JP2001290320A - Image density controller and image forming device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image density controller capable of highly accurately detecting the density of a toner image for image density detection formed on an image density detecting medium in the case of detecting the density of the toner image for image density detection forming on the image density detecting medium, and then, capable of highly accurately controlling the image density. SOLUTION: At least one of the emitted light wavelength of an optical density detecting means, the received light wavelength of the means, and the mirror reflectivity of the image density detecting medium is set so that the mirror reflectivity of the image density detecting medium at the emitted light wavelength and/or received light wavelength of the optical density detecting means may be increased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an electrophotographic system,
An image density control device used in an image forming apparatus such as a copying machine, a printer, a facsimile, etc., which adopts an image forming method such as an electrostatic recording method, an ionography method, a magnetic recording method, etc., and forms a color or monochrome image, and In particular, a toner image (test patch) for controlling the image density is formed on an image density detecting medium such as an intermediate transfer member or a transfer roll, and the density of the toner image for controlling the image density is controlled. And an image forming apparatus using the same, which detects an image density by an optical density detecting means and controls an image forming parameter, a toner supply parameter, and the like according to the result.

[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 adopting this type of electrophotographic system, an image having a desired density is formed and, consequently, a desired brightness. An image density control device for controlling image density is used in order to form a color image of color, saturation and chromaticity. This image density control device generally forms a toner image of a predetermined color for image density control (hereinafter, referred to as a “test patch”) on a photosensitive drum, and detects the density of the test patch by an optical density sensor. The image forming parameters and the toner supply parameters are controlled in accordance with the result.

Meanwhile, in such an image density control apparatus, a technique disclosed in Japanese Patent Application Laid-Open No. 8-44122 and the like has already been proposed as a technique which enables high-precision density control.

The image forming apparatus disclosed in Japanese Patent Application Laid-Open No. 8-44122 includes a detecting pattern forming means for forming an image density detecting pattern on a photoreceptor, and a density detecting means formed by the detecting pattern forming means. A primary transfer means for transferring the pattern onto the intermediate transfer member, a secondary transfer means for secondary transferring the density detection pattern transferred on the intermediate transfer member onto the transfer roller, and a density detection pattern on the transfer roller. A density detecting means for detecting the image density, and a control means for controlling the image density by comparing the density detected by the density detecting means with a reference density, and a white conductive transfer roller as the transfer roller It is configured to be used.

[0005]

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. 8-44122, as described in paragraph [0045], the density detection pattern is secondarily transferred to the transfer roller instead of the paper. Later, the concentration is detected,
The transfer roller uses a white whisker as a conductivity-imparting agent. By making the color of the transfer roller itself white, it is possible to easily detect the image density and to reduce the image after the secondary transfer. By measuring the density, a density closer to an actual image (image on paper) can be detected.

However, as disclosed in JP-A-8-44122, the density of the density detection pattern is detected on the transfer roller, and the color of the transfer roller itself is set to white, which is the color of paper. Even so, high-precision density control cannot be performed.

That is, in order to enable high-precision density control, whether on a transfer roller or an intermediate transfer member,
The only problem is how to accurately detect the density of the density detection pattern formed (transferred) on the image density detection medium, that is, to obtain a detection result that accurately corresponds to the density of the density detection pattern. .

[0008] The density of the density detection pattern formed on the image density detection medium is detected by an optical density sensor. The optical density sensor uses the density of the image density detection medium on which the density detection pattern is formed. Detecting the density of the density detection pattern by detecting the specular reflection component of the image or detecting the scattered light component from the image density detection medium on which the density detection pattern is formed. Then, in order to obtain a detection result accurately corresponding to the density of the density detection pattern using such an optical density sensor, the density of the density detection pattern, that is, the density of the toner constituting the density detection pattern attached to the image density detection medium It is important how accurately the specular reflection component and the scattered light component from the image density detection medium that change according to the amount can be detected.

