JP3401692B2 - 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 image forming apparatus for controlling an image forming condition by a density signal obtained by detecting a patch image. More specifically, it relates to control of image forming conditions during color image formation.

[0002]

2. Description of the Related Art An image forming apparatus is provided with a developing device for accommodating a developer, and a toner image is formed on an image bearing member by reversal development by the developing device and the toner image is transferred onto a recording material. Then, the image is recorded.

Further, at the time of forming a color image, for example, four developing devices for accommodating each of yellow (Y), magenta (M), cyan (C), and black (BK) developers are provided, each of which is provided with a developing device. The color toner image is formed by superposing the monochromatic toner images formed by the reversal development by the developing device on the image carrier, and the color toner image is transferred onto the recording material to record the color image.

In this case, whether or not the image density of the image recorded on the image carrier is stably maintained even when a large number of copies are made has a great influence on the image quality of the image.

Further, when forming a color image, in order to form a color image by superimposing a plurality of monochromatic toner images, each monochromatic toner image is developed to have a balanced image density in terms of the constitution of the color image. Whether or not
It greatly affects the reproducibility of color images. In particular,
It is difficult to stabilize secondary colors (red (R), green (G), blue (B), etc.) that are created by superimposing the primary colors of Y, M, and C.

For this reason, the image forming apparatus is usually provided with a control means for managing the image density of the toner image.

As means for managing the image density of the toner image,
A plate-shaped patch image having a standard density corresponding to the toner image is formed on the image carrier, and the image forming condition is controlled by a density signal obtained by detecting the patch image (Japanese Patent Laid-Open No. Sho 61-206).
63-106672) and a method of controlling the number of rotations of the developing sleeve of the developing device according to the humidity in the apparatus (JP-A-2-186368).

An optical detecting means composed of a light emitting element and a light receiving element is used for detecting the density of the patch image.
The relationship between the output voltage of the optical detection means obtained by detecting the patch image and the toner adhesion amount on the image forming body is as shown in FIG.

At a low density or a halftone density (points A and B in FIG. 1) with a relatively small toner adhesion amount, good detection sensitivity is shown, but a density of a solid image or a character with a large toner adhesion amount (see FIG. At points C and D in 1), there is a property that the detection sensitivity is significantly reduced.

In the optical detecting means, this is shown in FIG.
In the case of (a) and FIG. 2 (b), the difference can be detected relatively well, whereas in FIG. 2 (c) and FIG.
As shown in (d), when the toner adheres to the entire surface of the image carrier and then adheres to the surface of the image carrier, the surface of the image carrier is already covered with the toner. Therefore, the difference cannot be detected optically.
(FIGS. 2A, 2B, 2C, 2D, and 2D show the states of toner adhesion at points A, B, C, and D in FIG. 1). The patch image corresponding to the solid image or the character is not created and its density is not detected, but the patch image of low density or halftone density is created and the density is detected.

However, in order to maintain a stable image density even when copying a large amount, and when forming a color image, each color of Y, M, C and BK is developed to a balanced image density. In order to do so, it is necessary to accurately detect and control how a high-density toner image required for a solid image or characters is developed.

Further, there is a problem that the output of the above-mentioned optical detecting means is different for patch images of the same density due to surface stains and scratches due to long-term use of the image carrier.

Further, there is a problem that the outputs of the above-mentioned optical detecting means are not output in a well-balanced manner due to the difference in reflection density of toner of each color when forming a color image.

[0014]

SUMMARY OF THE INVENTION The present invention is directed to a potential (the lowest potential level in the case of reversal development) for forming a high-density toner image required for a solid image, characters, etc. on an image carrier. The first object is to accurately control the image density by a density signal obtained by forming a patch image with V _L ), and detecting the patch image.

A second object of the present invention is to improve the density detection method for patch images and control the image density satisfactorily regardless of surface stains, scratches, etc. due to long-term use of the image carrier. .

Further, according to the present invention, in the case of a color image forming apparatus, due to a difference in reflection density of each color toner,
A third object is to control the image density so that each monochromatic toner image is developed to a balanced image density in terms of the color image structure.

[0017]

The first to third objects are to provide an image carrier, a charging means for charging the image carrier, and an image carrier charged according to image information. a latent image forming unit that form a latent image of the image, a developing means for forming a toner image for image by developing the latent image for the image, a developing bias applying means for applying a developing bias to the developing means A color image forming apparatus having: a patch forming control unit that controls the charging unit, the latent image forming unit, the developing unit and the developing bias applying unit to form a patch image on the image carrier. An optical detection unit that detects the density of the patch image, wherein the patch formation control unit is a high-concentration device having a low detection sensitivity of the optical detection unit.
When exposed with laser power that forms a toner image
A patch in a region where the optical detection means has a high detection sensitivity.
In order to form an image, the patch image is formed on the image carrier under an image forming condition different from usual, and is formed on the image carrier according to the detection output of the optical detection means. An image forming apparatus (first invention) and an image carrier, characterized in that the charging means, the developing means or the developing bias applying means are controlled so that the density of the image toner image becomes a predetermined condition. A charging unit that charges the image carrier, a latent image forming unit that forms a latent image for an image on the image carrier charged according to image information, and a latent image for the image that are different in color from each other. In the image forming apparatus having a plurality of developing means for developing with the above toner to form a toner image for an image, and a developing bias applying means for applying a developing bias to the plurality of developing means, Image forming means, A patch formation control means for controlling a plurality of developing means and the developing bias applying means to form a plurality of patch images corresponding to respective toner images of the plurality of developing means on the image carrier, and the plurality of patches. An optical detection unit that detects the density of the image, and the patch formation control unit has a low detection sensitivity of the optical detection unit.
Exposed with laser power to form high density toner image
In this case, the area in which the detection sensitivity of the optical detection means is high is
A plurality of patch images are formed on the image carrier under different image forming conditions than usual so that a touch image is formed, and the patch images are formed on the image carrier according to the detection output of the optical detection means. An image forming apparatus (second invention), characterized in that the charging means, the plurality of developing means, or the developing bias applying means are controlled so that the density of the formed toner image for image becomes a predetermined condition. To be achieved.

