JP2001228699A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce toner consumption without lowering an image quality. SOLUTION: Relating to this image forming device, useless consumption of the toner is suppresed by saving the toner contributing to the development of the toner image without lowering the image quality, by controlling developing contrast potential decided by the difference between developing bias potential applied to a developing sleeve 4a and the surface potential to a photosensitive belt 1 imparting the maximum image density by the control device 12, based on the reflection density information and the transmission density information of a patch pattern (density gradation pattern) 13 formed on the photosensitive belt 1 being respectively inputted from a reflection density sensor 10 and the transmission density sensor 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, etc., which forms an image by an electrophotographic system or an electrostatic recording system.

[0002]

2. Description of the Related Art In recent years, the demand for electrophotographic copying machines and printers has increased, and the amount of developer (toner) consumed has also increased. On the other hand, energy conservation and reduction of waste are strongly demanded due to problems such as resource depletion and waste disposal. Under these circumstances, it has become an important issue to reduce the consumption of developer (toner) in copiers, printers, facsimile machines, etc. of electrophotographic and electrostatic recording systems. In addition to the response, running costs will be reduced for users.

In general, an electrophotographic image forming apparatus forms an electrostatic latent image on an image carrier by uniformly charging the image carrier and then performing image exposure using an analog exposure or a semiconductor laser or an LED. After that, this is visualized as a developer image by a developing device, and after this visible image is transferred to a transfer material, the transfer material is separated from the image carrier and output as an image fixed by a fixing device. Are known.

FIG. 12 is a schematic configuration diagram showing a conventional electrophotographic image forming apparatus. This image forming apparatus has a photosensitive drum 100 as an image carrier, and a photosensitive drum 1
00 is a photoconductive layer such as OPC or a-Si on the surface (not shown)
And driven to rotate at a predetermined process speed in the direction of arrow a. The surface of the photosensitive drum 100 is
1 is uniformly charged to, for example, -700V. And
The surface potential of the exposed portion on the photosensitive drum 100 is changed by the image exposure L on the uniformly charged surface of the photosensitive drum 100 using light modulated according to an image signal output from the exposure device (laser scanner device) 102. For example, the voltage is attenuated to −200 V, and an electrostatic latent image corresponding to image information is formed on the photosensitive drum 100. For the image exposure L, for example, a semiconductor laser or an LED array is used.

Then, the electrostatic latent image is developed by a developing sleeve 103a of the developing device 103 and is visualized as a toner image. The developing device 103 includes two-component development using a carrier and jumping development using a magnetic one-component developer. At the time of development, the developing sleeve 103a has, for example,
A DC bias of about V is applied to invert (or regular) develop the electrostatic latent image. Thereafter, if necessary, a pre-transfer process is performed using a charger (not shown) (usually, a corona is applied by DC or AC, or a combination of light elimination and the like is applied) to form the image on the surface of the photosensitive drum 100. The toner image is transferred by the transfer charger 104 onto the transfer material P supplied to the transfer nip. The transfer material P on which the toner image has been transferred is conveyed to a fixing nip portion between the fixing roller 105a and the pressure roller 105b of the fixing device 105, and the toner image is transferred by heating and pressing by the fixing roller 105a and the pressure roller 105b. The sheet P is thermally fixed on the surface of the sheet P and is discharged to the outside, thereby completing a series of image forming operations.

The photosensitive drum 100 after the transfer of the toner image
The transfer residual toner remaining on the surface is cleaned by the cleaning device 1
06 and removed and collected to prepare for the next image formation.

In the above-described image forming apparatus, as a technique for reducing the amount of toner consumed in the developing process of the developing device 103, for example, a toner save mode is provided in the image forming apparatus, and a user operates the image forming apparatus when forming an image. A method of reducing the toner density by selecting a toner save mode is known (for example,
JP-A-6-348094, JP-A-7-16015
No. 0).

[0008]

When an image is formed by selecting the toner save mode in order to reduce the toner consumption as described above, the toner consumption is reduced because the toner consumption is reduced. The line density of the image becomes lower than usual. For this reason, although it is effective as a test copy or a print only for the purpose of recognizing characters, it is not very effective as a normal business distribution document for printing a large amount. In the related art, fine adjustment of the image density in the toner save mode has to be manually performed by the user from time to time, and there is a problem that it is difficult to use.

Accordingly, it is an object of the present invention to provide an image forming apparatus capable of saving toner consumption without deteriorating image quality.

[0010]

According to the present invention, there is provided an image forming apparatus for developing an electrostatic latent image formed on a first image bearing member into a visible image as a developer image. In the apparatus, a detection image forming unit that forms a toner image for density detection on the first image carrier, and a detection image forming unit that detects the toner image for density detection or the first image carrier on the first image carrier. Reflection density information detection means for detecting reflection density information of the density detection toner image transferred onto the second image carrier;
Transmission density information detecting means for detecting transmission density information of the density detection toner image on the image carrier or the density detection toner image transferred from the first image carrier to the second image carrier. Providing a developing bias potential and a maximum image density based on reflection density information and transmission density information of the density detection toner image input from the reflection density information detecting means and the transmission density information detecting means, respectively. And control means for controlling a development contrast potential determined by a difference from the surface potential of the image carrier.

