JP2002162801A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device in which the size of a power source circuit and the cost can be reduced by sharing the power source circuit which supplies a voltage to a plurality of electrifying means or a plurality of developing means, with respect to the image forming device having the electrifying means and the developing means in correspondence with a plurality of electrostatic latent image carriers. SOLUTION: The device has a detection means for detecting a parameter due to a density of an image developed by the developing means. The device also has a control means for controlling an image forming condition based on a detection result of the detection means. At least a part of a power source circuit that supplies a voltage to the developing means or electrifying means is shared between both the means.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an electrophotographic system,
For image forming apparatuses such as copiers, printers, facsimile machines, etc., which adopt image forming methods such as electrostatic recording, ionography, and magnetic recording to form color or black and white images, in particular, the image density is estimated or detected. The present invention relates to an image forming apparatus that controls image density by adjusting an image forming parameter such as a developing bias based on an estimation or detection result.

[0002]

2. Description of the Related Art Heretofore, in an image forming apparatus employing the above-described electrophotographic method or the like, as an apparatus capable of forming a color image at high speed and high image quality, a single-color toner image such as yellow, magenta, cyan, and black is used. Four image forming units to be formed are arranged in parallel with each other, and yellow, magenta,
The single-color toner images of cyan and black are temporarily transferred onto the intermediate transfer belt in a multiplex manner, and then collectively transferred from the intermediate transfer belt onto the transfer paper, and the toner images are fixed on the transfer paper. Various so-called full-color tandem machines configured to form an image have been proposed and actually commercialized.

As such an image forming apparatus, the present applicant has
As disclosed in Japanese Patent Application Laid-Open No. H10-78686, it is possible to reduce the size of the apparatus and to form a high-quality color image without using a complicated image misalignment prevention technique. An image forming apparatus has already been proposed.

The image forming apparatus disclosed in Japanese Patent Application Laid-Open No. H10-78686 includes various embodiments. As one of the embodiments, as shown in FIG. A unit structure composed of 101 and 102 and one intermediate transfer member 151 and a unit structure composed of two photoconductors 103 and 104 and one intermediate transfer member 152 are provided. , 152 are proposed so as to be in contact with yet another intermediate transfer member 153. The four photoconductors 101, 102, 103, 104 shown here
Have a common tangent M and therefore these four
Charging devices 111, 121, 131, 141, exposure devices 112, 122, 132, 142, developing devices 113, 123, 133, 143, cleaning devices 114, 124, 134,
144 is arranged at the same position with respect to each of the photoconductors 101, 102, 103, and 104, and the common use of the devices is achieved for each device type.

In the case of the embodiment shown in FIG. 16, each of the toner images formed on the photosensitive members 101 and 102 is an intermediate transfer member.
After being transferred to 151, it is transferred to the intermediate transfer member 153,
Each toner image formed on 103, 104 is an intermediate transfer member 152
Is transferred to the intermediate transfer member 153, and is transferred to the intermediate transfer member 153.
The toner image transferred to 153 is collectively transferred onto the conveyed paper P. The toner image transferred onto the sheet P is fixed on the sheet P by a fixing device (not shown). Since the intermediate transfer members 151, 152, 153 are of a drum type and are made of a rigid body, misregistration between toner images hardly occurs.

[0006] Cleaning devices 114, 124, which remove residual toner after the primary transfer, are provided on the photoreceptors 101, 102, 103, 104.
When the photoconductors 101, 102, 103, and 104 are mounted, the surfaces of the photoconductors 101, 102, 103, and 104 are scraped by the rubbing of the cleaning devices 114, 124, 134, and 144, and the film thickness gradually decreases.
It causes the shortage of 3,104 lives.

Therefore, in order to extend the life of the photoconductors 101, 102, 103, 104, the cleaning devices 114, 124, 134, 144 are eliminated, and the intermediate transfer members 151, 152, 153 and the photoconductors 101, 102, 103, 104 are removed.
104, an image forming apparatus of a type in which toner on other members is collected on a final transfer roll 161 using a potential gradient and collected by a cleaning device 171 attached to the final transfer roll 161 has been proposed.

