JP2017207653A - Transfer device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a transfer device that, even when a recording medium to which an image is transferred has a small amount of margin at its leading end, can reduce the impact when moving a transfer member in the direction of image carriers to form a transfer nip while maintaining performance to transfer the image to the recording medium, and an image forming apparatus.SOLUTION: A transfer device calculates the image density of an image portion at the leading end corresponding to the leading end of a recording medium on the basis of image data of an image to be transferred to the recording medium, and controls contact/separation means to change, on the basis of the image density of the image portion at the leading end, the speed of movement of a transfer member when the transfer member separated from image carriers is moved by the contact/separation means toward the image carriers.SELECTED DRAWING: Figure 13

Description

  The present invention relates to a transfer device and an image forming apparatus.

  Conventionally, in order to reduce the impact when the leading edge of a recording medium such as paper enters a transfer portion where an image carrier such as an intermediate transfer belt and a transfer member such as a transfer roller face each other, the recording medium enters the transfer portion. There is known a transfer device in which a transfer member is previously separated from an image carrier. In this transfer apparatus, after the leading edge of the recording medium enters the transfer portion, the transfer member is moved in the direction of the image carrier to form a transfer nip having a nip pressure necessary for transferring the image.

  Japanese Patent Application Laid-Open No. 2004-228688 discloses a transfer apparatus that moves a transfer roller in the direction of an intermediate transfer belt after the leading edge of a sheet has entered a transfer portion based on a margin amount to which a toner image on the leading edge side of the sheet is not transferred. What changes is disclosed. According to this transfer apparatus, when there is a margin on the leading end side of the sheet, the transfer roller can be moved during a period when the margin passes through the transfer portion. Thereby, it is supposed that the impact when the transfer member comes into contact with the intermediate transfer belt through the paper can be reduced while maintaining the transfer performance of the toner image onto the paper.

  If the speed at which the transfer roller is moved in the direction of the intermediate transfer belt is changed based on the margin amount on the leading edge side of the paper, the margin passage time is shortened if the margin amount on the leading edge side of the sheet is small. Increases speed. For this reason, there is a possibility that the impact when the transfer roller abuts against the intermediate transfer belt via the sheet to form the transfer nip increases.

  In order to solve the above-described problems, the present invention relates to a transfer member that is disposed so as to face the image carrier at a transfer portion where an image on the image carrier is transferred to a recording medium, and to the image carrier. Contact / separation means for contacting and separating the transfer member; and when the image on the image carrier is not transferred to the recording medium, the transfer member is separated from the image carrier, and the tip of the recording medium is And a control unit that controls the contact / separation unit to move the transfer member toward the image carrier after entering the transfer unit, the transfer device comprising: Based on image data, it comprises image density calculation means for calculating the image density of the front end side image portion corresponding to the front end side of the recording medium, and the control means is based on the image density of the front end side image portion. The transfer separated from the image carrier. Member so as to change the moving speed of the transfer member by said moving means when moving toward said image bearing member, is characterized in that for controlling said moving means.

  According to the present invention, even when the amount of margin on the front end side of the recording medium to which the image is transferred is small, the transfer member holds the image via the recording medium while maintaining the transfer performance of the image to the recording medium. It is possible to reduce the impact when the transfer nip is formed in contact with the body.

1 is a schematic configuration diagram illustrating an example of an image forming apparatus according to an embodiment of the present invention. The perspective view explaining the apparatus which spaces apart a secondary transfer roller and a counter roller. The figure which shows the state of the cam just before a sheet | seat penetrates into a roller nip part. FIG. 4 is a diagram illustrating a state of a cam during transfer of a toner image to a sheet. The graph explaining the gap amount and secondary transfer pressure of a secondary transfer roller. The graph explaining the secondary transfer pressure required according to an image area ratio. The block diagram which shows an example of the principal part structure of a control system. Explanatory drawing about the determination method of the image area rate in the image data to print. (A) is explanatory drawing in case the image data of the front end side of the image to print has a low image density. (B) is a graph showing the relationship between the determination section [row] and the maximum image area ratio. (A) is explanatory drawing in case the image data of the front end side of the image to print has high image density. (B) is a graph showing the relationship between the determination section [row] and the maximum image area ratio. 10 is a graph showing the relationship between the distance from the leading edge of the paper to the head of each determination section and the amount of biting of the secondary transfer roller in the condition determination example described in FIG. 9 (low image). 11 is a graph showing the relationship between the distance from the leading edge of a sheet to the head of each determination section and the amount of biting of the secondary transfer roller in the condition determination example (low image) described in FIG. 6 is a flowchart illustrating an example of operation speed control of a secondary transfer roller. (A) is explanatory drawing of the image data whose image area ratio of the front end side image part is high compared with a rear end side image part. FIG. 14B is an explanatory diagram in a case where the image data of FIG. 14A is reversed and printed before and after the paper direction.

Hereinafter, embodiments will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram illustrating an example of an image forming apparatus 100 according to an embodiment of the present invention. An image forming apparatus 100 illustrated in FIG. 1 is a color image forming apparatus provided with an intermediate transfer belt as an intermediate transfer body. Within the apparatus main body, there are four drum-shaped photoreceptors 1Y and 1M as image carriers. 1C and 1K are arranged in parallel at equal intervals in the horizontal direction. The subscripts Y, M, C, and K indicate the colors yellow, magenta, cyan, and black, respectively. Hereinafter, these subscripts are omitted as appropriate.

