JP5409847B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a digital copying machine or a laser printer, and more particularly to a sheet conveyance control that eliminates a problem caused by a difference between a sheet conveyance speed in an image transfer unit and a sheet conveyance speed in a fixing device.

  In a conventional image forming apparatus, a sheet conveyance speed (hereinafter referred to as a transfer linear speed) in an image transfer unit and a sheet conveyance speed (hereinafter referred to as a fixation linear speed) in a fixing device disposed on the downstream side of the image transfer unit are generally used. ) Are controlled to be the same, but the fixing linear speed may vary due to the influence of the component accuracy of the fixing roller pair constituting the fixing device and the change over time due to thermal expansion. Further, the length of the transported paper in the transport direction is longer than the length from the nip portion (transfer nip portion) between the photosensitive drum and the transfer roller to the nip portion (fixing nip portion) of the fixing roller pair.

  For this reason, when the fixing linear velocity is higher than the transfer linear velocity, a tension is applied to the trailing edge of the sheet passing through the transfer roller when the leading edge of the sheet is nipped by the fixing roller pair, which causes image transfer deviation.

  Also, if the paper is pulled between the transfer and fixing, the paper may wrinkle during fixing. Conversely, if the paper is too slack, it will serve as a conveyance guide that forms a paper conveyance path from the transfer roller to the fixing device. There is also a problem in that the image forming surface is rubbed and an image defect occurs in an unfixed toner image.

  In view of this, various methods have been proposed in which variations in the fixing linear speed or transfer linear speed are absorbed to prevent image transfer deviation and image loss due to contact with the conveyance guide. Loop detection means for detecting the loop amount (slack amount) of the recording medium conveyed to the downstream unit, and speed switching means capable of switching the recording medium conveyance speed by the downstream unit in two or more steps are provided to detect the loop. An image forming apparatus that controls the loop amount of a recording medium in accordance with the detection result of the means is disclosed.

  Japanese Patent Application Laid-Open No. 2005-228561 discloses a detection unit that detects the amount of sheet slack in a slack forming unit between the transfer unit and the fixing device, and a control that adjusts the fixing linear velocity within a predetermined range based on the detection result of the detection unit. An image forming apparatus provided with a means is disclosed, and an example is described in which an optical displacement sensor capable of detecting a slack amount without contact with a sheet is used as a slack amount detection sensor.

JP 2007-52112 A JP 2006-219273 A

  However, since the method of Patent Document 1 uses loop detection means that combines an actuator and a photo interrupter, there is a possibility that the sheet conveyance state is affected by interference between the sheet and the actuator.

  Further, in the method of Patent Document 2, the amount of slackness can be detected without contact with the sheet. However, since the amount of slackness detection sensor is disposed on the image forming surface side (see FIG. 4 of Patent Document 2), unfixed. There is a possibility that the detection accuracy may be lowered due to toner scattering due to toner scattering.

  In view of the above problems, the present invention accurately detects the slack of the paper between the transfer and fixing, and maintains the amount of slack in a certain range, thereby preventing the occurrence of transfer deviation, paper wrinkles, or image loss. An object is to provide an apparatus.

  In order to achieve the above-described object, the present invention forms an image carrier and a transfer nip portion that is brought into contact with the image carrier with a predetermined pressure and allows a recording medium to pass therethrough, and a toner image formed on the image carrier. An image transfer unit including a transfer roller for transfer onto a recording medium, an endless fixing belt, a heat transfer roller and a fixing roller that are inscribed in the fixing belt and rotate in the same direction as the fixing belt, and the fixing roller And a pressure roller that is pressed by a predetermined pressure and rotated by a driving unit, and is transferred onto a recording medium by the image transfer unit at a fixing nip formed by the fixing belt and the pressure roller. An image forming apparatus comprising: a fixing device that heats and pressurizes the toner image; and a transfer roller side guide member and an image carrier side guide member that form a recording medium conveyance path between the fixing device and the image transfer unit. Detecting means for detecting the distance from the guide surface of the recording medium passing through the transfer nip portion and the fixing nip portion in a non-contact manner, disposed at a position recessed from the guide surface of the transfer roller side guide member. And a control means for adjusting the conveyance speed of the recording medium passing through the fixing nip portion based on the detection result of the detection means.

  According to the present invention, in the image forming apparatus configured as described above, the image carrier-side guide member is a conveyance roller that protrudes into the recording medium conveyance path.

  According to the present invention, in the image forming apparatus configured as described above, the control unit adjusts the conveyance speed at least twice while the recording medium passes through the fixing nip portion.

  According to the present invention, in the image forming apparatus configured as described above, a plurality of the detection units are arranged in the recording medium conveyance direction or in a direction orthogonal to the conveyance direction, and the conveyance speed of the recording medium is determined based on the detection result of each detection unit. It is characterized by adjusting.

  According to the present invention, in the image forming apparatus having the above-described configuration, a plurality of conveyance fans that blow air in a direction in which the recording medium is brought close to the guide surface of the transfer roller side guide member are arranged in a direction perpendicular to the conveyance direction. The means is characterized by adjusting the conveyance speed of the recording medium based on the detection results of a plurality of detection means arranged in a direction orthogonal to the conveyance direction and controlling the rotation of the conveyance fan.

  According to the present invention, in the image forming apparatus configured as described above, the transport fans are arranged in a plurality of rows in the transport direction.

  According to the present invention, in the image forming apparatus configured as described above, the detection unit is an infrared reflection type distance sensor.

  According to the first configuration of the present invention, the recording medium is not pulled between the transfer and fixing, and is not greatly loosened, and an appropriate amount of looseness can always be maintained. In addition, since the detecting means is disposed on the transfer roller side guide member on the opposite side to the image forming surface of the recording medium, there is no possibility that the detecting surface is contaminated by scattering of unfixed toner, and the detection accuracy is extended for a long time. Can be maintained over time. In addition, since the detection means detects the recording medium in a non-contact manner and is disposed at a position recessed from the guide surface of the transfer roller side guide member, the height from the guide surface is measured without applying a load to the recording medium. And there is no possibility of adversely affecting the conveyance of the recording medium.

  According to the second configuration of the present invention, in the image forming apparatus having the first configuration, a shuriken-shaped transport roller protruding into the recording medium transport path is used as the image carrier side guide member.

  According to the third configuration of the present invention, in the image forming apparatus having the first or second configuration, the control unit adjusts the conveyance speed twice or more while the recording medium passes through the fixing nip portion. This makes it possible to adjust the behavior of the recording medium such as slack and tension more accurately.

  According to the fourth configuration of the present invention, in the image forming apparatus having any one of the first to third configurations, a plurality of detection units are arranged in the conveyance direction of the recording medium or in the direction perpendicular to the conveyance direction. By adjusting the conveyance speed of the recording medium based on the detection result of each detection means, the fixing linear speed can be controlled using the detection results at a plurality of locations in the conveyance direction or the width direction. It is possible to detect accurately, and it is possible to more effectively suppress the transfer deviation in the transfer nip portion, the generation of wrinkles in the fixing nip portion, and the image defect.

  According to the fifth configuration of the invention, in the image forming apparatus having the fourth configuration, the transport fan that blows air in a direction in which the recording medium is brought close to the guide surface of the transfer roller side guide member is perpendicular to the transport direction. The recording medium is transported by adjusting the transport speed of the recording medium and controlling the rotation of the transport fan based on the detection results of the plurality of detecting means disposed in the direction orthogonal to the transport direction. While maintaining the amount of slack in the direction within an appropriate range, the amount of slack in the width direction can be maintained within the appropriate range by controlling the rotation of the transport fan.

  According to the sixth configuration of the present invention, in the image forming apparatus having the fifth configuration, the amount of slack in the width direction of the recording medium can be more easily adjusted by arranging a plurality of transport fans in the transport direction. It becomes possible.

  According to the seventh configuration of the present invention, in the image forming apparatus having any one of the first to sixth configurations, an appropriate detection can be achieved by using an infrared reflection type distance sensor with a fast response speed as the detection unit. The slack of the recording medium can be adjusted by feeding back the result.

Side surface sectional view showing the configuration of the color image forming apparatus of the present invention 1 is a block diagram showing a control path of an image forming apparatus according to a first embodiment. FIG. 3 is an enlarged view showing the periphery of an image transfer unit of the image forming apparatus according to the first embodiment. Graph showing an example of the relationship between the distance from the transport guide to the paper and the output voltage of the paper height sensor Timing chart when switching the fixing linear speed using the control of Table 1 FIG. 3 is an enlarged view showing how the slack of the paper is properly adjusted. The enlarged view which shows the image transfer part periphery of the image forming apparatus which concerns on 2nd Embodiment of this invention. The enlarged view which shows the image transfer part periphery of the image forming apparatus which concerns on 3rd Embodiment of this invention. FIG. 8A is a plan view of the transport fan used in the image forming apparatus according to the third embodiment as viewed from the back side of the transport guide (FIG. 8A), and FIG. 8 is a plan view of the intermediate transport fan as viewed from below in FIG. (B)) Graph showing change in guide-to-paper distance when fixing linear velocity and fan control are not performed in the embodiment (comparative example) Graph showing change in guide-paper distance when fixing linear velocity and fan control are performed in the embodiment (invention)

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a side sectional view showing the configuration of the image forming apparatus of the present invention. In the main body of the image forming apparatus (color printer) 100, four image forming portions Pa, Pb, Pc and Pd are sequentially arranged from the upstream side in the transport direction (the right side in FIG. 4). These image forming portions Pa to Pd are provided corresponding to images of four different colors (cyan, magenta, yellow, and black), and cyan, magenta, and yellow are respectively performed by charging, exposure, development, and transfer processes. And a black image are sequentially formed.

  Photosensitive drums 1a, 1b, 1c, and 1d that carry visible images (toner images) of the respective colors are disposed in the image forming portions Pa to Pd, and are formed on the photosensitive drums 1a to 1d. The transferred toner image is rotated clockwise in FIG. 1 by a driving means (not shown) and sequentially transferred onto the intermediate transfer belt 8 that moves adjacent to each image forming unit. The image is transferred onto the paper P at a time by the image transfer unit 13 constituted by the transfer roller 9, and further fixed on the paper P by the fixing device 7 and then discharged from the apparatus main body. An image forming process for each of the photosensitive drums 1a to 1d is executed while rotating the photosensitive drums 1a to 1d counterclockwise in FIG.

  The paper P to which the toner image is transferred is accommodated in a paper cassette 16 at the lower part of the apparatus, and is conveyed to the transfer roller 9 via the paper feed roller 12a and the registration roller pair 12b. A sheet made of a dielectric resin is used for the intermediate transfer belt 8, and a belt in which both ends thereof are overlapped and joined to form an endless shape, or a belt without a seam (seamless) is used. A cleaning blade 19 for removing toner remaining on the surface of the intermediate transfer belt 8 is disposed on the downstream side of the transfer roller 9.

  Next, the image forming units Pa to Pd will be described. There are chargers 2a, 2b, 2c, and 2d for charging the photosensitive drums 1a to 1d and image information on the photosensitive drums 1a to 1d around and below the photosensitive drums 1a to 1d that are rotatably arranged. The exposure unit 4 for exposing the toner, the developing units 3a, 3b, 3c and 3d for forming toner images on the photosensitive drums 1a to 1d, and the developer (toner) remaining on the photosensitive drums 1a to 1d are removed. Cleaning units 5a, 5b, 5c and 5d are provided.

  When the image formation start is input by the user, first, the surfaces of the photosensitive drums 1a to 1d are uniformly charged by the chargers 2a to 2d, and then light is irradiated by the exposure unit 4 to each of the photosensitive drums 1a to 1d. An electrostatic latent image corresponding to the image signal is formed on the top. Each of the developing units 3a to 3d is filled with a predetermined amount of cyan, magenta, yellow, and black toner by a replenishing device (not shown). The toner is supplied onto the photosensitive drums 1a to 1d by the developing units 3a to 3d and electrostatically attached, whereby a toner image corresponding to the electrostatic latent image formed by exposure from the exposure unit 4 is formed. It is formed.

  After an electric field is applied to the intermediate transfer belt 8 at a predetermined transfer voltage, cyan, magenta, yellow, and black toner images on the photosensitive drums 1a to 1d are transferred to the intermediate transfer belt 8 by the intermediate transfer rollers 6a to 6d. Transferred (primary transfer) on top. These four color images are formed with a predetermined positional relationship predetermined for forming a predetermined full-color image. Thereafter, the toner remaining on the surfaces of the photosensitive drums 1a to 1d is removed by the cleaning units 5a to 5d in preparation for the subsequent formation of a new electrostatic latent image.

  The intermediate transfer belt 8 is stretched between an upstream tension roller 10 and a downstream drive roller 11, and the intermediate transfer belt 8 rotates clockwise as the drive roller 11 is rotated by a drive motor (not shown). When the rotation starts, the sheet P is conveyed from the registration roller pair 12b to the image transfer unit 13 at a predetermined timing, and a full-color image is transferred (secondary) at the nip portion (transfer nip portion) between the intermediate transfer belt 8 and the transfer roller 9. Transferred). The paper P on which the toner image is transferred is conveyed to the fixing device 7.

  The paper P conveyed to the fixing device 7 is heated and pressurized when passing through the fixing device 7 (fixing nip portion), and the toner image is fixed on the surface of the paper P, whereby a predetermined full color image is formed. The paper P on which the full-color image is formed is distributed in the transport direction by the branching section 14 that branches in a plurality of directions. When an image is formed on only one side of the paper P, it is discharged as it is onto the discharge tray 17 by the discharge roller 15.

  On the other hand, when images are formed on both sides of the sheet P, a part of the sheet P that has passed through the fixing device 7 is once projected from the discharge roller 15 to the outside of the apparatus. Thereafter, the paper P is distributed to the paper transport path 18 by the branching section 14 by rotating the discharge roller 15 in the reverse direction, and is transported again to the transfer roller 9 with the image surface reversed. Then, the next image formed on the intermediate transfer belt 8 is transferred to the surface of the paper P on which the image is not formed by the transfer roller 9 and conveyed to the fixing device 7 to fix the toner image. 17 is discharged.

  FIG. 2 is a block diagram showing a control path of the image forming apparatus according to the first embodiment of the present invention. Portions common to FIG. 1 are denoted by the same reference numerals and description thereof is omitted. When the image forming apparatus 100 is a printer as shown in FIG. 1, the image input unit 40 is a receiving unit that receives image data transmitted from a personal computer or the like, and when the image forming apparatus 100 is a copying machine. A scanning optical system equipped with a scanner lamp that illuminates the document during copying and a mirror that changes the optical path of the reflected light from the document, a condensing lens that focuses the reflected light from the document and forms an image The image reading unit includes a CCD or the like that converts the image light into an electrical signal. The image signal input from the image input unit 40 is converted into a digital signal by the AD conversion unit 41 and then transmitted to an image memory 60 in the storage unit 44 described later.

  The storage unit 44 includes an image memory 60, a RAM 61, and a ROM 62. The image memory 60 stores an image signal input from the image input unit 40 and digitally converted by the AD conversion unit 41, and is stored in the control unit 43. Send it out. The RAM 61 and the ROM 62 store a processing program of the control unit 43, data necessary for the processing, and the like.

  The operation panel 45 includes an operation unit composed of a plurality of operation keys, and a display unit (none of which is shown) that displays setting conditions, apparatus states, and the like, and the user sets printing conditions and the like. In addition, when the image forming apparatus 100 has a facsimile function, it is also used for various settings such as registering a facsimile transmission destination in the storage unit 44 and further reading and rewriting the registered transmission destination.

  The paper height sensor 30a is disposed in the paper transport path 29 (see FIG. 3) between the transfer roller 9 and the fixing device 7, and the height of the paper passing through the paper transport path 29 (the transport guide 25 and the paper P). ). The detection result by the paper height sensor 30a is transmitted to the control unit 43, and the fixing linear velocity is adjusted based on the detection result.

  The main motor 47 responds to a control signal from the control unit 43. The fixing roller 23 and the pressure roller 24 (see FIG. 3) in the fixing device 7, the photosensitive drums 1a to 1d in the image forming units Pa to Pd, and development. The units 3a to 3d, the registration roller pair 12b, the transfer roller 9 and the like are driven. Note that the registration roller pair 12b needs to adjust the sheet supply timing in accordance with the image formation timing in the image forming units Pa to Pd, and therefore is connected to the main motor 47 via a clutch (not shown) and can be driven independently. It has become. The fixing drive motor 48 drives the pressure roller 24 in the fixing device 7 in accordance with a control signal from the control unit 43. The paper feed roller 12a sends out the paper from the paper cassette 16 toward the registration roller pair 12b in response to a print start command from the operation panel 45.

  The control unit 43 generally controls the image forming units Pa to Pd, the fixing device 7, the paper feed roller 12a, the registration roller pair 12b, the image input unit 40, the main motor 47 for driving them, and the like according to the set program. At the same time, the image signal input from the image input unit 40 is converted into image data by scaling or gradation processing as necessary. The exposure unit 4 irradiates a laser beam based on the processed image data, and forms latent images on the photosensitive drums 1a to 1d.

  FIG. 3 is an enlarged view showing a configuration around the image transfer unit in the image forming apparatus of the first embodiment. Portions common to FIGS. 1 and 2 are denoted by the same reference numerals and description thereof is omitted. As shown in FIG. 3, the fixing device 7 includes an endless fixing belt 21 that rotates clockwise in the drawing, a heat transfer roller 22 that contacts the fixing belt 21 and rotates in the same direction as the fixing belt 21, and fixing. The roller 23 includes a pressure roller 24 that is pressed against the fixing roller 23 with a predetermined pressure and rotates counterclockwise in the drawing.

  Between the transfer nip N1 between the intermediate transfer belt 8 and the transfer roller 9 and the fixing nip N2 between the fixing roller 23 and the pressure roller 24, a conveyance guide 25 and a shuriken-shaped conveyance roller 27 are arranged. A paper transport path 29 is formed between the transport guide 25 and the transport roller 27. The sheet P on which the toner image formed on the intermediate transfer belt 8 is transferred in the transfer nip portion N1 advances in the sheet conveyance path 29 in the upward direction in the figure, is carried into the fixing device 7, and passes through the fixing nip portion N2. To do. At this time, the toner is heated and pressurized at a predetermined temperature and pressure, and the unfixed toner on the paper P becomes a permanent image.

  A paper height sensor 30a that measures the distance from the guide surface 25a to the paper P is disposed at a position recessed from the guide surface 25a of the transport guide 25. As the paper height sensor 30a, an infrared reflection type distance sensor having a light emitting unit that emits infrared light to a measurement object and a light receiving element (position detection element) that receives reflected light from the measurement object is used.

The reflected light incident on the light receiving element is photoelectrically converted and output to the control unit 43 as a photocurrent. If the position of the object to be measured (distance from the light emitting part) changes, the amount of reflected light also changes. Can be obtained. An example of the relationship between the distance from the conveyance guide 25 to the paper P and the output voltage of the paper height sensor 30a is shown in FIG. Table 1 shows an example of fixing linear velocity control using the paper height sensor 30a shown in FIG.

  In the control example of Table 1, when the output voltage of the paper height sensor 30a is E, the distance from the guide surface 25a of the transport guide 25 to the paper P calculated using E (hereinafter referred to as guide-paper distance). ) Is 4 to 6 mm, the fixing linear speed is maintained at the initial speed, and when it is 4 mm or less, the fixing linear speed is increased stepwise, and when it is 6 mm or more, the fixing linear speed is decreased stepwise. doing. The guide-paper distance detection timing (fixing linear speed switching timing) may be from the time when the leading edge of the paper P reaches the fixing nip portion N2 until the trailing edge of the paper P passes through the transfer nip portion N1. It ’s fine.

  FIG. 5 is a timing chart when the fixing linear velocity is switched using the control of Table 1. A fixing linear velocity control method in the image forming apparatus according to the first embodiment will be described with reference to FIGS. 1 to 5 and Table 1. FIG. Here, the initial fixing linear velocity is 250 mm / sec, and 700 msec (175 mm from the front end of the paper P) after the paper height sensor 30a detects the front edge of the paper P (A3 size) and 1400 msec (paper P). The guide-paper distance is detected at 350 mm from the leading edge, and the controller 43 controls the fixing linear velocity based on the detection result transmitted from the paper height sensor 30a. Although FIG. 5 illustrates the case where the fixing line speed is increased, the same can be said for the case where the fixing line speed is decreased.

  In the example of FIG. 5, since the output voltage of the paper height sensor 30a is 2.3 V or more (the guide-paper distance is 0 to 2 mm) at 700 msec (at the first detection), the control unit 43 determines the paper height. At 900 msec after the sensor 30a detects the leading edge of the paper P (225 mm from the passage of the leading edge of the paper P), a control signal is transmitted to the fixing drive motor 48 to increase the fixing linear speed by 0.2% from the initial speed. ing. Even at 1400 msec (second detection), the output voltage of the paper height sensor 30a is similarly 2.3 V or higher, so that the fixing linear speed is maintained at a speed increased by 0.2%. Then, since the paper height sensor 30a detects the trailing edge of the paper P and 900 msec (225 mm from the trailing edge of the paper P), the paper P has completely passed through the fixing nip portion N2. The unit 43 transmits a control signal to the fixing drive motor 48 to return the fixing linear speed to the initial speed again.

  By performing such control, the paper P is not pulled between the transfer and fixing as shown by a broken line in FIG. 6 and conversely, the paper P is not greatly loosened as shown by a one-dot chain line, and is always a solid line. It is possible to maintain an appropriate amount of slack as shown by. Accordingly, transfer deviation at the transfer nip portion N1 and generation of wrinkles at the fixing nip portion N2 are effectively suppressed, and there is no possibility that an unfixed toner image is rubbed by the conveying roller 27 and image loss occurs.

  Further, since the paper height sensor 30a is disposed on the conveyance guide 25 side opposite to the image forming surface (the right side surface in FIG. 6) of the paper P, the sensor surface is contaminated by scattering of unfixed toner. The detection accuracy of the paper height sensor 30a can be maintained over a long period of time. Further, since the paper height sensor 30a is disposed at a position recessed from the guide surface 25a of the transport guide 25, there is no possibility of adversely affecting the transport of the paper P due to interference with the paper P.

  The detection of the guide-paper distance and the control of the fixing linear velocity by the paper height sensor 30a may be performed once while each paper passes between the transfer roller 9 and the fixing device 7, but the paper P In order to detect and correct the behavior such as loosening and pulling more accurately, it is preferable to set the number of times twice or more for each sheet. The guide-paper distance detection timing may be set as appropriate according to the size of the paper to be conveyed, the distance from the paper height sensor 30a to the fixing nip portion N2, the initial fixing linear velocity, and the like. An optical displacement sensor other than the infrared reflection type distance sensor can be used as the height sensor 30a.

FIG. 7 is an enlarged view showing a configuration around the image transfer unit in the image forming apparatus according to the second embodiment of the present invention. Portions common to FIG. 3 of the first embodiment are denoted by the same reference numerals and description thereof is omitted. In the present embodiment, two paper height sensors 30a and 30b are arranged along the paper conveyance direction inside the conveyance guide 25, and the detection result of the guide-paper distance by the paper height sensors 30a and 30b is shown. Based on this, the fixing linear velocity is controlled. Table 2 shows an example of controlling the fixing linear velocity using the paper height sensors 30a and 30b. The characteristic of the paper height sensor 30b is the same as that of the paper height sensor 30a shown in FIG.

  In the control example of Table 2, when the output voltage of the paper height sensor 30a is E1, and the output voltage of the paper height sensor 30b is E2, the guide-paper distance calculated using E1 and E2 is 4 to 4 together. When it is 6 mm, the fixing linear speed is maintained at the initial speed. When both are 4 mm or less, the fixing linear speed is increased stepwise, and when both are 6 mm or more, the fixing linear speed is decreased stepwise. Yes.

  That is, since the fixing linear speed is controlled using the guide-paper distance detected at two locations in the paper conveyance direction, the conveyance state (slack or tension) of the paper P is detected more accurately than in the first embodiment. Therefore, it is possible to more effectively suppress transfer deviation at the transfer nip portion N1, generation of wrinkles at the fixing nip portion N2, and image loss. The detection timing of the guide-paper distance (fixing linear velocity switching timing) and the number of detections can be set as appropriate according to the specifications of the apparatus as in the first embodiment.

  FIG. 8 is an enlarged view showing the configuration around the image transfer unit in the image forming apparatus according to the third embodiment of the present invention. Portions common to FIGS. 3 and 7 of the first and second embodiments are denoted by the same reference numerals and description thereof is omitted. In the present embodiment, the two paper height sensors 30 a and 30 b are arranged inside the conveyance guide 25 in a direction orthogonal to the paper conveyance direction (paper surface direction in FIG. 8), and the paper P is guided by the conveyance guide 25. A blower unit 31 and an intermediate blower unit 33 for blowing air are arranged so as to approach the surface 25a. The blowing direction of the blowing unit 31 and the intermediate blowing unit 33 is indicated by black arrows.

  9A is a plan view of the blower unit 31 as viewed from the back side (left side of FIG. 8) of the conveyance guide 25, and FIG. 9B is a plan view of the intermediate blower unit 33 as viewed from below in FIG. FIG. The blower unit 31 has center fans 35 and 36 disposed on the front side of the apparatus (the front side of the sheet of FIG. 8) and the rear side of the apparatus (the back side of the sheet of FIG. 8), respectively. The paper height sensors 30a and 30b are disposed adjacent to the downstream side (in the direction of white arrow 9 (a)).

  In the intermediate blower unit 33, sirocco fans 37 and 38 are arranged on the front side and the rear side of the apparatus, respectively, with the blowout ports 37a and 38a facing the sheet conveyance path 29 side. The center fans 35 and 36 and the sirocco fans 37 and 38 are normally in an ON state while the paper P passes between the transfer and fixing, so that contact between the image forming surface of the paper P and the conveying roller 27 is avoided. Yes.

  Next, the paper conveyance control of this embodiment will be described. In the present embodiment, when the output voltage of the paper height sensor 30a on the front side of the apparatus is E1, and the output voltage of the paper height sensor 30b on the rear side of the apparatus is E2, when E1-E2 is greater than a predetermined value, When the front side of the paper P is slack (solid line in FIG. 8) and the rear side of the paper P is pulled (broken line in FIG. 8), the fixing linear speed is decreased by a predetermined amount and the center on the front side of the apparatus The fan 35 and the sirocco fan 37 are turned off. Further, when E2-E1 is larger than a predetermined value, that is, when the apparatus front side of the paper P is pulled and the apparatus rear side of the paper P is slack, the fixing linear speed is decreased by a predetermined amount and the apparatus rear side The center fan 36 and the sirocco fan 38 are turned off.

  Thereby, even if there is a difference in the amount of slack of the paper P between the front side and the rear side (paper width direction), the center fan that constitutes the transport fan 31 and the intermediate transport fan 33 according to the slack of the paper P. The amount of slack in the width direction of the paper P can be equalized and maintained in an appropriate range by controlling ON and OFF of the 35 and 36 and the sirocco fans 37 and 38.

  In this example, the control example in which both of the fans with the larger amount of slack are turned off among the center fans 35 and 36 and the sirocco fans 37 and 38 is shown. It is also possible to turn off only. Further, instead of the ON / OFF control, the rotation speed (rotational speed) of the center fans 35 and 36 and the sirocco fans 37 and 38 may be varied according to the amount of slack.

  In addition, this invention is not limited to the said embodiment, A various change is possible in the range which does not deviate from the meaning of this invention. For example, in the second embodiment, the paper height sensors 30a and 30b are arranged at two places in the transport direction. However, if the detection results of the sensors are used at three places or more, detection and fixing lines with higher accuracy can be performed. Speed control is possible.

  In the third embodiment, the paper height sensors 30a and 30b arranged on the front side and the rear side of the apparatus are used, and the center fan 35 and the sirocco fan 37 on the apparatus front side constituting the air blowing unit 31 and the intermediate air blowing unit 33, Although the configuration is such that the rotation of the center fan 36 and the sirocco fan 38 on the rear side of the apparatus is controlled, three or more paper height sensors, center fans, and sirocco fans may be arranged in the paper width direction. Further, by combining the control of the first or second embodiment and the control of the third embodiment, it is possible to maintain the amount of slack in the conveyance direction and the width direction of the paper within an appropriate range, and transfer deviation, wrinkle, The image forming apparatus can more reliably prevent defects such as image defects.

  Although the tandem type color printer has been described in the above embodiment, the present invention is not limited to a color printer, but can be applied to various image forming apparatuses using an electrophotographic process such as a monochrome printer, a copying machine, and a facsimile. It is.

  The paper conveyance state between transfer and fixing when the image formation was performed using the color image forming apparatus of the third embodiment shown in FIGS. 8 and 9 was investigated. As test conditions, the initial fixing linear velocity was 250 mm / sec, and paper height sensors 30a and 30b having the characteristics shown in FIG. 4 were used. As a test method, output voltages E1 and E2 of the paper height sensors 30a and 30b are detected after 50 msec from the detection of the leading edge of the paper P by the paper height sensors 30a and 30b, and when E1-E2> 0.2V, the fixing line The speed is decreased by 0.2%, the center fan 35 and the sirocco fan 37 are turned OFF, and when E2-E1> 0.2V, the fixing linear speed is decreased by 0.2% and the center fan 36 and the sirocco fan 38 are turned OFF. The change in the distance between the guide and the paper when the paper P passes between the transfer and the fixing was measured by comparing the case where the control is performed and the case where the fixing linear velocity and the fan control are not performed as a comparative example. The results are shown in FIGS.

  In the comparative example in which the fixing linear velocity and the fan control are not performed, as is apparent from FIG. 10, the front side of the apparatus (solid line in the figure) is pulled away from the guide surface 25a of the conveyance guide 25 and is 10 mm from the guide surface. Image defects due to contact with a certain conveying roller 27 were observed. On the other hand, in the present invention in which the fixing linear velocity and the fan control are performed, as is apparent from FIG. 11, the guide-paper distance is maintained at 0 to 8 mm on the front side and the rear side of the apparatus, and no image defect occurs. . Although not described here, it has been confirmed that by controlling the fixing linear velocity using the image forming apparatuses of the first and second embodiments, an effect of preventing image loss can be obtained similarly.

  The present invention forms an image carrier and a transfer nip that contacts the image carrier with a predetermined pressure and allows the recording medium to pass therethrough, and transfers the toner image formed on the image carrier onto the recording medium. An image transfer unit including a roller, a fixing device having a fixing nip for heating and pressurizing a toner image transferred onto the recording medium by the image transfer unit, and a recording medium between the fixing device and the image transfer unit In an image forming apparatus including a transfer roller side guide member and an image carrier side guide member that form a conveyance path, the transfer nip portion and the fixing nip portion are disposed at positions recessed from the guide surface of the transfer roller side guide member. Detecting means for detecting the distance from the guide surface of the recording medium that is passing through in a non-contact manner, and control means for adjusting the conveyance speed of the recording medium passing through the fixing nip portion based on the detection result of the detecting means. Those digits.

  As a result, transfer deviation at the transfer nip portion and wrinkles at the fixing nip portion are effectively suppressed, and an unfixed toner image is not rubbed by the image end-member-side guide member to cause image loss. A forming apparatus can be provided. In addition, since the non-contact detection type detection means is disposed at a position recessed from the guide surface of the transfer roller side guide member, the detection surface is not contaminated by scattering of unfixed toner, and the detection accuracy can be maintained for a long period of time. In addition, it is possible to provide an image forming apparatus with a simple configuration that does not have a possibility of adversely affecting the conveyance due to the interference between the detection unit and the recording medium.

  If a plurality of detection means are provided in the transport direction or in a direction perpendicular to the transport direction, and the fixing linear velocity is controlled using the detection results at a plurality of locations in the transport direction or the width direction of the recording medium, the recording medium Thus, the image forming apparatus can detect the transfer state more accurately, and can effectively suppress the occurrence of transfer misalignment, wrinkles during fixing, and image defects.

  Further, a plurality of conveying fans that blow the recording medium in the direction approaching the transfer roller side guide member are arranged in a direction orthogonal to the conveying direction, and the detection results of the plurality of detecting means arranged in the direction orthogonal to the conveying direction are used. If the rotation of the conveying fan is controlled based on this, the image forming apparatus can maintain the amount of slack in the width direction of the recording medium within an appropriate range.

7 Fixing device 8 Intermediate transfer belt (image carrier)
9 Transfer roller 13 Image transfer unit 25 Conveyance guide (transfer roller side guide member)
25a guide surface 27 conveying roller (image carrier side guide member)
29 Paper transport path (recording medium transport path)
30a, 30b Paper height sensor (detection means)
31 Blower unit 33 Intermediate blower unit 35, 36 Center fan (conveyance fan)
37, 38 Sirocco fan (conveyance fan)
43 Control unit (control means)
48 Fixing drive motor 100 Image forming apparatus Pa to Pd Image forming portion N1 Transfer nip portion N2 Fixing nip portion P Paper (recording medium)

Claims (6)

An image carrier, and a transfer roller that forms a transfer nip portion that contacts the image carrier with a predetermined pressure and allows the recording medium to pass therethrough and that transfers a toner image formed on the image carrier onto the recording medium. An image transfer section;
An endless fixing belt, a heat transfer roller and a fixing roller which are inscribed in the fixing belt and rotate in the same direction as the fixing belt, and a pressure roller which is pressed against the fixing roller with a predetermined pressure and rotated by a driving unit And a fixing device that heats and pressurizes the toner image transferred onto the recording medium by the image transfer unit at a fixing nip formed by the fixing belt and the pressure roller, and
A transfer roller side guide member and an image carrier side guide member that form a recording medium conveyance path between the fixing device and the image transfer unit;
In an image forming apparatus comprising:
A plurality of distances from the guide surface of the recording medium passing through the transfer nip portion and the fixing nip portion are arranged in a direction perpendicular to the conveyance direction of the recording medium at positions recessed from the guide surface of the transfer roller side guide member. Non-contact detecting means, control means for adjusting the conveyance speed of the recording medium passing through the fixing nip portion based on the detection result of the detecting means, and the recording medium on the guide surface of the transfer roller side guide member A transport fan that blows air in the direction of approaching ,
When the distance from the guide surface of the recording medium detected by any of the detecting means is greater than a predetermined value, the control means slows down the recording medium conveyance speed by a predetermined amount, and the recording medium conveyance direction. An image forming apparatus , wherein the rotation of the conveying fan is controlled so that the amount of slack in a direction orthogonal to the direction is equalized .   The image forming apparatus according to claim 1, wherein the image carrier-side guide member is a shuriken-shaped transport roller protruding into the recording medium transport path.   The image forming apparatus according to claim 1, wherein the control unit adjusts the conveyance speed at least twice while the recording medium passes through the fixing nip portion. The image forming apparatus according to claim 1 , wherein a plurality of the transport fans are arranged in a direction orthogonal to a transport direction of the recording medium . 5. The image forming apparatus according to claim 4 , further comprising a blower unit in which a plurality of the transport fans are arranged in a direction orthogonal to a transport direction of the recording medium, wherein the plurality of blower units are arranged in the transport direction. apparatus. Said sensing means, the image forming apparatus according to any one of claims 1 to 5, characterized in that an infrared reflective distance sensor.

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