JP2002131998A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of realizing the appropriate correction control of the density of a toner image. SOLUTION: In the case of controlling the density of toner image, a toner image for detecting density is formed on an image carrier 1 and then transferred to a transfer material holding means 50. In the case of transferring the toner image, the density of the toner image for detecting the density is made thin by transferring the toner image for detecting the density to the holding means 50 on a different transfer condition from the case where the toner image is transferred to transfer material P.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, etc. for forming an image by an electrophotographic system, and more particularly to a structure for controlling the density of a toner image.

[0002]

2. Description of the Related Art Conventionally, some image forming apparatuses such as a copying machine, a printer, and a facsimile form an image by an electrophotographic system. In a copying apparatus as an example of such a conventional electrophotographic image forming apparatus, a latent image is formed on the surface of a photosensitive drum (image carrier), and the latent image is formed into yellow, magenta, A color toner image is formed on the surface of the photosensitive drum by developing with each color toner of cyan and black (hereinafter, referred to as Y toner, M toner, C toner, and BK toner, respectively).

[0005] The toner image formed on the surface of the photosensitive drum rotates to a position facing the transfer drum with the rotation of the photosensitive drum, and the rotating transfer charger is activated by activating the transfer charger. The image is transferred to the transfer material held on the drum.

In such a conventional image forming apparatus, a density detecting sensor for detecting whether or not the density of the toner image is appropriate is provided. The density of the density detection toner image formed on the surface is detected by the density detection sensor.

A density calculator calculates the density of the toner image based on the detection signal from the density detection sensor, and based on the calculation result, the controller determines whether the density is a predetermined value. If it is determined that the value is not the predetermined value, the latent image potential, the developing bias and the like are controlled to correct the toner image density so as to be appropriate.

FIG. 8 is a diagram showing the configuration of such a density detecting sensor. As shown in FIG. 8, the density detecting sensor includes a light emitting element 91, a light receiving element 92, and supports these elements. And a holder 93.

Here, the light emitting element 91 is formed of an LED, an incandescent bulb, or the like, and irradiates light to the surface of the photosensitive drum which is the surface to be measured. Also, the light receiving element 9
2 is a photodiode, phototransistor, CDS
After being irradiated from the light emitting element 91,
The light reflected on the surface of the object to be measured is received, and a signal corresponding to the amount of received light is output.

Then, when a density detection toner image is formed on the surface of the transfer drum at the time of density detection, when the light emitting element 91 irradiates the toner image with light, the light is reflected by the toner image, and the reflected light is reflected by the toner image. The light is received by the light receiving element 92. Then, the light receiving element 92 outputs a signal corresponding to the received light amount.

At this time, since the amount of reflected light changes according to the density of the toner image, the amount of light received by the light receiving element 92 also changes according to the density of the toner image. Therefore, the light receiving element 92 generates a signal corresponding to the density of the toner image, and the density calculating device calculates the density of the toner image based on the output signal of the light receiving element 92. Further, the control device corrects the density of the toner image so as to be appropriate according to the calculation result.

Incidentally, such density correction control is performed for each color toner. Here, FIG. 9 shows the relationship between the output of the density detection sensor and the toner density for all the toners of Y, M, C, and BK.

Here, as shown in FIG. 1, the sensor output of the Y, M, and C toners also increases as the toner density increases. This is because these toners have high densities (higher densities). This is because the amount of reflected light increases as).
Further, the sensor output of the BK toner decreases as the toner density increases. This is because the BK toner absorbs irradiation light for density detection because carbon is used, and This is because the absorption amount increases as the toner density increases (darkens).

[0012]

By the way, in such a conventional image forming apparatus, in order to accurately calculate the density using the output of the density detection sensor as described above, it is necessary to change the toner density. It is desirable to increase the output width of the sensor (hereinafter referred to as a dynamic range) so that even a small change in toner density can be detected.

Here, as a method of increasing the dynamic range in this way, there is a method of amplifying the output of the density detection sensor by an amplifier.

FIG. 10 shows the relationship between the output of the amplifier and the optical density of the toner image when the density of a certain color toner image is detected by the density detecting sensor and the output is amplified. It is. FIG. 3B shows the output of an amplifier having an amplification factor higher than that of FIG.

