JP2011022519A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus for carrying out a desired correction control for color shifting by stabilizing the density of a color shifting pattern when a color shifting correction pattern is detected by an optical sensor. <P>SOLUTION: A relationship of Vpatch (monochrome)<Vprint (monochrome) exists in image forming sections Sb, Sc among a plurality of image forming sections Sa, Sb, Sc for color toner images excluding an image forming section Sa for a first color toner image, when a primary transfer bias when a color toner image of an image carrier 1 is transferred to an intermediate transfer body 13 is Vpatch (monochrome) in a correction pattern forming mode, and a primary transfer bias when a color toner image of the image carrier 1 is transferred to the intermediate transfer body 13 is Vprint (monochrome) in a print image forming mode. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an image forming apparatus using an electrophotographic system such as a laser printer, a copying machine, and a facsimile, and more particularly to a color misregistration technique in a color image forming apparatus.

  Conventionally, in a color image forming apparatus using an electrophotographic system, four colors of yellow, magenta, cyan, and black are formed on a drum-shaped electrophotographic photosensitive member (hereinafter referred to as “photosensitive drum”) as an image carrier. A toner image is formed. Next, a transfer system in which the toner image on the photosensitive drum is primarily transferred to an intermediate transfer member serving as a second image carrier and then secondarily transferred to a transfer material.

  In such a color image forming apparatus, although all color images are designed to overlap without shifting, it is very difficult to completely eliminate variations in parts and assembly. Therefore, a means for adjusting the color misregistration is necessary.

  As a color misregistration adjusting unit, for example, Patent Document 1 discloses a technique for correcting a color misregistration by receiving a diffuse reflection light component while using a developer color having a small reflection component of diffuse reflection light such as black as a reference color. ing.

  Japanese Patent Application Laid-Open No. 2004-228561 discloses a technique for making transfer conditions for transferring onto an image carrier to perform color misregistration correction different from those during normal image formation.

Japanese Unexamined Patent Publication No. 2009-93155 Japanese Patent No. 3526412

  However, there have been cases where problems occur in the above technique. That is, “color misregistration correction” may occur depending on the use conditions of the apparatus.

  This problem is caused when the color misregistration correction cannot be controlled as desired because the density of the color misregistration pattern is not stable when the color misregistration correction pattern is detected by the optical sensor.

  Here, details of the problem will be described. In order to explain the problems, so-called “problems related to retransfer” and “pattern-specific problems” will be described.

<Retransfer issues>
First, the reason why the density of the color misregistration correction pattern is not stable is due to so-called retransfer.

  In retransfer, when the color misregistration correction pattern is formed on the image bearing member, the toner transferred in the upstream transfer unit is drawn toward the photoconductor side when passing through another downstream transfer unit. It is a phenomenon that will be

  The reason why retransfer occurs is that the surface of the photosensitive member is charged to the opposite polarity to the toner due to the bias of the transfer portion, so that the toner transferred in the upstream transfer portion passes through the other transfer portion. In this case, the phenomenon is drawn toward the photoconductor. Details are also described in Patent Document 2 and will be omitted.

  If such re-transfer occurs in the color misregistration correction pattern, the pattern edge may be crushed or the density of the color misregistration pattern itself may be reduced, making it impossible to detect the color misregistration correction pattern correctly. The accuracy of correcting this will decrease. Therefore, there are cases where a color image that is faithful to the original image cannot be reproduced.

<Patterns specific to the pattern>
Next, problems unique to the pattern will be described.

  A technique is disclosed in which transfer conditions for transferring onto an image carrier for color misregistration correction are different from those during normal image formation. Specifically, this is a technique for lowering the transfer bias when transferring the color misregistration correction pattern than when performing normal image formation. This technique is described in Patent Document 2.

  In such a technique, there is no problem when the primary color of the color misregistration correction pattern is transferred.

  However, as disclosed in Patent Document 1, when using a misregistration correction pattern formed by superimposing a developer pattern of another color on the basis of one developer pattern as a color misregistration correction pattern. The developer pattern is superimposed. Therefore, there are cases where sufficient transferability cannot be obtained.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus capable of stabilizing the density of a color misregistration pattern and performing desired color misregistration correction control when the color misregistration correction pattern is detected by an optical sensor. is there.

  Another object of the present invention is to provide an image forming apparatus capable of preventing re-transfer of a misregistration correction pattern and performing control for correct misregistration.

  Another object of the present invention is to accurately transfer a misregistration by stably transferring a misregistration correction pattern to be formed by superimposing a developer pattern of another color on the basis of one developer pattern. It is an object of the present invention to provide an image forming apparatus capable of performing control for performing the above.

The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention, according to the first aspect,
An image forming unit for a plurality of color toner images for forming a color toner image on an image carrier using a color developer;
An image forming unit for a black toner image that forms a black toner image on an image carrier using a black developer;
Primary transfer means for transferring a toner image formed on the image carrier of each image forming unit to an intermediate transfer member, wherein the color toner image is first transferred to the intermediate transfer member; Thereafter, primary transfer means provided facing the image carrier of each of the image forming units arranged to transfer the black toner image;
Secondary transfer means for transferring the toner image of the intermediate transfer body, which is transferred by the primary transfer means, onto the transfer material, the toner image formed on the image carrier of each image forming unit;
A correction pattern forming mode for forming a plurality of misregistration correction patterns on the intermediate transfer body, the pattern being made of the color toner image as a base, and superimposing the pattern of the black toner image; Control means for controlling a print image forming mode for forming a toner image for transfer;
Detecting means for irradiating the misalignment correction pattern with light and detecting reflected light reflected;
Based on a detection result by the detection means, a calculation means for calculating a relative positional deviation amount of the positional deviation correction pattern;
In an image forming apparatus having
In the correction pattern forming mode, the primary transfer bias when transferring the color toner image of the image carrier to the intermediate transfer member is Vpatch (single color), and in the print image forming mode, the image carrier When the primary transfer bias for transferring the color toner image to the intermediate transfer member is Vprint (single color), image formation for the first color toner image in the image forming unit for the plurality of color toner images In the image forming section excluding the
Vpatch (single color) <Vprint (single color)
And the relationship
In the correction pattern forming mode, a primary transfer bias when transferring the misregistration correction pattern to the intermediate transfer member is Vpatch (superposition), and in the print image forming mode, the toner image on the image carrier is transferred to the intermediate transfer member. When the primary transfer bias to be transferred to the transfer member is Vprint (superimposition), the image forming unit excluding the image forming unit for the first color toner image among the image forming units for the plurality of color toner images In
Vpatch (single color) / Vprint (single color) <Vpatch (superimposition) / Vprint (superimposition)
There is provided an image forming apparatus having the following relationship.

According to the second aspect,
An image forming unit for a plurality of color toner images for forming a color toner image on an image carrier using a color developer;
An image forming unit for a black toner image that forms a black toner image on an image carrier using a black developer;
Primary transfer means for transferring a toner image formed on the image carrier of each of the image forming units to a transfer material conveyed by a transfer material conveyance body; A primary transfer means provided to face the image carrier of each of the image forming units arranged to transfer a color toner image and then transfer the black toner image;
A correction pattern forming mode for forming, on the transfer material transport body, a plurality of misregistration correction patterns formed by superimposing the pattern consisting of the black toner image on the basis of the pattern consisting of the color toner image; and the transfer material A control means for controlling a print image forming mode for forming a toner image for transfer to a toner image;
Detecting means for irradiating the misalignment correction pattern with light and detecting reflected light reflected;
Based on a detection result by the detection means, a calculation means for calculating a relative positional deviation amount of the positional deviation correction pattern;
In an image forming apparatus having
In the correction pattern formation mode, the primary transfer bias when transferring the color toner image to the transfer material transport body is Vpatch (single color), and in the print image formation mode, the color toner image on the image carrier is When the primary transfer bias to be transferred to the transfer material is Vprint (single color), the image forming unit excluding the image forming unit for the first color toner image among the image forming units for the plurality of color toner images In the department,
Vpatch (single color) <Vprint (single color)
And the relationship
In the correction pattern formation mode, a primary transfer bias when transferring the misregistration correction pattern to the transfer material transport member is Vpatch (superimposition), and in the print image formation mode, the toner image on the image carrier is When the primary transfer bias transferred to the transfer material is Vprint (superimposition), the image forming unit excluding the image forming unit for the first color toner image among the image forming units for the plurality of color toner images In
Vpatch (single color) / Vprint (single color) <Vpatch (superimposition) / Vprint (superimposition)
There is provided an image forming apparatus having the following relationship.

  According to the present invention, when a color misregistration correction pattern is detected by an optical sensor, the density of the color misregistration pattern can be stabilized and color misregistration correction control as desired can be performed. Further, it is possible to perform control for preventing the re-transfer of the positional deviation correction pattern and performing the positional deviation correction accurately. That is, in order to stabilize the density of the misregistration correction pattern in a configuration in which the misregistration correction pattern is formed by superimposing the developer patterns of other different colors on the basis of one developer pattern, The retransfer of the correction pattern can be prevented. Therefore, it is possible to correct the misalignment accurately.

1 is a schematic configuration diagram of an embodiment of an image forming apparatus according to the present invention. It is a figure explaining a position shift correction pattern detection sensor. 6 is a diagram illustrating a color misregistration correction pattern according to the first exemplary embodiment. FIG. 6 is a diagram illustrating a color misregistration correction pattern according to the first exemplary embodiment. FIG. 6 is a diagram illustrating a color misregistration correction pattern according to the first exemplary embodiment. FIG. It is a figure explaining the position shift correction method in Example 1. FIG. FIG. 6 is a diagram for explaining a relationship between a transfer bias and transfer efficiency in Example 1. It is a schematic block diagram of the other Example of the image forming apparatus which concerns on this invention.

  The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.

Example 1
(Operation of the entire image forming apparatus)
First, the operation of the entire color image forming apparatus using four color toners, which is an embodiment of the image forming apparatus according to the present invention, will be described with reference to FIG.

  The image forming apparatus of the present embodiment includes first to fourth image forming stations S (Sa, Sb, Sc, Sd). In this embodiment, an image forming unit for a plurality of color toner images for forming a color toner image on an image carrier using a color developer, that is, a yellow (Y) first station Sa and a magenta (M) first. 2 stations Sb and a third station Sc of cyan (C). Further, the present embodiment includes an image forming unit for a black toner image that forms a black toner image on an image carrier using a black developer, that is, a fourth station Sd of black (Bk).

  The first station Sa includes a drum-shaped electrophotographic photosensitive member as an image carrier, that is, an OPC photosensitive drum 1a. Around the photosensitive drum 1a, a charging roller 2a as a charging unit, a cleaning unit 3a for cleaning the transfer residual toner on the photosensitive drum 1a, and a developing unit 8a as a developing unit are arranged. The developing unit 8a includes a developing sleeve 4a, a nonmagnetic one-component developer 5a, and a developer application blade 7a. The above-described 1a to 8a are integrated process cartridges 9a.

  The exposure unit 11a is composed of a scanner unit that scans laser light with a polygonal mirror, and irradiates the photosensitive drum 1a with a scanning beam 12a modulated based on an image signal.

  An intermediate transfer belt 13 is disposed below the first to fourth image stations S (Sa, Sb, Sc, Sd) and is rotated around the rollers 14, 15, and 24.

  Next, an image forming operation will be described.

  The image forming apparatus according to the present exemplary embodiment forms a toner image to be transferred onto a transfer material, a so-called normal print image forming mode, and forms a misregistration correction pattern on an intermediate transfer body, which will be described in detail later. A correction pattern forming mode. These print image formation mode and correction pattern formation mode are controlled by a control means 204 (FIG. 2) provided in the apparatus main body according to an instruction from an operator or periodically.

  First, the normal print image forming mode will be described.

  When the image forming operation starts, the photosensitive drums 1a to 1d, the intermediate transfer belt 13 and the like start to rotate in the arrow direction at a predetermined process speed.

  First, the operation of the first station Sa will be described.

  The photosensitive drum 1a is uniformly negatively charged by the bias supplied from the power source 20a to the charging roller 2a, and then an electrostatic latent image according to the image information is formed by the scanning beam 12a from the exposure unit 11a. . The toner 5a in the developing unit 8a is charged to a negative polarity by the developer applying blade 7a and applied to the developing sleeve 4a. The developing sleeve 4a is supplied with a bias from the developing bias power source 21a. When the photosensitive drum 1a rotates and the electrostatic latent image formed on the photosensitive drum 1a reaches the developing sleeve 4a, the electrostatic latent image is visualized by negative toner, and the first color (on the photosensitive drum 1a ( In this embodiment, a Y) toner image is formed.

  The second to fourth stations Sb, Sc, and Sd have the same configuration as the first station Sa, and thus the description thereof is omitted.

  On the other hand, in this embodiment, the intermediate transfer member that is a toner image carrier, that is, the intermediate transfer belt 13 is disposed so as to contact all four photosensitive drums 1a to 1d. The intermediate transfer belt 13 is supported by three rollers, ie, a supporting roller 24, a driving roller 14, and a tension roller 15 provided at a position facing the secondary transfer roller 25 as a stretching member, so that an appropriate tension is maintained. It has come to be. By driving the drive roller 14, the intermediate transfer belt 13 rotates in the direction of the arrow and moves in the forward direction at substantially the same speed with respect to the photosensitive drums 1 a to 1 d. Further, primary transfer rollers 10a to 10d, which are primary transfer units, are disposed on the opposite side of the photosensitive drum 1a with the intermediate transfer belt 13 interposed therebetween. Further, as described above, the secondary transfer roller 25 is disposed so as to face the support roller 24.

  The primary transfer rollers 10 a to 10 d are connected to primary transfer power sources 22 a to 22 d which are voltage supply means, and the secondary transfer roller 25 is connected to a secondary transfer power source 26.

  More specifically, primary transfer rollers 10a to 10d are arranged on the inner peripheral portion of the intermediate transfer belt 13 at the portions facing the photosensitive drums 1a to 1d, corresponding to the respective photosensitive drums 1a to 1d. Depending on the distance between the primary transfer positions of each color, an electrostatic latent image is formed on each of the photosensitive drums 1a to 1d while delaying the writing signal from the controller 204 (FIG. 2) at a certain timing for each color. To do. A voltage having a polarity opposite to that of the toner is applied to each of the primary transfer rollers 10a to 10d from the primary transfer power sources 22a to 22d.

  Through the above steps, the toner images on the photosensitive drums 10a to 10d are sequentially transferred to the intermediate transfer belt 13, and a multiple image is formed on the intermediate transfer belt 13. Thereafter, the transfer material P loaded on the transfer material cassette 16 is picked up by the paper feed roller 17 and conveyed to the registration roller 18 by a conveyance roller (not shown) in accordance with the electrostatic latent image formation by exposure. The The transfer material P is conveyed by a registration roller 18 to a contact portion (secondary transfer portion) formed by the intermediate transfer belt 13 and the secondary transfer roller 25 in synchronization with the toner image on the intermediate transfer belt 13. . A secondary transfer power supply 26 applies a voltage having a polarity opposite to that of the toner to the secondary transfer roller 25, and the four-color multiple toner images carried on the intermediate transfer belt 13 on the transfer material P are collectively collected into the secondary transfer roller 25. Transcribed.

In this embodiment, the primary transfer rollers 10a to 10d are made of a nickel-plated steel rod having a diameter of 8 mm and an outer diameter of 16 mm covered with an NBR foam sponge body having a resistance of 10 ⁶ Ω and a thickness of 4 mm. Using.

As the secondary transfer roller 25, a nickel-plated steel rod having a diameter of 12 mm and an outer diameter of 20 mm covered with an NBR foam sponge body having a resistance value adjusted to 10 ⁸ Ω and a thickness of 4 mm was used. The secondary transfer roller 25 is brought into contact with the intermediate transfer belt 13 with a linear pressure of about 5 to 15 g / cm, and rotates at a substantially constant speed in the forward direction with respect to the moving direction of the intermediate transfer belt 13. Arranged to be.

  On the other hand, the transfer residual toner remaining on the intermediate transfer belt 13 after the completion of the secondary transfer and the paper dust generated when the transfer material P is conveyed are cleaned by the belt cleaning arranged in contact with the intermediate transfer belt 13. By means 27, it is removed and recovered from the surface.

  In the image forming apparatus of this embodiment, an elastic cleaning blade formed of urethane rubber or the like is used as the belt cleaning unit 27. After the completion of the secondary transfer, the transfer material P is conveyed to the fixing unit 19, receives the toner image fixing, and is discharged out of the image forming apparatus as an image formed product (print, copy).

As the configuration of the intermediate transfer belt 13, PVDF having a thickness of 100 μm and a volume resistivity of 10 ¹⁰ Ωcm is used. The driving roller 14 as a tension member is a 25 mm in diameter coated with EPDM rubber having a resistance of 10 ⁴ Ω and a thickness of 1.0 mm in which carbon is dispersed in an Al metal core. The tension roller 15 as a tension member uses an Al metal rod with a diameter of 25 mm, and the tension is 19.6 N on one side and the total pressure is 39.2 N.

  Next, the correction pattern formation mode will be described. In the correction pattern formation mode, a plurality of misregistration correction patterns formed by superimposing a pattern made of a black toner image on a pattern made of a color toner image are formed on the intermediate transfer body, that is, the intermediate transfer belt 13. .

  The misregistration correction pattern on the intermediate transfer body, which is the intermediate transfer belt 13, is irradiated with light by a misregistration correction pattern detection sensor 28 serving as detection means, and reflected light reflected is detected. Based on the detection result of the detection means 28, the relative displacement amount of the displacement correction pattern is calculated and calculated by the calculation means 801 (FIG. 2).

(Position displacement correction control using an optical sensor)
Next, the positional deviation correction control method of the present embodiment will be described.

(Outline correction)
In FIG. 1, the image forming apparatus includes a color misregistration detection pattern detection sensor (hereinafter also referred to as “registration sensor”) 28 which is a detection unit for detecting a registration misalignment amount. This sensor 28 is a pattern detection sensor for detecting a color misregistration detection pattern formed on the intermediate transfer belt 13. Then, the position of each color image formed on the intermediate transfer belt 13 is read at a desired timing other than during image formation, and the image registration position for each color is adjusted.

(Register sensor details)
Next, an example of a circuit for detecting a color misregistration amount detection pattern is shown in FIG.

  Here, the color misregistration amount means a registration misregistration amount between colors, and the color misregistration amount detection pattern may be called a registration misregistration amount detection pattern (that is, a color registration pattern). Hereinafter, description will be made using the term “color misregistration amount”.

  The pattern detection sensor 28 includes a light emitting unit 281 (for example, an LED) and a light receiving unit 282 (for example, a phototransistor). The light reflected from the light emitting section 281 is diffused and reflected by the intermediate transfer body 13 and is detected by the light receiving section 282. The light receiving section 282 converts the detected light into IV and outputs it to the engine controller 210. A signal is sent to a certain comparator 211. The comparator 211 binarizes the analog signal sent from the light receiving unit 282 with reference to a predetermined threshold voltage and sends it to the signal detection unit 212. The signal detection unit 212 is configured by a function such as a CPU or ASIC that can capture and store signals in time series. The output (detection result) of the signal detection unit 212 is taken into a controller (control unit) 204 having a calculation unit 801 and used as registration deviation detection data. That is, based on the detection result by the pattern detection sensor 28, the relative position shift amount of the position shift correction pattern is calculated by the calculation unit 801 of the control unit 204.

(Details of color misregistration detection pattern)
Next, in this embodiment, a configuration of one set of color misregistration detection patterns in the correction pattern formation mode, an outline of the color misregistration detection patterns formed on the intermediate transfer belt 13 when performing color misregistration correction control, The color misregistration correction method will be described sequentially.

  FIG. 3 shows a configuration example of one set of color misregistration amount detection patterns. In the color misregistration amount detection pattern of FIG. 3, each pattern is a parallelogram. Depending on how much the color misregistration detection pattern deviates from the original position, the color misregistration in the main scanning direction and the sub-scanning direction can be calculated. In addition, the correction pattern (Bk toner image) of the second developer that is a black developer is superimposed on the correction pattern (Y, M, and C toner images) of the first developer that is a color developer.

  The color misregistration amount detection pattern shown in FIG. 3 has a measurement color yellow (Y), magenta (M), and cyan (C) pattern shown in FIG. The pattern of black (Bk), which is the reference color shown in b), is superimposed. This pattern is called a superimposed pattern.

  In this embodiment, as described above, the black developer is referred to as a second developer as a class of developer in which diffuse reflected light cannot be sufficiently detected (detected) by the sensor 28. On the other hand, yellow (Y), magenta (M), and cyan (C) developers, which are color developers, are referred to as first developers as a class of developers that can detect (detect) diffuse reflected light by the sensor 28. The first developer, the second developer, and the first developer pass under the sensor 28 in this order, and superimposition pattern detection (detection) by diffuse reflected light detection (detection) is performed.

  FIG. 5 shows a detection waveform when the pattern shown in FIG. 3 is detected by the pattern detection sensor 28. In the portion where the surface of the intermediate transfer belt 13 and the black (Bk) developer are present, the amount of diffusely reflected light output (irradiated) from the light emitting portion of the pattern detection sensor 28 is received in advance by the light receiving portion. Since it is insufficient to exceed the set threshold, the LOW level is indicated. In the portion where the developer of yellow (Y), magenta (M), and cyan (C) exists, the amount of diffuse reflection of the light output from the light emitting portion of the pattern detection sensor 28 is received by the light receiving portion. The HIGH level is indicated because the amount is sufficient to exceed a preset threshold.

(Displacement correction method)
With reference to FIG. 6, a method for correcting the positional deviation with respect to the moving direction of the intermediate transfer member serving as the intermediate transfer belt 13 in this embodiment will be described.

  The upper side of FIG. 6 shows a diagram of a pattern in which black is superimposed on a yellow background as a detection pattern, and the lower side is a diagram for explaining the detection level when the pattern passes through the pattern detection sensor 28. Indicates.

  In the lower graph, the horizontal axis represents time, and the vertical axis represents the detection level of the sensor. S0 is the detection level of the intermediate transfer member, S1 is the detection level of yellow, S2 is the threshold level for determining the boundary between the intermediate transfer member and yellow and the boundary between yellow and black, and S3 is the detection level of black Show.

  In the waveform as shown in FIG. 6, the black and yellow center values are calculated as black center (T2 + T3) / 2 and yellow center (T1 + T4) / 2 on the time axis.

  In the misregistration detection pattern shown in FIG. 6, the black center and the yellow center are properly aligned. If there is a misalignment amount, the misalignment amount is corrected, and the image data when the image is formed is corrected. The write timing is adjusted.

  Next, a method for controlling the primary transfer bias when transferring the misregistration correction pattern to the intermediate transfer member, which is a feature of the present invention, will be described.

  The transfer bias of each primary transfer portion is determined based on the detection result obtained by detecting the impedance of the transfer portion by constant current control.

  Specifically, before forming the misregistration correction pattern, a constant current is applied to the transfer portion for a predetermined time by constant current control, and the generated voltage is averaged to determine the transfer bias. This is a control method disclosed in Japanese Patent Application Laid-Open No. 2-123385.

  In this embodiment, the primary transfer bias when transferring the color toner image on the photosensitive drum to the intermediate transfer member in the correction pattern forming mode is Vpatch (single color). In the print image forming mode, the primary transfer bias for transferring the color toner image on the photosensitive drum to the intermediate transfer member is Vprint (single color).

  In this embodiment, Vpatch (monochrome) and Vprint (monochrome) are as shown in Table 1.

  Table 1 shows constant current control values used to determine the transfer voltage Vpatch and Vprint when the image formation and the misregistration correction pattern are transferred to the intermediate transfer member, respectively. That is, the values I (y), (m), I (c), and I (bk) for each station, that is, yellow, magenta, cyan, and black are shown, indicating the strength of the bias.

  The values of yellow, magenta, cyan, and black, i.e., I (y), I (m), and I (c) are different from those at the time of image formation. For example, I (m) at the time of forming the misregistration correction pattern is 70 because the bias intensity of the bias I (m) when the normal image forming pattern is transferred to the intermediate transfer member is set to 100. It is compared with.

  In this embodiment, the transfer bias at the time of printing is set to a constant voltage, and in order to determine the voltage, constant current control is performed and the average voltage is obtained and determined before the printing operation. For example, the constant current control value for determining the transfer voltage during printing is 10 μA. The transfer voltage determined based on this is set to 100, and the value for performing the constant current control in order to determine the transfer voltage when forming the color misregistration detection pattern is 10 μA × (70/100) = 7 μA. Means.

  Next, transfer bias, primary color transfer efficiency, secondary color transfer efficiency, and primary color retransfer will be described with reference to FIG.

  The horizontal axis in FIG. 7 indicates the intensity of the bias described above, and the vertical axis indicates the transfer efficiency and retransfer transfer of the primary color and the secondary color.

  The transfer efficiency indicates the ratio of the transferred weight M (after transfer) to the toner weight M (before transfer) before being transferred to the intermediate transfer member in%.

In the retransfer, the toner weight M (after transfer) transferred at the upstream transfer station is compared with the toner weight M (after transfer) remaining on the intermediate transfer body after passing through the downstream transfer station. Is represented by% and is defined by the following equation.
Transfer efficiency = (toner weight M (before transfer) / toner weight M (after transfer)) × 100%
Retransfer = (toner weight M (after passing) / toner weight M (after transfer)) × 100%

  In other words, the higher the transfer efficiency value, the more toner is transferred to the intermediate transfer member, and the higher the retransfer value, the less toner returns to the drum and the more toner remains on the intermediate transfer member. To do.

