JP3888069B2 - Image forming apparatus and image forming method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electrophotographic image forming apparatus, such as a printer, a copying machine, and a facsimile machine, which visualizes an electrostatic latent image formed on a photosensitive member such as a photosensitive drum or a photosensitive belt by attaching toner. And an image forming method.
[0002]
[Prior art]
In this type of image forming apparatus, the image density may change due to fatigue and aging of the photoconductor and toner, changes in temperature and humidity around the apparatus, and the like. Thus, many techniques have been proposed for stabilizing the image density by appropriately controlling density adjustment factors that affect the image density of the toner image, such as a charging bias, a developing bias, and an exposure amount. Specifically, while changing the density adjustment factor, a patch image is formed on the photoconductor, and after detecting the image density of each patch, the density adjustment factor necessary for obtaining the target density based on these detection values is determined. The optimum value is determined. A series of image formation is performed after setting the density adjustment factor to the optimum value.
[0003]
[Problems to be solved by the invention]
By the way, an image forming apparatus for forming a color image forms toner images of a plurality of colors, for example, four color toner images of yellow (Y), cyan (C), magenta (M), and black (K). A full color image is formed by superimposing the toner images. Therefore, in order to adjust the image density of each of these toner images, a series of patch processes (formation of patch images, detection of patch image density, and optimization of density adjustment factors) are conventionally performed for each toner color. Yes. That is, in a color image forming apparatus that forms a color image based on toner images of n colors (n ≧ 2), the patch processing is always executed n times in order to guarantee the image quality. As a result, it takes a relatively long time to optimize the density adjustment factor, and the toner is consumed for all toner colors in order to perform patch processing for all toner colors, which increases the running cost. It became one of.
[0004]
The present invention has been made in view of the above problems, and an image forming apparatus and an image forming method capable of calculating an optimum value of a density adjustment factor that affects the image density of a toner image in a short time and at a low running cost. The purpose is to provide.
[0005]
[Means for Solving the Problems]
In order to achieve the above object, an image forming apparatus according to the present invention has an exposure unit for forming an electrostatic latent image by exposing and scanning a light beam on the surface of the photosensitive member, and a toner of a different color on the photosensitive member. A first developing position having n (n ≧ 2) switching developing units for developing the electrostatic latent image, wherein one switching developing unit among the n switching developing units is selectively opposed to the photoconductor; Apart from the n number of switching developing devices and the developing means for forming the toner image by developing the electrostatic latent image with toner by the switching developing device and different from the first developing position. An independent developing device that is disposed opposite to the photoconductor at the second development position and develops the electrostatic latent image on the photoconductor with the (n + 1) th toner color to form a toner image, and for each toner color, Development bias is the most effective density adjustment factor that affects the image density of toner images. Control means for controlling the image density of the toner image formed on the photoconductor, and the toner image formed on the photoconductor by the developing means or the independent developing device, or the toner image is transferred. A density detection means for detecting the image density of the toner image transferred to the medium as a patch image, and the n switching developing devices have substantially the same attitude at the first development position. The control means is configured to change the density adjustment factor in multiple stages within a predetermined first variable range for the n switching developers. One of them is used to form a plurality of toner images on the photoconductor as patch images, and for all of the n colors based on the detection result of the density detection means for the patch images. While the density adjusting factor is optimized, the independent developing unit is configured to use the independent developing unit while changing and setting the density adjusting factor in multiple stages within the second variable range wider than the first variable range. A toner image is formed as a patch image on the photoconductor, and the density adjustment factor is optimized for the (n + 1) th toner color based on the detection result of the density detection means for the patch image.
[0006]
Further, the image forming method according to the present invention comprises substantially the same constituent members as the exposure means for forming an electrostatic latent image by exposing and scanning a light beam onto the surface of the photosensitive member, and is exposed to toners of different colors. And n (n ≧ 2) switching developers for developing the electrostatic latent image on the body, and one of the n switching developers is selectively opposed to the photoconductor. In addition to the developing means for positioning at one developing position and developing the electrostatic latent image with toner by the switching developer to form a toner image, the first developing position is further separated from the n switching developers. And an independent developing device that is disposed opposite to the photoconductor at a second development position different from the above and develops the electrostatic latent image on the photoconductor with the (n + 1) th toner color to form a toner image. Use the device to affect the image density of the toner image for each toner color An image forming method for controlling the image density of a toner image formed on the photoconductor by optimizing a developing bias as a degree adjustment factor, and in order to achieve the above object, the density adjustment factor is set to a predetermined value. A plurality of toner images are formed as patch images on the photosensitive member using one of the n switching developing devices while changing and setting in multiple stages within one variable area, and the density detection for the patch image is performed. The density adjustment factor is optimized for all of the n colors based on the detection result of the means, while the independent development is performed while the density adjustment factor is changed and set in multiple stages within a second variable range wider than the first variable range. A toner image is formed as a patch image on the photoconductor using a container, and the (n + 1) th toner color is determined based on the detection result of the density detection means for the patch image. And optimizing the density adjustment factor Te.
