JPH11216904A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reproduce good gradation at all times by correcting at least one of exposure time and intensity relative to one picture element, the surface electric potential of an image carrier, and the image forming parameter of a developing bias in accordance with the screen process given to input image signals. SOLUTION: The image data outputted from a client 50 is inputted in the image processing part 55 of a printer 52 to be given by processes such as color correction, rasterization, and gradation correction, and thereafter a screen process or the like is given thereto in the operation control part 59 of the printer. In this instance, screen sort signals are outputted from a rasterization processing part 57 to a gradation correction processing part 58, a screen processing part 60 and a correction table 63. In the screen processing part 60, screen processing operations of a concentration type, line type, or the like are given in accordance with screen sort signals. In addition, even in the correction table 63, screen processing operations of a concentration dot type, line type, or the like can be given according to the screen sort signals.

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 such as a printer and a digital copying machine, and more particularly to an image forming apparatus suitable for a color image forming apparatus such as a color printer and a digital color copying machine.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus such as a printer or a digital copying machine of this type, after uniformly charging the surface of a photosensitive drum or the like as an image carrier, a laser beam is irradiated with a predetermined resolution. Irradiation is performed in accordance with information, an electrostatic latent image is formed on the surface of the photosensitive drum, and the electrostatic latent image is developed to print or copy an image.

In such an image forming apparatus such as a printer or a digital copying machine, as disclosed in Japanese Patent Application Laid-Open No. 7-92749, the mode of changing the laser resolution in accordance with the selection of the image forming mode is not limited to each mode. In order to obtain a good image in each case, the laser resolution is set to 40 in accordance with the operation of the copy mode designation key or the print mode designation key as the mode selection means.
When changing to 0 dpi or 300 dpi, the CPU
A configuration in which the laser power of the semiconductor laser oscillator, the surface potential of the photosensitive drum, and the developing bias of the developing roller of the developing device are respectively changed to appropriate values by changing means shared by the above has already been proposed.

[0004]

However, the prior art described above has the following problems. That is, in the case of the image forming apparatus according to the above-mentioned Japanese Patent Application Laid-Open No. 7-92749, like the line reproduction and the maximum density,
Although good images can be obtained for image quality items that are dominant in binary and black-and-white printers and copiers, there is the problem that digital color printers and copiers are not sufficient.

More specifically, recent digital color printers and copiers are configured so that a user can select and use an arbitrary screen shape when irradiating a laser beam onto a photosensitive drum. is there. In addition, the resolution at the time of outputting an image other than the screen shape is expanded by a memory in the main scanning direction,
In the sub-scanning direction, a configuration has been proposed which can be changed relatively easily by a process speed of an image forming unit, processing by an image processing unit, or the like.

[0006] In the image forming apparatus constructed so that the screen shape and resolution can be changed, if the screen shape is different or the resolution is different, the gradation reproduction of the entire reproduction area is centered on the intermediate density area of the output image. Reproduction curve),
The highlight reproduction start point and gradation reproduction characteristics are converted.
For example, in the image forming apparatus of the digital color printer or the copying machine, since the response followability of the image forming unit to the exposure characteristic of the laser beam differs depending on the screen shape, Cin which is an input signal to the screen unit is used.
As shown in FIG. 7, the relationship between the (Cavage input) and the output density changes according to the screen shape, such as a concentrated dot type or a line type, and a color image with good image quality cannot be obtained. There was a problem. Further, since the gradation reproduction is different, the color reproduction characteristics when the toner images of each color are superimposed also change,
There was a problem that a color image with good image quality could not be obtained.

Further, in the above-described image forming apparatus of a digital color printer or a copying machine, in order to avoid the occurrence of a moire pattern in the formed image, the screen angle is changed to the color of the image to be formed. But
If the screen angle differs for each color to be formed, there is a problem that the gradation reproduction between the colors forming the image also changes.

Therefore, the present invention has been made to solve the above-mentioned problems of the prior art, and an object of the present invention is to always provide a good floor even when the screen shape, angle, or resolution changes. An object of the present invention is to provide an image forming apparatus having a function of correcting an image forming parameter and setting it to a desired value so that a tone reproduction can be obtained.

[0009]

According to a first aspect of the present invention, there is provided an image forming apparatus provided with an image exposing means for exposing an image on an image carrier based on an input image signal. The image forming conditions are corrected by correcting at least one of the exposure time and intensity for one pixel, and the image forming parameters of the surface potential of the image carrier and the developing bias according to the screen processing applied to the image signal. This is configured to include a correction unit that performs the correction.