However, in the case of the technique disclosed in Japanese Patent Application Laid-Open No. 8-44122, the density of the density detection pattern is detected on the transfer roller, and the color of the transfer roller itself is set to the white color which is the color of the paper. Although the amount of light having a wavelength in the visible light region absorbed by the surface of the transfer roller can be reduced to some extent by making the color of the transfer roller itself white, the surface condition of the transfer roller can be reduced. In some cases, the reflectance of light having a wavelength used for density detection of the density detection pattern cannot be improved.

[0010] To explain further, Japanese Patent Laid-Open Publication No.
In the case of the technology disclosed in Japanese Patent Publication No. 22, when the mirror surface reflectance of the transfer roller is low and the surface of the transfer roller is matte, the scattered light component on the transfer roller increases, and it is difficult to distinguish the component from the component scattered by the toner. Therefore, the detection accuracy of the density of the density detection pattern is not improved.

As described above, when the specular reflectance of the image density detection medium on which the density detection pattern is formed is low, the light amount of the light emitting element (LED) of the optical density sensor must be set high. In order to increase the light amount of the (LED), it is necessary to increase the current supplied to the light emitting element (LED), and there is a problem that the life of the light emitting element (LED) is shortened. In addition, when the reflectance of the transfer roller decreases due to a change over time on the surface of the transfer roller, the light amount of the light emitting element (LED) can be dealt with by increasing the light amount of the light emitting element (LED). There is a problem that not only is there a limit in increasing the height, but also the life of the light emitting element (LED) is shortened.

In the case where the image density detection medium on which the density detection pattern is formed has a large amount of scattered light components, if toner adheres to the image density detection medium, scattered light is generated on the surface of the toner. To detect the amount,
As described above, there is a problem that it is difficult to distinguish toner adhesion.

Further, even when the scattered light component of the image density detection medium on which the density detection pattern is formed is small, if the specular reflectance is small due to the absorption of light by the image density detection medium, the specular reflection component is detected. Then, it is necessary to increase the light amount of the light emitting element. For this reason, there is a problem that the influence of a part of the scattered light entering the light emitting element becomes large, and the detection error of the toner density becomes large.

Accordingly, the present invention has been made to solve the above-mentioned problems of the prior art, and an object of the present invention is to provide an image density detecting toner image formed on an image density detecting medium. When the density is detected by the optical density detection unit, the density of the toner image for image density detection formed on the image density detection medium can be detected with high accuracy, and the image density can be controlled with high accuracy. It is to provide a possible image density control device.

[0015]

That is, according to the first aspect of the present invention, a toner image for controlling image density is formed on the surface of the image density detecting medium, and the toner image is formed on the surface of the image density detecting medium. In the image density control device which detects the density of the toner image by the optical density detecting means and controls the image density based on the detection result of the optical density detecting means, an emission wavelength, a light receiving wavelength, and At least one of the specular reflectivity of the image density detecting medium is set so that the specular reflectivity of the image density detecting medium with respect to the emission wavelength and / or the received light wavelength of the optical density detecting means is high. It is. Since the specular reflectance of the image density detecting medium has wavelength dependence, the specular reflectance of the image density detecting medium is set to be high with respect to the emission wavelength and / or the received wavelength of the optical density detecting means. This is very important. For this purpose, the specular reflectance of the image density detecting medium itself may be set high, or a light emitting element that emits light having a wavelength that increases the specular reflectivity of the image density detecting medium may be used. A light-receiving element having high light-receiving sensitivity to light reflected by the medium with high specular reflectance may be used, or any of these may be arbitrarily combined.

According to a second aspect of the present invention, a coating layer having a high specular reflectance with respect to the emission wavelength and / or the reception wavelength of the optical density detecting means is provided on the surface of the image density detecting medium. The image density control device according to claim 1, wherein:

Further, according to the present invention, the optical density detecting means is provided on the surface of an image density detecting medium having a high specular reflectance with respect to the emission wavelength and / or the received light wavelength of the optical density detecting means. The image density control device according to claim 1, further comprising a surface coat layer that transmits light having a light emission wavelength and / or a light reception wavelength.