[0008]

However, the prior art described above has the following problems. That is, in the case of the image forming apparatus disclosed in Japanese Patent Application Laid-Open No. H10-78686, there are provided four photoconductors 101, 102, 103, 104 as electrostatic latent image carriers, and each photoconductor 101,
The charging devices 111, 121, 131, 141 and the developing devices 113, 123, 133, 143 are provided in 102, 103, 104, respectively. Therefore, in the case of an image forming apparatus typified by the full-color tandem machine, a plurality of charging devices 111, 121, 131, 141
In addition, a plurality of developing devices 113, 123, 133, and 143 require a power supply for individually supplying a bias voltage to each of the developing devices 113, 123, 133, and 143, so that there is a problem that an increase in the size and cost of the power supply circuit cannot be avoided.

Therefore, the present invention has been made to solve the above-mentioned problems of the prior art, and an object thereof is to provide a plurality of charging means corresponding to a plurality of electrostatic latent image carriers. In an image forming apparatus provided with a plurality of developing units, at least a part of a power supply circuit for supplying a voltage to the plurality of charging units or the plurality of developing units is shared, so that the power supply circuit can be reduced in size and cost can be reduced. It is an object of the present invention to provide an image forming apparatus which can be integrated.

[0010]

In order to solve the above-mentioned problems, the invention described in claim 1 provides a plurality of electrostatic latent image carriers and a plurality of electrostatic latent image carriers corresponding to the plurality of electrostatic latent image carriers. A plurality of charging means for charging each electrostatic latent image carrier; and a plurality of electrostatic means provided corresponding to the plurality of electrostatic latent image carriers and formed on a surface of each electrostatic latent image carrier. In an image forming apparatus including a plurality of developing units for developing a latent image, a detecting unit for detecting a parameter caused by a density of an image developed by each of the developing units, and an image based on a detection result of the detecting unit. And control means for controlling the forming conditions, wherein at least a part of a power supply circuit for supplying a voltage to the plurality of developing means or the plurality of charging means is configured to be common.

The detecting means for detecting the parameter resulting from the density of the image developed by each of the developing means may directly detect the image density, or the developing means such as the toner density in the developing means. A parameter resulting from the density of the image to be performed may be detected.

According to a second aspect of the present invention, at least a part of a power supply circuit for supplying a voltage to the plurality of charging units is common, and the power supply circuit supplies the voltage to the developing unit based on a detection result of the detection unit. When controlling the developing bias voltage, each developing bias voltage is set so as to fall within a predetermined range from values obtained from the developing bias voltages of a plurality of developing means corresponding to the charging means using the common power supply. It is configured as follows.

Further, according to a third aspect of the present invention, at least a part of a developing bias voltage supplied to the plurality of developing units is common, and a charging potential is set for each of the developing units based on a detection result of the detecting unit. And the exposure potential is controlled.

Still further, the invention described in claim 4 is:
A power supply circuit for supplying a voltage to a charging unit provided corresponding to at least the electrostatic latent image carrier for forming a color toner image among the plurality of electrostatic latent image carriers is configured to be common. Things.

As the plurality of electrostatic latent image carriers, for example, cyan (C), magenta (M), yellow (Y),
And black (K) toner images are used, but the order and type of these colors may of course be other.

The detecting means may be configured to detect the density of an image density detecting toner image formed on a photosensitive drum as an electrostatic latent image carrier, for example. It may be configured to detect the density of the intermediate transfer body onto which the image density detecting toner image is transferred from the body drum, the final transfer roll, or the density of the image density detecting toner image transferred onto the transfer medium.

[0017]

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

FIG. 2 shows a tandem-type full-color printer as an image forming apparatus according to Embodiment 1 of the present invention.

In FIG. 2, reference numeral 01 denotes a main body of a tandem type full-color printer.
The print head device (Print Head Device) 02 for performing full-color image formation is roughly divided into 01 inside.
An ROS (Raster Output Scanner) 03 as an exposure device for performing image exposure on four photosensitive drums 11, 12, 13, and 14 as electrostatic latent image carriers of the print head device 02.
And the developing device 4 for each color of the print head device 02
Four toner cartridges 04Y, 04M, 04C and 04K for supplying toners of colors corresponding to 1, 42, 43 and 44, and a paper feed cassette 05 for supplying transfer paper P as a transfer medium to the print head device 02; The above printhead device 02
A fixing device 06 for performing a fixing process on a sheet P on which a toner image has been transferred from the printer P, and a sheet P on which an image is fixed on one side by the fixing device 06 are turned over again with the print head device 02 , A double-sided conveyance path 07 for conveying the desired paper P from outside the printer main body 01, a controller 09 for controlling the operation of the printer, An image processing circuit for performing image processing, an electric circuit 10 including a high-voltage power supply circuit, and the like are provided. In FIG. 2, T indicates a discharge toilet for discharging the paper P on which an image is formed, and the discharge toilet T is integrally disposed on the upper portion of the printer main body 01.

