JP2922035B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus such as a copying machine or a laser beam printer (LBP), and more particularly to an image forming apparatus having a plurality of image carriers and capable of forming a multicolor image. Related to the device.

[0002]

2. Description of the Related Art There is known an image forming apparatus for forming a multicolor image using a plurality of photosensitive drums (image carriers). In such an image forming apparatus, a process unit in which a charging device, a scanning optical device, a developing device, a cleaning device, and the like are disposed around the photosensitive drum is used to set the number of toner colors (for example, 4 if yellow, magenta, cyan, and black toners are used). Set), and a transfer belt (transfer material transfer means) for holding and transporting the transfer material is provided below the process unit, and formed by each process unit on the transfer material that moves together with the transfer belt. It is well known that a multicolor image is formed while transferring the transferred toner images in an overlapping manner.

In such an image forming apparatus, a test density pattern (test patch) is transferred onto a transfer belt via a process unit, the toner density of the test patch is detected, and the toner density in a developing device is detected. 2. Description of the Related Art An image forming apparatus which controls an image (especially when a two-component developer including a toner and a carrier is used) and forms an appropriate image is known (Japanese Patent Application Laid-Open No. 63-147177). Further, test patches are superimposed and transferred from each process unit onto the transfer belt, and the change in the size of one dot of the image is measured from the amount of displacement of the test patch of each color, and the exposure time, output of image light L, development There is also known an image forming apparatus which forms a proper image by properly maintaining the size of one dot by changing a process condition such as a bias (Japanese Patent Application Laid-Open No. 63-280275).

Further, by changing the exposure amount to the photosensitive drum,
There is also known an image forming apparatus which predicts a light potential at which a reference maximum density is obtained from test patches having different light potentials, and can form an appropriate image even if a change in the light potential occurs due to an environmental change (Japanese Patent Laid-Open No. 1-261668). No.).

[0005]

However, in the image forming apparatus capable of forming a multicolor image, control of the toner density in the developing device and control of the size of one dot of the image are performed by using a test patch. And the control of the light potential of the photosensitive drum that fluctuates depending on environmental conditions, but it does not affect the subtle hue fluctuation in the multicolor image caused by the deterioration of the photosensitive drum, the deterioration of the toner, the error of the control system, etc. Was not controlled. Therefore,
In particular, in a multicolor image containing a picture, there is a problem that the color balance including the gray balance (density balance) lacks stability.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to form a multicolor image on a transfer material on a transfer material transporting transfer means using a plurality of image carriers. An object of the present invention is to provide an image forming apparatus capable of forming a proper image by controlling even a slight change in color.

[0007]

In order to achieve the above-mentioned object, the present invention provides a multi-color toner image formed by developing means on a plurality of image carriers based on image information of a plurality of colors. A multicolor image can be formed by superimposing and transferring the toner image onto a transfer material moved by a transfer material transporting and transferring means, and the toner image is formed on the transfer material transporting and transferring means via an image carrier. In an image forming apparatus to which a test density pattern using a predetermined color toner is transferred, a density detecting means for detecting the density of the density pattern, and when a detection result by the density detecting means is different from a predetermined density, the cause is as follows. It is determined whether it is due to the toner concentration in the developing means or to the latent image potential of the image carrier. If neither is the case, a signal is sent to a masking device to change the masking coefficient, Characterized by providing a control means for controlling the image density, a by changing the output of the positive device.

[0008]

According to the present invention, when the reason that the result of detection by the density detecting means differs from the predetermined density is not due to any of the toner density in the developing means and the latent image potential of the image carrier,
It sends a signal to the masking device to change the masking factor,
Since the image density is controlled by changing the output of the gradation correction device, the cause of the color balance of the multicolor image being disrupted is other than environmental conditions or other peripheral conditions (for example,
(Deterioration due to aging of the image carrier or the toner itself, which determines the latent image potential and the development density), the cause is detected and the masking coefficient is changed according to the detection result to change the tone correction device. The output can be changed, and the color balance can be set with higher accuracy than the conventional image forming apparatus that sets the masking coefficient assuming that the characteristics of the toner and the image carrier are constant.

[0009]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

First, a first embodiment of the present invention will be described with reference to FIGS.
This will be described below.

FIG. 2 shows a cross section of an image forming apparatus (LBP) capable of forming a four-color full-color image using magenta, cyan, yellow, and black toners. The image forming apparatus has four photosensitive drums (electrophotographic photosensitive members) 1 (specifically, 1a to 1d) as image carriers that are independently arranged in parallel. A scanning optical device 2 (specifically, 2a to 2d) is provided, and a photosensitive drum 1 is previously provided around each photosensitive drum 1.
Primary charger 3 (specifically, 3a to 3a)
d), a developing device 4 (specifically, 4a to 4d) having each color toner of magenta, cyan, yellow, and black, and a transfer material P as a transfer medium using the toner image on each photosensitive drum 1 as a transfer medium.
Are provided with transfer chargers 5 (specifically, 5a to 5d) for transferring the images.

The scanning optical device 2 includes a semiconductor laser as a light source, a polygon mirror that scans image light L from the semiconductor laser, and f that focuses the image light L on the surface of the photosensitive drum.
θ lens, a reflecting mirror for changing the direction of the image light L, and the like. Further, a two-component developer composed of a toner and a carrier is used in the developing device 4, and a new toner is replenished as needed as the toner is consumed for image formation. The toner has an average particle size of 3-20μ
m, a dispersion obtained by dispersing a color pigment in a polyester resin and applying silica as an external additive is used. Depending on the toner color, etc., a styrene-acrylic resin, carbon black as a colorant, a benzene-based yellow pigment, an anthraquinone Dyes, copper phthalocyanine pigments and the like may be used.

Below the four photosensitive drums 1, the transfer material P is rotated and moved in the direction of the arrow in FIG. 1 to sequentially hold and convey the transfer material P between each photosensitive drum 1 and the transfer charger 5. 1
A transfer belt 7 is provided as a transfer material transporting transfer unit for transferring the upper toner image. A paper feed cassette 11 for supplying a transfer material P to the transfer belt 7 is provided on a paper feed side of the transfer belt 7, and a toner image superimposed and transferred on the transfer material P is provided on a paper discharge side. And a paper discharge tray 13 on which the transfer material P after fixing is loaded.

The transfer belt 7 is made up of an endless belt-like sheet member stretched between two rollers 8 and 9, and the transfer material P is positioned and held on the transfer belt P while the rollers 8 and 9 rotate. 2. The transfer material P is rotated from the first station to the fourth station (described later) by rotating in the direction indicated by the arrow 2 in FIG. Examples of the material of the transfer belt 7 include a polyurethane type, a polycarbonate type, and PVdF (polyvinylidene fluoride). Reference numeral 10 denotes a tension roller.

In FIG. 2, a magenta image is used in the first station (an image forming station including a photosensitive drum with a suffix a) in the order in which the transfer material P advances, and a magenta image is used in the second station (an image forming station related to a suffix b). A cyan image, a yellow image are formed at the third station (image forming station relating to the subscript c), and a black image is formed at the fourth station (image forming station relating to the subscript d).

That is, in the first station, image light L based on magenta image information is applied to the photosensitive drum 1a uniformly charged by the primary charger 3a via the scanning optical device 2a.
Is exposed and an electrostatic latent image is formed on the photosensitive drum 1a. The electrostatic latent image is directed toward the developing device 4a together with the rotation of the photosensitive drum 1a, and magenta toner is supplied by the developing device 4a. And is visualized as a toner image. Then, the toner image is directed to the transfer charger 5a, and is transferred to the transfer material P on the transfer belt 7 by the transfer charger 5a. After the transfer, the photosensitive drum 1a is prepared for the next image formation after the residual toner is cleaned by the cleaning device 6a. Similarly, in the second, third, and fourth stations, cyan, yellow, and black toner images are transferred onto the transfer material P in a superimposed manner.

On the other hand, the transfer material P in the paper feed cassette 11 is
The photosensitive drums are supplied from the inside of the paper cassette 10 to the transfer belt 7 via a paper feeding means (not shown), and are positioned and fixed on the transfer belt 7 so that the photosensitive drums of the first, second, third, and fourth stations are fixed. Four color toner images are transferred while passing between the drum 1 and the transfer charger 5. Then, the transfer material P after the transfer is completed
Is transferred from the transfer belt 7 to the fixing device 12, where the toner image is melted and mixed and fixed by the fixing device 12, and then stacked on a paper discharge tray 13.

Next, the control for forming an image in the image forming apparatus will be described with reference to FIG. FIG. 1 is a diagram showing processing and control of image light L in an image reading output unit and each station (in this case, a first station for forming a magenta image is illustrated).

In the image reading and outputting section, after the image on the document 20 is read by the reader, the read image light L is sent to the CCD 21 and is read as R (red), G (green) and B (blue). The image is separated into color image signals. The three output signals R, G, and B are converted by the A / D converter 22 into 8-bit digital signals.
Next, the R, G, and B digital signals are converted by the density converter 23.
And C1 (cyan), M1
(Magenta), Y1 (yellow), and K1 (black) signals, and then sent to a masking device 24, where the masking device 24 performs masking, and C2 (cyan), M2 (magenta), and Y2 (yellow) , K2
(Black) signal. The output signals C2, M2, Y2, and K2 are output from the C3 (cyan), M3 (magenta), Y3 (yellow), and K3 (black) signals via a look-up table or the like provided in the device by the gradation correction device 25. After the gradation correction is performed on the controller 2,
Sent to 6.

Here, the masking means to correct the difference between the spectral distribution by the spectral filter of the CCD 21 and the color wavelength of each toner, and the input signals Y1, M1, C1, K1 to the masking device 24 and the masking device 24 Between output signals Y2, M2, C2 and K2 from

[0021]

(Equation 1) There is a relationship. And, for example, in the yellow signal (Y2),

[0022]

Y2 = b11Y1 + b12M1 + b13C1 + b14K1 In this case, b11, b12... B43 are called masking coefficients, and the Y1, M1, C1, and K1 signals are
2, M2, C2, K2 are coefficients used in the masking device to correct the signal.

On the other hand, a potential sensor 30 for detecting the surface potential of the photosensitive drum 1 is attached to the photosensitive drum 1,
A signal from the potential sensor 30 is sent to a controller 26 via an electrometer 31. A toner density sensor 32 is also attached to the developing device 4, and this signal is sent to the controller 26 in order to prompt proper replenishment of toner. Has been sent. The toner density sensor 32 is of a light reflection type, an inductance type, a patch detection type, or the like.

At a predetermined position on the transfer belt 7 near the photosensitive drum 1, a visible image (test patch K) of toner for image density inspection (in this case, magenta toner) is passed through the photosensitive drum 1 and the like. Formed, the test patch K
A patch density detector 33 composed of an LED 33a as a light emitting element and a photodiode 33b as a light receiving element is disposed in the vicinity. Then, the LED 33a irradiates the test patch K with light according to an instruction from the controller 26, and the reflected light is received by the photodiode 33b, which is sent to the controller 26 as a density signal. Although the image density of the test patch K is output as 80 hex, output of 8 bits and 256 gradations from 0 hex (white) to 256 hex (solid black) is possible.

As shown in FIG. 3, the controller 26 supplies the latent image potential information of the photosensitive drum 1 from the potential sensor 30, the toner density information in the developing device 4 from the toner density sensor 32, and the patch density detector 33, as shown in FIG. Are converted into digital signals by the A / D converters 34, 35, and 36, and are input. The controller 26 controls the masking device 24 based on the information, and outputs the image of the scanning optical device 2. The image density can be controlled by changing the light amount (lens light amount).

That is, a masking coefficient table for increasing or decreasing the output signals Y2, M2, C2, and K2 is separately provided in the masking device 24, and the controller 26
For example, when it is desired to increase the image density based on the yellow signal Y2 by a predetermined amount according to the signal from b, b'11, b '
Masking factors such as 12, b'13, b'14 are used,

[0027]

## EQU00003 ## Y2 = b'11Y1 + b'12M1 + b'13C1 + b'14K1. When the image density is reduced by a predetermined amount, b "11, b" 12, b "13, b" 1
Masking factors such as 4 are used

[0028]

[Formula 4] Y2 = b "11Y1 + b" 12M1 + b "13C1 + b" 14K1

Therefore, by changing the masking coefficient of the masking device 24 according to the signal from the controller 26, the output signals Y3, M3,
C3 and K3 also change, whereby the image light amount of the scanning optical device 2 is changed via the controller 26, so that the image density can be changed.

When the image density of the test patch K formed on the transfer belt 7 is detected by the patch density detector 33 and the controller 26 determines that the density is different from the predetermined density (80 hex), The controller 26 determines whether this is due to the toner density in the developing device 4 or the latent image potential of the photosensitive drum 1. Then, when it is determined that the density change of the test patch P is not due to the toner density in the developing device 4 or the latent image potential of the photosensitive drum 1, that is, the sensitivity of the photosensitive drum 1 changes due to a change over time or the like, and the latent image is changed. When the image and the development characteristics are changed, when the toner is deteriorated, or when the accuracy error of the control system is overlapped, the controller 26 issues a predetermined signal to the masking device 24, and calculates the masking coefficient. The output signal after the gradation correction device 25 is changed to form an image having an appropriate density by the output signal.

If the controller 26 determines that the density signal from the toner density sensor 32 deviates from the reference density, the controller 26 waits for the toner to be supplied to the developing device 4 properly. It is left as it is without sending a signal to the masking device 24. Further, in response to a signal from the potential sensor 30, the controller 26 controls the contrast potential (the difference between the bright potential (latent image portion potential) on the photosensitive drum 1 and the bias voltage from the developing device 4) and the back potential (the bright potential (non-latent potential)). If it is determined that the image density of the test patch K has changed because the difference between the image portion potential) and the bias potential from the developing device 4) is not correctly obtained,
An error message is issued.

However, even when the toner density is not proper or the latent image potential of the photosensitive drum 1 is not proper, the controller 26 issues a predetermined signal to the masking device 24,
It is a matter of course that an image having an appropriate density may be formed by changing the masking coefficient.

Here, the test patch K is formed for each color of toner at each image station (in this case, each test patch K is formed on the transfer belt 7 with a slightly shifted position). The above control may be performed for each station by detecting the patch density detector 33 provided in each image station, or may be performed only for a specific station.

As described above, the density of the test patch K is detected, and if the density is not appropriate, the masking device 2
4, the image density of the scanning optical device 2 is increased or decreased so that the image density can be changed to an appropriate value. A subtle change in color tone in a multi-color image caused by the accumulation of system errors can be corrected to an appropriate one. Therefore, especially in a multicolor image with a picture, a high-quality image with stable color balance including gray balance can be obtained.

Next, a second embodiment of the present invention will be described with reference to FIGS.
This will be described below. Components having the same functions as those according to the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

The present embodiment relates to a case where the patch density detector 33 for detecting the density of the test patch K is used as a registration sensor for detecting a shift of a transfer position in forming a full-color image.

That is, each test patch K composed of magenta, cyan, yellow, and black toners is transferred onto the transfer belt 7 in a superimposed manner, and the multiplely transferred test patches K are provided at the first to fourth stations. The density is detected by the detected patch density detector 33. In this case, in the first station, a test patch K of magenta toner is detected by the patch density detector 33, and if the density is not appropriate, the masking coefficient of the masking device 24 is changed by the controller 26 to form an image of an appropriate density. Is done. Next, in the second station, the cyan toner test patch K is superimposed and transferred on the magenta toner test patch K. This is detected by the patch density detector 33, and the displacement of the test patch K is detected. Is detected.

Similarly, in the third and fourth stations, a transfer position shift is detected by the patch density detectors 33,33. Therefore, the patch density detectors 33 in the second to fourth stations function as registration sensors.

Further, as shown in FIG.
If the test patches K, K are transferred not only in the transport direction of the transfer belt 7 but also on both ends in the width direction of the transfer belt 7 and are detected by the patch density detectors 33, 33, respectively, The transfer position shift on the width direction side of the transfer belt 7 can also be detected.

In the first and second embodiments, the relative positional relationship of the test patches K at each station is determined. However, it is not clear where the test patches K are located on the transfer belt 7. Therefore, if the test patch K is formed in a portion where the transfer belt 7 has a flaw or the like, there is a possibility that an appropriate density detection cannot be performed. Therefore, the positional relationship between the test patch K and the transfer belt 7 may be controlled so that the test patch K is always transferred to a predetermined position where the transfer belt 7 is not damaged.

Further, for example, black toner containing carbon black absorbs near-infrared light, so that the density may not be detected by the patch density detector 33. In this case, magenta, cyan, and yellow toners are used. A test patch K similar to the test patch K using black toner may be created, and the density may be detected by the patch density detector 33.

The test patch K formed on the transfer belt 7 at the station on the upstream side in the moving direction of the transfer belt 7
However, in order to prevent re-transfer to the photosensitive drum 1 in the downstream station, the photosensitive drum 1 and the test patch K are not mechanically and electrically contacted.

[0043]

As is apparent from the above description, according to the present invention, the reason that the result of the detection by the density detecting means differs from the predetermined density is either the toner density in the developing means or the latent image potential of the image carrier. If this is not the case, a signal is sent to the masking device to change the masking coefficient, and the output of the gradation correction device is changed to control the image density. And other conditions (for example, deterioration due to aging of the image carrier and toner itself that determine the latent image potential and development density), the cause is detected, and masking is performed according to the detection result. The output of the gradation correction device can be changed by changing the coefficient, and the masking coefficient is set as compared with the conventional image forming device that assumes that the characteristics of the toner and the image carrier are constant. Effect that highly accurate setting of color balance is possible.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining processing and control of image light in an image reading and outputting unit and each station of an image forming apparatus according to a first embodiment.

FIG. 2 is a side sectional view of the image forming apparatus.

FIG. 3 is a diagram illustrating control of image density of the image forming apparatus.

FIG. 4 is a diagram illustrating a state in which the density of a test patch on a transfer belt of an image forming apparatus according to a second embodiment is read by a patch density detector.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photosensitive drum (image carrier) 4 Developing device (developing means) 7 Transfer belt (transfer material transfer means) 15 Controller (control means) 33 Patch density detector (density detecting means) K Test patch (density pattern)

Continuation of the front page (56) References JP-A-1-207764 (JP, A) JP-A 1-167769 (JP, A) JP-A 1-169467 (JP, A) JP-A 1-266564 (JP) JP-A-61-111071 (JP, A) JP-A-62-152270 (JP, A) JP-A-62-27769 (JP, A) JP-A-63-296062 (JP, A) 1-206368 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G03G 13/01 G03G 15/01-15/01 117 G03G 15/00 303 G03G 21/00 370-502 G03G 21/02-21/04 G03G 21/14 H04N 1/46

Claims (3)

(57) [Claims] A latent image formed on a plurality of image carriers on the basis of image information of a plurality of colors is visualized as a multicolor toner image by a developing unit, and the toner image is transferred by a transfer material conveying transfer unit. and transferred superimposed onto the transfer material which is moved together with the multi-color image can be formed, the image formation density pattern for the test by a predetermined color toner through the image bearing member to the transfer material conveying transfer means on is transferred In the apparatus, a density detecting unit for detecting the density of the density pattern , and a detection result by the density detecting unit is different from a predetermined density.
The cause is caused by the toner concentration in the developing means.
To determine whether or not due to the latent image potential of the image carrier,
If neither of these is true, signal the masking device.
To change the masking coefficient and change the output of the gradation correction device.
Control To control means and the image density by Rukoto
And an image forming apparatus. 2. The control means communicates with the masking device.
The cause of the signal is deterioration of the image carrier due to aging.
The image forming apparatus according to claim 1, characterized in that. 3. The control means communicates with the masking device.
The reason for this is that the toner in the developing means changes over time.
It is due to a degraded image forming apparatus according to claim 1, wherein.