Still further, the invention described in claim 4 is as follows.
4. The image density control device according to claim 1, wherein said optical density detection means detects a specular reflection component.

Further, the invention described in claim 5 is the image density control device according to any one of claims 1 to 3, wherein the optical density detecting means detects a scattered light component. .

According to a sixth aspect of the present invention, the optical density detecting means detects both the specular reflection component and the scattered light component, and based on the values of both the specular reflection component and the scattered light component. The image density control device according to any one of claims 1 to 3, wherein the image density control device detects the toner density.

Further, the invention described in claim 7 is:
Forming each latent image according to the input information for each color, developing each latent image with a toner of the corresponding color to obtain a plurality of single color toner images,
An image forming apparatus that forms a color image by fixing the plurality of single-color toner images on a recording medium,
Three or more image carriers on which each latent image is formed in accordance with the input information for each color and each latent image is developed with a toner of the corresponding color to form a single color toner image, or input information for each color A single image carrier in which each latent image is sequentially formed, and each latent image is developed with a toner of a corresponding color to form each single-color toner image in sequence, and is in contact with or close to the image carrier. One or a plurality of intermediate transfer members to which each monochromatic toner image formed on the image carrier is transferred, and the toner image transferred to the one or a plurality of intermediate transfer members. A final transfer rotator for transferring to a recording medium and a toner image for controlling image density are formed on the surface of the intermediate transfer member or the final transfer rotator, and formed on the surface of the intermediate transfer member or the final transfer rotator. The density of the toner image is detected by an optical density An image density control unit for controlling an image density based on a detection result of the density detection unit, wherein the image forming apparatus forms a color image through at least two or more toner image transfer steps. At least one of the emission wavelength, the reception wavelength, and the specular reflectance of the image density detection medium is set so that the specular reflectance of the image density detection medium with respect to the emission wavelength and / or the reception wavelength of the optical density detection unit is increased. An image forming apparatus characterized by setting.

[0022]

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

Embodiment 1

FIG. 1 shows a tandem type full-color printer as an image forming apparatus to which an image density control device according to Embodiment 1 of the present invention is applied. In addition, the arrow in FIG. 1 has shown the rotation direction of each rotating member.

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 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, a DC voltage of about -840 V is applied to the charging rolls 12, 22, 32, and 42 as contact-type charging devices to charge the surface to about -300 V, for example. 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 formed in cyan (C), magenta (M), yellow (Y), and black (K) colors by a laser optical unit as an exposure device. Corresponding laser beams 31, 32, 33, and 34 are applied to form an electrostatic latent image corresponding to input image information for each color. When an electrostatic latent image is written on the photosensitive drums 11, 12, 13, and 14 by the laser optical unit, the surface potential of the image exposed portion is removed 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).

In this embodiment, the developing devices 41, 42, 4
3, 44, a magnetic brush contact type two-component developing method is adopted, but the scope of the present invention is not limited to this developing method, and other developing methods such as a non-contact type developing method are used. It goes without saying that the present invention can be sufficiently applied also to the above.

The developing devices 41, 42, 43, and 44 contain toners of cyan (C), magenta (M), yellow (Y), and black (K) of different colors, and a developer composed of a carrier. Is filled. These developing devices 41, 42,
When the toner is supplied from a toner supply device (not shown), the supplied toner is sufficiently stirred with the carrier by the auger 404 and charged by friction. 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 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
It is about 35 μC / g.

The toner supplied onto the developing roll 401 is in the form of a magnetic brush composed of a carrier and toner due to the magnetic force of the magnet roll, and the magnetic brush is applied to 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 30V.

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 , + 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.

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 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 +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 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). 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 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 +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 of 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 above is the image forming process 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 fluctuations and 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.