[0010] The invention described in claim 2 is the same as the claim 1.
3. The image forming apparatus according to claim 1, wherein an image forming condition is corrected based on a screen shape and a resolution.

Further, the invention according to a third aspect is the image forming apparatus according to the first aspect, wherein an image forming condition is corrected by a color for forming the image.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on an embodiment shown in the drawings.

Embodiment 1 FIG. 2 is a system configuration diagram showing a color image forming apparatus according to Embodiment 1 of the present invention.

In FIG. 2, reference numeral 01 denotes a photosensitive drum as an image bearing member.
After being uniformly charged to a predetermined initial surface potential by the charging unit 02, the exposure unit 03 irradiates a laser beam in accordance with image information to form an electrostatic latent image. As will be described later, image data subjected to predetermined processing by the image processing unit 04 is input to the exposure unit 03 via the screen processing unit 05 and the laser driving unit 06. The image processing unit 04 performs image processing such as color correction and gamma correction on image data input from a client such as a scanner of a copying machine (not shown) or an external personal computer, so that yellow, magenta, It is converted into a raster image signal in a printing color such as cyan, black, and a specific color. The image that has been subjected to the image processing is converted into a signal of a laser lighting time and a lighting position of a semiconductor laser by a screen processing unit 05 by an area gradation method using various screen parameters. Then, the semiconductor laser of the exposing unit 03 is driven via the laser driving unit 06 based on the signal of the laser lighting time and the lighting position converted by the screen processing unit 05.

The electrostatic latent image formed on the surface of the photosensitive drum 01 is developed by a developing unit 07 to become a toner image, and the toner image formed on the photosensitive drum 01 is
At a position facing the transfer drum 08, the image is transferred onto a transfer sheet adsorbed on the surface of the transfer drum 08, and is fixed by a fixing unit 09 to be a permanent image.

FIG. 3 is a block diagram specifically showing a digital color copying machine having a function as a printer as an image forming apparatus according to the first embodiment of the present invention.

In FIG. 3, reference numeral 1 denotes a main body of a digital color copying machine.
An eInput Terminal (hereinafter, referred to as “IIT”) 3 is provided. The IIT 3 illuminates the image of the original 2 placed on the platen glass 4 with the light source 6 while pressing the original 2 placed on the platen glass 4 with the platen cover 5, and The reflected light image is converted into first and second scanning mirrors 7 and 8.
The CCD sensor 10 scans and exposes the color material reflected light image of the original 2 to a predetermined dot density (for example, 16 dots / m) by the CCD sensor 10 via the imaging lens 9.
m).

Original 2 read by IIT 3
Is transmitted to the image processing unit 12 as document reflectance data of three colors, for example, red (R), green (G), and blue (B) (each of 8 bits). Then, shading correction, positional deviation correction, brightness / color space conversion, gamma correction, frame erasing,
Predetermined image processing such as color / movement editing is performed.

The image data subjected to the predetermined image processing by the image processing section 12 as described above includes black (K), yellow (Y), magenta (M), and cyan (C) (each 8 bi).
The image data is converted into three-color original color material gradation data of t) and output as a color image by the engine 13 which is an image output unit configured as follows. The image data subjected to the predetermined image processing by the image processing unit 12 includes black (K), yellow (Y), magenta (M), and cyan (C) (each 8 bi).
t) is converted into three-color original color material gradation data,
13 Raster Output Scanners
(Hereinafter referred to as “ROS”) 15. This RO
In S15, image exposure with laser light is performed according to the original color material gradation data.

As shown in FIG. 3, the ROS 15 modulates the semiconductor laser 16 according to the original color material gradation data, and emits a laser beam LB from the semiconductor laser 16 according to the gradation data. The laser beam LB emitted from the semiconductor laser 16 is deflected and scanned by the rotary polygon mirror 17 and is reflected by the photosensitive drum 2 via the reflection mirror 18.
Scanning exposure is performed on 0.