[0007]
One of the main factors affecting the image density of the toner image is the surface potential of the electrostatic latent image at the time of development processing, that is, the bright portion potential. For example, as shown in FIG. 1, the bright portion potential has time dependency, and when the development position is different for each toner color, the bright portion potential may be different from each other. Even if an image is formed under the same conditions, the image density may differ due to the difference in the bright part potential. In such a case, it is necessary to optimize the density adjustment factor by forming a patch image for each toner color.
[0008]
In contrast, in the present invention, the n switching developing devices are selectively positioned at the developing position, and then the electrostatic latent image on the photosensitive member is visualized with toner to form a toner image. In the toner color as well, the time from when the electrostatic latent image is formed by irradiating the photosensitive member with the light beam until the electrostatic latent image moves to the developing position is constant, and the bright portion potential has the same value. Will have. Therefore, a patch image is typically formed on the photosensitive member by one switching developer, and the development bias as a density adjustment factor is optimized for all n colors based on the image density of each patch image. This eliminates the need for patch image formation and density detection for at least one toner color, shortens the time required to optimize the density adjustment factor, and reduces running costs by suppressing toner consumption. Can be achieved. Further, since the postures of the switching developing devices at the first development position are substantially the same and are constituted by substantially the same constituent members, the development γ characteristics of the respective colors can be made substantially the same. Therefore, the optimum value set for each toner color is almost the same as the optimum value obtained by patch processing as in the prior art, which is more preferable.
[0009]
Further, as the toner consumption progresses, the deteriorated toner increases in the developing unit of the toner color, leading to a decrease in image quality. If the presence of the deteriorated toner is within an allowable range, it is possible to guarantee the image quality by optimizing the density adjustment factor, but if it exceeds the allowable range, the optimum value of the density adjustment factor is also obtained by patch processing. I can't do that. Therefore, if a patch image is formed for a switching developer that consumes the largest amount of toner, patch processing is always performed for the toner color where the problem of deteriorated toner is most important, and development is performed by detecting the influence of deteriorated toner. It is possible to reliably detect the necessity of replacing the toner cartridge or the toner cartridge.
[0010]
Here, in order to optimize the density adjustment factor most efficiently, a patch image may be formed using one switching developer among n switching developers. That is, one of the n toner colors is set as a reference toner color, and a plurality of patch images are formed for the reference toner color by a switching developer corresponding to the reference toner color while changing the density adjustment factor in multiple stages. Then, while obtaining the optimum value of the density adjustment factor for the reference toner color based on the image density of each patch image, for the (n-1) toner colors excluding the reference toner color, the density adjustment factor for each toner color is respectively set. What is necessary is just to set to the said optimal value.
[0011]
In addition to the n switching developing devices described above, the electrostatic latent image on the photosensitive member is developed with the (n + 1) th toner color to be disposed opposite to the photosensitive member at a different developing position to form a toner image. However, the density adjustment factor may be optimized as follows for the (n + 1) th toner color. That is, a toner image is formed as a patch image on the photosensitive member using an independent developing device, and the density adjustment factor is optimized for the (n + 1) th toner color based on the detection result of the density detection means. In this way, the image density of the toner image can be controlled for the (n + 1) th color.
[0012]
In the developing devices having different development positions as described above, the bright portion potential may be different depending on the development position. Further, the developing device posture at the developing position (particularly the posture with respect to the direction of gravity) and the constitution of the developing device may differ, and the development γ characteristics may differ. Accordingly, the optimum value of the density adjustment factor finally obtained may differ depending on the development position. Therefore, it is desirable to execute patch processing in consideration of the development position. For example, the first and second variable areas are set according to the distances from the exposure position exposed by the exposure means to the first and second development positions, respectively, and a density adjustment factor is set for the n toner colors. While a plurality of patch images are formed by the switching developer while changing between the first variable areas, an independent developer is used to change the density adjustment factor for the (n + 1) th toner color between the second variable areas. It is desirable to form a plurality of patch images. By doing so, the probability that the optimum values for the switching and independent developing devices are included in the first and second variable regions, respectively, is high, and the density adjustment factor can be reliably optimized. In particular, in the independent developing device, the degree of toner stirring and circulation in the interior is small, and the development fluctuation of the development γ characteristic is large.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
A. Principle of invention
In this type of image forming apparatus, a light beam is scanned and exposed on a uniformly charged photoreceptor surface, and the surface potential of the photoreceptor is partially changed to form an electrostatic latent image. Then, while applying a developing bias to the developing device, toner is attached to the electrostatic latent image to form a toner image. Here, if the surface potential of the electrostatic latent image, that is, the bright portion potential is Von and the developing bias is Vb, the contrast potential Vcon closely related to the amount of toner adhering to the photoreceptor is
Vcon = | (development bias Vb) − (light portion potential Von of photoconductor) |
It becomes.
[0014]
By the way, as is well known in the art, an undercoat layer, a charge generation layer, and a charge transport layer are laminated in this order on a conductive substrate such as drum-shaped aluminum. When the photosensitive member charged with a predetermined surface potential is irradiated with the light beam, the surface charge corresponding to the irradiated portion disappears and an electrostatic latent image is formed. Taking a negatively charged OPC as an example, holes and electrons generated in the charge generation layer by irradiation with a light beam move according to the electric field. That is, the holes move in the charge transport layer toward the surface of the photoreceptor so that the holes are attracted to the negative charge on the surface of the photoreceptor, and cancel the negative charges on the surface. Thereby, an electrostatic latent image is formed.
