JP2004333794A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform stable density control through patch detection density control with a resin belt that can be formed at a low cost. <P>SOLUTION: A seamless belt formed from a thermoplastic resin is used as a transfer belt or an intermediate transfer belt. The patch detection density control on the belt is performed with a density sensor of a diffuse ray density type. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electrophotographic image forming apparatus, and more particularly to an apparatus using a transfer material carrier or an intermediate transfer body.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, as an example of an image forming apparatus that forms an image by an electrophotographic method, such as a copying machine or a laser beam printer, each color component image of Y (yellow), M (magenta), C (cyan), and Bk (black) is superimposed. There is a full-color image forming apparatus that forms an image together.
[0003]
In such a full-color image forming apparatus, the maximum density and the halftone density of each of the Y, M, C, and Bk color component images are defined in order to improve the image quality. It is important to control the density so that a constant density image is always obtained without being affected. For this reason, a conventional full-color image forming apparatus is provided with a density detecting means for performing density control.
[0004]
A full-color image forming apparatus includes a plurality of image carriers, and transfers a toner image formed on each image carrier onto a transfer material carried on a transfer belt serving as a transfer material carrier to obtain a full-color image. In the image forming apparatus, the number of density sensors is reduced for cost reduction, Y, M, C, and Bk test patterns are transferred onto the transfer belt, and the test is performed using one density sensor provided facing the transfer belt. A method of controlling the toner density by detecting the density by detecting the reflected light of the reference light applied to the pattern is disclosed in JP-A-63-147177. This is similarly effective in an intermediate transfer system in which a plurality of image carriers are provided, a multicolor toner image is primarily transferred to an intermediate transfer member, and collective transfer is performed on a transfer material. Japanese Patent Application Laid-Open Publication No. 2002-40722 discloses a method for detecting density by detecting specularly reflected light and diffused light of reference light applied to a test pattern primarily transferred onto a body.
[0005]
In recent years, a seamless belt made of thermosetting polyimide has been widely used as a transfer material carrier or an intermediate transfer member. Thermosetting polyimide has high hardness characteristics, heat resistance, and resistance to mechanical expansion and contraction. However, thermosetting polyimides are not only expensive in raw materials, but also when manufacturing seamless films. Since heat deformation processing cannot be performed, it is necessary to go through a number of steps such as application of polyamic acid varnish to the tubular mold, drying, imidization, and demolding. In particular, the imidization step requires complicated management of the temperature rise gradient and the like. The resulting tubular film is very expensive, and the image forming apparatus using the tubular film is necessarily expensive.
[0006]
On the other hand, thermoplastic films such as polyvinylidene fluoride (PVdF) and polyethylene terephthalate (PET) not only have low raw material costs but also have been proposed in Japanese Patent Application Laid-Open No. 07-205274. In many cases, a seamless belt can be easily formed at low cost and without thickness unevenness by a method of forming a simple tubular belt.
[0007]
[Problems to be solved by the invention]
However, since the thermoplastic resin belt described above is inferior in hardness to the thermosetting polyimide belt, when used as a transfer material carrier or an intermediate transfer member, as a large amount of image formation is repeated, the photosensitive member and the transfer member are transferred. The belt surface is easily scratched due to wear with the body cleaning blade and the like.
[0008]
Therefore, a test toner pattern is formed on the transfer material carrier or the intermediate transfer body to control the density, and when the density is detected by the reflected light, the reflectance changes due to the damage of the belt. There is a problem that the density of the pattern is erroneously detected. This phenomenon is particularly remarkable in the specularly reflected light among the reflected light. Therefore, when the specularly reflected light is used as a means for detecting the toner density, it is necessary to detect a change in the reflectance of the belt surface and perform the correction. Further, when the reflectance of the belt surface is significantly reduced, the amount of reflected light itself is reduced, so that a change in density cannot be detected.
