JP2007065072A - Image forming apparatus and image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize highly accurate image formation by preventing transfer shifts between colors. <P>SOLUTION: The image forming apparatus forms an image by transferring a multi-color image to a printing medium, the multi-color image being formed by sequentially transferring visible images, obtained by corresponding photoreceptors, to the surface of the intermediate transfer body. The image forming apparatus includes the intermediate transfer body having predetermined tension; and a drive control means for driving at least one among the photoreceptor, the printing medium, or the intermediate transfer body at a predetermined speed. The drive control means drives them so that the speed of the intermediate transfer body becomes higher than the speed of conveyance of the printing medium, and the speed of each photoreceptor becomes higher than the speed of the intermediate transfer body. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus and an image forming method, and more particularly, to an image forming apparatus and an image forming method for preventing misalignment of transfer positions between colors and realizing highly accurate image formation.

  2. Description of the Related Art Conventionally, there is an image forming apparatus that forms a color image on a print medium such as paper using toner images having different characteristics (colors and the like). These devices transfer images from the photoconductor to the intermediate transfer body by slip transfer that gives a difference in speed between the photoconductor, intermediate transfer body, and paper. The transfer position may be misaligned.

  Therefore, conventionally, a method for suppressing the above-described shift of the transfer position has been proposed (see, for example, Patent Document 1 and Patent Document 2).

  The technique disclosed in Patent Document 1 prints a test pattern on a plurality of sheets in order to optimize the first sheet conveyance speed, and changes the sheet conveyance speed for each of the plurality of print sheets. The transfer speed is optimized to minimize the image smear by determining the speed distribution for each of the plurality of print sheets and determining the optimum speed for sheet conveyance as a function of the speed distribution.

Further, the technique disclosed in Patent Document 2 determines the relative speed between the image support member and the image receiving member, and there seems to be a discrepancy in speed within a range in which the relative speed between the image support member and the image receiving member is selected in advance. The relative speed between the image supporting member and the image receiving member of the printing press adjusted to be controlled.
JP-A-8-234532 JP-A-8-227189

  However, the above-described conventional technology only shows a method for suppressing the shift of the transfer position due to slip transfer that gives a speed difference between the photosensitive member, the intermediate transfer member, and the paper transport. The relationship (order) of the speeds of the photosensitive member, the intermediate transfer member, and the paper, which are important in the above, is not shown.

  Further, in order to control the speed with high accuracy, the tension of the intermediate transfer member is set so that the intermediate transfer member and a rotating member (intermediate transfer member transporting means) such as a drive roller that transports the intermediate transfer member do not slip. Necessary. Generally, when setting the tension, the tension is determined from an experimental or empirical value, but excessive tension in the speed control, reduction of bending load, and the like are not taken into consideration.

  From the above, high-precision image formation has not been realized.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus and an image forming method for preventing misalignment of transfer positions between colors and realizing highly accurate image formation. To do.

  In order to solve the above problems, the present invention employs means for solving the problems having the following characteristics.

  The invention described in claim 1 is an image forming apparatus that forms an image by transferring a multicolor image obtained by sequentially transferring a visualized image obtained by a photosensitive member onto an intermediate transfer member to a printing medium. An intermediate transfer body having a predetermined tension; and a drive control means for driving at least one of the photoconductor, the printing medium, and the intermediate transfer body at a predetermined speed, and the drive control means The speed of the intermediate transfer member is set to be equal to or higher than the conveyance speed of the printing medium, and the speed of the photosensitive member is driven to be higher than the speed of the intermediate transfer member.

  According to a second aspect of the present invention, in the drive control unit, the speed difference between the speed of the intermediate transfer member and the conveyance speed of the print medium is 0 or more, and the speed of the intermediate transfer member and the speed of the intermediate transfer member The speed ratio with respect to the print medium conveyance speed is set to be 3.0% or less.

  According to a third aspect of the invention, the drive control means has a speed difference between the speed of the photosensitive member and the speed of the intermediate transfer member larger than 0, and further the speed of the photosensitive member and the speed of the intermediate transfer member. And the speed ratio is set to be 2.0% or less.

