JPH09244343A - Image forming device and its method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device which stabilizes the gradation, forms the image of excellent quality, and is excellent in durability and environmental adaptability by detecting the density information of the pattern of the prescribed gradation by a plurality of colors formed on an image carrier using a filter of approximately same color as that of the developer to correct the gradation. SOLUTION: In a density sensor, the reflected light by a patch pattern 22 formed on a photosensitive body 21 is detected by a photo-detector 43 through a filter 41, and the density of the patch pattern 22 is detected. In detecting the density of each color component, the patch pattern image 22 having gradation of two colors of black and red is formed on the photosensitive body 21, and the red component is removed using a red filter 41 from the transmitted light or the reflected light consisting of the mixed color of black and red. The density of only residual black component can be measured, the gradation of the density in the black component can be corrected, and the gradation stability can be improved for both black and red components by correcting the gradation by the monochromatic (red) light of other color component at the same time.

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 a method thereof, for example, an image forming apparatus and a method thereof for forming a multicolor image by an electrophotographic method.

[0002]

2. Description of the Related Art With the recent development of image processing technology, an image forming apparatus capable of forming a high quality multicolor image by an electrophotographic system has become widespread. In the electrophotographic multicolor image forming apparatus, there are a multiple transfer system for forming a toner image and transferring to a transfer material for each color, and a batch transfer system for collectively transferring a toner image of a plurality of colors onto a transfer material. . Among them, the batch transfer method is excellent in image forming speed and cost.

In a batch transfer type image forming apparatus,
An electrostatic latent image carrier (hereinafter, simply referred to as “image carrier”) is provided, and electrostatic latent images of a plurality of colors are sequentially formed on the carrier while the carrier rotates once. Then, the electrostatic latent images are sequentially developed by developing devices of corresponding colors, and toner images of a plurality of colors are superposed on the holder. Then, the obtained toner images of a plurality of colors are collectively transferred onto a transfer material to obtain a multicolor image.

An image forming process will be described below with reference to FIGS. 16 and 17 by taking a red and black two-color image forming device as an example of the multi-color image forming device of the batch transfer system.

FIG. 16 shows the structure around the image carrier in the two-color image forming apparatus, and FIG. 17 shows the surface potential of the image carrier in each step of image formation.

In FIG. 16, reference numeral 1 denotes an image carrier (hereinafter, photosensitive drum), and the photosensitive drum 1 has OPC, a- on the surface thereof.
It has a photoconductive layer such as Si (amorphous silicon) and is rotated in the direction of arrow A in the figure. The surface of the photosensitive drum 1 is uniformly charged to, for example, −700 V by the primary charger 2 (FIG. 17A). Then, the first image exposure 12 is performed by the first image signal information, the surface potential of the exposed portion on the photosensitive drum 1 is attenuated to, for example, −200 V, and the first image signal on the photosensitive drum 1 is responded to. A first latent image is formed (FIG. 17 (b)). Here, for example, a semiconductor laser, an LED array, or the like is used to perform the first image exposure 12.

Next, the first latent image formed on the photosensitive drum 1 is developed by the first developing device 4, which is a red two-component developing device, and visualized as a red toner image. In the first developing device 4, a two-component developer in which a negatively charged insulating red toner and a carrier having hard magnetism are mixed is used. At the time of development, a DC bias of about -500 V is applied to the developer holder as a development bias to reverse develop the first latent image (FIG. 17C). The surface potential of the obtained first toner image (first toner image potential) is increased by about -100V to about -300V with respect to the potential of the photosensitive drum (-200V) of the first image portion due to the toner charge.

Next, the photosensitive drum 1 is recharged uniformly by the recharging 5 to raise the potential of the first toner image. This time,
The non-image portion potential on the photosensitive drum 1 also rises slightly. As a result, the potential of the non-image portion after recharging is −740V, and the potential of the first image portion is approximately −670V (FIG. 17D). A second image exposure 13 is performed on the photosensitive drum 1,
A second latent image is formed according to the second image signal information (see FIG. 1).
7 (e)).

After that, the second developing device 7 reversely develops the second latent image by a developing method similar to that described above using a two-component developer containing negatively charged, for example, insulating black toner. FIG. 17 (f)). As a result, a two-color image of a black toner image and a red toner image is formed on the photosensitive drum 1.

The image forming process described above is generally called a negative recharging system because both the black toner and the red toner are subjected to reversal development. In addition, as a method for forming a two-color image on a photosensitive drum, Japanese Patent Application Laid-Open No. 55-13753
There is a negative-positive process in which one color is reversely developed and the other color is normally developed, and a ternary process described in JP-A-52-81855.

The red and black two-color images formed on the photosensitive drum 1 by the negative negative method described above are subjected to a pre-transfer treatment (usually by applying DC or AC corona, or by using a charger 18), if necessary. A process in which light elimination and the like are combined) is performed. Then, the charge amounts of the two-color toner images are aligned so as to be easily transferred, and then the transfer material 9 is applied to the transfer material 9 supplied onto the photosensitive drum 1 by the transfer charger 8.
Transfer color toner images all at once.

