JP2003015484A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of preventing an image defect caused by the unnecessary transfer of patch toner to a transfer material carrier or an intermediate transfer body without causing drastic cost rising or the increase of necessary space. SOLUTION: This image forming device has a means for forming an electrostatic latent image for detecting density on an image carrier, and a developing means develops the electrostatic latent image for detecting density and forms a developed image for detecting density on the image carrier and is equipped with a density detection means for detecting the developing density of the developed image for detecting density around the image carrier. Then, an image forming condition is controlled based on the developing density detected by the density detection means in the image forming device, where the part of the transfer material carrier corresponding to the developed image for detecting density is destaticized or made to have the same polarity as developer.

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 an electrophotographic type or an electrostatic recording type, and further, an image forming which can be embodied in various color copying machines having a plurality of developing devices and color printers. It relates to the device.

[0002]

2. Description of the Related Art Generally, an electrophotographic system, especially a color copying machine using a plurality of color toners, a color printer, etc., has an image signal in a characteristic of an engine in order to obtain a desired density gradation. It has a lookup table for converting it into a signal value.

In the case of a color copying machine, this look-up table is provided for each color of yellow, magenta, cyan, and black, and it is possible to output a desired full-color image by optimizing each color. ing.

However, the characteristics of the electrophotographic image forming apparatus are likely to change depending on the surrounding environment, usage conditions, etc., and under a fixed image forming condition, it is difficult to always output an image having a stable tint. . Therefore, the density of the developed image formed on the image bearing member such as the photosensitive drum is detected, and the image forming conditions are controlled so that desired gradation characteristics can be obtained by the information. More specifically, the look-up table is corrected, and the charging condition and the developing condition of the photosensitive drum that forms the electrostatic latent image are changed.

An image forming apparatus having such a developing density detecting means will be described. As an example, FIG. 7 shows an overall configuration example of an electrophotographic digital copying machine.

First, the image of the original 21 is read by the CCD 100 by the imaging lens. The CCD 100 decomposes the image into a large number of pixels and generates a photoelectric conversion signal corresponding to the density of each pixel. The obtained analog image signal is amplified to a predetermined level by the amplifier 2 and is converted to, for example, 8 bits (0 by the analog / digital converter (A / D converter) 3).
Up to 255 gradations).

Next, this digital image signal is supplied to each optimized γ converter (in this example, a converter which is composed of 256-byte data and performs density conversion by a look-up table method) 5, and γ After being corrected, it is input to the digital / analog converter (D / A converter) 9. Here, the digital image signal is converted into an analog image signal again and supplied to one input of the comparator 11.

The other input of the comparator 11 is supplied with a triangular wave signal of a predetermined cycle generated from the triangular wave generating circuit 10, and the analog image signal supplied to one of the comparators 11 is compared with this triangular wave signal to obtain a pulse width. Is modulated. This pulse-width-modulated binary image signal is input to the laser drive circuit 12, and this pulse width forms a laser drive pulse of a width (time length) corresponding to the level for each pixel image signal, and a laser drive pulse is formed. It is used as an ON / OFF control signal for light emission of the diode 13.

The laser beam L emitted from the laser diode 13 is scanned in the main scanning direction by the well-known polygon mirror 14, passes through the fθ lens 15 and the reflection mirror 16, and is a photosensitive member which is an image carrier rotating in the arrow direction. Drum 17
It is irradiated on top and forms an electrostatic latent image.

On the other hand, the photosensitive drum 17 is an exposure device 18,
After being uniformly discharged, the primary charger 19 uniformly charges the negative charge, for example. After that, the above-mentioned laser light L
The electrostatic latent image corresponding to the image signal is formed in response to the irradiation of.

This electrostatic latent image is developed into a developed image (toner image) of a visible image by the developing device 20 of the developing means. At this time, a DC bias component corresponding to the electrostatic latent image forming condition and an AC bias component for improving the developing efficiency are applied to the developing device 20 in a superimposed manner. This toner image is transferred and charged onto a transfer material 23 held on a belt-shaped transfer material carrier (transfer belt) 27 which is endlessly driven in the direction of the arrow shown by being applied between two rollers 25 and 26. It is transferred by the action of the container 22. The transfer material 23 fixes the image on the transfer material 23 through the fixing means 28 and is discharged to the outside of the main body.

The residual toner remaining on the photosensitive drum 17 is then scraped off by the cleaner 24 and collected. or,
The transfer belt 2 remaining after the transfer material 23 is separated
Residual toner on the transfer material 27 around the transfer belt 27
3 is scraped off by a cleaner 30 such as a blade, which is a transfer material carrier cleaning means installed downstream of the position where the material 3 is delivered to the fixing means 28.