Of the various members disposed inside the printer main body 01, ROS03 as an exposure device corresponds to each color of yellow (Y), magenta (M), cyan (C), and black (K). Four semiconductor lasers that are turned on and driven based on the obtained image data, an f-θ lens or a polygon mirror for deflecting and scanning four laser lights emitted from these four semiconductor lasers, or a plurality of reflections It is composed of a mirror and the like.

FIG. 3 shows a print head device of a tandem type full color printer as an image forming apparatus according to Embodiment 1 of the present invention. In addition, the arrow in FIG. 3 has shown the rotation direction of each rotating member.

As shown in FIG. 3, the print head device 02 includes photosensitive drums (electrostatic latent image carriers) for yellow (Y), magenta (M), cyan (C), and black (K). Image forming unit 1 having 11, 12, 13, 14
2, 3, 4, and charging rolls (contact-type charging devices) 21, 2 for primary charging that contact the photosensitive drums 11, 12, 13, 14
2, 23, 24 and laser light 31, 32, 3 of each color of yellow (Y), magenta (M), cyan (C), black (K)
ROS (exposure equipment) 03 that irradiates 3, 34 (see Fig. 2)
Then, the electrostatic latent images formed on the photosensitive drums 11, 12, 13, and 14 are developed with toner of each color of yellow (Y), magenta (M), cyan (C), and black (K). Developing devices 41, 42, 43, 44 and the four photosensitive drums 11, 1
A first primary intermediate transfer drum (intermediate transfer member) 51 that contacts two of the photosensitive drums 11 and 12 out of 2, 13 and 14, and a second primary contact that contacts the other two photosensitive drums 13 and 14 An intermediate transfer drum (intermediate transfer member) 52, a secondary intermediate transfer drum (intermediate transfer member) 53 that contacts the first and second primary intermediate transfer drums 51 and 52, and a contact with the secondary intermediate transfer drum 53 The main part is constituted by the final transfer roll (transfer member) 60 to be formed.

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-symmetric relation with a predetermined plane of symmetry 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.

Signals corresponding to the image information for each color are rasterized by an image processing circuit provided in the electric circuit 10 (see FIG. 2) and input to the ROS03. This ROS
In 03, laser beams 31, 32, 33, and 33 of each color of yellow (Y), magenta (M), cyan (C), and black (K)
34 is modulated, and the photoconductor drums 11, 12, 13,
Irradiated at 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. 3, the surface of is charged to about -300 V, for example, by applying a DC voltage of about -840 V to the charging rolls 21, 22, 23, and 24 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 correspond to the respective colors of yellow (Y), magenta (M), cyan (C) and black (K) by ROS03 as an exposure device. The laser beams 31, 32, 33, and 34 are applied to form an electrostatic latent image corresponding to the input image information for each color. When an electrostatic latent image is written by ROS03 on the photosensitive drums 11, 12, 13, and 14, the surface potential of the image exposed portion is
The charge is removed to about -60 V or less.

An electrostatic latent image corresponding to each color of yellow (Y), magenta (M), cyan (C), 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 yellow (Y), magenta (M), cyan (C), and black (K) are formed on the photosensitive drums 11, 12, 13, and 14, respectively. Are visualized as toner images of the respective colors.

In this embodiment, the developing devices 41, 42, 4
The magnetic brush contact type two-component developing method is adopted as 3, 44. However, the scope of the present invention is not limited to this developing method, such as a non-contact type developing method and a one-component developing method. Of course, the present invention can be sufficiently applied to other developing systems.

The developing devices 41, 42, 43, and 44 contain toners of yellow (Y), magenta (M), cyan (C), and black (K) toners of different colors and a developer composed of a carrier. Is filled. These developing devices 41, 42,
As shown in FIG. 2, when toner is supplied from the toner cartridges 04Y, 04M, 04C, and 04K of the corresponding colors, the supplied toner is sufficiently stirred with the carrier by the auger 404. Is charged by friction. Inside the developing roll 401, a magnet roll (not shown) having a plurality of magnetic poles arranged at a predetermined angle is arranged in a fixed state.
The amount of the developer conveyed to the vicinity of the surface of the developing roll 401 by the paddle 403 that conveys the developer to the developing roll 401 is regulated by the developer amount regulating member 402 to the amount conveyed to the developing section. In this embodiment, the amount of the developer is 30 to 50 g / m ² , and the charge amount of the toner present on the developing roll 401 at this time is approximately −20 to 35 μm.
It is about C / 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, for example,
When the AC component of the developing bias voltage is 4 kHz and 1.5 kVpp,
The DC component is set to about -230V.