  Around the photosensitive member 1, a photosensitive member cleaning blade 6, a charger 2, an optical writing device 3 as an exposure unit, a developing unit 4 as a developing unit, an intermediate transfer belt 5, and the like are arranged. The optical writing device 3 adjusts the amount of light based on resistance detection information of the intermediate transfer belt 5 described later. The developing means includes four developing devices 4 of yellow, magenta, cyan, and black. When forming a full-color image, a visible image is formed in the order of the yellow developing device 4Y, the magenta developing device 4M, the cyan developing device 4C, and the black developing device 4K, and the visible images of each color are sequentially transferred onto the intermediate transfer belt 5. As a result, a full-color image is formed.

  The intermediate transfer belt 5 is stretched by a driving roller 7 and a tension roller 8 and is driven by a driving motor 25, and its process speed is adjusted to 415 [mm / sec]. The intermediate transfer belt 5 has a primary transfer bias roller 9 as a driven roller inside and a belt cleaning counter roller. Each roller is supported from both sides of the intermediate transfer belt 5 by the intermediate transfer belt unit side plate via each bearing and arm.

  The primary transfer bias roller 9 is disposed at a contact portion between the photoreceptor 1 and the intermediate transfer belt 5, and a predetermined transfer bias is applied to the primary transfer bias roller 9. In the present embodiment, +1800 [V] is set to be applied.

The intermediate transfer belt 5 is composed of PVDF (vinylidene fluoride), ETFE (ethylene-tetrafluoroethylene copolymer), PI (polyimide), PC (polycarbonate) or the like in a single layer or a plurality of layers, such as carbon black. Conductive material is dispersed. The volume resistivity is adjusted to be in the range of 10 ⁸ to 10 ¹² [Ωcm] and the surface resistivity is in the range of 10 ⁹ to 10 ¹³ [Ωcm]. If necessary, a release layer may be coated on the surface of the intermediate transfer belt 5. As materials used for the coating, fluorine resins such as ETFE (ethylene-tetrafluoroethylene copolymer), PTFE (polytetrafluoroethylene), PVDF (vinylidene fluoride), PEA (perfluoroalkoxy fluororesin), etc. Can be used. In addition, as a material used for the coating, fluorine resins such as FEP (tetrafluoroethylene-hexafluoropropylene copolymer) and PVF (vinyl fluoride) can be used, but are not limited thereto.

  The method of manufacturing the intermediate transfer belt 5 includes a casting method and a centrifugal molding method, and the surface thereof may be polished as necessary. If the volume resistivity of the intermediate transfer belt 5 exceeds the above-described range, the bias required for transfer increases, which increases the power supply cost. Further, since the charging potential of the intermediate transfer belt 5 becomes high and the self-discharge becomes difficult in the transfer process, the transfer paper peeling process, etc., it is necessary to provide a static elimination means. Also, if the volume resistivity and surface resistivity are below the above ranges, the charge potential decays quickly, which is advantageous for static elimination by self-discharge, but toner scatter occurs because the current during transfer flows in the surface direction. End up. Therefore, it is desirable that the volume resistivity and the surface resistivity of the intermediate transfer belt 5 in this embodiment are within the above ranges. The volume resistivity and surface resistivity were measured by connecting an HRS probe (inner electrode diameter 5.9 [mm], ring electrode inner diameter 11 [mm]) to a high resistivity meter (manufactured by Mitsubishi Chemical Corporation: Hiresta). . Then, a voltage of 100 [V] (surface resistivity is 500 [V]) was applied to the front and back of the intermediate transfer belt 5, and the measured value after 10 seconds was used.

  The cleaning blade 10 made of urethane rubber is pressed against the intermediate transfer belt 5 to block the toner and clean it. In order to facilitate cleaning, the solid lubricant 11 is applied by a brush 12 which is a lubricant application member. In order to suppress the vibration of the brush 12 to the intermediate transfer belt 5, the belt is pressed by the pressure roller 17. In this embodiment, the pressure roller 17 is provided on the outer side of the intermediate transfer belt 5, but the same effect can be obtained on the inner side.

  Of the primary transfer rollers 9K, 9C, 9M, and 9Y, the primary transfer rollers 9C, 9M, and 9Y for color can be brought into contact with and separated from the intermediate transfer belt 5 by a contact and separation mechanism similar to the conventional one. In the full color mode, the primary transfer rollers 9C, 9M, and 9Y contact the intermediate transfer belt 11 from the state in the monochrome mode as shown in FIG. The transfer belt comes into contact with and winds. The intermediate transfer belt 5 is wound around the primary transfer roller 9K for monochrome use regardless of the contact / separation mechanism. Further, in the image forming apparatus 100 of the present embodiment, a paper feeding unit 26 that stores paper P as a recording medium, and a registration roller pair 27 are provided on the downstream side of the paper feeding unit 26 in the paper transport direction. .