The difference between the surface potential of the first image carrier and the developing bias potential when the transmission density of the density detecting toner image is equal to or higher than the reflection density is defined as the developing contrast potential. Features.

Further, the present invention is characterized in that the gradation of the output developer image is corrected together with the control of the developing contrast potential.

Further, the invention is characterized in that the control of the development contrast potential is performed every predetermined number of image formations.

Further, the control of the development contrast potential is performed when the power of the image forming apparatus is turned on.

Further, the first image bearing member is an endless belt-shaped photosensitive member capable of transmitting light.

Further, the second image bearing member contacts the first image bearing member, adsorbs a transfer material to a peripheral surface, and transfers a developer image formed on the first image bearing member. The peripheral surface is a light-transmissible transfer material carrier.

Further, the second image carrier is brought into contact with the first image carrier to temporarily transfer the developer image formed on the first image carrier once to the transfer material, and then to the transfer material. Next transfer,
The peripheral surface is an intermediate transfer member capable of transmitting light.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the illustrated embodiments.

<First Embodiment> FIG. 1 is a schematic configuration diagram showing an image forming apparatus according to a first embodiment of the present invention. This image forming apparatus uses an endless belt-shaped photosensitive member (hereinafter, referred to as a photosensitive belt) 1 as an image carrier. The photosensitive belt 1 is an OPC belt capable of transmitting light, is stretched between a driving roller 9a and three support rollers 9b, 9c, 9d, and is moved in the direction of arrow a by driving of the driving roller 9a.

Around the photosensitive belt 1, a primary charger 2,
An exposure device 3, a developing device 4, a transfer charger 5, a separation charger 6, and a cleaning roller 7 are provided. A fixing device 8 having a fixing roller 8a and a pressure roller 8b is provided downstream of the separation charger 6 in the moving direction of the transfer material P.
Further, between the support rollers 9b and 9c of the photosensitive belt 1, a reflection density sensor 10 for detecting the reflection density of a later-described density gradation pattern (hereinafter, referred to as a patch pattern; see FIG. 5) formed on the photosensitive belt 1 is provided. And a transmission density sensor 11 for detecting the transmission density of the patch pattern (details of the reflection density sensor 10 and the transmission density sensor 11 will be described later).

Reflection density sensor 10 and transmission density sensor 11
Is connected to a control device (CPU) 12. The control device 12 is based on the reflection density information and the transmission density information of the patch pattern on the photosensitive belt 1 detected by the reflection density sensor 10 and the transmission density sensor 11, respectively. The developing contrast potential (the difference between the developing bias potential applied to the developing sleeve 4a of the developing device 4 and the surface potential of the photosensitive belt 1 that gives the maximum image density) is controlled to suppress toner consumption. See below).

The primary charger 2 charges the surface of the photosensitive belt 1 to a predetermined potential and polarity by corona ions generated by corona discharge. The exposure device (LED device) 3 performs image exposure L on the surface of the photosensitive belt 1 with LED light modulated according to a time-series electric digital pixel signal of image information input from a personal computer (not shown). An electrostatic latent image corresponding to image information is formed on the surface of the photosensitive belt 1 charged by the primary charger 2. The exposure device 3
For example, a semiconductor laser element can be used other than the LED. The developing device 4 uses a two-component developer including a toner and a carrier, and reversely develops the electrostatic latent image with a developing sleeve 4a. The developing sleeve 4a is supplied with, for example, a peak-to-peak voltage of 1.5K from a developing bias power supply (not shown).
V, a frequency of 2.7 KHz, and a developing bias in which a DC voltage of -550 V is superimposed on an AC voltage of a rectangular wave having a duty of 50%. The alternating current has, for example, a waveform as shown in FIG.

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

At the time of image formation, the photosensitive belt 1 is moved (rotated) at a predetermined process speed by driving the driving roller 9a, and in the course of the movement, the surface of the photosensitive belt 1 is, for example, −680 V (dark portion potential) by the primary charger 2. )
Is uniformly charged. Then, the charged photosensitive belt 1
An electrostatic latent image corresponding to the image information is formed on the surface by image exposure L using LED light output from the exposure device 3 and modulated according to an image signal input from a personal computer (not shown). . In the present embodiment, the image exposure L is performed by a LED of 600 dpi, and the wavelength is 680 nm. The surface potential of the photosensitive belt 1 on which the electrostatic latent image is formed is, for example, a maximum density portion (FFH).
At -200V.