The photosensitive drum 20 on which the laser light LB is scanned and exposed by the ROS 15 is driven to rotate at a predetermined speed in a direction indicated by an arrow by driving means (not shown). The surface of the photosensitive drum 20 is
After being charged to a predetermined potential by the charging corotron 21 in advance, an electrostatic latent image is formed by scanning and exposing a laser beam LB in accordance with document color material gradation data. The electrostatic latent images formed on the photoreceptor drum 20 include four color developing units 22K, 22Y, 22M, 22C of black (K), yellow (Y), magenta (M), and cyan (C).
Are sequentially developed by a rotary type developing device 22 provided with a toner image having a predetermined color.

The toner image formed on the photosensitive drum 20 is transferred onto a transfer material 24 such as a transfer sheet held on a transfer drum 23 disposed adjacent to the photosensitive drum 20 by a transfer corotron. The images are sequentially transferred by the charging of 25. As shown in FIG. 3, the transfer material 24 includes a plurality of paper feed cassettes 2 stored in a lower portion in the copying apparatus main body 1.
8, 29, 30, or a manual feed tray 38 disposed on a side surface outside the copying apparatus main body 1. The material 24 is conveyed to the surface of the transfer drum 23 by the conveying roller 32 and the registration roller 33 at a predetermined timing. The transfer material 24 is held on the surface of the transfer drum 23 in a state where the transfer material 24 is electrostatically attracted to the surface of the transfer drum 23 by charging of the transfer corotron 25 which also serves as a charger for electrostatic attraction. In addition, from the manual feed tray 38, a transparent OH for an overhead projector other than a non-standard-size transfer paper such as a postcard is provided.
A P sheet or the like can be fed, and an image can be formed on an OHP sheet or the like. From the manual feed tray 38, the transfer material 24 on which an image is formed on one side is fed upside down, so that double-sided copying is possible.

The transfer material 24 onto which the toner image of a predetermined number of colors has been transferred from the photoreceptor drum 20 is separated from the surface of the transfer drum 23 by discharging the corotron 34 for separation, and then the fixing device 35 The toner image is transferred to the transfer material 24 by heat and pressure by the fixing device 35.
The color image is fixed on the sheet and discharged onto the sheet discharge tray 36, thereby completing the color image forming process.

In FIG. 3, reference numeral 37 denotes a charge removing corotron pair for removing charge from the transfer drum 23.

FIG. 4 is a block diagram showing the image forming unit of the digital color copying apparatus of the multiple transfer system.

In FIG. 4, reference numeral 20 denotes the photosensitive drum, and a transfer drum 23 as a transfer material carrier is provided so as to be in contact with the surface of the photosensitive drum 20 with a small gap therebetween. I have. The transfer drum 23 is driven to rotate at the same speed as the peripheral speed of the photosensitive drum 20 by a drive mechanism (not shown). As shown in FIG. 5, the transfer drum 23 includes a pair of ring members 40, 4 as annular members disposed at both ends in the axial direction.
And a tie bar plate 41 as a connecting member for connecting the ring members 40 and 40 to each other. The tie bar plate 41 is made of a dielectric film such as polyethylene terephthalate or polyvinylidene fluoride. A circumferential front end portion 42a of the transfer film 42 is fixed, and both side ends are wound around a frame along the outer peripheral surfaces of the ring members 40, 40, and a circumferential rear end portion of the transfer film 42 is formed. 42b is fixed to the tie bar plate 41 and formed in a hollow cylindrical shape.

As described above, the transfer material 24 is supplied to the transfer drum 23 from any one of the plurality of paper feed cassettes 28, 29, and 30. The transfer material 24 is adsorbed from the back side of the transfer drum 23. It is charged by the transfer corotron 25, which also functions as a charging device, and is electrostatically attracted onto the transfer film 42 of the transfer drum 23. This transfer drum 23
On the transfer material 24 adsorbed thereon, black (K), yellow (Y), magenta (M), and cyan (C) toner images sequentially formed on the photosensitive drum 20 are transferred.
5 is transferred by charging.

The transfer material 24 to which the toner image of a predetermined number of colors has been transferred from the photosensitive drum 20 is discharged by a peeling corotron 34 and peeled off from the surface of the transfer drum 23 by a peeling device 44. The toner image is conveyed to the fixing device 35 via the conveyance guide 45, the toner image is fixed on the transfer material 24 by heat and pressure by the fixing roller 35 a and the pressure roller 35 b of the fixing device 35, and the outside of the device is fixed by the fuser outlet roll 46. Is discharged onto the discharge tray 36 of the.

FIG. 1 is a block diagram showing a control section of the digital color copying machine.