In this embodiment, on the image density detecting medium such as the final transfer roll 60 and the secondary intermediate transfer drum 53, the position is shifted in the process direction to the same position in the axial direction, and the image density is controlled. (Hereinafter, referred to as “test patch”), a single optical density detecting unit can detect the test patch of each color.

In order to detect a test patch on the photosensitive drums 11, 12, 13, and 14, the respective photosensitive drums 11, 12, 13, and 14 are detected.
, That is, four optical density detecting means are required. 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, 1
One optical density detecting means is sufficient. 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 used as 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 intervals of 3 mm as shown in FIG.

As shown in FIG. 4, 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 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.

The image density control apparatus according to this embodiment is configured to determine at least one of the emission wavelength and the reception wavelength of the optical density detection means and the specular reflectance of the image density detection medium by the optical density detection means. Emission wavelength of the means and / or
Alternatively, it is configured such that the specular reflectance of the image density detection medium with respect to the received light wavelength is increased.

Further, on the surface of the image density detecting medium,
If necessary, the emission wavelength of the optical density detection means and / or
Alternatively, a coat layer having a high specular reflectance with respect to the light receiving wavelength is provided.

That is, in this embodiment, as shown in FIG. 2, the final transfer roll 60 forms a coating layer 62 made of a carbon-dispersed conductive phenol resin on a metal shaft 61 having a diameter of 8 mm. The surface of the coating layer 62 is polished to a mirror surface. The reflectance of the surface of the final transfer roll 60 with respect to light having a wavelength of 900 nm is 6%.
Met. The reflectance of the surface of the final transfer roll 60 was measured using a spectrophotometer. In this case, the incident angle and the reflection angle of the measurement light were set to 6 °. The coating layer 62 made of the conductive phenol resin is 230 mm in the axial direction. The resistance value of the final transfer roll 60 is set to 10 ⁸ Ω.

In the first embodiment, as shown in FIG. 7, the surface of the coating layer 62 of the final transfer roll 60 is configured to be mirror-finished by polishing. The specular reflectance of the 62 surfaces is set high. In the final transfer roll 60, a component having a reflection angle of 6 ° needs to be 3% or more with respect to light having a wavelength of an incident angle of 6 ° irradiated from the light emitting element 102 of the optical density sensor 100. The reflectivity of the conventional final transfer roll 60 is 1.5
%, And as will be described later, the value of Vpatch / Vcln is low. However, if the reflectance is 3% or more, the reflectance is about twice that of the conventional case, and the value of Vpatch / Vcln is And it becomes stable over time, so 3%
It is necessary to be above. The component having a reflection angle of 6 ° is preferably at least 6%, more preferably at least 10%.

On the other hand, as the optical density sensor 100, an LED is used as the light emitting element 102.
The emission wavelength of No. 2 is a wavelength in the infrared region, specifically, about 800 to 1500 nm. In this embodiment,
The light emitting element 102 has a peak at 880 nm. Also,
As the light receiving element 103, an element having light receiving sensitivity with respect to a wavelength corresponding to the emission wavelength of the light emitting element 102 is used.

FIG. 8 is a block diagram showing a control circuit of the image density control device according to this embodiment.

In FIG. 8, reference numeral 300 denotes the optical density sensor 100.
A control circuit 301 comprising 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 Vftc applied to the charging devices 21, 22, 23, 24
And the developing bias voltage Vbi to the developing devices 41, 42, 43, 44
A potential control circuit for controlling as, 302 is a charging device 21, 22, 2
A high-voltage power supply for applying a predetermined voltage Vc to the developing devices 3 and 24, and a predetermined developing bias voltage Vbias 303 to developing devices 41, 42, 43 and
The reference numeral 304 denotes a high-voltage power supply, and 304 denotes a toner density control circuit for controlling toner supply to the developing device based on an output signal from the control circuit 300.

In the above configuration, the image density control device according to this embodiment performs the following operations when the density of the toner image formed on the image density detection medium is detected by the optical density detection means as follows. The density of the toner image formed on the image density detection medium can be detected with high accuracy, and the image density can be controlled with high accuracy.

That is, in the image density control device according to this embodiment, first, as shown in FIG.
If the test patch is not transferred, the surface of the final transfer roll 60 is detected by the optical density sensor 100, and the output Vcln of the optical density sensor 100 at this time is stored (step 101). Next, under the same charging, exposure, development, and transfer conditions as those used in image formation, a 12 × 12 mm 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 are formed on the final transfer roll 60 at intervals of 3 mm (step 102).

Thereafter, the cyan (C), magenta (M), yellow (Y),
Figure 1 shows the test patch 200 for each color of black (K).
0 (a) or FIG. 10 (b), the optical density sensor 100 detects 16 points at a pitch of 0.5 mm and detects the average value Vpa.
tch is obtained (step 103). Here, as shown in FIG. 10A, a specular reflection type optical density sensor is used.
100 is used. Then, a 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 (step 104). 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, 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. 11B, the charged potential of the photosensitive drum is increased (step 106). By doing so, as shown in FIG. 11B, 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.

On the contrary, if 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. 11C, 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. At this time, the adjustment amount of the developing bias and the supply voltage to the charging device is determined by the detected density of the test patch.

Here, the developing bias and the supply voltage to the charging device are adjusted, but any device that adjusts the density or gradation of an 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.

In this embodiment, the surface of the coating layer 62 of the final transfer roll 60 is polished to a mirror surface, and the reflectance of the surface of the final transfer roll 60 is 6%. Has become.

Therefore, the coating layer of the final transfer roll 60
Since the surface of the surface 62 has a high specular reflectance as shown in FIG. 7, the amount of specular reflection from the surface of the coating layer 62 before the test patch 200 is formed is large, and the amount of light emitted from the light emitting element 102 is large. It is possible to obtain a large output voltage from the light receiving element 103 without setting a large value. Further, in a state where the test patch 200 is formed on the surface of the coating layer 62 of the final transfer roll 60, as shown in FIG. 10A, light emitted from the light emitting element 102 is scattered by the test patch 200,
Since the diffuse light component increases, the specular reflected light component incident on the light receiving element 103 decreases according to the density of the test patch 200. As a result, the output of the light receiving element 103 is
Thus, the density of the test patch 200 can be detected with high accuracy, and the image density can be controlled with high accuracy.

EXPERIMENTAL EXAMPLE 1 Next, the present inventors prototyped a printer as shown in FIGS. 1 and 2, and made the final transfer roll 60 under the following image forming conditions.
An experiment was conducted in which a test patch 200 having a predetermined density was formed thereon, and the density of the test patch 200 was detected by the optical density sensor 100.

Image forming conditions Photoconductor charge potential -300V Solid image potential -20V DC component for development -220V AC component for development pp 1.3kV Frequency 4kHz Waveform Sine wave Primary intermediate transfer member potential + 380V Secondary intermediate transfer member Potential +880 V Final transfer roll +6 μA Toner concentration of developer 6.8% Toner charge amount in developer -28 μC / g Environment 22 ° C./55% RH

As shown in FIG. 5, the current supplied to the LED as the light emitting element 102 by the mirror reflection type optical density sensor 100 is set to 20 mA, and the output of the light receiving element 103 is applied to the elementary surface of the final transfer roll 60 as shown in FIG. It was 4.1 V when measured.

On the other hand, a 12 × 12 mm test patch 200 having an image density of 40% is formed on the surface of the final transfer roll 60, and the density of the test patch 200 is measured by a specular reflection type optical density sensor 100. When the output current of the light receiving element 103 was measured with the supply current to the LED as 20 mA, an output of 0.8 V was obtained.