The developer (toner) is applied to the electrostatic latent image on the photosensitive belt 1 by the developing sleeve 4a of the developing device 4 to which the developing bias is applied, and is developed as a toner image (visualization). I do. Then, a voltage obtained by superimposing an AC voltage on a DC voltage is applied from a charger (not shown) to the toner image on the photosensitive belt 1 to optimize the toner tribo. Then, a transfer material P such as a sheet fed from a cassette (not shown) by a sheet feed roller (not shown) moves to a transfer nip portion between the toner image on the photosensitive belt 1 and the transfer charger 5. The toner image on the photosensitive belt 1 is transferred onto the transfer material P by the transfer charger 5 at the timing.

The transfer material P onto which the toner image has been transferred is separated from the photosensitive belt 1 by the charging of the separation charger 6 and the curvature of the photosensitive belt 1. Then, the transfer material P peeled from the photosensitive belt 1 is transported to the fixing device 8, and
The toner image is heated and pressed at the fixing nip portion between the fixing roller 8a and the pressing roller 8b of the fixing device 8 to thermally fix the surface of the transfer material P, and then discharged outside to complete a series of image forming operations. At the time of the above-described transfer, the transfer residual toner remaining on the photosensitive belt 1 is removed by the cleaning roller 7.
And is subjected to the next image forming process.

Next, the configurations of the reflection density sensor 10 and the transmission density sensor 11 will be described.

As shown in FIG. 3, the reflection density sensor 10 includes a light emitting element 10a and a light receiving element 10b.
The light emitted from the light emitting element 10a is
c, the light is reflected on a patch pattern (density gradation pattern) 13 formed on the photosensitive belt 1 through the transparent belt 10c, and the reflected light is received by the light receiving element 10b through the transparent acrylic plate 10c to detect the reflection density. .

On the other hand, as shown in FIG. 4, the transmission density sensor 11 has a light emitting element 11a and a light receiving element 11b, and the light emitted from the light emitting element 11a is formed on the surface of the light transmitting element 11 through the transparent photosensitive belt 1. Patch pattern 13
Is transmitted, and the transmitted light is received by the light receiving element 11b to detect the transmission density. The reflection density sensor 10 outputs a value obtained by subtracting the reflection density of the photosensitive belt 1 and the transparent acrylic plate 10c, which are measured in advance, from the detected reflection density of the patch pattern 13, and the transmission density sensor 11 detects the value. A value obtained by subtracting the previously measured transmission density of the photosensitive belt 1 from the transmission density of the patch pattern 13 is set as an output value.

FIG. 5 is a diagram showing an example of the patch pattern 13. For the sake of simplicity, it is assumed that the patch pattern 13 is a seven-step gradation pattern. This patch pattern 13 is, for example, 7 patterns from 0 to 25.
When expressed in hexadecimal notation among the 5 levels, A0H, B0
H, C0H, D0H, E0H, F0H, and FFH.
Further, in the present embodiment, L emitted from exposure apparatus 3
In order to change the amount of ED light (image exposure L), the potential of the photosensitive belt 1 is not at equal intervals, but is approximately 20 V at 10 H as a guide.

The image exposure L by the LED light from the exposure device (LED section) 3 is controlled by an image signal control section 20 shown in FIG. The image signal control unit 20 includes the signal processing unit 2
1, γ correction unit 22, LUT calculation unit 23, binary unit 24, pattern generator 25, CPU 26, ROM 27, R
AM28 is provided.

In the image signal control section 20, a signal processing section 21 performs image processing desired by a user such as resolution conversion on an image signal input from a host computer (not shown). For the processed image signal, a look-up table (LUT) 22a
Is performed with reference to. The binary section 24 generates a drive signal for the exposure device (LED section) 3 based on the image signal after the γ correction, and the exposure apparatus (LED section) 3 causes the LED to emit light based on the drive signal to generate an image. Exposure L is performed.

The LUT calculation unit 23 is provided with the reflection density sensor 10
And patch pattern 1 input from transmission density sensor 11
3, a developing contrast potential is determined according to the density detection value,
At the same time, the look-up table (LU
T) 22a is newly calculated and updated as appropriate in the current operating environment. Pattern generator 25
Holds the image data of the sample pattern in advance and outputs the image data to the binary section 24. In addition, the CPU 26
The image signal control unit 20 is generally controlled based on a control program and the like stored in M27. RAM 28
Used as a work area of the CPU 26.

In the present embodiment, an appropriate gradation correction (for example, γ correction, etc.) is performed in addition to an appropriate development contrast potential that can reduce the toner consumption without deteriorating the image quality, which will be described later. Then, the obtained tone characteristic is an ideal density reproduction curve (TRC; tone reprod).
LUT calculation unit 23 to look up table (LU)
T) Update 22a. The TRC is, for example, R
It is stored in the OM 27.

Here, before describing the operation of reducing toner consumption by the development contrast potential control of the present invention, excess toner consumption in a conventional image forming apparatus will be described.