[0009]
Further, a thermoplastic resin belt such as polyvinylidene fluoride (PVdF) or polyethylene terephthalate (PET) has a feature that the belt surface has a lower reflectance than a thermosetting polyimide belt. Therefore, since the sensitivity for detecting the density when the test toner pattern is formed on the belt is low, erroneous detection is likely to occur.
[0010]
The present invention has been made in order to solve the above-mentioned problems, and even if a thermoplastic resin belt that can be formed at low cost is used as a transfer material carrier or an intermediate transfer member, the transfer material carrier or the intermediate transfer member can be used. An object of the present invention is to provide an image forming apparatus capable of performing stable density control by forming a test toner pattern having a predetermined density on a body and detecting the density.
[0011]
[Means for Solving the Problems]
The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention is a color image forming apparatus that transfers a toner image formed on an image carrier by a plurality of developing devices to a transfer material carried on a transfer material carrier to obtain an output image, and In an image forming apparatus, the density of a test toner pattern formed on the image carrier and transferred to the transfer material carrier is detected by density detection means, and density control is performed based on the detection result. Is a seamless transfer belt made of a thermoplastic resin, wherein the density detecting means irradiates the test toner pattern with reference light and is only a diffused light sensor for detecting reflected diffused light. Image forming apparatus.
[0012]
Further, according to the present invention, after a toner image formed on a first image carrier by a plurality of developing devices is primarily transferred to a second image carrier, the toner image is transferred by the second image carrier to a transfer material. A color image forming apparatus that secondary-transfers the image onto the image carrier to obtain an output image, and detects the density of the test toner pattern formed on the image carrier and primary-transferred to the second image carrier by a density detector. In the image forming apparatus in which the density control is performed based on the detection result, the second image carrier is a seamless intermediate transfer belt made of a thermoplastic resin, and the density detecting means includes a reference light for the test toner pattern. An image forming apparatus comprising only a diffused light sensor that irradiates light and detects reflected diffused light.
[0013]
Further, the invention is characterized in that the reflection density of the transfer material carrier or the second image carrier is a color corresponding to Bk 0.3 to 0.8.
[0014]
Further, according to the invention, among the plurality of developing devices, the developer filled in the black developing device is a one-component developer.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0016]
(First Embodiment)
FIG. 1 is a sectional view showing an example of a tandem-type direct transfer type color image forming apparatus according to a first embodiment of the present invention. In the apparatus, a transfer material carrier (hereinafter, referred to as a transfer belt 21) that is stretched around several tension rollers is installed. The transfer belt 21 rotates in the direction of the arrow to convey the transfer material P carried on the transfer belt 21. Along the transfer belt 21, first, second, third, and fourth image forming units Pa, Pb, Pc, and Pd are provided in parallel, and yellow, magenta, cyan, and black toner images are sequentially formed as latent images and developed images. , Formed through a transfer process.
[0017]
Each of the image forming units Pa, Pb, Pc, and Pd has a dedicated image carrier (photosensitive drum) 3a, 3b, 3c, or 3d, and a toner image of each color is formed on each of the photosensitive drums 3a, 3b, 3c, or 3d. It is formed. A transfer belt 21 is installed adjacent to each of the photosensitive drums 3a, 3b, 3c, and 3d, and toner images of respective colors formed on the photosensitive drums 3a, 3b, 3c, and 3d are carried on the transfer belt 21 and conveyed. Is transferred onto the transfer material P. Further, the transfer material P to which the toner images of each color have been transferred is separated from the transfer belt 21 by the separation charger 31, and the fixing unit 9 fixes the toner image by heating and pressurizing, and then is discharged out of the apparatus as a recording image. You.