Here, in the case of (a), the optical density is 0.
From 1 to 0.8, the output of the amplifier has changed sufficiently and the dynamic range is wide, so that accurate density detection can be performed. However, when the density is 0.8 or more, the change is small and sufficient detection must be performed. Can not. In the case of (b), even if the density is 0.8 or more, the output of the amplifier is sufficiently changed, so that accurate detection can be performed. And accurate detection cannot be performed.

That is, as shown in (a) and (b),
Whatever the amplification factor of the amplifier is selected, accurate density detection cannot always be performed in all optical density regions. As a result, accurate density calculation is performed using the output of the density detection sensor. Therefore, there is a problem that it is not possible to perform appropriate correction control of the density of the toner image.

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and it is an object of the present invention to provide an image forming apparatus capable of performing appropriate toner image density correction control.

[0018]

According to the present invention, there is provided an image carrier,
Exposure means for forming an electrostatic latent image on the image carrier; developing means for developing the electrostatic latent image to form a toner image; transfer means for transferring the toner image to a transfer material; A transfer material holding unit for holding a material, and wherein when controlling the density of the toner image, a toner image for density detection is formed on the image carrier. After forming a toner image for density detection on the body, the toner image for density detection is transferred onto the transfer material holding unit, and when transferring the toner image, the toner image is transferred to the transfer material. Is characterized in that the toner image for density detection is transferred onto the transfer material holding means under different transfer conditions.

The present invention further comprises control means for controlling the transfer conditions, wherein the control means, when transferring the toner image for density detection onto the transfer material holding means, comprises a control means for controlling the density detection. It is characterized in that the transfer conditions are controlled so that the density of the toner image is reduced.

The present invention further comprises control means for controlling the exposing means so as to form a plurality of the toner images for density detection having different densities, and controlling the transfer conditions. When transferring the toner image for density detection onto the transfer material holding means, the transfer conditions are controlled so that the density of the toner image for density detection is reduced.

Further, the present invention is characterized in that the transfer condition is a transfer voltage, and the transfer voltage is reduced when transferring the toner image for density detection.

In the present invention, the transfer condition is a contact pressure between the image carrier and the transfer material holding means, and the contact pressure is reduced when the toner image for density detection is transferred. It is characterized by the following.

The present invention also provides an image carrier, an exposure device for forming an electrostatic latent image on the image carrier, a developing device for developing the electrostatic latent image to form a toner image, An image carrier that primarily transfers an image, and a secondary transfer unit that secondarily transfers the toner image primarily transferred to the other image carrier to a transfer material, and a density of the toner image. In an image forming apparatus configured to form a toner image for density detection on the image carrier so as to perform control, after forming a toner image for density detection on the image carrier, the toner for density detection is formed. An image is transferred to the other image carrier, and the toner image for density detection is transferred to the other image carrier under different transfer conditions when transferring a toner image to the transfer material at the time of toner image transfer. It is characterized by being transcribed on the body.

The present invention further comprises control means for controlling the transfer conditions, wherein the control means controls the density detection when transferring the density detection toner image onto the other image carrier. The transfer condition is controlled so that the density of the toner image is reduced.

The present invention further comprises a control means for controlling the exposure means so as to form a plurality of the toner images for density detection having different densities, and a control means for controlling the transfer conditions. When transferring the toner image for density detection onto the other image carrier, the transfer conditions are controlled so that the density of the toner image for density detection is reduced.

In the present invention, the transfer condition is a transfer voltage, and the transfer voltage is lowered when transferring the toner image for density detection.

In the present invention, the transfer condition is a contact pressure between the image carrier and the other image carrier, and the contact pressure is reduced when the toner image for density detection is transferred. It is characterized by the following.

Further, when controlling the density of the toner image as in the present invention, after forming the toner image for density detection on the image carrier, the toner image for density detection is transferred onto the transfer material holding means. At the same time, when the toner image is transferred, the toner image for density detection is transferred onto the transfer material holding means under transfer conditions different from those for transferring the toner image to the transfer material, so that the density of the toner image for density detection is transferred. To make it thinner.

[0029]

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

FIG. 1 is a diagram showing a configuration of an image forming section of an image forming apparatus according to an embodiment of the present invention.

In FIG. 1, reference numeral 1 denotes a photosensitive drum (image carrier) rotatably supported by an unillustrated apparatus main body, and the photosensitive drum 1 is rotationally driven in the direction of an arrow by an unillustrated driving device. It has become so. Around the photosensitive drum 1, a primary charging device (charging means) 2 for sequentially charging the surface of the photosensitive drum 1 to a uniform potential, and an exposure for exposing the surface of the photosensitive drum 1 to form an electrostatic latent image. Device (exposure means) 3, a rotary developing device (developing means) 4 for developing an electrostatic latent image to form a toner image (visible image), and transfer for transferring the toner image onto a transfer material (described later) Device 5 and cleaning device 6 for removing residual toner on the surface of photosensitive drum 1
And are arranged.