  FIG. 2 is a diagram illustrating an apparatus for separating the secondary transfer roller and the counter roller. The secondary transfer roller 15 and the counter roller 18 as transfer members are arranged as shown in FIG. 2 with the intermediate transfer belt 5 interposed therebetween. A biasing force is applied to the secondary transfer roller 15 by an appropriate biasing means 24 so as to be directed to the opposing roller 18. Examples of the urging means include a compression spring and a tension spring. A specified nip pressure can be applied to the sheet P and the intermediate transfer belt 5 by the urging means. The secondary transfer roller 15 and the counter roller 18 have a structure that can be freely separated within a certain range by appropriate means.

  Next, a separation mechanism using a stepping motor and an eccentric cam will be described. Eccentric cams 19 are installed coaxially with the opposing roller 18 at both ends of the opposing roller 18. The eccentric cam 19 is configured to abut against ball bearings 23 attached to both ends of the secondary transfer roller 15 so as not to prevent the rotation of the secondary transfer roller 15. When the shaft to which the eccentric cam 19 is attached rotates, the eccentric cam 19 is also attached to each other by a D-cut groove or the like so as to rotate at the same timing and at the same angle. The shape of the eccentric cam 19 is such that the portion where the distance between the rotation center of the eccentric cam 19 and the outer portion is the shortest is shorter than the diameter of the opposing roller 18, and the distance between the rotation center of the eccentric cam 19 and the outer portion is the longest. The portion is shaped to be longer than the diameter of the opposing roller 18. The shaft to which the eccentric cam 19 is attached is configured such that the rotation can be freely controlled by the stepping motor 22. In FIG. 2, the rotation of the stepping motor 22 is transmitted to the shaft attached to the eccentric cam 19 through a gear and a timing belt. The stepping motor 22 can control the rotation at a step angle of 1.8 [°].

The eccentric cam 19 is abutted against the ball bearing 23. When the following equation (1) is satisfied by rotating the eccentric cam 19, the secondary transfer roller 15 fixed by the biasing means 24 is a counter roller. It is pushed down in a direction away from 18.
(Distance connecting the rotation cam of the eccentric cam 19 to the contact portion of the ball bearing 23 of the eccentric cam 19 + radius of the ball bearing 23)> (radius of the opposing roller 18 + radius of the secondary transfer roller 15) (1 )

Then, the rotation of the eccentric cam 19 is started by the stepping motor 22, and when the following equation (2) is satisfied, the secondary transfer roller 15 and the opposing roller 18 come into contact with each other, and a specified transfer pressure can be applied.
(Distance connecting the rotation cam of the eccentric cam 19 to the contact portion of the ball bearing 23 of the eccentric cam 19 + radius of the ball bearing 23) <(radius of the opposing roller 18 + radius of the secondary transfer roller 15) (2) )

  3 and 4 are diagrams showing the state of the cam immediately before the paper enters the transfer nip portion and the state of the cam during transfer of the toner image to the paper. The eccentric cam 19 has three stop positions A, B, and C. When the cam position is stopped at the position A, the secondary transfer roller 15 and the opposing roller 18 are separated by a gap amount GA. It has a configuration.

  As shown in FIG. 3, when the cam position is stopped at the position C, the secondary transfer roller 15 and the counter roller 18 are separated by a gap amount GC.

Further, as shown in FIG. 4, when the cam position is stopped at B, the following expression (3) is satisfied, so that the secondary transfer roller 15 and the opposing roller 18 are in contact with each other. The urging unit 24 can obtain a nip pressure necessary for transferring the toner image onto the paper P.
(Cam radius from the center of the eccentric cam 19 to the cam outer periphery at point B + radius of the ball bearing 23) <(radius of the opposing roller 18 + radius of the secondary transfer roller 15) (3)

  The eccentric cam 19 can continuously change the cam position in the order of C → B → A → C by driving parts such as the stepping motor 22 and control. At the moment when the paper P enters the secondary transfer roller nip portion, a gap is secured between the secondary transfer roller 15 and the intermediate transfer belt 5 by the secondary transfer roller push-down mechanism (contact / separation mechanism). Let this gap amount be Y1. This gap amount Y1 is secured in order to reduce the impact when the paper P enters the roller nip portion, and it is desirable to secure the thickness of the paper P and the above thickness. Further, no matter how much the gap amount Y1 is greater than the thickness of the paper P, the impact when the paper P enters is not changed. However, the larger the gap amount Y1, the more necessary for contact and separation of the secondary transfer roller 15. Will be large. Therefore, it is desirable to ensure that the gap amount Y1 is slightly larger than the thickness of the paper P. At this moment, since the secondary transfer roller 15 and the intermediate transfer belt 5 are separated from each other, no nip pressure is generated.

  Conventionally, from the separated state where the secondary transfer roller 15 and the intermediate transfer belt 5 are separated and no nip pressure is generated, from the separated state to the moment when the toner image on the intermediate transfer belt 5 is transferred to the paper P (the leading edge of the image), The next transfer roller 15 and the intermediate transfer belt 5 are shifted to the contact state via the paper P. The gap amount between the intermediate transfer belt 5 and the secondary transfer roller 15 at the moment when the leading edge of the image reaches the secondary transfer roller nip is Y2. The gap amount Y2 is a gap amount that ensures a sufficient nip pressure for transferring the toner image on the intermediate transfer belt 5 to the paper P. After the leading edge of the sheet enters the secondary transfer roller nip, the secondary transfer roller push-down mechanism (contact / separation mechanism) is operated to contact the secondary transfer roller 15 in the direction in which it contacts the intermediate transfer belt 5. For this reason, the gap amount Y2 between the intermediate transfer belt 5 and the secondary transfer roller 15 is Y1 or less.