In this embodiment, the developing devices 41, 4
2, 43 and 44, the toner is a so-called "spherical toner" which is a substantially spherical toner and has an average particle diameter of 3 to
For example, the average particle diameter of the black toner is set to 8 μm, and the average particle diameter of the color toner is set to 7 μm.

Next, the respective photosensitive drums 11, 12, 13, 14
The toner images of the respective colors of yellow (Y), magenta (M), cyan (C), 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 yellow (Y) and magenta (M) toner images formed on the photoconductor drums 11 and 12 are formed on the first primary intermediate transfer drum 51 by the cyan (C) formed on the photoconductor drums 13 and 14. The toner images of C) 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 , + 380V is desirable.

The first and second primaries used in this embodiment
The intermediate transfer drums 51 and 52 have, for example, an outer diameter of 42 mm.
And the resistance is 10⁸It 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^ThreeΩ)
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~Ten⁹Ω)
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~Ten⁹About Ω
Yes, as long as the material has a high mold release property, the material is particularly limited
Not done.

As described above, the single-color or double-color toner images 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 yellow (Y), magenta (M), cyan (C), 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 +380 V under normal temperature and normal humidity environment. In this case, the surface potential of the secondary intermediate transfer drum 53 is about +880 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 +880 V. It is desirable to set to about 500V.

The secondary intermediate transfer drum 53 used in this embodiment has an outer diameter of, for example, 42 mm, which is the same as the first and second primary intermediate transfer drums 51 and 52, and 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). here,
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, and it is 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 P passing through the sheet transport path. The paper P passes through a paper transport roll 90 through a paper feeding process (not shown), and is transferred to the secondary intermediate transfer drum 53.
Is transferred to the nip portion of 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. 4, 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 applying a coating thereon 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 +6 μA is applied under a normal temperature and normal humidity environment, so that an almost appropriate transfer voltage (+1600
~ 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 by 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 with 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 photosensitive drums 11, 12, 13, 14 are toners having a normal (−) polarity, if necessary.
And the toner remaining on the surfaces of the first and second primary intermediate transfer drums 51 and 52 and the secondary intermediate transfer drum 53 are removed by the same method (by inverting only the polarity of the applied voltage). be able to.

The above is the image forming process in the full-color printer configured as described above. In the electrophotographic system and the like, since the static electricity is used, the image density is liable to fluctuate due to environmental fluctuation or aging. For this reason, it is desirable to control the process in response to environmental fluctuations and changes over time.

As one of the methods, a test toner patch is formed on the surface of an image density detecting medium such as a photoreceptor, an intermediate transfer member, or a transfer roll or a transfer belt on paper, and the density is determined by optical density. There is a method of detecting and controlling with a sensor.

Therefore, in this embodiment, the image forming apparatus is provided with detecting means for detecting the density of the image density detecting toner image developed by each developing means.

That is, in this embodiment, on the image density detecting medium such as the final transfer roll 60 and the secondary intermediate transfer drum 53, the image density is shifted in the process direction to the same position in the axial direction. Control toner image (hereinafter referred to as
It is called a "test patch." ) To form 1
The configuration is such that a test patch of each color can be detected by one optical density detecting means.

In order to detect a test patch on the photosensitive drums 11, 12, 13, and 14, it is necessary to provide four optical density detecting means for each of the photosensitive drums 11, 12, 13, and 14. I will. On the first and second primary intermediate transfer drums 51 and 52, two optical density detecting means may be used. If it is on the secondary intermediate transfer drum 53 or on the final transfer roll 60, one optical density detecting means may be used. Further, in the case where the image density is controlled by the test patch, the downstream process is preferable because the condition is closer to the paper. That is, the secondary intermediate transfer drum
53, more preferably, the final transfer roll 60 is preferably an image density detection medium for detecting the density of the test patch.

