JP2002244369A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a simple image forming device capable of stably outputting a high-quality image by applying appropriate transfer bias in accordance with the electrified amount of toner. SOLUTION: This image forming device is provided with a latent image carrier carrying a latent image, a developing means to which specified developing bias is applied, whereby a latent image is developed as a toner image, and a transfer means to which specified transfer bias is applied, whereby the toner image is transferred to a recording medium. The device is provided with a transfer control means controlling the value of the transfer bias based on the value of the developing bias.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an electrophotographic system,
Employs image forming methods such as electrostatic recording, ionography, and magnetic recording, and controls image forming devices such as copiers, printers, and facsimile machines that form color and black-and-white images. The present invention relates to an image forming apparatus.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus such as a copying machine or a printer for forming a color or black-and-white image employing this type of electrophotographic system, charging, exposure, development, transfer,
An image based on a toner image is obtained on a recording medium through a predetermined image forming process such as fixing. In this transfer process, there is a close relationship between the charge amount of the toner image (toner constituting the toner image) and the transfer bias applied to the image carrier.

[0003]

For example, when a normal transfer bias is applied when the amount of charge of the toner is lower than usual due to some circumstances, an excessive electric stress is applied to the toner. As a result, the charge amount of the toner may be deteriorated, and in some cases, the charge polarity may be reversed. As a result, the transfer efficiency is reduced, and in some cases, the toner is retransferred in a direction opposite to the original transfer direction. In particular, in an image forming apparatus using a latent image carrier itself or an intermediate transfer member and not having a special cleaning device provided thereon, the re-transferred toner contaminates a charging device and the like, and poor charging of the latent image carrier itself, As a result, problems such as image defects are caused. On the other hand, it is difficult to directly measure the charge amount of the toner.

The present invention has been made in view of such a technical problem, and an object of the present invention is to apply a proper transfer bias in accordance with a charge amount of a toner to stably provide a high-quality image. An object of the present invention is to provide a simple image forming apparatus capable of outputting an image.

[0005]

According to the present invention, there is provided a latent image carrier for carrying a latent image, developing means for applying a predetermined developing bias to develop the latent image as a toner image, and applying a predetermined transfer bias. An image forming apparatus having a transfer unit for transferring the toner image onto a recording medium, the image forming apparatus having a transfer control unit for controlling the value of the transfer bias based on the value of the developing bias.

As a more specific method of controlling the value of the transfer bias based on the value of the developing bias, for example, when the absolute value of the developing bias is smaller than its reference value, the absolute value of the transfer bias becomes smaller. When the absolute value of the developing bias is larger than the reference value, the value of the transferring bias may be changed so that the absolute value of the transferring bias is increased.

Since the developing bias is generally determined by process control (toner density control mode), the developing bias indirectly reflects the charge amount of the toner. Therefore, controlling the value of the transfer bias based on the value of the developing bias results in controlling the value of the transfer bias based on the charge amount of the toner. Such a configuration is simpler and more cost effective than, for example, providing a sensor for measuring the amount of toner charge in the developing unit.

More specifically, the image forming apparatus for performing the process control includes an image forming mode for forming a toner image as an output image and a toner density control mode for forming a toner image (toner patch) as a detection target. And detecting means for detecting the density of the toner image (toner patch) as the detection target, and including the developing bias based on the density of the detected toner image (toner patch) as the detection target. And a process control means for controlling image forming conditions. The image forming conditions include, in addition to the developing bias, image forming parameters (such as the surface potential of the latent image carrier) and toner supply parameters (such as the amount of toner supplied to the developing unit).

Further, the process control (toner density control mode) depends on the difference of the control object and whether the image forming parameter is changed or the toner supply parameter is changed.
First process control (first toner density control mode)
And the second process control (second toner density control mode).

That is, the developing means is a two-component developing means using a toner and a carrier as a developer, and the toner density control mode is performed by changing a toner supply parameter and changing the toner concentration in the two-component developing means. A first toner density control mode for controlling (ratio of toner and carrier) and a second toner density control for controlling the density of a toner image as an output image in the image forming mode (by changing image forming parameters) Mode.

The transfer control means is configured to increase the transfer efficiency in the first toner density control mode in comparison with the second toner density control mode in order to improve the detection accuracy of the detection target. It is preferable to control the value of the transfer bias. Further, the transfer control means also sets the value of the transfer bias in the image forming mode and the second toner density control mode so that the transfer efficiency becomes equal in order to improve the detection accuracy of the detection target. It is preferable to control.

The transfer control means may control the value of the transfer bias based on the value of the developing bias set in the first toner density control mode or the second toner density control mode. The transfer bias value may be controlled based on the developing bias value set in the first toner density control mode and the second toner density control mode. In the image forming mode and the second toner density control mode, the developing bias has a DC component and an AC component, and in the first toner density control mode, the developing bias may have only a DC component. However, in any case, the transfer control unit can change the value of the transfer bias based on the value of the DC component of the developing bias.

In one aspect of the image forming apparatus, the transfer means includes an intermediate transfer member on which a toner image is transferred in opposition to a latent image carrier, and a final transfer member which contacts a recording medium and finally transfers the toner image. In some cases, the transfer control means may independently control the value of the transfer bias applied to each transfer member.
Further, the intermediate transfer member may be configured in a plurality of stages (for example, a primary intermediate transfer member and a secondary intermediate transfer member). Also,
The detection unit may be configured to detect a toner image on the final transfer body.

[0014]

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

FIG. 1 shows a tandem-type full-color printer as an image forming apparatus according to an embodiment of the present invention. In addition, the arrow in FIG. 1 has shown the rotation direction of each rotating member. Hereinafter, the basic configuration of the image forming apparatus and the operation in the image forming mode will be described.

As shown in FIG. 1, this full-color printer has photosensitive drums (image carriers) 11, 12, and 13 for cyan (C), magenta (M), yellow (Y), and black (K). Image forming units 1, 2, 3,
4 and charging rolls for primary charging (contact type charging devices) 21, 22, 23,
24 and laser beams 31, 32, 33, of respective colors of cyan (C), magenta (M), yellow (Y), and black (K).
A laser optical unit (exposure device) (not shown) for irradiating the light, 34, developing devices 41, 42, 43, 44, and two of the four photosensitive drums 11, 12, 13, and 14;
1st primary intermediate transfer drum (intermediate transfer body) that contacts 12
A second primary intermediate transfer drum (intermediate transfer member) 52 that contacts the first and second photosensitive drums 13 and 14; and a secondary intermediate contact drum that contacts the first and second primary intermediate transfer drums 51 and 52. The transfer drum (intermediate transfer body) 53 and the secondary intermediate transfer drum 53
The main part is constituted by a final transfer roll (transfer member) 60 that comes into contact with the transfer roller.

The photosensitive drums 11, 12, 13, and 14 are arranged at regular intervals so as to have a common tangent plane M. Further, the first primary intermediate transfer drum 51 and the second primary intermediate transfer drum 52 have their respective rotating shafts of the photosensitive drums 11, 1.
They are arranged so as to be parallel to the axes 2, 13, and 14 and have a plane object relation with a predetermined object plane as a boundary. Further, the secondary intermediate transfer drum 53 includes the photosensitive drums 11, 12, 13, 14
And the rotation axis are parallel to each other.

A signal corresponding to the image information for each color is rasterized by an image processing unit (not shown) and input to a laser optical unit (not shown). In this laser optical unit, laser beams 31, 3 of cyan (C), magenta (M), yellow (Y), and black (K) are used.
2, 33, 34 are modulated, and the photoconductor drums 11, 1 of the corresponding color are modulated.
Irradiated on 2, 13, 14

Around the photosensitive drums 11, 12, 13, and 14, an image forming process for each color is performed by a known electrophotographic method. First, the photosensitive drums 11, 12, 1
For example, photosensitive drums using an OPC photosensitive member having a diameter of 20 mm are used as the photosensitive drums 3, 14, and these photosensitive drums 11, 12, 13, and 14 are driven to rotate at a rotation speed of, for example, 95 mm / sec. You. The photosensitive drums 11, 12, 13, 14
As shown in FIG. 1, the surface of is charged to about -300 V, for example, by applying a DC voltage of about -840 V to the charging rolls 12, 22, 32, and 42 as contact-type charging devices. The contact-type charging device includes a roll-type charging device, a film-type charging device, and a brush-type charging device, but any type may be used.
In this embodiment, a charging roll generally used in an electrophotographic apparatus in recent years is employed. Further, in this embodiment, in order to charge the surfaces of the photosensitive drums 11, 12, 13, and 14, a charging method of applying only DC is used, but a charging method of applying AC + DC may be used.

Thereafter, the surfaces of the photosensitive drums 11, 12, 13, and 14 are coated with cyan (C), magenta (M), yellow (Y), and black (K) by a laser optical unit as an exposure device (not shown). Laser light 31, corresponding to each color
32, 33, and 34 are irradiated, and an electrostatic latent image corresponding to the input image information for each color is formed. Photoconductor drum 11, 12, 13, 14
In the method, when an electrostatic latent image is written by the laser optical unit, the surface potential of the image exposed portion is eliminated to about -60 V or less.

An electrostatic latent image corresponding to each color of cyan (C), magenta (M), yellow (Y) and black (K) formed on the surface of the photosensitive drums 11, 12, 13, and 14. Are developed by the developing devices 41, 42, 43, and 44 of the corresponding colors, and cyan (C) is formed on the photosensitive drums 11, 12, 13, and 14,
It is visualized as a toner image of each color of magenta (M), yellow (Y), and black (K).

The developing devices 41, 42, 43, and 44 contain toners of cyan (C), magenta (M), yellow (Y), and black (K) toners of different colors and a developer composed of a carrier. Is filled. As the type of toner to be used, pulverized toner or spherical toner can be considered, but in this embodiment, spherical toner is used. In addition, since the irregular shaped toner such as the pulverized toner has a large contact surface with respect to the adhesion surface, the adhesion force is large, and it is difficult to transfer the toner to the surface of the transfer destination. On the other hand, since the spherical toner has a small contact surface with respect to the adhesion surface, the adhesion force is small and the transfer efficiency is high. Further, as a method for producing a spherical toner, a method of subjecting a toner produced by an emulsion polymerization method, a suspension polymerization method, a dissolution suspension method, or a kneading and pulverizing method to a heat treatment is known. Note that the spherical toner means that when the shape factor M1 is represented by the following equation, M1 ≦ 125,
Preferably, M1 ≦ 120. M1 = (π · dmax2 / 4A) × 100, dmax:
Maximum diameter of toner, A: cross-sectional area of toner

When the toner is replenished from a toner replenishing device (not shown), the replenished toner is sufficiently stirred with the carrier by the auger 404 to have a negative polarity. It is triboelectrically charged. Developing roll 40
Inside 1, a magnet roll (not shown) having a plurality of magnetic poles arranged at a predetermined angle is arranged in a fixed state. A paddle 403 for transporting the developer to the developing roll 401
Accordingly, the amount of the developer transported to the vicinity of the surface of the developing roll 401 is regulated by the developer amount regulating member 402 to the amount transported to the developing section. In this embodiment, the amount of the developer on the developing roll 401 is 30 to 50 g / m ² ,
At this time, the charge amount of the toner present on the developing roll 401 is about 20 to 35 μC / g.

The toner supplied onto the developing roll 401 is in the form of a magnetic brush composed of carrier and toner by the magnetic force of the magnet roll, and this magnetic brush is used as the photosensitive drums 11, 12, 13, and 14. Is in contact with An AC + DC developing bias voltage is applied to the developing roll 401 to apply toner on the developing roll 401 to the photosensitive drums 11, 12, and 12.
By developing the electrostatic latent image formed on 13, 14
A toner image is formed. In this embodiment, the developing bias voltage is 4 kHz for AC, 1.5 kVpp, and -2 for DC.
It is about 00V.

Next, the respective photosensitive drums 11, 12, 13, 14
The toner images of the respective colors of cyan (C), magenta (M), yellow (Y), and black (K) formed on the first primary intermediate transfer drum 51 and the second primary intermediate transfer drum 52
Is electrostatically secondary-transferred. The cyan (C) and magenta (M) toner images formed on the photoconductor drums 11 and 12 are formed on the first primary intermediate transfer drum 51 by yellow (C) and magenta (M) toner images formed on the photoconductor drums 13 and 14, respectively. The toner images of Y) and black (K) are respectively transferred onto the second primary intermediate transfer drum 52. Accordingly, on the first primary intermediate transfer drum 51, the monochrome image transferred from either of the photosensitive drums 11 and 12 and the two-color toner image transferred from both of the photosensitive drums 11 and 12 are superimposed. A double-color image is formed. Also, on the second primary intermediate transfer drum 52, similar single color images and double color images are formed from the photosensitive drums 13 and 14.

The first and second primary intermediate transfer drums 5
The surface potential required for electrostatically transferring the toner images from the photosensitive drums 11, 12, 13, and 14 onto the surface 1, 52 is approximately +250 to 500 V. This surface potential is set to an optimum value depending on the charged state of the toner, the ambient temperature, and the humidity. The ambient temperature and the humidity can be easily known by detecting the resistance value of a member having a characteristic in which the resistance value changes depending on the ambient temperature and the humidity. As described above, when the charge amount of the toner is in the range of 20 to 35 .mu.C / g and the environment is normal temperature and normal humidity, the surface potential of the first and second primary intermediate transfer drums 51 and 52 becomes + 400V is desirable.

The first and second primary modes used in this embodiment
The intermediate transfer drums 51 and 52 have, for example, an outer diameter of 42 mm.
And the resistance is 10⁸ It is set to about Ω. 1st, 2nd
The primary intermediate transfer drums 51 and 52 are single-layer or
Consists of flexible or elastic cylindrical
Rotating body, generally made of metal such as Fe or Al
Conductive silicone rubber on metal pipe as core
Low resistance elastic rubber layer (R = 10^Two ~Ten^Three Ω)
Is provided with a thickness of about 0.1 to 10 mm. Furthermore,
The outermost surfaces of the first and second intermediate transfer drums 51 and 52 are typically
Is fluororubber with fluororesin microparticles dispersed in a thickness of 3 to
100 μm high release layer (R = 10^Five ~Ten⁹ Ω)
And connect with a silane coupling agent-based adhesive (primer).
Is being worn. What is important here is the resistance value and surface release.
And the resistance of the high release layer is R = 10 ^Five ~Ten⁹ About Ω
Yes, as long as the material has a high mold release property, the material is particularly limited
Not done.

The single-color or double-color toner images thus formed on the first and second primary intermediate transfer drums 51 and 52 are
The image is electrostatically tertiarily transferred onto the secondary intermediate transfer drum 53. Therefore, on the secondary intermediate transfer drum 53, a final toner image from a single color image to a quadruple color image of cyan (C), magenta (M), yellow (Y), and black (K) is formed. Will be.

The surface potential required for electrostatically transferring the toner images from the first and second primary intermediate transfer drums 51 and 52 onto the secondary intermediate transfer drum 53 is about +600 to 1200 V. . The surface potential is the same as when the toner is transferred from the photosensitive drums 11, 12, 13, and 14 to the first primary intermediate transfer drum 51 and the second primary intermediate transfer drum 52. Will be set to the optimum value. Also, since what is necessary for the transfer is the potential difference between the first and second primary intermediate transfer drums 51 and 52 and the secondary intermediate transfer drum 53, the first and second primary intermediate transfer drums 51 and 5 are required.
It is necessary to set the value according to the surface potential of 2.
As described above, the charge amount of the toner is in the range of 20 to 35 .mu.C / g, and the surface potential of the first and second primary intermediate transfer drums 51 and 52 is about +400 V under normal temperature and normal humidity environment. In this case, the surface potential of the secondary intermediate transfer drum 53 is about +800 V, that is, the potential difference between the first and second primary intermediate transfer drums 51 and 52 and the secondary intermediate transfer drum 53 is +400 V It is desirable to set to about.

The secondary intermediate transfer drum 53 used in this embodiment is formed, for example, to have the same outer diameter as the first and second primary intermediate transfer drums 51 and 52 of 42 mm, and has a resistance value of 10 ¹¹ Ω.
Set to about. Also, the secondary intermediate transfer drum 53 has a single-layer structure, similarly to the first and second primary intermediate transfer drums 51 and 52.
Alternatively, the rotating body is a cylindrical rotating body having a flexible or elastic surface having a plurality of layers, and is generally made of conductive silicone rubber or the like on a metal pipe as a metal core made of Fe, Al, or the like. A typical low-resistance elastic rubber layer (R =
10 ² to 10 ³ Ω) in a thickness of about 0.1 to 10 mm. Further, the outermost surface of the secondary intermediate transfer drum 53 is typically made of a fluoro rubber in which fluoro resin fine particles are dispersed, having a thickness of 3 to
It is formed as a high release layer having a thickness of 100 μm, and is bonded with a silane coupling agent-based adhesive (primer). What is important here is the resistance and the releasability of the surface as in the case of the first and second primary intermediate transfer drums 51 and 52. However, the resistance value of the secondary intermediate transfer drum 53 needs to be set higher than those of the first and second primary intermediate transfer drums 51 and 52. Otherwise, the secondary intermediate transfer drum 53 charges the first and second primary intermediate transfer drums 51 and 52, making it difficult to control the surface potential of the first and second primary intermediate transfer drums 51 and 52. Become. The material is not particularly limited as long as it satisfies such conditions.

Next, the final toner image from the single color image to the quadruple color image formed on the secondary intermediate transfer drum 53 is
The third transfer is performed by the final transfer roll 60 onto the sheet passing through the sheet transport path P. This paper passes through a paper transport roll 90 through a paper feeding step (not shown), and is fed into a nip portion between the secondary intermediate transfer drum 53 and the final transfer roll 60. After this final transfer step, the final toner image formed on the paper is fixed by the fixing device 70, and a series of image forming processes is completed.

The final transfer roll 60 has, for example, an outer diameter of 20 m.
m, and the resistance value is set to about 10 ⁸ Ω. As shown in FIG. 2, the final transfer roll 60 is formed by providing a coating layer 62 made of urethane rubber or the like on a metal shaft 61 and coating the coating layer 62 as necessary. The optimal value of the voltage applied to the final transfer roll 60 varies depending on the ambient temperature, humidity, type of paper (resistance value, etc.), and is generally about +1200 to 5000 V. In this embodiment, a constant current method is adopted, and a current of about +10 μA is applied under a normal temperature and normal humidity environment, so that an almost appropriate transfer voltage (+160
0-2000V).

In the series of transfer steps, when the toner image passes through the transfer portion in each transfer step, a part of the positive toner in the (-) charged image is reversed due to Paschen discharge or charge injection. Polar (+) charged toner may occur. The (+) charged toner flows back to the upstream side without being transferred to the next step, and thus adheres and accumulates on the charging devices 21, 22, 23, and 24 having the highest negative potential. The portions of the charging devices 21, 22, 23, and 24 to which toner adheres are activated by discharging, and the surface potential of the photoconductor drums 11, 12, 13, and 14 tends to increase, and thus the portions where toner adheres frequently In addition, the surface potentials of the photosensitive drums 11, 12, 13, and 14 are uneven at portions where toner is little attached and portions where toner is not attached. When unevenness occurs in the surface potential of the photoconductor drums 11, 12, 13, and 14, an image is uniformly exposed on the surface of the photoconductor drums 11, 12, 13, and 14 to form an electrostatic latent image. Also, since the latent image potential becomes uneven and the development amount becomes different, the density unevenness becomes conspicuous especially when a halftone image is to be developed.

Therefore, such charging devices 21, 22, 23,
In this embodiment, in order to prevent the occurrence of density unevenness due to the toner adhered to the sheet 24, the following cleaning operation is performed at a predetermined timing such as before a printing operation, after a printing operation, or at a predetermined number of sheets during continuous printing. It has become.

Charging devices 21, 22, 23, 24, photosensitive drum 1
1, 12, 13, 14, the first and second primary intermediate transfer drums 51,
52, the secondary intermediate transfer drum 53, the final transfer roll 60, so that the final transfer roll 60 has the highest negative potential,
By applying a voltage with a potential gradient in order,
During the printing operation, the (+) charged toner of the opposite polarity deposited and deposited on the charging devices 21, 22, 23, and 24 is sequentially transferred and moved to the final transfer roll 60, and contacts the final transfer roll 60. It is collected by a cleaning device 80 including a final cleaning member 801 such as a blade provided.

In this embodiment, the charging devices 21, 22, 2
The surface potential of 3, 24 is 0 V, and the photosensitive drums 11, 12, 13, 14
, The surface potential of the first and second primary intermediate transfer drums 51 and 52 is -800 V, the surface potential of the secondary intermediate transfer drum 53 is -1300 V, and the surface potential of the final transfer roll 60 is-. Two
000 V is set. This potential gradient is obtained by supplying a voltage to the metal part (shaft, pipe) of each member. For example, the first and second primary intermediate transfer drums 51 and 52 or the secondary intermediate transfer drum 53 are used. If a desired surface potential can be obtained depending on the relationship between the resistance values of these members by electrically floating them, such a method may be adopted. In such a minus application cleaning mode, that is, a (+) charged toner collection mode of opposite polarity, it is possible to prevent the occurrence of density unevenness due to the toner attached to the charging devices 21, 22, 23, and 24.

The above is the image forming mode in the full-color printer configured as described above. In the xerography method and the like, since static electricity is used, the image density tends to fluctuate due to environmental changes and aging. For this reason, in response to environmental changes and changes over time, separately from the image forming mode,
Process control mode (toner density control mode)
Is preferably provided to control the electrophotographic process.

Next, the process control mode in the full-color printer configured as described above and the configuration related thereto will be described.

The process control mode includes a TC process control mode (first toner density control mode) for controlling the toner density (ratio of toner and carrier) in each of the developing devices 41, 42, 43, and 44. There is a potential process control mode (second toner density control mode) for controlling the toner density of the toner image finally transferred onto the sheet. In any of these process control modes, a test toner patch is formed on the surface of an image density detection medium such as a photoreceptor, an intermediate transfer member, or a transfer roll or transfer belt on paper, and the density is optically measured. Various image forming processes (image forming conditions) are detected by the density sensor and controlled, but a preferable image density detecting medium differs depending on the characteristics of each process control.

That is, in the TC process control mode, each of the developing devices 41, 42, 43, and 44 can detect the ratio of toner and carrier in each of the developing devices 41, 42, 43, and 44 more accurately. It is preferable to detect a toner patch on the surface of an image density detection medium close to 44, for example, the surface of each of the photosensitive drums 11, 12, 13, and 14. On the other hand, in the potential process control mode, an image density detection medium close to the paper, for example, a toner patch on the surface of the secondary intermediate transfer drum 53 or the final transfer roll 60 is detected so that the toner density on the paper can be detected more accurately. Is preferred.

On the other hand, to detect a test patch on the photosensitive drums 11, 12, 13, and 14, the respective photosensitive drums 11, 12, 1
For 3 and 14, that is, four optical density detection means are required. First and second primary intermediate transfer drum 5
If it is above 1,52, two optical density detecting means are sufficient. As long as it is on the secondary intermediate transfer drum 53 or on the final transfer roll 60, one optical density detecting means may be used.

Therefore, in this embodiment, a single optical density detecting means is used with an emphasis on the simplicity of the configuration of the apparatus, and the toner patch on the final transfer roll 60 is detected in both process control modes. I decided that. On the other hand, in the TC process control mode, the ratio of toner and carrier in each of the developing devices 41, 42, 43, and 44 can be detected as accurately as possible (even on the final transfer roll 60 that has undergone multiple transfers). In order to make the transfer rate in the TC process control mode particularly high, for example, the toner amount of the test patch toner image formed on the photosensitive drums 11, 12, 13, and 14 is changed to the final transfer roll 6
The transfer bias is controlled so that 90% or more, or 95% or more, is transferred on the zero.

In the test patch, a non-image area, in which no image is formed, under the same charging, exposure, and development conditions as in image formation, cyan (C), magenta (M), yellow (Y), As shown in FIG. 3, for each color of black (K), 12 × 12 mm test patches 200 having an image density of 40% are formed on the final transfer roll 60 at intervals of 3 mm. The transfer conditions of the test patch are set differently for each of the TC process control mode and the potential process control mode. The specific method including the transfer conditions in the image forming mode will be described later.

As shown in FIG. 4, the optical density sensor 100 is arranged at the center of the final transfer roll 60 in the axial direction so as to be located on the radially extended line on the outer periphery of the final transfer roll 60. ing. This optical density sensor 100
Is fixedly mounted in the holder 101. A cleaning device 80 having a blade-like final cleaning member 801 is provided below the final transfer roll 60.
Are arranged. In FIG. 4, reference numeral 802 denotes a toner collection box; 803, a support frame for the final transfer roll 60;
Denotes a static eliminator provided on the support frame 803, and 805 denotes a bias plate.

As shown in FIG. 5, the optical density sensor 100 is a specular reflection type sensor for detecting specular reflection light. A light emitting element 102 composed of an LED or the like disposed at an angle φ, and a light reflected from the light emitting element 102 to a detection position on the surface of the final transfer roll 60 and specularly reflected from the detection position. And a light receiving element 103 composed of a phototransistor or the like arranged at an angle of reflection equal to the predetermined incident angle with respect to the detection position on the surface of the final transfer roll 60.

The optical density sensor 100 includes:
As shown in FIG. 6, a diffuse reflection type sensor for detecting diffused light may be used. Further, both a specular reflection type sensor and a diffuse reflection type sensor may be used. In this case, the detection accuracy of the toner density can be further improved by detecting the toner density based on both the specular reflection component and the scattered light component.

FIG. 7 is a block diagram showing a control circuit of the toner density control device according to this embodiment.

In FIG. 7, reference numeral 300 denotes the optical density sensor 100.
A control circuit 301 including a CPU or the like for controlling the image density based on the detection result of the control circuit 301, based on an output signal from the control circuit 300, a voltage Vc applied to the charging devices 21, 22, 23, and 24;
A potential control circuit for controlling the developing bias voltage Vbias applied to the developing devices 41, 42, 43, 44, and 302 is a charging device 21, 22, 23, 24
A high-voltage power supply for applying a predetermined voltage Vc to the
A high-voltage power supply for applying a predetermined developing bias voltage Vbias to 41, 42, 43, and 44; 304, a toner density control circuit for controlling toner supply to the developing device based on an output signal from the control circuit 300; And a transfer bias control circuit for applying a transfer bias to each of the first and second primary intermediate transfer drums 51 and 52, the secondary intermediate transfer drum 53, and the final transfer roll 60 based on an output signal from the circuit 300. It is.

Then, the optical density sensor 100 and the control circuit 30
0, the potential control circuit 302 and the like constitute a potential process control system as a whole. The optical density sensor 100, the control circuit 300, the toner density control circuit 304, and the like constitute a TC process control system as a whole. Further, the optical density sensor 100, the control circuit 300, the transfer bias control circuit 305
And others constitute a transfer bias control system as a whole.

In the above configuration, in the image forming apparatus according to this embodiment, potential process control, TC
Process control is performed, and the transfer bias in the image forming mode is controlled based on the result of the potential process control (a predetermined developing bias voltage Vbias to the developing devices 41, 42, 43, and 44). Hereinafter, more specific methods will be described.

In the image forming apparatus according to the present embodiment, as shown in FIG. 8, first, the control circuit 300 controls the surface of the final transfer roll 60 in a state where the test patch is not transferred. Is detected by the optical density sensor 100, and the output Vcln of the optical density sensor 100 at this time is stored (step 10).
1). Next, under the same charging, exposure, development, and transfer conditions as in image formation, 12% of the image density of 40% for each color of cyan (C), magenta (M), yellow (Y), and black (K).
As shown in FIG. 3, test patches 200 of × 12 mm are formed on the final transfer roll 60 at intervals of 3 mm (step 102).

Thereafter, the cyan (C), magenta (M), yellow (Y),
In the test patch 200 of each color of black (K), FIG.
(A) or as shown in FIG.
At 0, 16 points are detected at a pitch of 0.5 mm and the average value Vpatch is detected.
Is obtained (step 103). Here, FIG.
As shown in (a), a specular reflection type optical density sensor 100 is used.
Is used. Then, the average value of each color is
The ratio Vpatch / Vcln divided by the value of the elementary surface of 60 is used as a substitute value of the density (step 104). Here, the ratio with the value of the elementary surface of the final transfer roll 60 is determined by the final transfer roll 60
This is for correcting the variation in the reflectance of the 60 elementary surfaces and the variation in the LED light emission amount.

As a result, Vpatch / Vcln for each color
Is compared with a predetermined value (step 105). When the obtained density of the test patch is lower than the predetermined density, the absolute value of the DC of the developing bias is increased according to the difference, and at the same time, the voltage applied to the charging device is increased. Then, as shown in FIG. 10B, the charging potential of the photosensitive drum is increased (step 106). By doing so, as shown in FIG. 10B, the electric field in the developing direction formed between the developing roll of the developing device and the image portion of the electrostatic latent image on the photosensitive drum becomes large, and the image is developed. And the image density increases.

Conversely, when the obtained density of the test patch is higher than the predetermined density, the absolute value of the DC of the developing bias is reduced in accordance with the difference, and at the same time, the voltage applied to the charging device is reduced. As shown in c), the charged potential of the photosensitive drum is reduced (step 108). By doing so, as shown in FIG. 10C, the electric field in the developing direction formed between the developing roll of the developing device and the image portion of the electrostatic latent image on the photosensitive drum is reduced, and the image is developed. The amount of toner to be used decreases, and the image density decreases.

Here, the developing bias and the supply voltage to the charging device are adjusted, but any device that adjusts the density or gradation of the image may be used. The exposure condition and the gradation characteristics of the image may be adjusted, or the peripheral speed ratio between the developing roll and the photosensitive drum may be adjusted. Further, these may be combined.

ＴTC Process Control Toner replenishment measures the image density from the print image signal, and controls the replenishment time so as to replenish the toner corresponding to the amount of toner used according to the result. However, in this method, when the development amount fluctuates, the amount of toner used fluctuates, and the balance with the amount of replenished toner deviates, and the toner density in the developing device fluctuates.

For this reason, a test patch is created to detect the density, and the toner supply amount is corrected according to the result.

The test patch has an image density of 100% for each color under a predetermined charging, exposure, and developing condition (DC component Vdc-240V of developing bias, AC component is off) at a timing when no image is formed here. % 12mm x 1
Test patches of 2 mm are formed on the final transfer roll 60 at intervals of 3 mm.

In the image forming apparatus according to this embodiment,
As shown in FIG. 11, first, the control circuit 300 detects the surface of the final transfer roll 60 with the optical density sensor 100 in a state where the test patch is not transferred, and outputs the output Vcln of the optical density sensor 100 at this time. Remember (Step 2
01). Next, under the same charging, exposure, development, and transfer conditions as in image formation, 12% of the image density of 40% for each color of cyan (C), magenta (M), yellow (Y), and black (K).
As shown in FIG. 3, test patches 200 of × 12 mm are formed on the final transfer roll 60 at intervals of 3 mm (step 202).

Thereafter, cyan (C), magenta (M), yellow (Y),
In the test patch 200 of each color of black (K), FIG.
(A) or as shown in FIG.
At 0, 16 points are detected at a pitch of 0.5 mm and the average value Vpatch
Is obtained (step 203). Here, FIG.
As shown in (a), a specular reflection type optical density sensor 100 is used.
Is used. Then, the average value of each color is
The ratio Vpatch / Vcln divided by the value of the elementary surface of 60 is used as a substitute value of the density (step 204).

As a result, when the obtained test patch is lower than the predetermined density, the toner density is low. Therefore, according to the difference, the toner supply is determined by measuring the image density in advance from the print image signal (step 210). Amount (step 22
Correction is made so as to increase the toner supply amount from 0) (step 206). Conversely, when the test patch is higher than the predetermined density, the toner density is high, and the toner supply amount determined in advance by measuring the image density from the print image signal (step 210) according to the difference (step 22)
Correction is made so as to reduce the toner supply amount as compared with 0) (step 208).

Transfer bias control In the image forming apparatus according to the present embodiment, the first and second primary intermediate transfer drums 51 are differently provided by an image forming mode, a TC process control mode, and a potential process control mode. , 52, the secondary intermediate transfer drum 53, and the final transfer roll 60 are determined. FIG. 12 is a flowchart illustrating a method of transfer bias control. Hereinafter, based on this flowchart, how each transfer bias in each mode is determined, and the primary intermediate transfer drums 51, 5
2. A description will be given as to whether the voltage is applied to the secondary intermediate transfer drum 53 and the final transfer roll 60.

Image Forming Mode When the state of the image forming apparatus is the image forming mode (step 300), the result of the potential process control performed immediately before, specifically, the developing bias determined by the potential process control _{Depending on} the magnitude of the value of the DC component V _bias (DC) (FIG. 8, steps 106, 107, 108)
Transfer bias V1 applied to the primary intermediate transfer drums 51 and 52, the secondary intermediate transfer drum 53, and the final transfer roll 60,
V2 and I are determined (step 301).

Determined by the potential process control
DC component V of developing bias_bias(DC) value is the standard
Value V_bias(N), the primary intermediate transfer driver
Drums 51, 52, secondary intermediate transfer drum 53, and final transfer roll 60
Transfer bias V to be applied₁, V _Two, I are also standards
Value V₁(N), V_Two(N), take I (N) (step
303).

On the other hand, the potential
DC component V of fixed development bias _biasOf the value of (DC)
When the absolute value is large (V_bias(H)) has a primary intermediate rotation
Photo drums 51 and 52, secondary intermediate transfer drum 53, final transfer row
Transfer bias V applied to₁, V_Two, I
Reference value V₁(N), V_Two(N), more than I (N)
Value V with large absolute value₁(N) × β₁, V_Two(N) × β_Two, I
(N) × β_Three(Step 304). On the other hand,
Process bias determined by process control
Flow component V_biasWhen the absolute value of the value of (DC) is small (V
_bias(L)) includes primary intermediate transfer drums 51 and 52,
Transfer bias applied to the intermediate transfer drum 53 and the final transfer roll 60
Ass V₁, V_Two, I are also reference values V₁(N),
V_Two(N), a value V whose absolute value is smaller than I (N).
₁(N) × α₁, V_Two(N) × α_Two, I (N) × α_ThreeTake
(Step 302).

[0066]

[Table 1] Table 1 shows the magnitude of the absolute value of the value of the DC component V _bias (DC) of the developing bias determined by the potential process control, and the transfer bias V ₁ , which is determined based on the absolute value.
It summarizes the relationship between the values of V ₂ and I. here,
α _1, α _2, α ₃ are those determined by the difference between V _{b ias} (N) and _{V bias (L), 0 <} α 1, α 2, α 3 <1 satisfies the condition. Further, α ₁ , α ₂ , and α ₃ can each take an independent value, or all or a part can have the same value. Similarly, β ₁ , β ₂ and β ₃ are V _bias
(N) and V _bias (H).
The condition of 1 <β ₁ , β ₂ , β ₃ is satisfied. Further, β ₁ , β ₂ , and β ₃ may take independent values, or may take the same value in whole or in part.

[0067]

[Table 2] Table 2 shows the magnitude of the absolute value of the value of the DC component V _bias (DC) of the developing bias determined by the potential process control, and the transfer bias V ₁ , which is determined based on the absolute value.
An example of the values of V ₂ and I is summarized. Here, α ₁ , α ₂ , and α ₃ are the same values for the difference (50 [V]) between V _bias (N) and V _bias (L), and (0 <) α ₁ = α ₂ =
α ₃ = 0.9 (<1) is adopted. Similarly, β ₁ ,
β ₂ and β ₃ are the difference (50) between V _bias (N) and V _bias (H).
[V]), (1 <) β ₁ = β ₂ = β ₃ =
1.1 is adopted.

Thus, the potential process control
DC component V of developing bias determined from_bias(DC)
Of each transfer bias V based on the value of₁, V_TwoDetermine the value of I
Is determined by the potential process control.
DC component V of developing bias _bias(DC)
This is because the charge amount of the toner at the time of can be estimated. Toes
As shown in Table 2, the DC component V
_biasWhen the value of (DC) is -150 [V], the toner
The charge amount is estimated to be 20 [μC / g]._bias(DC)
Is -200 [V], the toner charge amount is 25
[ΜC / g] and V_bias(DC) value is -25
In the case of 0 [V], the charge amount of the toner is 30 [μC / g].
It is estimated to be. Then, depending on the charge amount of the toner,
Proper transfer bias V₁, V_TwoYou can set the value of I
It is configured as follows.

○ TC process control mode and potential process control mode
In case of C process control mode (Step 3
10), a transfer bias V1 applied to the primary intermediate transfer drums 51 and 52, the secondary intermediate transfer drum 53, and the final transfer roll 60,
V2 and I are preset V ₁ ′ (N) and V
₂ '(N) and I' (N) are calculated (step 311). On the other hand, when the state of the image forming apparatus is the potential process control mode, the transfer biases V1, V2, and I applied to the primary intermediate transfer drums 51 and 52, the secondary intermediate transfer drum 53, and the final transfer roll 60 are set in advance. V
₁ (N), V ₂ (N) and I (N) are taken (step 32)
0).

[0070]

[Table 3] Table 3 shows each transfer bias V ₁ , V ₂ , I in the TC process control mode and the potential process control mode.
Are summarized. Here, each transfer bias V ₁ ′ (N) in the TC process control mode,
V ₂ ′ (N) and I ′ (N) are transfer biases V ₁ (N) in the normal image forming mode in view of the fact that each transfer is a single-color toner and that high transfer efficiency is required. , V
The absolute values are set to be smaller than ₂ (N) and I (N) (see step 303). On the other hand, each transfer bias V in the potential process control mode
₁ (N), V ₂ (N), and I (N) are each transfer bias (step 30) in the normal image forming mode in view of the fact that it is preferable that the transfer is performed under the same conditions as in the image forming mode.
3).

In addition, the transfer biases V ₁ , V ₂ and I in the TC process control mode and the potential process control mode can be set equal, and the transfer biases in the potential process control mode and the image forming mode can be set equal. V ₁ , V ₂ , and I can be set differently.

[0072]

[Table 4] Table 4 shows each transfer bias V ₁ , V ₂ , I in the TC process control mode and the potential process control mode.
Is an example of the values of.

[0073]

As described above in detail, according to the present invention, a high quality image can be stably output by applying an appropriate transfer bias in accordance with the charge amount of the toner. It is possible to provide a simple image forming apparatus.

[Brief description of the drawings]

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

FIG. 2 is a sectional view showing a final transfer roll of a color printer as an image forming apparatus according to the embodiment of the present invention.

FIG. 3 is a perspective view showing a final transfer roll of a color printer as an image forming apparatus according to the embodiment of the present invention.

FIG. 4 is a configuration diagram showing an optical density sensor of the image density control device according to the embodiment of the present invention.

FIG. 5 is a configuration diagram showing an optical density sensor of the image density control device according to the embodiment of the present invention.

FIG. 6 is a configuration diagram showing an optical density sensor of the image density control device according to the embodiment of the present invention.

FIG. 7 is a block diagram showing a control circuit of the image forming apparatus according to the embodiment of the present invention.

FIG. 8 is a flowchart showing a control operation (potential process control) of the image density control device according to the embodiment of the present invention.

FIGS. 9A and 9B are configuration diagrams respectively showing a detection state of an optical density sensor of the image forming apparatus according to the embodiment of the present invention.

FIGS. 10A to 10C are potential explanatory diagrams showing an image density control method of the image forming apparatus according to the embodiment of the present invention.

FIG. 11 is a flowchart showing a toner concentration control operation (TC process control).

FIG. 12 is a flowchart illustrating a transfer bias control operation (transfer bias control).

[Explanation of symbols]

1, 2, 3, 4 ... image forming unit, 11, 12, 13, 14 ... photosensitive drum (latent image carrier), 41, 42, 43, 44 ... developing device (two-component developing means), 51, 52 ... primary intermediate transfer drum (intermediate transfer member), 53 ... secondary intermediate transfer drum (intermediate transfer member),
60 ... final transfer roll (final transfer rotating body) 100 ... optical density sensor (detection means), 300 ... control circuit (process control means), 301 ... potential control circuit (process control means), 304 ...
Toner density control circuit (process control means), 305 ... Transfer bias control circuit (transfer control means)

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Tadashi Goyama 3-7-1, Fuwa, Iwatsuki-shi, Saitama, Fuji Xerox Co., Ltd. Iwatsuki Office (72) Inventor Noritaka Ide 3--7, Fuuchi, Iwatsuki-shi, Saitama No. 1, F-term in Iwatsuki Office of Fuji Xerox Co., Ltd. (reference) 2H027 DA04 DA09 DD07 DE02 DE07 DE09 EA03 EA05 EA06 EA20 EC03 EC06 EC09 ED09 ED10 ED24 2H073 AA02 BA01 BA13 BA28 CA03 2H077 AD06 AD35 DA02 DA10 DB08 DB14 FA18 GA12 GA23 GA45 GA56 HA02 HB12 HB22 JA02 JA29 JB02 JB10 JB15 JC02 PA03 PA18 PA22

Claims (6)

[Claims] A latent image carrier for carrying a latent image; developing means for applying a predetermined developing bias to develop the latent image as a toner image; and applying a predetermined transfer bias to apply the toner image to a recording medium. An image forming apparatus comprising: a transfer unit configured to perform transfer; and a transfer control unit that controls a value of the transfer bias based on the value of the developing bias. 2. An image forming mode for forming a toner image as an output image, and a toner density control mode for forming a toner image as a detection target, and detecting a density of the toner image as a detection target. 2. The image forming apparatus according to claim 1, further comprising: a detecting unit configured to detect the density of the toner image as a detection target, and a process control unit configured to control image forming conditions including the developing bias. 3. The developing means is a two-component developing means using a toner and a carrier as a developer, and the toner density control mode is a first toner density controlling a density of the toner in the two-component developing means. A control mode, and a second toner density control mode for controlling the density of a toner image as an output image in the image forming mode, wherein the transfer control unit performs the development set in the second toner density control mode. The image forming apparatus according to claim 2, wherein the value of the transfer bias is controlled based on a value of the bias. 4. The developing means is a two-component developing means using a toner and a carrier as a developer, and the toner density control mode is a first toner density for controlling the density of the toner in the two-component developing means. A control mode, and a second toner density control mode for controlling the density of a toner image as an output image in the image forming mode. 4. The image forming apparatus according to claim 2, wherein the value of the transfer bias is controlled such that the transfer efficiency is higher than in the toner density control mode. 5. The transfer unit includes: an intermediate transfer member on which a toner image is transferred in opposition to a latent image carrier; and a final transfer member for contacting a recording medium and finally transferring the toner image. The image forming apparatus according to claim 1, wherein the control unit independently controls a value of a transfer bias applied to each transfer body. 6. The transfer device includes an intermediate transfer member facing the latent image carrier and transferring the toner image from the latent image carrier, and a final member facing the recording medium and finally transferring the toner image to the recording medium. The image forming apparatus according to claim 1, further comprising a transfer member, wherein the detection unit detects a toner image on the final transfer member.