  FIG. 5 is a diagram for explaining the gap amount and the secondary transfer pressure of the secondary transfer roller 15. The gap amount of the secondary transfer roller 15 is the size of the gap existing between the secondary transfer roller and the opposing member when the value is positive, and the sponge with which the secondary transfer roller 15 is opposed when the value is negative. The amount of elastic deformation due to contact with the roller, that is, the amount of biting of the secondary transfer roller 15. Since the secondary transfer pressure is always 0 [N] when the gap amount is positive, only an example when the gap amount is negative is shown.

  As shown in FIG. 5, the larger the amount of biting in the secondary transfer roller 15, the stronger the secondary transfer pressure. When ± 0 [mm], the transfer pressure that was 0 [N] is -1.0 [ mm], the transfer pressure is about 60 [N]. Since the transfer pressure during this period is substantially proportional to the biting amount, the secondary transfer pressure can be managed by managing the biting amount of the secondary transfer roller 15. As described with reference to FIGS. 3 and 4, it is desirable that the sheet P be 0 [N] before entering the sheet P. Therefore, a gap amount of 0 [mm] or more is opened before entering the sheet, and a predetermined secondary transfer is performed until the leading edge of the image. It is necessary to bite in to the amount of pressure. Therefore, the greater the secondary transfer pressure required to transfer the leading edge of the image, the greater the amount of movement required for the biting operation (hereinafter also referred to as “operation amount”). Therefore, it is necessary to increase the moving speed (hereinafter also referred to as “operation speed”) when the secondary transfer roller 15 is brought into contact with the intermediate transfer belt 5 inevitably. However, as the operation speed increases, the impact due to the kinetic energy when the secondary transfer roller 15 contacts the intermediate transfer belt 5 increases, leading to deterioration of shock jitter. Therefore, shock jitter can be reduced when the operating speed when contacting is as slow as possible. During secondary transfer, the secondary transfer roller 15 comes into contact with the intermediate transfer belt 5 via the paper P.

  Here, the shock jitter means that the surface transfer speed of the intermediate transfer belt 5 fluctuates due to an impact when the secondary transfer roller 15 contacts the intermediate transfer belt 5, and the speed between the intermediate transfer belt 5 and the photoreceptor 1. It is a horizontal stripe-like density unevenness of an image caused by the difference. In the prior art, when the margin amount of the paper P is small, the secondary transfer roller 15 is brought into contact with the intermediate transfer belt 5 in accordance with the small margin amount, so the speed of the secondary transfer roller 15 is increased and the intermediate transfer belt 5 is increased. There is a case where an impact at the time of abutting on the surface becomes large. In this case, shock jitter tends to occur.

  In the prior art, when the margin amount of the sheet P is small, the margin amount of the sheet P is increased and the operation speed of the secondary transfer roller 15 is decreased, so that the interval between the secondary transfer roller 15 and the intermediate transfer belt 5 is increased. It is possible to reduce the impact when forming the secondary transfer nip. As a result, shock jitter can be prevented, but in order to increase the margin amount of the paper P, a user's adjustment work is required, or the paper P is required for the adjustment work. In addition, when the format of the image to be formed and the size of the paper are already determined, the margin of the paper P may not be set large. In this case, if a shock jitter occurs, the margin is increased to prevent the shock jitter. Can not.

  FIG. 6 is a diagram for explaining the secondary transfer pressure required according to the image area ratio. The required secondary transfer pressure is proportional to the image area ratio = toner adhesion amount when the secondary transfer bias is equal. For example, in the case of an image having a very low image area ratio such as a trim image, the secondary transfer to the paper P without causing a transfer defect due to the secondary transfer bias even with a secondary transfer pressure of about 5 [N]. Can be transferred. On the other hand, a solid image of two-color superimposition (image area ratio 200%) such as blue solid cannot be sufficiently transferred only by the force of the secondary transfer bias, and therefore a sufficient secondary transfer pressure, for example, 60 [N in this embodiment]. ] Must be applied. The image area ratio during this period requires a transfer pressure during that period. For example, when the image area ratio is 20%, a transfer pressure of about 20 [N] is required. Thus, the required secondary transfer pressure varies depending on the image area ratio. Since the secondary transfer pressure cannot be varied in a normal image forming apparatus, the secondary transfer pressure at the time of printing is configured so that a sufficient transfer pressure is applied even at the maximum image area ratio. In this embodiment, 60 [N]. The transfer pressure is applied.

  As described with reference to FIG. 6, the required secondary transfer pressure varies depending on the image area ratio. For this reason, when the image area ratio of the front end image portion of the image is low, in addition to the margin of the paper P, the maximum transfer until the front end image portion having a low image area ratio passes through the secondary transfer nip portion. If the pressure is applied, the transfer performance can be maintained.