In this embodiment, a test patch is transferred onto the final transfer roll 60, and the density of the test patch transferred onto the final transfer roll 60 is detected by an optical density sensor.

In the test patch, a non-image area, in which no image is formed, under the same charging, exposure, development, and transfer conditions as during image formation, cyan (C), magenta (M), and yellow (Y ) And black (K), test patches 200 of 12 × 12 mm with an image density of 40% are formed on the final transfer roll 60 at an interval of 3 mm, as shown in FIG.

As shown in FIG. 6, the optical density sensor 100 is disposed at the center of the final transfer roll 60 in the axial direction so as to be located on the outer circumference of the final transfer roll 60 on a radial extension line. 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. 7, 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. 8, 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.

In the image forming apparatus according to this embodiment, a plurality of electrostatic latent image carriers are provided corresponding to the plurality of electrostatic latent image carriers, and each electrostatic latent image carrier is provided. A plurality of charging means for charging, and a plurality of developing means provided corresponding to the plurality of electrostatic latent image carriers and developing the electrostatic latent images formed on the surface of each electrostatic latent image carrier. An image forming apparatus comprising: a detecting unit configured to detect a parameter caused by a density of an image developed by each of the developing units;
A control unit for controlling image forming conditions based on the detection result of the detection unit; and a common power supply circuit for supplying a voltage to the plurality of developing units or the plurality of charging units.

Further, in this embodiment, a common power supply circuit is used for supplying a voltage to the plurality of charging means, and when controlling the developing bias voltage supplied to the developing means based on the detection result of the detecting means, Each of the developing bias voltages is set so as to fall within a predetermined range from values obtained from the developing bias voltages of a plurality of developing means corresponding to the charging means using the common power supply.

Further, in this embodiment, a power supply for supplying a voltage to a plurality of charging means corresponding to at least the electrostatic latent image carrier for forming a color toner image among the plurality of electrostatic latent image carriers. The circuit is configured to be common.

FIG. 1 is a block diagram showing a control circuit of the image forming apparatus according to this embodiment.

In FIG. 1, reference numeral 300 denotes an optical density sensor 100.
A control circuit 301 comprising a CPU or the like for controlling image forming conditions such as a developing bias voltage based on the detection result of the charging device 21, 22, 22 based on an output signal from the control circuit 300.
The applied voltage Vftc to 23, 24 and the developing devices 41, 42, 43, 44
A voltage control circuit 302 for directly controlling the developing bias voltage Vbias to the charging devices 21, 22, 23, and 24;
The high-voltage power supply for the charging device as a common power supply circuit for applying voltage, 303Y, 303M, 303C, and 303K are the developing devices 41, 42, 43, and 44, respectively.
And a high-voltage power supply for a developing device that individually applies a predetermined developing bias voltage Vbias to the developing device. Are respectively shown in FIG.

In the above configuration, the image forming apparatus according to the present embodiment includes a plurality of charging means and a plurality of developing means corresponding to the plurality of electrostatic latent image carriers as follows. In such an image forming apparatus, the power supply circuit for supplying a voltage to the plurality of charging units or the plurality of developing units is shared, thereby making it possible to reduce the size and cost of the power supply circuit.

That is, in the full-color printer according to this embodiment, 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 has not been transferred. The output Vcln of the optical density sensor 100 is stored. Next, control circuit 3
As shown in FIG. 9, 00 is the same charging, exposure, development, and transfer conditions as during image formation, and for each color of yellow (Y), magenta (M), cyan (C), and black (K),
As shown in FIG. 5, test patches 200 of 12 × 12 mm having an image density of 40% are formed on the final transfer roll 60 at intervals of 3 mm (step 101). As shown in FIG. 10, the conditions for forming the test patch 200 are, as described above, the charging potential VH of the photosensitive drum, the surface potential VL1 of the photosensitive drum associated with image exposure, and the developing bias voltage Vdc1 as described above. Is set to

In this embodiment, a test patch 200 of each color of yellow (Y), magenta (M), cyan (C), and black (K) is formed, and the image density of the test patch 200 of each color is determined. Although the description has been given of the case where the detection is performed, the present invention is not limited to this. The toner density in each of the developing devices 41, 42, 43, and 44 is detected to estimate the density of the image actually formed. May be configured. Further, it is more preferable to combine with a control means for controlling the toner density.