FIG. 7A is a diagram showing the relationship between the conventional development contrast potential (Vcont) and the reflection density.
(B) is a diagram showing the relationship between the development contrast potential and the transmission density in the related art. Each of the reflection densities in FIGS. 7A and 7B includes the density of the paper that is the transfer material P, and FIG. 7C illustrates the case where the density of the paper (the transfer material P) is subtracted. FIG. 5 is a diagram illustrating a relationship between a development contrast potential and a density (reflection density, transmission density). Specifically, it is a value obtained by subtracting 0.08 for the reflection density and 0.5 for the transmission density. In FIG. 7C, the reflection density shows a saturation characteristic (range A in the figure) where the development contrast potential is high. This saturation means that the image density looks almost the same to the user.

On the other hand, the transmission density almost increases with the development contrast potential. This means that the toner amount increases substantially with the development contrast potential. That is, as shown in FIG. 8, surplus toner 14a (hatched portion) not reflected in the reflection density is placed on the toner 14 formed on the transfer material (paper) P. The surplus toner 14a consumes extra toner.

Therefore, in the present invention, the reflection density sensor 10
And the photosensitive belt 1 respectively detected by the transmission density sensor 11
The development contrast potential is controlled based on the reflection density information and the transmission density information of the upper patch pattern 13 to reduce the excess toner.

Next, control of the development contrast potential for reducing the excess toner in this embodiment will be described.

When the operation for detecting the toner density is started, the photosensitive belt 1 is moved by driving the drive roller 9a, and the patch pattern (see FIG. 5) is formed on the photosensitive belt 1 in the same manner as the toner image forming operation described above. 13 are formed. The patch pattern 13 is formed at a position facing the reflection density sensor 10 and the transmission density sensor 11 on the photosensitive belt 1 so as to be aligned along the moving direction of the photosensitive belt 1. Then, the reflection density Da and the transmission density Db of the patch pattern 13 formed on the photosensitive drum 1 are detected by the reflection density sensor 10 and the transmission density sensor 11, respectively.

At this time, the value of the transmission density Db is equal to the reflection density Da.
Is the maximum contrast potential when the value exceeds the value for the first time. Specifically, development contrast potential (Vcont) and density (reflection density, transmission density)
In the present embodiment, the relationship shown in FIG. 9 was obtained. As is clear from FIG. 9, the reflection density reaches saturation at a certain value (1.3 in the figure), while the transmission density keeps increasing. The region where the reflection density reaches saturation is a region that sufficiently satisfies the user's requirements, and the fact that the transmission density continues to increase means that excess toner is attached. Note that the densities (reflection densities and transmission densities) shown in FIG. 9 are the densities of the patch pattern 13 with respect to the video signal that is the image information signal. This is an example, and A0H to FFH shown in FIG. 5 are actually used.

The controller 12 calculates the difference between the reflection density information and the transmission density information (see FIG. 9) input from the reflection density sensor 10 and the transmission density sensor 11, and calculates the transmission density D.
The difference between the maximum contrast potential when b> reflection density Da and the developing bias potential applied to the developing sleeve 4a is controlled to be the developing contrast potential. Specifically, the maximum contrast potential is about -295 from FIG.
V and the developing bias potential are −550 V as described above, and the developing contrast potential is the normal −350 V before control.
It became -255V from V. Further, an output signal (here, C0H) when the transmission density Db> the reflection density Da is obtained,
The maximum output of the exposure device 3 was set.

As for the reflection density Da and the transmission density Db, the reflection density Da1 and the transmission density Db1 of only the photosensitive belt 1 are detected in advance, and then the patch pattern 1 is detected.
3, the reflection density Da2 and the transmission density Db2 are detected, and the reflection density Da (= Da2−Da1) and the transmission density Db
(= Db2-Db1) was determined.

By controlling the developing contrast potential, the reflection density of the patch pattern 13 is 1.3 on the photosensitive belt 1, and the reflection density is 1.4 in the actual output image.
While maintaining the development contrast potential. Further, when the development contrast potential is changed, tone correction (for example, γ correction, etc.) is newly set for an image signal input in accordance with the change.

In the above-described image forming apparatus using the photosensitive belt 1, when the above-described developing contrast potential is controlled to output an A4 image having an image ratio of 6%, the toner consumption is normally 50 mg per sheet. 40mg
Approximately 20% of toner was saved. As described above, by performing the development contrast potential control of the present embodiment, the amount of toner consumption can be reduced without lowering the image quality, so that the running cost can be reduced.

The timing of performing the above-described development contrast potential control is, for example, because the potential of the photosensitive belt 1 and the charged state of the toner often differ between morning and evening. When the power of the image forming apparatus is turned on and the number of formed images is, for example, every 2,000 sheets, an image having good image quality and density can be obtained, and excess toner can be effectively reduced.

<Second Embodiment> FIG. 10 is a schematic configuration diagram showing an image forming apparatus according to a second embodiment of the present invention.
The image forming apparatus according to the present embodiment includes a drum type electrophotographic photosensitive member (hereinafter, referred to as a photosensitive drum) 30 as an image carrier.
Is formed by transferring the toner image formed on the transfer material P adsorbed on a transfer drum 34 as a transfer material carrier to obtain an image.