Accordingly, in this embodiment, the ratio of the output of the light receiving element 103 when the test patch 200 is formed on the surface of the final transfer roll 60 to the surface of the final transfer roll 60 is 0.8 / 4. Since 1 = 0.20, a large output ratio of the light receiving element 103 of 0.20 can be obtained, and the density of the test patch 200 formed on the surface of the final transfer roll 60 can be detected with high accuracy. It was found that the image density could be controlled with high accuracy.

As shown in FIG. 12, when the surface of the final transfer roll 60 is not in a mirror state but has irregularities, the mirror reflection component, which is an effective component of the optical density sensor 100, is reduced. , Undesirable. Note that components absorbed on the surface of the final transfer roll 60 are also lost.

As shown in FIG. 13, even when the surface of the final transfer roll 60 is not mirror-finished and has irregularities, the surface of the final transfer roll 60 has the optical density sensor 100. By providing the coating layer 63 having a high specular reflectance with respect to the emission wavelength and / or the reception wavelength, the final transfer roll 60 does not have a mirror surface state, and even if the final transfer roll 60 has irregularities, Since the specular reflection component increases, the density of the test patch 200 can be detected with high accuracy.

Second Embodiment FIG. 14 shows a second embodiment of the present invention. The same parts as those in the first embodiment are denoted by the same reference numerals. A surface coat layer for transmitting light having a light emission wavelength and / or a light reception wavelength of the optical density detection means on a surface of an image density detection medium having a high specular reflectance with respect to a light emission wavelength and / or a light reception wavelength of the optical density detection means; Is provided.

That is, in the second embodiment, FIG.
As shown in (1), a final transfer roll 60 is formed on a metal shaft 61 having a diameter of 8 mm by forming a coating layer 62 made of ion-conductive urethane rubber, and polishing the surface to form a mirror-finished surface with a diameter of 20 mm. . Further, a fluorine-based urethane resin is coated on the surface of the coating layer 62 as a coating layer 63 to a predetermined thickness. This coat layer 63 is formed as shown in FIG.
As shown in FIG. 5, light of a wavelength emitted from the light emitting element 102 of the optical density sensor 100 is transmitted, and light transmitted through the coating layer 63 is reflected on the surface of the coating layer 62.

In this way, as shown in FIG. 15, when the mirror base 62 is provided with the coating layer 63 which is transparent and mirror-irradiated with respect to the irradiation light, the optical density sensor 100 is effective in detecting the density of the test patch. The component is a specular reflection component on the surface of the coat layer 63 and a component specularly reflected on the underlayer 62.
The amount absorbed by 63 and the amount absorbed by base 62 are losses. Therefore, the transmittance of the coating layer 63 to the irradiation light is high,
It is preferable that the base 62 has a small absorption component.

Further, as shown in FIG.
When a coating layer 63 which is transparent and mirror-reflective to the irradiation light is provided, the effective component when the density of the test patch is detected by the optical density sensor 100 is the specular reflection component on the surface of the coating layer 63 and the coating layer 63. Is a component that is transmitted through the mirror and is specularly reflected by the underlayer 62. The component absorbed by the coat layer 63, the component absorbed by the substrate 62, and the component scattered by the substrate 62 is a loss. Therefore,
It is preferable that the transmittance to the coat layer 63 is high and the base 62 has a small absorption component.

Further, as shown in FIG.
When an uneven coating layer 63 is provided on 62, the optical density sensor 10
The effective components for detecting the density of the test patch at 0 are the specular reflection component on the surface of the coat layer 63 and the component transmitted through the coat layer 63 and specularly reflected on the underlayer 62.
63, the scattered component of the reflected light on the surface of the coat layer 63, the component transmitted through the coat layer 63 and absorbed by the base 62, and scattered by the coat layer 63 when exiting from the coat layer 63. Is lost. Therefore, it is preferable that the coat layer 63 has a high transmittance to the irradiation light and the base 62 has a small absorption component.

When a transparent and uneven coating layer is provided on an uneven base, the loss shown in FIGS. 16 and 17 overlaps, which is not good.