In FIG. 1, reference numeral 50 denotes a client such as a personal computer. The client 50 is connected to a printer 52 via a communication line 51. The client 50 uses the application software 53 to create document data including a document, a chart, or a photographic image input from a scanner or the like. The screen shape and resolution of the image data created by the client 50 are specified by a user interface (UI) at the time of a print command. Document data with this screen shape specified
The data is converted into a page description language (PDL) by the driver 54 and sent to the printer 52 via the communication line 51.
Thereafter, in the image processing unit 55 inside the printer, after the color correction is performed by the color correction processing unit 56, the image is developed into a raster image by the rasterization processing unit 57. This rasterization processing unit 5
After the raster image is developed into a raster image in step 7, the tone correction processing unit 58 performs an optimum tone correction process based on a tone reduction curve (TRC) according to the screen type signal. Data is output.

In the screen processing section 60 of the printer operation control section 59, the image data is screened according to the designated screen shape. Thereafter, the image data is modulated by the laser drive unit 61 and output to the engine 62 which is an image forming unit, where an image is formed. The screen type signal is also sent to a correction table 63 as correction means for correcting image forming process parameters such as the ROS power, the initial surface potential Vh, and the development potential Vd. Is selected and set in the engine 62 based on the setting signal.

The screen processing unit 60 of the printer 52
In the above, screen processing for applying a screen to image data is performed based on a screen designation signal designated by a user interface. The shape of the screen provided by the screen processing unit 60 is characterized by a printing order and a position in a basic cell composed of a plurality of pixels (for example, 3 × 3 pixels and 4 × 4 pixels). And the position, that is, the growth method is a parameter. As the screen shape, for example, as shown in FIG. 6, a concentrated dot type grown from the center of a basic cell, a line type grown in a line shape, a dispersed dot, an error diffusion method, etc. It greatly affects the output image quality. Similarly, the number of pixels constituting the basic cell also has a great effect on the final output image quality. For example, as shown in FIG. 7, the curve of the output density with respect to the input signal to the screen processing unit 60 is different between the concentrated dot method and the line-by-line method. ), The output density curve is different. Further, the reproduction start point at which printing is started by the input signal to the screen processing unit 60 and the curve of the highlight output density near the reproduction start point also change.

FIGS. 8 and 9 show the parameters of the image forming process in the print engine.

FIG. 8 shows a laser driving unit 61 and a charging unit 0.
2 shows the relationship between the exposure unit 03 and the input signal to the screen processing unit 60 is an example of eight levels. Case A shows the case where the initial surface potential Vh of the photosensitive drum 20 is large and the laser exposure time and intensity are large, as shown in FIG.
FIG. 8B shows a case where the initial surface potential Vh of the photosensitive drum 20 and the laser exposure time and intensity are both small, as shown in FIG. When both of them are developed at a certain development potential Vd, the difference between the surface potential Vh of the photosensitive drum 20 and the development potential Vd in the input signal to the screen processing unit 60 is obtained according to the development characteristics shown in FIG. The output density changes according to the development potential difference. To explain further,
In the case A, since the initial surface potential Vh of the photosensitive drum 20 is large and the laser exposure time and intensity are large, the output density according to the 8-level gradation data is as shown in FIG.
As shown by the broken line, the output density is zero where the laser exposure time and intensity are small, and as the laser exposure time and intensity gradually increase, the output density gradually increases from zero beyond the reproduction start point. It reaches the maximum value. On the other hand, in case B, since the initial surface potential Vh of the photosensitive drum 20 and the laser exposure time and intensity are both small, the output density according to the 8-level gradation data is as shown by the solid line in FIG. In the place where the laser exposure time and intensity are small, there is already a reproduction start point where the output density exceeds zero, and as the laser exposure time and intensity gradually increase, the output density gradually increases from zero beyond the reproduction start point. It grows and reaches a maximum. In FIG. 9, since the lowest density is zero in both cases A and B, the horizontal axis is expressed as seven development potential differences.

As described above, in case A, as shown in FIG. 9, as the 8-level gradation data increases, the output density is initially zero, but the reproduction start point in the middle is changed. In contrast, in case B, the output density is greater than zero from the beginning of the 8-level gradation data, and exceeds the reproduction start point. It has the characteristic that the output density increases accordingly. Therefore, the process parameters for Case A are:
It is suitable for image data such as characters in which high-density gradation data is faithfully reproduced without reproducing errors such as large changes in image density and low values of gradation data. On the other hand, case B
Are suitable for image data such as photographs and graphs including halftone images in which the density of an image gradually changes from a low density portion to a high density portion.