Thereafter, the yellow (Y), magenta (M), cyan (C),
Figure 1 shows the test patch 200 for each color of black (K).
As shown in FIG. 1 (a) or FIG. 11 (b), the optical density sensor 100 detects 16 points at a pitch of 0.5 mm and averages Vpa.
tch is obtained (step 101). Here, as shown in FIG. 11A, a specular reflection type optical density sensor is used.
100 is used. Then, the ratio Vpatch / Vcln obtained by dividing the average value of each color by the value of the elementary surface of the final transfer roll 60 is used as a substitute value of the density. Here, the reason for taking the ratio with the value of the elementary surface of the final transfer roll 60 is to correct the variation of the reflectance of the elementary surface of the final transfer roll 60 and the variation of the LED light emission amount.

As a result, the control circuit 300 compares Vpatch / Vcln for each color with a predetermined target value, and, based on the result of comparison between the obtained test patch density and the target value, as shown in FIG. A temporary developing bias voltage Vdc corresponding to the toner image is calculated (step 102). Here, as a method of calculating the temporary developing bias voltage Vdc corresponding to the toner image of each color, for example, assuming that the obtained density of the test patch is Y and the target value of the density of the test patch is YA, The difference between the target value YA of the patch density and the obtained density Y of the test patch (YA−Y current = Δdensity) is calculated, and based on the difference Δdensity, a correction equation as shown in FIG. A method is used in which a correction value ΔVdc from the current developing bias is obtained from the correction table and a temporary Vdc that is a temporary developing bias voltage is obtained.

Next, the average value Vave of the developing bias voltage is calculated from the temporary developing bias voltages Vdc of the four colors of yellow (Y), magenta (M), cyan (C), and black (K) obtained as described above. (Step 103).

Thereafter, as shown in FIG. 12, the control circuit 300 determines that the provisional developing bias voltage Vdc corresponding to the toner image of each color is obtained by subtracting a predetermined value α from the average developing bias voltage Vave (Vave). -Α) It is determined whether or not it is equal to or greater than (step 104). Then, the temporary developing bias voltage V
dc is a predetermined value α from the average value Vave of the developing bias voltage.
Is greater than or equal to (Vave-α), whether or not the provisional developing bias voltage Vdc is equal to or less than a value (Vave + β) obtained by adding a predetermined value β to the average value Vave of the developing bias voltage. Is determined (step 105). On the other hand, if the provisional developing bias voltage Vdc is not equal to or more than the value (Vave-α) obtained by subtracting the predetermined value α from the average value Vave of the developing bias voltage, that is, if Vdc <(Vave-α), The bias voltage Vdc is the lower limit value (Vave
-Α) (step 106).

The temporary developing bias voltage Vdc is
If it is equal to or less than the value (Vave + β) obtained by adding the predetermined value β to the average value Vave of the developing bias voltage, the temporary developing bias voltage Vdc is directly set to the developing bias voltage Vdc (step 107). On the other hand, the temporary developing bias voltage Vdc
Is not less than the value (Vave + β) obtained by adding the predetermined value β to the average value Vave of the developing bias voltage, that is, Vdc>
(Vave + β), the developing bias voltage Vdc
Is set to its upper limit value (Vave + β) (step 108). The provisional developing bias voltage does not have upper and lower limits, and the upper and lower limits are set when the final developing bias is determined from the provisional developing bias voltage.

Note that α and β, which are the upper and lower limits of the variation between the four colors of the developing bias voltage Vdc, are set, for example, to about 20 V, respectively.

As described above, the upper and lower limits of the variation between the four colors are set in the set value of the developing bias voltage Vdc.
When changing the value of the developing bias voltage Vdc, if the value of the developing bias voltage Vdc is set too low compared to the other color Vdc, the cleaning electric field becomes too large,
The carrier charged to the opposite polarity to the toner adheres to the surface of the photosensitive drum, causing image quality defects such as color spots and spots caused by so-called BCO, and the value of the developing bias voltage Vdc is too high compared to other colors Vdc. If it is set too high, the cleaning electric field becomes too small and fogging occurs. This is to prevent this.

According to the characteristics of the image forming apparatus, the average value Vave of the developing bias voltage may have an upper limit value and a lower limit value. That is, the average value Vave corresponding to the upper limit Vh of the charging voltage at which the charging device can be favorably charged is set as the upper limit,
It is effective to set the developing bias voltage at which a stable and uniform image density is obtained as the lower limit of the average value Vave. More specifically, the average value Vave is set to an upper limit of 280 V and a lower limit of 150 V separately from the upper and lower limit values of the four-color variation, and the developing bias voltage Vdc of each color is set within the range according to the rule according to the present embodiment. .

As described above, by controlling the value of the developing bias voltage for each color, among the four colors of yellow (Y), magenta (M), cyan (C), and black (K),
When yellow (Y), magenta (M), and cyan (C) are light and black (K) is dark, as shown in FIG. 14, each of yellow (Y), magenta (M), and cyan (C) By changing the developing bias voltage Vdc to each of the developing bias voltages Vdc2 obtained as described above, and changing the black (K) developing bias voltage Vdc to the developing bias voltage Vdc2, an image of each color can be improved. An image having a high density can be obtained, and a full-color image can be obtained with an excellent coloring property.

In the above-described embodiment, the upper and lower limits of the developing bias voltage are determined based on the average value Vave of the developing bias voltages of the four colors. However, the present invention is not limited to this. May be determined by weighting.

Thereafter, the image density control circuit 300 adds the cleaning field voltage Vcln to the average value Vave of the developing bias voltage, and adds (Vave + Vcln) the photosensitive element charged by each of the charging devices 21, 22, 23, and 24. Body drum 1
A common charging voltage Vh is set so that the surface potentials of 1, 12, 13, and 14 become equal (step 109). At this time, the common charging voltage Vh does not necessarily need to be changed.

Even when the developing bias voltage Vdc is controlled as described above, at the same time, each of the charging devices 21, 22, 22 is added to the value (Vave + Vcln) obtained by adding the cleaning field voltage Vcln to the average value Vave of the developing bias voltage. 23, 24
By controlling the surface potential Vh of the photosensitive drums 11, 12, 13, and 14 by the cleaning, the cleaning field voltage Vcln
Can be maintained within a certain range for each color, so that a desired image density can be obtained,
It is possible to reliably prevent image quality defects such as color points and spots caused by CO from occurring.

The image density control circuit 300 sends a signal to the potential control circuit 301 so as to change to the developing bias voltage Vdc and the charging voltage Vh of each color set as described above. Via the high voltage power supply 303 for each developing device and the high voltage power supply 302 for the common charging device,
The developing bias voltage Vdc and the charging voltage Vh of each color are output to the developing devices 41, 42, 43, 44 and the charging devices 21, 22, 23, 24 (step 110).

As described above, in the case of the above embodiment,
Since the high-voltage power supply 302 for the charging device that supplies a voltage to each of the charging devices 21, 22, 23, and 24 can be shared, the size and cost of the power supply can be reduced.

Further, in the case of the above-described embodiment, when the power supply of the charging device is common, the developing contrast can be varied for each color while keeping the cleaning field during development within a predetermined range for all colors. The configuration is simplified only by individually changing only the bias, and a high-quality image with stable image density without BCO or fogging can be obtained while achieving low cost.

Further, in the case of the above embodiment, it is possible to independently adjust the particle size and the developing property different from those of the image in which the black character image is prioritized and the color toner, and by making the YMC common, A reduction in size and cost can be achieved.

Second Embodiment FIG. 15 shows a second embodiment of the present invention. The same parts as those in the first embodiment are denoted by the same reference numerals and described. The developing bias voltage supplied to the plurality of developing units is made common, and the charging potential and the exposure potential are controlled for each of the developing units based on the detection result of the detecting unit.

That is, in the second embodiment, FIG.
As shown in FIG. 5, a developing device high-voltage power supply 303 for supplying a developing bias voltage to the four developing devices 41, 42, 43, and 44 is common, and each of the charging devices 21, 22, 23, and 24 includes: High-voltage power supplies 302Y, 302M, 302C, and 302K for charging devices are individually provided.

As described above, the charging devices 21, 22, 23, and 24 are individually provided with the charging device high-voltage power supplies 302Y, 302M, 302C, and 302K. In order to obtain the desired image density, the charging potential Vh of the photosensitive drums 11, 12, 13, and 14 of each color is controlled, and the exposure potential VL of each color by the ROS03 is controlled. Accordingly, the developing bias voltage common to the four developing devices 41, 42, 43, and 44 is controlled.

Further, in the case of the second embodiment, the ratio between the development contrast and the cleaning field can be kept almost constant in addition to the reduction in size and cost of the power supply, so that there is no BCO or fogging. A high quality image with a stable image density can be obtained, and the halftone reproducibility is high.