EXPERIMENTAL EXAMPLE 2 A final transfer roll 60 was mounted on a metal shaft 61 having a diameter of 8 mm.
Form a coating layer 62 made of ion conductive urethane rubber,
The surface was polished to form a mirror surface with a diameter of 20 mm. A fluorine-based urethane resin was formed as a coating layer 63 on the surface to a thickness of 12 μm. The reflectance of the final transfer roll 60 was 3%.

The output of the final transfer roll 60 was 2.2 V when the current supplied to the LED was 20 mA with a mirror reflection type sensor.

When a test patch was formed under the image forming conditions, an output of 0.4 V was obtained.

Therefore, in this embodiment, the ratio of the output of the light receiving element 103 when the test patch 200 is formed on the surface of the final transfer roll 60 and the surface of the final transfer roll 60 is 0.4 / 2. 2 = 0.18, and a large output ratio of the light receiving element 103 of 0.18 can be obtained, and the density of the test patch 200 formed on the surface of the final transfer roll 60 can be detected with high accuracy. It was found that the image density could be controlled with high accuracy.

COMPARATIVE EXAMPLE An ion-conductive urethane rubber 62 was formed on a metal shaft 61 having a diameter of 8 mm, and polished to a mirror-like state.
And A 10 μm thick film of a fluorine-based carbon-dispersed urethane resin was formed as a coating layer 63 on the surface. The reflectance of the final transfer roll 60 was 1.5%.

The output of the final transfer roll 60 was 1.0 V when the current supplied to the LED was set to 20 mA by a mirror reflection type sensor.

When a test patch was formed under image forming conditions, only an output of 0.1 V was obtained.

The ratio was 0.1 / 1.0 = 0.10, which was much lower than that of Experimental Examples 1 and 2, and the detection accuracy of the test patch 200 formed on the surface of the final transfer roll 60 was improved. Was low.

The other configuration and operation are the same as those of the first embodiment, and the description thereof will be omitted.

[0092]

As described above, according to the present invention,
When the density of the toner image formed on the image density detection medium is detected by the optical density detection means, the density of the toner image formed on the image density detection medium can be detected with high accuracy. Image density control device capable of controlling the image density with high accuracy.

[Brief description of the drawings]

FIG. 1 is a configuration diagram illustrating a color printer to which an image density control device according to a first embodiment of the present invention is applied.

FIG. 2 is a sectional view showing a final transfer roll of a color printer to which the image density control device according to the first embodiment of the present invention is applied.

FIG. 3 is a perspective view showing a final transfer roll of a color printer to which the image density control device according to the first embodiment of the present invention is applied.

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

FIG. 7 is a cross-sectional view illustrating a final transfer roll of a color printer to which the image density control device according to the first embodiment of the present invention is applied.

FIG. 8 is a block diagram showing a control circuit of the image density control device according to the first embodiment of the present invention.

FIG. 9 is a flowchart showing a control operation of the image density control device according to the first embodiment of the present invention.

FIGS. 10A and 10B are configuration diagrams respectively showing a detection state of an optical density sensor of the image density control device according to the first embodiment of the present invention.

FIGS. 11A to 11C are potential explanatory diagrams showing an image density control method of the image density control device according to the first embodiment of the present invention.

FIG. 12 is a sectional view showing a final transfer roll.

FIG. 13 is a sectional view showing a final transfer roll.

FIG. 14 is a sectional view showing a final transfer roll of a color printer to which the image density control device according to the second embodiment of the present invention is applied.

FIG. 15 is a sectional view showing a final transfer roll.

FIG. 16 is a sectional view showing a final transfer roll.

FIG. 17 is a sectional view showing a final transfer roll.

