to appropriate image processing, and then stored as image data in a memory (not shown).

The image data of, for example, the first surface stored in the memory is sequentially read, dot exposure of laser light according to the image data is applied on the photosensitive drum 500, and an electrostatic latent image is formed on the photosensitive drum. Is formed.

The electrostatic latent image is converted into a toner image by the action of the developing device 504. Then, the transfer material S, which has already reached the second paper feed roller 620, is sent toward the transfer area in synchronization with the rotation of the photosensitive drum 500 so as to be superposed on the toner image, and the transfer device 506 operates. Is transcribed by.

The transfer material S having a transfer image on one side is a belt B.
The toner image is fed to the fixing device H via a roller, and the toner image is fixed on the transfer material S by the action of the pressure and heating roller pair.

After that, the transfer material S is moved in the transport path switched by the switching member 670, that is, in the transport path extending downward in the drawing, and a part of the transfer material S is fed to the paper feed cassette OA.
Is sent to the space below.

When the rear end of the transfer material S approaches the lower conveying roller 630 as seen in the moving direction and is sandwiched, the conveying roller 630 is stopped, and then rotation is controlled in the opposite direction, which is not shown. The transfer material is conveyed into the reversing unit RU via the conveyance path selected by the second conveyance path switching member and is reversed, so that the surface of the blank sheet (the second surface) is placed at the position of the second paper feed roller 620. Stop on top.

On the other hand, a toner image corresponding to the image data of the second surface of the original is formed on the photosensitive drum 500 by the same process as described above, and the toner image is sent out in synchronization with the photosensitive drum. Transfer device 5 on the transfer material S
It is transcribed by the action of 06.

The transfer material S is then subjected to the action of the fixing device, and then discharged to the outside of the apparatus via the discharge roller 680 and the discharge portion 690.

When there are a plurality of originals, the image forming operation and the storing operation in the memory via the reading means are simultaneously performed.

FIG. 2 is a block diagram of an image processing system including the structure of the first image reading means and the second image reading means and the correction means according to the present invention, and FIG. 3 schematically shows the characteristics of the image reading means. It is a characteristic view to show.

In the figures, the same members (means) as the members (means) described above are designated by the same reference numerals.

Contact type image sensor 250 schematically shown
In addition to the LED array (light source), the rod lens array, and the line CCD, a circuit for driving the line CCD such as a timing circuit, a driver, an amplifier for amplifying the output from the line CCD, and an analog / digital converter ( A /
It is composed of a structure integrally having signal processing means such as D).

Reading output of the original image from the contact image sensor (first image reading means) 250 (line C)
(Synonymous with the output of CD) is the correction means 253 in the image processing circuit.
Γ correction is performed by the correction unit 25, and the correction unit 25 further includes a filter.
After the MTF is corrected by 5, the image is taken into another image processing circuit 7 such as a compression process.

On the other hand, the read output from the second image reading means 3 (synonymous with the output of the CCD 350) is amplified by an amplifier, converted by an analog / digital converter (A / D), and then corrected by a correcting means 373. Further, the MTF is corrected by the correction means 375 including a filter, and the MTF is taken into the image processing circuit 7.

Circuits such as an amplifier, an analog / digital converter, and a driver circuit related to the second image reading means 3 are different from those of the first image reading means 250 in CCD.
Although it is not an integral structure with 350, it may be an integral structure.

For γ correction, the output characteristics of the CCD output 3 of the first and second image reading means 250 and 3 are measured in advance by experiments, and the input / output characteristic diagram (γ characteristic diagram) of FIG. ), A correction coefficient (a coefficient for forming a line shown as a correction value) that matches or approximates the characteristic representatively shown as the measured value to the reference characteristic is obtained, and the correction means 253 and 373 perform the calculation processing with the correction coefficient. Then, the output characteristics are corrected by the individual image reading means.

The characteristics which become the reference as described above are, for example,
As the output characteristic of the first image reading means, the output characteristic of the second image reading means can be matched with it, and vice versa, and it is appropriate depending on where to set the target gradation. You can take the way.