When the screen processing is performed by the screen processing unit 60, if the image is a character image, as shown in FIG. 6, it is better to perform image exposure using a line-type screen. The lines in the vertical and horizontal directions are clearly displayed, so that image reproducibility is excellent, and a line-type screen is selected. On the other hand, when the image is a halftone image such as a photograph or a graph, as shown in FIG. 6, it is better to perform image exposure using a concentrated dot type screen so that the density change of an image such as a photograph is more faithful. Since it can be reproduced, the reproducibility of the image is excellent, and a screen of a concentrated dot system is selected.

For this reason, in the case of the printer according to this embodiment, for example, if the image is a character image, a line-type screen is used, and the process parameters of Case A, which is excellent in the reproducibility of the character image, are Selected. on the other hand,
When the image is a halftone image such as a photograph or a graph, a correction table 63 is used so that a concentrated dot type screen is used and process parameters of case B having excellent reproducibility of the halftone image are selected. Is set by

In the printer having the function as a digital color copying machine according to this embodiment having the above-described structure, good tone reproduction is always achieved even when the screen shape and resolution change as follows. Can be obtained, and parameters for image formation are corrected and set to desired values.

That is, in the printer having a function as a digital color copier according to this embodiment, as shown in FIG. 1, a client 50 such as a personal computer transmits an image to a printer 52 via a communication line 51. Data is sent. At that time, the client 5
In the user interface 0, the screen shape is designated according to the image data to be printed. The screen shape is specified by, for example, selecting whether the image to be printed is a black and white image, a color character or a photograph by the client 50, and automatically selecting a suitable screen shape according to the type of the image. May be specified.

Next, the image data converted into the page description language output from the client 50 as described above is input to the image processing unit 55 of the printer 52, where the processing such as color correction, rasterization, and gradation correction is performed. After the application, the operation control section 59 of the printer performs a screen process or the like. At this time, the rasterization processing unit 57 outputs a screen type signal to the gradation correction processing unit 58, the screen processing unit 60, and the correction table 63. Then, the screen processing unit 60 performs a screen processing such as a concentrated dot type or a line type according to the screen type signal as shown in FIG. In the screen processing unit 60, as described above, a line-type screen is used when the image is a character image, and a concentrated dot type screen is used when the image is a halftone image such as a photograph or a graph. Used. In the correction table 63, a screen processing such as a concentrated dot type or a line type is performed according to the screen type signal as shown in FIG. In the screen processing unit 60, as described above, a line-type screen is used when the image is a character image, and when the image is a halftone image such as a photograph or a graph, the halftone image such as a photograph is used. A concentrated dot screen with excellent reproducibility is selected.

In the correction table 63, when the image data is a character image, the initial surface potential Vh of the photosensitive drum 20 is high, and the laser exposure time and light amount are low, as in the case A shown in FIG. A process parameter that increases is selected, and the process parameter is output to the engine unit 62. When the image data is a halftone image such as a photograph, the initial surface potential Vh of the photosensitive drum 20 is low, and the laser exposure time and light amount are small, as in case B shown in FIG. 8B. Such a process parameter is selected, and the process parameter is output to the engine unit 62.

As described above, in the above-described printer, even when the screen shape and the resolution change, good tone reproduction can always be obtained by correcting the image forming parameters and setting them to desired values. A high-quality color image can be formed.

Second Embodiment FIG. 10 shows a second embodiment of the present invention. In the second embodiment, not a four-cycle system in which the number of image forming units is one and the transfer drum rotates four times, It is a tandem type having a total of four image forming units for each color, and is capable of forming a high-speed color image, and has a feature that parameters of each process in each image forming unit can be independently set and controlled at high speed. Things.

FIG. 10 is a block diagram showing a tandem type digital color copying machine as an image forming apparatus according to Embodiment 2 of the present invention.

