JP4923479B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus in which an image carried on an image carrier roll is transferred to a sheet that is stretched and conveyed by a conveying unit.

  In an image forming apparatus using an electrophotographic method, the rotational speed of an image carrier roll such as a photosensitive drum and the sheet conveyance speed are made different to improve transfer efficiency and prevent paper from slacking. (For example, refer to Patent Document 1). This method is also employed in continuous paper printers.

  Here, since the continuous paper is stretched and conveyed as a whole, friction force is generated in the continuous paper at the transfer nip between the image carrier roll and the transfer roll, and the continuous paper is fed before and after the image carrier roll. There is a difference in tension. As shown in FIG. 2, when the continuous paper P passes through a plurality of transfer nips, the tension Tn (n = 0, 1, 2,...) Of the continuous paper P gradually increases from the downstream side in the transport direction to the upstream side. F0, F0 + F1, F0 + F1 + F2,. For this reason, the continuous paper P is stretched in proportion to the tension, expanding from the downstream side in the transport direction to the upstream side.

On the other hand, since the rotation speed of the image carrier roll is constant, the image transferred onto the continuous paper P is displaced as shown in FIG. This image misalignment can be eliminated by predicting the continuous paper elongation and changing the peripheral speed of the image carrier roll in advance, but the continuous paper elongation varies depending on the printing rate, humidity, paper type, etc. Therefore, it is estimated that the control becomes complicated.
JP 05-241397 A

  The present invention has been made in consideration of the above facts, in an image forming apparatus in which the conveyance speed of a sheet conveyed in a stretched manner and the rotation speed of an image carrier roll are different, without using complicated control, It suppresses the difference in sheet elongation and suppresses image misalignment.

The image forming apparatus according to claim 1 is provided with a plurality of conveying units that stretch and convey a sheet that is continuous paper, along a conveying direction of the sheet conveyed by the conveying unit, and carries an image. an image bearing member roll rotating with a speed difference relative to the sheet conveyed by said conveying means and sandwich the sheet between the image carrier roll each, from the image carrier roll, A plurality of transfer rolls for transferring an image to the sheet conveyed by the conveying means, and the conveying means upstream of the image carrier roll disposed on the most upstream side in the conveying direction of the sheet member . Braking force applying means for applying a braking force to the conveyed sheet and applying a tension in the conveying direction to the sheet.

  In the image forming apparatus according to the first aspect, the transfer unit transfers the image carried on the image carrier roll onto the sheet conveyed by being stretched by the carrying unit.

  Here, since the rotation speed of the image carrier roll and the conveyance speed of the sheet by the conveyance means are different, the tension applied to the sheet is different before and after the image carrier roll, and the amount of elongation of the sheet is different. For this reason, when a plurality of image carrier rolls are arranged along the sheet conveyance direction, a difference occurs in the position and magnification of the image transferred from each image carrier roll to the sheet, and color misregistration occurs.

  Therefore, in the present invention, the tension in the conveyance direction is applied to the sheet conveyed by the conveyance unit by the tension applying unit on the upstream side in the conveyance direction from the image carrier roll, and the sheet is stretched in the conveyance direction in advance. To the image carrier roll. Accordingly, the amount of the sheet that is stretched by receiving the frictional force from the image carrier roll can be reduced, so that the difference in the elongation amount of the sheet before and after the image carrier roll can be suppressed. Therefore, a difference in position and magnification of images transferred from each image carrier roll to the sheet can be suppressed without using complicated control, and color misregistration can be suppressed.

Specifically , the braking unit applies a braking force to the sheet conveyed by the conveying unit on the upstream side in the conveying direction from the image carrier roll. As a result, the sheet is once stretched upstream in the conveying direction from the image carrier roll, so that the amount of the sheet that is stretched by receiving frictional force from the image carrier roll can be reduced thereafter. Differences in sheet elongation can be suppressed.

The image forming apparatus according to claim 2 is the image forming apparatus according to claim 1 , wherein the tension applying unit is rotated by following the sheet conveyed by the conveying unit; Load torque applying means for applying load torque to the driven roll.

In the image forming apparatus according to the second aspect , the driven roll rotates following the sheet conveyed by the conveying unit on the upstream side in the conveying direction from the image carrier roll. The driven roll is given a load torque from the load torque applying means, and serves as a sheet conveyance load. As a result, the sheet is stretched by applying a braking force from the driven roll, so that the amount of the sheet that is stretched by receiving the frictional force from the image carrier roll can be reduced, and the difference in the amount of elongation of the sheet before and after the image carrier roll can be reduced. Can be suppressed.

  Since the present invention has the above-described configuration, in an image forming apparatus in which the conveyance speed of the sheet conveyed in a stretched manner and the rotation speed of the image carrier roll are different, the difference in the elongation amount of the sheet can be achieved without using complicated control. Can be suppressed, and image displacement can be suppressed.

  Embodiments of the present invention will be described below with reference to the drawings.

  As shown in FIG. 1, in a color laser printer (hereinafter referred to as a printer) 10 as an image forming apparatus, yellow (Y), magenta (M), cyan (C), and black (K) toner images are respectively stored. Print units 12Y, 12M, 12C, and 12K (hereinafter, referred to as print units 12Y to 12K) that are sequentially transferred and superimposed on the continuous paper P are sequentially arranged from the upstream side in the transport direction. A paper transport unit 14 that transports the continuous paper P to the print units 12Y to 12K is provided on the upstream side in the transport direction of the print units 12Y to 12K. Further, on the downstream side in the transport direction of the printing units 12Y to 12K, the fixing unit 16 that fixes the unfixed toner image transferred by the printing units 12Y to 12K to the continuous paper P, and the continuous paper P that has passed through the fixing unit 16 are discharged. A paper discharge unit 17 for paper is provided.

  In addition, when it is necessary to distinguish YMCK, it explains by adding any of Y, M, C, and K after the code, and when it is not necessary to distinguish YMCK, Y, M, C, and K are changed. Omitted.

  The paper transport unit 14 includes a main drive roll 18 around which the continuous paper P is wound. The main drive roll 18 is driven by a paper transport motor (not shown) that is an AC servomotor, and a control unit (not shown) that controls the entire printer 10 is operated on the continuous paper P based on the servo control of the paper transport motor. Control the feed amount.

  Further, an idle roll 19A and a drive roll 70 around which the continuous paper P is wound are provided on the upstream side in the transport direction of the main drive roll 18 of the paper transport unit 14, and on the downstream side in the transport direction of the main drive roll 18, An idle roll 19B around which the continuous paper P is wound is provided. The nip roll 72 is pressed against the main drive roll 18. The nip roll 72 and the main drive roll 18 sandwich and convey the continuous paper P. Further, the nip roll 74 is pressed against the drive roll 70. The nip roll 74 and the drive roll 70 sandwich and convey the continuous paper P.

  A conveyance guide 26 and an aligning roll 27 are disposed between the idle roll 19 </ b> A and the drive roll 70. The conveyance guide 26 is formed with a U-shaped curved surface around which the continuous paper P is wound and a side guide (not shown) that guides one end of the continuous paper P in the width direction (a direction orthogonal to the conveyance direction). Yes.

  The aligning roll 27 is a roll whose roll width is narrower in each stage than the idle rolls 19A and 19B, the drive roll 70, and the nip roll 72, and whose rotation axis is obliquely intersected with the conveying direction of the continuous paper P. The continuous paper P is brought close to one end in the width direction by coming into contact with one end in the width direction of the paper P. As a result, one end of the continuous paper P in the width direction is abutted against the guide rib of the conveyance guide 26, and the skew of the continuous paper P is corrected.

  The main drive roll 18, the idle rolls 19A and 19B, the drive roll 70, the nip roll 72, the nip roll 74, the conveyance guide 26, and the aligning roll 27 are supported by the paper conveyance frame 21 directly or via a support member. . The paper transport frame 21 is supported by the base 23.

  Each of the printing units 12Y to 12K includes a photosensitive drum 22, and around the photosensitive drum 22, a transfer roll 24, a cleaning device 28, and the like are sequentially arranged in the rotation direction of the photosensitive drum 22 (arrow direction in the drawing). A charging charger 30, an LED head 32, and a developing unit 34 as a consumable unit are disposed. The print units 12Y to 12K include print frames 38Y to 38K that support the photosensitive drum 22, the cleaning device 28, the charging charger 30, and the LED head 32, respectively.

  The transfer roll 24 abuts on the upper surface of the photosensitive drum 22 and sandwiches and conveys the continuous paper P together with the photosensitive drum 22. At this time, the toner image formed on the photosensitive drum 22 by the developing unit 34 is transferred to the continuous paper P. Transfer to P. Two guide rolls 40 are disposed on the upstream side and the downstream side in the transfer direction of the transfer roll.

  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. Further, the cleaning device 28 scrapes off and removes untransferred residual toner remaining on the surface of the photosensitive drum 22 without being transferred to the paper P. In addition, guide rolls 40 are disposed on the left and right sides of the transfer roll 24, and the continuous paper P is conveyed along the guide rolls 40.

  The developing unit 34 is provided with three developing magnet rolls 42 provided along the axial direction of the photosensitive drum 22, and is provided along the axial direction of the three developing magnet rolls 42. A magnetic roller 44 for conveying the two-component toner constituted by the three developing magnet rolls 42, and a toner and a carrier that are disposed along the axial direction of the conveying magnet roll 44 and are filled in the developer cartridge 46. Are stirred and charged, and two stirring screws 48 that mix evenly are provided.

  The fixing unit 16 includes a flash fixing device 52, a scuff roll 76, idle rolls 54 </ b> A and 54 </ b> B, and a paper discharge roll 56. The scuff roller 76, the idle rolls 54A and 54B, the flash fixing device 52, and the paper discharge roll 56 are arranged in this order in the transport direction, and these support both ends in the direction orthogonal to the transport direction on the fixing frame 58. Has been.

  The scuff flow 76 is a pair of rolls that sandwich and convey the continuous paper P. The idle rolls 54A and 54B are disposed on the back side of the printing surface of the continuous paper P, and the idle roll 54B is disposed above the idle roll 54A. For this reason, the continuous paper P wound around the idle rolls 54A and 54B is reversed and conveyed with the printing surface facing upward.

  The flash fixing device 52 is disposed on the printing surface side of the continuous paper P conveyed with the printing surface facing upward, and irradiates the printing surface of the continuous paper P with infrared rays. As a result, the unfixed toner on the continuous paper P is heated and melted, and then solidified and fixed on the continuous paper P.

  The paper discharge roll 56 discharges the toner-fixed area of the continuous paper P from the printer 10, but the continuous paper P that has passed through the flash fixing device 52 is once discharged from the fixing unit 16 and passed through the paper discharge unit 17. After passing, the paper returns to the fixing unit 16 and is discharged by the paper discharge roll 56.

  In the paper discharge unit 17, an idle roll 59A, a tension applying roll 60, a sub drive roll 61, an idle roll 59B, a conveyance guide 62, an aligning roll 63, and an idle roll 59C are arranged in order in the conveyance direction. Are supported by the paper discharge frame 65 directly or via a support member at both ends in a direction orthogonal to the transport direction. The paper discharge frame 65 is connected to the print frame 38K and the fixing frame 58.

  The sub drive roll 61 is disposed above the idle roll 59A, and the continuous paper P wound around the idle roll 59A and the sub drive roll 61 is redirected and conveyed upward. The idle roll 59 </ b> B is in pressure contact with the sub drive roll 61, rotates following the rotation of the sub drive roll 61, and sandwiches and conveys the continuous paper P together with the sub drive roll 61.

  Further, a tension applying roll 60 is disposed between the idle roll 59A and the sub drive roll 61, and the continuous paper P is between the idle roll 59A and the tension applying roll 60, and between the tension applying roll 60 and the sub drive roll. It is meandering between 61 and being conveyed.

  The tension applying roll 60 is supported at both ends in the axial direction so as to be swingable by arms (not shown). The arm is biased toward the continuous paper P by a biasing means (not shown) such as a spring, and the tension applying roll 60 is biased toward the continuous paper P. As a result, tension is applied to the continuous paper P.

  Further, the position of the arm is detected by a sensor (not shown), and the rotation speed of the sub drive roll 61 is controlled so that the position of the arm is always located at a fixed position.

  Further, a transport guide 62 and an aligning roll 63 are disposed downstream of the sub drive roll 61 in the transport direction. The conveyance guide 62 and the aligning roll 63 have the same configuration as the conveyance guide 26 and the aligning roll 27 disposed in the paper conveyance unit 14 and correct the skew of the continuous paper P.

  An idle roll 59 </ b> C is disposed downstream of the conveyance guide 62 in the conveyance direction. The continuous paper P is wound around the idle roll 59 </ b> C, and the direction is changed toward the paper discharge roll 56 of the fixing unit 16.

  By the way, as shown in FIG. 2, the rotational speed Vd of the photosensitive drum 22 is set to be faster than the rotational speed Vp of the main drive roll 18 and the transport speed Vp of the continuous paper P. For this reason, there is a difference in the magnitude of the tension applied to the continuous paper P before and after each photosensitive drum 22. Specifically, with respect to the tension T0 (= F0) in the transport direction that acts on the continuous paper P from the scuff flow 76, the tension in the transport direction that acts on the continuous paper P from the photosensitive drum 22 is downstream in the transport direction. In this order, T1 = F0 + F1, T2 = F0 + F1 + F2, T3 = F0 + F1 + F2, and T4 = F0 + F1 + F2 + F3 (see the graph of FIG. 3).

  On the other hand, as indicated by the solid line in the graph of FIG. 4, since the continuous paper P increases in elongation in proportion to the magnitude of the tension, the extension of the continuous paper P between the photosensitive drums 22 depends on the conveyance direction. It increases from the downstream side to the upstream side. As a result, for example, as shown in FIG. 5A, the writing positions of the photosensitive drum 22 on the downstream side in the transport direction and the photosensitive drum 22 on the downstream side in the transport direction are aligned, and the transfer position is overlapped on the rear end side. In addition, the transfer position (illustrated by a dotted line) by the photosensitive drum 22 on the upstream side in the transport direction is shifted to the writing side with respect to the transfer position (illustrated by a solid line) by the photosensitive drum 22 on the downstream side in the transport direction. Such transfer misregistration due to the photosensitive drums 22 accumulates toward the upstream side in the transport direction, so that a difference occurs in the position and magnification of the toner image transferred from each photosensitive drum 22 to the continuous paper P, and color misregistration occurs. Will occur.

  Therefore, in the present embodiment, as shown in FIG. 6, with respect to the continuous paper P conveyed by the tension applying mechanism 80 by the conveyance force such as the main drive roll 18 on the upstream side of the photosensitive drum 22 in the conveyance direction, A tension is applied in the transport direction, and the continuous paper P is stretched in advance and then transported to the photosensitive drum 22.

  Hereinafter, the tension applying mechanism 80 will be described.

  The tension applying mechanism 80 includes a drive roll 70, a nip roll 74, and a motor 78 that drives the drive roll 70. The rotation speed Vr of the drive roll 70 by the motor 78 is set slower than the conveyance speed Vp of the continuous paper P due to the conveyance force of the main drive roll 18 and the like. Further, the continuous paper P is held between the main drive roll 18 and the nip roll 74 on the downstream side in the transport direction of the drive roll 70 and on the upstream side in the transport direction from the photosensitive drum 22, and the main drive roll 18 and the continuous paper P slip. Is prevented. For this reason, a frictional force is generated between the drive roll 70 and the continuous paper P, and the tension in the transport direction acts on the continuous paper P, so that the continuous paper P is stretched. As a result, the continuous paper P is once stretched and then transported to the photosensitive drum 22, and as shown in the graph of FIG. 4, the continuous paper P has an extension amount ΔLb of the continuous paper when the tension applying mechanism 80 is not provided. It is reduced as compared with the elongation amount ΔLa of P. Therefore, as compared with the case where the tension applying mechanism 80 is not provided, the difference in the amount of extension of the continuous paper P before and after each photosensitive drum 22 can be suppressed, so that as shown in FIG. The amount of shift of the transfer position (illustrated by a dotted line) by the photosensitive drum 22 on the side to the writing side can be reduced, and the difference in the position and magnification of the image transferred from each photosensitive drum 22 to the continuous paper P can be suppressed. Therefore, color shift can be suppressed.

  The tension applied to the continuous paper P can be adjusted by adjusting the pinch pressure between the drive roll 70 and the nip roll 74. In addition, since the slip of the continuous paper P with respect to the main drive roll 18 is prevented at the nip portion between the main drive roll 18 and the nip roll 72, the drive roll 50 applies tension in the transport direction to the continuous paper P. Even so, there is no fluctuation in the transport speed of the continuous paper P between the main drive roll 18 and the photosensitive drum 22Y. Therefore, good image quality without color misregistration can be obtained.

  Next, another embodiment of the tension applying mechanism 80 will be described.

  As shown in FIG. 7, the tension applying mechanism 90 includes a driven roll 82 that rotates following the conveyed continuous paper P, and a torque limiter 84 that serves as a load torque applying unit that applies load torque to the driven roll 82. It is configured. The torque limiter 84 is attached between the rotating shaft 82A of the driven roll 82 and the roll part 82B, and always generates a constant torque in the roll part 82B.

  Here, the torque generated in the driven roll 82 acts in the direction in which the conveyance of the continuous paper P by the rotational force of the main drive roll 18 or the like is stopped. For this reason, a braking force is applied to the conveyed continuous paper P, and the continuous paper P is tensioned between the main drive roll 18 and the driven roll 82, so that the continuous paper P is stretched.

  As a result, the continuous paper P is once stretched and then transported to the photosensitive drum 22, so that the amount of continuous paper P can be reduced as compared with the case where the tension applying mechanism 90 is not provided. The difference in the amount of elongation of the continuous paper P can be suppressed. Therefore, since the shift of the transfer position between the photosensitive drums 22 can be suppressed, the difference in the position and magnification of the image transferred from each photosensitive drum 22 to the continuous paper P can be suppressed, and thus the color shift can be suppressed. Can be suppressed. Note that the tension applied to the continuous paper P can be adjusted by adjusting the torque of the torque limiter 84.

  In the embodiment, the present invention has been described by taking as an example a configuration in which the rotational speed Vd of the photosensitive drum 22 is faster than the conveying speed Vp of the continuous paper P. However, the rotational speed Vd of the photosensitive drum 22 is continuously increased. The present invention can also be applied to a configuration in which the paper P is transported at a speed lower than the transport speed Vp. In this case, the increasing tendency of the tension acting on the continuous paper P from the photosensitive drum 22 is reversed. However, regardless of the increasing tendency of the tension, the continuous paper P is stretched in advance so that the continuous paper P becomes the photosensitive drum. The amount of elongation due to the frictional force from 22 can be reduced.

  In the embodiment, a tension applying mechanism 80 including a drive roll 70 that is rotationally driven with a speed difference with respect to the conveyance speed of the continuous paper P, and a tension applying mechanism including a driven roll 82 whose rotation is limited by a torque limiter 84. 90 is used as the tension applying unit, but the present invention is not limited to these mechanisms, and any mechanism that can apply tension in the transport direction to the continuous paper P on the upstream side of the photosensitive drum 22 in the transport direction is applicable. is there. Further, although a torque limiter is used as means for applying a load torque to the driven roll 82, a brake can also be applied.

  In the embodiments, the present invention has been described by taking an image forming apparatus for continuous paper P as an example. However, an image for forming an image on a sheet made of a material other than paper, such as an OHP sheet, or a long cut paper. The present invention can also be applied to a forming apparatus.

  Further, in the embodiments, the present invention has been described by taking an image forming apparatus using an electrophotographic method as an example, but the present invention is also applied to other image forming apparatuses such as an image forming apparatus using an inkjet offset printing method. Applicable.

1 is a schematic view of an image forming apparatus according to an embodiment of the present invention. FIG. 6 is a diagram for explaining a change in tension applied to continuous paper in the image forming apparatus according to the embodiment of the present invention. 6 is a graph for explaining a change in tension applied to continuous paper in the image forming apparatus according to the embodiment of the present invention. 6 is a graph for explaining the relationship between tension and elongation applied to continuous paper in the image forming apparatus according to the embodiment of the present invention. (A) is a figure which shows the shift | offset | difference of the image which generate | occur | produces on continuous paper in the conventional image forming apparatus, (B) is a figure which shows the shift | offset | difference of the image generate | occur | produced on continuous paper in the image forming apparatus which concerns on embodiment of this invention. is there. 1 is a schematic view of a tension applying mechanism of an image forming apparatus according to an embodiment of the present invention. It is the schematic of the tension | tensile_strength provision mechanism of the image forming apparatus which concerns on other embodiment of this invention.

Explanation of symbols

10 Printer (image forming device)
18 Main drive roll (conveying means)
22 Photosensitive drum (image carrier roll)
24 Transfer roll (transfer means)
70 Drive roll
72 Nip roll 80 Tension applying mechanism (tension applying means)
82 Followed roll 84 Torque limiter (load torque applying means)
90 Tension applying mechanism (tension applying means, braking force applying means)
P Continuous paper (sheet)

Claims (2)

Conveying means for stretching and conveying a sheet of continuous paper ;
A plurality of image carrier rolls provided along a conveyance direction of a sheet conveyed by the conveyance unit, carrying an image, and rotating with a speed difference with respect to the sheet conveyed by the conveyance unit;
Together sandwich the sheet between the image carrier roll each, from the image carrier roll, a plurality of transfer rolls for transferring the image to the sheet conveyed by said conveying means,
A braking force is applied to the sheet conveyed by the conveying means on the upstream side in the conveying direction from the image carrier roll arranged on the most upstream side in the conveying direction of the sheet member, and the sheet is moved in the conveying direction. Braking force applying means for applying tension;
An image forming apparatus comprising: The braking force applying means is
A driven roll that rotates following the sheet conveyed by the conveying means;
Load torque applying means for applying load torque to the driven roll;
The image forming apparatus according to claim 1, further comprising:

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