The transfer device 5 includes a transfer drum 50, which is rotatably supported by a device main body (not shown) and is a transfer material holding means that rotates in the direction of the arrow in the figure. Here, the transfer drum 50 has a cylindrical transfer substrate 501 as shown in FIG.
01, a dielectric sheet 502 of PET, PVDF, etc.
Is affixed. The transfer material P is electrostatically or mechanically held on the surface of the transfer drum 50.

As shown in FIG. 1, the photosensitive drum 1 is located inside the transfer drum 50 with the transfer drum 50 interposed therebetween.
The transfer charger 52 is disposed so as to face the transfer member P. By applying a transfer voltage by the transfer charger 52, the toner image formed on the photosensitive drum 1 is transferred onto the transfer material P. Has become.

A pair of separation chargers 53 are disposed inside and outside the transfer drum 50, and the separation chargers 53, 53 are configured to remove the charge of the transfer material P after the transfer. . Further, a cleaning device 54 is provided so as to face the transfer drum 50, and after the transfer is completed, the surface of the transfer drum 50 is cleaned.

Further, a separation claw 56 is provided at a position facing the surface of the transfer drum 50, and when the transfer is completed, the tip of the separation claw 56 contacts the surface of the transfer drum 50.
The transfer material P is separated from the transfer drum 50. The transfer material P separated from the transfer drum 50 is
The toner image passes through the fixing device 7 and is fixed.

On the other hand, the rotary developing device 4 has four developing units 4a, 4b, 4c, and 4d for individually storing toners of four colors, for example, Y toner, M toner, C toner, and BK toner.
And a substantially cylindrical developing device support 410 which holds these four developing devices 4a to 4d and is rotatably supported by a developing device main body (not shown).

Here, the developing device 4 includes a developing device support 4
10 in the direction indicated by the arrow in FIG.
4d is moved to a position facing the surface of the photosensitive drum 1, so that the electrostatic latent image on the surface of the photosensitive drum 1 is developed with a toner of a desired color, and the developing device supporter 410 makes one rotation so-called. It is configured so that full-color development for four colors can be performed.

The photosensitive drum 1 is provided with a photosensitive layer on a conductive substrate as an image carrier, and the exposure device 3 is constituted by a light emitting element such as a laser or an LED.

Next, an image forming operation of the image forming apparatus thus configured will be described.

When the image forming operation is started, the image forming section first charges the surface of the photosensitive drum 1 on which the primary charging device 2 rotates to a uniform potential, and then sets the exposure device 3 to a predetermined timing. Image exposure is performed based on image information of a color (for example, yellow) to form an electrostatic latent image of the first color.

When the electrostatic latent image is thus formed, the Y toner that has moved to a position facing the surface of the photosensitive drum 1 by the rotation of the developing device 4 (developing device support 410) is stored. The electrostatic latent image on the surface of the photosensitive drum 1 is developed and visualized by the developing device 4a. At this time, the transfer material P fed by a feeding device (not shown) is held on the surface of the transfer drum 50 in a wound state.

Next, the visualized yellow toner image is rotated to a position facing the transfer drum 50 with the rotation of the photosensitive drum 1, and then the transfer voltage applied when the transfer charger 52 is activated. The transfer drum 5
The image is transferred to the transfer material P on 0. During this transfer, the toner remaining on the surface of the photosensitive drum 1 is thereafter cleaned by the cleaning device 6, and the photosensitive drum 1 is ready for the next image formation.

Next, when a second color (for example, magenta) electrostatic latent image is formed on the surface of the photosensitive drum 1 by the exposure device 3, the developing device 4 rotates to move to a position facing the surface of the photosensitive drum 1. Developing device 4 containing stored M toner
As a result, a second magenta toner image is formed on the surface of the photosensitive drum 1, and thereafter, a second magenta toner image is transferred onto the surface of the transfer material P on which the first yellow toner image has already been transferred. Hereinafter, cyan and black toner images are formed in the same manner.

