JP2003241471A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus made compact and inexpensive by preventing a density detection means from being used severally, and always accurately detecting density without being influenced by the condition of the surface of a transfer material carrying belt or an intermediate transfer body on which a developer image for detecting density is formed and capable of yielding a stable high-quality image as an image forming apparatus using a plurality of image carriers and performing image control by forming the developer image for detecting density. <P>SOLUTION: The image forming apparatus is provided with a roller member 91 coming into contact with transfer material carrier 8 or the intermediate transfer body on a downstream side from a plurality of image carriers 1a to 1d in the moving direction of the carrier 8 or the intermediate transfer body, and the density detection means 92 installed to be opposed to the member 91 and detecting the image density of the developer image on the member 91. The developer image for detecting density is transferred and carried on the carrier 8 or the intermediate transfer body, and then transferred to the member 91 from the carrier 8 or the intermediate transfer body, and the image density of the developer image for detecting density on the member 91 is detected by the density detection means 92. Thus, an image forming condition for a plurality of image carriers 1a to 1d is controlled based on the result of detecting the density. <P>COPYRIGHT: (C)2003,JPO

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 forming a multiple developer image by a plurality of types of developer images on a transfer material, and is particularly suitable for a color copying apparatus having a plurality of electrophotographic photoconductors. Furthermore, a density detecting developer image (patch) is formed, this patch is irradiated with light, and the light amount of the reflected light is detected. The present invention relates to an image forming apparatus that controls image density based on reflectance.

[0002]

2. Description of the Related Art Conventionally, various image forming apparatuses, more specifically, various color copying apparatuses for forming a multiple image by a plurality of color developers (toners) on a transfer material have been proposed. FIG. 4 shows a typical example thereof.

FIG. 4 is a vertical sectional view of a color copying machine. Inside the copying apparatus main body C, there are four image forming units P.
a, Pb, Pc, and Pd are arranged at substantially the same height, and these image forming portions Pa to Pd are photosensitive drums (electron-sensing drums having an endless electrophotographic photosensitive layer formed on their surfaces as image carriers). Photographic photoreceptors 1a, 1b, 1c, 1d.

These photosensitive drums 1a arranged in parallel
1d is rotatably supported by the apparatus main body C such that the rotation axes thereof are parallel to each other, and is configured to rotate in the direction of the arrow by a driving unit (not shown).

On the upper side of these photosensitive drums 1a to 1d, an exposure device (optical information irradiation means) L for irradiating each photosensitive drum 1a to 1d with color-separated optical information is opposed to the photosensitive drums 1a to 1d. The rotating polygon mirror 17 irradiates the photosensitive drums 1a to 1d with light from a light source device (not shown), and the respective drums 1a to 1d.
An electrostatic latent image is formed on the.

Further, around these photosensitive drums 1a to 1d, primary charging devices 2a, 2b, 2c and 2d that charge the surfaces of the photosensitive drums 1a to 1d to a uniform potential, and the surfaces of the photosensitive drums 1a to 1d. Potential sensors 22a, 2 for detecting the potential
2b, 22c, 22d and the developer of each color (yellow, magenta, cyan, and black) are housed in the photosensitive drum 1.
Developing devices (developing means) 3a, 3b, 3c, 3d that use the electrostatic latent images on a to 1d (electrostatic latent images formed in the irradiation area by the exposure device L) as developer images (toner images) of the respective colors. , Transfer charging devices (transfer blades) 4a, 4b, 4c, 4d, which are transfer members for electrostatically transferring the toner images of the respective colors developed by these developing devices 3a to 3d to the transfer material S, and the photosensitive drums 1a to. Cleaning devices 5a, 5b, 5c, and 5d for removing the toner remaining on 1d are sequentially arranged.

Then, these photosensitive drums 1a to 1d
Are arranged at equal intervals along the conveyance direction of the transfer material S, and toner images of four colors of yellow, magenta, cyan, and black are sequentially arranged from the front side (right side in FIG. 4) of the apparatus main body C. Configured to form.

On the other hand, below the photosensitive drums 1a to 1d, a transfer belt 8 serving as a transfer material carrier is disposed, and the transfer belt 8 is wound between rollers 10 and 11 to be rotationally driven. It is designed to be moved endlessly. The transfer belt 8 includes the photosensitive drum 1a facing the transfer charging devices (transfer blades) 4a to 4d, which are transfer means.
1 to 1d (hereinafter referred to as “transfer position”) are in contact with each other, and a plurality of transfer materials S are simultaneously supported and conveyed to the transfer position.

The transfer belt 8 is formed of a dielectric resin film such as a polyethylene terephthalate resin film sheet (PET sheet), a polyvinylidene fluoride resin film sheet or a polyurethane resin film sheet, and both ends thereof are Endless shapes such as seamless belts that have no seams are used, or endless shapes are formed by overlapping and joining each other. In the case of a belt having a seam, a means for detecting the position of the seam may be provided so that the toner image is not transferred on the seam.

Further, a belt cleaning means 16 is arranged at a position facing the transfer belt 8 so that toner stains attached to the side of the transfer belt 8 facing the photosensitive drums 1a to 1d are removed by the belt cleaning means. It is designed to be removed by 16. The belt cleaning unit 16 uses the blade 161 to collect the waste toner in the cleaning container 162.
A rotating fur brush or a non-woven fabric may be used instead of, or they may be used in combination.

On the other hand, on the front side (right side in FIG. 4) of the apparatus main body C, a cassette 60 accommodating a large number of transfer materials S on a cut sheet is provided outside the apparatus main body C so as to project.
A pickup roller 26 that sequentially discharges the transfer material S from the cassette 60 is disposed above the back side of the cassette. A pair of registration rollers 13 are provided near the pickup roller 26.
The registration roller 13 is rotatably supported by the main body C of the apparatus, and is rotationally driven by a driving unit (not shown). The cassette 60, the pickup roller 26, and the registration roller 13 constitute a transfer material supply unit, and supply the transfer material S to the conveyor belt 8.

Further, the fixing device 7 is provided on the inner side of the apparatus main body C.
Is arranged and is configured to fix the toner image on the transfer material S conveyed by the transfer belt 8.