  In this embodiment, a bias intensity of 100 is used during normal image formation. In view of the transfer efficiency of the primary color, the transfer efficiency of the secondary color, and the efficiency of retransfer, this is balanced against various practical images such as character images, halftone images, and solid images of secondary colors. This is because a good place is selected.

  On the other hand, the transfer bias Vpatch when forming the misregistration detection pattern is as shown in the table. The reason why I (m) and I (c) are lower than the transfer bias Vprint at the time of image formation is that only the primary color is transferred to both the magenta station and the cyan station when the misregistration detection pattern is formed. This is because it is not necessary to use a very strong bias. It can also be seen that retransfer can be reduced by lowering the bias to a weaker one.

  The reason why the value of I (bk) is not changed from that at the time of image formation is that the black station superimposes black on the yellow, magenta, and cyan patterns, so that the same strong bias as at the time of normal image formation is used. This is because it is necessary.

  In addition, since I (y) is strengthened at the most upstream station, a place where the transfer efficiency of yellow toner is the best is selected without worrying about retransfer. The reason why I (y) at the time of normal print image formation is not strengthened is because transferability when transferring a halftone image other than a misregistration detection pattern or a small character image is taken into consideration.

  In this embodiment, among the toners that form the background of the color misregistration correction pattern, the reflected light component detected by the detection sensor 28 is the lowest in yellow toner. Therefore, the setting is made so that the yellow toner is transferred as much as possible and is not retransferred.

That is, in this embodiment, in the image forming units for the plurality of color toner images, except for the image forming unit for the first color toner image,
Vpatch (single color) <Vprint (single color)
It is said that

In addition, the primary transfer bias when transferring the misregistration correction pattern to the intermediate transfer member in the correction pattern forming mode is Vpatch (superimposition), and the toner image on the photosensitive drum is transferred to the intermediate transfer member in the print image forming mode. The transfer bias is Vprint (superimposition). That is, in this embodiment, Vpatch (superimposition) and Vprint (superimposition) correspond to the primary transfer bias of I (bk). At this time, as understood from Table 1, in the image forming unit for the plurality of color toner images, except for the image forming unit for the first color toner image,
Vpatch (single color) / Vprint (single color) <Vpatch (superimposition) / Vprint (superimposition)
Are in a relationship.

  As described above, according to this embodiment, it is possible to reduce the retransfer of the background developer that forms the misregistration correction pattern and to improve the developer superimposed on the base that forms the misalignment correction pattern. Can be transferred.

  Therefore, in order to stabilize the density of the misregistration correction pattern, it is possible to realize an image forming apparatus capable of preventing re-transfer of the misregistration correction pattern and performing control for performing correct misregistration.

Example 2
In the second exemplary embodiment, an image carrier that forms a misregistration correction pattern using a color developer and a black developer is a transfer material carrier that carries and conveys a transfer material, and detects the misregistration correction pattern. As the sensor, a sensor that detects a specularly reflected light component is used.

  FIG. 8 shows a schematic configuration of the image forming apparatus of this embodiment. With reference to FIG. 8, the configuration of the image forming apparatus of this embodiment will be described.

  In this embodiment, the first station Sa is Y (yellow), the second station Sb is M (magenta), the third station Sc is C (cyan), and the fourth station Sd is Bk (black).

  In the first station Sa, a charging roller 2a, a cleaning unit 3a for cleaning residual toner on the photosensitive drum 1a, and a developing unit 8a are disposed around an OPC photosensitive drum 1a as an image carrier. The developing unit 8a includes a developing sleeve 4a, a nonmagnetic one-component developer 5a, and a developer application blade 7a.

  The photosensitive drum 1a, the charging roller 2a, the cleaning unit 3a, and the developing unit 8a are an integrated process cartridge 9a.

  The exposure unit 11a is composed of a scanner unit that scans laser light with a polygonal mirror, and irradiates the photosensitive drum 1a with a scanning beam 12a modulated based on an image signal. The transfer belt 110, which is a transfer material conveyance body, is stretched by a driving roller 14 that drives the transfer belt 110 and a tension roller 15 that applies tension to the transfer belt 110, and rotates in the direction of the arrow to convey the transfer material P. The transfer roller 111a is disposed on the opposite side of the photosensitive drum 1a with the transfer belt 110 interposed therebetween. The charging roller 2a, the developing sleeve 4a, and the transfer roller 111a are respectively connected to a charging power source 20a that is a charging roller voltage supply unit, a developing power source 21a that is a developing sleeve voltage supply unit, and a transfer power source 22a that is a transfer member voltage supply unit. It is connected.

  The above is the configuration of the first station Sa, and the second, third, and fourth stations Sb, Sc, and Sd have the same configuration, and members having the same function have the same reference numerals and suffixes b, c, d is attached.

  Next, an image forming operation will be described.

  When the image forming operation starts, the photosensitive drums 1a, 1b, 1c, 1d, the transfer belt 110, and the like start to rotate in the direction of the arrow at a predetermined process speed. The photosensitive drum 1a is uniformly charged to the negative polarity by the power supply 20a on the charging roller 2a, and then an electrostatic latent image according to the image information is formed by the scanning beam 12a from the exposure unit 11a. The toner 5a in the developing unit 8a is charged to a negative polarity by the developer applying blade 7a and applied to the developing sleeve 4a. The developing sleeve 4a is supplied with a voltage from the developing power source 21a. When the photosensitive drum 1a rotates and the electrostatic latent image formed on the photosensitive drum 1a reaches the developing sleeve 4a, the electrostatic latent image is visualized by negative toner, and the first color (on the photosensitive drum 1a ( In this embodiment, a Y) toner image is formed.

  On the other hand, the transfer material P loaded on the transfer material cassette 16 is picked up by the paper feed roller 17 and conveyed to the registration roller 18. Then, in synchronization with the toner image on the photosensitive drum 1 a, the transfer material P is fed to the transfer material conveyance body, that is, the transfer belt 110 by the registration roller 18. The transfer material P carried and transported by the transfer belt 110 is transferred onto the transfer material P by the transfer roller 111a to which the toner image on the photosensitive drum 1a is supplied with a positive voltage from the transfer power source 112a in the first station Sa. Is done. Then, in synchronization with the transfer material P being conveyed by the transfer belt 110, the M, C, and Bk toner images are formed from the second station Sb to the transfer material P in the fourth station Sd. . The transfer material P onto which the Y, M, C, and Bk toner images have been transferred is separated from the transfer belt 110 and sent to the fixing device 19, and the toner image on the transfer material P is melted and fixed to obtain a color image. . The toner remaining on the photosensitive drums 1a to 1d is cleaned by the cleaning devices 3a to 3d using blade means.

  In the present embodiment, a color misregistration detection pattern detection sensor, that is, a reflective optical sensor 28 is provided in FIG. 8 in the same manner as that used in the first embodiment. The optical sensor 28 irradiates the toner image (patch) T of the misregistration correction pattern formed on the transfer belt 110 with light from the light emitting element, and receives reflected light from the light receiving element. The toner of the misalignment correction pattern is detected.

  As the sensor 28 for detection, a sensor that irradiates the toner image with light and receives a regular reflection component is used. As the sensor itself that receives the specular reflection component, a known sensor may be used, and detailed description thereof is omitted here.

  The misregistration correction control method and misregistration correction pattern using an optical sensor are the same as those in the first embodiment, and thus description thereof is omitted.

  Next, Table 2 shows a table comparing the bias Vpatch when the misregistration correction pattern of Example 2 is transferred to the transfer material conveyance body, that is, the transfer belt 110, and the bias Vprint during normal image formation.

  As described above, by using the bias as in the second embodiment, in the case of the developer transferred on the upstream side, that is, the magenta station Sb, the retransfer of yellow can be reduced. In the case of the cyan station Sc, retransfer of yellow and magenta can be reduced. In addition, although the bias is slightly lower than the transfer bias when transferring the black corresponding to the fourth station Sd, the bias is not lowered at the fourth station Sd as in the second station Sb and the third station Sc. The reason is as follows. That is, in order to transfer black after forming a base with yellow, magenta, cyan, etc., a transfer bias larger than that of yellow or magenta station is required. For this reason, if the transfer bias is lowered, transfer of black toner becomes defective.

  Compared to the first embodiment, the amount of lowering the transfer bias when forming the misregistration correction pattern is larger. The reason is as follows.

  In the second embodiment, the image carrier that forms the misregistration correction pattern is a transfer material carrier that carries and conveys a transfer material. Therefore, during normal image formation, toner is transferred via the transfer material. A relatively strong transfer bias is required. On the other hand, when transferring the misregistration correction pattern directly to the transfer material conveyance body without using the transfer material, a very large transfer bias is not required.

  Further, the transfer bias of the yellow station Sa is larger than that during normal print image formation. This is because yellow toner has less reflected light component and is the most upstream station compared to other magenta toner and cyan toner. The toner at the most upstream station has more opportunities to pass through the downstream station than other toners, and the toner is returned to the drum side by retransfer. This is because the detection means 28 can finally obtain a sufficient reflected light component even in such a situation.

That is, in this embodiment, the primary transfer bias when transferring the color toner image to the transfer material conveyance body in the correction pattern forming mode is set to Vpatch (single color). In the print image forming mode, the primary transfer bias for transferring the color toner image on the photosensitive drum to the transfer material is Vprint (single color). In the present embodiment, among the image forming units for a plurality of color toner images, in the image forming unit excluding the image forming unit for the first color toner image,
Vpatch (single color) <Vprint (single color)
It is said that

Further, in the correction pattern forming mode, the primary transfer bias when transferring the misregistration correction pattern to the transfer material transport member is Vpatch (superposition), and in the print image forming mode, the toner image on the photosensitive drum is transferred to the transfer material. The primary transfer bias is Vprint (superimposition). At this time, as understood from Table 2, in the image forming unit for the plurality of color toner images, except for the image forming unit for the first color toner image,
Vpatch (single color) / Vprint (single color) <Vpatch (superimposition) / Vprint (superimposition)
Are in a relationship.

  As described above, in an image forming apparatus having a configuration in which a plurality of image forming units are provided as in the configuration of the second embodiment of the present invention, and a test image formed by each image forming unit is sequentially transferred onto a transfer medium. Can also produce exceptional effects. That is, also in this embodiment, the density of the misregistration correction pattern to be formed is stabilized by using one developer pattern as a base and superimposing other different color developer patterns. Accordingly, it is possible to realize an image forming apparatus capable of preventing re-transfer of the misregistration correction pattern and performing control for performing misregistration correction accurately.

1 (1a, 1b, 1c, 1d) Photosensitive drum (image carrier)
2 (2a, 2b, 2c, 2d) Charging roller (charging means)
5a, 5b, 5c Color developer 5d Black developer 8 (8a, 8b, 8c, 8d) Development unit 9 (9a, 9b, 9c, 9d) Process cartridge 10 (10a, 10b, 10c, 10d) Primary transfer roller (Primary transfer means)
11 (11a, 11b, 11c, 11d) Exposure means 13 Intermediate transfer belt (intermediate transfer member)
19 Fixing means 20 Power supply 21 Developing bias power supply 22 (22a, 22b, 22c, 22d) Primary transfer power supply 25 Secondary transfer roller (secondary transfer means)
26 Secondary transfer power supply 28 Misalignment correction pattern detection sensor (optical sensor, detection means)
110 Transfer belt (transfer material carrier)
204 controller (control means)
801 Calculation means P Transfer material

Claims (4)

An image forming unit for a plurality of color toner images for forming a color toner image on an image carrier using a color developer;
An image forming unit for a black toner image that forms a black toner image on an image carrier using a black developer;
Primary transfer means for transferring a toner image formed on the image carrier of each image forming unit to an intermediate transfer member, wherein the color toner image is first transferred to the intermediate transfer member; Thereafter, primary transfer means provided facing the image carrier of each of the image forming units arranged to transfer the black toner image;
Secondary transfer means for transferring the toner image of the intermediate transfer body, which is transferred by the primary transfer means, onto the transfer material, the toner image formed on the image carrier of each image forming unit;
A correction pattern forming mode for forming a plurality of misregistration correction patterns on the intermediate transfer body, the pattern being made of the color toner image as a base, and superimposing the pattern of the black toner image; Control means for controlling a print image forming mode for forming a toner image for transfer;
Detecting means for irradiating the misalignment correction pattern with light and detecting reflected light reflected;
Based on a detection result by the detection means, a calculation means for calculating a relative positional deviation amount of the positional deviation correction pattern;
In an image forming apparatus having
In the correction pattern forming mode, the primary transfer bias when transferring the color toner image of the image carrier to the intermediate transfer member is Vpatch (single color), and in the print image forming mode, the image carrier When the primary transfer bias for transferring the color toner image to the intermediate transfer member is Vprint (single color), image formation for the first color toner image in the image forming unit for the plurality of color toner images In the image forming section excluding the
Vpatch (single color) <Vprint (single color)
And the relationship
In the correction pattern forming mode, a primary transfer bias when transferring the misregistration correction pattern to the intermediate transfer member is Vpatch (superposition), and in the print image forming mode, the toner image on the image carrier is transferred to the intermediate transfer member. When the primary transfer bias to be transferred to the transfer member is Vprint (superimposition), the image forming unit excluding the image forming unit for the first color toner image among the image forming units for the plurality of color toner images In
Vpatch (single color) / Vprint (single color) <Vpatch (superimposition) / Vprint (superimposition)
An image forming apparatus having the following relationship: An image forming unit for a plurality of color toner images for forming a color toner image on an image carrier using a color developer;
An image forming unit for a black toner image that forms a black toner image on an image carrier using a black developer;
Primary transfer means for transferring a toner image formed on the image carrier of each of the image forming units to a transfer material conveyed by a transfer material conveyance body; A primary transfer means provided to face the image carrier of each of the image forming units arranged to transfer a color toner image and then transfer the black toner image;
A correction pattern forming mode for forming, on the transfer material transport body, a plurality of misregistration correction patterns formed by superimposing the pattern consisting of the black toner image on the basis of the pattern consisting of the color toner image; and the transfer material A control means for controlling a print image forming mode for forming a toner image for transfer to a toner image;
Detecting means for irradiating the misalignment correction pattern with light and detecting reflected light reflected;
Based on a detection result by the detection means, a calculation means for calculating a relative positional deviation amount of the positional deviation correction pattern;
In an image forming apparatus having
In the correction pattern formation mode, the primary transfer bias when transferring the color toner image to the transfer material transport body is Vpatch (single color), and in the print image formation mode, the color toner image on the image carrier is When the primary transfer bias to be transferred to the transfer material is Vprint (single color), the image forming unit excluding the image forming unit for the first color toner image among the image forming units for the plurality of color toner images In the department,
Vpatch (single color) <Vprint (single color)
And the relationship
In the correction pattern formation mode, a primary transfer bias when transferring the misregistration correction pattern to the transfer material transport member is Vpatch (superimposition), and in the print image formation mode, the toner image on the image carrier is When the primary transfer bias transferred to the transfer material is Vprint (superimposition), the image forming unit excluding the image forming unit for the first color toner image among the image forming units for the plurality of color toner images In
Vpatch (single color) / Vprint (single color) <Vpatch (superimposition) / Vprint (superimposition)
An image forming apparatus having the following relationship: In the image forming unit for the first color toner image among the image forming units for the plurality of color toner images,
Vpatch (single color)> Vprint (single color)
The image forming apparatus according to claim 1, wherein the image forming apparatus has a relationship of:   Among the image forming units for the plurality of color toner images, the color developer of the image forming unit for the first color toner image is the developer that forms the background of the color misregistration correction pattern. The image forming apparatus according to claim 1, wherein the developer has the least amount of reflected light component detected by the detection unit.

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