Thereafter, the transferred transfer material 9 is fixed to the fixing device 10.
By feeding the toner image to and fixing the toner image, red and black images are obtained. Then, the untransferred toner on the photosensitive drum 1 is removed by the cleaning device 11 to prepare for the next image formation.

In the conventional image forming apparatus using electrophotographic batch transfer, multicolor image formation is performed as described above.

[0014]

However, the above-described multicolor image forming apparatus that performs batch transfer has the following problems.

In the multiple transfer system, the potential on the image carrier is reset for each color by the pre-exposure device. On the other hand, in the batch transfer method, multiple development of a plurality of colors is performed on the image carrier, and then batch transfer is performed on the transfer material. Therefore, the toner (developer) layer potential, the recharging process, and the Due to, for example, developing the second toner by superposing it on the first toner, the gradation of the image density becomes unstable, and the image quality level deteriorates. In order to solve this problem, even if adjustments are made to correct the gradation at the time of initial installation of the image forming apparatus, the degree of deviation of the gradation due to deterioration over time due to deterioration over time and changes in the operating environment, etc. Changes extremely, so the initial adjustment becomes invalid.

Further, in order to correct the gradation of the formed image density, a density sensor 14 or the like is arranged in FIG. 16 to optically detect the density of the toner image on the image carrier, and the detection is performed. A method of feeding back the result to the image forming process can be considered. However, in the batch transfer method, since toner images of a plurality of colors are superimposed on the image carrier, it is difficult to detect the density for each color from the superimposed image. In particular, for an image in which black is mixed, it is impossible in principle to detect the density of each color by the method of measuring the reflected light by the density sensor. That is, it is difficult to accurately detect the density of the black component, but the black component is most easily visually recognized after image formation, so that it is particularly required to stabilize the gradation of the black component.

Further, when the color of the developer filled in the developing device is changed when the color forming the image is changed or the like, the charging characteristic and the developing characteristic of the developer for each color, and the transfer and separation which are accompanied with it. Since the characteristics and the like are different, the gradation of the formed mixed color image becomes very unstable. Further, in this case, not only the gradation but also the charging means, the exposing means, the developing means, the recharging means, the transfer means, the separating means, etc.
Since it was not optimized for the changed developer, a low-quality image was formed.

The present invention has been made to solve the above-mentioned problems, and in an image forming apparatus for forming a multicolor image by an electrophotographic method, the density of each color is appropriately detected from a gradation pattern of a plurality of colors. The present invention aims to provide an image forming apparatus and method that stabilizes the gradation and realizes high-quality image formation by correcting the gradation, and is excellent in durability and environmental adaptability. To do.

Further, even when the color of the developer in the developing device is changed, the image forming process such as the charging property and the developing property of the developer is optimized, and a high quality image having no image deterioration other than the gradation is obtained. The purpose is to enable provision.

[0020]

As one means for achieving the above object, the image forming apparatus of the present invention has the following configuration.

That is, an image forming apparatus for forming an image with a developer of at least two colors on an image carrier by an image forming means and transferring the image onto a recording material, wherein a pattern of a predetermined gradation of the at least two colors is generated. Generating means, a density detecting means for detecting density information of the pattern formed on the image carrier by the image forming means by using a filter having substantially the same color as the color of the developer, and the density detecting means. And a gradation correction unit that performs gradation correction based on the density information detected by.

For example, the image forming means forms an image by the developer of the first color and then forms an image by the developer of the second color, and the generating means forms the image by the developer of the first color and the second color. A density gradation pattern is generated by color mixing, and the density detecting unit detects density information of the second color of the pattern formed by the image forming unit by using a filter having substantially the same color as the first color, The correction means is characterized by performing gradation correction in image formation of the second color based on the density information of the second color.

For example, the generating means is characterized in that the uniform density pattern of the first color is generated, and the gradation pattern of the second color is superimposed on the uniform density pattern.

For example, the generating means generates the gradation pattern of the first color, and the density detecting means detects the density information of the first color of the pattern using the complementary color filter of the first color, The correction means may perform gradation correction in image formation of the first color based on the density information of the first color.

For example, the generating means generates the gradation pattern of the second color, the density detecting means detects the density information of the second color of the pattern without using a filter, and the correcting means , The second color based on the density information of the second color
It is characterized in that gradation correction is performed in color image formation.

For example, the second color is black.

For example, the density detecting means detects the reflection density of the pattern.

For example, the density detecting means detects the transmission density of the pattern.

For example, the first color is variable, and the density detecting means switches the color of the filter to be used according to the first color.

For example, the gradation correction means performs gamma correction.

For example, the gradation correction means is a charging means,
It is characterized in that it is at least one of an exposing means, a developing means, a recharging means, a transferring means, and a separating means.

For example, each of the images formed by the developers of at least two colors is formed by reversal development.

Further, as one method for achieving the above-mentioned object, the image forming method of the present invention comprises the following steps.

That is, an image processing method in an image forming apparatus in which an image is formed by a developer of at least two colors on an image carrier by an image forming means and is transferred to a recording material, which is a predetermined gradation of at least two colors. Of the pattern, the density information of the pattern formed on the image carrier by the image forming unit is detected by using a filter having substantially the same color as the color of the developer, and the detected density information is obtained. It is characterized in that gradation correction is performed based on this.