[0018]
The drum chargers 2a, 2b, 2c, 2d, the exposure devices 6a, 6b, 6c, 6d, the developing devices 1a, 1b, 1c, 1d, the transfer charger 5a are provided on the outer periphery of the photosensitive drums 3a, 3b, 3c, 3d, respectively. , 5b, 5c, and 5d and photosensitive drum cleaners 4a, 4b, 4c, and 4d, and a light source device (not shown) and a polygon mirror 11 are further provided above the device. The laser light emitted from the light source device is scanned by the rotation of the polygon mirror 11, the light beam of the scanning light is deflected by the reflection mirror, and is condensed on the generatrix of the photosensitive drums 3a, 3b, 3c and 3d by the fθ lens. The exposure forms a latent image on the photosensitive drums 3a, 3b, 3c, and 3d in accordance with the image signals.
[0019]
The developing devices 1a, 1b, 1c, and 1d are filled with a predetermined amount of yellow, magenta, cyan, and black toners, respectively, as a developer by a supply device (not shown). The developing devices 1a, 1b, 1c, and 1d develop the latent images on the photosensitive drums 3a, 3b, 3c, and 3d, respectively, and develop the latent images into a yellow toner image, a magenta toner image, a cyan toner image, and a black toner image. .
[0020]
The transfer material P is accommodated in a transfer material cassette 10, is supplied to the transfer belt 21 through a plurality of transfer rollers and registration rollers, and is transferred by the transfer belt 21 to face the photosensitive drums 3 a, 3 b, 3 c, and 3 d. Sent to the department.
[0021]
As the transfer belt 21, an endless shape belt or a seamless (seamless) belt is used. Then, the transfer belt 21 is rotated by the drive roller 14, the transfer material P is sent out from the registration roller to the transfer belt 21, and the transfer material P is transported toward the transfer unit of the first image forming unit Pa. At the same time, the image writing signal is turned on, and an image is formed on the photosensitive drum 3a of the first image forming unit Pa at a certain timing based on the signal. Then, the transfer charger 5a applies an electric field or charge in the lower transfer section of the photosensitive drum 3a, so that the first color toner image formed on the photosensitive drum 3a is transferred onto the transfer material P. By this transfer, the transfer material P is firmly held on the transfer belt 21 by electrostatic attraction, and is conveyed to the second image forming portion Pb and thereafter.
[0022]
Image formation and transfer in the second to fourth image forming units Pb to Pd are performed in the same manner as in the first image forming unit Pa. Next, the transfer material P to which the four color toner images have been transferred is separated from the end of the transfer belt 21 by removing the charge by the separation charger 31 at the downstream portion of the transfer belt 21 in the transport direction and attenuating the electrostatic attraction force. .
[0023]
Further, a transfer belt cleaning blade 22 for cleaning fog toner, scattered toner and the like attached to the surface of the transfer belt 21 is always in contact with the transfer belt downstream from the position where the transfer material P separates from the transfer belt 21 in the direction of travel of the transfer belt 21. ing.
[0024]
The transferred transfer material P is conveyed to the fixing device 9, where the color of the toner image is mixed and fixed to the transfer material P by fixing, a full-color copy image is formed, and the copy image is discharged to the discharge tray 20.
[0025]
On the other hand, the toner remaining on the photosensitive drums 3a, 3b, 3c and 3d is cleaned by photosensitive drum cleaners 4a, 4b, 4c and 4d such as fur brushes and blade means. The toner adhered on the transfer belt 21 is cleaned by a belt cleaner 22 such as a fur brush or a blade.
[0026]
The printer also has a CPU 61 for controlling the printer. The CPU 61 includes a RAM 62 used as a working memory, a ROM 63 storing programs executed by the CPU and various data, and a test pattern generating means 64. It is connected. The test pattern generating means 64 may be mounted in a video controller (not shown).
[0027]
In the present embodiment, as the transfer belt 21, a sheet-like film of polyvinylidene fluoride (PVdF) whose resistance is adjusted to about 10 ¹³ Ωcm with acetylene black and conductive titanium oxide is wound in a tubular shape and both ends are thermally welded. And a seamless belt having a thickness of 150 μm and a ten-point average roughness (Rz) of 0.7 μm was used. The added amounts of acetylene black and conductive titanium oxide were 2.5 parts by weight of acetylene black and 2 parts by weight of conductive titanium oxide with respect to 100 parts by weight of polyvinylidene fluoride resin, and the reflection density of the belt was Bk 0.6. The corresponding color was shown. In order to detect the toner density of each color of Y, M, C, and Bk with high sensitivity in a diffuse light type density sensor described later, the reflection density of the belt is preferably a color corresponding to Bk 0.3 to 0.8.
[0028]
Other materials for the belt include polyethylene terephthalate, polyethylene, polypropylene, polymethylpentene-1, polystyrene, polyamide, polycarbonate, polysulfone, polyarylate, polybutylene terephthalate, polyphenylene sulfide, thermoplastic polyimide, and polyether ether ketone. It is suitable for forming a large amount of thermoplastic resin at low cost.
[0029]
Further, a density sensor 41 is provided downstream of the fourth image forming unit Pd in the transfer belt traveling direction so as to face the transfer belt. As shown in FIG. 2, the density sensor 41 is formed by incorporating a light emitting element 43 such as an LED and a light receiving element 44 such as a photodiode and CdS into a holder 42. The density sensor 41 measures the density of the patch T by irradiating light from the light emitting element 43 to the toner patch T on the transfer belt 21 and receiving diffused light from the patch T by the light receiving element 44. In general, reflected light that is reflected when the reference light is irradiated includes specularly reflected light and diffused light. The specularly reflected light is light that is reflected at the position of the incident angle θ = reflection angle の of the reference light, and the diffused light is light that is reflected at the position of the incident angle θ ≠ reflection angle ψ. The output of the density sensor with respect to the density of the patch T shows different characteristics depending on the regular reflection light and the diffused light. In the present embodiment, a diffusion light type density sensor is used as the density sensor 41, and an angle of incidence θ = 15 ° and a reflection angle ψ = 45 are used.
[0030]
The Y, M, C, and Bk toner patch images are formed on the polyvinylidene fluoride transfer belt 21 used in the present embodiment, and the density of the patch image, that is, the density of the toner sensor when the applied toner amount is changed. The output is shown in FIGS. FIG. 3 shows output characteristics when density is detected by diffused light, and FIG. 4 shows output characteristics when density is detected by specularly reflected light. 3 and 4, a patch image of C was formed on a polyvinylidene fluoride transfer belt having a ten-point average roughness (Rz) of 2 μm by scratching the belt surface and changing the density of the patch image. The output of the density sensor at this time is indicated by a broken line. As shown in the figure, when the belt surface is deteriorated due to scratches, the output characteristics indicated by the diffused light hardly change, but the output characteristics indicated by the specularly reflected light show a large change particularly in the low-density portion, and the correction for that is not possible. is necessary.
[0031]
In FIG. 5, the light-emitting element of the concentration sensor used in the present embodiment is used as a reference light to irradiate a thermosetting polyimide sheet, a polyvinylidene fluoride sheet, and a polyethylene terephthalate sheet (all added with acetylene black and colored black). The reflected light amounts of the specularly reflected light and the diffused light when the light is reflected are shown. At this time, the ten-point average roughness of these resin sheets is set to 0.7 μm. As shown here, the polyvinylidene fluoride sheet or the polyethylene terephthalate sheet, which is a thermoplastic resin sheet, has an extremely low regular reflection light amount as compared with the thermosetting polyimide sheet. For this reason, the sensitivity when a patch image is formed on a polyvinylidene fluoride or polyethylene terephthalate belt and the density is detected by specular reflection light is considerably low. Easy to detect. On the other hand, the diffused light hardly changes due to the material of the sheet, and the problem does not occur.
[0032]
In the above configuration, the following control was performed. First, a latent image of a patch image, which is a reference image for density control, is formed on the photosensitive drums 3a, 3b, 3c, and 3d by the test pattern generating means 64, and developed on the developing sleeves of the developing devices 1a, 1b, 1c, and 1d. The density of each color patch image obtained by developing the patch latent image by applying a bias and transferring the patch latent image to the transfer belt 21 is measured by the density sensor 41, and the image density signal is read as an initial setting value, and is read into the RAM 62. Remember. Then, while the image forming operation is repeated, a patch image is formed at appropriate times, for example, every predetermined number of image formations, the patch image density is measured by the density sensor 41, and the obtained image density signal is initialized. The image density can be reduced by controlling the replenishment of the toner to the developer and controlling the conditions such as the exposure of the latent image and the developing bias by feeding back the comparison result to the image forming conditions. Controlled.
[0033]
Then, even if deterioration such as damage to the surface of the transfer belt was progressed by repeating a large amount of image forming operations, stable density control could be performed without performing a correcting operation for belt deterioration.
[0034]
As described above, the present invention uses a thermoplastic transfer belt that can be formed at low cost, detects a patch image density with a density sensor that detects density with diffused light, and performs density control, thereby achieving a low-cost main body configuration. Thus, stable density control could be performed without performing correction due to belt deterioration.
[0035]
(Second embodiment)
Next, a second embodiment will be described. The configuration diagram showing this embodiment is the same as FIG. 1 shown in the first embodiment, and will be described with reference to FIG.
[0036]
In the present embodiment, a sheet-like film of polyvinylidene fluoride (PVdF) whose resistance is adjusted to about 10 ¹³ Ωcm with acetylene black as a transfer belt 21 is wound in a tubular shape and both ends are joined by heat welding. A seamless belt having a thickness of 150 μm and a ten-point average roughness (Rz) of 0.7 μm was used. The amount of acetylene black added was 4 parts by weight of acetylene black based on 100 parts by weight of polyvinylidene fluoride resin.
[0037]
In the first embodiment, a two-component developer composed of a non-magnetic Bk toner and a magnetic carrier is used in the fourth image forming portion Pd. However, in the present embodiment, a magnetic one-component Bk toner is used. For this, a non-magnetic one-component Bk toner may be used.
[0038]
In the first embodiment, the resistance value and the color of the belt are adjusted by adding and dispersing two types of acetylene black and conductive titanium oxide as the resistance adjusting agent of the transfer belt. However, if the dispersion state fluctuates at the stage of adding and dispersing the resistance value adjusting agent, color unevenness occurs on the belt, and reading variation by the density sensor occurs depending on the position where the patch image is formed. However, in the present embodiment, the resistance adjusting agent is only acetylene black, and the color of the transfer belt is black, so that there is no large variation.
[0039]
FIG. 6 shows the output of the diffusion light type density sensor when the density of the patch image in the transfer belt is changed. Since the color of the transfer belt is black, the sensitivity for the Bk patch image is extremely low, and detection cannot be performed. However, for the color patch image, the detection of the density sensor can be used from almost 0 V, so that the detection accuracy is further improved. Can be.
[0040]
In the above-described configuration, the color patch image formed on the transfer belt 21 is measured by the density sensor 41, and the obtained image density signal is fed back to the image forming condition to control the toner supply to the developer. In addition, the image density was controlled by controlling the conditions such as the exposure of the latent image and the developing bias.
[0041]
Then, as in the first embodiment, even if deterioration such as damage to the surface of the transfer belt is progressing by repeating a large number of image forming operations, stable density control can be performed without performing a correcting operation for belt deterioration. I was able to do it.
[0042]
(Third embodiment)
Next, a third embodiment will be described with reference to FIG. This embodiment is an example in which the belt of the first embodiment is applied to an intermediate transfer belt type image forming apparatus.
[0043]
In this embodiment, a sheet-like film of polyvinylidene fluoride (PVdF) whose resistance is adjusted to about 10 ¹² Ωcm with acetylene black and conductive titanium oxide is wound around the intermediate transfer belt 241 in a tubular shape, and both ends are heated. A seamless belt having a thickness of 150 μm and a ten-point average roughness (Rz) of 0.7 μm joined by welding was used. Amounts of acetylene black and conductive titanium oxide were 2.5 parts by weight of acetylene black and 2 parts by weight of conductive titanium oxide with respect to 100 parts by weight of polyvinylidene fluoride resin. At this time, the belt concentration was equivalent to Bk 0.6. Colors to show.
[0044]
A diffusion light density sensor 241 is provided downstream of the fourth image forming unit Pd in the traveling direction of the intermediate transfer belt 201 so as to face the intermediate transfer belt. By performing the same control as in the first embodiment, a similar effect was obtained. Further, in the image forming apparatus of the intermediate transfer belt type, similar control is performed in a configuration using a thermoplastic intermediate belt adjusted in resistance with carbon and a one-component Bk toner, as in the second embodiment. However, it goes without saying that the same effect was obtained.
[0045]
【The invention's effect】
As described above, as in the present invention, a thermoplastic endless belt is used, and a diffusion light type density detection sensor facing the endless belt is provided to detect the density of the toner pattern formed on the endless belt. By performing density control based on the detection result, stable density control can be performed with a low-cost main body configuration without performing correction due to belt deterioration.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing a first embodiment of an image forming apparatus according to the present invention.
FIG. 2 is a sectional view showing a diffused light type density sensor in the image forming apparatus of FIG.
FIG. 3 is a graph showing the diffused light output of the density sensor when the density of the patch image is changed on the transfer belt used in the first embodiment.
FIG. 4 is a graph showing the regular reflection light output of the density sensor when the density of the patch image is changed on the transfer belt used in the first embodiment.
FIG. 5 is a relative view showing the amount of reflected specular light and diffused light when a reference light is applied to a thermosetting polyimide sheet, polyvinylidene fluoride sheet, or polyethylene terephthalate sheet.
FIG. 6 is a graph showing diffused light output of a density sensor when the density of a patch image is changed on the transfer belt used in the second embodiment.
FIG. 7 is a schematic configuration diagram showing a third embodiment of the image forming apparatus according to the present invention.
[Explanation of symbols]
1a to 1d Developing devices 3a to 3d Photosensitive drum 21 Transfer belt 41, 241 Density sensor 61 CPU
64 Test pattern generating means 201 Intermediate transfer belt

Claims (6)

A color image forming apparatus that transfers a toner image formed on an image carrier by a plurality of developing devices to a transfer material carried on a transfer material carrier, and obtains an output image, and
In an image forming apparatus, the density of a test toner pattern formed on the image carrier and transferred to the transfer material carrier is detected by density detection means, and density control is performed based on the detection result.
The transfer material carrier is a seamless transfer belt made of a thermoplastic resin,
The density detecting means irradiates the test toner pattern with reference light, and is only a diffused light sensor that detects reflected diffused light,
An image forming apparatus comprising: The image forming apparatus according to claim 1, wherein the transfer material carrier has a reflection density of a color corresponding to Bk 0.3 to 0.8. The image forming apparatus according to claim 1, wherein the developer filled in the black developing device among the plurality of developing devices is a one-component developer. After a toner image formed on a first image carrier by a plurality of developing devices is primarily transferred to a second image carrier, the toner image is secondarily transferred to a transfer material by the second image carrier. A color image forming apparatus for obtaining an output image, and
In an image forming apparatus, the density of a test toner pattern formed on the image carrier and primarily transferred to the second image carrier is detected by density detection means, and density control is performed based on the detection result.
The second image carrier is a seamless intermediate transfer belt made of a thermoplastic resin,
The density detecting means irradiates the test toner pattern with reference light, and is only a diffused light sensor that detects reflected diffused light,
An image forming apparatus comprising: 5. The image forming apparatus according to claim 4, wherein the second image carrier has a reflection density of a color corresponding to Bk 0.3 to 0.8. The image forming apparatus according to claim 4, wherein the developer filled in the black developing device among the plurality of developing devices is a one-component developer.

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