[0015]
The surface potential at the electrostatic latent image portion thus formed, that is, the bright portion potential, has time dependency. For example, as shown in FIG. 1, when a negatively charged OPC negatively charged to the surface potential Vs0 is irradiated with a light beam, a hole group generated in the charge generation layer is generated. This group of holes moves through the charge transport layer and counteracts negative charges on the surface. Although the absolute value of the surface potential of the photoconductor decreases sharply after a time until the head of the hole group arrives at the surface, the electric field for moving the holes decreases as the absolute value of the potential decreases. Therefore, the degree of decrease gradually decreases. When the predetermined time Ts has elapsed, an electric field sufficient to move the holes cannot be formed, the bright part potential settles to a constant potential Von, and the bright part potential Von2 at the subsequent time T2 is equal to the bright part potential Von. Become. On the other hand, the light portion potential Von1 at a time shorter than the time Ts, for example, the light portion potential Von1 at the time T1, does not fall down to the potential Von, and the relationship between the surface potential Vs0, the light portion potential Von1 at the time T1 and the light portion potential Von after the time Ts is
| Vs0 | >> | Von1 | >> | Von |
It becomes.
[0016]
Here, as shown in FIG. 2, distances Ly, Lc, Lm, Lk from the exposure position to the development position (developer) for forming the toner image of each toner color (Y, C, M, K) are respectively represented. Further, when the peripheral speed of the photosensitive member is a speed V, times Ty, Tc, Tm, and Tk from the exposure to the start of toner development by each developer are expressed by the following equations:
Ty = Ly / V
Tc = Lc / V
Tm = Lm / V
Tk = Lk / V
It becomes. Therefore, for example, in an image forming apparatus in which a plurality of developing devices are arranged in order along the rotation direction of the photosensitive member, the development positions of the toner colors are different from each other, and the light portion potential is different for each toner color. As in the prior art, it is necessary to optimize the density adjustment factor by executing patch processing for each toner color.
[0017]
On the other hand, if the developing units are configured so that the developing positions of the toner colors coincide with each other, the distances Ly, Lc, Lm, and Lk are the same, and the light portion potential Von for each toner color is constant. Further, when the switching developing device is configured so that the developing positions coincide with each other, the configuration is as follows: 1) The developing devices of the respective colors are provided to be rotatable about the axis (= provided so as to be able to circulate in a rotary manner), or 2) The developing devices for each color are arranged in a row, and the developing devices are moved in the arrangement direction. In such a configuration, the postures of the developing units of the respective colors at the developing positions can be made substantially the same, and can be constituted by substantially the same constituent members. In extreme terms, it can be considered that only the toner is different.
[0018]
Here, “the posture at the development position is substantially the same” means that the relative positional relationship between the photoconductor and the development roller at the development position is substantially the same. It is further desirable that the relative positional relationship of the peripheral members of the developing roller with respect to the developing roller is the same so that the toner flows toward the developing roller are substantially the same. Further, “consisting of substantially the same constituent members” means that the materials and appearances of the developing roller and its peripheral members such as the supply roller and the regulating blade are made substantially the same. By using the same parts, it is possible to improve the assembly and reduce the cost. As for the toner, although the colors are different, it is more preferable to adjust the internal and external additives so that the particle diameter, the charge amount, and the fluidity are uniform.
[0019]
As described above, the factors (attitude difference and configuration) contributing to the development γ characteristics can be made substantially the same for each developing device, so that the development γ characteristics of the respective colors can be made substantially the same. Or, even if the characteristics are different, most of the contributing factors are combined, so it is easy to analogize the development γ characteristics of other colors by grasping the development γ characteristics of one developer by patch processing. can do. As a result, for example, patch processing is performed for one of the four toner colors to obtain the optimum value of the density adjustment factor, and the optimum value is used as it is or the value that can be inferred from the value is adjusted for the density of other toner colors. It can be set as the optimum value of the factor. Therefore, in the embodiment described in detail below, by using such “principle of the invention”, it is possible to reduce the number of times of patch processing and calculate the optimum value of the concentration adjustment factor in a short time and at a low running cost. It is possible.
[0020]
B. First embodiment
FIG. 3 is a diagram showing a first embodiment of the image forming apparatus according to the present invention. FIG. 4 is a block diagram showing an electrical configuration of the image forming apparatus of FIG. This image forming apparatus forms a full color image by superposing four color toners of yellow (Y), cyan (C), magenta (M), and black (K), or uses only black (K) toner. This is an apparatus for forming a monochrome image. In this image forming apparatus, when an image signal is given to the main controller 11 of the control unit 1 from an external device such as a host computer, the engine controller 12 controls each part of the engine unit EG according to a command from the main controller 11. Thus, an image corresponding to the image signal is formed on the sheet S.
[0021]
In this engine unit EG, the photosensitive member 2 is rotatably provided in the arrow direction D1 in the figure. Further, a charging unit 3 as a charging unit, a rotary developing unit 4 as a developing unit, and a cleaning unit 5 are arranged around the photoreceptor 2 along the rotation direction D1. The charging unit 3 is applied with a charging bias from the charging bias generator 121 and uniformly charges the outer peripheral surface of the photoreceptor 2.
[0022]
Then, the light beam L is irradiated from the exposure unit 6 toward the outer peripheral surface of the photosensitive member 2 charged by the charging unit 3. As shown in FIG. 4, the exposure unit 6 is electrically connected to an image signal switching unit 122, and the exposure power control unit 123 performs exposure in accordance with an image signal given through the image signal switching unit 122. The unit 6 is controlled to scan and expose the light beam L onto the photoconductor 2 to form an electrostatic latent image corresponding to the image signal on the photoconductor 2. For example, when the image signal switching unit 122 is electrically connected to the patch creation module 125 based on a command from the CPU 124 of the engine controller 12, the patch image signal output from the patch creation module 125 is sent to the exposure power control unit 123. Given, a patch latent image is formed. On the other hand, when the image signal switching unit 122 is electrically connected to the CPU 111 of the main controller 11, the light beam L is applied to the photoconductor 2 in accordance with an image signal given through an interface 112 from an external device such as a host computer. The electrostatic latent image corresponding to the image signal is formed on the photosensitive member 2 by scanning exposure.
[0023]
The electrostatic latent image thus formed is developed with toner by the developing unit 4. That is, in this embodiment, as the developing unit 4, a black developing device 4K, a cyan developing device 4C, a magenta developing device 4M, and a yellow developing device 4Y are rotatably provided around the axis. . The developing devices 4K, 4C, 4M, and 4Y are rotationally positioned and selectively positioned at the contact or separation positions with respect to the photoreceptor 2, and a developing bias is applied by the developing bias generator 126. The toner of the selected color is applied to the surface of the photoreceptor 2. As a result, the electrostatic latent image on the photoreceptor 2 is visualized with the selected toner color.
[0024]
Further, in the developing unit 4 configured in this way, the developing positions of the respective toner colors coincide with each other. That is, as shown in FIG. 5, distances Ly, Lc, from the exposure position to the development positions (developers 4Y, 4C, 4M, 4K) for forming toner images of the respective toner colors (Y, C, M, K). Lm and Lk have the same value L1, and times Ty, Tc, Tm, and Tk from the exposure to the start of toner development by each developing device have a constant value T1. As a result, the light portion potential for each toner color is constant despite the time dependency of the light portion potential. As described above, in the first embodiment, the position separated from the exposure position by the distance L1 corresponds to the “first development position” of the present invention, and each of the developing devices 4Y, 4C, 4M, 4K at the first development position. Functions as a “switching developer” of the present invention.
[0025]
Further, the developing devices 4Y, 4C, 4M, and 4K of the respective colors can have substantially the same posture at the first developing position, and can be configured by substantially the same constituent members. As described above, since the factors (attitude difference and configuration) contributing to the development γ characteristics can be made substantially the same for each developing device, the development γ characteristics of the respective colors (Y, C, M, K) can be made substantially the same. Or, even if the characteristics are different, most of the contributing factors are combined, so it is easy to analogize the development γ characteristics of other colors by grasping the development γ characteristics of one developer by patch processing. can do.
[0026]
The toner image developed by the developing unit 4 as described above is primarily transferred onto the intermediate transfer belt 71 of the transfer unit 7 in the primary transfer region TR1. Further, in the vicinity of the primary transfer region TR1, a patch sensor PS is disposed as a “density measuring unit” of the present invention so as to face the surface of the intermediate transfer belt 71. The optical density of the patch image formed on the outer peripheral surface is measured. Further, a cleaning unit 5 is disposed at a position advanced in the circumferential direction (rotation direction D1 in FIG. 3) from the primary transfer region TR1, and the toner remaining on the outer peripheral surface of the photoreceptor 2 after the primary transfer. Scrap off. If necessary, the charge of the photoreceptor 2 is reset by a charge removal unit (not shown).
[0027]
The transfer unit 7 includes an intermediate transfer belt 71 spanned by a plurality of rollers, and a drive unit (not shown) that rotationally drives the intermediate transfer belt 71. When a color image is transferred to the sheet S, a color image is formed by superimposing the toner images of the respective colors formed on the photoreceptor 2 on the intermediate transfer belt 71, and a predetermined secondary transfer region TR2. 2, the color image is secondarily transferred onto the sheet S taken out from the cassette 8. Further, the sheet S on which the color image is formed in this way is conveyed via the fixing unit 9 to a discharge tray portion provided on the upper surface portion of the apparatus main body.
[0028]
After the secondary transfer, toner remaining on the outer peripheral surface of the intermediate transfer belt 71 after the secondary transfer is removed from the intermediate transfer belt 71 by a cleaning unit (not shown).
[0029]
In FIG. 4, reference numeral 113 denotes an image memory provided in the main controller 11 for storing an image given from an external device such as a host computer via the interface 112, and reference numeral 127 denotes an arithmetic program executed by the CPU 124. A memory (storage means) for storing calculation results in the CPU 124, control data for controlling the engine unit EG, and the like.
[0030]
Next, density adjustment factor optimization processing executed in the image forming apparatus configured as described above will be described with reference to FIG.
[0031]
FIG. 6 is a flowchart showing optimization processing in the image forming apparatus according to the first embodiment. In this image forming apparatus, first, a color for creating a patch image is set to black in consideration of the frequent use of a reference toner color such as a business document (step S11). Then, a plurality of patch creation conditions are set (step S12). Here, in this type of image forming apparatus, examples of the density adjusting factor that affects the image density of the toner image include a charging bias, a developing bias, exposure energy of the light beam L, and the like. These can be changed within an appropriate variable range, and these can be used as patch creation conditions.
[0032]
Each patch image is primarily transferred onto the outer peripheral surface of the intermediate transfer belt 71 while sequentially forming patch images on the photoreceptor 2 under such patch creation conditions (step S13). In the next step S14, the optical density of each patch image is measured by the patch sensor PS. In this embodiment, the optical density of the patch image is sequentially measured every time each patch image is formed.
[0033]
Subsequently, in step S15, a patch creation condition that matches the target density is extracted, a value corresponding to the patch creation condition is set as an optimum value of the density adjustment factor for the black toner image, and other toner colors, That is, yellow, cyan, and magenta are also set as optimum values of the density adjustment factor for each toner image. As a result, the density adjustment factor is optimized, the image density of the toner image is controlled to the target density, and a high-quality image can be formed.
[0034]
For example, when the development γ characteristics of each color are substantially the same and the contrast potential for obtaining the target density of each color is also substantially the same, the optimum value of the density adjustment factor for the black toner image may be set as the optimum value of each color. Further, for example, when the development γ characteristics of each color are substantially the same, but the contrast potential for obtaining the target density of each color is different, the optimum value of the density adjustment factor for the black toner image is changed by the difference of the contrast potential, It may be set as the optimum value of the density adjustment factor of the color. Furthermore, for example, when the development γ characteristics are different, the optimum value of the density adjustment factor for the black toner image is changed by the difference in consideration of the previously known difference in the characteristics, and is changed to the density adjustment factor of the color. What is necessary is just to set it as an optimal value.
[0035]
As described above, in this embodiment, patch image formation and image density detection are executed only for the black toner color as the reference toner color, and the density adjustment factor for all toner colors based on the information obtained by the patch processing. Therefore, patch image formation and density detection are omitted for the other three toner colors, and the time required to optimize the density adjustment factor can be shortened. In addition, toner consumption associated with the formation of the patch image can be suppressed, and the running cost can be effectively reduced.
[0036]
In the above embodiment, black is used as a reference toner color in consideration of the importance of black character reproducibility in business documents, but of course the reference toner color is not limited to this. It can be set arbitrarily. In particular, in an image forming apparatus that mainly prints pictorials (natural images), it is desirable to set a toner color other than black as a reference toner color because color gradation reproduction is important. Further, the reference toner color may be changed or set automatically or manually according to the print target.
[0037]
Further, the reference toner color may be selected based on the level of toner consumption. For example, as the toner consumption progresses, the deteriorated toner increases in the developing unit of the toner color, which may lead to a decrease in image quality. If the presence of the deteriorated toner is within an allowable range, it is possible to guarantee the image quality by optimizing the density adjustment factor, but if it exceeds the allowable range, the optimum value of the density adjustment factor is also obtained by patch processing. I can't do that. Therefore, if the toner color that consumes a large amount of toner and the toner color where the problem of deteriorated toner is regarded as the most important is used as the reference toner color, patch processing is always executed, and the influence of the deteriorated toner is detected to replace the developing device or the toner cartridge It is possible to reliably detect the necessity.
[0038]
In the above embodiment, the reference toner color is fixed. However, the reference toner color may be changed and set each time the density adjustment factor optimization process is performed. For example, each time the optimization process is performed, the reference toner color may be cyclically changed and set as black → yellow → cyan → magenta → black →. By doing so, it is possible to prevent the toner color consumed by the patch processing from deviating.
[0039]
C. Second embodiment
In the first embodiment, the case where the present invention is applied to the image forming apparatus in which the developing unit 4 includes the rotary developing devices 4Y, 4C, 4M, and 4K has been described. For example, as illustrated in FIG. The present invention can also be applied to an image forming apparatus in which the developing unit 4 includes a rotary developing unit 41 and an independent developing unit 42. Hereinafter, the second embodiment will be described in detail.
[0040]
FIG. 7 is a diagram showing a second embodiment of the image forming apparatus according to the present invention. This image forming apparatus is greatly different from the first embodiment only in the configuration of the developing unit 4, and the other configurations are the same. Therefore, here, different configurations will be mainly described, and the same components will be denoted by the same reference numerals and description thereof will be omitted.
[0041]
In this embodiment, as shown in the figure, the developing unit 4 includes two developing units 41 and 42. One developing section 41 is a so-called rotary developing section, and is rotatable about the axes of a cyan developing device 4C, a magenta developing device 4M, and a yellow developing device 4Y. The developing units 4C, 4M, and 4Y function as the “switching developing unit” of the present invention, as in the first embodiment. That is, each of the developing devices 4C, 4M, and 4Y is rotationally positioned and selectively positioned at a contact or separation position with respect to the photoreceptor 2, and is selected by applying a developing bias by the developing bias generator 126. A colored toner is applied to the surface of the photoreceptor 2. As a result, the electrostatic latent image on the photoreceptor 2 is visualized with the selected toner color. As described above, for the three toner colors (Y, C, M), the development positions of the toner colors coincide with each other at the predetermined development position (first development position). As shown in FIG. The distances Ly, Lc, Lm from the first developing position (developing devices 4Y, 4C, 4M) to form toner images of the respective toner colors (Y, C, M) to the same value L1, Times Ty, Tc, and Tm until toner development is started are constant values T1. As a result, the light portion potential for each toner color is constant despite the time dependency of the light portion potential.
[0042]
Further, the developing devices 4Y, 4C, and 4M of the respective colors can be made substantially the same in the first developing position, and can be constituted by substantially the same constituent members. As described above, since the factors (attitude difference and configuration) contributing to the development γ characteristics can be made substantially the same for each developing device, the development γ characteristics of the respective colors (Y, C, M) can be made substantially the same. Or, even if the characteristics are different, most of the contributing factors are combined, so it is easy to analogize the development γ characteristics of other colors by grasping the development γ characteristics of one developer by patch processing. can do.
[0043]
The other developing unit 42 is composed of a black developing device 4K, and is disposed opposite to the photosensitive member 2 at a second developing position different from the first developing position, and is in contact with or separated from the photosensitive member 2. And a developing bias is applied by the developing bias generator 126 to apply black toner to the surface of the photoreceptor 2. In this embodiment, the second development position is located farther from the exposure position than the first development position, and the distance Lk from the exposure position to the second development position (developing device 4K) is that of the first development position. The time Tk from the exposure to the start of toner development by the developing device 4K is a value T2 longer than that of the other toner colors. As a result, the absolute value | Von2 | of the black toner color light portion potential is smaller than the absolute value | Von1 | of the other toner colors due to the time dependency of the light portion potential, for example, as shown in FIG. It has become.
[0044]
Since the developing unit 4K is different in developing position from the developing units 4Y, 4C, and 4M in the other developing positions (first developing positions), the developing unit 4K is different in attitude from the developing units 4Y, 4C, and 4M. As can be seen from FIG. 7, the developing device 4K has a developing position in the downward direction, and the other developing devices have a developing position in the upward direction. When the toner is moved upward with respect to the developing position, it is necessary to convey and supply the toner against gravity. Further, when the toner is moved downward with respect to the developing position, it is necessary to regulate the conveyance supply so that the toner is not packed at the lower position due to gravity. As described above, since the concept of toner conveyance and supply is different, the development γ characteristics are likely to be different. Furthermore, there are restrictions on the arrangement of the developing units, and the layout of peripheral members around the developing roller is also different. This also changes the state of toner conveyance and supply, and may cause development γ characteristics to be different. Furthermore, there is a difference in toner stirring and circulation. The developing device 4K is a fixed developing device, but the other developing devices 4Y, 4C, and 4M have a structure that can be circularly moved in a rotary manner. Since the developing devices 4Y, 4C, and 4M are circulated and rotated during image formation, the toner in the developing devices 4Y, 4C, and 4M is well stirred and circulated by the rotation. Thereby, the toner in the developing device is in a highly fluid state. On the other hand, in the developing device 4K which is a fixed developing device, the toner in the developing device is stirred by an agitator, but the situation is worse than that of other color developing devices. Therefore, the toner fluidity is different. Depending on this, the development γ characteristics may be different.
[0045]
Due to the above, the development γ characteristics of the two may be greatly different. Also, considering environmental durability, it is difficult to match both development γ characteristics.
[0046]
Therefore, in the second embodiment, the three toner colors (Y, C, M) developed at the first development position are optimized for the density adjustment factor for each toner color in the same manner as in the first embodiment. On the other hand, the black developed at the second development position is subjected to a separate patch process to optimize the density adjustment factor. Hereinafter, a detailed description will be given with reference to FIGS. 9 and 10.
[0047]
FIG. 9 is a flowchart illustrating optimization processing in the image forming apparatus according to the second embodiment. In this image forming apparatus, first, steps S20 to S24 are executed to optimize the density adjustment factor for the three toner colors (Y, C, M), and then black is executed by executing steps S25 to S29. Concentration adjustment factors are optimized.
[0048]
In step S20, one of the three toner colors (Y, C, M) is set as a reference toner color on the rotary developing unit 41 side. After a plurality of patch creation conditions are set between the first variable regions (step S21), each patch image is formed on the intermediate transfer belt 71 while sequentially forming patch images on the photosensitive member 2 under each patch creation condition. Primary transfer is performed on the outer peripheral surface (step S22). Subsequently, after the optical density of each patch image is measured by the patch sensor PS (step S23), a patch creation condition that matches the target density is extracted, and a value corresponding to this patch creation condition is set for the three-color toner image. Set as the optimum value of the concentration adjustment factor.
[0049]
In the subsequent step S25, the patch creation color is set to the toner color of the independent developing unit 42, that is, black. After setting a plurality of patch creation conditions between the second variable regions (step S26), the patch images are sequentially formed on the photosensitive member 2 under the respective patch creation conditions, and the patch images are transferred to the intermediate transfer belt 71. Primary transfer is performed on the outer peripheral surface (step S27). Subsequently, after the optical density of each patch image is measured by the patch sensor PS (step S28), a patch creation condition that matches the target density is extracted, and a value corresponding to this patch creation condition is adjusted for density with respect to the black toner image. Set as the optimal value of the factor.
[0050]
Thus, the density adjustment factor is optimized for all toner colors, and the image density of the toner image is controlled to the target density, so that a high-quality image can be formed.
[0051]
As described above, also in this embodiment, on the rotary developing unit 41 side, any one of the three toner colors is set as the reference toner color, and patch image formation and image density detection are executed only for this reference toner color. Since the density adjustment factor is optimized for these three colors based on the information obtained by the patch processing, patch image formation and density detection are omitted for the other two toner colors. The time required for optimization of the concentration adjustment factor can be shortened. In addition, toner consumption associated with the formation of the patch image can be suppressed, and the running cost can be effectively reduced.
[0052]
Further, in the image forming apparatus according to the second embodiment, it is better to vary the amplitude (variable area) of the patch creation condition for each development position. This is because the bright portion potentials are different from each other due to the difference between the first development position and the second development position, and the development units 4Y, 4C, 4M at the first development position and the second development position are different from each other. This is because the developing γ characteristics of the developing device 4K are different.
[0053]
Here, the developing devices 4Y, 4C, and 4M rotate in the developing device at the first developing position. Therefore, the toner in the developing devices 4Y, 4C, and 4M is stirred and circulated by the rotational movement. Therefore, the development γ characteristic environment and endurance fluctuation are small. On the other hand, the developing device 4K at the second developing position is a fixed-position developing device, and unlike the first developing position, the degree of toner agitation / circulation is small. Therefore, the endurance fluctuation of the development γ characteristic is particularly large. Therefore, when developing bias is used as a density adjustment factor, the amplitude of patch processing in the developing device 4K at the second developing position is larger than the amplitude of patch processing in the developing devices 4Y, 4C, 4M at the first developing position. Better.
[0054]
When the exposure power is used as a density adjustment factor, the distance from the exposure position is different between the first development position and the second development position, so | Von2 | is smaller than | Von1 | as in the above embodiment. In consideration of this, it is better to determine the amplitude in the patch processing.
[0055]
In the second embodiment, the optical density of each patch image is detected after the patch image is formed on the first development position side, but the optical density of the patch image is sequentially measured each time the patch image is formed. Or after the patch images are formed at the first and second development positions, the optical density of all the patch images is detected at once, the patch image is divided into several blocks, and the optical density for each block is determined. You may make it measure.
[0056]
The present invention is not limited to the above-described embodiment, and various modifications other than those described above can be made without departing from the spirit of the present invention. For example, in the above embodiment, one or more switching developers among the plurality of switching developers are selectively positioned at the first development position by configuring the three or four switching developers so as to be circularly movable. However, as in the image forming apparatus described in, for example, Japanese Patent Application Laid-Open No. 7-298078, a plurality of switching developing devices are arranged in a line, and the switching developing devices are integrally moved in the arranging direction. The switching developer may be selectively positioned with respect to the photoreceptor.
[0057]
Also, the number of switching developing devices is not limited to three or four, but for an image forming apparatus that selectively positions n (n ≧ 2) switching developing devices with respect to the photosensitive member. It goes without saying that the present invention can also be applied.
[0058]
In addition, patch processing is performed on the reference toner color using one of the n switching developing devices, thereby obtaining an optimum value of the density adjustment factor for the reference toner color, Although it is set as the optimum value of the toner color, the reference toner color to be subjected to patch processing is not limited to one color. In other words, the optimum value of the density adjustment factor for each toner color is obtained by performing patch processing on (n-1) colors using (n-1) switching developers among n switching developers. The remaining toner color density adjustment factors may be optimized based on these optimum values.
[0059]
The image forming apparatus according to the above embodiment is a printer that forms an image given from an external device such as a host computer via an interface 112 on a sheet such as copy paper, transfer paper, paper, and an OHP transparent sheet. However, the present invention can be applied to all electrophotographic image forming apparatuses such as copying machines and facsimile machines.
[0060]
Further, in the above-described embodiment, the toner image on the photosensitive member 2 is transferred to the intermediate transfer belt 71, the toner image is used as a patch image, its optical density is detected, and the optimum value of the density adjustment factor is determined based on the detection result. However, the toner image is transferred onto a transfer medium other than the intermediate transfer belt (transfer drum, transfer belt, transfer sheet, intermediate transfer drum, intermediate transfer sheet, reflective recording sheet, or transmissive storage sheet) and patched. The present invention can also be applied to an image forming apparatus that forms an image. Further, a density reading sensor different from the patch sensor PS may be arranged along the outer peripheral surface of the photosensitive member 2 to measure the optical density of the patch image formed on the photosensitive member 2 by the sensor. .
[0061]
【The invention's effect】
As described above, according to the present invention, there are n switching developing devices for developing the electrostatic latent image on the photosensitive member with toners of different colors, and these switching developing devices are selected. Since the electrostatic latent image on the photoconductor is visualized with toner and a toner image is formed after positioning at the development position, a light beam is applied to the photoconductor for any toner color. The time from when the electrostatic latent image is formed by irradiation until the electrostatic latent image moves to the developing position can be made constant, and the bright portion potential can be made the same value. Therefore, a patch image is formed on the photoconductor while changing the developing bias as the density adjustment factor in the first variable region by one of the n switching developers, and the image density of each patch image is changed. Based on the above, the development bias as the density adjustment factor is optimized for all n colors. In addition, an independent developing device provided separately from the switching developing device optimizes the density adjustment factor by forming a patch image while changing the developing bias in the second variable region wider than the first variable region. This eliminates patch image formation and density detection for at least one toner color, shortens the time required to optimize the density adjustment factor, reduces toner consumption, and reduces running time. Cost can be reduced. In particular, in the independent developing device, the degree of toner agitation / circulation in the inside is small and the development γ characteristic has a large endurance fluctuation. Therefore, it is better to increase the amplitude of the density adjusting factor (second variable range) for the independent developing device. Good. In this way, the density adjustment factor is optimized for all toner colors.
[Brief description of the drawings]
FIG. 1 is a graph showing time dependence of a bright part potential.
FIG. 2 is a schematic diagram illustrating distances from an exposure position to each developing device in an image forming apparatus including a plurality of developing devices.
FIG. 3 is a diagram illustrating a first embodiment of an image forming apparatus according to the present invention.
4 is a block diagram showing an electrical configuration of the image forming apparatus in FIG. 3;
FIG. 5 is a schematic diagram showing the distance from the exposure position to each developing device in the image forming apparatus according to the first embodiment.
FIG. 6 is a flowchart showing optimization processing in the image forming apparatus according to the first embodiment.
FIG. 7 is a diagram illustrating a second embodiment of the image forming apparatus according to the present invention.
FIG. 8 is a schematic diagram showing the distance from the exposure position to each developing device in the image forming apparatus according to the second embodiment.
FIG. 9 is a flowchart showing optimization processing in the image forming apparatus according to the second embodiment.
FIG. 10 is a schematic diagram for explaining a patch creation condition setting method in the image forming apparatus according to the second embodiment.
[Explanation of symbols]
1 ... Control unit (control means)
2 ... Photoconductor
4. Development unit (developing means)
4K, 4C, 4M, 4Y ... Developer
6 ... Exposure unit
41 ... Rotary developing section
42. Independent development section
71. Intermediate transfer belt (transfer medium)
124 ... CPU (control means)
L1 (distance from exposure position to first development position)
L2 ... Distance from exposure position to second development position
L ... Light beam
PS ... Patch sensor (Density detection means)

Claims (2)

Exposure means for exposing and scanning the surface of the photoreceptor with a light beam to form an electrostatic latent image; and
There are n (n ≧ 2) switching developing units for developing the electrostatic latent image on the photoconductor with different color toners, and one switching developing unit is selectively selected from the n switching developing units. A developing unit that positions the first developing position facing the photoconductor and visualizes the electrostatic latent image with toner by the switching developer to form a toner image;
In addition to the n switching developing devices, the electrostatic latent image on the photoconductor is arranged opposite to the photoconductor at a second development position different from the first development position, and the (n + 1) th toner color is displayed. An independent developing device for developing the toner image to form a toner image;
Control means for controlling the image density of the toner image formed on the photoreceptor by optimizing the development bias as a density adjustment factor that affects the image density of the toner image for each toner color;
A toner image formed on the photosensitive member by the developing means or the independent developing device, or a toner image formed by transferring the toner image onto a transfer medium as a patch image, and a density detecting means for detecting the image density. Prepared,
The n switching developing devices have substantially the same posture at the first developing position and are constituted by substantially the same constituent members,
The control means includes
With respect to the n number of switching developers, the density adjustment factor is changed and set in multiple stages within a predetermined first variable range, and one of the n number of switching developers is used on the photosensitive member. While forming a toner image as a patch image and optimizing the density adjustment factor for all of the n colors based on the detection result of the density detection means for the patch image,
For the independent developing device, the density adjustment factor is changed and set in multiple steps within a second variable region wider than the first variable region, and a toner image is formed on the photoconductor as a patch image using the independent developing device. An image forming apparatus comprising: forming and optimizing the density adjustment factor for the (n + 1) th toner color based on a detection result of the density detection unit for the patch image. An exposure unit that forms an electrostatic latent image by exposing and scanning a light beam onto the surface of the photoconductor and substantially the same constituent members, and develops the electrostatic latent image on the photoconductor with different color toners. (N ≧ 2) switching developers, and one switching developer among the n switching developers is selectively positioned at a first developing position facing the photosensitive member, and the switching developer In addition to the developing means for visualizing the electrostatic latent image with toner to form a toner image and the n switching developing devices, the photoconductor at a second developing position different from the first developing position. For each toner color, using an image forming apparatus that is disposed opposite to the electrostatic latent image on the photoconductor and develops an electrostatic latent image with the (n + 1) th toner color to form a toner image. Optimize development bias as a density adjustment factor that affects the image density of toner images An image forming method for controlling the image density of the toner image formed on said photosensitive member by Rukoto,
Forming a plurality of toner images as patch images on the photosensitive member using one of the n switching developing devices while changing and setting the density adjustment factor in multiple stages within a predetermined first variable range; While optimizing the density adjustment factor for all of the n colors based on the detection result of the density detection means for the patch image,
A toner image is formed as a patch image on the photoconductor using the independent developing device while changing and setting the density adjustment factor in multiple stages within a second variable range wider than the first variable range. An image forming method comprising optimizing the density adjustment factor for the (n + 1) -th toner color based on the detection result of the density detection means.

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