By this correction, it is possible to obtain an image having a close gradation. For MTF correction, the characteristics of each image reading means (substantially the line CCD 250 and CCD 350) are measured in advance, and
It is possible to obtain individual modulation transfer coefficients that match or approach the characteristics set as the reference, and cut off frequency components in appropriate ranges in the correction means 255 and 375 including filters to correct the output characteristics. it can.

FIG. 3B is a diagram schematically showing the MTF characteristics of the first image reading means and the second image reading means 3.

In the present embodiment, the reading is performed with a low MTF, in other words, a low-pass filter matching the filter of the second image reading means 3 is applied to the first image reading means 250 for correction. .

By this correction, it is possible to obtain an image with little difference in sharpness (resolution).

In the above-mentioned image forming apparatus, the γ correction and the MTF correction are performed as the output characteristic correction targets. However, it is possible that either one of the corrections can be used, and the combination of both corrections is not necessarily required.

Further, for example, a reflection reference white plate is provided at an appropriate position of the image forming apparatus, the reflection reference white plate is read before reading the original, and the output correction (shading correction) of the reading means is performed by the same intensity as the above method. It is also possible to carry out the present invention, and it is also conceivable that it is configured alone or in combination with other correction.

[0058]

EFFECTS OF THE INVENTION By correcting the output characteristics of two image reading means having different forms so as to be as close to each other as possible, it is possible to form images of equal quality based on the original image on both sides of the transfer material.

[Brief description of drawings]

FIG. 1 is a schematic diagram illustrating a configuration of an image forming apparatus that forms an image by an electrophotographic method.

FIG. 2 is a block diagram of an image processing system including a configuration of a first image reading unit and a second image reading unit and a correction unit according to the present invention.

FIG. 3 is a characteristic diagram schematically showing characteristics of an image reading unit.

[Explanation of symbols]

1 Image forming device 2 Automatic document feeder 250 First image reading means 253, 255, 373, 375 Correction means 3 Second image reading means 4 Image writing section 5 Image forming area 6 transport paths

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H04N 1/409 H04N 1/40 101D F term (reference) 5B047 AA01 AB02 BA01 BA07 BB03 BC05 BC09 BC11 BC14 BC18 CB05 DB01 DC06 5B057 AA11 CA02 CA08 CA12 CA16 CB02 CB12 CB16 CC01 CE03 CE11 CH08 5C072 AA01 BA20 CA02 DA02 DA04 DA25 EA05 EA07 FB18 UA06 UA17 UA20 WA02 XA01 5C077 LL04 LL08 LL09 MP01 PP01 PP15 P0612 Q0612

Claims (8)

[Claims] 1. A second mode different from the first image reading means for reading the image on the first side of the document being conveyed and the first image reading means for reading the image on the second side of the document being conveyed. An image forming apparatus having an image reading unit, comprising: a correction unit that brings an output characteristic from at least one of the image reading units closer to an output characteristic of the other reading unit. 2. The image forming apparatus according to claim 1, further comprising a correction unit that individually corrects the output characteristics from the first image reading unit and the second image reading unit. 3. The correction of the output characteristic by the correction means is γ
The image forming apparatus according to claim 1 or 2, which is a correction. 4. The correction of the output characteristic by the correction means is M
Claim 1 or Claim 2 which is TF correction.
The image forming apparatus according to item 1. 5. The first image reading unit is a contact image sensor, and the second image reading unit includes a reduction optical system and an image pickup device. Image forming apparatus. 6. A second mode different from the first image reading means for reading the image on the first side of the document being conveyed and the first image reading means for reading the image on the second side of the document being conveyed. At least one output characteristic of the image reading unit is corrected to be closer to the output characteristic of the other image reading unit, and a toner image corresponding to two read outputs including the corrected read output is formed on the image carrier, and An image forming method, which comprises transferring the toner image to both surfaces of a transfer material. 7. The image forming method according to claim 6, wherein the correction is γ correction. 8. The image forming method according to claim 6, wherein the correction is MTF correction.