In FIG. 10, 70K, 70Y, 70
M and 70C indicate four image forming units of black, yellow, magenta, and cyan, respectively. In each of the image forming units 70K, 70Y, 70M, and 70C, black,
Yellow, magenta, and cyan toner images are respectively formed. Each of the image forming units 70
K, 70Y, 70M, and 70C have the same configuration, and their photosensitive drums 71K, 71Y, 71M, and 71C
Is charged by the charging units 72K, 72Y, 72M, and 72C.
After being uniformly charged to a predetermined initial surface potential, the exposure unit 73
A laser beam is irradiated by K, 73Y, 73M, and 73C according to image information, and an electrostatic latent image is formed. Each of the exposure units 73K, 73Y, 73M, and 73C stores image data that has been subjected to predetermined processing by one image processing unit 74, to each of the screen processing units 75K, 75Y, 75M, and 7C.
5C and laser driving units 76K, 76Y, 76M, 76
Input via C. The image processing unit 74 performs image processing such as color correction and gamma correction on image data input from a scanner such as a copier scanner or an external personal computer (not shown), and performs processing such as yellow, magenta, cyan, It is converted into a raster image signal in a printing color such as black and a specific color. This image-processed image is output to each screen processing unit 75.
At K, 75Y, 75M, and 75C, the signals are converted into laser lighting time and lighting position signals of the semiconductor laser by an area gradation method modulation process using various screen parameters. Then, the screen processing units 75K, 75
Based on the laser lighting time and the lighting position signal converted by Y, 75M, 75C, laser driving units 76K, 76
Each of the exposure units 73K, 73Y,
The semiconductor lasers 73M and 73C are driven.

Each of the photosensitive drums 71K, 71Y, 71
The electrostatic latent images sequentially formed on the surfaces of the photoconductor drums 71K, 71Y, 71C are developed by the developing units 74K, 74Y, 74M, 74C.
The toner images formed on the M and 71C are transferred onto a transfer sheet held on a transfer belt 77 disposed over the transfer positions of 70K, 70Y, 70M and 70C of each image forming unit, and are fixed by a fixing unit 78. And a permanent image is formed.

FIG. 11 is an overall configuration diagram specifically showing the configuration of the digital color copying machine.

In FIG. 11, a document 102 placed on a platen glass 101 is scanned by a color CCD sensor 103 via a scanning optical system including a light source and a scanning mirror.
R (red), G by image scanner equipped with
(Green) and B (blue) are read as analog image signals. The RGB analog image signals read by the color CCD sensor 103 are converted into K (black), Y (yellow), M (magenta), and C (cyan) digital image signals by the image processing unit 104. ,
After predetermined image processing is performed, the image is temporarily stored in a memory provided inside the image processing unit 104. The digital color copying machine forms a color image based on color image information transmitted from a client such as a personal computer (not shown), in addition to reading the image of the color document 102 and forming a color image. It is also possible. In this case, the image processing unit 10
4, color image information is input from a client such as an external personal computer.

FIG. 11 and FIG.
As shown in FIG. 2, the image forming units 105 for each color of black (K), yellow (Y), magenta (M), and cyan (C)
K, 105Y, 105M, 105C ROS (Rast
er Output Scanner) 108K, 10
8Y, 108M, and 108C sequentially output image data of each color.
A laser beam LB emitted from each of the photoconductor drums 106K,
Scanning exposure is performed on the surfaces of 06Y, 106M, and 106C to form electrostatic latent images. Each of the photosensitive drums 106K, 1
The electrostatic latent images formed on 06Y, 106M and 106C are respectively subjected to black (K), yellow (Y), magenta (M) and cyan (C) by developing units 109K, 109Y, 109M and 109C. It is developed as a toner image.

Each of the photosensitive drums 106K, 106Y,
As shown in FIG. 12, transfer paper 114 as a sheet for transferring the toner image of each color formed on 106M and 106C has a predetermined size from one of a plurality of paper feed cassettes 115, 116 and 117. Thing is paper feed roller 1
18 and a pair of rollers 119, 120, 121 for conveying the paper
The paper is conveyed via a paper conveyance path 122 composed of The transfer paper 114 supplied from any one of the paper feed cassettes 115, 116, and 117 is sent out onto a transfer belt 124 as an endless carrier by a registration roll 123 that is driven to rotate at a predetermined timing. The transfer belt 124 is endlessly wound around the drive roll 125, the stripping roll 126, the tension roll 127, and the idle roll 128 with a constant tension, and has excellent constant speed (not shown). Drive roll 12 rotated and driven by a dedicated drive motor
5, the circulating drive is performed at a predetermined speed in the direction of the arrow. As the transfer belt 124, for example, an endless belt is formed by forming a synthetic resin film such as PET having flexibility in a belt shape and connecting both ends of the synthetic resin film formed in a belt shape by means such as welding. What was formed in the shape is used.

The leading end of the transfer sheet 114 conveyed by the transfer belt 124 and the first image forming unit 10
The paper feed timing and the image writing timing are determined such that the leading end of the image formed on the first photosensitive drum 106K formed at 5K coincides with the lowest transfer point of the photosensitive drum 106K. I have. The transfer paper 114 that has reached the transfer point is a corotron 111K for transfer.
As a result, the visible image on the photosensitive drum 106K is transferred, and reaches the transfer point immediately below the photosensitive drum 106Y. On the transfer sheet 114 that has reached the transfer point immediately below the photosensitive drum 106Y, a visible image on the photosensitive drum 106Y is transferred in the same manner as the transfer image transferred on the photosensitive drum 106K. Transfer paper 1 after all transfer is completed
The stripping roll 14 is further conveyed by the transfer belt 124 and reaches the vicinity of the stripping roll 126. When the stripping roll 14 reaches the vicinity of the stripping roll 126, the stripping charge is removed by the stripping discharge corotron 129, and the stripping roll 1 having a small radius of curvature is set.
The transfer belt 124 is separated from the transfer belt 124 by the stripper 26 and the separation claw 130. Thereafter, the transfer paper 114 onto which the four color toner images have been transferred is heated by the fixing device 131 to the heating roll 13.
2a and the fixing roller 132b, the image is fixed onto the discharge tray 134 shown in FIG. 2 by the discharge roller pair 133, and a color image is copied. In this embodiment, four color toner images are transferred. Transfer paper 114
Is not directly discharged onto the discharge tray 134, but the transfer paper 114 discharged from the digital copying machine.
As shown in FIG. 11, a post-processing device that performs post-processing such as stapling is connected in place of the discharge tray 134.

When copying a full-color image on both sides of the transfer sheet 114, as shown in FIG.
The transfer sheet 114 on which the color image is formed on one side is not discharged as it is by the discharge roll pair 133, but the transfer direction of the transfer paper 114 is switched downward by the switching plate 135, and the paper transfer roll pair 136, 137, 1
38, 139, etc., via a paper transport path 140,
The transfer sheet 114 is conveyed onto the transfer belt 124 again through the sheet conveyance path 122 in a state where the transfer sheet 114 is turned over, and a color image is formed on the back surface of the transfer sheet 114 by the same process as described above.

The four black, yellow, magenta and cyan image forming units 105K, 105Y,
As shown in FIG. 12, all of the four image forming units 105M and 105C have the same configuration.
In 05K, 105Y, 105M, and 105C, as described above, black, yellow, magenta, and cyan toner images are sequentially formed at a predetermined timing. Image forming unit 1 for each of the above colors
05K, 105Y, 105M, and 105C denote photosensitive drums 106K, 106Y, 106M, and 1 as image carriers.
06C, and these photosensitive drums 106K,
The surfaces of 106Y, 106M, and 106C are provided with scorotrons 107K, 107Y, 107M, and 107C for primary charging.
ROS 108K, 108
The image forming laser beam LB emitted from Y, 108M, 108C in accordance with the image data is scanned and exposed,
An electrostatic latent image corresponding to each color is formed. The electrostatic latent images formed on the surfaces of the photosensitive drums 106K, 106Y, 106M, and 106C are stored in the respective image forming units 105K, 105K,
05Y, 105M, 105C developing units 109K, 109
Y, 109M, and 109C respectively develop black, yellow, magenta, and cyan toners to form visible toner images. These visible toner images are
Pre-transfer charger 110K, 110Y, 110M, 110C
After the transfer, the transfer chargers 111K, 1K
The transfer belt 1 is charged by charging of 11Y, 111M, and 111C.
The image is sequentially transferred to a transfer sheet 114 held on the sheet 24.
The transfer paper 114 on which the toner images of the black, yellow, magenta, and cyan colors are transferred is a transfer belt 1
After being separated from the fixing device 131, the fixing device 131
, And a color image is formed.

Further, as described above, the transfer paper 114 is supplied from one of the plurality of paper feed cassettes 115, 116, and 117, and is conveyed onto the transfer belt 124 by the registration roll 123 at a predetermined timing. , Paper holding charger 141 and charging roll 142
Is held and conveyed on the transfer belt 124.