[Explanation of symbols]

 1, 2, 3, 4 Image forming unit 11, 12, 13, 14 Photoconductor drum (image carrier) 21, 22, 23, 24 Charging roll (contact type charging device) 31, 32, 33, 34 Laser beam 41 , 42, 43, 44 Developing device 401 Developing roll 402 Developer amount regulating member 403 Paddle 404 Auger 51, 52 Primary intermediate transfer drum (Intermediate transfer body 53 Secondary intermediate transfer drum (Intermediate transfer body) 60 Final transfer roll (Final transfer Rotating body) 61 Metal shaft 62 Coating layer 80 Cleaning device 801 Final cleaning member 802 Toner collection box 803 Support frame 804 Static eliminator 805 Bias plate 90 Paper transport roll 100 Optical density sensor 101 Holder 102 Light emitting element 103 Light receiving element 200 Test patch P paper Transport path

Continued on the front page (72) Inventor Hideaki Tanaka 3-7-1, Funai, Iwatsuki-shi, Saitama, F-term in Fuji Xerox Co., Ltd. Iwatsuki Office (Reference) 2G059 AA01 EE02 GG02 HH01 KK01 LL04 MM17 NN01 2H027 DA09 DA10 DE02 DE10 EC03 HA13 2H030 AB02 AD16 BB23 BB24 BB36 BB42 2H077 DA04 DA10 DA31 DA63 DA67 GA12

Claims (7)

[Claims] An optical density detecting means for forming a toner image for controlling image density on a surface of the image density detecting medium, and detecting a density of the toner image formed on the surface of the image density detecting medium by an optical density detecting means; In an image density control device that controls the image density based on the detection result of the optical density detection unit, at least one of the emission wavelength of the optical density detection unit, the reception wavelength, and the mirror reflectance of the image density detection medium, An image density control device, wherein the specular reflectance of the image density detection medium with respect to the emission wavelength and / or the reception wavelength of the optical density detection means is set to be high. 2. The image density detecting medium according to claim 1, wherein a coating layer having a high mirror reflectance with respect to a light emission wavelength and / or a light reception wavelength of the optical density detection means is provided on a surface of the image density detection medium. Image density control device. 3. An emission wavelength of said optical density detection means and / or
A surface coat layer for transmitting light having a light emission wavelength and / or a light reception wavelength of the optical density detection means is provided on a surface of an image density detection medium having a high specular reflectance with respect to a light reception wavelength. 2. The image density control device according to 1. 4. The image density control device according to claim 1, wherein said optical density detection means detects a specular reflection component. 5. The image density control device according to claim 1, wherein said optical density detection means detects a scattered light component. 6. The optical density detecting means detects both a specular reflection component and a scattered light component, and detects a toner density based on a value of both the specular reflection component and the scattered light component. The image density control device according to claim 1. 7. A latent image corresponding to input information of each color is formed, and each latent image is developed with a toner of a corresponding color to obtain a plurality of single-color toner images. An image forming apparatus that forms a color image by being fixed thereon, wherein each latent image is formed according to input information for each color, and each latent image is developed with a toner of a corresponding color to form a single color toner. Three or more image carriers on which images are formed, or each latent image according to input information for each color is sequentially formed, and each latent image is developed with a toner of a corresponding color to sequentially form a single-color toner image. A single image carrier, and one or a plurality of intermediate transfer members that are arranged in contact with or in close proximity to the image carrier, and onto which each single-color toner image formed on the image carrier is transferred. Recording the toner image transferred onto the one or more intermediate transfer members on a recording medium; A final transfer rotator for transferring to a body, and a toner image for controlling image density were formed on the surface of the intermediate transfer member or the final transfer rotator, and formed on the surface of the intermediate transfer member or the final transfer rotator. Image density control means for detecting the density of the toner image by the optical density detection means and controlling the image density based on the detection result of the optical density detection means, and at least two or more toner image transfer steps In an image forming apparatus for forming a color image, at least one of a light emission wavelength and a light reception wavelength of the optical density detection means and a mirror reflectance of an image density detection medium is determined by an emission wavelength of the optical density detection means and / or An image forming apparatus, wherein the specular reflectance of an image density detection medium with respect to a light receiving wavelength is set to be high.