Around the photosensitive drum 30, a primary charger 3
1, an exposure device 32, a developing device 33, a transfer drum 34, and a cleaning roller 35 are provided. Photosensitive drum 3
Numeral 0 denotes a negatively charged OPC photoreceptor having a photoreceptor layer on a conductive drum substrate made of aluminum or the like, which is driven to rotate at a predetermined peripheral speed in the direction of arrow a.
The secondary charger 31 receives a uniform charge of negative polarity. The primary charger 31 charges the surface of the photosensitive drum 30 to a predetermined potential and polarity by corona ions generated by corona discharge. The exposure device (LED device) 32 performs image exposure L on the surface of the photosensitive drum 30 with LED light modulated according to a time-series electric digital pixel signal of image information input from a personal computer (not shown), thereby An electrostatic latent image corresponding to image information is formed on the surface of the photosensitive drum 30 charged by the next charger 31. In addition, as the exposure device 32,
Semiconductor laser elements other than LEDs can be used.

The developing device 33 includes a yellow developing device 33a,
A magenta developing device 33b, a cyan developing device 33c, and a black developing device 33d are supported by a rotating body 33A rotatable in the direction of arrow b. The electrostatic latent image formed on the surface of the photosensitive drum 30 is reversely developed to be visible. Imaging (visualization). In the present embodiment, the yellow developing device 33a and the magenta developing device 33
The b, cyan developing device 33c and black developing device 33d use a two-component developer composed of toner and carrier, and develop in the order of yellow, magenta, cyan, and black. Each of the yellow developing device 33a, the magenta developing device 33b, the cyan developing device 33c, and the black developing device 33d receives, for example, a peak-to-peak voltage of 2.5 KV from a developing bias power supply (not shown).
A developing bias in which a -550 V DC voltage is superimposed on a rectangular wave AC voltage having a frequency of 2.0 KHz and a duty of 35% is applied.

The transfer drum 34 has a transfer sheet (not shown) made of a transparent resin film stretched over its surface.
The photosensitive drum 30 is installed so as to be able to contact and separate therefrom. The transfer drum 34 is rotated in the direction of arrow c. Around the transfer drum 34, a transfer charger (not shown), an adsorption charger, a cleaning roller, and the like are provided. Also,
Around the transfer drum 34, a reflection density sensor 10 for detecting the reflection density of a patch pattern (see FIG. 5) formed on the photosensitive drum 30 transferred onto a transfer sheet (not shown) of the transfer drum 34; A transmission density sensor 11 for detecting the transmission density of the patch pattern is provided. The configurations of the reflection density sensor 10 and the transmission density sensor 11 are the same as those in the above-described first embodiment, and a description thereof will be omitted in this embodiment.

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

At the time of image formation, the photosensitive drum 30 is rotated at a predetermined process speed by driving of a driving device (not shown), and during the moving process, the surface of the photosensitive drum 30 is, for example, −680 V (dark potential) by the primary charger 31. )
Is uniformly charged. Then, the charged photosensitive drum 3
On the surface 0, the first color toner image of the target color image is formed by image exposure L using LED light output from the exposure device 32 and modulated according to an image signal input from a personal computer (not shown). In this embodiment, an electrostatic latent image corresponding to the yellow toner image is formed. In the present embodiment, the image exposure L is performed by a LED of 600 dpi, and the wavelength is 680 nm. The surface potential of the photosensitive drum 30 on which the electrostatic latent image is formed is, for example, -200 V at the maximum density portion (FFH). And
The electrostatic latent image is reversely developed by the yellow developing device 33a of the developing device 33, and is visualized as a yellow toner image.

On the other hand, in synchronization with the formation of the yellow toner image on the photosensitive drum 30, a transfer material P such as paper is fed to the transfer drum 34 at a predetermined timing, and is transferred by an attraction charger (not shown). The material P is electrostatically attracted onto a transfer sheet (not shown) on the surface of the transfer drum 34. Transfer drum 3
The transfer material P electrostatically attracted to the surface of the transfer material P is moved to a position facing the photosensitive drum 30 by rotation of the transfer drum 34 in the direction of arrow c, and toner is transferred to the rear side of the transfer material P by a transfer charger (not shown). And a yellow toner image on the surface of the photosensitive drum 30 is transferred to the front side.
After the transfer, the transfer residual toner remaining on the surface of the photosensitive drum 30 is removed by the cleaning roller 35.

Thereafter, similarly, the electrostatic latent images corresponding to the respective colors (magenta, cyan, black) of the second, third, and fourth colors are respectively processed by the magenta developing device 33b and the cyan developing device 3 respectively.
3c, a magenta toner image which is reversely developed by the black developing device 33d and sequentially formed on the surface of the photosensitive drum 30;
The cyan toner image and the black toner image are transferred to the transfer drum 34.
A transfer charger (not shown) sequentially superimposes and transfers the toner image on the transfer material P on which the yellow toner image on the surface is transferred, thereby forming a full-color image. Then, the transfer material P on which the full-color image is formed is separated from the transfer drum (transfer sheet) 34 by the charging of the separation charger 36 and the curvature of the transfer drum 34, and the separated transfer material P is transported to the fixing device 37. . Transfer material P conveyed to fixing device 37
Are the fixing roller 37a and the pressure roller 37 of the fixing device 37.
After the full-color image is fixed on the surface by heating and pressurizing during the period b, the image is discharged to the outside and a series of image forming operations is completed.

Next, the control of the development contrast potential for reducing the excess toner in the present embodiment will be described.

When the operation of detecting the toner density is started, the photosensitive drum 30 and the transfer drum 34 are driven to rotate by the driving of a driving device (not shown), and the photosensitive drum 30 is placed on the photosensitive drum 30 in the same manner as the toner image forming operation described above. The above-mentioned patch pattern (see FIG. 5) 13 is formed. This patch pattern 13
Is transferred onto a transfer sheet (not shown) of the transfer drum 34. Then, the reflection density sensor 10 and the transmission density sensor 1
1, the patch pattern 1 formed on the transfer drum 34
3, the reflection density Da and the transmission density Db are detected.

At this time, the value of the transmission density Db is equal to the reflection density Da.
Is the maximum contrast potential when the value exceeds the value for the first time. Here, A0 is a video signal.
H. In the present embodiment, as in the first embodiment, the reflection density sensor 10 and the transmission density sensor 11 are used.
The difference between the reflection density information and the transmission density information input from the controller is calculated by a control device (not shown), and the transmission density Db> the reflection density Da
Contrast potential and developing sleeve 4a when
Is controlled so as to become a development contrast potential. Specifically, in the present embodiment, for example, the maximum contrast potential is about -300
V and the developing bias potential are −550 V as described above, and the developing contrast potential is the normal −350 V before control.
From -V to -250V.

When measuring the reflection density Da and the transmission density Db on the transfer drum 34, the transfer material (paper) P is adsorbed on the transfer drum 34, and the reflection density sensor 10 and the transmission density sensor 11 are first operated. When passing, transfer material (paper) P
Only the reflection density Da1 and the transmission density Db1 of the patch pattern 13 are measured, and then the reflection density Da2 and the transmission density Db2 of the patch pattern 13 with the toner thereon are measured.
a (= Da2-Da1) and transmission density Db (= Db2-D)
b1).

As described above, in this embodiment, since the development contrast potential is controlled by the reflection density information and the transmission density information of the toner including the transfer material (paper) P on the transfer drum 34, the user can use it. It is possible to control the amount of toner reflecting the water content of the transfer paper, the transfer efficiency, and the like in accordance with the state of the transfer paper.

Then, in the image forming apparatus, the developing contrast potential is controlled to control the image ratio A to 6%.
When four images were output, the consumption of toner, which was normally 50 mg per sheet, became 40 mg, and about 20% of toner was saved. By performing the development contrast potential control of the present embodiment in this manner, even in a full-color image forming apparatus, the consumption of toner for four colors can be reduced without deteriorating the image quality, so that the running cost can be reduced. .

The timing for controlling the development contrast potential in the above-described embodiment is set only when the power of the image forming apparatus is turned on (usually the first turn on in the morning).

<Embodiment 3> FIG. 11 is a schematic configuration diagram showing an image forming apparatus according to Embodiment 3 of the present invention.
Members having the same functions as those of the image forming apparatus according to the second embodiment are denoted by the same reference numerals, and redundant description will be omitted. In the image forming apparatus according to the present embodiment, the toner image formed on the photosensitive drum 30 as the image carrier is once primarily transferred onto the intermediate transfer drum 38 as the intermediate transfer body, and then secondarily transferred onto the transfer material P. This is a configuration for obtaining an image.

Around the photosensitive drum 30, a primary charger 3
1, exposure device 32, developing device 33, intermediate transfer drum 3
8. A cleaning roller 35 is provided. The intermediate transfer drum 38 has an elastic layer (not shown) made of a medium-resistance rubber or the like on the surface of a drum base (not shown) made of aluminum or the like, and comes into contact with the photosensitive drum 30 at the primary transfer portion N. , And is opposed to the transfer charger 39 at the secondary transfer section M. The intermediate transfer drum 38 is rotated in the direction of arrow c. The intermediate transfer drum 3 is provided around the intermediate transfer drum 38.
A reflection density sensor 10 for detecting a reflection density of a patch pattern (see FIG. 5) formed on a photosensitive drum 30 transferred onto the photosensitive drum 8, a transmission density sensor 11 for detecting a transmission density of the patch pattern, and a cleaning roller (Not shown) are arranged. The configurations of the reflection density sensor 10 and the transmission density sensor 11 are the same as those in the above-described first embodiment, and a description thereof will be omitted in this embodiment. Note that the intermediate transfer drum 38 of the present embodiment is
A transparent member (not shown) is provided in the circumferential direction where the and the transmission density sensor 11 are located so as to transmit light.

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

At the time of image formation, the photosensitive drum 30 is rotated at a predetermined process speed by driving of a driving device (not shown), and during the moving process, the surface of the photosensitive drum 30 is, for example, −680 V (dark potential) by the primary charger 31. )
Is uniformly charged. Then, the charged photosensitive drum 3
On the surface 0, the first color toner image of the target color image is formed by image exposure L using LED light output from the exposure device 32 and modulated according to an image signal input from a personal computer (not shown). In this embodiment, an electrostatic latent image corresponding to the yellow toner image is formed. In the present embodiment, the image exposure L is performed by a LED of 600 dpi, and the wavelength is 680 nm. The surface potential of the photosensitive drum 30 on which the electrostatic latent image is formed is, for example, -200 V at the maximum density portion (FFH). And
The electrostatic latent image is reversely developed by the yellow developing device 33a of the developing device 33, and is visualized as a yellow toner image. The yellow developing unit 33a receives a rectangular wave AC voltage of, for example, a peak-to-peak voltage of 2.5 KV, a frequency of 2.0 KHz, and a duty of 35% from a developing bias power supply (not shown).
A developing bias on which a DC voltage of 550 V is superimposed is applied.

This yellow toner image is primarily transferred to the surface of the intermediate transfer drum 38 rotating at the primary transfer portion N. The transfer residual toner remaining on the surface of the photosensitive drum 30 after the primary transfer is removed by the cleaning roller 35. Hereinafter, similarly, the respective electrostatic latent images corresponding to the respective colors (magenta, cyan, and black) of the second, third, and fourth colors are reversely developed by the magenta developing device 33b, the cyan developing device 33c, and the black developing device 33d, respectively. Then, a magenta toner image, a cyan toner image, and a black toner image sequentially formed on the surface of the photosensitive drum 30 are sequentially superimposed and transferred on the yellow toner image transferred on the surface of the intermediate transfer drum 38, and a full-color image is formed. It is formed.

The transfer material P is transferred by a registration roller (not shown) at the timing when the leading end of the full-color image transferred (primary transfer) to the surface of the intermediate transfer drum 38 is moved to the secondary transfer portion M. The sheet is conveyed to the secondary transfer section M, and a secondary transfer bias (in the opposite polarity to the toner) is applied to the rear surface of the transfer material P by the transfer charger 39 to transfer the full-color image to the surface of the transfer material P at once (secondary transfer). ). The transfer material P on which the full-color image has been transferred is conveyed to the fixing device 37, where the full-color image is heated and pressurized at a fixing nip portion between the fixing roller 37a and the pressure roller 37b and thermally fixed on the surface of the transfer material P, and then externally The image is discharged, and a series of image forming operations ends.

Next, the control of the development contrast potential for reducing the excess toner in the present embodiment will be described.

When the operation for detecting the toner density is started, the photosensitive drum 30 and the intermediate transfer drum 38 are driven to rotate by the driving of a driving device (not shown), and the photosensitive drum 30 is rotated on the photosensitive drum 30 in the same manner as the toner image forming operation described above. Then, the above-mentioned patch pattern (see FIG. 5) 13 is formed. This patch pattern 1
3 is transferred onto the intermediate transfer drum 38. Then, the reflection density Da and the transmission density Db of the patch pattern 13 formed on the intermediate transfer drum 38 are detected by the reflection density sensor 10 and the transmission density sensor 11, respectively.

At this time, the value of the transmission density Db is equal to the reflection density Da.
Is the maximum contrast potential when the value exceeds the value for the first time. Here, A0 is a video signal.
H. In the present embodiment, as in the first embodiment, the reflection density sensor 10 and the transmission density sensor 11 are used.
The difference between the reflection density information and the transmission density information input from the controller is calculated by a control device (not shown), and the transmission density Db> the reflection density Da
Contrast potential and developing sleeve 4a when
Is controlled so as to become a development contrast potential. Specifically, in the present embodiment, for example, the maximum contrast potential is about -300
V and the developing bias potential are −550 V as described above, and the developing contrast potential is the normal −350 V before control.
From -V to -250V.

The reflection density D on the intermediate transfer drum 38
a and the transmission density Db, the reflection density Da1 of only the intermediate transfer drum 34 where no toner is loaded
And the transmission density Db1, and then the patch pattern 13
Density Da2 and transmission density D with the toner
b2 is measured, and the difference is referred to as the reflection density Da (= Da2-Da).
1) and the value of the transmission density Db (= Db2−Db1).

With this control, the present control is further performed for each predetermined number of sheets without performing test printing when the power of the image forming apparatus is turned on (usually the first turn on in the morning). It is possible to eliminate waste and control the toner amount and the image density accurately.

In the image forming apparatus, the developing contrast potential is controlled to control the image ratio of A to 6%.
When four images were output, the consumption of toner, which was normally 48 mg per sheet, became 39 mg, and about 20% of toner was saved. By performing the development contrast potential control of the present embodiment in this manner, even in a full-color image forming apparatus, the consumption of toner for four colors can be reduced without deteriorating the image quality, so that the running cost can be reduced. .

[0074]

As described above, according to the present invention, development is performed based on the reflection density information and the transmission density information of the density detecting toner image input from the reflection density information detecting means and the transmission density information detecting means, respectively. By controlling the developing contrast potential determined by the difference between the developing bias potential applied to the means and the surface potential of the first image carrier that gives the maximum image density, the developer image can be developed without deteriorating the image quality. Since the amount of developer to be used can be reduced and wasteful consumption of the developer can be suppressed, the running cost can be reduced.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing a waveform of a developing bias.

FIG. 3 is a diagram showing a reflection density sensor.

FIG. 4 is a diagram showing a transmission density sensor.

FIG. 5 is a diagram showing an example of a patch pattern.

FIG. 6 is a block diagram showing a control system of the exposure apparatus.

7A is a diagram illustrating a relationship between a development contrast potential and a reflection density, FIG. 7B is a diagram illustrating a relationship between a development contrast potential and a transmission density, and FIG. FIG. 9 is a diagram illustrating a relationship between a development contrast potential, a reflection density, and a transmission density when subtraction is performed.

FIG. 8 is a view for explaining useless toner on a transfer material.

FIG. 9 is a diagram illustrating a relationship between a development contrast potential and a reflection density and a transmission density according to the first embodiment.

FIG. 10 is a schematic configuration diagram showing an image forming apparatus according to Embodiment 2 of the present invention.

FIG. 11 is a schematic configuration diagram showing an image forming apparatus according to Embodiment 3 of the present invention.

FIG. 12 is a schematic configuration diagram showing an image forming apparatus in a conventional example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Photosensitive belt (first image carrier) 2, 31 Primary charger (detection image forming means) 3, 32 Exposure device (detection image forming means) 4, 33 Developing device (detection image forming means) 5, 39 Transfer Charger 8, 37 Fixing device 10 Reflection density sensor (reflection density information detection means) 10a, 11a Light emitting element 10b, 11b Light reception element 11 Transmission density sensor (transmission density information detection means) 12 Control device (control means) 13 Patch pattern ( Density detection toner image) 20 Image signal controller 30 Photosensitive drum (first image carrier) 34 Transfer drum (second image carrier) 38 Intermediate transfer drum (second image carrier)

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H030 AA03 BB34 BB36 BB43 2H032 BA08 CA15 2H073 AA02 BA02 BA23 BA28 BA41 2H077 DA03 DA47 DA63 DA64 DA80 DA82 DB08 DB18 GA12

Claims (8)

[Claims] 1. An image forming apparatus for developing an electrostatic latent image formed on a first image carrier and visualizing the electrostatic latent image as a developer image, wherein a density detection image is formed on the first image carrier. Detection image forming means for forming a toner image; and the density detection toner image on the first image carrier or the density detection transferred from the first image carrier to a second image carrier. Reflection density information detection means for detecting reflection density information of the toner image; and the density detection toner image on the first image carrier or the transfer from the first image carrier to the second image carrier. Transmission density information detecting means for detecting transmission density information of the density detection toner image, reflection density information of the density detection toner image input from the reflection density information detection means and the transmission density information detection means, respectively. Based on the transmission density information, the developing bias potential and And control means for controlling the developing contrast potential determined by the difference between the surface potential of the first image bearing member to provide a large image density, with a, an image forming apparatus characterized by. 2. The development contrast potential is defined as a difference between a surface potential of the first image carrier and a development bias potential when a transmission density of the density detection toner image is equal to or higher than a reflection density. The image forming apparatus according to claim 1, wherein: 3. The image forming apparatus according to claim 1, wherein a gradation correction of an output developer image is performed while controlling the development contrast potential. 4. The image forming apparatus according to claim 1, wherein the control of the developing contrast potential is performed for each predetermined number of image formations. 5. The image forming apparatus according to claim 1, wherein the control of the development contrast potential is performed when the power of the image forming apparatus is turned on. 6. The image forming apparatus according to claim 1, wherein the first image bearing member is a light-transmissible endless belt-shaped photosensitive member. 7. The second image bearing member contacts the first image bearing member, adsorbs a transfer material to a peripheral surface, and transfers a developer image formed on the first image bearing member. The image forming apparatus according to claim 1, wherein the peripheral surface is a light-transmissible transfer material carrier. 8. The image forming apparatus according to claim 1, wherein the second image carrier abuts on the first image carrier, temporarily transfers a developer image formed on the first image carrier, and then transfers the developer image onto the transfer material. The image forming apparatus according to claim 1, 2, 3, 4, or 5, wherein the next transfer is performed, and the peripheral surface is an intermediate transfer body capable of transmitting light.