[0035]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment according to the present invention will be described below in detail with reference to the drawings.

<First Embodiment> FIG. 1 shows a configuration around an image carrier in an electrophotographic two-color image forming apparatus to which the present embodiment is applied. FIG. 2 shows the image carrier in each step of image formation. The surface potential of the body is shown. In the present embodiment, a red and black two-color image forming apparatus will be described as an example.

In FIG. 1, reference numeral 21 is an image carrier. The image carrier 21 is an OPC belt photosensitive member that can transmit light from the back surface, and moves in the direction of arrow A in the figure. Hereinafter, in the present embodiment, the image carrier 21 will be referred to as the photoconductor 21. The photoconductor 21 is uniformly charged by the primary charger 22 to, for example, −600 V (dark part potential) (FIG. 2A), and then subjected to the first image exposure 23 corresponding to the image signal of the red component. .

The first image exposure 23 is LE of 600 dpi.
D, whose wavelength is 680 nm. The L
The image exposure emitted by the ED passes through the imaging lens,
An image-like first latent image is formed by irradiating the photoconductor 21 and attenuating the surface potential of the exposed portion according to the image signal level. At this time, the photoconductor 2 on which the latent image is formed
The surface potential of 1 is, for example, −100 V in the maximum concentration part (FIG. 2 (b)).

The first latent image is developed by a red developing device 24 using a two-component developer consisting of negatively charged red toner and magnetic particles such as ferrite. In the red developing device 24, for example, a bias voltage obtained by superimposing a DC voltage (Vdc1) of −500 V on an AC voltage of 2000 Hz and 1500 Vpp is applied to reverse develop the first latent image (FIG. 2 (c)). . At this time, the electric potential of the toner image decreases to about −150 V due to the toner charge, for example, about −50 V at the maximum density portion.

After the first latent image is developed by the red developing device 24 to form a red toner layer, the photoconductor 21 is subjected to E. L. (electro
Luminance) or LED etc. for full exposure 31
Is applied. As a result, the red toner layer potential of the maximum density portion on the photoconductor 21 is −100 V, and the dark portion potential is −20.
It becomes 0V. That is, the potential difference between the red toner layer potential and the dark portion potential becomes small (FIG. 2 (d)).

Next, the secondary charger 2 is attached to the photoconductor 21.
5, the red toner layer potential in the maximum density portion becomes −670V and the dark portion potential becomes −700V (FIG. 2 (e)). That is, the potential of the dark portion is slightly lower than the potential of the red toner layer in the maximum density portion, and the potential of the red toner layer is such that it can be in contrast with the second latent image (latent image of black component).

Next, similarly to the first image exposure 23, the second image is generated by the LED modulated based on the image signal of the black component.
Image exposure 26 is performed to form a second latent image. Here, FIG. 2F shows the second latent image potential (−80 V) when dot color mixing is not performed. The second image exposure 26
The LED for performing the operation is 600d as in the first image exposure 23.
pi and its wavelength is 680 nm.

The exposure apparatus of this embodiment is LE
Not only D but also a semiconductor laser element or the like can be used.

The second latent image formed as described above is developed by the black developing device 27 using a two-component developer consisting of black toner and carrier, for example. In the black developing device 27, for example, 2000 Hz, 2500 Vpp, 35
The DC voltage of -570V (Vdc
By applying the bias voltage superposed with 2), the red toner image portion on the photoconductor 21 is not developed, but only the second latent image portion on which the black toner should be developed is developed (FIG. 2 (f )).

In this way, two color toner images of red and black are formed on the photoconductor 21. Next, the toner tribo is optimized by applying a voltage obtained by superimposing the AC voltage on the DC voltage to the toner image by a charger (not shown). Then, the toner images of the two colors are transferred to the transfer charger 2
8 is transferred to a transfer material 32 such as recording paper, and the transfer material 3
2 is separated from the photoconductor 21 by the charging by the separation charger 33 and the curvature of the belt of the photoconductor 21. Then, after being conveyed to the fixing device 29 and fixed, it is discharged out of the machine as a two-color color print.

On the other hand, the photosensitive member 21 is subjected to the next image forming process after the residual toner is removed by the cleaning device 30.

As the black developing device 27 described above, a non-contact developing system using a non-magnetic one-component developer may be used.
Further, the static elimination step before recharging is not always necessary.

Reference numeral 40 is a reflection density sensor (hereinafter referred to as a density sensor), which measures the patch pattern density of a predetermined density formed on the photoconductor 21 as described later. In the present embodiment, gradation correction is performed based on the density data obtained by the density sensor 40.

Next, the detailed configuration of the image signal control unit for controlling each LED for performing the above-mentioned first image exposure 23 and second image exposure 26 will be described with reference to FIG.

In FIG. 3, an image processing unit 201 performs image processing desired by the operator, such as resolution conversion, on input red and black image signals. 202 and 2
Reference numeral 03 denotes a gamma correction unit that performs gamma correction on the red and black image signals with reference to look-up tables (LUTs) 2021 and 2031. And 20
Reference numerals 4 and 205 denote pulse width modulation based on the red and black image signals after gamma correction.
Is a PWM unit that generates a drive signal for the LED. P
The LED 2 that performs the first image exposure 23 corresponding to red color based on the drive signals output from the WM units 204 and 205
20 and LE for performing the second image exposure 26 corresponding to black
D230 and are driven.