  FIG. 7 is a block diagram illustrating an example of a main configuration of a control system in the image forming apparatus 100 according to the present embodiment. The image forming apparatus 100 includes a control unit 500 as a control unit configured by a computer device such as a microcomputer. The control unit 500 includes an input image data analysis unit 28, a drive motor 25 for driving the drive roller 7 of the intermediate transfer belt 5, a registration roller pair drive motor 29, a timer 30, and a stepping through an I / O interface unit 505. A motor 22 and the like are connected.

  The control unit 500 includes a CPU (Central Processing Unit) 501. In addition, a ROM (Read Only Memory) 503 and a RAM (Random Access Memory) 504 as storage means connected to the CPU 501 via the bus line 502, and an I / O interface unit 505 are provided. The CPU 501 executes various calculations and drive control of each unit by executing a control program which is a computer program incorporated in advance. The ROM 503 stores in advance fixed data such as computer programs and control data. The RAM 504 functions as a work area for storing various data in a rewritable manner. The control unit 500 may be configured using, for example, an IC or LSI as a semiconductor circuit element manufactured for control in the image forming apparatus, instead of a computer device such as a microcomputer. The control unit 50 may also be used as the input image data analysis unit 28.

  The input image data processing unit 28 is composed of, for example, an image processor made up of a dedicated IC, LSI, etc., and analyzes the image density of the front end side image portion of the image to be printed. Is determined. The timer 30 is a timer that determines that the leading edge of the paper P has entered the secondary transfer nip portion. Specifically, after the registration roller pair drive motor 29 is turned on, the timer 30 The time required for the leading end to enter the secondary transfer nip is measured. Then, the timer 30 outputs a time-up signal to the control unit 500.

  Next, a method for determining the image area ratio of image data to be printed by the image forming apparatus of this embodiment will be described. FIG. 8 is a diagram illustrating a method for determining the image area ratio of image data to be printed in the input image data analysis unit 28. As shown in FIG. 8, a predetermined range L [mm] from the leading edge of the paper P is divided as an arbitrary number of matrices. Then, each divided matrix is set as a determination section [n, m] of n columns and m rows, and the image area ratio in each matrix is calculated. Then, the matrix of the maximum image area ratio in each same row is stored as the image area ratio of that row. Note that the above-described calculation and determination of the image area ratio can be performed by the input image data analysis unit 28 as image density calculation means.

  9 and 10 are diagrams illustrating more specific determination examples. FIG. 9A is an explanatory diagram when the image data of the front end image portion of the image to be printed has a low image density, and FIG. 9B is a graph showing the relationship between the determination section [row] and the maximum image area ratio. It is. FIG. 10A is an explanatory diagram when the image data of the front end image portion of the image to be printed has a high image density, and FIG. 10B shows the relationship between the determination section [row] and the maximum image area ratio. It is a graph to show.

  In the case of FIG. 9, since the maximum image area ratio in the entire matrix of the first row is 0%, the image area ratio of the first row is stored as 0% in the storage unit. Since the maximum image area ratio in the entire matrix of the second row is 0.5%, the second row is stored as 0.5%. Similarly, the image area ratio of the (m-1) th row is stored as 20%, and the image area ratio of the mth row is stored as 200%.

  On the other hand, in the case of FIG. 10, the maximum image area ratio of the first line is 200%, the maximum image area ratio of the second line is also 200%, and the image area ratios of the m−1 and m lines are also 200%. is there. For this reason, the image area ratio is stored as 200% in the first row, the second row, the m−1th row, and the mth row.

  By storing the image area ratio in each row automatically according to the image pattern to be printed in this way, the secondary transfer pressure required from the leading edge of the paper to the beginning of each determination section is automatically set according to each image pattern. Is set. In order to ensure the secondary transfer pressure necessary for each determination section, the minimum transfer speed is required by bringing the secondary transfer roller 15 into contact with the intermediate transfer belt 5 via the paper P at the minimum required operation speed. The secondary transfer roller 15 can be brought into contact with the operation speed.

  FIGS. 11 and 12 are diagrams illustrating the amount of biting of the secondary transfer roller 15 and the operation speed thereof in each determination section depending on the difference in determination of the image area ratio. FIG. 11 is a graph of the operation speed in the determination example (low image) under the conditions described in FIG. FIG. 12 is a graph of the operation speed in the determination example (high image) described in FIG.

  The graphs shown in FIGS. 11 and 12 indicate that the smaller the graph inclination is, the slower the operation speed of the secondary transfer roller 15 is. Such control of the operation speed can be realized by controlling the rotation speed of the stepping motor 22 by the control unit 500 as a control means. Note that y, which will be described later, is a margin length, and a is the length per section of the image determination area matrix in the image transport direction.

  In the case of FIG. 11, since the maximum image area ratio in the determination section [row] 1 is 0.0%, there is no need to perform secondary transfer from the leading edge of the paper to y [mm]. That's fine. Since the maximum image area ratio of the next determination section [row] 2 is 0.5%, −0.05 [mm] from the beginning of the determination section [row] 2, that is, a × 1 + y [mm] from the front end of the sheet. It is necessary to secure the above biting amount. Similarly, since the maximum image area ratio in the determination section [row] 3 is 20%, it is necessary to secure a biting amount of −0.2 [mm] or more from the leading edge of the sheet to a × (m−2) + y. . In addition, since the maximum image area ratio of the determination section [row] 4 is 200%, it is necessary to secure a biting of −1.0 [mm] or more from the front end of the sheet to a × (m−1) + y. By bringing the secondary transfer roller 15 into contact with the intermediate transfer belt 5 via the paper P at an operation speed that satisfies the minimum biting speed that satisfies all the determination sections [rows], the minimum necessary The contact can be made at the operating speed. Thereby, the shock jitter can be automatically improved according to the image area ratio.

  On the other hand, in the case of FIG. 12, since the maximum image area ratio is 200% in the determination section [row] 1, it is necessary to secure a biting amount of −1.0 [mm] or more from the leading edge of the sheet to y [mm]. There is. For this reason, it is only necessary to make contact at a normal operation speed, so that it is possible to secure the transfer pressure at the tip while ensuring the same performance as usual as the ability to prevent shock jitter.

  By adopting such a configuration, the operation speed of the secondary transfer roller can be automatically increased so that a minimum secondary transfer pressure can be applied in accordance with the image area ratio of the specific area at the front end of the sheet (the image portion on the front end side). Can be changed. Therefore, the operation speed at which the secondary transfer roller contacts the intermediate transfer belt can be made as slow as possible according to the image area ratio, and the shock jitter can be automatically suppressed without performing adjustment work. By using such a configuration, a shock jitter automatic improvement mode as described below can also be realized.

  FIG. 13 is a flowchart illustrating an example of operation speed control of the secondary transfer roller 15 capable of automatically improving shock jitter in the image forming apparatus 100 according to the present embodiment. The image forming apparatus 100 according to the present embodiment uses the secondary transfer roller 15 when the nip pressure is applied to the secondary transfer nip portion based on the image area ratio corresponding to the image density of the front end image portion of the input image data. Change the operating speed.

  In FIG. 13, first, the secondary transfer roller 15 is separated from the intermediate transfer belt 5, and a gap larger than the thickness of the paper P is formed in advance (S1). The nip pressure at the secondary transfer nip portion at this time is 0 [N].

  Next, the input image data is analyzed using the method described with reference to FIGS. 8 to 10 (S2). Then, based on the image area ratio corresponding to the image density of the front end image portion of the image based on the analysis of the input image data in S1, it is determined whether or not to implement the shock jitter automatic improvement mode (S3).

  Next, when the shock jitter automatic improvement mode is performed based on the image area ratio of the image portion on the front end side of the image (Y in S3), the rotation speed of the stepping motor 22 is changed to be slow (S4). On the other hand, when the shock jitter automatic improvement mode is not performed (N in S3), the rotation speed of the stepping motor 22 is not changed.

  Then, the registration roller pair drive motor 29 is turned on to convey the paper P to the secondary transfer nip (S5). The timer 30 starts measurement when the registration roller pair drive motor 29 is turned on, and measures the predetermined time required for the leading edge of the paper P to enter the secondary transfer nip portion to increase the time (S6). This time-up signal is output to the controller 500.

  When the timer 30 expires, the stepping motor 22 starts to be driven at the set rotational speed (S7), and the nip pressure is applied to the secondary transfer nip portion. When the shock jitter automatic improvement mode is performed, the operation speed when the secondary transfer roller 15 moves in the direction of the intermediate transfer belt 5 is slow, and the impact when contacting the intermediate transfer belt 5 via the paper P is reduced. Reduced and can prevent shock jitter.

  When the eccentric cam 19 rotates to the position B, the stepping motor 22 stops driving (S8). At this time, the secondary transfer nip portion is pressurized with a maximum nip pressure of, for example, 60 [N].

  In the image forming apparatus 100 according to the present embodiment, the shock jitter automatic improvement mode that reverses the printing direction according to the image area ratio of the leading edge side image portion and the trailing edge side image portion of the paper P may be performed. Good.

  FIGS. 14A and 14B are diagrams showing a shock jitter automatic improvement mode in which the printing direction is automatically reversed according to the image area ratio of the leading edge side image portion and the trailing edge side image portion of the paper P. FIG. . In the present embodiment, the original image data to be printed is such that data having a high image area ratio is drawn in the front end side image portion as shown in FIG. 14A, and the image area ratio is low in the rear end side image portion. Shock jitter can be improved under conditions where data is drawn. When the input image data for printing has a higher image area ratio in the front end image portion than in the rear end image portion, as shown in FIG. By printing in the direction opposite to the paper direction, it is possible to reduce the image area ratio of the front end side image portion. As a result, the operation speed when the secondary transfer roller 15 contacts the intermediate transfer belt 5 via the paper P can be made slower than when printing without inverting the image data. Therefore, the impact when the secondary transfer roller 15 contacts the intermediate transfer belt 5 via the paper P can be reduced.

  By implementing such a shock jitter automatic improvement mode, the lower image area ratio of the front end side image portion or the rear end side image portion of the image is set to the front end side, and the image area of the set front end side image portion is set. Printing can be performed at an operation speed corresponding to the rate. Thus, printing can be performed by moving the secondary transfer roller 15 in the direction of the intermediate transfer belt 5 at the slowest operation speed according to the image pattern, so that the shock jitter can be automatically improved.

  In the above embodiment, the configuration in which the secondary transfer roller 15 contacts and separates from the intermediate transfer belt 5 has been described, but at least one of the secondary transfer roller 15 and the intermediate transfer belt 5 contacts and separates from the other. There may be.

  In the above embodiment, the image area ratio corresponding to the image density of the tip image portion of the input image is calculated and used for setting control of the operation speed (moving speed) of the secondary transfer roller 15. The pixel density (pixel density) of the image portion may be calculated and used for control.

  Note that it is easy for a person skilled in the art to make other embodiments by changing or correcting the present invention within the scope of the claims, and these changes and modifications are included in the scope of the claims. . Moreover, the above description is an example of the form in this invention, Comprising: This claim is not limited.

What was demonstrated above is an example, and there exists an effect peculiar for every following aspect.
(Aspect A)
A transfer member such as a secondary transfer roller 15 disposed opposite to the image carrier at a transfer portion where an image such as a toner image on the image carrier such as the intermediate transfer belt 5 is transferred to a recording medium such as paper P; An eccentric cam 19 or a stepping motor 22 that contacts and separates the transfer member with respect to the image carrier, and the transfer member is separated from the image carrier when the image on the image carrier is not transferred to the recording medium. And a control unit such as a control unit 500 for controlling the contact / separation unit so that the transfer member moves toward the image carrier after the leading edge of the recording medium enters the transfer unit. An image density calculation means such as an input image data analysis unit 28 for calculating the image density of the front end image portion corresponding to the front end side of the recording medium based on the image data of the image transferred to the recording medium, and the control The means is Based on the image density of the end-side image portion, the contact / separation means is changed so as to change the moving speed of the transfer member by the contact / separation means when moving the transfer member separated from the image carrier toward the image carrier. Control.
According to this, even when the amount of margin of the recording medium is small, when the image density of the leading edge side image portion following the margin is low, the moving speed of the transfer member by the contact / separation means is changed to change the leading edge side image portion. The moving speed of the transfer member can be reduced to the extent that the toner passes through the transfer portion. By slowing the moving speed of the transfer member in this way, it is possible to reduce the impact when the transfer member contacts the image carrier via the recording medium to form a transfer nip having a predetermined nip pressure. In addition, by slowing down the transfer member movement speed, even if the transfer member movement is not completed when the front end image portion passes the transfer portion and the transfer portion nip pressure is lowered, the front end image portion is Since the image portion has a low image density that can be transferred at a low nip pressure, the transfer performance can be maintained. As described above, the transfer member is moved in the direction of the image carrier while maintaining the transfer performance of the image to the recording medium even when the margin amount on the leading end side of the recording medium to which the image is transferred is small. Thus, the impact when forming the transfer nip can be reduced.
(Aspect B)
In the aspect A, the control unit performs control so that the moving speed of the transfer member is decreased as the image density of the front end image portion is lower.
According to this, as described in the above embodiment, even when the margin amount of the recording medium is small, the lower the image density of the front end image portion is, the more the transfer member that is separated from the image carrier becomes. Slow down the movement speed when moving toward. Thus, by reducing the moving speed of the transfer member in accordance with the image density of the front end image portion, it is possible to more reliably reduce the impact when the transfer nip is formed while maintaining the transfer performance.
(Aspect C)
In the above aspect A or B, the control unit performs control so that the moving speed of the transfer member is decreased as the position of the leading edge of the image transferred to the recording medium is farther from the leading edge of the recording medium.
According to this, as described in the above embodiment, it is possible to further reduce the impact when the transfer nip is formed.
(Aspect D)
In any one of the above aspects A to C, the image density calculation unit divides the image data by a preset number in the width direction orthogonal to the conveyance direction of the recording medium, and the image density of the divided plurality of divided image data The maximum image density is calculated, and the control means controls to change the moving speed when the transfer member separated from the image carrier is moved toward the image carrier based on the maximum image density. .
According to this, as described in the above embodiment, even when a high image density portion such as a solid patch exists only in one place in the width direction of the recording medium, the optimum according to the image density of the high image density portion. The operation speed can be adjusted automatically.
(Aspect E)
In any one of the above aspects A to D, the image carrier is an intermediate transfer belt such as an intermediate transfer belt 5 on which an image formed on a latent image carrier such as the photoreceptors 1Y, 1M, 1C, and 1K is primarily transferred. And the transfer member is a secondary transfer member disposed to face the intermediate transfer body so as to secondarily transfer the image primarily transferred onto the intermediate transfer body onto a recording medium.
According to this, as described in the above embodiment, even when the amount of margin on the front end side of the recording medium to which the image is transferred is small, the recording medium is maintained while maintaining the transfer performance of the image to the recording medium. The impact when the secondary transfer member is brought into contact with the intermediate transfer member via the gap to form the transfer nip can be reduced.
(Aspect F)
In any one of the aspects A to E, the image density calculating unit calculates an image area ratio or a pixel density of the tip side image portion as an image density of the tip side image portion, and the control unit is configured to calculate the tip side image portion. Based on the image area ratio or pixel density of the image portion, the moving speed of the transfer member by the contact / separation means when moving the transfer member separated from the image carrier toward the image carrier is changed. The contact / separation means is controlled.
According to this, as described in the above embodiment, the contact / separation means can be easily controlled by using the image area ratio or the pixel density of the front end side image portion that can be easily calculated from the image data.
(Aspect G)
An image forming apparatus comprising: an image carrier; an image forming unit that forms an image on the image carrier; and the transfer device according to any one of the aspects A to F.
According to this, as described in the above embodiment, the transfer nip is maintained while maintaining the transfer performance of the image to the recording medium even when the margin amount on the leading end side of the recording medium to which the image is transferred is small. The impact when forming can be reduced.
(Aspect H)
In the above aspect G, the image density calculation unit is configured to determine the image density of the front end image portion corresponding to the front end side of the recording medium and the rear end side of the recording medium based on the image data of the image transferred to the recording medium. The image density of the corresponding rear end side image portion is calculated, and the image forming means, when the image density of the front end side image portion is higher than the image density of the rear end side image portion of the recording medium, the conveyance direction of the recording medium The image is formed by inverting the leading end side and the trailing end side of the image.
According to this, as described in the above embodiment, when the image density of the rear end side image portion is lower than that of the front end side image portion, the front end side and the rear end side are reversed in the sheet passing direction. By forming an image, the moving speed of the transfer member when forming the transfer nip can be reduced compared to the case where the image is not reversed, and the impact when forming the transfer nip can be further reduced.

1Y, M, C, K photoconductor 2Y, M, C, K charger 3 optical writing device 4Y, M, C, K developing device 5 intermediate transfer belt 6Y, M, C, K photoconductor cleaning blade 7 drive roller 8 Tension roller 9Y, M, C, K Primary transfer roller 10 Cleaning blade 11 Solid lubricant 12 Brush 15 Secondary transfer roller 17 Pressure roller 18 Opposing roller 19 Eccentric cam 22 Stepping motor 23 Ball bearing 24 Energizing means 25 Intermediate transfer belt Motors for driving rollers 27 Registration roller pair 28 Input image data analysis unit 29 Registration roller pair driving motor 30 Timer 500 Control unit P Paper

Japanese Patent Laying-Open No. 2015-135394

Claims (8)

A transfer member disposed to face the image carrier at a transfer portion where an image on the image carrier is transferred to a recording medium;
Contacting / separating means for contacting / separating the transfer member to / from the image carrier;
When the image on the image carrier is not transferred to the recording medium, the transfer member is separated from the image carrier, and the transfer member is moved to the image after the leading edge of the recording medium enters the transfer portion. A control unit that controls the contact / separation unit to move the carrier toward the carrier,
Based on image data of an image transferred to the recording medium, comprising image density calculation means for calculating the image density of the front end side image portion corresponding to the front end side of the recording medium,
The control means moves the transfer member by the contact / separation means when moving the transfer member separated from the image carrier toward the image carrier based on the image density of the front end image portion. The transfer device is characterized in that the contact / separation means is controlled to change the distance. The transfer device according to claim 1.
The transfer device is characterized in that the transfer unit controls the moving speed of the transfer member to be slower as the image density of the front end image portion is lower. The transfer device according to claim 1 or 2,
The transfer device controls the transfer unit to control the moving speed of the transfer member to be slower as the position of the leading edge of the image transferred to the recording medium is farther from the leading edge of the recording medium. The transfer device according to any one of claims 1 to 3,
The image density calculation means divides the image data by a preset number in a width direction orthogonal to the conveyance direction of the recording medium, and sets the maximum image density among the image densities of the divided divided image data. Calculate
The control means controls to change a moving speed when the transfer member separated from the image carrier is moved toward the image carrier based on the maximum image density. Transfer device. In the transfer device according to any one of claims 1 to 4,
The image carrier is an intermediate transfer member on which an image formed on the latent image carrier is primarily transferred,
The transfer member is a secondary transfer member disposed so as to face the intermediate transfer member so as to secondarily transfer the image primarily transferred onto the intermediate transfer member to the recording medium. apparatus. The transfer apparatus according to any one of claims 1 to 5,
The image density calculating means calculates an image area ratio or a pixel density of the tip side image portion as an image density of the tip side image portion;
The control means transfers the transfer member by the contact / separation means when moving the transfer member separated from the image carrier toward the image carrier based on the image area ratio or the pixel density of the front end image portion. A transfer apparatus that controls the contact / separation means so as to change a moving speed of a member. An image carrier;
Image forming means for forming an image on the image carrier;
An image forming apparatus comprising: the transfer device according to claim 1. The image forming apparatus according to claim 7.
The image density calculation means corresponds to the image density of the front end image portion corresponding to the front end side of the recording medium and the rear end side of the recording medium based on the image data of the image transferred to the recording medium. Calculate the image density of the rear end image part,
The image forming unit reverses the front end side and the rear end side of the image in the conveyance direction of the recording medium when the image density of the front end side image portion is higher than the image density of the rear end side image portion. An image forming apparatus for forming an image.