Although only a single image forming station (including the photosensitive drum 17, the exposing device 18, the primary charging device 19, the developing device 20, etc.) is shown in the drawing for simplification of description,
In the case of a color image forming apparatus, for example, image forming stations for each color of yellow, magenta, cyan, and black are sequentially arranged on the transfer material belt 27 along the moving direction thereof, or when one photosensitive drum 17 is provided. In some cases, the developing devices 20 of the respective colors are arranged around the peripheral surface, or in the rotatable housing, the developing devices 20 of the respective colors of yellow, magenta, cyan, and black are arranged.
The desired developing device 20 is opposed to the photosensitive drum 17 so as to develop a desired color.

Further, in order to correct the changed developing density in the developing device 20 due to the development of the latent image, a video count type developing density correcting means is provided, and the output level of the digital type image signal for each pixel is adjusted. Calculate and calculate toner supply. That is, the output level of the image signal converted into a digital signal by the A / D converter 3 is integrated for each pixel, the video counter 4 converts the output level into a video count number, and the video count number is sent to the CPU 6. The motor drive circuit 7 drives the motor 81 only for the time corresponding to the toner replenishment signal, and rotationally drives the toner conveying screw 82 in the developer replenishing tank 8 containing the replenishment developer T ′ for the above-mentioned predetermined time. An appropriate amount of developer is replenished from the replenishing tank 8 into the developing device 20, and the developing device 2
The development density within 0 is kept constant.

On the other hand, such a video count type developing density correcting means alone causes a slight error due to fluctuations in the developer consumption system and the replenishing system. Therefore, as the second developing density correcting means, the photosensitive drum 17 surface is exposed to light. A patch sensor 60, which is a density detecting unit, is provided at a position between the developing device 20 and the facing portion of the transfer belt 27 in the rotation direction of the drum 17, and a developed image for density detection developed on the photosensitive drum 17 ( The method of detecting the density of the patch) and controlling the development density of the developer of the developing device 20, that is, the development amount, so as to maintain the patch image density constant, is combined with the density correction means by the video counter 4 described above. Have been taken.

An example of the patch sensor 60 is shown in FIG.
The patch sensor 60 includes a light source 50 such as an LED, a light receiving element 51 for density measurement that irradiates a patch from the light source 50 and receives the reflected light thereof, and a light source 5 for maintaining a constant light amount of the light source
It is composed of a light amount adjusting light receiving element 52 for directly receiving the light amount of 0.

In other words, the development density of a patch-shaped development image for density detection (hereinafter referred to as a "patch") obtained by developing the electrostatic latent image formed by the image signal for density control is referred to as an LED or the like. Of the light source 50, the reflected light thereof is received by the light receiving element 51 for density measurement which is a photoelectric element, the output value thereof is subjected to density conversion and detected to correct the density signal from the CPU 6, and the information thereof. According to this, a look-up table included in the γ converter 5 is newly created or correction is performed to maintain a desired gradation characteristic.

[0018]

However, the multicolor electrophotographic image forming apparatus having the structure shown in FIG. 7 described in the conventional example operates extremely well, but the following problems occur.

When the patch T is formed on the surface of the drum 17 or the like, as shown in FIG. 8 in which the transfer belt 27 and the photosensitive drum 17 are charged, the transfer material 23 is held from the photosensitive drum 17, for example. A transfer material carrying member 27 such as a transfer drum or a transfer belt, or an intermediate transfer member type, which will be described in detail later, is, for example, a patch on an intermediate transfer member 27 'installed in the image forming apparatus having the configuration shown in FIG. T is transferred, and a large load is applied to the cleaner 30 that cleans the transfer material carrier 27 and the intermediate transfer body 27 '.

The cleaning performance of the transfer cleaner 30 is limited to cleaning a small amount of toner such as transfer residual toner and fog toner. But for example,
For cleaning a large amount of toner generated when a paper jam occurs, the transfer material carrier 27 and the intermediate transfer member 27 'are repeatedly rotated, and the cleaning process is repeated many times to remove a large amount of toner. Therefore, the toner forming the patch, that is, the patch toner T is transferred to the transfer material carrier 2
When a large amount of the toner T was transferred to the No. 7 or the intermediate transfer member 27 ', the toner T could not be completely cleaned and unnecessary toner adhered to the transfer material in the subsequent image formation, resulting in an image defect.

In order to avoid these problems, a separating mechanism for separating the transfer material carrying member 27 and the intermediate transfer member 27 'from the photosensitive drum 17, and the transfer material carrying member 27 and the intermediate member so that the patch T does not come into direct contact. The transfer body 27 'is the photosensitive drum 17
It is necessary to provide a method of strengthening the cleaning function of the transfer material carrier 27 and the intermediate transfer body 27 'by forming a patch avoiding portion that does not contact with the sheet, which causes problems of cost increase and space.

Therefore, an object of the present invention is to prevent an image defect caused by unnecessary transfer of patch toner to a transfer material carrier or an intermediate transfer member without significantly increasing the cost or the required space. An image forming apparatus is provided.

[0023]

The above object can be achieved by an image forming apparatus according to the present invention. In summary, the present invention is
An image carrier, a developing unit for developing an electrostatic latent image formed on the image carrier according to an image signal with a developer, and a transfer material for transferring the developed image developed by the developing unit are held. A transfer material carrier and density detecting electrostatic latent image forming means for forming a density detecting electrostatic latent image on the image carrier, and the developing means includes the density detecting electrostatic latent image. Is formed to form a density detection developed image on the image carrier, and density detecting means for detecting the development density of the density detecting developed image is provided around the image carrier, and is detected by the density detecting means. In the image forming apparatus for controlling the image forming condition based on the developed density, the portion of the transfer material carrier corresponding to the developed image for density detection is neutralized or has the same polarity as the developer. An image forming apparatus is provided.

According to another aspect of the present invention, a first image carrier, developing means for developing an electrostatic latent image formed on the first image carrier in response to an image signal, and the developing means. A second image carrier to which the developed image developed by the means is primarily transferred;
Density detection for forming a density detection electrostatic latent image on the first image carrier by secondary transfer of the developed image, which is primarily transferred onto the second image carrier, onto the transfer material. Electrostatic latent image forming means for developing the density detecting electrostatic latent image to form a developed image for density detection on the first image carrier, In the image forming apparatus, the density detecting means for detecting the development density of the developed image is provided around the first image carrier, and the image forming condition is controlled based on the development density detected by the density detecting means. The portion of the image bearing member corresponding to the developed image for density detection is discharged or made to have the same polarity as the developer.

[0025]

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.

Here, as an image forming apparatus to which the present invention can be applied, a latent image corresponding to an image information signal is formed on an image carrier such as a photoconductor or a dielectric by an electrophotographic system, an electrostatic recording system or the like. Then, this latent image is developed by a developing device which is a developing means to form a developed image (toner image) which is a visible image, and the visible image is directly or indirectly transferred onto a transfer material such as paper and fixed. The permanent image may be formed by any means, but it is particularly applied to various color copying machines and color printers having a plurality of developing devices and the like.

In this embodiment, a multicolor electrophotographic apparatus will be described, but the image forming apparatus of the present invention is not limited to this, as described above.

Embodiment 1 FIG. 1 is a schematic block diagram showing an embodiment of the image forming apparatus of the present invention. First, an example of the overall configuration of the image forming apparatus will be described with reference to FIG.

Since the steps from the conversion of the image information to the irradiation of the latent image on the photosensitive drum 17 are the same as those described in the conventional example in FIG. 7, detailed description thereof will be omitted here.
Further, in FIG. 1, the developer replenishing tank 8 for the developing device 20 and circuits around it are omitted.

In FIG. 1, the photosensitive drum 17, which is an image carrier, is uniformly discharged by the exposing device 18, and then uniformly charged, for example, by the primary charging device 19, for example, to be negative. After that, upon receiving the irradiation of the above-mentioned laser light L, an electrostatic latent image corresponding to the image signal is formed.

This electrostatic latent image is developed by a developing device 20 which is a developing means.
Is developed into a toner image which is a visible image. Here, as the developing device 20, the developing devices 20Y, 20M, 20C, and 20Bk provided for each of yellow, cyan, magenta, and black developers are used.
Laser light L for forming an electrostatic latent image along the rotation direction of 7.
Are arranged side by side downstream from the irradiation position.

On the other hand, at the time of forming the electrostatic latent image, since the image signals of the component colors of the respective colors obtained from the original 21 are projected as the exposure L on the surface of the photosensitive drum 17,
An electrostatic latent image of each component color is formed on the photosensitive drum 17.
When this latent image reaches the developing portion where the photosensitive drum 17 and the developing devices 20Y, 20M, 20C, and 20Bk containing the developer (toner) face each other, toner of each color is supplied from each developing device 20 to form a latent image. Is developed as a developed image (toner image).

During development, the developing devices 20Y and 20Y
Between the M, 20C, 20Bk and the photosensitive drum 17, a DC bias component corresponding to the electrostatic latent image forming condition and an AC bias component are applied in a superimposed manner in order to improve the developing efficiency.

On the other hand, in this apparatus, the transfer material 23
On the transfer drum 27, which is a drum-shaped transfer material carrier,
It is supplied through the registration rollers 29. Transfer drum 27
Is composed of a cylindrical body in which a transfer sheet 33 is stretched in the circumferential direction in an empty area of a frame having rings (not shown) at both ends, and a recording material gripper (not shown) is provided at one position in the circumferential direction. (Illustration) is provided.

When the transfer material 23 reaches the transfer drum 27, the transfer material 23 is adsorbed and fixed on the transfer drum 27 by the adsorbing means 31 composed of an adsorbing charging member and a counter electrode, and rotates together with the transfer drum 27. .

When the photosensitive drum 17 and the transfer drum 27 reach a transfer site where they face each other, the transfer material 23 arrives at the transfer site so as to match the timing, which is a transfer means provided inside the transfer drum 27. A toner image on the transfer drum 27 is transferred to the transfer material 23 by applying a transfer bias from the power supply 32 to the transfer charger 22.

Transfer material 2 after transfer of four color toner images
3 is separated from the transfer drum 27 and reaches the fixing unit 28, where the toner images of the respective colors are mixed, fixed on the transfer material 23, and converted into a full-color print image, and then the apparatus is removed from the apparatus. Is discharged.

In the case of the color image forming apparatus shown in FIG. 1, the developing devices 20 for the respective colors are arranged side by side along the circumference of the photosensitive drum 17, but in addition, as shown in FIG. In the rotatable housing, the developing devices 20Y, 20M, 20 for yellow, magenta, cyan, and black are provided.
When C and 20Bk are arranged and a desired developing device 20 is opposed to the photosensitive drum 17 to develop a desired color,
A belt-shaped transfer material carrier (transfer belt) is used in place of the transfer drum, and image forming stations for each color of yellow, magenta, cyan, and black are sequentially arranged on the transfer material belt 27 along the moving direction thereof. There are also cases.

In this case, when the term "developing device 20" is used, it indicates the developing devices 20Y, 20M, 20C, 20Bk for the respective colors.

The residual toner remaining on the photosensitive drum 17 is then scraped off by the cleaner 24 and collected.

The transfer drum 27 used here will be described. For the transfer sheet 33 which is a dielectric film on the surface of the transfer drum 27, PET, polyvinylidene fluoride, (PVDF), polycarbonate resin (PC), polyurethane resin ( A dielectric resin such as PU) or a polyimide resin (PI) or a rubber resin is used, and a conductive filler is appropriately mixed in the dielectric resin so as to have appropriate electric characteristics and strength.

On the other hand, in the electrophotographic image forming apparatus, the image density changes depending on the surrounding environment, the number of sheets used, etc. In particular, a color image appears as a change in tint or a gradation change in the highlight portion, and It becomes a destabilizing factor of formation. As a countermeasure, a developed image (patch) for density detection is formed on the photosensitive drum 17, and a look-up table (hereinafter referred to as “LUT”) of the γ converter 5 is created again based on the detected density information. A desired gradation characteristic is maintained by performing γ correction based on that.

Also in the image forming apparatus shown in FIG. 1, as in the conventional case, on the surface of the photosensitive drum 17, at a position between the developing device 20 and the facing portion of the transfer drum 27 in the rotating direction of the photosensitive drum 17, Patch sensor 6 which is a density detecting means
0 is set. With this patch sensor 60,
The developing density of the patch developed on the photosensitive drum 17 is detected, and the developing density (toner density) of the developer of the developing device 20 is controlled so as to keep the patch developing density constant.

A method of forming a patch-shaped density detecting development image (patch) on the photosensitive drum 17 and a method of detecting the patch density will be described in detail.

As shown in FIG. 1, in this embodiment, a reference image generating circuit 72 which is an electrostatic latent image forming means for density detection for generating a reference image signal having a signal level corresponding to a predetermined density is provided. The reference image signal from the generation circuit 72 is provided to the pulse width modulation circuit 35, and the laser drive pulse circuit 12 generates the laser drive pulse having the pulse width corresponding to the predetermined density. This laser drive pulse is supplied to the semiconductor laser 13, and this laser 13 is caused to emit light for a time corresponding to the pulse width,
The photosensitive drum 17 is scanned. As a result, a density detecting electrostatic latent image (reference electrostatic latent image) corresponding to the predetermined density is formed on the photosensitive drum 17, and the reference electrostatic latent image is developed by the developing device 20.

The development density of the patch thus obtained is detected by the patch sensor 60 having the structure shown in FIG. As described in the conventional example, in the patch sensor 60, light is emitted from the light source 50 such as an LED, and the reflected light is received by the density measuring light receiving element 51, and the output value is density converted. . The output signal of this patch sensor 60 is shown in FIG.
The development density of the patch can be associated with the conversion formula obtained from the graph showing the relationship between the output voltage (sensor output voltage) and the toner density for the black toner and the toners of the other three colors shown in FIG.

The image forming apparatus according to the present embodiment has a toner image forming mode of a density control patch composed of a plurality of reference toner image patches.

The gradation control is to maintain the initial gradation characteristics by rewriting the LUT in the γ converter 5 based on the development density characteristic curve of the reference toner image detected by the density control patch.

In this embodiment, the LUT is formed so as to have a linear gradation characteristic with respect to the image signal, and a desired gradation characteristic is obtained. That is, in the graph of the image signal and the density data shown in FIG. 6, by inverting the density data of the standardized patch corresponding to the image signal level in line symmetry with respect to the ideal line of the density characteristics, An LUT with characteristics can be obtained.

In the case of full color, a patch is formed for each color and the same operation is performed.

By the way, in the image forming apparatus shown in this embodiment, the photosensitive drum 17 and the transfer drum 27 are always in contact with each other during the image forming sequence, and the formed patch always passes through the transfer drum 27. . The maximum amount of toner used in the patch is about 75 mg / m ² . The density control by the patch in this embodiment is performed during post-processing (hereinafter, post-rotation) at the end of image formation. When the final image formation is completed, patches of each color are sequentially formed and read by the patch sensor 60.

On the other hand, the transfer drum 27 is wound with a transfer sheet 33 for holding the transfer material, and a transfer bias is applied from the transfer bias power source 32 to the transfer means 22 to transfer the toner image onto the carried transfer material 23. To do. As described above, the transfer sheet 33 is made of a material such as PVDF or PET.

In normal image formation, the transfer bias applies a polarity opposite to the charging polarity of the toner. In this embodiment, since the negative polarity toner is used, the positive polarity bias is applied. Therefore, as shown in FIG.
The transfer sheet 33 and the transfer material 23 are polarized by the applied transfer bias, and the positive charge 53 on the photosensitive drum 17 side.
Occurs, and the negative toner T is transferred to the transfer material 23. Due to these effects, the negative toner T is easily transferred onto the transfer sheet 33,
The transfer sheet 33 is not required to apply the transfer bias.
Is polarized, the toner forming the patch, that is, the patch toner T is transferred. Particularly, when the patch T has a large toner amount and is transferred, unnecessary toner adheres to the transfer sheet 33.

Transfer drum of image forming apparatus shown in this embodiment
The transfer drum cleaning unit 27 is a transfer material cleaning unit.
Although the leaner 30 is arranged, a small amount of toner
The ability to remove
-Like T, 75mg / m ²About toner T is transferred
If it comes, it is difficult to clean it.

The uncleanable toner T remains on the transfer sheet 33, and sometimes adheres to the entire surface of the transfer sheet 33 in a stretched state, and adheres to the back side of the next-transferred transfer material 23 to stain an image. The image becomes defective.

Therefore, as a characteristic part of the present invention, in this embodiment, as shown in FIG. 1, the transfer drum 27 is provided with two outer charge eliminators 1b and one inner charge eliminator 1a, which are static eliminators. Downstream of the transfer position and transfer drum cleaner 3
0 is arranged upstream, and the transfer drum 27 is operated at a portion corresponding to the patch T on the surface of the transfer drum 27 and charged to the same polarity as the transfer drum 27 and the toner T to prevent the transfer of the patch T to the transfer drum 27.

Although non-contact corona chargers are used as the static eliminators 1a and 1b in this embodiment, for example, contact rollers or the like may be used as long as the transfer sheet 33 can be neutralized and charged. . Further, both the outside and the inside are not necessarily required, and it is sufficient that the surface of the transfer sheet 33 can be discharged and charged. The static eliminator 1 for the transfer drum 27
The positions a and 1b may be any positions around the transfer drum 27 as long as the charge-removed portion passes through the transfer portion so as to correspond to the patch later.

In this embodiment, the static eliminators 1a and 1b are connected to AC
A high voltage of + DC is applied, and the AC component has a frequency of 500 Hz and 10 kVpp both inside and outside. The DC component is -500V for the outer static eliminator 1b and + 500V for the inner static eliminator 1b for the purpose of negatively charging the surface of the transfer sheet 33.
Is set to.

FIG. 3 shows the state of the patches on the transfer drum 27 when the charge removers 1a and 1b are operated. As shown in FIG. 3, since the surface charge 54 of the transfer sheet 33 is negatively charged, the patch toner image T on the photosensitive drum 17 is not attracted to the surface.

Remove the static eliminators 1a and 1d from the patch T that is being rotated backward.
It is possible to charge the surface of the transfer sheet 33 to about -200V to -400V by operating the part of the transfer sheet 33 facing the sheet. Unless the static eliminators 1a and 1b were operated, a potential of + 100V to + 500V remained on the surface of the transfer sheet 33, and 60% to 70% of the toner in the patch was transferred. On the other hand, by using the present invention, it became possible to suppress the transfer to about 5% to 10%.

Further, in the image forming apparatus of FIG. 1, as shown in FIG. 4, a bias having a polarity opposite to the transfer bias can be applied in the transfer charger 22 at the patch portion, that is, the same polarity as the toner T. By being connectable to a high voltage power source 34 capable of outputting (negative polarity in this embodiment), the transfer sheet 33 is charged with the same polarity, so that the inside of the transfer sheet 33 has a positive polarity and the surface has a negative polarity. , And is polarized in the sheet 33, and the same effect is obtained. That is, the transfer charger 22
The static eliminators 1a and 1b can be used instead. in this case,
Since the toner is not transferred to the transfer material carrier 27, the transfer drum 27 is not soiled.

Further, in the static eliminator, for example, even in a system which does not have a DC transformer of the same polarity as the toner, it is effective even if the charge of the transfer sheet charged to the opposite polarity to the toner is neutralized, and it can be adopted. Even when it is adopted in this embodiment, the transfer to the transfer sheet is 20% to 30% and the effect is reduced, but it can be adopted.

Although the method of changing the LUT has been described as the image density correction method in this embodiment, it is also applicable to a correction method of controlling the charging bias, the developing bias potential, etc. according to the patch density to perform the density correction. And is not limited.

Further, although the present embodiment is applied to the image forming apparatus having one photosensitive drum, an image forming apparatus having a plurality of drums, for example, an image forming apparatus having four stations of Y, M, C and Bk is used. However, it goes without saying that it is applicable.

Embodiment 2 In this embodiment, the case where the present invention is applied to an image forming apparatus using an intermediate transfer member as a second image bearing member for a photosensitive drum which is a first image bearing member will be described. To do.

FIG. 2 shows the image forming apparatus of this embodiment. Although the intermediate transfer body shown in this embodiment uses the intermediate belt 27 ', the intermediate transfer body is not limited to the belt and may be a drum shape or the like. Since the processes of primary charging, image exposure, charge removal and cleaning on the photosensitive drum 17 are the same as those in the first embodiment, description thereof will be omitted. Regarding the development, in FIG. 2, as the developing means, the developing device 20 is provided, and the developing device 20 for each color is provided in the rotating casing.
Y, 20M, 20C and 20Bk are arranged. Therefore, in the image forming apparatus of the present exemplary embodiment, after the image forming process on the photosensitive drum 17 for charging, image exposure, developing, transferring, and cleaning is performed once for each color, the housing is rotated to move to the next color. A similar image forming process is performed on the intermediate transfer belt 27 ', and primary transfer is performed on the intermediate transfer belt 27' in order by the primary transfer roller 22 which is the primary transfer means, and the toner images of yellow, cyan, magenta, and black are overlaid.

The intermediate transfer belt 27 'is in contact with the photosensitive drum 17, and here, the intermediate transfer belt 27' is tensioned between the two rollers 25 and 26 and driven endlessly in the direction of the arrow in the figure. In the image forming apparatus according to the first exemplary embodiment, a full-color image is directly formed on the transfer material 23 by transferring and overlapping the toner images of the respective colors on the transfer material 23 attracted to the transfer drum 27.
In this embodiment, the toner images of the respective colors are primarily transferred and superposed on the intermediate transfer belt 27 'to form a composite toner image of the respective colors, and then the secondary transfer roller 2 which is the secondary transfer means.
A full-color image, which is a composite toner image of each color, formed on the intermediate transfer belt 27 ′ at a position facing 2 ′ is collectively transferred onto the transfer material 23.

On the intermediate transfer belt 27 ', an intermediate transfer body cleaner 30 which is a second image carrier cleaning means is arranged, and appropriately contacts the intermediate transfer belt 27', for example, a secondary transfer on the intermediate transfer belt 27 '. Unnecessary toner such as residual toner after transfer is cleaned.

As the cleaning means, for example, mechanical cleaning with a cleaning blade, a fur brush, or the like, or the toner on the intermediate transfer belt 27 'is recharged by a corona charger or a charging roller and returned to the photosensitive drum 17, and the photoreceptor cleaner 24 is used. Various methods such as cleaning the intermediate transfer belt 27 ′ by using electrostatic force, such as recovery by the method described above, can be selected.

In this embodiment, the patch is a so-called inter-paper patch which is formed during image formation so that image correction can be performed even during continuous image formation.

As the inter-paper patch, for example, when an image is formed by the developing device 20Y, a desired patch is formed on the photosensitive drum 17 outside the image area transferred to the transfer material 23, and the developing devices 20M and 20C are sequentially formed. , 20Bk, it is possible to provide feedback in real time when needed.

Even when the intermediate transfer belt 27 'is used similarly to the transfer drum 27 shown in the first embodiment, the photosensitive drum 1
The patch formed in 7 is transferred onto the intermediate transfer belt 27 '. In the case of the intermediate transfer belt 27 ′, the surface of the intermediate transfer belt 27 ′ becomes the image surface as it is. Therefore, the image forming apparatus for supporting the transfer material 23 on the conventional belt-shaped or drum-shaped transfer material carrier 27 is mainly used for transfer. While the back side of the material 23 is soiled, in the image forming apparatus using the conventional intermediate transfer belt 27 ', the surface of the transfer material 23, that is, the image surface is soiled.

A power source for applying a primary transfer bias to the primary transfer roller 22 which is the primary transfer means of the intermediate transfer belt 27 'shown in this embodiment, that is, a high voltage power source for transferring a toner image from the photosensitive drum 17 to the intermediate transfer belt 27'. 37 can output both positive polarity and negative polarity. As a result, when the image is transferred to the intermediate transfer belt 27 ', a positive polarity output having a polarity opposite to that of the toner and a negative polarity output having the same polarity as the patch toner T when the patch T passes through the primary transfer roller portion 22 are possible. Is.

That is, the primary transfer bias during image formation is
Y: + 300V, M: + 350V, C: + 380V, B
k: + 400V, -750V is applied as a reverse bias when passing through the patch, and the intermediate belt 2 of the patch toner is applied.
Adhesion to 7'is reduced. In this embodiment, the transfer of the patch toner to the intermediate belt 27 'can be suppressed to 5% or less by applying the reverse bias, and the image defect did not occur.