[0018]

In the image forming apparatus according to the first and second aspects of the present invention, the first object is to control the image density by detecting the patch image formed on the image carrier by the optical detecting means. In, the patch image is formed on the image bearing member under the developing condition different from the usual condition.

More specifically, the developing condition different from the normal condition means that the developing sleeve of the developing device, the developing bias, the charging voltage, or the like is set to a condition different from that during the normal image formation,
It refers to forming a patch image at a potential (the lowest potential level V _{L in} the case of reversal development) that forms a high-density toner image required for a solid image or characters on the image carrier.

The above second object is achieved by properly correcting the output signal of the optical detecting means.

The third object is achieved by switching the formation conditions of the patch image of each color according to the color of each color toner. It can also be achieved by appropriately correcting the output signal of the optical detecting means according to the color of each color toner.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The construction and operation of the image forming apparatus of the present invention will be described with reference to the embodiment shown in FIG.

In FIG. 3, reference numeral 10 denotes a photosensitive drum which is an image bearing member, which is formed by coating an OPC photosensitive member on the drum, and is grounded and rotated clockwise. Reference numeral 12 denotes a scorotron charger, which applies uniform charge of V _{H to} the peripheral surface of the photosensitive drum 10 by corona discharge by a grid and a corona discharge wire whose potential is held at V _G. Prior to the charging by the scorotron charger 12, a PCL using a light emitting diode or the like to eliminate the history of the photosensitive member until the previous printing.
The surface of the photoconductor is neutralized by exposure using 11.

After uniformly charging the photosensitive member, the image exposing means 13 performs image exposure based on the image signal. Image exposure means
Reference numeral 13 is a reflection mirror 1 through a polygon mirror 131 that rotates using a laser diode (not shown) as a light emitting source, an fθ lens, and the like.
The optical path is bent by 32 and scanning is performed, and a latent image is formed by the rotation (sub-scanning) of the photosensitive drum 10.
In this embodiment, the character portion is exposed to form an inverted latent image in which the character portion has a lower potential V _L.

Yellow (Y)
There is provided a developing device 14 in which a developer composed of toner such as magenta (M), cyan (C), and black (BK) and a carrier is built in. First, the developing of the first color incorporates a magnet and a developer. This is performed by the developing sleeve 141 that holds and rotates. The developer consists of a carrier in which ferrite is used as a core and is coated with an insulating resin around it, and a toner whose main component is polyester and pigments according to the color and charge control agents, silica, titanium oxide, etc. are added. The agent is regulated to a layer thickness (developer) of 100 to 600 μm on the developing sleeve 141 by the layer forming means, and is conveyed to the developing area.

The gap between the developing sleeve 141 and the photosensitive drum 10 in the developing area is 0.2 to more than the layer thickness (developer).
As 1.0mm, D of the AC bias and V _DC of V _AC during this time
The C bias is superimposed and applied. Since V _DC and V _H and the toner are charged with the same polarity, the toner given the opportunity to be separated from the carrier by V _AC does not adhere to the V _H portion, which has a higher potential than V _{DC, and} has a potential higher than V _DC. attached to a lower V _L portion of visualized (reversal development) is carried out.

After the visualization of the first color is completed, the process proceeds to the image forming process of the second color, the uniform charging is performed again by the scorotron charger 12, and a latent image based on the image data of the second color is formed by the image exposing means 13. To be done. At this time, the charge elimination by the PCL 11 performed in the image forming process of the first color is not performed because the toner attached to the image portion of the first color scatters due to the rapid decrease in the potential around the image.

Again, V is applied over the entire peripheral surface of the photosensitive drum 10.
A latent image similar to that of the first color is formed on the portion of the photoconductor having the _H potential and the image of the first color is not developed, but development is performed again on the portion having the image of the first color. In the portion to be performed, the latent image of V _M ′ is formed due to the light shielding by the toner of the first color and the electric charge of the toner itself, and V _DC
And development is performed according to the potential difference between V _M ′ and V _M ′. In the overlapping portion of the images of the first color and the second color, the development of the first color is V _L
Performed to create a latent image, since the balance between the first color and the second color is lost, reducing the exposure amount of the first color V _H> V _M '>
It may be an intermediate potential that becomes V _L.