The photosensitive drums 106K and 106K
As shown in FIG. 12, Y, 106M, and 106C deactivate the pre-cleaning static eliminator 112K after the toner image transfer process is completed.
The charges are removed by 112Y, 112M, 112C and cleaners 113K, 113Y, 113M, 11C.
3C removes residual toner and the like, and prepares for the next image forming process.

The transfer belt 124 is neutralized by a pair of neutralizing corotrons 143 and 144 for the transfer belt in the orbit around the transfer paper 114 after the transfer paper 114 is peeled off, and the surface of the transfer belt 124 is A cleaning device 147 including a rotating brush 145 and a blade 146 removes toner, paper dust, and the like.

As shown in FIG. 10, the digital color copying machine according to the second embodiment has a screen processing unit 75K, 75Y, 75M, 75C for each image forming unit.
And the laser drive units 76K, 76Y, 76M, and 76C, so that the screen shape and resolution can be set for each image forming unit, and to avoid the occurrence of moire patterns in the formed color image. The screen angle is set to be changed for each image forming unit.

When the screen shape and the screen angle are changed in the screen processing units 75K, 75Y, 75M, and 75C of each of the image forming units, the correction table is used to adjust the photosensitive drum according to the screen shape and the screen angle. At least one of the initial surface potential Vh of 71K, 71Y, 71M, and 71C, the exposure time and / or intensity of the laser beam, and the development potential Vd is changed.

As described above, the tone reproduction characteristics and the reproduction start point can be controlled by the initial surface potential, the laser exposure time and intensity, and the development potential. Good gradation reproduction and color reproduction can be achieved by varying the number of lines and the angle for each different color. further,
By setting target values of the initial surface potential, the laser exposure time and intensity, and the development potential, sensing the state and output density, and performing feedback control, it is possible to control fluctuations between environments and models. By the above,
Adjustment by a process parameter optimized for a screen or the like can be performed.

Although the present invention can be applied to all printing engines, it is useful for a one-component developing system in which the toner concentration is fixed.

Further, the present invention is useful for a tandem engine system in which printing parameters are provided between printing engines and setting is easy.

[0062]

As described above, according to the present invention, even if the screen shape, angle, or resolution changes, the image forming parameters are corrected so that good tone reproduction can be always obtained. Thus, an image forming apparatus having a function of setting a desired value can be provided.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a control unit of a printer as an embodiment of an image forming apparatus according to the present invention.

FIG. 2 is a configuration diagram illustrating a printer as an embodiment of the image processing apparatus according to the present invention.

FIG. 3 is a configuration diagram showing a digital color copying machine according to Embodiment 1 of the present invention.

FIG. 4 is a configuration diagram illustrating an image forming unit.

FIG. 5 is a perspective view showing a transfer drum.

FIG. 6 is an explanatory diagram showing a screen shape.

FIG. 7 is a graph showing a relationship between an input signal to a screen unit and an output density.

FIG. 8 is an explanatory diagram showing process parameters.

FIG. 9 is an explanatory diagram showing process parameters.

FIG. 10 is a block diagram illustrating a control unit of a printer as an image forming apparatus according to a second embodiment of the present invention;

FIG. 11 is a configuration diagram showing a digital color copying machine according to Embodiment 2 of the present invention.

FIG. 12 is a configuration diagram showing a digital color copying machine according to Embodiment 2 of the present invention.

[Explanation of symbols]

50: client, 51: communication line, 52: printer, 53: application software, 54: driver,
55: image processing unit, 56: color correction processing unit, 57: rasterization processing unit, 58: gradation correction processing unit, 59: printer operation control unit, 60: screen processing unit, 61: laser driving unit, 62: engine , 63: correction table.

Claims (3)

[Claims] 1. An image forming apparatus comprising an image exposing means for exposing an image on an image carrier based on an input image signal, the image forming apparatus comprising: An image forming apparatus comprising: a correction unit that corrects an image forming condition by correcting at least one of an image forming parameter of an exposure time and an intensity, a surface potential of an image carrier, and a developing bias. 2. The image forming apparatus according to claim 1, wherein an image forming condition is corrected based on a screen shape and a resolution. 3. The image forming apparatus according to claim 1, wherein an image forming condition is corrected based on a color in which the image is formed.