According to a fourth aspect of the present invention, there is provided an intermediate transfer member conveying unit comprising a rotating member for conveying the intermediate transfer member, an intermediate transfer member cleaning unit for cleaning the intermediate transfer member, and a tension of the intermediate transfer member. Tension control means for adjusting the tension, and the tension control means includes a force F applied to the intermediate transfer body by each of n photoconductors provided in accordance with the multicolor, and the print medium is the intermediate The force Rp applied to the transfer member, the winding angle θ between the rotating member and the intermediate transfer member, the winding angle θ _r of the intermediate transfer member on the downstream side with respect to the point of transfer from the intermediate transfer member to the printing medium, the intermediate When the load Fc applied to the intermediate transfer member by the transfer member cleaning unit and the friction coefficient between the intermediate transfer member and the intermediate transfer member conveying unit is μ, the tension Ti applied to the intermediate transfer member is

となるよう制御することを特徴とする。

It is characterized by controlling to become.

  According to a fifth aspect of the present invention, there is provided an image for forming an image by transferring a multicolor image obtained by sequentially transferring a visualized image obtained by a photoreceptor onto an intermediate transfer member to a printing medium. In the forming method, the speed of the intermediate transfer body is set to be equal to or higher than the conveyance speed of the printing medium, and the speed of the photoconductor is higher than the speed of the intermediate transfer body, the photoconductor, the intermediate transfer body, and the printing A drive control step for driving and controlling each drive means for driving each medium, and a transfer from the photosensitive member to the intermediate transfer member and from the intermediate transfer member transfer to the printing medium at a speed controlled by the drive control step. And an image forming step.

  Further, in the invention described in claim 6, in the drive control step, a speed difference between the speed of the intermediate transfer member and the conveyance speed of the printing medium is 0 or more, and further, the speed of the intermediate transfer member and the speed of the intermediate transfer member Control is performed such that the speed ratio with respect to the conveyance speed of the print medium is 3.0% or less.

  According to a seventh aspect of the present invention, in the drive control step, a speed difference between the photosensitive member speed and the intermediate transfer member speed is greater than 0, and the photosensitive member speed and the intermediate transfer member speed are further increased. And the speed ratio is controlled to be 2.0% or less.

The invention described in claim 8 further includes a tension control step for adjusting the tension of the intermediate transfer member, and the tension control step is performed for each of n photoconductors provided in accordance with the multicolor. The force F applied to the intermediate transfer member, the force Rp applied to the intermediate transfer member by the print medium, the winding angle θ between the rotating member and the intermediate transfer member that conveys the intermediate transfer member, and printing from the intermediate transfer member. The winding angle θ _r of the intermediate transfer member on the downstream side with respect to the transfer point to the medium, the load Fc applied to the intermediate transfer member by the cleaning means for cleaning the intermediate transfer member, the intermediate transfer member, and the intermediate transfer member conveyance When the coefficient of friction with the means is μ, the tension Ti applied to the intermediate transfer member is

となるよう制御することを特徴とする。

It is characterized by controlling to become.

  According to the present invention, it is possible to prevent misalignment of the transfer position between the respective colors and realize high-precision image formation.

  Hereinafter, embodiments in which an image forming apparatus and an image forming method according to the present invention are suitably implemented will be described with reference to the drawings.

  FIG. 1 is a diagram illustrating a configuration example of an image forming apparatus according to the present invention. Note that the image forming apparatus 10 shown in FIG. 1 is an example of a multicolor image obtained by sequentially transferring (primary transfer) a visualized image obtained by a plurality of electrophotographic image forming units onto an intermediate transfer member. The image forming apparatus according to the present invention is not limited to this, but will be described using an electrophotographic printing apparatus that collectively transfers (secondary transfer) to a printing medium (web) such as paper and forms a multicolor image. Is not to be done.

  An image forming apparatus 10 shown in FIG. 1 includes an image forming unit 11, an intermediate transfer belt 12 as an intermediate transfer member, a drive roller 13 as an intermediate transfer member conveying unit, a driven roller 14, a tension roller 15, A spring 16 as an elastic body, a secondary transfer unit 17, an intermediate transfer unit cleaner 18 as an intermediate transfer unit cleaning unit, a fixing unit 19, a print medium transport roller 20, a yoke 21, and a drive control unit 22 And tension control means 23. The image forming apparatus 10 controls the entire image forming apparatus 10 such as the image forming unit 11, the secondary transfer unit 17, the fixing unit 19, the drive control unit 22, and the tension control unit 23 in the above-described configuration. Means (not shown) and the like.

  The image forming unit 11 serving as a printing unit includes a photoconductor 30, a charger 31, a light source 32 such as an LED (Light Emitting Diode) or a laser, a developing device 33, and a photoconductor cleaner 34. And a primary transfer unit 35. As shown in FIG. 1, the image forming unit 11 has a plurality of identical configurations and forms toner images having different characteristics (colors, etc.).

The image forming unit 11 uniformly charges the surface of the photosensitive member 30 that is rotationally driven by the drive control unit 22 with a charger 31 and then exposes it with a light source 32 to form an electrostatic latent image of a printed image. Further, on the photosensitive member 30 of the image forming unit 11, granular toner is attracted and adhered along the electrostatic latent image by the developing device 33, and the toner (image) is visualized. The toner visualized on the photoreceptor 30 is attracted and transferred to the intermediate transfer belt 12 by an electrostatic force by a primary transfer unit 35 composed of a rubber roller or the like to which a voltage having a polarity opposite to that of corona discharge or toner is applied. For transfer, all of the toner adhering to the photoconductor 30 is not transferred to the intermediate transfer belt, and therefore the photoconductor 30 is cleaned by the photoconductor cleaner 34 made of a brush or a blade.
The intermediate transfer belt 12 of the image forming apparatus 10 in FIG. 1 is conveyed at a predetermined speed by a drive roller 13 that is rotationally driven by a drive control unit 22, and a conveyance path is formed by driven rollers 14-1 to 14-3. The number of driven rollers 14 is not limited to that shown in FIG.

  The tension of the intermediate transfer belt 12 is given by the tension roller 15. The tension roller 15 applies tension to the intermediate transfer belt 12 with a spring 16. The tension control unit 23 controls the tension applied to the intermediate transfer belt 12 by the tension roller 15 and the spring 16.

  That is, each color is sequentially transferred onto the intermediate transfer belt 12 by each photoconductor 30 included in each of the plurality of image forming units 11, thereby forming a multicolor toner image on the intermediate transfer belt 12. The The formed multicolor toner image is transferred to a paper 41 such as a continuous paper as a printing medium by a secondary transfer device 17 made of a rubber roller or the like to which a voltage having a polarity opposite to that of the toner is applied. The paper 41 is transported at a predetermined speed by the print medium transport roller 20 that is rotationally driven by the drive control means 22. In FIG. 1, a yoke 21 is provided as a member that supports the secondary transfer unit 17 and the print medium conveyance roller 20.

  Further, the toner that could not be transferred is cleaned by means such as a brush or a blade by the intermediate transfer body cleaner 18. The transferred image on the paper 41 is conveyed to the fixing unit 19 and heated and pressed to be fixed on the paper 41.

  The drive control unit 22 drives each of the drive roller 13, the print medium conveyance roller 20, and the photosensitive member 30 at a predetermined speed. Specifically, drive control is performed so that “paper speed ≦ intermediate transfer belt speed <photosensitive member speed”. The drive control means 22 is set in consideration of expansion / contraction, processing tolerance, control accuracy, etc. depending on the usage environment of each part in order to set the speed at which each component is driven.

  Further, the tension control means 23 uses the tension roller 15 and the spring 16 to achieve stable conveyance that is resistant to disturbance and does not cause slippage between the intermediate transfer belt 12 and the drive roller 13. A predetermined tension is applied to 12.

  The details of the drive control in the drive control means 22 and the tension control in the tension control means 23 will be described later. Further, the drive control by the drive control unit 22 and the tension control by the tension control unit 23 can be appropriately performed before the start of the printing process or at a predetermined timing or condition during printing.

  By the image forming apparatus 10 described above, the shift of the transfer position between the colors due to the speed fluctuation of the intermediate transfer is prevented, and high-precision image formation is realized.

<About the tension applied to the intermediate transfer belt>
Next, the tension applied to the intermediate transfer belt 12 in the vicinity of the drive roller 13 that drives the intermediate transfer belt 12 in the present invention will be described with reference to the drawings. FIG. 2 is a diagram illustrating an example of tension applied to the intermediate transfer belt.

For example, the drive control unit 22 determines the relationship among the speeds of the paper 41, the intermediate transfer belt 12, and the photosensitive member 30.
"Paper speed ≤ Intermediate transfer belt speed <Photoconductor speed"
Is set such that the tension on the upstream side of the intermediate transfer belt 12 wound around the drive roller 13 is “Ti-nF”, the tension on the secondary transfer point is “Tt”, and the tension on the downstream side is “Ti−”. Fc "can be expressed. Here, Ti represents the tension applied to the intermediate transfer belt 12, n represents the number of image forming units 11, F represents the force applied by one of the photoreceptors 30 to the intermediate transfer belt 12, and Fc is The load applied to the intermediate transfer belt 12 by the intermediate transfer body cleaner 18 is shown.

  Moreover, each relationship of each tension | tensile_strength mentioned above can be represented by (1) Formula and (2) shown below.

ここで、μは中間転写ベルト１２とドライブローラ１３間の摩擦係数を示し、θ_ｒは二次転写点からドライブローラ１３の下流側の中間転写ベルト１２の巻角を示し、Ｒｐは用紙４１が中間転写ベルト１２に与える負荷を示し、θ_fは二次転写点からドライブローラ１３の上流側の中間転写ベルト１２の巻角を示している。

Here, μ represents a coefficient of friction between the intermediate transfer belt 12 and the drive roller 13, θ _r represents a winding angle of the intermediate transfer belt 12 downstream of the drive roller 13 from the secondary transfer point, and Rp represents the sheet 41 A load applied to the intermediate transfer belt 12 is indicated, and θ _f indicates a winding angle of the intermediate transfer belt 12 on the upstream side of the drive roller 13 from the secondary transfer point.

  Further, when the tension Ti applied to the intermediate transfer belt is derived from the above-described equations (1) and (2), the following equation (3) is obtained.

ここで、θは、ドライブローラ１３と中間転写ベルト１２の巻角θ（θ_ｒ＋θ_ｆ）を示している。

Here, θ represents a winding angle θ (θ _r + θ _f ) between the drive roller 13 and the intermediate transfer belt 12.

  That is, since Ti here is the minimum initial tension necessary for the intermediate transfer belt 12 (the tension of the intermediate transfer belt 12 in the printing stop state), the tension control means actually satisfies the following expression (4). 23 is controlled.

ここで、駆動制御手段２２により、例えば、用紙４１、中間転写ベルト１２、感光体３０のそれぞれの速度の関係が「用紙速度≦中間転写ベルト速度＞感光体速度」となるように設定された場合、張力Ｔｉは机上計算上、上述した（４）式の結果より大きくなる。

Here, for example, when the relationship between the speeds of the paper 41, the intermediate transfer belt 12, and the photoconductor 30 is set by the drive control means 22 so that “paper speed ≦ intermediate transfer belt speed> photoconductor speed”. The tension Ti is larger than the result of the above-described equation (4) in the desktop calculation.

  Therefore, in order to reduce deterioration due to bending fatigue of the intermediate transfer belt 12, it is necessary to reduce the tension applied to the intermediate transfer belt 12 as much as possible. Therefore, it is preferable that the speed setting of each part is set as “paper speed ≦ intermediate transfer belt speed <photoreceptor speed”, and further, the initial tension of the intermediate transfer belt 12 satisfying the above-described expression (4) is determined. .

  On the other hand, when setting the speeds of the paper 41, the intermediate transfer belt 12, and the photoreceptor 30 in setting the speed of each part, as one means for determining the image forming (printing) processing speed by the image forming apparatus 10. There is a process speed (number of printed pages per unit time) inside the apparatus. Basically, the process speed and the paper speed need to match. Therefore, the speeds of the intermediate transfer belt 12 and the photoconductor 30 can be set based on the speed of the paper 41. Note that the speed of the intermediate transfer belt 12 or the photoreceptor 30 may be used as a reference without being limited to the reference speed or the paper 41.

  Further, in the image forming apparatus 10 shown in FIG. 1, since unfixed toner adheres to the printing surface of the downstream paper 41 by the secondary transfer by the secondary transfer device 17, printing on the non-printing surface or both ends is performed. It is necessary to transport the paper 41 using a region that is not to be used. Therefore, it is preferable that the conveyance force of the paper 41 is a small value. On the contrary, the sheet holding force (conveyance force) can be sufficiently secured in the sheet 41 before the secondary transfer. Also from the above, the paper 41 can be accurately conveyed by setting “paper speed ≦ intermediate transfer belt speed”. Similarly, it is preferable to set “intermediate transfer belt speed <photoconductor speed” between the intermediate transfer belt 12 and the photoconductor 30.

<Speed difference setting for each configuration>
Here, the setting of the respective speed differences of the paper, the intermediate transfer belt, and the photoconductor in the present invention will be described with reference to the drawings. FIG. 3 is a diagram illustrating an example of the speed difference ratio setting. In FIG. 3, A indicates the speed difference ratio between the sheet 1 and the intermediate transfer belt 12, and B indicates the speed difference ratio between the intermediate transfer belt 12 and the photoconductor 30. That is, FIG. 3 shows the result of evaluation by changing the ratios A and B from 1% to 5% in 1% increments.

  Also, the symbols in FIG. 3 are respectively “O: Acceptable without noticeable extreme image quality degradation”, “△: Increased to an unacceptable level with respect to the desired line width”, “X: Dragged images It appeared to be smeared. "

  In addition, the results shown in FIG. 3 are practically problematic in consideration of “mechanical part processing tolerance”, “temperature / humidity expansion”, “drive motor control accuracy”, etc., so that the ratios A and B fall within an allowable range. There is no tolerance assignment set.

  According to the result shown in FIG. 3, it can be determined that the ratio A of the speed difference between the paper 41 and the intermediate transfer belt 12 is 3% or less, and the speed difference between the intermediate transfer belt 12 and the photoreceptor 30 is appropriate. It can be determined that the ratio B is 2% or less.

  Accordingly, the drive control unit 22 performs drive control based on these data, thereby determining the necessary tension and optimum speed of the intermediate transfer belt 12, and shifting between the colors due to the speed fluctuation of the intermediate transfer belt 12. Can be prevented, and high-precision image formation can be realized.

  Further, the driving speed is set so that the speed difference δv1 (= vi−vp) between the speed vi of the intermediate transfer belt and the paper speed vp satisfies δv1 ≧ 0, and the relationship between the intermediate transfer belt speed vi and the paper speed vp. In this case, the speed ratio is preferably set to 3.0% (= δv1 / vp × 100 (%)) or less.

  The speed difference δv2 (= vo−vi) between the photosensitive member speed vo and the intermediate transfer belt speed vi is set so that δv2> 0, and the photosensitive member speed vo and the intermediate transfer belt speed vi In this relation, it is preferable to set the speed ratio to be 2.0% (= δv2 / vi × 100 (%)) or less.

  As described above, according to the present invention, it is possible to prevent the shift of the transfer position between the respective colors and realize high-precision image formation. Specifically, the relationship among the speeds of the paper, the intermediate transfer belt, and the photosensitive member is set so that “paper speed ≦ intermediate transfer belt speed <photosensitive member speed”. In addition, by controlling the tension Ti applied to the intermediate transfer belt to satisfy the above-mentioned expression (4), there is no slip between the intermediate transfer belt and the drive roller, and stable conveyance resistant to disturbance is realized. can do. Thereby, it is possible to prevent a shift between the colors due to the speed fluctuation of the intermediate transfer belt 12 and to realize high-precision image formation.

  Although the preferred embodiment of the present invention has been described in detail above, the present invention is not limited to the specific embodiment, and various modifications, within the scope of the gist of the present invention described in the claims, It can be changed.

1 is a diagram illustrating a configuration example of an image forming apparatus according to the present invention. FIG. 4 is a diagram illustrating an example of tension applied to an intermediate transfer belt. It is a figure of an example for demonstrating the ratio setting of a speed difference.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 11 Image forming unit 12 Intermediate transfer belt 13 Drive roller 14 Drive roller 15 Tension roller 16 Spring 17 Secondary transfer device 18 Intermediate transfer body cleaner 19 Fixing means 20 Print medium conveyance roller 21 Yoke 22 Drive control means 30 Photoconductor 31 Charger 32 Light source 33 Developer 34 Photoconductor cleaner 35 Primary transfer device 41 Paper

Claims (8)

In an image forming apparatus that transfers a multicolor image obtained by sequentially transferring a visualized image obtained by a photoreceptor onto an intermediate transfer member to a printing medium, and forms an image,
An intermediate transfer member having a predetermined tension;
Drive control means for driving at least one of the photosensitive member, the printing medium, and the intermediate transfer member at a predetermined speed;
The image forming apparatus characterized in that the drive control means drives the speed of the intermediate transfer body to be equal to or higher than the transport speed of the printing medium and makes the speed of the photosensitive body faster than the speed of the intermediate transfer body. . The drive control means includes
The speed difference between the speed of the intermediate transfer body and the transport speed of the printing medium is 0 or more, and the speed ratio between the speed of the intermediate transfer body and the transport speed of the print medium is 3.0% or less. The image forming apparatus according to claim 1, wherein The drive control means includes
The speed difference between the speed of the photoconductor and the speed of the intermediate transfer body is larger than 0, and the speed ratio between the speed of the photoconductor and the speed of the intermediate transfer body is set to 2.0% or less. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. Intermediate transfer member conveying means comprising a rotating member for conveying the intermediate transfer member;
An intermediate transfer member cleaning means for cleaning the intermediate transfer member;
Tension control means for adjusting the tension of the intermediate transfer member,
The tension control means includes a force F applied to the intermediate transfer member by each of n photoconductors provided according to the multicolor, a force Rp applied to the intermediate transfer member by the print medium, and the rotating member. The intermediate transfer body, the winding angle θ between the intermediate transfer body, the winding angle θ _r of the intermediate transfer body downstream from the transfer point from the intermediate transfer body to the printing medium, and the intermediate transfer body cleaning means When the friction coefficient between the load Fc and the intermediate transfer member and the intermediate transfer member transporting unit is μ, the tension Ti applied to the intermediate transfer member is

The image forming apparatus according to claim 1, wherein the image forming apparatus is controlled so as to satisfy the following condition. In an image forming method for forming an image by transferring a multicolor image obtained by sequentially transferring a visualized image obtained by a photoreceptor onto an intermediate transfer member to a printing medium,
The speed of the intermediate transfer member is set to be equal to or higher than the conveyance speed of the printing medium, and the photosensitive member, the intermediate transfer member, and the printing medium are driven so that the speed of the photosensitive member is higher than the speed of the intermediate transfer member. A drive control step for controlling the drive of each drive means;
An image forming method comprising: an image forming step of transferring from the photosensitive member to the intermediate transfer member and from the intermediate transfer member transfer to a printing medium at a speed controlled by the drive control step. The drive control step includes
The speed difference between the speed of the intermediate transfer body and the transport speed of the printing medium is 0 or more, and the speed ratio between the speed of the intermediate transfer body and the transport speed of the print medium is 3.0% or less. The image forming method according to claim 5, wherein the image forming method is controlled as follows. The drive control step includes
Control is performed so that a speed difference between the speed of the photosensitive member and the speed of the intermediate transfer member is larger than 0, and a speed ratio between the speed of the photosensitive member and the speed of the intermediate transfer member is 2.0% or less. The image forming method according to claim 5, wherein the image forming method is an image forming method. A tension control step for adjusting the tension of the intermediate transfer member;
The tension control step includes a force F applied to the intermediate transfer member by each of n photoconductors provided in accordance with the multicolor, a force Rp applied to the intermediate transfer member by the print medium, and the intermediate transfer. The winding angle θ between the rotating body and the intermediate transfer body that conveys the body, the winding angle θ _r of the intermediate transfer body on the downstream side with respect to the transfer point from the intermediate transfer body to the printing medium, and the intermediate transfer body are cleaned. When the load Fc applied to the intermediate transfer member by the cleaning unit and the friction coefficient between the intermediate transfer member and the intermediate transfer member conveying unit is μ, the tension Ti applied to the intermediate transfer member is

The image forming method according to claim 5, wherein control is performed so that

Images