Thereafter, when cyan and black toner images are similarly formed and the toner images of all colors are transferred to the surface of the transfer material P, the separation chargers 53 and 53 are activated, and the transfer material P It is separated from the transfer charger 52. And
The toner on the surface of the transfer material P is fixed by the fixing device 7, and the image formation is completed.

In FIG. 1, reference numeral 9 denotes a density detecting sensor (density detecting means) for detecting whether or not the density of the toner image is appropriate. It is provided at the opposite position,
The detection signal of the density detecting sensor 9 is input to a density calculating device 10 as shown in FIG. 3, and the calculation result of the density calculating device 10 is input to a control device 11 which is a control means. I have.

Here, the control device 11 controls the driving of the exposure device 3, the developing device 4, and the transfer device 5 so as to form an image on the surface of the transfer material P. In addition, the density of the toner image is detected at a predetermined timing, and at the time of the density detection, the exposure device 3, the developing device 4, and the transfer device 5 are activated, and the toner image for density detection is formed on the surface of the transfer drum. An image patch is formed. Then, the image patch is read by the density detection sensor 9, and based on the detection signal from the density detection sensor 9, control is performed so that the density of the toner image becomes a desired density.

Incidentally, in the density detecting sensor 9, as shown in FIG. 9 described above, the control accuracy is not sufficient because the output change with respect to the density change is small in each color especially in a high density region. Therefore, in the present embodiment, at the time of density control,
The voltage applied to the transfer charger 52 is controlled to make the transfer voltage different from that at the time of image formation so that the transfer efficiency is reduced, and the density of the image patch transferred onto the transfer drum 50 is reduced.

Specifically, at the time of density control, the voltage applied to the transfer charger 52 is controlled as shown in the flowchart of FIG.
From 100V (S100).
Then, an image patch is formed with the transfer voltage set to 100 V (S101), and density measurement is performed by the density detection sensor 9 (S102).

Here, the detection signal from the density detecting sensor 9 is input to a density calculating device 10, and the calculation result of the density calculating device 10 is input to a control device 11.
When the control device 11 determines from the calculation result that the image patch density is the predetermined density (S1).
03, Y), the transfer voltage was returned from 100 V to 300 V,
Preparation for normal image formation (S105).

On the other hand, if it is determined that the image patch density is not the predetermined density (N in S103), the primary charging high voltage power supply (not shown) is controlled to control the primary charging high voltage applied to the primary charging device 2. Then, the operations of S101 and S102 are performed again to determine whether or not the image patch density is a predetermined density (S103). And
This operation is performed until the image patch density reaches a predetermined density.

As described above, when performing the density control, the image patch density can be reduced by transferring the image patch onto the transfer drum 50 under the transfer condition (transfer voltage) different from that at the time of image formation. Accordingly, accurate density calculation can be performed using the output of the density detection sensor 9 even in an area where the output change of the density detection sensor 9 with respect to the density change is small, and the density control can be performed with high accuracy.

In the above description, an image forming apparatus in which one type of image patch is formed for density detection has been described. However, the present invention is not limited to this. The present invention can also be applied to an apparatus in which a plurality of types of image patches are formed while performing image formation, and density control is performed by detecting the density of the image patches.

Next, an image forming apparatus according to the second embodiment of the present invention will be described.

Here, in the image forming apparatus according to the present embodiment, an exposure device capable of exposing at 256 gradations is used, and predetermined four gradations, for example, all pixels are turned off. An image is formed using four gradations in a state, a first halftone, a second halftone, and a state in which all pixels are turned on.

Further, in the present image forming apparatus, in addition to the density control in the state where all the pixels are turned on in the above-described first embodiment, image patches of two types of densities by the first halftone and the second halftone. Are formed, and these three types of image patches are read by the density detection sensor 9 respectively.

Here, in the case of such a halftone density control, as shown in FIG. 5, the output change of the density detection sensor 9 is not so large in the second halftone density area as in the density area where the exposure is all on. However, since each color is small with respect to the density change, the control accuracy is not sufficient.

Therefore, in the present embodiment, the transfer voltage is made different from that at the time of image formation, and the transfer efficiency is controlled to be small when the exposure is all on and the density control of the second halftone is performed. Image patch density is reduced (lightened). Further, the exposure amount of the exposure device 3 is controlled so as to obtain a desired density.

More specifically, the transfer voltage is set to 30 during image formation.
From 0 V, the voltage is set to 100 V during the exposure full on-density control and to 150 V during the second halftone density control. By performing such control, the density control can be performed with high accuracy even when a plurality of density patches are formed.

FIG. 6 is a flowchart showing such a density control operation. When performing the density control, first, the transfer voltage is increased from 300 V to 100 V during normal image formation.
(S200). Then, with the transfer voltage set to 100 V, all exposure on patches are formed (S201), and density measurement is performed by the density detection sensor 9 (S202).

Here, the detection signal from the density detecting sensor 9 is input to the density calculating device 10, and the calculation result of the density calculating device 10 is input to the control device 11. When the control device 11 determines from the calculation result that the image patch density is not the predetermined density (S20).
3N), the primary charging high voltage applied to the primary charging device 2 is controlled by controlling the primary charging high voltage power supply (not shown) (S20).
4) The operations of S201 and S202 are performed again, and it is determined whether or not the image patch density is a predetermined density (S203). This operation is performed until the image patch density reaches a predetermined density.

On the other hand, if it is determined that the image patch density is the predetermined density (Y in S203), then the transfer voltage is reduced because the density of the second halftone patch is lower than that of all the exposure on patches. Increase from 100V to 150V (S20
5) The second halftone patch is formed with the transfer voltage set to 150 (S206), and the density detecting sensor 9
(S207).

Here, if the control device 11 determines from the calculation result that the image patch density is not the predetermined density (N in S208), it controls the exposure device 3 to control the exposure amount (N in S208). S209), S206 and S207 again
Is performed to determine whether or not the image patch density is a predetermined density (S208). This operation is performed until the image patch density reaches a predetermined density.

On the other hand, if it is determined that the image patch density is the predetermined density (Y in S208), the transfer voltage is set to 150 V because the density of the first halftone patch is lower than that of the second halftone patch. To 300V (S210),
In this way, the first halftone patch is formed with the transfer voltage set to 300 V at the time of image formation (S211), and density measurement is performed by the density detection sensor 9 (S212).

If the control device 11 determines from the calculation result that the image patch density is not the predetermined density (N in S213), it controls the exposure device 3 to control the exposure amount (N in S213). S214), again, S211 and S212
Is performed, and it is determined whether or not the image patch density is a predetermined density. This operation is performed until the image patch density reaches a predetermined density.

As described above, when a plurality of image patches having different densities are formed and each image patch is transferred onto the transfer drum 50, the transfer conditions are controlled so that the density of each image patch is reduced. Thus, the density control can be performed with high accuracy even in a region where the output change of the density detecting sensor 9 with respect to the density change is small.

In the above description, the case where the transfer voltage is controlled so that the image patch density becomes a predetermined density has been described. However, the present invention is not limited to this.
The image patch density may be controlled by controlling the pressing force between the transfer drum 50 and the photosensitive drum 1.

FIG. 7 is a diagram showing the configuration of the image forming section of the image forming apparatus according to the third embodiment of the present invention. In the figure, the same reference numerals as those in FIG. 1 indicate the same or corresponding parts.

Referring to FIG. 5, reference numeral 520 denotes a pressurizing control mechanism provided in the transfer charger 52. During the density control, the pressurizing control mechanism 520 applies a pressing force (contact force) of the transfer drum 50 to the photosensitive drum 1. , The transfer efficiency is reduced.

With this configuration, the same effects as those of the first and second embodiments can be obtained.

By the way, the first to the third described so far.
The image forming apparatus according to the embodiment includes a photosensitive drum 1,
Although the exposure device 3, the development device 4, and the transfer device 5 were provided, the present invention is not limited to this, and the photosensitive drum 1,
In addition to the exposing device 3 and the developing unit 4, another image carrier for primary transfer of the toner image, and a secondary transfer unit for secondary transfer of the toner image primary-transferred to the other image carrier to a transfer material. Needless to say, the present invention can also be applied to an apparatus having a transfer unit for transferring the toner image to a transfer material.

Here, in the image forming apparatus having such a configuration, the toner image for density detection is transferred to another image carrier, and the toner image is secondarily transferred to a transfer material when transferring the toner image. The toner image for density detection is transferred to another image carrier under different transfer conditions. In addition,
The transfer conditions are the same as those described above.

[0072]

As described above, according to the present invention, when controlling the density of a toner image, the case where a toner image for density detection formed on an image carrier is transferred to a transfer material is described. By transferring the toner image onto the transfer material holding means under different transfer conditions, the density of the toner image for density detection can be reduced, and accordingly, appropriate density correction control of the toner image can be performed.