An image forming process similar to that for the second color is performed for the third and fourth colors, and an image of four colors is formed on the peripheral surface of the photosensitive drum 10.

On the other hand, the recording paper carried out from the paper feeding cassette 15 via the half-moon roller 16 is temporarily stopped and is fed to the transfer area by the rotation operation of the paper feeding roller 17 when the transfer timing is adjusted.

The image forming apparatus shown in FIG. 3 can be manually fed in addition to the automatic paper feeding mechanism. The recording paper P manually fed by the manual paper feed tray 60 is conveyed by the rotation of the pickup roller 61, and is fed to the transfer area through the same process as the paper feed from the paper feed cassette 15 described above.

In the transfer area, the transfer roller 18 is pressed against the peripheral surface of the photosensitive drum 10 in synchronization with the transfer timing,
The supplied recording paper is sandwiched and the multicolor image is transferred at once.

Then, the recording paper is discharged at almost the same time by a separating brush 19 which is brought into a pressure contact state, separated by the peripheral surface of the photosensitive drum 10 and conveyed to a fixing device 20, where the heating roller 201 and the pressure roller 202 are heated and pressed. After the toner is welded by the means, it is discharged to the outside of the apparatus through the paper discharge roller 21. The transfer roller 18 and the separation brush 19 are retracted and separated from the peripheral surface of the photosensitive drum 10 after the recording paper has passed to prepare for the next toner image formation.

On the other hand, the photosensitive drum 10 from which the recording paper is separated is
Residual toner is removed and cleaned by pressing the blade 221 of the cleaning device 22. The charge is again removed by the PCL 11 and charged by the charger 12, and the next image forming process starts. The blade 221 moves immediately after cleaning the surface of the photoconductor and retracts from the peripheral surface of the photoconductor drum 10.

The features of the functions and performances of the respective equipments constituting the image forming section of the above apparatus will be described below.

(Photosensitive member) The photosensitive drum 10 is stably rotated so that the OPC photosensitive member on the peripheral surface is uniformly charged by the scorotron charger 12. During charging, the grid potential is controlled to stabilize the charging potential.
The specifications of the photoconductor and the charging conditions thereof are set as follows as an example.

Photosensitizer: OPC φ120 Linear velocity 100 mm / sec Negative charging Charging condition: Charging wire: Platinum wire (clad or alloy) is preferably used. _VH- 850V, _VL- 50V (Image exposure) FIG. 4A shows the plane and side of the layout of the image exposure means 13, and FIG. 4B shows the semiconductor laser unit used for the image exposure means 13. It is explanatory drawing of 135.

The OPC photosensitive member on the peripheral surface of the photosensitive drum 10 is negatively charged by the charger 12 and then exposed by the light emission of the semiconductor laser unit 135 of the image exposing means 13 to form an electrostatic latent image.

The image data from the formatter which decodes the printer command is sent to the laser diode (LD) modulation circuit, and when the LD of the semiconductor laser unit 135 emits light by the modulated image signal, the light beam is reflected by the mirror 1.
The scanning lines are synchronized with each other by the beam index 136 via 32 and projected onto the polygon mirror 131.

The polygon mirror 131 reflects the beam light on the polyhedron and scans it. The beam shape of the scanning light is corrected by the fθ lens 133 and the cylindrical lens 134, and then the photosensitive member is exposed through the reflection mirror 132. Main scanning is performed to form an electrostatic image.

The beam diameter of the laser light is narrowed to an equivalent of 600 DPI by the optical system. Therefore, in order to obtain a high quality image, it is necessary to reduce the particle size of the toner. In this embodiment, toner of 8 μm size is used for each color. But most important to the user is the black text quality,
The black toner is preferably a small particle size toner (7 μm to 11 μm).

As the image exposure optical system, for example, the one having the construction described below is used.

Polygon mirror: 6 surfaces, rotation speed 23600 rpm, lens with air bearing focal length: f = 140 mm Dot clock: 20 MH ₂ beam diameter: approx. 60 × 80 μm (current image) FIG. 5 shows the configuration of the developing device 14. The toner supplied from the toner box is dropped to the right end of the developing device, and is agitated and mixed with the carrier by a pair of agitating screws 142 that rotate in opposite directions to give a predetermined charge amount (Q / M). Is set to.

The agitated two-component developer is supplied to the supply roller 143.
Is conveyed to the developing sleeve 141 via the layer thickness regulating member 144.
Is transferred to the developing area of the photosensitive drum 10 as a thin layer, and reversal development of the electrostatic latent image is performed under the developing conditions described below.

Current image gap: 0.5 mm toner transport amount: 20-30 mg / cm ² Development bias (AC): 2 KV, 8 KH ₂ (DC): -750 V Rotation direction of developing sleeve: Positive with respect to photoconductor drum Next, the image density adjustment of the present invention will be described.

First, FIG. 6 shows an outline of the image density adjustment.
A description will be given using (a) and (b).

The control circuit 31 controls the image exposure means 13, the grid voltage power supply 32, the developing sleeve control circuit 34, the developing bus ass power supply 35, and the like, and four patch images P corresponding to the toners of the respective colors on the photosensitive drum 10. To form.

The patch image P formed for each color is shown in FIG.
As shown in (a), the photoconductor drum 10 of the cleaning device 20.
Patch detection unit 100 located upstream of the rotation direction of
The reflectance, that is, the image density of the patch image is detected by.

As shown in FIG. 6B, the patch detection unit 100 is composed of a light emitting portion 101 formed of an LED and a light receiving portion 102 formed of a phototransistor, and each of the colors is classified according to the rotation of the photosensitive drum 10. The reflectance of the formed patch image P is detected, and an output signal corresponding to the reflectance is sent to the detection circuit 33.

FIG. 10 shows an example of the circuit configuration of the detection circuit 33. Here, Vout corresponds to the output voltage.

Here, one patch detection unit 100
However, four patch detection units may be provided corresponding to each patch image of yellow (Y), magenta (M), cyan (C), and black (BK). Yellow (Y), magenta (M), cyan (C) and black (B
All the densities of the respective patch images of K) may be detected.

The detection circuit 33 converts the output signal corresponding to the reflectance of the patch image detected by the patch detection unit 100 into a voltage and outputs it to the control circuit 31.

The control circuit 31 is based on the method described later.
The grid voltage power source 32, the developing sleeve drive circuit 34, or the developing bias power source 35 is adjusted to control the toner adhesion amount of the patch image P to a predetermined value. As a result of such control, the toner adhesion amount of the toner image by the image signal formed on the photosensitive drum 10 is eventually controlled to be constant.

As an example of a method of controlling the toner adhesion amount of the patch image P to a predetermined value, a case where the peripheral speed of the developing sleeve 141 of the developing device 14 is adjusted will be described.

The developing bias and the grid voltage are also detected by the detection circuit 33 in the same manner as the control of the peripheral speed of the developing sleeve.
It is possible to control the toner adhesion amount of the patch image P to a predetermined value by controlling it in accordance with the output voltage of.

The output voltage of the detection circuit 33 has a relationship as shown in FIG. 7A with respect to the toner adhesion amount of the patch image P, and for the toner adhesion in the range to be controlled,
As shown in the figure, an output voltage that decreases almost linearly with respect to the toner adhesion amount can be obtained.

On the other hand, the toner adhesion amount of the patch image P is determined by the developing device.
Since there is a proportional relationship as shown in FIG. 7B with respect to the peripheral speed of the developing sleeve 141 of No. 14, the peripheral speed of the developing sleeve 141 as shown in FIG. It is possible to control the toner adhesion amount of the patch image P to a predetermined value by changing it in proportion to.

The control circuit 31 controls the developing sleeve drive circuit.
By controlling 34 to adjust the peripheral speed of the developing sleeve 141, the toner adhesion amount of the patch image P is controlled to a predetermined value, and as a result, the toner adhesion amount of the toner image by the image signal becomes constant. Controlled.

Therefore, it is possible to realize accurate control of the image density of the toner image by the image signal.

A specific method for controlling the image density of the toner image will be described below.

The patch image P is formed at a relatively short interval for each of a very small number of prints, for example, about 3 to 4 sheets, and a fine adjustment of the image density is made based on the image density detection signal of the patch image P each time. The image density is maintained at a level close to the reference value by repeating the detection and adjustment operations frequently.

The above-mentioned image density adjustment process will be described with reference to the flowchart shown in FIG. When the printing is started, (1) the patch image P is formed, the image density thereof is detected by the patch detection unit 100 as in the first embodiment, and (2) the output voltage is set by the detection circuit (3).

This output voltage is compared with the reference value of the output voltage in the case of standard density (4) If the difference is smaller than the specified value, the image density is not adjusted, and if it is larger than the specified value, the density adjustment signal is output. Output to the control circuit to control a minute amount of the developing sleeve peripheral speed (5).

The control circuit for controlling the minute amount described above controls the peripheral speed of the developing sleeve 141 with respect to the output voltage of the detection circuit.
As shown in FIG. 5, a program capable of changing in a stepwise manner is provided, and when the above-mentioned density adjustment signal is input, the peripheral speed of the developing sleeve 141 is UP or DOWN in several steps according to the program. The number of revolutions (hereinafter, simply referred to as the number of revolutions) is controlled. That is, for example, when the image density of the patch image P is low and the output voltage is higher than the reference value, the image density is adjusted by increasing the peripheral speed of the developing sleeve 141, and the feedback is obtained by repeating this operation. The image density is adjusted so that the output voltage of the detection circuit is always close to the reference value.

Next, description will be made on the point that a patch image is formed under the development condition different from that during normal image formation during patch image formation.

In the case of the present embodiment, in order to form a high-density toner image required for a solid image, characters, etc. on the photoconductor drum 10, a laser power of 0.4 μJ / cm ² is applied to the photoconductor drum 10. A latent image of potential _VL- 50V must be formed on it.

However, as shown in FIG. 15 (a), a latent image having a potential _VL- 50V is formed on the photoconductor drum 10 to obtain 0.7 mg.
Even if a patch image with a large amount of toner adhering to / cm ² is formed, detection is performed at 2 V or less in a region where the detection sensitivity of the patch detection unit 100 is low, and its accuracy is extremely poor.

Therefore, in order to perform detection at around 4 V in the region with good detection sensitivity of the patch detection unit 100, as shown in FIG. 15 (b), a laser power of 0.07 μJ / cm ² is used for exposure. A patch image with 0.2 mg / cm ² of toner adhered on the body drum 10 must be formed.

In this way, the laser power (0.4 μJ / cm ²⁾ for forming the high-density toner image required for solid images and characters, which must be detected most reliably, on the photosensitive drum 10 (0.4 μJ / cm ² ), It is not possible to determine what kind of toner image is formed on the photosensitive drum 10.

Therefore, in the present invention, the patch detection unit 100 is also operated by the laser power (0.4 μJ / cm ² ) for forming the high-density toner image required for a solid image or characters on the photosensitive drum 10. In order to form a patch image in a region with high detection sensitivity, the image forming condition different from the normal condition is set.

FIG. 16 (a) shows a first embodiment of image forming condition switching, in which the sleeve peripheral speed of the developing sleeve 141 is changed from 280 rpm (fixed) during normal image formation to 80 rpm.
It is lowered to (fixed), and patch images are formed for each of yellow (Y), magenta (M), cyan (C), and black (BK).

By reducing the sleeve peripheral speed,
As shown in 16 (a), it is possible to obtain the development characteristics for a patch image.

By doing so, the laser power (0.4 μJ / cm ² ) for forming the high-density toner image required for a solid image, characters, etc. on the photoconductor drum 10 is used. A latent image of the potential _VL- 50V is formed on the upper portion, and a patch image with 0.2 mg / cm ² toner adhered is formed, and the area has a high detection sensitivity of the patch detection unit 100 (output voltage of about 4V).

In such a state, the density of each of the yellow (Y), magenta (M), cyan (C), and black (BK) patch images is detected, and the patch detection unit 10
In accordance with the output voltage of 0, the control circuit 31 of FIG. 6A controls the grid so that the toner adhesion amount of the patch image becomes a predetermined value regardless of the fluctuation of the characteristics of the photosensitive drum and the fluctuation of the developing characteristics. The voltage power supply 32 is controlled to adjust the charging voltage. After adjusting the charging voltage, when the toner image is formed by the image signal, the sleeve peripheral speed is returned to the original 280 rpm.

Since there is a proportional relationship between the sleeve peripheral speed and the toner adhesion amount, by controlling in this way,
When the toner image is formed by the image signal, the toner adhesion amount of the toner image is controlled to be constant.

FIG. 16B shows a second example of image forming condition switching, in which the developing bias (DC) is lowered from -750V during normal image formation to -250V to obtain yellow (Y). , Magenta (M), cyan (C) and black (BK)
To form a patch image for each of the.

By reducing the developing bias,
As shown in FIG. 16 (b), it is possible to obtain the development characteristics at the patch image.

By doing so, the laser power (0.4 μJ / cm ² ) for forming the high-density toner image required for a solid image, characters, etc. on the photoconductor drum 10 is used. A latent image of the potential _VL- 50V is formed on the upper portion, and a patch image with 0.2 mg / cm ² toner adhered is formed, and the area has a high detection sensitivity of the patch detection unit 100 (output voltage of about 4V).

In such a state, the density of each of the yellow (Y), magenta (M), cyan (C), and black (BK) patch images is detected, and the patch detection unit 10
In accordance with the output voltage of 0, the control circuit 31 of FIG. 6A controls the grid so that the toner adhesion amount of the patch image becomes a predetermined value regardless of the fluctuation of the characteristics of the photosensitive drum and the fluctuation of the developing characteristics. The voltage power supply 32 is controlled to adjust the charging voltage. After adjusting the charging voltage, when the toner image is formed by the image signal, the developing bias is returned to the original −750V.

Since the developing potential ( _VL - _VDC ) and the toner adhesion amount have a proportional relationship, by controlling in this way, the toner adhesion amount of the toner image at the time of forming the toner image by the image signal. Will be controlled to be constant.

FIG. 16C shows a third embodiment of image forming condition switching, in which the sleeve peripheral speed of the developing sleeve 141 is changed from the rotation speed N1 rpm during normal image formation to the rotation speed N2 rpm of 2/7. , And yellow (Y), magenta (M), cyan (C), and black (BK) patch images are formed.

By decreasing the sleeve peripheral speed,
As shown in 16 (c), it is possible to obtain the development characteristics at the patch image.

By doing so, the laser power (0.4 μJ / cm ² ) for forming a high-density toner image required for a solid image, characters, etc. on the photoconductor drum 10 is used. A latent image of potential _VL- 50V is formed on the upper surface, and a power image with 0.2 mg / cm ² toner adhered is formed, and the area has a high detection sensitivity of the patch detection unit 100 (output voltage of about 4 V).

In this state, the density of each of the patch images of yellow (Y), magenta (M), cyan (C) and black (BK) is detected, and the patch detection unit 10
In accordance with the output voltage of 0, the toner adhesion amount of the patch image corresponding to each color toner is set to a predetermined value regardless of the fluctuation of the characteristics of the photosensitive drum and the fluctuation of the developing characteristics.
The control circuit 31 of (a) controls the developing sleeve drive circuit 34 to adjust the sleeve peripheral speed of each sleeve (the adjusted rotational speed of the sleeve is N ₂ ′ rpm).