Reference numeral 206 denotes an LUT calculation unit, which corresponds to the density measurement value of the sample pattern obtained by the density sensor 40, and the LUT 202 in the gamma correction units 202 and 203.
1, 2031 are newly calculated and updated so as to be appropriate in the current operating environment. A pattern generator 207 holds image data of sample patterns in advance.

Reference numeral 208 designates each component of the image signal control unit as RO
This is a CPU that performs overall control according to a control program stored in the M209. 210 is RAM, CP
Used as a work area for U208.

The present embodiment is characterized in that an appropriate gradation correction (for example, gamma correction) is performed in the batch transfer type image forming apparatus having the above-mentioned structure. Hereinafter, the gradation correction processing in this embodiment will be described in detail.

FIG. 4 shows the relationship between the potential difference between the dark portion potential and the light irradiation potential of the photoconductor 21 (photoconductor potential difference). That is, the three arrows 121, 122, and 123 shown in FIG. 4 indicate the dark area potential (corresponding to FIG. 2C) at the starting point and the light irradiation after the light irradiation by the whole surface exposure 31 at the end point. The electric potential (corresponding to FIG. 2D) is shown. The photoconductor 21
Is an organic photoconductor (OPC), and it is assumed that the amount of light emitted when measuring the potential difference shown in FIG. 4 is constant. It can be seen from FIG. 4 that the higher the dark portion potential of the photoconductor 21, the larger the potential difference from the light irradiation potential, that is, the larger the voltage drop due to light irradiation.

FIG. 5 shows the surface potential 131 of the photoconductor 21 and the red toner layer surface potential 132 with respect to the first image signal after recharge. The first image signal is 16
It is assumed that the signal is an 8-bit signal expressed in the base system. FIG.
2A, the surface potential 131 of the photoconductor has a larger inclination than the surface potential 132 of the toner layer, and the shaded portion in between indicates the voltage of the toner layer, which corresponds to 111 in FIG. 2E. According to FIG. 5, the larger the first image signal is, that is,
It can be seen that the higher the density of the first image signal, the smaller the surface potential of the photoconductor 21. This is because the voltage division ratio changes due to the change in the thickness of the developed toner layer.

As described above, the surface potential of the photoconductor 21 becomes low in the portion where the first toner concentration is high,
As described with reference to FIG. 4, as the surface potential of the photoconductor 21 decreases, the voltage drop due to light irradiation decreases. Therefore, the toner layer potential after the second exposure becomes higher in the portion of the photoconductor 21 where the first toner concentration is higher.

As described above, in the image forming apparatus of the present embodiment in which multiple development is performed on the image carrier and then batch transfer is performed on the transfer material 32, there is an advantage of high productivity. Due to the developer layer potential, the recharging process, and the development of the second developer (black toner) on top of the first developer (red toner), the gradation of the image density is particularly high. Quality becomes unstable and the image quality level deteriorates. Therefore, in order to stabilize the gradation of the image density, which is indispensable for digital image quality improvement, the density of the patch pattern of a predetermined density formed on the photoconductor 21 is measured by the reflection density sensor (hereinafter, density sensor) 40. It is conceivable to perform gradation correction based on the obtained density data. According to this method, for example, if the developers are only yellow (Y), magenta (M), and cyan (C),
Even if the three colors are overlapped, by using the complementary color filters, the densities of the respective color components can be separated to some extent. However, in the case where the black developer and the other color developers are mixed, the black color contains all the color components of Y, M, and C, and the color developers other than black are usually red ( Since it is composed of R), green (G), blue (B), etc., it is theoretically impossible to separate each color component using a complementary color filter. Therefore, it is difficult to accurately detect the density of only the black component, and the black component is most easily visually recognized after the image formation. Therefore, it is most important to stabilize the gradation of the black component.

The method for detecting the density of each color component in this embodiment will be described below. First, a patch pattern image having gradations of two colors, black and red, as shown in FIG. 6, is output from the pattern generator 207 and formed on the photoconductor 21, and the density sensor 40 measures the image density without a filter. Think about when you do. In FIG. 6, 71,
Arrows 72 and 73 indicate patch rows each having a black gradation at a predetermined red density. The density measurement result for each patch is shown in FIG. As a result, even if the black or red patch density increases, the detected density detected also increases, that is, the detected density value has a correlation with both black and red density. , It is difficult to detect the density for each color.

Therefore, in this embodiment, a black component is mixed in an image in which the black developer is mixed by using a filter having a substantially same color (red in the present embodiment) as the color developer other than black and having a high transparency. It is characterized in that only the detection of only is possible. That is, in the density sensor 40, the red component is removed from the transmitted light or the reflected light composed of a mixture of black and red by using the red filter, so that the density of only the remaining black component can be measured. As a result, it is possible to correct the density gradation of the black component, for example, updating the LUT 2031 in gamma conversion, and at the same time perform gradation correction with another color component (red), so that both the black component and the color component can be corrected. It is possible to improve gradation stability.