[Brief description of the drawings]

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

FIG. 2 is a perspective view illustrating a configuration of a transfer drum provided in a transfer device disposed in the image forming unit.

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

FIG. 4 is a flowchart illustrating a toner image density control operation of the image forming apparatus.

FIG. 5 is a diagram showing an output of a density sensor of an image forming apparatus according to a second embodiment of the present invention.

FIG. 6 is a flowchart illustrating a toner image density control operation of the image forming apparatus.

FIG. 7 is a diagram illustrating a configuration of an image forming unit of an image forming apparatus according to a third embodiment of the present invention.

FIG. 8 is a diagram showing a configuration of a conventional density detection sensor.

FIG. 9 is a diagram showing the relationship between the output of the conventional density detection sensor and the toner image density.

FIG. 10 is a diagram showing a relationship between an amplified output of the conventional density detection sensor and a toner image density.

[Explanation of symbols]

 Reference Signs List 1 photosensitive drum 2 charging device 3 exposure device 4 developing device 5 transfer device 9 density detection sensor 10 density calculation device 11 control device 50 transfer drum 520 pressure control mechanism P transfer material

Claims (10)

[Claims] 1. An image carrier, an exposure device for forming an electrostatic latent image on the image carrier, a developing device for developing the electrostatic latent image to form a toner image, and transferring the toner image A transfer unit for transferring the transfer material to a transfer material; and a transfer material holding unit for holding the transfer material. When the density control of the toner image is performed, a toner image for density detection is formed on the image carrier. In the image forming apparatus, after forming a toner image for density detection on the image carrier,
The toner image for density detection is transferred onto the transfer material holding means, and the toner image for density detection is transferred under a different transfer condition than when the toner image is transferred to the transfer material during the transfer of the toner image. An image forming apparatus for transferring an image onto a transfer material holding unit. 2. The image forming apparatus according to claim 1, further comprising control means for controlling the transfer condition, wherein the control means, when transferring the toner image for density detection onto the transfer material holding means, controls the transfer of the toner image for density detection. 2. The image forming apparatus according to claim 1, wherein the transfer condition is controlled so that the density is reduced. 3. The image forming apparatus according to claim 1, further comprising a control unit configured to control the exposing unit so as to form a plurality of the toner images for density detection having different densities, and to control the transfer condition. 2. The image forming apparatus according to claim 1, wherein when the toner image is transferred onto the transfer material holding unit, transfer conditions are controlled so that the densities of the toner images for density detection are reduced. . 4. The transfer method according to claim 1, wherein the transfer condition is a transfer voltage, and the transfer voltage is reduced when transferring the toner image for density detection. Image forming device. 5. The transfer condition is a contact pressure between the image carrier and the transfer material holding means, and the contact pressure is reduced when transferring the toner image for density detection. The image forming apparatus according to claim 1, wherein: 6. An image carrier, an exposure unit for forming an electrostatic latent image on the image carrier, a developing unit for developing the electrostatic latent image to form a toner image, and The image forming apparatus further includes another image carrier to be next transferred, and secondary transfer means for secondarily transferring the toner image primarily transferred to the other image carrier to a transfer material, and performs density control of the toner image. In the image forming apparatus configured to form a toner image for density detection on the image carrier as described above, after forming a toner image for density detection on the image carrier,
The toner image for density detection is transferred to the other image carrier, and the toner image for density detection is transferred under a different transfer condition than when the toner image is secondarily transferred to the transfer material during the transfer of the toner image. Wherein the image is transferred onto the other image carrier. 7. A control device for controlling the transfer condition, wherein the control device is configured to transfer the toner image for density detection when transferring the toner image for density detection onto the other image carrier. 7. The image forming apparatus according to claim 6, wherein the transfer condition is controlled so that the density of the image is reduced. 8. A control device for controlling the exposing means so as to form a plurality of density detecting toner images having different densities and controlling the transfer condition, wherein the control means controls the plurality of density detecting toner images. 7. The image forming apparatus according to claim 6, wherein, when the toner image is transferred onto the other image carrier, transfer conditions are controlled so that the densities of the toner images for density detection are reduced. apparatus. 9. The apparatus according to claim 6, wherein the transfer condition is a transfer voltage, and the transfer voltage is reduced when transferring the toner image for density detection. Image forming device. 10. The transfer condition is a contact pressure between the image carrier and the other image carrier, and the contact pressure is reduced when transferring the toner image for density detection. The image forming apparatus according to claim 6, wherein: