JP4701915B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus that forms an image by transferring a toner image formed on an image carrier onto an image forming medium (intermediate transfer body, recording medium, etc.).

  In a tandem color image forming apparatus for copying a color image, yellow (Y), magenta (M), cyan (C), and black (K) toner images are formed on an image carrier such as a photosensitive drum. Then, the toner images of these colors are superimposed on the recording medium and transferred to form a color image. Some tandem color image forming apparatuses use continuous paper as a recording medium (see Patent Document 1).

  In a color image forming apparatus using continuous paper, it is common to provide a paper conveyance means such as a conveyance reference roller on the upstream side of the photosensitive drum, and to set the peripheral speed of the photosensitive drum faster than the feeding speed of the paper conveyance means. Is. This is because when the peripheral speed of the photosensitive drum is slower than the paper speed, the continuous paper is loosened between the photosensitive drum and the paper transporting unit, and normal paper feeding cannot be performed. That is, since continuous paper is conveyed while receiving tension in the conveyance direction, different elongation occurs between the photosensitive drums.

  In addition, when the toner image on the photosensitive drum is transferred to the continuous paper, the portion of the photosensitive drum surface where the toner image is not formed is charged, so the continuous paper is electrostatically attracted to the photosensitive drum surface. To do. At this time, the ratio of the area occupied by the toner image on the surface of the photosensitive drum depending on the print pattern is different for each photosensitive drum. . For this reason, the tension of the continuous paper fluctuates and a difference occurs in the amount of elongation. As a result, an error occurs in the transfer position on the continuous paper for each color, causing a color shift.

Such a situation can also occur in an image forming apparatus including a so-called intermediate transfer belt in which toner images of respective colors are once transferred to an intermediate transfer belt and then transferred to a recording medium. Therefore, as a method for solving the above problem, there is a method in which the transfer is started after the elongation of the intermediate transfer belt is stabilized (see Patent Document 2). However, in Patent Document 2, it is necessary to wait until the elongation of the intermediate transfer belt is stabilized. Also, if the intermediate transfer belt stretches during printing, it is difficult to absorb this stretch, and when an image is transferred from the photosensitive drum onto the intermediate transfer belt, an error occurs in the transfer position, resulting in color Deviation occurs.
JP 2004-184922 A Japanese Patent Laid-Open No. 11-182403

  An object of the present invention is to prevent the occurrence of color misregistration even when a recording medium or an intermediate transfer member is stretched during printing, or even when a difference in elongation occurs depending on a printing pattern.

  According to the first aspect of the present invention, a toner formed on the image carrier by applying a transfer bias to a plurality of image carriers provided for each color and an image transfer medium in contact with the image carrier. A transfer member that transfers an image to the image transfer medium, a load torque detection unit that detects a load torque applied to a first drive motor that rotationally drives the first image carrier, and the load torque Calculation means for calculating an extension amount of the image transfer medium at the time of transfer of the toner image from a load torque at the start of transfer by the first image carrier detected by the detection means; and the first image carrier according to the extension amount And a control means for modulating the rotational speed of the second drive motor for rotating the second image carrier on the downstream side of the body.

  According to the first aspect of the present invention, the load torque applied to the first drive motor that rotationally drives the first image carrier at the beginning of the transfer of the first image carrier is detected by the load torque detector. Thus, the amount of elongation of the image transfer medium when the toner image is transferred is calculated from the detected load torque. Then, according to the amount of extension of the image transfer medium, the rotation speed of the second drive motor that rotates the second image carrier on the downstream side of the first image carrier by the control means is set at the normal time (continuous paper P). Modulation (faster) than when there is no elongation.

  That is, the toner image on the first image carrier is transferred to the extended image transfer medium. The image transfer medium onto which the toner image has been transferred further expands when the toner image on the second image carrier is transferred. Therefore, if the rotation speed of the second image carrier is increased according to the amount of extension of the image transfer medium when the toner image is transferred by the first image carrier, the first image is formed on the second image carrier. A toner image is formed by extending in accordance with the extension amount of the image transfer medium extended on the carrier. Thereby, when the toner image is transferred by the first image carrier, the color shift in the second image carrier due to the extension of the image transfer medium is canceled out.

  According to a second aspect of the present invention, there is provided a toner formed on an image carrier by applying a transfer bias to a plurality of image carriers provided for each color and an image transfer medium in contact with the image carrier. A transfer member that transfers an image to the image transfer medium, a load torque detection unit that detects a load torque applied to a first drive motor that rotationally drives the first image carrier, and the load torque Calculation means for calculating a distribution ratio of the toner transferred to the image transfer medium from a change in load torque at the time of transfer of the first image carrier detected by the detection means, and the first ratio according to the distribution ratio of the toner. And a control means for changing the rotational speed after a predetermined time of a second drive motor for rotating the second image carrier downstream of the one image carrier.

  According to the second aspect of the present invention, when the toner image is transferred from the first image carrier by the load torque detection means, the load torque applied to the first drive motor that rotationally drives the first image carrier is detected. Then, the toner distribution ratio of the image transfer medium is calculated from the detected load torque by the calculating means.

  By the way, when the toner image on the second image carrier is transferred to the image transfer medium onto which the toner image on the first image carrier is transferred, the toner distribution ratio on the first image carrier is small. In contrast, the image transfer medium has a large elongation due to electrostatic attraction from the image carrier.

  Therefore, by detecting the load torque of the first image carrier, it is possible to predict the extension amount of the image transfer medium when the toner image of the second image carrier is transferred to the image transfer medium.

  Therefore, the rotational speed after a predetermined time of the second drive motor for rotating the second image carrier on the downstream side of the first image carrier is changed by the control means according to the distribution ratio of the toner. By offsetting the influence of the elongation of the image transfer medium, an image having no color shift is formed on the image transfer medium.

  Since the present invention is configured as described above, it is possible to prevent color misregistration even when the recording medium or the intermediate transfer member is stretched during printing, or even if a difference occurs in the stretch amount depending on the print pattern.

  The first embodiment of the present invention will be described below with reference to the drawings.

  As shown in FIG. 1, a color laser printer (hereinafter, referred to as a printer) 10 as an image recording apparatus receives yellow (Y), magenta (M), cyan (C), and black (K) toner images. Print units 12Y, 12M, 12C, and 12K that are transferred to the continuous paper P and overlapped are sequentially arranged from the upstream side in the transport direction. In addition, when it is necessary to distinguish YMCK, it demonstrates by attaching | subjecting any of Y, M, C, and K after a code | symbol, and when it is not necessary to distinguish YMCK, Y, M, C, and K are shown. Omitted.

  On the upstream side of the printing unit 12 in the conveyance direction, a paper conveyance unit 14 that conveys the wound continuous paper P to the printing unit 12 is provided. A fixing unit 16 that fixes the unfixed toner image transferred by the printing unit 12 to the continuous paper P is provided on the downstream side in the transport direction of the printing unit 12.

  The paper transport unit 14 includes a drive roller 18 around which the continuous paper P is wound. An idle roller 20 is in contact with the drive roller 18, and the continuous paper P is conveyed with the continuous paper P sandwiched between the nip portions of the drive roller 18 and the idle roller 20. Further, both end portions of the drive roller 18 in the axial direction are rotatably supported by a paper transport frame of the paper transport section 14 via a bearing (not shown).

  The printing unit 12 includes a photoconductor drum 22. As shown in FIG. 2, the photosensitive drum 22 is rotationally driven by a drive motor 50. A motor drive circuit 52 is connected to the drive motor 50. Electric power is supplied to the motor drive circuit 52 from a power supply unit (not shown), and the drive motor 50 is rotated at a predetermined voltage value according to a drive signal sent from a control unit 54 connected to the motor drive circuit 52. It is designed to rotate with a number.

  As shown in FIG. 1, around the photosensitive drum 22, a transfer roller 24, a cleaning device 26, a charge removal charger 28, a charging charger 30, and a rotation direction of the photosensitive drum 22 (counterclockwise in the drawing) An LED head 32 and a developing device 34 are provided.

  A guide roller 36 is disposed before and after the transfer roller 24 in the conveying direction, and presses the continuous paper P and wraps it on the photosensitive drum 22. In FIG. 2, the guide roller 36 is not shown.

  The charging charger 30 charges the surface of the photosensitive drum 22, and the LED head 32 forms a latent image by performing line exposure on the surface of the photosensitive drum 22. The developing unit 34 forms a toner image by attaching toner onto the latent image formed on the photosensitive drum 22. The cleaning device 26 scrapes off and removes the untransferred residual toner remaining on the surface of the photosensitive drum 22 without being transferred to the paper P.

  The continuous paper P conveyed from the paper conveyance unit 14 is conveyed to the printing unit 12Y, and a yellow toner image is transferred thereto. Then, the magenta toner image is transferred onto the yellow toner image by the printing unit 12M, and the cyan toner image is transferred onto the yellow and magenta toner images of the continuous paper P by the printing unit 12C. . Further, the black toner image is transferred onto the yellow, magenta, and cyan toner images on the continuous paper P by the printing unit 12K.

  A fixing unit 16 is provided on the downstream side in the transport direction of the printing unit 12K. The continuous paper P on which the toner images of yellow, magenta, cyan, and black are transferred by the printing units 12Y, 12M, 12C, and 12K is conveyed to the fixing unit 16. The toner image on the continuous paper P is heated and melted by flash light emitted from the flash fixing device 40 provided in the fixing unit 16. As a result, the toner image is fixed on the continuous paper P.

  The continuous paper P that has passed through the flash fixing device 40 is discharged from the fixing unit 16, passes through the paper discharge unit 17, and is then discharged from the fixing unit 16 by the paper discharge roll 42.

  On the other hand, when the continuous paper P is conveyed to form an image, a position where the drive roller 18 and the idle roller 20 are nipped (nip portion) and a position where each photosensitive drum 22 abuts (transfer portion). A predetermined tension is applied between them. That is, the rotational speed of the yellow photosensitive drum 22Y is set to be higher than the rotational speed of the drive roller 18. The rotational speed of the magenta photosensitive drum 22M is set to be higher than that of the yellow photosensitive drum 22Y, and the rotational speed of the cyan photosensitive drum 22C is set to be magenta photosensitive drum 22M. It is set to be faster than the rotation speed. Further, the rotational speed of the black photosensitive drum 22K is set to be higher than the rotational speed of the cyan photosensitive drum 22C.

  As a result, the continuous paper P is conveyed while receiving a tension in the conveyance direction, and therefore, between the nip portion of the drive roller 18 and the transfer portion of the photosensitive drum 22Y and the photosensitive drums 22Y, 22M, 22C, and 22K. There is no slack between the transfer parts. As described above, since the predetermined tension is applied to the continuous paper P, elongation occurs along the transport direction.

  When elongation occurs in the continuous paper P, the path length (conveyance path) of the continuous paper P changes, and the transfer position (transfer position of the toner image) of the photosensitive drum 22 of each color for each print page changes. Therefore, color misregistration is caused.

For example, as shown in FIG. 2, the continuous paper P is stretched by Δx ₁ due to the tension between the nip portion of the drive roller 18 and the transfer portion of the photosensitive drum 22Y. Also,
Due to the tension between the transfer portion of the photoconductive drum 22Y and the transfer portion of the photoconductive drum 22M, the continuous paper P is stretched by Δx ₂ during this time. Although not shown, the photosensitive drum 2
Due to the tension between the transfer portion of 2M and the transfer portion of the photosensitive drum 22C, the continuous paper P is stretched between them, and due to the tension between the transfer portion of the photosensitive drum 22C and the transfer portion of the photosensitive drum 22K. The continuous paper P is stretched during this time.

Here, the relationship between the photosensitive drum 22Y and the photosensitive drum 22M will be described as an example. The continuous paper P has Δx ₁ between the transfer portion of the photosensitive drum 22Y and the transfer portion of the photosensitive drum 22M.
An elongation of + Δx ₂ occurs.

Therefore, in accordance with the position of the upstream side of the photosensitive drum 22Y by [Delta] x ₁ extended toner image transferred onto the continuous paper P, in order to transfer the toner image on the photosensitive drum 22M of the downstream side, each of the photoreceptors It is necessary to control the transfer position of the drum 22M.

That is, the rotational speed of the photosensitive drum 22M on the downstream side in the conveyance direction of the photosensitive drum 22Y is increased in accordance with the amount of extension Δx ₁ between the nip portion of the drive roller 18 and the yellow photosensitive drum 22Y. on the drum 22Y, it is necessary to form a toner image at intervals corresponding to [Delta] x _1.

Therefore, a method for obtaining Δx ₁ will be described.

The elongation amount Δx ₁ of the continuous paper P is obtained by the equation (1). Here, the Young's modulus of the continuous paper P and E, when the continuous paper P is in contact with the photosensitive drum 22Y, a force applied to the continuous paper P and F _1.

Δx ₁ = E · F ₁ (1)
When the continuous paper P to the photosensitive drum 22Y is in contact, by detecting the load torque T ₁ applied to the drive motor 50Y, the load torque T ₀ that is inputted in advance in the computing equation, it applied to the continuous paper P The force F ₁ is obtained by equation (2). Here, R is the radius of the photosensitive drum 22Y, and T ₀ is the load torque when the continuous paper P is not in contact with the photosensitive drum 22Y.

F ₁ = (T ₁ −T ₀ ) / R (2)
Then, from Equation (1) and Equation (2), an equation for obtaining the elongation amount Δx ₁ of the continuous paper P is derived.
Δx ₁ = E · ((T ₁ −T ₀ ) / R) (3)
It becomes.

Therefore, by detecting the load torque T ₁ applied to the drive motor 50Y when the toner image is transferred onto the continuous paper P by the photosensitive drum 22Y, the gap between the transfer portion of the photosensitive drum 22Y and the nip portion of the drive roller 18 is detected. The elongation amount Δx ₁ of the continuous paper P can be obtained.

Δx ₁ is calculated by the calculation unit 56 connected to the motor drive circuit 52Y by the above formula.

The calculation unit 56 is connected to the control unit 54M of the photosensitive drum 22M, and a drive signal modulated according to the elongation amount Δx ₁ of the continuous paper P obtained by the calculation unit 56 is motor-driven from the control unit 54M. It is sent to the circuit 52M.

Thereby, the rotational speed of the drive motor 50M is controlled, and the rotational speed of the photosensitive drum 22M is increased according to the extension amount Δx ₁ . At this time, the LED head 32 (see FIG. 1) forms a latent image on the surface of the photosensitive drum 22M in accordance with the image data at a predetermined timing. Therefore, the extension amount Δx ₁ is formed on the photosensitive drum 22M. A magenta toner image corresponding to the above is formed. That is, the elongation amount Δx of the continuous paper P between the yellow toner image and the magenta toner image.
Color shift due to ₁ is offset. Therefore, even if an extension of Δx ₁ + Δx ₂ occurs between the transfer position of the photosensitive drum 22Y and the transfer position of the photosensitive drum 22M, the amount of color misalignment between the magenta toner image and the yellow toner image becomes Δx ₂ . It can be suppressed.

Similarly, if the rotational speed of the photosensitive drum 22C is increased in accordance with the elongation Δx ₁ + Δx ₂ of the continuous paper P between the transfer portion of the photosensitive drum 22M and the transfer portion of the photosensitive drum 22Y, the continuous paper P
The amount of elongation Δx ₁ + Δx ₂ is canceled out, and the color deviation of the cyan toner image with respect to the magenta toner image is suppressed. Further, when the elongation of the continuous paper P generated by the tension between the transfer portion of the photosensitive drum 22M and the transfer portion of the photosensitive drum 22C and a [Delta] x _3, the photosensitive drum 2
Elongation Δx ₁ + Δx ₂ + Δx of the continuous paper P between the transfer portion of 2C and the transfer portion of the photosensitive drum 22M
If the rotational speed of the photosensitive drum 22K is increased according to ₃ , the elongation amount Δx ₁ + Δx of the continuous paper P is increased.
₂ + Δx ₃ is canceled out, and the color deviation of the black toner image is suppressed with respect to the cyan toner image.

  In the present embodiment, the configuration has been described in which the load torque T of the photosensitive drum 22 is detected by the motor driving circuit 52 connected to the driving motor 50 that rotationally drives the photosensitive drum 22. The load torque T may be obtained by measuring the current value and converting it.

  Next, a second embodiment of the present invention will be described with reference to FIG. In addition, the description about the part similar to 1st Embodiment is omitted.

  Here, the explanation will be made by taking the photosensitive drum 22Y and the photosensitive drum 22M as an example.

  When the toner image is transferred onto the continuous paper P, the toner powder is sandwiched between the continuous paper P and the photosensitive drum 22Y at the portion where the toner image is transferred, and the continuous paper P on the photosensitive drum 22Y. The electrostatic attraction force with respect to is reduced. Further, in the portion where the toner image is not transferred or the portion where the toner distribution ratio is small, the photosensitive drum 22Y is charged to a predetermined surface potential, so the continuous paper P is electrostatically attracted to the surface of the photosensitive drum 22Y. To do. As a result, a difference occurs in the amount of elongation of the continuous paper P.

  At this time, in a portion where the toner distribution ratio is large, a large amount of toner is interposed between the photosensitive drum 22Y and the continuous paper P. Therefore, the load torque T applied to the drive motor 50Y that rotates the photosensitive drum 22Y is increased. Get smaller. Further, in a portion where the toner image has not been transferred, that is, a portion where the toner distribution ratio is small, the amount of toner interposed between the photosensitive drum 22Y and the continuous paper P is small, and therefore the continuous paper P is the same as the photosensitive drum 22Y. Since the electrostatic attraction force attracts the photosensitive drum 22Y, the load torque T increases.

  Therefore, if the distribution ratio of the toner on the photosensitive drum 22Y is calculated from the load torque T by the calculation unit 56, the amount of elongation of the continuous paper P when the toner image is transferred to the continuous paper P by the photosensitive drum 22M is predicted. can do. Then, a drive signal modulated according to the toner distribution ratio is sent from the controller 54M to the motor drive circuit 52M to control the rotational speed of the photosensitive drum 22M.

Here, the distance between the photosensitive drum 22M of the photosensitive drum 22Y and magenta yellow and L _12, when the conveyance speed of the continuous paper P was Vp, transcribed in the photosensitive drum 22Y after L ₁₂ / Vp Time The toner image reaches the transfer position of the photosensitive drum 22M. Using this as a trigger, the rotation speed of the photosensitive drum 22M is controlled in accordance with the toner distribution ratio (the amount of elongation of the continuous paper P predicted by the toner distribution ratio). For example, in the portion where the yellow toner image is transferred, the rotational speed of the photosensitive drum 22M is slowed down, and in the portion where the yellow toner image is not transferred or in the portion where the toner distribution ratio is small, the photosensitive drum 22M. Increase the rotation speed.

  As a result, the color deviation of the magenta toner image can be halved with respect to the yellow toner image.

  Note that the detected value of the load torque T varies due to the influence of noise or the like. Therefore, data exceeding a predetermined value (upper limit value) is rounded down, and at the same time, an average value of data every predetermined time is obtained. A so-called averaging process is performed. Thereby, the data amount is not affected by noise or the like, and the data amount is reduced by discarding the data, so that the data is smoothly transmitted from the calculation unit 56 to the control unit 54M.

  In this embodiment, the image forming apparatus 10 of the type that sequentially transfers the toner image formed on the photosensitive drum 22 onto the continuous paper P has been described. However, the toner image on the photosensitive drum is transferred to the intermediate transfer belt. The present invention can also be applied to an image forming apparatus that transfers an image from an intermediate transfer belt to a recording medium. As described above, by applying the above configuration to an image forming apparatus using an intermediate transfer belt, an intermediate transfer belt having a tensile elastic modulus set within a certain range can be used, or waiting until the elongation of the intermediate transfer belt is stabilized. There is no need to do.

  In this embodiment, the image forming apparatus 10 that transfers the toner image on the photosensitive drum 22 to the continuous paper P with the transfer roller has been described. However, the present invention is applied to an image forming apparatus that uses a corona transfer device as a transfer unit. You may apply.

1 is a schematic configuration diagram illustrating an image forming apparatus according to a first embodiment of the present invention. 1 is a schematic configuration diagram illustrating an image forming unit of an image forming apparatus according to a first embodiment of the present invention. FIG. 5 is a schematic configuration diagram illustrating an image forming unit of an image forming apparatus according to a second embodiment of the present invention.

Explanation of symbols

22 Photosensitive drum (image carrier)
22Y Photosensitive drum (first image carrier)
22M photosensitive drum (second image carrier)
24 Transfer roller (transfer member)
50Y drive motor (first drive motor)
50M drive motor (second drive motor)
52 Motor drive circuit (load torque detection means)
54M Control unit (control means)
56 Calculation unit (calculation means)

Claims (2)

Transfer that applies a transfer bias to a plurality of image carriers provided for each color and an image transfer medium in contact with the image carrier, and transfers a toner image formed on the image carrier to the image transfer medium An image forming apparatus comprising: a member;
Load torque detecting means for detecting a load torque applied to a first drive motor for rotating the first image carrier;
Calculating means for calculating an elongation amount of the image transfer medium at the time of transfer of a toner image from a load torque at the start of transfer by the first image carrier detected by the load torque detecting means;
Control means for modulating the rotational speed of a second drive motor for rotating the second image carrier downstream of the first image carrier in accordance with the extension amount;
An image forming apparatus comprising: Transfer that applies a transfer bias to a plurality of image carriers provided for each color and an image transfer medium in contact with the image carrier, and transfers a toner image formed on the image carrier to the image transfer medium An image forming apparatus comprising: a member;
Load torque detecting means for detecting a load torque applied to a first drive motor for rotating the first image carrier;
Calculating means for calculating a distribution ratio of the toner transferred to the image transfer medium from a change in load torque at the time of transfer of the first image carrier detected by the load torque detecting means;
Control means for changing a rotational speed after a predetermined time of a second drive motor for rotating the second image carrier downstream of the first image carrier in accordance with the distribution ratio of the toner;
An image forming apparatus comprising:

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