The filter used for density detection in this embodiment will be described below.

FIG. 8 shows the result of measuring the density by the density sensor 40 for each patch row 71 to 73 shown in FIG. 6 described above, using a red filter having the same density as the predetermined red density in the patch row. Show. From this, it can be seen that most of the correlation with the red component density has been removed. Therefore, by performing origin correction on the measurement result shown in FIG. 8 based on the red density data obtained for a single red color, the black density can be similarly measured regardless of which red density filter is used. You can

Here, FIG. 9 shows an example of a patch pattern formed on the photoconductor 21 in this embodiment. For simplicity of explanation, it is assumed that the patch pattern is a gradation pattern of 5 steps. As shown in FIG. 9A, the patch pattern first forms a highlighted solid image with a constant density of 30H (density 0.3) using red toner. That is, the solid image data is output from the pattern generator 207 to the PWM unit 204, and the LED
By driving 220 to perform the first image exposure 23, a first latent image is formed on the photoconductor 21 and developed with red toner. Then, black toner development is performed by superimposing the red toner pattern on the latent image pattern in five stages as shown in FIG. 9B. That is, the pattern generator 2
The gradation image data of five stages is output to the PWM unit 205 from 07, the LED 230 is driven and the second image exposure 26 is performed, so that the second image is formed on the photoconductor 21.
Latent image is formed and developed with black toner. In the patch pattern shown in FIG. 9B, the black densities are 00H, 30H, 60H, 90H, and C0H in order from the top.

Next, a method of detecting the density by the density sensor 40 will be described with reference to FIG. In FIG. 10, 42 is a light emitter and 43 is a light receiver, and the light transmitting surfaces of these are covered with a transparent acrylic plate 44. 41 is a filter.
In the density sensor 40, the light emitted from the light emitter 42 is reflected by the patch pattern 22 formed on the photoconductor 21, and the reflected light is transmitted through the filter 41 and detected by the light receiver 43. The concentration of.

An example of the filter 41 is shown in FIG. In the figure, 101 and 102 correspond to the filter 41 shown in FIG. 10, and when the rotary plate 103 rotates about the axis, either of the filters 101 and 102 is set as the filter 41. Here, the filter 101 is a filter having substantially the same color as the color developer, and in the present embodiment, a filter having a red toner color. Also, 1
No filter is set for 02, that is, the reflected light from the patch pattern is transmitted as it is. Hereinafter, 102 is referred to as a through filter. In the present embodiment, the through filter 102 is used when measuring the density of a single black color. In this case, the pattern generator 207 outputs a patch pattern having a black monochrome gradation.

When it is also possible to perform gradation correction for a single color, as the filter 41, as shown in FIG. 11 (b), the same color filter 104 (red (R) toner color filter) is used. , 105 complementary color filters (cyan color (C) filters) and 106 through filters are preferably switchable. By using the complementary color filter 105 as the filter 41, it is possible to perform gradation correction using a single red color. In this case, the pattern generator 207 outputs a patch pattern having a gradation of monochromatic red.

The density detection processing of this embodiment having the above-mentioned configuration will be described below. The patch pattern of red-black mixed color shown in FIG. 9B is formed on the photoconductor 21,
The density of the patch pattern is measured by the density sensor 40. After the patch pattern is formed, the filter 41 is used to remove the influence of the red toner density which is the background density of the patch pattern. Is "0
(Or about 0.5) ”. That is, in the density sensor 40, a filter having a red density of 0.3 is set as the filter 41. Then, the density measurement is performed, and the resulting black component density is corrected based on the density data obtained in the red single-color image as described above to obtain the gradation characteristics of the black component in the current image forming process. Is obtained. Then, the obtained tone characteristic of the black component is an ideal density reproduction curve (TRC; to
The LUT 2031 of the gamma correction unit 203 corresponding to the black component is updated in the LUT calculation unit 206 so that the ne reproduction curve) is obtained. The TRC is, for example, a ROM
It is stored in 209.

Here, an example of the TRC in this embodiment is shown in FIG. In FIG. 12, (a) shows a red TRC, and (b) shows a black TRC. The broken line shows a case of a character / line image, and the solid line shows a case of a halftone image such as a photograph. The character / line image and the halftone image may be separated by manual switching by the operator, or may be subjected to image area separation processing by known image processing. That is, for the black component density value measured by the density sensor 40 as described above, the origin correction may be performed based on TRC shown in FIG. 12A as density data for a single red color. Further, in the present embodiment, when performing gradation correction on the red component, a patch pattern of a single color of red is measured,
The correction may be performed so as to approximate the TRC shown in FIG.

FIG. 13 shows the relationship between the surface potential 141 of the photoconductor 21 and the red toner layer potential 142 with respect to the density of the first image (red component image) when a constant second exposure 26 is performed after recharging. Shown (corresponding to FIG. 2 (f)). In FIG. 13, recharging causes a large decrease in the toner layer potential in the high density portion. In FIG. 5, the above-mentioned FIG.
Similarly, the shaded area corresponds to the voltage of the toner layer. In order to reproduce the second image (black component image) with the same density regardless of the first image (red component image) signal, the red toner layer potential 142 may be kept constant. Therefore, FIG.
It can be seen that the potential component corresponding to the halftone dot portion should be corrected.

In this embodiment, the correction corresponding to the halftone dot portion in FIG. 13 is performed at the time of forming the second latent image. That is, based on the density value of the black component obtained by measuring the patch pattern density through the red filter as described above,
The LUT calculation unit 206 calculates the optimum LUT for correcting the above-mentioned halftone dot portion in the gamma correction for performing the gradation correction of the black component. By replacing the calculated LUT with the LUT in the gamma correction unit 203, the gamma correction unit 2
In 03, the black component image signal is subjected to optimum gamma correction in the current image forming process. Then, the corrected image signal is subjected to PWM in the PWM unit 205, and the light emission amount of the second LED 230 is temporally modulated.

As described above, according to this embodiment, it is possible to appropriately detect the density of each color in an image in which developers of a plurality of colors are mixed, by passing through the same color filter. Therefore, it is possible to perform appropriate gradation correction at any time in both single color and mixed colors, and it is possible to obtain a stable, high-quality image with excellent density gradation.

Although the gradation correction by gamma correction has been described as an example in the present embodiment, the gradation correction means in the present embodiment is not limited to this, and other image signal processing and , Charging means, exposure means,
It is also possible to correct the operating conditions of at least one means for controlling the image forming process, such as the developing means, the recharging means, the transfer means, and the separating means.

In this embodiment, the photoconductor belt has been described as an example of the image bearing member, but it goes without saying that the present embodiment is similarly applicable to a photoconductor drum. Further, the color order in the first development and the second development, the developing method, and the like are not limited to the examples described above.

The density measuring method is not limited to the above-mentioned example, and the density sensor 40 may have the structure shown in FIG. In the configuration of FIG. 14, 50 is a transparent photoreceptor, and the light emitter 51 and the light receiver 52 are set so that the transparent photoreceptor 50 is sandwiched. Then, the irradiation light from the light emitter 51 is filtered by the filter 53 and the transparent photoconductor 5.
0, and further the toner image 54 on the transparent photoreceptor 50. Then, the density of the toner image 54 is measured by detecting the transmitted light in the light receiver 52. Although the filter 53 may be provided between the toner image 54 and the light receiving body 52, the durability is deteriorated at this position due to toner scattering or the like.

In the present embodiment, the image forming apparatus for forming a two-color image in red and black has been described, but it goes without saying that a two-color image in another color (for example, blue and black) is formed. However, the present embodiment is applicable. Further, the invention is not limited to the two-color image formation, and can be similarly applied to the case of forming an image of three or more colors.

<Second Embodiment> The second embodiment of the present invention will be described below.
An embodiment will be described.

In the second embodiment, it is shown that gradation correction can be similarly performed in an image forming apparatus that forms an image with a configuration different from that of the above-described first embodiment.

Since the configuration around the image carrier of the image forming apparatus and the image forming process thereof in the second embodiment are the same as those in FIG. 16 shown in the above-mentioned conventional example, the description thereof will be omitted. Also,
The configuration of the image signal control unit in the second embodiment is the same as that in FIG. 3 of the first embodiment described above.

In the second embodiment, a-Si (amorphous silicon) is used as the photosensitive member of the photosensitive drum 1. Since a-Si has a larger relative dielectric constant than an organic photoconductor (OPC), the ratio of voltage division between the photoconductor surface and the toner layer is small. Further, the charging potential is relatively low and the second latent image potential cannot be sufficiently obtained, but it has high durability, and
It is suitable for high-speed machines because it can withstand over 10,000 copies.

The photosensitive drum 1 is uniformly charged to, for example, 500 V by the primary charger 2, and then subjected to the first image exposure 12. The first image exposure 12 is a laser beam having a first semiconductor laser as a light source, and the first semiconductor laser is driven by a drive signal modulated based on an image signal corresponding to the component. The laser beam is polarized by a polygon mirror that rotates at a constant number of rotations by a motor, passes through an imaging lens, is reflected by a folding mirror, and is raster-scanned on the photosensitive drum 1. Attenuate to 100V. As a result, the first image
Is formed.

Then, the first development with the red toner is performed, the potential of the surface of the photosensitive drum 1 is raised by the recharger 5, and the second image exposure 13 corresponding to the black component image is similarly performed by the semiconductor laser. As a result, the second latent image is formed. The wavelength of the exposure is 680 nm for both the first image exposure 12 and the second image exposure 13.

After that, the second development with black toner is performed. Incidentally, in the second embodiment, the first developing device 4 carries out the red non-magnetic single-component development, and the toner particle size is 8 μm. Further, in the second developing device 7, magnetic one-component jumping development is performed in a non-contact manner with black toner, and the toner particle size is 7 μm.
m. In addition, the toner polarity is positive at the time of development, and thus negative reversal development is performed. The resolution of the image formed in the second embodiment is 600 dpi.

As described above, in the image forming apparatus using a-Si as the photoconductor, since the potential contrast on the photoconductor becomes relatively small, a minute potential change leads to a large density change. That is, a more accurate correction is required in the gradation correction.

Therefore, in the second embodiment, in the pattern generator 207, every 00H to 10H,
A sample pattern having a black image density of 16 gradations is formed for each density area of a red image of 16 gradations in total.

Then, in the density sensor 14, as in the density sensor 40 shown in the above-described first embodiment, the sample pattern density of 16 gradations is detected through the red filter to correct the gradation. Measurement density values of 16 gradations are obtained. Therefore, the gradation characteristic can be brought closer to TRC.

As described above, according to the second embodiment, the correction accuracy at the time of gradation correction can be improved,
Therefore, it is possible to stabilize the gradation in the image forming apparatus.

<Third Embodiment> The third embodiment of the present invention will be described below.
An embodiment will be described.

In the above-mentioned first and second embodiments, the toner colors have been described as red and black. In the third embodiment, an example of using another color toner will be described. The configuration of the image forming apparatus according to the third embodiment is similar to that of the above-described second embodiment.

In the third embodiment, the red toner and the blue toner can be selected in the first developing device 4, and they are automatically selected appropriately according to the color of the input image. Black toner is set in the second developing device 7.

Tribo (Q / M) of red toner is 26 μC /
g, M / S is 0.6 mg / cm @ 2, whereas the blue toner has tribo (Q / M) of 20 .mu.C / g and M / S of 0.
6 mg / cm2. Therefore, since the VD curve at the time of development is different, the required latent image contrast, transfer current, separation current, etc. are different between when red is selected and when blue is selected.

Therefore, in the third embodiment, the gradation correction characteristic is optimized according to the toner color selected in the first developing device 4. For example, the LUT calculation unit 206 switches between the LUT calculation method corresponding to red toner and the LUT calculation method corresponding to blue toner. At the same time, the color filters in the density sensor 14 are also controlled to be automatically switched. Of course, the gradation correction means is not limited to the gamma correction, and any one of the image forming processes such as the charging means, the exposing means, the developing means, the recharging means, the transfer means and the separating means may be appropriately controlled for each color. good.

An example of a filter in the density sensor 14 is shown in FIG. In FIG. 15, 41 is a red (R) toner color filter, 42 is a yellow (Y) color filter, 43 is a through filter, 44 is a cyan (C) color filter, and 45.
Is a blue (B) toner color filter. That is, the red toner color filter 41 and the cyan color filter 44, and the blue toner color filter 45 and the yellow color filter 42 are complementary colors. When the red toner is selected in the first developing device 4, the red toner color filter 4 is used when measuring the black toner density.
1 is a cyan color filter 4 when measuring the red toner single color density
4 is set in the density sensor 14. When blue toner is selected in the first developing device 4, the blue toner color filter 45 is set in the density sensor 14 when measuring the black toner density, and the yellow color filter 44 is set in the density sensor 14 when measuring the blue toner single color density.

As described above, according to the third embodiment,
It is possible to switch the toner color set in the developing device, at the same time appropriately switch the filter used in the density sensor, and prepare a gradation correction method for each color, so that high-quality gradation with good gradation is achieved for all toner colors. Image formation becomes possible. As a result, an image forming apparatus that performs two-color image formation can form images in two colors according to the original.

Further, even when the toner color of the developing device is changed, by optimizing the image forming process such as the charging characteristic and the developing characteristic of the toner, a high quality image without image deterioration other than the gradation can be obtained. Can be provided.

<Other Embodiments> The present invention can be applied to a system including a plurality of devices (for example, a host computer, an interface device, a reader, a printer, etc.), but an apparatus including one device ( For example, it may be applied to a copying machine, a facsimile machine, etc.).

Further, an object of the present invention is to provide a storage medium storing a program code of software for realizing the functions of the above-described embodiments to a system or an apparatus, and to provide a computer (or CPU) of the system or apparatus.
And MPU) read and execute the program code stored in the storage medium.

In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiments, and the storage medium storing the program code constitutes the present invention.

Examples of a storage medium for supplying the program code include a floppy disk, hard disk, optical disk, magneto-optical disk, CD-ROM, and CD.
-R, a magnetic tape, a nonvolatile memory card, a ROM, or the like can be used.

Further, not only the functions of the above-described embodiments are realized by executing the program code read by the computer, but also the OS (operating system) running on the computer based on the instructions of the program code. It is needless to say that this also includes a case where the above) performs a part or all of the actual processing and the processing realizes the functions of the above-described embodiments.

Further, after the program code read from the storage medium is written in the memory provided in the function expansion board inserted into the computer or the function expansion unit connected to the computer, based on the instruction of the program code, It goes without saying that a case where the CPU or the like included in the function expansion board or the function expansion unit performs some or all of the actual processing and the processing realizes the functions of the above-described embodiments is also included.

[0100]

As described above, according to the present invention, in an image forming apparatus for forming a multicolor image by an electrophotographic method, it is possible to appropriately detect the density of each color from a gradation pattern of a plurality of colors, and to reproduce the gradation. By correcting the above, it is possible to provide an image forming apparatus and method that stabilizes gradation and realize high-quality image formation, and that is excellent in durability and environmental adaptability.

Further, even when the color of the developer in the developing device is changed, the image forming process such as the charging property and the developing property of the developer is optimized, and a high quality image without image deterioration other than the gradation is obtained. Can be provided.

[0102]

[Brief description of drawings]

FIG. 1 is a diagram illustrating a schematic configuration of an image forming apparatus according to an embodiment of the invention.

FIG. 2 is a diagram for explaining a photosensitive member surface potential in each process of image formation in the present embodiment.

FIG. 3 is a block diagram showing a configuration of an image processing unit in the image forming apparatus of this embodiment.

FIG. 4 is a diagram showing a potential difference between a photoconductor dark portion and a light irradiation portion in the present embodiment.

FIG. 5 is a diagram showing a relationship between a first image signal and a photosensitive member surface potential in the present embodiment.

FIG. 6 is a diagram showing an example of a gradation patch pattern in this embodiment.

FIG. 7 is a diagram showing density values measured without using a filter in the present embodiment.

FIG. 8 is a diagram showing black density values measured using a red filter in the present embodiment.

FIG. 9 is a diagram showing an example of a patch pattern formed on the photoconductor in the present embodiment.

FIG. 10 is a diagram showing a configuration of a concentration sensor according to the present embodiment.

FIG. 11 is a diagram showing a configuration of a filter according to the present embodiment.

FIG. 12 is a diagram showing an example of an ideal density reproduction curve in the present embodiment.

FIG. 13 is a diagram for explaining a correction example in the present embodiment.

FIG. 14 is a diagram showing another configuration of the concentration sensor according to the present embodiment.

FIG. 15 is a diagram showing a configuration of a filter according to a third embodiment of the present invention.

FIG. 16 is a diagram showing a schematic configuration of a conventional batch transfer type image forming apparatus.

FIG. 17 is a diagram showing an image forming process in a batch transfer type image forming apparatus.

[Explanation of symbols]

 21 Photoreceptor Belt 22 Primary Charger 24 First Developing Device 25 Recharging Device 27 Second Developing Device 23 First Image Exposure 26 Second Image Exposure 40 Reflection Density Sensor 200 Image Processing Unit 201 Signal Processing Unit 202, 203 Gamma Correction unit 204, 205 PWM unit 206 LUT calculation unit 207 Pattern generator 208 CPU 209 ROM 210 RAM 220 First LED 230 Second LED

Claims (13)

[Claims] 1. An image forming apparatus for forming an image of a developer of at least two colors on an image carrier by an image forming means and transferring the image onto a recording material, wherein a pattern of a predetermined gradation of at least two colors is generated. Generating means, a density detecting means for detecting density information of the pattern formed on the image carrier by the image forming means by using a filter having substantially the same color as the color of the developer, and the density detecting means. An image forming apparatus comprising: a gradation correcting unit that performs gradation correction based on the density information detected by the image forming apparatus. 2. The image forming means forms an image with a developer of the first color and then forms an image with a developer of the second color so that the image forming means forms an image with the developer of the first color. Generating a pattern of a predetermined gradation by color mixture, wherein the density detecting unit detects density information of the second color of the pattern formed by the image forming unit by using a filter having substantially the same color as the first color; The image forming apparatus according to claim 1, wherein the correction unit performs gradation correction in the image formation of the second color based on the density information of the second color. 3. The generating means generates the uniform density pattern of the first color, and superimposes the uniform density pattern on the uniform density pattern to generate the gradation pattern of the second color. Image forming apparatus. 4. The generation means generates the gradation pattern of the first color, and the density detection means detects density information of the first color of the pattern using a complementary color filter of the first color, The image forming apparatus according to claim 4, wherein the correction unit performs gradation correction in image formation of the first color based on the density information of the first color. 5. The generation means generates the gradation pattern of the second color, the density detection means detects density information of the second color of the pattern without using a filter, and the correction means. 5. The image forming apparatus according to claim 4, wherein gradation correction in image formation of the second color is performed based on the density information of the second color. 6. The image forming apparatus according to claim 2, wherein the second color is black. 7. The image forming apparatus according to claim 1, wherein the density detecting unit detects a reflection density of the pattern. 8. The image forming apparatus according to claim 1, wherein the density detecting unit detects a transmission density of the pattern. 9. The image forming apparatus according to claim 2, wherein the first color is variable, and the density detecting unit switches a color of a filter to be used according to the first color. 10. The image forming apparatus according to claim 1, wherein the gradation correction unit performs gamma correction. 11. The image forming apparatus according to claim 1, wherein the gradation correction unit is at least one of a charging unit, an exposing unit, a developing unit, a recharging unit, a transferring unit, and a separating unit. apparatus. 12. The image forming apparatus according to claim 1, wherein the images of the at least two color developers are formed by reversal development. 13. An image processing method in an image forming apparatus for forming an image by a developer of at least two colors on an image bearing member by an image forming means and transferring the image onto a recording material, wherein the predetermined method is a mixture of at least two colors. A gradation pattern is generated, the density information of the pattern formed on the image carrier by the image forming unit is detected using a filter having a color substantially the same as the color of the developer, and the detected density information is detected. An image forming method, characterized in that gradation correction is performed based on the above.