When the toner image is formed by the image signal, the sleeve peripheral speed is always set to 7/2 of the adjusted sleeve peripheral speed N ₂ ′ rpm at the time of forming the patch image.

Since there is a proportional relationship between the sleeve peripheral speed and the toner adhesion amount, by controlling in this way,
When the toner image is formed by the image signal, the toner adhesion amount of the toner image is controlled to be constant.

Corresponding to Embodiments 1 and 2 described above, the peripheral speed of the sleeve is compared with the comparison 1 in which the density of the patch image is detected without changing the peripheral speed of the sleeve and the developing bias, and the embodiment 3 described above. Table 1 shows the results of the print test conducted by the inventor of the present invention for 100,000 sheets for Comparative 2 in which the density of the patch image was detected without reducing the value to 2/7.

[0088]

[Table 1]

As a result, in Examples 1 to 3 in which the patch image was formed under the image condition different from the normal image condition, good patch image detectability and color stability could be obtained. In Nos. 1 and 2, as shown in Table 1, it was recognized that the patch image was poor in detectability and lacked in stability of color tone and density.

In the first and second embodiments described above, the charging voltage is adjusted by controlling the grid voltage power supply 32 so that the toner adhesion amount of the patch image becomes a predetermined value. ) And magenta (M), cyan (C), and black (BK) developing bias power supplies
The developing bias may be adjusted by controlling 35 or the developing sleeve driving circuit 34 may be adjusted by adjusting the sleeve peripheral speed.

In Examples 1 to 3 above, yellow (Y), magenta (M), cyan (C) and black (B) were used.
Although the correction at the time of forming a color image by K) is shown, the density control can be similarly performed at the time of forming a monochrome image by only black (BK).

In the present invention, the image density adjustment is performed as described above, but the output voltage of the detection circuit 33 in FIG. 6 (a) fluctuates due to the following causes, so that it may be corrected. preferable.

The correction of the output voltage of the detection circuit 33 will be described below.

There are two correction methods for the output voltage of the detection circuit 33: correction due to fluctuations in light reflection characteristics from the photosensitive surface of the first photosensitive drum 10 and correction due to difference in light transmittance depending on the color of the second toner. Two corrections are possible.

Both of the above two corrections may be performed, or only one of them may be performed.

First, the correction (hereinafter referred to as the baseline correction) due to the difference in the light reflection characteristic from the photosensitive surface of the photosensitive drum 10 will be described.

The image density detected from the patch image P also depends on the light reflection characteristics of the photosensitive surface of the photosensitive drum 10 and the difference in the reflected light detection ability of the patch detection unit 100.

The photosensitive surface of the photosensitive drum 10 is provided with a light absorbing layer on the substrate. This light absorbing layer varies in thickness depending on the product, and therefore the reflectance of the photosensitive surface slightly varies. Inevitable.

FIGS. 11A to 11C show changes in the output voltage from the detection circuit with respect to the toner adhesion amount on the photosensitive surface. FIG. 11A shows the photosensitive member S having a standard reflectance. Is a comparison of the change in the output voltage V _S with respect to the amount of adhered toner when using, and the change in the output voltage V _H and V _L when using the photoconductors H and L having reflectances that are around that. The output voltage has a substantially constant difference regardless of the change in the toner adhesion amount.

The photosensitive surface of the photosensitive drum 10 becomes a diffuse reflection surface due to scratches or the like due to long-term use, and its reflectance gradually decreases. FIG. 11B shows the change of the output voltage V _I with respect to the toner adhesion amount by the photoconductor I at the start of use, for example, 1
00,000 sheets obtained by comparing the change in the output voltage V _P by the photoreceptor P printed at the end, in this case it can be seen that substantially produce a constant difference in the output voltage regardless of the change in the adhesion amount of toner also.

Further, even if the new photosensitive drum 10 having a standard reflectance is used, the patch detection unit 10
If 0 is used for a long period of time and toner or dust adheres to the light emitting portion or the light receiving portion to reduce the ability to detect reflected light, the output voltage from the detection circuit naturally lowers. FIG. 11C shows the change in the output voltage V _A with respect to the toner adhesion amount when detected by the patch detection unit 100A in a clean state, and the detection by the patch detection unit 100B whose detection capability has decreased due to, for example, printing 100,000 sheets. This shows the comparison with the change in the output voltage V _{B in} the case where the output voltage V _B changes. In this case as well, a substantially constant difference in the output voltage is recognized regardless of the change in the toner adhesion amount.

In order to correct the deviation of the output voltage from the detection circuit due to these factors, in the present invention, the patch detection unit 100 measures the reflectance of the photoconductor of the new photoconductor drum 10 without toner adhesion. The measured value is stored in advance in the memory of the control logic circuit. Then, after the printing of a predetermined number of sheets, for example, 100 sheets, the measurement of the reflectance of the photoconductor is repeated in the state that the toner is not adhered, the difference of the output voltage is calculated each time, and the patch image P is detected by the difference of the output voltage. To correct the baseline of the output voltage from the detection circuit. As a result, the unevenness of the output voltage due to the variation and noise of the photoconductor and the deterioration of the detection capability of the patch detection unit 100 due to the long-term use are automatically corrected, and the correct density detection of the patch image P and the appropriate image density based on it are detected. Accurate control is realized.

In FIG. 12, V1 and V2 represent the output voltages by the detection of the photosensitive surface after the new printing and the printing of a predetermined number of sheets in the state where the toner does not adhere, and the deviation (V1-V2) of the output voltage shows the toner adhesion. In the latter case, the output voltage V1S corresponding to the case where a new photosensitive surface is used can be obtained by adding to the latter output voltage V2S.

The present inventor applies the baseline correction to the output voltage by the density detection of the patch image P as shown in the embodiment, and does not add the baseline correction as in the conventional case (comparison). As a result of comparison with Example), as shown in Table 1, no particular problem was found in both examples at the beginning of use, but in the comparative example, the color balance collapsed when the number of printed sheets was 50,000, When the number of sheets reached 100,000, the image density further decreased, whereas in the examples, it was confirmed that a color image in which the densities of the respective colors were appropriate and well-balanced was obtained from the beginning of use.

[0105]

[Table 2]

Next, the correction based on the difference in light transmittance depending on the toner color will be described.

Regarding the detection of the image density of the patch image P,
It is desirable that each of the attached yellow (Y), magenta (M), cyan (C), and black (BK) toners be detected by a wavelength having a small light transmittance.

However, as shown in FIG. 13, since each toner has a large difference in light transmittance depending on the wavelength region,
When the density of the patch image P of each color is detected by the light having a constant wavelength, the output voltage of the detection circuit 33 may differ even though the image density is the same.

Therefore, in the present invention, in consideration of the light transmittance of the toner, the amount of toner adhered to the patch image is provided with a color difference in advance, and when the image density is the same, the detection circuit 33 is used. The output voltage from is controlled to be the same.

FIG. 14 shows the relationship between the toner adhesion amount and the output voltage in the patch image P corresponding to each color toner when an LED having a wavelength of 660 nm is used for the light emitting unit 101.

According to FIG. 14 described above, the toner adhesion amount for yellow (Y) and magenta (M) is 0.3 mg / cm ² and the toner adhesion amount for cyan (C) and black (BK) is 0.2 m.
g / cm ² produces the same output voltage.

Therefore, the relationship between yellow (Y) and magenta (M) and cyan (C) and black (BK) is stored in the memory in advance, and the output voltage is corrected in proportion to the above relationship. When the image densities are the same, the output voltage from the detection circuit 33 can be controlled to be the same.

Specifically, the same toner adhesion amount 0.2 mg / cm ²
On the other hand, the output voltage A for yellow (Y) and magenta (M) and the output voltage B for cyan (C) and black (BK) should be corrected so that they are output from the detection circuit 33 as the same output voltage. Good. Further, such a correction may be performed in the control circuit 31.

The present inventor checks the color stability of each image with or without performing the above-mentioned correction after printing about 10,000 sheets with the same image forming apparatus. As a result, when the correction was carried out, stable color tone was obtained for all the colors, whereas when the correction was not carried out, there was a tendency that some of the colors lack stability.

Further, the difference in light transmittance depending on the color of the toner can be corrected by the following method.

That is, the output of the image exposure means 13 is different between the case of forming a patch image for yellow (Y) and magenta (M) and the case of forming a patch image for cyan (C) and black (BK). Switching, developing sleeve
The sleeve peripheral speed of 141, the developing bias, or the charging voltage is adjusted according to the difference in the toner adhesion amount of FIG. 14 described above, and if the image density is the same regardless of the toner color, the output voltage from the detection circuit 33 is It is possible to control the same.

In the above description, the L of the wavelength of 660 nm is used.
Although the case where the ED is used has been described, when the LED having the wavelength of 570 nm is used, as shown in FIG. 13, yellow (Y), magenta (M), cyan (C), and black (B) are used.
K), and if the image densities are the same, the detection circuit 33
It suffices to perform correction so that the output voltages from the same are the same.

[0118]

According to the present invention, it is possible to detect the density of a patch image due to the exposure amount for forming a high density toner image required for a solid image or characters, with high sensitivity, and to always achieve color stability. A color image forming apparatus capable of obtaining a color image having excellent properties is provided.

Although the image density adjustment in the digital color image forming apparatus has been described in the present embodiment, the present invention can be applied to an analog color image forming apparatus or a monochrome image forming apparatus. Therefore, it is extremely useful for forming an image with rich color tone and gradation.

[Brief description of drawings]

FIG. 1 is a graph showing a relationship between an output voltage of a patch detection unit and a toner adhesion amount.

FIG. 2A to FIG. 2D are sample diagrams showing a toner adhesion state on an image carrier.

FIG. 3 is a configuration diagram of a color image forming apparatus of the present invention.

4A and 4B are configuration diagrams of an image exposure unit.

FIG. 5 is a configuration diagram of a developing device.

6A and 6B are explanatory views of detection of a patch image and a signal processing path thereof.

7A to 7C are graphs showing the relationship between the toner adhesion amount, the peripheral speed of the developing sleeve, and the output voltage of the patch detection unit.

FIG. 8 is a flowchart for controlling the peripheral speed of the developing sleeve.

FIG. 9 is an example of a program for controlling the peripheral speed of the developing sleeve.

FIG. 10 is an example of a circuit configuration of a patch detection unit.

11A to 11C are graphs showing changes in the output voltage of the patch detection unit according to changes in the state of the photoconductor and the density detection capability.

FIG. 12 is a graph showing baseline correction of the output voltage of the patch detection unit.

FIG. 13 is a graph showing the light transmittance of each toner.

FIG. 14 is a graph showing the output voltage of the patch detection unit and the toner adhesion amount.

15A and 15B are graphs showing development characteristics of patch images.

16A to 16C are graphs showing the developing characteristics of the patch image of the present invention.

[Explanation of symbols]

10 photoconductor drum 12 Scorotron charger 13 Image exposure means 14 Developer 15 paper cassettes 18 Transfer roller 20 Fixing device 31 Control circuit 32 grid voltage power supply 33 Detection circuit 34 Development sleeve drive circuit 35 Development bias power supply 100 patch detection unit 101 Light emitting part 102 Light receiving part 141 Development sleeve P patch image

─────────────────────────────────────────────────── ─── Continuation of front page (31) Priority claim number Japanese Patent Application No. 6-1327 (32) Priority date January 11, 1994 (Jan. 11, 1994) (33) Country claiming priority Japan (JP) (56) References JP-A-4-267270 (JP, A) JP-A-5-158316 (JP, A) JP-A-5-207275 (JP, A) JP-A-1-169468 (JP, A) Kaihei 5-11553 (JP, A) JP-A-6-214451 (JP, A) JP-A-6-27756 (JP, A) JP-A-1-285970 (JP, A) JP-A-4-204766 ( JP, A) JP 63-131153 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G03G 15/01-15/01 117 G03G 15/00 303 G03G 21/00 370 G03G 15/08-15/095

Claims (10)

(57) [Claims] 1. An image carrier, a charging unit that charges the image carrier, and a latent image forming unit that forms a latent image for an image on the image carrier charged according to image information. A color image forming apparatus comprising: a developing unit that develops the latent image for image to form a toner image for the image; and a developing bias applying unit that applies a developing bias to the developing unit, wherein the charging unit, the It has a patch formation control means for controlling the latent image forming means, the developing means and the developing bias applying means to form a patch image on the image carrier, and an optical detection means for detecting the density of the patch image. However , the patch formation control means detects the optical detection means.
Laser power to form high density toner image with low sensitivity
If the exposure sensitivity is high, the detection sensitivity of the optical detection means is good.
The patch image is formed on the image carrier under different image forming conditions so as to form a patch image in a certain area, and the patch image is formed on the image carrier according to the detection output of the optical detecting means. An image forming apparatus, wherein the charging unit, the developing unit, or the developing bias applying unit is controlled so that the density of the formed toner image for image satisfies a predetermined condition. 2. The patch formation control means sets a peripheral speed of a developing sleeve of the developing means at a speed different from that at the time of forming the image toner image when the patch image is formed. The image forming apparatus described. 3. The image forming apparatus according to claim 1, wherein the patch formation control unit sets the developing bias at a value different from that at the time of forming the image toner image when the patch image is formed. . 4. The image forming apparatus according to claim 1, further comprising a detection output correction unit that corrects the detection output of the optical detection unit based on the reflectance of the surface of the image carrier. 5. An image carrier, a charging unit that charges the image carrier, and a latent image forming unit that forms a latent image for an image on the image carrier charged according to image information. It has a plurality of developing means for developing the latent images for images with toners of different colors to form toner images for images, and a developing bias applying means for applying a developing bias to the plurality of developing means. In the image forming apparatus, the charging unit, the latent image forming unit, the plurality of developing units, and the developing bias applying unit are controlled to control a plurality of toner images corresponding to respective toner images of the plurality of developing units on the image carrier. A patch formation control unit that forms a patch image and an optical detection unit that detects the densities of the plurality of patch images are provided, and the patch formation control unit detects the optical detection unit.
Laser power to form high density toner image with low sensitivity
If the exposure sensitivity is high, the detection sensitivity of the optical detection means is good.
A plurality of patch images are formed on the image carrier under different image forming conditions than usual so that a patch image of a certain area is formed, and the image carrier is detected according to the detection output of the optical detection means. An image forming apparatus, which controls the charging unit, the plurality of developing units, or the developing bias applying unit so that the density of the image toner image formed on the upper surface satisfies a predetermined condition. 6. The patch formation control means sets the peripheral speed of the developing sleeves of the plurality of developing means at a speed different from that at the time of forming the image toner image when forming the plurality of patch images. The image forming apparatus according to claim 5. 7. The image formation according to claim 5, wherein the patch formation control unit sets the developing bias to a value different from that at the time of forming the image toner image when forming the plurality of patch images. apparatus. 8. The image forming apparatus according to claim 5, further comprising a detection output correction unit that corrects the detection output of the optical detection unit based on the reflectance of the surface of the image carrier. 9. The detection output correction means for correcting the detection output of the optical detection means according to the color of the toner forming the plurality of patch images.
The image forming apparatus described. 10. The image forming apparatus according to claim 5, wherein the patch formation control unit switches a condition for forming the plurality of patch images in accordance with a color of a toner forming the plurality of patch images. .