Upon receipt of a predetermined image forming signal, the photosensitive drums 1a to 1d are rotationally driven by a driving means (not shown), and the primary charging devices 2a to 2d are uniformly moved on the photosensitive drums 1a to 1d. Begins to be charged. Further, the exposure device L performs exposure corresponding to each color on the photosensitive drums 1a to 1d to form an electrostatic latent image, and the developing devices 3a to 3d further apply yellow, magenta, cyan and black color toners to the photosensitive drums. A developer image (toner image) of each color is formed by being attached to the electrostatic latent image portions on 1a to 1d.

On the other hand, since the pickup roller 26 is rotationally driven by receiving a predetermined signal, the transfer material S previously stored in the cassette 60 is fed into the apparatus main body C and placed on the conveyor belt 8. Placed. The conveyor belt 8 is rotationally driven by a driving unit (not shown), and the transfer material S is held by electrostatic attraction force to the photosensitive drums 1a to 1d.
Is conveyed to the inner side (left side in FIG. 4) of the apparatus main body C while contacting the. Then, when the transfer material S is in contact with each of the photosensitive drums 1a to 1d, the transfer blade 4 serving as a transfer charging device.
A high voltage is applied to a, 4b, 4c, and 4d, and the toner images of the respective colors on the photosensitive drums 1a to 1d are sequentially superimposed and transferred onto the transfer material S. Multiple images are formed by the color toners.

After that, the transfer material S is conveyed to the fixing device 7, and after the toner image on the transfer material S is fixed by the fixing device 7, the transfer material S is discharged out of the apparatus main body C.

On the other hand, the toner remaining on the photosensitive drums 1a to 1d is removed by the photosensitive member cleaning devices 5a to 5d, and the photosensitive drums 1a to 1d are ready for image formation again.

By the way, in the color copying apparatus C having the above construction, image density control is carried out in order to make the density of the toner image thus formed on the transfer material S optimum for the original image. ing. Next, the image density control will be described.

Density detecting means (density detecting sensors) 31a, 31 are provided at predetermined positions facing the photosensitive drums 1a to 1d.
b, 31c and 31d are provided, and the copying machine main body C has a built-in control means 24 (image forming condition adjusting means) for optimizing image forming conditions.

When controlling the density of the toner image formed on the photosensitive drums 1a to 1d, the photosensitive drums 1a to 1d are controlled.
An electrostatic latent image for density detection, which is a reference latent image for density detection, shows optical information based on a predetermined signal generated by an electrostatic latent image forming unit (not shown) for density detection of the apparatus body control unit. By irradiation, the toner is formed outside the image forming area on the photosensitive drums 1a to 1d, and the electrostatic latent images for density detection are visualized by the developing devices 3a to 3d, that is, the developer images for density detection, that is, It becomes a developer image for image density control (hereinafter referred to as "patch").

The density detecting sensors 31a, 31b, 31c and 31d on the photosensitive drums 1a to 1d are the photosensitive drums 1a to 31d of the patch formed outside the image forming area of the photosensitive drums 1a to 1d by the developing devices 3a to 3d. The image forming state on 1d, that is, the image density, which is the amount of toner forming a patch, is detected.

Then, the control means 24 adjusts the image forming conditions on the photosensitive drums 1a to 1d based on the patch image density detection results by the density detection sensors 31a to 31d.

In the conventional example shown in FIG. 4, since the density detecting sensors 31a to 31d are arranged downstream of the transfer blades 4a to 4d in the rotation direction of the photosensitive drums 1a to 1d, the patches are arranged on the photosensitive drums. When formed on the transfer belts 1a to 1d, the transfer blades 4a to 4d are separated from the transfer belt 8 so that the patches are not transferred to the transfer belt 8.

There are various control methods by the control means 24. Typical examples are (1) a charging bias applied to the primary charging devices 2a to 2d, an exposure amount by the exposure device L, Alternatively, a method of controlling the developing bias applied to the developing devices 3a to 3d to change the so-called developing contrast, and (2) in a digital copying apparatus, in order to guarantee a density gradation for an input video signal. , A method of changing or correcting the look-up table, and (3) in the two-component developing method, the developing devices 3a to 3d are provided with an amount of toner corresponding to the amount consumed by copying.
There is a method of replenishing to. Of these control methods,
(1) and (2) are known as methods for keeping image reproducibility more stable.

Here, an example of the density detection sensor will be described. Here, the density detection sensor 31a in the image forming portion Pa in the image forming apparatus C will be described.
Density detection sensor 31b in the other image forming units Pb to Pd
.About.31d has the same configuration. Concentration detection sensor 31a
Is composed of an optical sensor 31 as shown in FIG. In FIG. 5, the optical sensor 31 is installed so as to face the patch 100a formed on the photoconductor 1a. The optical sensor 31 has an LED 311 that emits light at one end in the longitudinal direction and the toner image patch 10 at the other end.
0a, the photodiode 312 receives the reflected light, and the optical axis of the irradiation light from the LED 311 and the optical axis of the reflected light to the photodiode 312 form an angle θ. Then, the amount of reflected light received by the photodiode 312 is detected and detected as the image density. That is, it is a mechanism for detecting the image density by the light reflectance of the patches on the photosensitive drums 1a to 1d.

FIG. 6 is a graph showing the relationship between the toner amount of a patch formed on a photosensitive member such as the photosensitive drums 1a to 1d, that is, the image density and the specular reflection light detection output of the optical sensor. Here, as an example, the color toner is used and normalized so that the output value of the sensor when the toner amount is 0 is 3.5V.

When the amount of toner in the patch formed on the photosensitive member increases, the area ratio of the toner covering the photosensitive member, which is the photosensitive drum, increases, and the specular reflection light from the photosensitive member decreases. That is, the output value of the sensor becomes maximum when the toner amount is 0. Referring to FIG. 6, it can be seen that the specular reflection light detection output of the optical sensor 31 decreases as the toner amount increases.

It can be seen that if the inclination of the specular reflection light with respect to the increase / decrease of the toner amount is large, it is possible to detect with high sensitivity with respect to the increase amount of toner, that is, the copy density.

[0028]

However, in the image forming apparatus that detects the patch density on each photoconductor by using the four photoconductors as in the copying apparatus C described above, the four photoconductor drums that are photoconductors are used. Since the density detecting sensors 31a to 31d are provided for the respective 1a to 1d, there is a problem that the device becomes large, complicated and expensive.

As a method for solving this, patches for image density detection formed on the photosensitive drums 1a to 1d are transferred to a transfer belt 8 or an intermediate transfer member in an intermediate transfer type image forming apparatus, 1 provided opposite to
There is a method of detecting the image density of a patch with each density detection sensor.

However, the material used for the transfer belt 8 and the intermediate transfer body is a dielectric resin film such as a polyethylene terephthalate resin film sheet (PET sheet), a polyvinylidene fluoride resin film sheet or a polyurethane resin film sheet. Although formed of an elastic body, these materials generally have a problem that the toner density cannot be detected with high sensitivity because of their low light reflectance.

Since these materials are relatively soft,
When used for a long period of time, the cleaning means and the tip of the transfer material are rubbed or abutted to cause roughening and unevenness, which further reduces the light reflectance of the belt. Therefore, it becomes impossible to detect the normal density after long-term use, and it is necessary to replace the belt regularly. For example, the amount of light reflected by a polyvinylidene fluoride resin (PVdF) belt used for a long period of time detected by the concentration detection sensor 31a (in FIG. 7,
Indicated as "PVdF". 7) is compared with that detected on the photoconductor, the result is as shown in FIG. Here, measurement is performed with the same amplification factor as in FIG. Although it is possible to electrically amplify the output voltage, noise is also amplified and becomes large, so the detection accuracy cannot be improved.

Therefore, the sensitivity of toner density detection is determined by the dynamic range. As shown in FIG. 6, with a base material having a relatively high regular reflectance such as a photoconductor, the difference in the amount of reflected light between when the toner image is on the base material and when there is no toner image is large, that is, a large dynamic range can be obtained. , High precision detection can be expected. However, as shown in FIG. 7, in the transfer belt used for a long period of time, since the light reflectance in the absence of toner is smaller than that of the photoconductor, the difference in the amount of specular reflection light with and without toner is small. Therefore, it is difficult to accurately detect the toner density on the belt.

Therefore, an object of the present invention is to provide an image forming apparatus which uses a plurality of image carriers to form a density detecting developer image and performs image control, by not using a plurality of density detecting means. Downsizing and cost reduction are possible,
In addition, an image for which a stable high-quality image can be obtained by always performing accurate density detection without being affected by the state of the surface of the transfer material carrier or the intermediate transfer body on which the density detection developer image is formed. A forming device is provided.

[0034]

The above object can be achieved by an image forming apparatus according to the present invention. In summary, the first aspect of the present invention includes a plurality of image carriers on which an electrostatic latent image is formed,
Each of the plurality of image carriers is provided with a developer of a different color contained in each of the plurality of image carriers, and the electrostatic latent image is developed with the developer, and the electrostatic latent image is developed on the image carrier. A developing unit that forms a developer image, a transfer material carrier that holds a transfer material on which the developer images formed for each of the plurality of image carriers are transferred, and a transfer material carrier on the plurality of image carriers. A density detecting electrostatic latent image forming means for forming a density detecting electrostatic latent image, and the density detecting electrostatic latent image is developed by the developing means on the plurality of image carriers. An image forming apparatus for forming density detecting developer images of different colors for each of the plurality of image carriers, further, in the moving direction of the transfer material carrier, downstream from the plurality of image carriers. A roller member that comes into contact with the transfer material carrier and a roller member that is installed so as to face the roller member. Density detecting means for detecting the image density of the developer image on the transfer member, and the density detecting developer image formed on the plurality of image carriers is transferred onto the transfer member carrier. Is conveyed and then transferred from the transfer material carrier onto the roller member, the density detecting means detects the image density of the density detecting developer image on the roller member, and based on the density detection result. An image forming apparatus is provided which controls the image forming conditions in each of the plurality of image carriers.

In the second aspect of the present invention, a plurality of image bearing members on the surface of which an electrostatic latent image is formed, and a plurality of image bearing members installed for each of the plurality of image bearing members are provided with different colors. Developing means for containing a developer and developing the electrostatic latent image with the developer to form a developer image on the image carrier, and the developing unit formed for each of the plurality of image carriers. A transfer material carrier that holds a transfer material on which the agent images are transferred in superimposition, and a density detecting electrostatic latent image forming unit that forms a density detecting electrostatic latent image on the plurality of image carriers. Then, on the plurality of image carriers,
In the image forming apparatus, wherein the density detecting electrostatic latent image is developed by the developing unit to form a density detecting developer image having a different color for each of the plurality of image carriers. Out of the plurality of image carriers, the most downstream image carrier has a density detection unit that is installed to face the most downstream image carrier located on the most downstream side in the moving direction of the transfer material carrier. The density detecting developer image formed on the image carrier other than the body is electrostatically transferred onto the transfer material carrier, and is transported to a position facing the most downstream image carrier according to the movement thereof. Next, the density detection means is electrostatically transferred to the most downstream image carrier, and the density detecting means is configured to set the image density of the density detecting developer image formed on the most downstream image carrier, and the most downstream image density. The density test formed on an image carrier other than the image carrier. An image density of the developer image for transfer transferred onto the most downstream image carrier, and based on the detection result, the image forming conditions in each of the plurality of image carriers are controlled. An image forming apparatus is provided.

According to a third aspect of the present invention, a plurality of image bearing members on the surface of which an electrostatic latent image is formed, and a plurality of image bearing members provided for each of the plurality of image bearing members are provided with different colors. Developing means for containing a developer and developing the electrostatic latent image with the developer to form a developer image on the image carrier, and the developing unit formed for each of the plurality of image carriers. An image forming apparatus for secondary-transferring the developer images collectively from the intermediate transfer body to a transfer material, the intermediate transfer body having a primary transfer of the agent images superimposed thereon. A density detecting electrostatic latent image forming means for forming a density detecting electrostatic latent image is formed on a body, and the density detecting electrostatic latent image is developed by the developing means on the plurality of image carriers. In the image forming apparatus for forming the density detecting developer images of different colors for each of the plurality of image carriers. A roller member that comes into contact with the intermediate transfer member downstream of the plurality of image carriers in the moving direction of the intermediate transfer member, and an image density of a developer image on the roller member that is installed so as to face the roller member. And a density detecting unit for detecting the density, and the density detecting developer image formed on the plurality of image carriers is transferred onto the intermediate transfer member and conveyed, and then from the intermediate transfer member. The image is transferred onto the roller member, the density detecting means detects the image density of the density detecting developer image on the roller member, and based on the density detection result, image formation on each of the plurality of image carriers is performed. Provided is an image forming apparatus characterized by controlling conditions.

According to a fourth aspect of the present invention, a plurality of image bearing members on the surface of which electrostatic latent images are formed, and a plurality of image bearing members provided for each of the plurality of image bearing members are provided with different colors. Developing means for containing a developer and developing the electrostatic latent image with the developer to form a developer image on the image carrier, and the developing unit formed for each of the plurality of image carriers. An image forming apparatus for secondary-transferring the developer images collectively from the intermediate transfer body to a transfer material, the intermediate transfer body having a primary transfer of the agent images superimposed thereon. A density detecting electrostatic latent image forming means for forming a density detecting electrostatic latent image is formed on a body, and the density detecting electrostatic latent image is developed by the developing means on the plurality of image carriers. In the image forming apparatus for forming the density detecting developer images of different colors for each of the plurality of image carriers. Of the plurality of image bearing members, the density detecting unit is installed facing the most downstream image bearing member located on the most downstream side in the moving direction of the intermediate transfer member, The density detecting developer image formed on an image carrier other than the downstream image carrier is electrostatically transferred onto the intermediate transfer member, and according to the movement, to a position facing the most downstream image carrier. The image is conveyed and then electrostatically transferred to the most downstream image carrier, and the density detecting means,
The image density of the density detecting developer image formed on the most downstream image carrier, and the density detecting developer image formed on an image carrier other than the most downstream image carrier. An image forming apparatus characterized by detecting an image density of what is transferred onto the most downstream image carrier, and controlling image forming conditions in each of the plurality of image carriers based on the detection result. provide.

[0038]

BEST MODE FOR CARRYING OUT THE INVENTION An image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.

Embodiment 1 FIG. 1 shows a main structure of an image forming apparatus to which the present invention is applied. In this embodiment, a color copying machine A that forms a multiple image with a plurality of types of developers (toners) on a transfer material by an image forming process similar to the conventional example will be described. Each photosensitive drum 1a, 1b, 1
The normal image forming operation is the same as that of the conventional color copying machine C, except for the density detecting process by the patch which is the density detecting developer image formed in c and 1d.
The description is omitted.

In the conventional example, each photosensitive drum 1a which is an image carrier
Although the four density detecting means (density detecting sensors) 31a to 31d are arranged so as to be opposed to 1d to 1d, the configuration of the present embodiment is such that the density detecting sensors are opposed to all of the photosensitive drums 1a to 1d. Is not provided, a conductive roller member 91 is arranged so as to contact the transfer belt 8 on the downstream side of each of the photoconductors 1a to 1d in the moving direction of the transfer belt 8, and the roller member 91 includes: A power source (not shown) is connected. The density detection sensor 92 is arranged so as to face the roller member 91.

Then, on the surface of each of the photosensitive drums 1a to 1d,
Similarly to the conventional example, the density detecting electrostatic latent image is irradiated with light information based on a predetermined signal generated by a density detecting electrostatic latent image forming unit (not shown) of the apparatus body control unit, whereby the photosensitive drum 1a is irradiated.
To 1d are formed outside the image forming area and are visualized by the developing devices (developing means) 3a to 3d to form a patch which is a density detecting developer image.

The patches formed on the photosensitive drums 1a to 1d are transferred onto the transfer belt 8 which is a transfer material carrier by transfer blades 4a to 4d which are transfer members.

The patch transferred onto the transfer belt 8 is electrostatically transferred onto the roller member 91. And
The image density of the patch transferred onto the roller member 91 can be detected by the density detection sensor 92 arranged to face the roller member 91. In this way, the characteristic of the present embodiment is to control the image forming conditions of the photosensitive drums 1a to 1d based on the density detection result. The details will be described below.

Further, as the roller member 91, a cleaning roller which is a member of the cleaning means 9 for removing the residual toner on the transfer belt 8 can be used as in the present embodiment, but the transfer belt cleaning means 9 can be used. Separately from the cleaning means, each photosensitive member 1a-1
The roller member 91 on which the patch is formed may be independently arranged downstream of d or downstream of each of the photoconductors 1a to 1d in the image forming apparatus in which the belt cleaning unit 9 is not provided.

In normal image formation, a developer image (toner image) is formed on each of the four photoconductors 1a to 1d at the same timing as the transfer material S is conveyed, and the formed toner image is transferred at the transfer portion. , A transfer belt 8 serving as a transfer material carrier
Transfer blade 4 provided so as to contact the back side
The toner is transferred onto the transfer material S by applying a transfer bias that applies a positive charge having a polarity opposite to the charging polarity (minus) of the toner to a to 4 d. The transfer material S on which the image has been transferred is separated from the transfer belt 8 and enters the fixing device 7 to fix the image. This transfer bias is applied to the photosensitive drum 1.
By controlling the potential of a to 1d, the potential of the transfer belt 8 and the resistance of the transfer belt 8, the environment such as temperature and humidity, the surface potential on the transfer paper S is stabilized and the change in transfer efficiency is eliminated. I have to.

On the transfer belt 8, an image area where a transfer material S is placed and a document image is formed and a non-image generated between the image areas where the transfer material S is not placed during normal image formation are formed. There is a part corresponding to the area.

In the apparatus of this embodiment, a density detection developer image (patch) for density detection is non-imaged on each of the photosensitive drums 1a to 1d every time a predetermined number of images, for example, 100 sheets are formed. It is formed between the image areas (paper intervals) which are the formation areas. The formed patch is transferred between the transfer materials S on the transfer belt 8.

The patch transferred to the transfer belt 8 comes into contact with the surface of the transfer belt 8 downstream of the four image forming portions Pa to Pd in the conveying direction of the transfer belt 8 and is rotated at a constant speed with the transfer belt 8. It is transferred to 91 by a cleaning bias.

The cleaning roller 91 is used as a cleaning roller of the cleaning means 9 of the transfer belt 8 which transfers the toner stains attached to the transfer belt 8 and collects it in a toner tank (not shown) during normal image formation. It is a thing. In this embodiment, the belt cleaning means 9 provided with this cleaning roller 91 is provided in place of the belt cleaning means 16 provided in the conventional example.

In this embodiment, the cleaning roller 91 is made of a conductive metal, is connected to a cleaning bias power source (not shown), and the toner is attracted to the roller 91 side between the cleaning roller 91 and the belt 8. By forming an electric field, the toner on the transfer belt 8 is transferred.

Therefore, when a patch is formed on the transfer belt 8, the patch is also transferred to the cleaning roller 91.

The toner amount of the patch transferred to the cleaning roller 91 is detected by a density detection sensor 92 arranged opposite to the cleaning roller 91, and the detection result is formed in each of the image forming portions Pa to Pd. The condition is fed back to control so that the image density is kept constant.

In this embodiment, the look-up table is corrected in order to guarantee the development contrast and gradation according to the density detection result.

The density detecting sensor 92 used here is a sensor 31a shown in FIG. 5 which is used to detect the amount of toner on the photosensitive drums 1a to 1d in the conventional example.
˜31d, which is configured by an optical sensor that utilizes the light reflectance of the patch, irradiates the patch with light, and detects the image density by the amount of specularly reflected light. Since the metal roller is used as the cleaning roller 91 on which the patch facing the roller 92 is formed, the regular reflectance of the base is large, and the surface is not likely to have irregularities even if it is used for a long period of time. The concentration can be detected with good sensitivity in the range.
That is, the density can be controlled with high accuracy.

The patch after detecting the image density, which is the toner amount, is removed by the roller cleaning blade 93 that rubs the surface of the cleaning roller 91 in the cleaning means 9 provided oppositely, and the unit of the cleaning means 16 is removed. Toner recovery coil 94 provided at the bottom
Is conveyed to a waste toner tank (not shown). still,
During normal image formation, toner stains attached to the transfer belt 8 are also conveyed to the toner tank.

As described above, the patches are sequentially formed in the four image forming portions Pa to Pd for each sheet interval, and the patches are transferred to the cleaning roller 91. The image forming state of the image forming portions Pa to Pd can be detected.

Here, the roller member 91 is preferably a metal roller, but is not limited thereto. However, a material having a relatively high reflectance is preferable, and a material having a reflectance at least higher than that of the transfer belt 8 is used. However, when the cleaning roller 91 is a metal roller, there is a fear that current will leak to the transfer belt 8 side. Therefore, in order to prevent this, the cleaning roller 91 is
It is preferable to use a coating roller in which the surface of the metal roller is coated with a high resistance paint.

Further, as described above, in this embodiment, the cleaning roller 91 functions as a member of the belt cleaning means 9 which is provided so as to face each other during the normal image formation, and the scattered toner and the photoconductor are used. Even the toner fogged on the background is electrostatically transferred onto the cleaning roller 91 to clean the surface of the belt. That is, the back side of the next transfer material is kept clean. However, the roller member on which the patch is formed may be a roller member having a high light reflectance such as a metal roller, which is arranged downstream of all the photosensitive drums in the transfer belt conveyance direction,
It is not always provided as a member of the belt cleaning means.

Embodiment 2 FIG. 2 shows a main structure of an image forming apparatus in this embodiment to which the present invention is applied. In this embodiment, a color copying machine B that forms a multiple image with a plurality of types of developer (toner) on a transfer material by an image forming process similar to the conventional example and the first embodiment will be described. . The operations other than the density detection process by the patches formed on the photosensitive drums 1a to 1d are the same as those of the conventional color copying machine C, and thus the description thereof is omitted.

In the color copying machine B of the present embodiment shown in FIG. 2, of the four photosensitive drums 1a to 1d, here,
The density detection sensor 31d is provided only at the position facing the photosensitive drum 1d, that is, the most downstream image carrier, in the image forming portion Pd that forms the black image disposed on the most downstream side, and the density detection sensor 31d is provided in the other image forming portions Pa to Pc. No density detection sensor is arranged on the photosensitive drums 1a to 1c.

In this apparatus, a plurality of photosensitive drums 1a
The density of the patch formed in the non-image forming area of the photosensitive drum 1d, which is the most downstream image carrier disposed at the most downstream side of 1d to 1d, is detected by the sensor 31d as in the conventional apparatus. However, the patches formed on the other photosensitive drums 1a to 1c are transferred to the transfer belt 8 in a non-image area on the transfer belt 8, that is, between sheets, and the transfer blade 4d provided on the most downstream photosensitive drum 1d. The patch is transferred to the most downstream photosensitive drum 1d by applying a negative charge, which is the reverse of the transfer process of the image portion.

By carrying out such a method, it is possible to detect all the densities of the four color patches with one sensor 31d, and the four color image formation is performed by the same control method as in the first embodiment. The image forming conditions formed by the portions Pa to Pd can be respectively corrected.

In the method of this embodiment, the patch density is detected on the photosensitive drum 1d, which is the photosensitive member disposed on the most downstream side of the transfer belt 8. Therefore, the higher the detection from the patch on the metal roller 91 of the first embodiment, the higher the density. Although it cannot be detected with sensitivity,
Since the image density, which is the amount of toner on the photosensitive drum 1d, is detected as in the conventional apparatus, the detection can be performed with sufficient accuracy for practical use.

Further, without using a special member such as the roller member 91, the density of the four color image forming conditions can be accurately controlled with one sensor, so that the size and cost can be further reduced. . In this embodiment, since the roller member 91 as the cleaning roller is not used, the transfer belt cleaning means 16 similar to the conventional example is used as the cleaning means for the transfer belt 8.

Embodiment 3 The features described in Embodiment 1 and Embodiment 2 according to the present invention can be applied to an intermediate transfer type image forming apparatus using an intermediate transfer member. In a color image forming apparatus,
The intermediate transfer type has advantages that there is no fear of color mixing and that various transfer materials having different qualities and thicknesses can be used.

FIG. 3 is a block diagram of an electrophotographic copying machine A'which is an example of an image forming apparatus using an intermediate transfer member according to the present invention. In the image forming apparatus using the intermediate transfer system, the copying machine A ′ is provided with the metal roller 91 described in the first embodiment at the downstream side of all the image bearing members, and the metal roller 91 is formed with a patch, which is used for densification. This is an example of detection by the detection sensor 92. Here again, the roller member 91 is not limited to the metal roller.

In the color copying machine A using the transfer belt 8 described in the first embodiment, the toner images of the respective colors formed in the respective image forming portions Pa to Pd are directly transferred to the transfer material S.
In the color copying machine A ′ using the intermediate transfer body 8 ′ shown in FIG. 3, the toner images formed in the image forming portions Pa to Pd are temporarily transferred onto the intermediate transfer belt 8 ′ serving as an intermediate transfer body and superposed. After they are matched, they are collectively transferred to the transfer material S.

The image forming apparatus A'of this embodiment comprises a driving roller 10, a tension roller 11, and a secondary transfer counter roller 1.
It has an intermediate transfer belt 8 ′ wound around three rollers No. 4 and rotated in the direction of the arrow in the figure. Generally, the intermediate transfer belt 8'is made of synthetic resin, rubber, or a combination thereof. The intermediate transfer belt 50 used here uses a polyimide resin film as an example,
It has a single-layer structure having a volume resistance of about 10 ⁹ Ω · cm and a thickness of 100 μm.

Image forming portions for black, magenta, cyan, and yellow, that is, image forming portions Pa to Pd for respective colors are arranged along the peripheral surface of the intermediate transfer belt 8 '.

The latent images on the photosensitive drums 1a to 1d in the image forming units are visualized by the toner in the developing means 3a to 3d, and the latent images are sequentially transferred to the intermediate transfer belt 8 ', whereby the intermediate transfer belt 8'is formed. Form a full color image on top.

On the other hand, the transfer material S is supplied from the paper feed cassette 60 by the paper feed roller 26 at a predetermined timing,
Secondary transfer, which is a facing portion between the secondary transfer counter roller 14 on which the intermediate transfer belt 8 ′ is wound by the registration roller 13 and the secondary transfer roller 15 as a secondary transfer member to which the secondary transfer bias is applied. Sent to the department.

The toner image formed on the intermediate transfer belt 8'is transferred onto the transfer material S fed to the secondary transfer portion.
Secondary transfer is performed collectively using the secondary transfer roller 15. The transferred image is conveyed to the fixing unit 7 where it is pressed and heated to obtain a permanent image.

On the other hand, the secondary transfer residual toner remaining on the intermediate transfer belt 8'after the image formation is removed by the intermediate transfer belt cleaning means 9. The belt cleaning unit 9 is located at a position downstream of the secondary transfer roller 15 and until the intermediate transfer belt 8 ′ reaches the most upstream photosensitive drum 1a among the photosensitive drums 1a to 1d in a week, that is, the secondary transfer roller. It is provided between 15 and the photosensitive drum 1a.

Here, the image density by the patch is controlled by the method described in the first embodiment. That is, the density detection sensor is not provided so as to face all of the photosensitive drums 1a to 1d, but the intermediate transfer belt 8'is located downstream of the photosensitive members 1a to 1d in the moving direction of the intermediate transfer belt 8 '. The roller 91 is arranged so as to come into contact with the roller 91, and a power source is connected to the roller 91 so that a bias is applied. The density sensor 92 is arranged so as to face the roller 91.

Also here, the roller 91 is provided as a cleaning roller in the intermediate transfer belt cleaning means 9. Therefore, in the present embodiment, the cleaning roller 91 is located downstream of each of the photosensitive drums 1a to 1d, further downstream of the secondary transfer roller 15 and the intermediate transfer belt 8'is a week, and the photosensitive drums 1a to 1d.
It is provided at a position where it reaches the most upstream photosensitive drum 1a, that is, between the secondary transfer roller and the photosensitive drum 1a. Then, when the intermediate transfer belt 8 ′ conveys the patch, the secondary transfer roller 15 is separated from the intermediate transfer belt 8 ′.

When the roller 91 does not also serve as a cleaning roller during normal image formation, it may be provided at any position downstream of the photosensitive drums 1a to 1d regardless of the position of the secondary transfer roller. At the time of formation, they should be separable.

Then, the transfer belt 8 in the first embodiment
Is replaced with the intermediate transfer belt 8 ', and the image density is controlled by the same method.

That is, the intermediate transfer belt 8'also has a portion corresponding to an image area in which an original image to be secondarily transferred to the transfer material is formed and a non-image area formed between the image areas.

In the apparatus of this embodiment, a density detecting developer image (patch) for density detection is formed on each of the photosensitive drums 1a to 1d in the image area every time a predetermined number of images, for example, 100 sheets are formed. Form in the space (paper interval). The formed patch is transferred between the papers on the intermediate transfer belt 8 ′, which is a non-image forming area.

The patch transferred to the intermediate transfer belt 8'is more than the four image forming portions Pa to Pd.
The cleaning bias is transferred to the cleaning roller 91 which comes into contact with the surface of the intermediate transfer belt 8 ′ downstream in the transport direction and is rotated at a constant speed with the intermediate transfer belt 8 ′.

The cleaning means 9 provided with the cleaning roller 91 is located downstream of the secondary transfer roller 15, but while the intermediate transfer belt 8'conveys the patch, the secondary transfer roller is located above the intermediate transfer belt 8 '. It is separated.

The cleaning roller 91 is the same as the cleaning roller 91 of the first embodiment, a cleaning bias power source (not shown) is connected, and the toner is attracted to the roller 91 side between the cleaning roller 91 and the belt 8 '. By forming such an electric field, the patch formed on the intermediate transfer belt 8'is transferred.

The toner amount of the patch transferred to the cleaning roller 91 is detected by the density detecting sensor 92 arranged opposite to the cleaning roller 91, and the detection result is formed in each of the image forming portions Pa to Pd. The look-up table is used for control so that the image density is maintained constant by being fed back under the conditions.

The density detection sensor 92 used here
5 is similar to that of the first embodiment, and is composed of an optical sensor for irradiating a patch with light and detecting the amount of specular reflection light thereof, as shown in FIG. 5, and uses a metal roller which is a cleaning roller 91 as a base of the patch. Therefore, the light reflectance of the base is large, and the surface is not likely to have irregularities even if it is used for a long period of time, so that the density can be detected with a large dynamic range and high sensitivity over a long period of time. That is, the density can be controlled with high accuracy.

After the toner amount is detected, the patch is removed from the cleaning roller 91 by the cleaning blade 93 and collected in a toner tank (not shown) in the same manner as in the first embodiment.

Also, the photosensitive drum 1 described in the second embodiment.
A method of transferring the patches formed on a to 1c to the most downstream photosensitive drum 1d of the most downstream photosensitive drum 1d and detecting the image density by the density detection sensor 31d provided in the photosensitive drum 1d is also available. The present invention can be applied to the image forming apparatus of the intermediate transfer system of this embodiment. At that time, instead of the transfer belt 8 in the second embodiment, the patches formed on the photosensitive drums 1a to 1c are transferred to the intermediate transfer belt 8 '. ,
They are reverse-transferred to the photosensitive drum 1d which is the most downstream photosensitive drum, and their image densities are detected by the density detection sensor 31d together with the patch formed on the most downstream photosensitive drum 1d, which is described in the second embodiment. Such an effect can be obtained.

As described above, by adopting the method of the present invention described in Embodiments 1 to 3, even in a device using a plurality of electrophotographic photosensitive members, one sensor can be provided, and the device can be downsized and the cost can be reduced. Becomes

Further, the present invention relates to one having a plurality of image carriers, but the number of image carriers and the color of the developer are not limited to the above.

[0089]

As described above, the image forming apparatus of the present invention has a plurality of image carriers on which electrostatic latent images are formed, and a plurality of image carriers provided for each of the plurality of image carriers. Developing means for accommodating a developer of a different color for each body, developing the electrostatic latent image with the developer, and forming a developer image on the image carrier,
A transfer material carrier that holds a transfer material on which a developer image formed for each of a plurality of image carriers is transferred, and a density detection device that forms an electrostatic latent image for density detection on the plurality of image carriers Electrostatic latent image forming means, and a density detecting electrostatic latent image is developed by the developing means on a plurality of image bearing members, and a density of a different color for each of the plurality of image bearing members. In an image forming apparatus for forming a developer image for detection, (A) further, a roller member that comes into contact with the transfer material carrier downstream of the plurality of image carriers in the transfer material carrier moving direction, and a roller member facing the roller member. Density detection means for detecting the image density of the developer image on the roller member, and the density detection developer images formed on the plurality of image carriers are Is transferred to a roller member and then transferred from a transfer material carrier to a roller member. The density detecting means detects the image density of the density detecting developer image on the roller member, and controls the image forming conditions in each of the plurality of image carriers based on the density detection result, or ( B) Further, it has a density detecting means installed facing the most downstream image carrier located at the most downstream side in the moving direction of the transfer material carrier among the plurality of image carriers, and has the highest density among the plurality of image carriers. The density detecting developer image formed on the image carrier other than the downstream image carrier is electrostatically transferred onto the transfer material carrier, and according to the movement, is conveyed to a position facing the most downstream image carrier, Then, it is electrostatically transferred to the most downstream image carrier, and the density detecting means transfers the image density of the density detecting developer image formed on the most downstream image carrier and the most downstream image carrier. Density detection on image carriers other than the most downstream image carrier By detecting the image density of the developer image and controlling the image forming conditions in each of the plurality of image carriers based on the detection result, the density detection sensor that was conventionally required in the same number as each image carrier. Since it is possible with only one unit, it is possible to reduce the size and cost of the device. Further, in the configuration of (A), by using a metal roller or the like as the roller member, it is possible to detect the density with high sensitivity even during long-term use, and thereby the density control can be accurately performed. Further, in the configuration of (B), it is possible to detect the toner amount on all the photoconductors without using a special part such as a roller member, and it is possible to further reduce the size and cost. was gotten.

Further, in the above invention, instead of the above-mentioned transfer material carrier, there is provided an intermediate transfer member on which a developer image formed for each of a plurality of image carriers is primarily transferred in an overlapping manner. Can also be applied to an image forming apparatus that secondarily transfers a developer image to a transfer material at once. In this case, the density detection developer image is transferred onto an intermediate transfer member instead of the transfer material carrier described above. , It is possible to obtain the same effect.

[Brief description of drawings]

FIG. 1 is a schematic vertical sectional view showing an example of an image forming apparatus according to the present invention.

FIG. 2 is a schematic vertical sectional view showing another example of the image forming apparatus according to the present invention.

FIG. 3 is a schematic vertical sectional view showing another example of the image forming apparatus according to the present invention.

FIG. 4 is a schematic vertical sectional view showing an example of a conventional image forming apparatus.

FIG. 5 is a schematic configuration diagram showing an example of a density detecting unit.

FIG. 6 is a graph showing a relationship between an image density of a patch on a photoconductor and a detection value of a density detection sensor.

FIG. 7 is a graph showing a comparison of density detection sensor detection values with respect to image density of patches formed on the surfaces of a photoconductor and a transfer belt.

[Explanation of symbols]

1a to 1d photosensitive drum (image carrier) 1d photosensitive drum (downstream image carrier) 3a to 3d developing device (developing means) 4a to 4d transfer blade 8 transfer belt (transfer material carrier) 8'intermediate transfer belt (intermediate transfer belt) Transfer body) 9 Belt cleaning means 15 Secondary transfer roller (secondary transfer member) 16 Belt cleaning means 31a to 31d, 92 Density detection sensor (density detection means) 91 Cleaning roller (roller member) 93 Cleaning blade (cleaning means) 94 Toner recovery coil (cleaning means) 100a Patch (developer image for density detection) S Transfer material

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G03G 15/16 G03G 15/16 103 103 F term (reference) 2H027 DA09 DE02 DE07 DE09 EA00 EB04 2H030 AA06 AB02 AD03 AD16 BB02 BB21 BB36 BB42 BB46 BB52 2H200 FA16 GA12 GA23 GA34 GA44 GA47 GB15 GB25 HA02 HA12 HA22 HA28 HB03 HB12 HB22 HB26 HB28 JA02 JA30 JB06 JB10 JB49 JB50 JC03 JC19 JC20 LA11 LA12 LB13 PA02 PB17

Claims (12)

[Claims] 1. A plurality of image bearing members on the surface of which electrostatic latent images are formed, and a plurality of image bearing members, each of which is provided with a developer of a different color. , A developing means for developing the electrostatic latent image with the developer to form a developer image on the image carrier, and the developer image formed for each of the plurality of image carriers are superposed. A transfer material carrier for holding a transfer material to be transferred, and an electrostatic latent image for density detection for forming an electrostatic latent image for density detection on the plurality of image carriers. In an image forming apparatus, wherein the density detecting electrostatic latent image is developed on the image carrier by the developing means to form a density detecting developer image having a different color for each of the plurality of image carriers. Further, in the transfer material carrier moving direction, the transfer material carrier is provided downstream of the plurality of image carriers. A roller member for touching, is placed opposite to the roller member, a density detecting means for detecting the image density of the developer image on the roller member,
The density detecting developer image formed on the plurality of image carriers is transferred onto the transfer member carrier and conveyed, and then transferred from the transfer material carrier onto the roller member. The density detecting means detects the image density of the density detecting developer image on the roller member, and controls the image forming conditions in each of the plurality of image carriers based on the density detection result. A characteristic image forming apparatus. 2. The image forming apparatus according to claim 1, wherein the surface of the roller member has a higher light reflectance than the surface of the transfer material carrier. 3. The image forming apparatus according to claim 2, wherein the roller member is a metal roller, and the transfer material carrier is belt-shaped. 4. The surface of the roller member also serves as a cleaning roller for removing residual developer adhered to the transfer material carrier during image formation on the transfer material and removing the residual developer from the transfer material carrier. 4. The image forming apparatus according to claim 1, wherein cleaning means for removing the density detecting developer image transferred to the sheet are installed opposite to each other. 5. A plurality of image bearing members on the surface of which electrostatic latent images are formed, and a plurality of image bearing members, each of which is provided with a developer of a different color. , A developing means for developing the electrostatic latent image with the developer to form a developer image on the image carrier, and the developer image formed for each of the plurality of image carriers are superposed. A transfer material carrier for holding a transfer material to be transferred, and an electrostatic latent image for density detection for forming an electrostatic latent image for density detection on the plurality of image carriers. In an image forming apparatus, wherein the density detecting electrostatic latent image is developed on the image carrier by the developing means to form a density detecting developer image having a different color for each of the plurality of image carriers. Further, among the plurality of image carriers, the most downstream image carrier located at the most downstream in the moving direction of the transfer material carrier. The density detection developer image formed on an image carrier other than the most downstream image carrier among the plurality of image carriers is the transfer material. Electrostatically transferred onto the carrier, and according to its movement,
The density detection unit is conveyed to a position facing the most downstream image carrier and is then electrostatically transferred to the most downstream image carrier, and the density detecting unit is configured to detect the density formed on the most downstream image carrier. Image density of the developer image for, and the image density of the density detection developer image formed on an image carrier other than the most downstream image carrier is transferred to the most downstream image carrier, And an image forming condition for each of the plurality of image carriers is controlled based on the detection result. 6. The image forming apparatus according to claim 5, wherein the transfer material carrier has a belt shape. 7. A plurality of image bearing members on the surface of which electrostatic latent images are formed, and a plurality of image bearing members are provided for each of the plurality of image bearing members, and each of the plurality of image bearing members contains a developer of a different color. , A developing means for developing the electrostatic latent image with the developer to form a developer image on the image carrier, and the developer image formed for each of the plurality of image carriers are superposed. An intermediate transfer member that is primarily transferred,
An image forming apparatus for secondary-transferring the developer image collectively from the intermediate transfer member to a transfer material, the density forming an electrostatic latent image for density detection on the plurality of image carriers. The electrostatic latent image forming means for detection is provided, and the electrostatic latent image for density detection is developed by the developing means on the plurality of image carriers, and each of the plurality of image carriers has a different color. In an image forming apparatus that forms different density detecting developer images, further, a roller member that is in contact with the intermediate transfer member downstream of the plurality of image carriers in the moving direction of the intermediate transfer member, and the roller member. A density detection unit that is installed to face each other and that detects the image density of the developer image on the roller member, and the density detection developer image formed on the plurality of image carriers is Transferred onto an intermediate transfer member and conveyed, and then the intermediate The image is transferred from the image carrier onto the roller member, the density detecting means detects the image density of the density detecting developer image on the roller member, and based on the density detection result, each of the plurality of image carriers is detected. An image forming apparatus characterized by controlling image forming conditions in. 8. The light reflectance of the surface of the roller member is higher than that of the surface of the intermediate transfer member.
Image forming device. 9. The image forming apparatus according to claim 8, wherein the roller member is a metal roller, and the intermediate transfer member has a belt shape. 10. The cleaning for removing residual developer remaining on the intermediate transfer body from the intermediate transfer body after the developer image is secondarily transferred onto the transfer material, the roller member being cleaned. Cleaning means for removing the density detecting developer image transferred to the surface, which also serves as a roller, are installed to face each other, and the secondary transfer member for performing the secondary transfer is configured such that the intermediate transfer member is the density detecting developer. 10. The image forming apparatus according to claim 7, wherein when the agent image is conveyed, it is separated from the intermediate transfer body. 11. A plurality of image carriers on which an electrostatic latent image is formed, and a plurality of image carriers, each of which is provided with a developer of a different color. , A developing means for developing the electrostatic latent image with the developer to form a developer image on the image carrier, and the developer image formed for each of the plurality of image carriers are superposed. An image forming apparatus for secondary-transferring the developer image from the intermediate transfer body to a transfer material at a time, the intermediate transfer body being primary-transferred, and detecting density on the plurality of image carriers. A density detecting electrostatic latent image forming means for forming an electrostatic latent image for use on the plurality of image carriers, and the density detecting electrostatic latent image is developed by the developing means on each of the plurality of image bearing members. An image forming apparatus for forming density detecting developer images of different colors for each of a plurality of image carriers, further comprising: Among the plurality of image carriers, the most downstream image carrier has a density detecting means installed facing the most downstream image carrier located at the most downstream side in the moving direction of the intermediate transfer member. The density detecting developer image formed on the image carrier other than the above is electrostatically transferred onto the intermediate transfer member, and is transported to a position facing the most downstream image carrier according to the movement, and The density detection means is electrostatically transferred to the most downstream image carrier, and the density detecting means is an image density of the density detection developer image formed on the most downstream image carrier, and the most downstream image carrier. The image density of the density detecting developer image formed on the image carrier other than the body is transferred onto the most downstream image carrier, and based on the detection result, the plurality of Characterized by controlling image forming conditions for each image carrier Image forming apparatus. 12. The image forming apparatus according to claim 11, wherein the intermediate transfer member has a belt shape.