In the case of an image forming apparatus using the intermediate transfer member 27 ', the secondary transfer portion for transferring to a transfer material such as paper is generally a secondary transfer compared to the transfer drum system shown in the first embodiment. It is composed of a secondary transfer means 22 'such as a roller and a very simple cleaning means (compared to a photoconductor drum, an intermediate transfer body, and a cleaner used for the transfer drum).

With such a structure, the damage caused by the toner adhering to the secondary transfer portion 22 'is caused by the contamination of the secondary transfer roller 22' and the like even with a small amount of toner which is not affected by the transfer drum system. Dirt on the back side is likely to occur.

The secondary transfer roller 22 'usually has a diameter of 1
It is about 5 mm to 40 mm, and when roller stains occur on the paper gap patch or the like, it occurs as back stain after one round of the roller. Contamination occurs and it is difficult to avoid it in an image forming sequence. By applying the present invention in the intermediate transfer system, the transfer of toner such as patches on the intermediate transfer body 27 'is prevented as much as possible, and even a small amount of toner attached to the intermediate transfer body 27' is cleaned on the intermediate transfer body 27 '. By doing so, it is possible to prevent the secondary transfer roller 22 'from being soiled by the patch toner.

Further, preferably, a bias having the same polarity as the patch toner polarity is also applied to the secondary transfer roller 22 'at a position corresponding to the patch portion, whereby the secondary transfer roller 22' can be almost completely prevented from being soiled. It will be possible.

In the present embodiment, the sheet-to-sheet patch has been described, but the same effect can be obtained by applying the present invention during post-rotation or in a patch-only sequence.

In order to prevent the transfer of the patch T to the intermediate transfer belt 27 ', a reverse bias (having the same polarity as the toner) at the primary transfer portion by the primary transfer means 22 is used in this embodiment. The surface of the intermediate transfer belt 27 ′ corresponding to the patch passage portion may be neutralized at the upstream side of the primary transfer portion or charged to the same polarity as the toner by using the static elimination means as in the first embodiment, or the intermediate toner of the patch toner may be charged. It is possible to reduce the transfer to.

For example, in order to secure the secondary transfer (transfer to the transfer material) property, the charged state of the toner is adjusted, and the intermediate transfer belt 27 'is electrostatically cleaned. It is also possible to use a corona charger or a charging roller disposed at to remove the charge from the patch-corresponding part, preferably to the same polarity as the toner.

A portion of the intermediate transfer belt 27 'corresponding to the patch is discharged by the secondary transfer roller 22', or a bias having the same polarity as the secondary transfer bias is applied to make it have the same polarity as the patch toner. It can also be charged.

In this embodiment, the method of changing the LUT is described as the image density correction method, but it can be applied to a correction method of controlling the charging bias, the developing bias potential, etc. according to the patch density to correct the density. And is not limited.

Further, although the present embodiment is applied to the image forming apparatus having one photosensitive drum, an image forming apparatus having a plurality of drums, for example, four stations of Y, M, C and Bk are provided on the intermediate transfer belt. It is needless to say that the present invention can be applied to an image forming apparatus in which the image is transferred to the transfer material and then collectively transferred to a transfer material.

[0085]

As described above, according to the present invention, a patch is formed on an image carrier, and a density detecting means for detecting the development density of the patch is provided, and the image forming condition is determined by the detected development density. In the image forming apparatus, the transfer material carrier portion or the intermediate transfer body portion corresponding to the patch toner is
By removing the charge or setting the same polarity as the toner, the patch toner is prevented from being unnecessarily transferred to the transfer material carrier or the intermediate transfer member, and the image defect caused by the transfer of the patch toner is reduced. It has become possible to prevent it without significantly increasing the cost or increasing the required space.

[Brief description of drawings]

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

FIG. 2 is a schematic configuration diagram showing another embodiment of the image forming apparatus of the present invention.

FIG. 3 is an explanatory diagram showing a charging state of a patch image on a transfer drum according to the present invention.

FIG. 4 is an explanatory diagram showing how transfer of a patch according to the present invention is reduced.

FIG. 5 is a graph showing a change in image density with respect to a patch sensor detection voltage.

FIG. 6 is an explanatory diagram showing a method of creating an LUT.

FIG. 7 is a schematic configuration diagram showing an example of a conventional image forming apparatus.

FIG. 8 is an explanatory diagram showing a conventional patch transfer state.

FIG. 9 is a schematic configuration diagram showing an example of the configuration of a patch sensor.

[Explanation of symbols]

1a, 1b Static eliminator (static eliminator) 5 γ converter 6 CPU 17 Photosensitive drum (image carrier, first image carrier) 19 Primary charger 20 Developer (developing means) 22 Transfer charger (transfer means, primary) Transfer means) 22 'secondary transfer roller (secondary transfer means) 23 transfer material 24 photosensitive drum cleaner (image carrier cleaning means) 27 transfer drum, transfer belt (transfer material carrier) 27' intermediate transfer body (second Image carrier 30 Cleaner (transfer material carrier (intermediate transfer member) cleaning means) 32 Transfer bias power supply 33 Transfer sheet 34 Reverse transfer bias power supply 37 Primary transfer bias power supply 60 Patch sensor (density detection means) 72 Reference image generation circuit ( Electrostatic latent image forming means for density detection) T patch (developed image for density detection), patch toner

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 2H027 DA09 DE02 EA01 EA05 EB01                       EC03 ED15 ED24                 2H030 AD03 BB36 BB42 BB44 BB54                 2H077 DA05 DA31 DA47 DA63 DB08                       DB12 GA13                 2H200 FA08 HB48 JB02 JB39 JB41                       JB42 JB45 JC04 JC11 JC12                       LB09 LB13 MA03 MA04 NA02                       NA09 NA13 PA01 PA02 PB13

Claims (11)

[Claims] 1. An image carrier, developing means for developing an electrostatic latent image formed on the image carrier according to an image signal with a developer, and a developed image developed by the developing means is transferred. A transfer material carrier for holding a transfer material, and a density detecting electrostatic latent image forming means for forming a density detecting electrostatic latent image on the image carrying body; and the developing means for detecting the density. An electrostatic latent image for development to form a developed image for density detection on the image carrier, and further comprising density detecting means around the image carrier for detecting the development density of the developed image for density detection, In an image forming apparatus for controlling an image forming condition based on a development density detected by the density detection means, a portion of the transfer material carrier corresponding to the density detection developed image is discharged or discharged with a developer. An image forming apparatus having the same polarity. 2. A portion of the transfer material carrier, which corresponds to the density-developed developed image, is neutralized or made to have the same polarity as the developer by means of a charge removing means for removing the charge of the transfer material carrier. The image forming apparatus according to claim 1. 3. By applying a transfer bias,
A transfer unit that transfers a developed image from the image carrier to the transfer material on the transfer material carrier is provided, and a bias having a polarity opposite to the transfer bias is applied to the transfer material carrier by the transfer unit. The image forming apparatus according to claim 1, wherein the portion of the transfer material carrier corresponding to the developed image for density detection is neutralized or has the same polarity as the developer. 4. A transfer material carrying member cleaning means is provided,
The developer on the transfer material carrier is removed by the transfer material carrier cleaning means.
The image forming apparatus according to any one of 3 above. 5. The electrostatic latent image on the image carrier is developed by a plurality of developing means of different colors,
The image forming apparatus according to claim 1, which forms a full-color image on the transfer material. 6. A first image carrier, developing means for developing an electrostatic latent image formed on the first image carrier in response to an image signal, and a developed image developed by the developing means. And a second image carrier on which the primary transfer is performed, and the developed image that is primarily transferred on the second image carrier is secondarily transferred to a transfer material on the first image carrier. Has a density detecting electrostatic latent image forming means for forming a density detecting electrostatic latent image, and the developing means develops the density detecting electrostatic latent image on the first image carrier. A density detecting unit that forms a density detecting developed image and further detects a developing density of the density detecting developing image is provided around the first image carrier, and based on the developing density detected by the density detecting unit. An image forming apparatus for controlling image forming conditions by using the second image carrier, which corresponds to the developed image for density detection. That portion of the image forming apparatus, characterized in that the or developer having the same polarity to neutralize. 7. A portion of the second image carrier corresponding to the density-developed developed image is neutralized or made to have the same polarity as that of the developer by a neutralizing unit that neutralizes the second image carrier. The image forming apparatus according to claim 6, wherein the image forming apparatus comprises: 8. A primary transfer unit for primary-transferring a developed image from the first image carrier to the second image carrier by applying a primary transfer bias, and the primary transfer unit is provided with the primary transfer unit. By applying a bias having a reverse polarity to the primary transfer bias to the second image carrier, the portion of the second image carrier corresponding to the density detection developed image is discharged or developed. The image forming apparatus according to claim 6, which has the same polarity as that of the agent. 9. A secondary transfer means for secondarily transferring a developed image from the second image bearing member onto a transfer material by applying a secondary transfer bias, the secondary transfer means comprising:
9. The image forming apparatus according to claim 6, 7, or 8, wherein a portion of the second image carrier corresponding to the developed image for density detection is neutralized or has the same polarity as a developer. 10. A second image carrier cleaning means is further provided, and the developer on the second image carrier is removed by the second image carrier cleaning means. The image forming apparatus according to any one of 6 to 9. 11. An electrostatic latent image on the first image bearing member is developed by a plurality of developing units of different colors, and developed images of a plurality of colors are formed on the first image bearing member. Further, the developed images of the plurality of colors are sequentially superposed on the second image bearing member and primary-transferred to form a composite developed image on the second image bearing member. The image forming apparatus according to any one of claims 6 to 10, wherein an image is secondarily transferred onto a transfer material in a batch to form a full-color image on the transfer material.