The other structure and operation are the same as those of the first embodiment, and the description is omitted.

[0084]

As described above, according to the present invention,
A plurality of charging means corresponding to the plurality of electrostatic latent image carriers,
In an image forming apparatus having a plurality of developing units, at least a part of a power supply circuit for supplying a voltage to the plurality of charging units or the plurality of developing units is shared, thereby reducing the size and cost of the power supply circuit. An enabled image forming apparatus can be provided.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a control circuit of a tandem-type full-color printer as an image forming apparatus according to Embodiment 1 of the present invention.

FIG. 2 is an overall configuration diagram showing a tandem-type full-color printer as an image forming apparatus according to Embodiment 1 of the present invention.

FIG. 3 is a configuration diagram showing a print head device of a tandem-type full-color printer as an image forming apparatus according to Embodiment 1 of the present invention.

FIG. 4 is a sectional view showing a final transfer roll.

FIG. 5 is a configuration diagram illustrating a toner patch formed on a final transfer roll.

FIG. 6 is a sectional view showing an optical density sensor.

FIG. 7 is a configuration diagram showing an optical density sensor.

FIG. 8 is a configuration diagram showing an optical density sensor.

FIG. 9 is a flowchart showing a control operation of a tandem-type full-color printer as an image forming apparatus according to Embodiment 1 of the present invention.

FIG. 10 is a schematic diagram showing image forming conditions.

FIG. 11 is a schematic diagram illustrating a detection state of a toner patch by an optical density sensor.

FIG. 12 is an explanatory diagram illustrating a control method of a developing bias.

FIG. 13 is a graph showing a method of controlling a developing bias.

FIG. 14 is an explanatory diagram illustrating a control state of a developing bias.

FIG. 15 is a block diagram showing a control circuit of a tandem-type full-color printer as an image forming apparatus according to Embodiment 2 of the present invention.

FIG. 16 is a configuration diagram showing a tandem-type full-color printer as a conventional image forming apparatus.

[Explanation of symbols]

1, 2, 3, 4 ... image forming unit, 11, 12, 13, 14 ... photosensitive drum (electrostatic latent image carrier), 21, 22, 23, 24 ... charging roll (charging means), 41, 42 , 43,44… Developing device (developing means),
51, 52: primary intermediate transfer drum (intermediate transfer member), 53: secondary intermediate transfer drum (intermediate transfer member), 60: final transfer roll (transfer rotating member), 300: control circuit (control means), 302
... High voltage power supply (power supply circuit) for charging device, 303 ... High voltage power supply (power supply circuit) for developing device.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G03G 15/06 101 G03G 15/06 101 (72) Inventor Hiroo Soga 3-7-1, Funai, Iwatsuki City, Saitama Prefecture No., F-term in Fuji Xerox Co., Ltd. BA25 BA28 BA41 CA22

Claims (4)

[Claims] 1. A plurality of electrostatic latent image carriers, a plurality of charging means provided corresponding to the plurality of electrostatic latent image carriers, and charging each electrostatic latent image carrier, An image forming apparatus provided with a plurality of developing means for developing an electrostatic latent image formed on a surface of each of the electrostatic latent image carriers; Detecting means for detecting a parameter resulting from the density of the image to be developed by the control means for controlling image forming conditions based on the detection result of the detecting means, the plurality of developing means or the plurality of charging means An image forming apparatus, wherein at least a part of a power supply circuit for supplying a voltage is shared. 2. A power supply circuit for supplying a voltage to the plurality of charging means, wherein at least a part of the power supply circuit is common, and when controlling a developing bias voltage supplied to the developing means based on a detection result of the detecting means, 2. The developing bias voltage according to claim 1, wherein each developing bias voltage is set so as to fall within a predetermined range from values obtained from developing bias voltages of a plurality of developing means corresponding to the charging means having a common power supply. Image forming device. 3. A method according to claim 1, wherein at least a part of a developing bias voltage supplied to said plurality of developing units is common, and a charging potential and an exposure potential are controlled for each of said developing units based on a detection result of said detecting unit. The image forming apparatus according to claim 1. 4. A common power supply circuit for supplying a voltage to charging means provided corresponding to at least an electrostatic latent image carrier for forming a color toner image among the plurality of electrostatic latent image carriers. The image forming apparatus according to claim 1, wherein: