JP2018043876A - Image formation apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image formation apparatus which can suppress slack of a paper sheet.SOLUTION: An image formation apparatus 1A includes: an image formation unit 11 which forms an image on a paper sheet; a fixation unit 30 which has a fixation roller 31 for fixing the image on the paper sheet; a discharge roller 27 which discharges the paper sheet fixed with the image; and a detection sensor 102 which detects slack of the paper sheet. When a prescribed amount of slack of the paper sheet is detected by the detection sensor 102, slack of the paper sheet between the fixation roller 31 and the discharge roller 27 is resolved by increasing the relative speed of the discharge roller 27 with respect to the fixation roller 31.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an image forming apparatus that forms an image by transferring and fixing a toner image onto a sheet.

  Conventionally, an image forming apparatus that forms an image on a sheet using toner is known. Such an image forming apparatus includes a transfer unit that forms an image on a sheet, and a fixing unit that fixes the image formed on the sheet by the transfer unit.

  The fixing unit is a pair of rollers and belts that sandwich and convey the sheet in order to fix the image on the sheet by conveying the sheet on which the toner image is formed while being pressurized and heated. Etc. are provided.

  The fixing unit includes a separation claw that separates the sheet that has passed through the nip composed of a pair of rollers, a belt, and the like from the roller, and presses the sheet in the direction of the separation claw with pressure of air or the like. A configuration for separating the sheet from a roller or the like is provided (for example, see Patent Document 1).

Japanese Patent Laying-Open No. 2015-72368

  In the image forming apparatus, in order to convey the sheet on which the image is formed by the fixing unit, a conveying member including a pair of rollers or the like is provided on the downstream side of the fixing unit. A roller or the like is driven at a constant speed between the conveying member constituting the fixing unit and the conveying member on the downstream side of the fixing unit. However, when the roller or the like is worn, there is a difference in the sheet conveyance speed, and the sheet may be loosened between the fixing unit and the conveyance member on the downstream side.

  When the sheet is loosened on the downstream side of the fixing unit, the pressing force of the sheet on the separation claw becomes excessive, which causes image noise such as a trace of the separation claw being rubbed on the sheet.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus capable of suppressing looseness of a sheet.

  In order to solve the above-described problem, the invention according to claim 1 is directed to an image forming unit that forms an image on a sheet, a first conveying member that conveys the sheet, and a sheet conveying direction. A second conveying member that is located downstream of the first conveying member and conveys the sheet conveyed by the first conveying member, and is provided between the first conveying member and the second conveying member. Separating means for separating the sheet from the first conveying member, detecting means for detecting the sheet between the first conveying member and the second conveying member, and the sheet detected by the detecting means The image forming apparatus includes a control unit that increases the relative speed of the second transport member with respect to the first transport member based on the slackness of the paper.

  In the invention according to claim 2, the detection means detects looseness of the sheet toward the side where the separation means is provided with respect to the sheet conveyance path by the first conveyance member and the second conveyance member. The image forming apparatus according to Item 1.

  According to a third aspect of the present invention, the detecting means detects the looseness of the sheet to the side opposite to the side where the separating means is provided with respect to the sheet conveying path by the first conveying member and the second conveying member. The image forming apparatus according to claim 1, wherein the image forming apparatus is detected.

  In the invention according to claim 4, the control unit increases the sheet conveyance speed by the second conveyance member with respect to the sheet conveyance speed by the first conveyance member. The image forming apparatus according to claim 1, wherein the relative speed of the second transport member is increased.

  In the invention according to claim 5, the control unit reduces the sheet conveyance speed by the first conveyance member with respect to the sheet conveyance speed by the second conveyance member, so that the first conveyance member The image forming apparatus according to claim 1, wherein the relative speed of the second transport member is increased.

  According to a sixth aspect of the present invention, the control means increases the relative speed of the second conveying member with respect to the first conveying member by stopping the conveyance of the sheet by the first conveying member. 4. The image forming apparatus according to any one of items 3.

  In the invention according to claim 7, the control means increases the relative speed of the second transport member with respect to the first transport member, and then passes through the first transport member after the elapse of a recovery time for eliminating the looseness of the sheet. 7. The image forming apparatus according to claim 1, wherein the relative speed of the second conveying member with respect to is returned.

  In the invention according to claim 8, the control means acquires information for specifying the rigidity of the sheet, and varies the relative speed of the second conveying member with respect to the first conveying member in accordance with the rigidity of the sheet. The image forming apparatus according to any one of claims 1 to 7.

  The invention according to claim 9 includes a third transport member positioned on the upstream side of the first transport member with respect to the transport direction of the sheet, and between the first transport member and the second transport member. The detection means for detecting the sheet constitutes the first detection means, and includes a second detection means for detecting the sheet between the first conveyance member and the third conveyance member, and the control means Based on the looseness of the sheet detected by the first detection means and the second detection means, the relative speed of the first conveyance member with respect to the third conveyance member is made variable, and the relative to the first conveyance member The image forming apparatus according to claim 1, wherein the relative speed of the second conveying member is variable.

  According to the present invention, when slack occurs in the sheet between the first conveying member located upstream in the sheet conveying direction and the second conveying member located downstream, the first By increasing the relative speed of the second conveying member with respect to the conveying member, the looseness of the sheet can be eliminated. Thereby, it is possible to suppress an excessive pressing force with respect to the sheet separating means, and it is possible to suppress the occurrence of image noise.

1 is a configuration diagram illustrating an example of an image forming apparatus according to an exemplary embodiment. 1 is a main part configuration diagram illustrating an example of an image forming apparatus according to an exemplary embodiment; 3 is a functional block diagram illustrating an example of a control function of the image forming apparatus according to the present exemplary embodiment. FIG. 4 is a flowchart illustrating an example of an operation of the image forming apparatus according to the present exemplary embodiment. FIG. 6 is an operation explanatory diagram illustrating an example of an operation of the image forming apparatus according to the present exemplary embodiment. It is a principal part block diagram which shows the modification of the image forming apparatus of this Embodiment. 10 is a flowchart showing a modification of the operation of the image forming apparatus of the present embodiment. FIG. 10 is an operation explanatory diagram illustrating another modified example of the operation of the image forming apparatus according to the present embodiment. FIG. 10 is an operation explanatory diagram illustrating another modified example of the operation of the image forming apparatus according to the present embodiment.

  Hereinafter, an embodiment of an image forming apparatus of the present invention will be described with reference to the drawings.

<Example of Configuration of Image Forming Apparatus of Embodiment>
FIG. 1 is a configuration diagram illustrating an example of an image forming apparatus according to the present embodiment. FIGS. 2A and 2B are main configuration diagrams illustrating an example of the image forming apparatus according to the present embodiment. . The image forming apparatus 1A according to the present embodiment is an electrophotographic image forming apparatus. In this example, a plurality of photoconductors are arranged in a vertical direction so as to face a single intermediate transfer belt. This is a so-called tandem color image forming apparatus that forms an image.

  Hereinafter, the details of the image forming apparatus 1A will be described. The image forming apparatus 1A includes an image forming unit 11 that forms an image on a sheet of paper P1, long paper P2, or the like cut into a predetermined length, or roll paper. In addition, the image forming apparatus 1A includes a conveyance unit 21 that conveys a sheet or the like. In the following description, a sheet P will be described as an example of an image formation target.

  First, a configuration for forming an image on the sheet P will be described. The image forming unit 11 is an example of an image forming unit, and forms an image on the sheet P by a process of charging, exposure, development, transfer, and fixing. The image forming unit 11 forms a toner image forming unit 11Y that forms a yellow (Y) toner image, a toner image forming unit 11M that forms a magenta (M) toner image, and a cyan (C) toner image. A toner image forming unit 11 </ b> C and a toner image forming unit 11 </ b> BK for forming a black (BK) toner image are provided.

  The toner image forming unit 11Y includes a photosensitive drum Y and a charging unit 12Y, an optical writing unit 13Y, a developing device 14Y, and a drum cleaner 15Y arranged around the photosensitive drum Y. Similarly, the toner image forming units 11M, 11C, and 11BK are the photosensitive drums M, C, and BK and the charging units 12M, 12C, and 12BK, the optical writing units 13M, 13C, and 13BK, and the developing device 14M that are disposed around the photosensitive drums M, C, and BK. , 14C, 14BK and drum cleaners 15M, 15C, 15BK.

  The developing devices 14Y, 14M, 14C, and 14BK are examples of developing units, and the developing device 14Y supplies toner to the photosensitive drum Y that is a photosensitive member. The developing device 14M supplies toner to the photosensitive drum M that is a photosensitive member, the developing device 14C supplies toner to the photosensitive drum C that is a photosensitive member, and the developing device 14BK is a photosensitive member that is a photosensitive member. Toner is supplied to the body drum BK.

  The photosensitive drum Y is an example of a first image carrier, and the surface is uniformly charged by the charging unit 12Y, and a latent image is formed on the photosensitive drum Y by scanning exposure by the optical writing unit 13Y. The photosensitive drum Y is supplied with toner from the developing device 14Y, and the latent image is developed to be visualized. As a result, a toner image corresponding to yellow is formed on the photosensitive drum Y as a predetermined color image.

  The photosensitive drum M is an example of a first image carrier, and the surface is uniformly charged by the charging unit 12M, and a latent image is formed on the photosensitive drum M by scanning exposure by the optical writing unit 13M. The photosensitive drum M is supplied with toner from the developing device 14M, and the latent image is developed to be visualized. As a result, a toner image corresponding to magenta is formed on the photosensitive drum M as an image of a predetermined color.

  The photosensitive drum C is an example of a first image carrier, and the surface is uniformly charged by the charging unit 12C, and a latent image is formed on the photosensitive drum C by scanning exposure by the optical writing unit 13C. The photosensitive drum C is supplied with toner from the developing device 14C, and the latent image is developed to be visualized. As a result, a toner image corresponding to cyan is formed on the photosensitive drum C as an image of a predetermined color.

  The photosensitive drum BK is an example of a first image carrier, and the surface is uniformly charged by the charging unit 12BK, and a latent image is formed on the photosensitive drum BK by scanning exposure by the optical writing unit 13BK. The photosensitive drum BK is supplied with toner from the developing device 14BK, and the latent image is developed to be visualized. As a result, a toner image corresponding to black is formed as an image of a predetermined color on the photosensitive drum BK.

  The image forming unit 11 includes a transfer unit 16 that transfers an image to the sheet P. The transfer unit 16 is an example of a transfer unit, and an intermediate transfer belt 17 on which images formed on the photosensitive drums Y, M, C, and BK are primarily transferred, and an image that is primarily transferred to the intermediate transfer belt 17 are transferred. A secondary transfer roller 18 for secondary transfer to the sheet P is provided.

  The intermediate transfer belt 17 is an example of a second image carrier, and is provided on the side facing one surface of the sheet P conveyed through the conveyance unit 21. The images formed on the photoconductive drums Y, M, C, and BK are printed on the intermediate transfer belt 17 by the primary transfer rollers 17Y, 17M, 17C, and 17BK when the intermediate transfer belt 17 is driven in the arrow direction. Sequentially transferred to position.

  The secondary transfer roller 18 is an example of a secondary transfer unit, and is provided to face the intermediate transfer belt 17 on the side facing the other surface of the sheet P conveyed through the conveyance unit 21. The transfer unit 16 is provided so that the secondary transfer roller 18 can move in a direction to be separated from and in contact with the intermediate transfer belt 17, and the transfer nip portion 19 is formed by pressing the secondary transfer roller 18 against the intermediate transfer belt 17. Is done.

  The secondary transfer roller 18 applies a positive voltage from the other side of the sheet P. As a result, the sheet P passing between the secondary transfer roller 18 and the intermediate transfer belt 17 is charged with one surface serving as an image forming surface onto which an image is transferred as a negative electrode and the other surface as a positive electrode.

  In the transfer nip portion 19, the secondary transfer roller 18 is rotationally driven at a constant speed with the intermediate transfer belt 17 in synchronization with the conveyance of the sheet P by the conveyance portion 21. As a result, the sheet P conveyed by the conveying unit 21 enters between the secondary transfer roller 18 and the intermediate transfer belt 17. The intermediate transfer belt 17 is pressed by the secondary transfer roller 18. Therefore, each color image primarily transferred to the intermediate transfer belt 17 is secondarily transferred to the sheet P conveyed between the intermediate transfer belt 17 and the secondary transfer roller 18, and the image is transferred to the sheet P. Is formed.

  The image forming apparatus 1 </ b> A includes a fixing unit 30 that fixes an image on a sheet P. The fixing unit 30 is an example of a fixing unit, and performs a fixing process for fixing the image on the sheet P on which the image is formed. The fixing unit 30 includes a pair of fixing rollers 31 that convey and heat the sheet P. In this example, the heat of the heater 32 a is transmitted by the fixing belt 32 to one fixing roller 31 provided on the side facing the one surface of the sheet P on which the image is formed by the transfer unit 16.

  The fixing unit 30 includes a separation claw 34 that suppresses winding of the sheet P around the fixing roller 31. In this example, the separation claw 34 is provided below the sheet P conveyance path corresponding to the other fixing roller 31 provided on the side facing the other surface of the sheet P.

  In the fixing unit 30, a fixing nip portion 33 is formed by pressing a pair of fixing rollers 31. The fixing roller 31 is rotated and the heater 32a is energized, whereby the sheet P sandwiched by the fixing nip 33 is conveyed and the image is fixed to the sheet P by pressure and heat. The

  Next, a configuration for conveying the sheet P will be described. The image forming apparatus 1A includes an external paper feed port 22 through which a long sheet P2 which is an example of a sheet P is fed, and a paper feed cassette 23 in which a sheet P1 which is another example of the sheet P is stored. Is provided. The external paper feed port 22 is provided on one side of the apparatus main body 10. The paper feed cassette 23 is provided in the lower part of the apparatus main body 10 so as to be able to be pulled out.

  In the image forming apparatus 1A, for the long paper P2 whose length in the transport direction exceeds the first length that can be stored in the paper feed cassette 23 in this example, the image forming apparatus 1A is connected to the main body 10 from the external paper feed port 22. Paper is fed from the outside. Further, the image forming apparatus 1 </ b> A determines that the paper P <b> 1 whose length along the transport direction is at most the first length that can be stored in the paper feed cassette 23 is from the paper feed cassette 23 inside the apparatus main body 10. Paper is fed.

  The transport unit 21 is an example of a transport unit, and includes a main transport path 24 through which the sheet P on which an image is formed by the image forming unit 11 is transported, and a reverse transport path 20 that reverses the front and back of the sheet P.

  Further, the transport unit 21 feeds a sheet P such as a long sheet P2 fed from the external paper feed port 22 to the main transport path 24, and feeds paper from the paper feed cassette 23. A paper feed transport path 26 is provided for transporting the paper P1 to the main transport path 24.

  One end of the main transport path 24 is connected to the external paper feed transport path 25 and the paper feed transport path 26. Further, the other end of the main transport path 24 is connected to a discharge port 27 a provided on the other side of the apparatus main body 10. The main transport path 24 includes a pair of discharge rollers 27 that transport the sheet P on which the image is fixed by the fixing unit 30 to the discharge port 27a.

  One end of the external paper feed transport path 25 is connected to the external paper feed port 22, and the other end is connected to the main transport path 24. An upper end portion of the paper feed conveyance path 26 is connected to the main conveyance path 24, and a lower end portion is connected to the paper feed cassette 23.

  The transport unit 21 has an image which is the inclination of the sheet P called skew and the width direction of the sheet P perpendicular to the transport direction with respect to the sheet P transported in the forward direction on the main transport path 24. Are provided with a registration roller 28 that corrects a positional deviation in the main scanning direction. The transport unit 21 includes a loop roller 29 that abuts the sheet P against the registration roller 28.

  The registration roller 28 is an example of a swinging member that constitutes a correction unit, and includes a pair of rollers facing each other with the sheet P conveyed through the main conveyance path 24 therebetween. The registration roller 28 includes an axis extending along the main scanning direction of the image formed on the sheet P, and conveys the sheet P in a direction orthogonal to the axis.

  The registration roller 28 is configured to be movable in a direction in which the pair of rollers are separated from each other by a driving mechanism (not shown), and the nip portion 28a is formed by the pair of rollers being pressed against each other. With the registration roller 28 stopped rotating, the sheet P is abutted against the nip portion 28a, whereby the inclination of the sheet P is corrected. Further, the registration roller 28 conveys the sheet P by sandwiching the sheet P when the sheet P enters between the pair of pressure-contacted rollers and rotating.

  Further, the registration roller 28 corrects the position of the sheet P in the main scanning direction by sandwiching the sheet P and moving in the axial direction. Further, the registration roller 28 corrects the position of the sheet P in the main scanning direction, and then the pair of rollers move apart in the axial direction so that the initial position is independent of the conveyance of the sheet P. Return to.

  The loop roller 29 constitutes a correction unit, and is composed of a pair of rollers opposed to each other with the sheet P conveyed through the main conveyance path 24 interposed therebetween, upstream of the registration roller 28 with respect to the sheet P conveyance direction. Provided. The loop roller 29 includes an axis extending along the main scanning direction of the image formed on the sheet P, and conveys the sheet P in a direction orthogonal to the axis.

  With the registration roller 28 stopped, the sheet P is transported by the loop roller 29, and the leading end of the sheet P is abutted against the nip portion 28a formed by the contact portion of the pair of rollers. The sheet P is conveyed until it is in a curved state, so that the inclination in the direction along the surface of the sheet P is corrected.

  After the inclination of the sheet P is corrected, the registration roller 28 is rotationally driven along the sheet P conveyance direction so that the sheet P is nipped and conveyed. Further, the position of the sheet P in the main scanning direction is corrected by moving the registration roller 28 in the axial direction. As described above, a series of sheet position correction operations for correcting the inclination of the sheet P and the deviation of the position in the main scanning direction is referred to as registration swing.

  The reverse conveyance path 20 includes a first reflux conveyance path 20 a that branches from the main conveyance path 24 on the downstream side of the fixing unit 30, and a second reflux conveyance path 20 b that merges with the main conveyance path 24 on the upstream side of the transfer unit 16. Is provided.

  In the image forming apparatus 1 </ b> A, the sheet P that has been conveyed in the forward direction along the main conveyance path 24 and passed through the fixing unit 30 forms an image on the surface facing upward. When images are formed on both sides of the sheet P, the sheet P on which an image is formed on one side facing upward is conveyed from the main conveyance path 24 to the reverse conveyance path 20 through the first reflux conveyance path 20a. Is done. Then, the sheet P is reversed in the conveyance direction and conveyed from the reverse conveyance path 20 to the main conveyance path 24 through the second reflux conveyance path 20b, so that the image forming surface faces downward. As a result, the sheet P is turned upside down, and an image can be formed on the other side facing upward.

  The transport unit 21 includes a switching gate 24a that switches the transport direction at a location where the main transport path 24 and the first reflux transport path 20a branch, and the transport path is switched based on settings such as the presence / absence of duplex printing.

  The image forming apparatus 1 </ b> A includes a document reading unit 40. The document reading unit 40 scans and exposes an image of a document with the optical system of the scanning exposure apparatus, reads the reflected light with a line image sensor, and obtains an image signal. Note that the image forming apparatus 1A may have a configuration in which an automatic document feeder (not shown) that feeds a document is provided at the top.

<Example of Control Function of Image Forming Apparatus of Present Embodiment>
FIG. 3 is a functional block diagram illustrating an example of a control function of the image forming apparatus according to the present embodiment. The image forming apparatus 1A includes a control unit 100 that performs a series of controls for feeding a sheet P, forming an image, and discharging the sheet. The control unit 100 is an example of control means, and includes a microprocessor called CPU and MPU, and memory such as RAM and ROM as storage means.

  In addition, the image forming apparatus 1A includes an operation unit 101 that performs various operations such as setting the type of sheet P for forming an image, setting the basis weight, and setting the number of image formations. Furthermore, the image forming apparatus 1 </ b> A includes a detection sensor 102 that detects whether or not the sheet P is slack and the amount of slack.

  The detection sensor 102 is an example of detection means, and is provided below the conveyance path of the sheet P between the fixing roller 31 and the discharge roller 27 as shown in FIGS. 2 (a) and 2 (b). It is done. In the fixing unit 30, a separation claw 34 is provided below the sheet P conveyance path. The detection sensor 102 detects whether or not there is a slack Pr in the downward direction between the fixing roller 31 and the discharge roller 27 and the amount of the slack Pr. Thereby, the presence or absence of the slack Pr of the sheet P toward the side where the separation claw 34 is provided and the amount of the slack Pr can be detected. The detection sensor 102 may also be used as a sensor that detects that a sheet has been discharged.

  In this example, the pair of fixing rollers 31 provided on the upstream side with respect to the conveyance direction of the sheet P constitutes the first conveyance member, and the pair of discharge rollers 27 provided on the downstream side includes the first Two conveying members are configured. The interval between the fixing roller 31 and the discharge roller 27 is set to be shorter than the minimum length of the sheets P to be processed, and the leading end of the sheet P is held between the discharge rollers 27. At the same timing, the rear end of the sheet P is configured not to pass through the fixing roller 31.

  In this example, as shown in FIGS. 2A and 2B, the detection sensor 102 includes a movable element 102a that is displaced by contact with the sheet P, and a sensor 102b that detects the movable element 102a. . The detection sensor 102 is configured such that when the amount of the slack Pr of the sheet P increases to a predetermined value or more, the movable element 102a is displaced and retracted from the detection position by the sensor 102b.

  As shown in FIG. 2B, when the amount of the slack Pr of the sheet P increases to a predetermined value or more, the detection sensor 102 changes the output of the sensor 102b from ON to OFF, for example. Thereby, it is possible to detect that the amount of slack Pr of the sheet P has increased more than a predetermined amount. The detection sensor 102 may be configured to detect the amount of the slack Pr of the sheet P. Further, the detection sensor 102 may be a non-contact sensor using an optical sensor other than the contact sensor.

  As shown in FIG. 2B, when a predetermined amount of slack Pr occurs in the sheet P between the fixing roller 31 and the discharge roller 27, the sheet P is conveyed by the fixing roller 31 at a conveyance speed V 1. Thus, by increasing the conveyance speed V2 of the sheet P by the discharge roller 27 continuously or intermittently, the slack Pr of the sheet P is eliminated. Further, the sheet Pr can be slackened Pr by continuously or intermittently lowering the sheet transport P V1 by the fixing roller 31 with respect to the sheet transport P V2 by the discharge roller 27. Disappears. Furthermore, the slack Pr of the sheet P can also be eliminated by stopping the conveyance by the fixing roller 31 continuously or intermittently.

  Therefore, the control unit 100 controls the motor M1 that drives the fixing roller 31 and the motor M2 that drives the discharge roller 27 according to the amount of slack Pr of the sheet P detected by the detection sensor 102, The relative speed V2-V1 of the discharge roller 27 with respect to the fixing roller 31 is increased.

<Example of Operation of Image Forming Apparatus of Present Embodiment>
FIG. 4 is a flowchart showing an example of the operation of the image forming apparatus according to the present embodiment. FIGS. 5A and 5B are operation explanatory views showing an example of the operation of the image forming apparatus according to the present embodiment. Hereinafter, the operation of the image forming apparatus according to the present embodiment will be described with reference to the drawings.

  When the operation of forming an image is started in step SA1 in FIG. 4, the control unit 100 determines that the conveyance speed V1 of the sheet P by the fixing roller 31 and the conveyance speed V2 of the sheet P by the discharge roller 27 are constant. Then, the motor M1 that drives the fixing roller 31 and the motor M2 that drives the discharge roller 27 are controlled. If the conveyance speed V1 of the sheet P by the fixing roller 31 and the conveyance speed V2 of the sheet P by the discharge roller 27 are constant, the feed amount per unit time by the fixing roller 31 and the discharge roller 27 is equal. .

  However, the sheet P caused by the fixing roller 31 is caused by a variation in diameter due to wear of the fixing roller 31 and the discharge roller 27, a shift in driving timing of the motor M1 that drives the fixing roller 31 and the motor M2 that drives the discharge roller 27, and the like. And the amount of sheet P fed by the discharge roller 27 may fluctuate. When the feed amount of the sheet P by the fixing roller 31 is larger than the feed amount of the sheet P by the discharge roller 27, as shown in FIG. 5A, between the fixing roller 31 and the discharge roller 27, Loose Pr occurs on the sheet P.

  When the amount of slack Pr of the sheet P increases more than a predetermined value, the detection sensor 102 changes the output of the sensor 102b from ON to OFF in this example. In step SA2 of FIG. 4, the control unit 100 determines from the output of the detection sensor 102 whether the amount of slack Pr of the sheet P has increased more than a predetermined amount.

  When the control unit 100 determines that the amount of the slack Pr of the sheet P has increased more than a predetermined amount, in step SA3 in FIG. 4, the control unit 100 turns on the motor M1 that drives the fixing roller 31 and the motor M2 that drives the discharge roller 27. By controlling, the relative speed (V2-V1) of the discharge roller 27 with respect to the fixing roller 31 is increased.

  Thereby, the feed amount of the sheet P by the discharge roller 27 is increased more than the feed amount of the sheet P by the fixing roller 31, and as shown in FIG. The slack Pr of the sheet P in the meantime is eliminated. Thus, before the pressing force of the sheet P against the separation claw 34 becomes excessive, the occurrence of a predetermined amount of slack Pr can be detected and the slack Pr can be eliminated, and the separation claw 34 of the sheet P can be eliminated. The generation of image noise due to contact with can be suppressed.

  If the controller 100 determines in step SA2 in FIG. 4 that the slack Pr of the sheet P does not exceed the predetermined amount, the control unit 100 determines in step SA4 in FIG. Then, the control that the conveyance speed V2 of the sheet P by the discharge roller 27 becomes constant is maintained.

  When the control unit 100 forms an image on the set number of sheets P, the operation of forming the image ends in step SA5 in FIG.

<Modification of Image Forming Apparatus According to Embodiment>
FIGS. 6A and 6B are main part configuration diagrams showing a modification of the image forming apparatus according to the present embodiment. In FIG. 6, the detection sensor 102 is provided on the upper side of the sheet P conveyance path. The detection sensor 102 detects the presence or absence of the slack Pr in the upward direction and the amount of slack Pr between the fixing roller 31 and the discharge roller 27. Thereby, the presence or absence of the slack Pr of the sheet P to the side opposite to the side where the separation claw 34 is provided and the amount of the slack Pr can be detected. The detection sensors 102 may be provided on both the lower side and the upper side of the sheet P conveyance path.

  FIG. 7 is a flowchart showing a modified example of the operation of the image forming apparatus according to the present embodiment. When the operation of forming an image is started in step SB1 in FIG. 7, the control unit 100 determines that the conveyance speed V1 of the sheet P by the fixing roller 31 and the conveyance speed V2 of the sheet P by the discharge roller 27 are constant. Then, the motor M1 that drives the fixing roller 31 and the motor M2 that drives the discharge roller 27 are controlled. In step SB2 of FIG. 7, the control unit 100 determines from the output of the detection sensor 102 whether the amount of loose Pr of the sheet P has increased more than a predetermined amount.

  When the control unit 100 determines that the amount of the slack Pr of the sheet P has increased more than a predetermined value, the motor M1 that drives the fixing roller 31 and the motor M2 that drives the discharge roller 27 are turned on in step SB3 in FIG. By controlling, the relative speed (V2-V1) of the discharge roller 27 with respect to the fixing roller 31 is increased.

  Thereby, the feeding amount of the sheet P by the discharge roller 27 is larger than the feeding amount of the sheet P by the fixing roller 31, and the slack Pr of the sheet P between the fixing roller 31 and the discharging roller 27 is generated. Eliminate.

  The control unit 100 increases the relative speed (V2−V1) of the discharge roller 27 with respect to the fixing roller 31 until the recovery time T seconds set to be necessary for eliminating the slack Pr has elapsed in Step SB4 of FIG.

  In step SB4 of FIG. 7, when the recovery time T seconds set to be necessary for eliminating the slack Pr elapses, the control unit 100, in step SB5, the conveyance speed V1 of the sheet P by the fixing roller 31 and the discharge roller. 27, the conveyance speed V2 of the sheet P is returned to the constant speed. After the looseness Pr of the sheet P is eliminated, if there is a difference in the conveyance speed between the fixing roller 31 and the discharge roller 27, a load is applied to the sheet P. Therefore, after the looseness Pr of the sheet P is eliminated, the load applied to the sheet P can be reduced by returning the conveyance speed by the fixing roller 31 and the discharge roller 27 to a constant speed.

  The control unit 100 returns the conveyance speed V1 of the sheet P by the fixing roller 31 and the conveyance speed V2 of the sheet P by the discharge roller 27 to a constant speed, and then in step SB6 in FIG. From the output, it is determined whether the amount of slack Pr of the sheet P has increased beyond a predetermined level.

  When the control unit 100 determines that the amount of the slack Pr of the sheet P has increased more than a predetermined value, the control unit 100 returns to step SB3 in FIG. 7 and increases the relative speed (V2-V1) of the discharge roller 27 with respect to the fixing roller 31.

  If the control unit 100 determines in step SB2 in FIG. 7 that the slack Pr of the sheet P does not exceed a predetermined amount, the control unit 100 determines in step SB7 in FIG. 7 the conveyance speed V1 of the sheet P by the fixing roller 31. Then, the control that the conveyance speed V2 of the sheet P by the discharge roller 27 becomes constant is maintained.

  When the control unit 100 forms an image on the set number of sheets P, the operation of forming the image ends in step SB8 in FIG.

  FIG. 8A and FIG. 8B are operation explanatory views showing another modified example of the operation of the image forming apparatus of the present embodiment. In the sheet P having low rigidity, the amount of slack Pr tends to increase as shown in FIG. On the other hand, in the sheet P having high rigidity, the amount of slack Pr is small as shown in FIG.

  Therefore, the control unit 100 acquires information for specifying the rigidity of the sheet P from the type, basis weight, and the like of the sheet P set by the operation unit 101 and the like, and according to the rigidity of the sheet P, The increase / decrease amount of the relative speed V2-V1 of the discharge roller 27 with respect to the fixing roller 31 is switched.

  When the control unit 100 determines that the rigidity of the sheet P is below a predetermined threshold, the controller 100 increases the increase amount of the relative speed V2-V1 of the discharge roller 27 with respect to the fixing roller 31 and eliminates the slack Pr in a short time. On the other hand, if it is determined that the rigidity of the sheet P is equal to or greater than a predetermined threshold, the increase amount of the relative speed V2-V1 of the discharge roller 27 with respect to the fixing roller 31 is determined, and the rigidity of the sheet P is equal to the predetermined threshold. The slack Pr is gradually eliminated by lowering compared to the case of lowering.

  FIG. 9A, FIG. 9B, FIG. 9C, and FIG. 9D are operation explanatory views showing another modified example of the operation of the image forming apparatus of the present embodiment.

  In this example, the pair of fixing rollers 31 provided on the upstream side with respect to the conveyance direction of the sheet P constitutes the first conveyance member, and the pair of discharge rollers 27 provided on the downstream side includes the first Two conveying members are configured. Further, the secondary transfer roller 18 provided on the upstream side of the fixing roller 31 constitutes a third conveying member.

  As described above, the interval between the fixing roller 31 and the discharge roller 27 is set shorter than the minimum length of the sheets P to be processed, and the leading edge of the sheet P is discharged. It is configured so that the trailing edge of the sheet P does not pass through the fixing roller 31 at the timing of being pinched by the roller 27. The interval between the fixing roller 31 and the secondary transfer roller 18 is set to be shorter than the minimum length of the sheets P to be processed, and the leading edge of the sheet P is the fixing roller. The rear end of the sheet P is configured not to pass through the secondary transfer roller 18 at the timing of being pinched by 31.

Further, the single as a detection means for detecting the slack of the leaf paper P, includes a first detection sensor 102 ₁ between the fixing roller 31 and the discharge roller 27, the second between the fixing roller 31 and the secondary transfer roller 18 comprising a detection sensor 102 _2. First detecting sensor 102 ₁ and the second detection sensor 102 _2, FIG. 2 (a), the may be the same configuration as the sensor 102 described in FIG. 2 (b).

  In the image forming apparatus 1 </ b> A, when the sheet P conveyed by the secondary transfer roller 18 is pulled by the fixing roller 31, the transferred image is shifted. Therefore, in order to prevent the sheet P conveyed by the secondary transfer roller 18 from being pulled by the fixing roller 31, a slack Pr is generated in the sheet P between the fixing roller 31 and the secondary transfer roller 18. To control. However, when the amount of slack Pr between the fixing roller 31 and the secondary transfer roller 18 exceeds a predetermined value, control is performed to reduce the amount of slack Pr.

In FIG. 9 (a), a predetermined or more slack Pr to the sheet P between the fixing roller 31 and the discharge roller 27 is generated, the first detection sensor 102 ₁ is OFF. The fixing roller 31 and the secondary transfer roller 18 in the sheet more than the predetermined amount of slack Pr occurs in P between the second detection sensor 102 ₂ is OFF.

  In this case, in order to reduce the amount of slack Pr between the fixing roller 31 and the secondary transfer roller 18, the fixing roller 31 with respect to the secondary transfer roller 18 is increased by increasing the conveyance speed V1 of the sheet P by the fixing roller 31. The relative speed (V1-V3) is increased.

  However, when the conveyance speed V1 of the sheet P by the fixing roller 31 is increased, the amount of slack Pr between the fixing roller 31 and the discharge roller 27 increases. Accordingly, the relative speed (V2− of the discharge roller 27 with respect to the fixing roller 31) is increased by increasing the transport speed V2 of the sheet P by the discharge roller 27 in accordance with the change in the transport speed V1 of the sheet P by the fixing roller 31. Increase V1).

  As a result, the amount of looseness Pr of the sheet P between the fixing roller 31 and the secondary transfer roller 18 can be reduced, and the looseness of the sheet P generated between the fixing roller 31 and the discharge roller 27 can be reduced. Pr can be eliminated.

In FIG. 9 (b), no slack Pr occurs in a sheet-fed P in between the fixing roller 31 and the discharge roller 27, the first sensor 102 ₁ is ON. The fixing roller 31 and the secondary transfer roller 18 in the sheet more than the predetermined amount of slack Pr occurs in P between the second detection sensor 102 ₂ is OFF.

  In this case, in order to reduce the amount of slack Pr between the fixing roller 31 and the secondary transfer roller 18, the fixing roller 31 with respect to the secondary transfer roller 18 is increased by increasing the conveyance speed V1 of the sheet P by the fixing roller 31. The relative speed (V1-V3) is increased.

  However, when the conveyance speed V1 of the sheet P by the fixing roller 31 is increased, a slack Pr between the fixing roller 31 and the discharge roller 27 is generated. Accordingly, the relative speed (V2− of the discharge roller 27 with respect to the fixing roller 31) is increased by increasing the transport speed V2 of the sheet P by the discharge roller 27 in accordance with the change in the transport speed V1 of the sheet P by the fixing roller 31. Increase V1).

  As a result, the amount of slack Pr of the sheet P between the fixing roller 31 and the secondary transfer roller 18 can be reduced, and the slack Pr of the sheet P between the fixing roller 31 and the discharge roller 27 can be reduced. The state which has not occurred can be maintained.

In FIG. 9 (c), a predetermined or more slack Pr to the sheet P between the fixing roller 31 and the discharge roller 27 is generated, the first detection sensor 102 ₁ is OFF. Further, between the fixing roller 31 and the secondary transfer roller 18 does not slack Pr occurs in a sheet-fed P, the second detection sensor 102 ₂ is ON.

  In this case, the slack Pr is generated between the fixing roller 31 and the secondary transfer roller 18 and the slack Pr between the fixing roller 31 and the discharge roller 27 is eliminated. By reducing the transport speed V1, the relative speed (V2-V1) of the discharge roller 27 with respect to the fixing roller 31 is increased.

  As a result, the slack Pr of the sheet P can be generated between the fixing roller 31 and the secondary transfer roller 18, and the slack Pr of the sheet P generated between the fixing roller 31 and the discharge roller 27. Can be eliminated.

In FIG. 9 (d), no slack Pr occurs in a sheet-fed P in between the fixing roller 31 and the discharge roller 27, the first sensor 102 ₁ is ON. Further, between the fixing roller 31 and the secondary transfer roller 18 does not slack Pr occurs in a sheet-fed P, the second detection sensor 102 ₂ is ON.

  In this case, in order to generate a slack Pr between the fixing roller 31 and the secondary transfer roller 18, the relative speed of the discharge roller 27 with respect to the fixing roller 31 is reduced by lowering the conveyance speed V1 of the sheet P by the fixing roller 31. Increase (V2-V1).

  However, when the conveyance speed V1 of the sheet P by the fixing roller 31 is decreased, the sheet P is pulled by the discharge roller 27. Therefore, the relative speed (V2− of the discharge roller 27 with respect to the fixing roller 31) is decreased by decreasing the transport speed V2 of the sheet P by the discharge roller 27 in accordance with the change in the transport speed V1 of the sheet P by the fixing roller 31. Lower V1).

  Thereby, the slack Pr of the sheet P can be generated between the fixing roller 31 and the secondary transfer roller 18, and the slack Pr of the sheet P can be generated between the fixing roller 31 and the discharge roller 27. You can maintain the state that is not.

  The present invention is applied to an image forming apparatus that forms an image by transferring and fixing a toner image on a sheet.

  DESCRIPTION OF SYMBOLS 1A ... Image forming apparatus, 10 ... Apparatus main body, 11 ... Image forming part, 17 ... Intermediate transfer belt, 18 ... Secondary transfer roller, 19 ... Transfer nip part, 21. ..Conveying section, 24... Main conveying path, 27... Discharge roller, 28. ..Control unit 102 ... Detection sensor

Claims (9)

Image forming means for forming an image on a sheet;
A first conveying member for conveying a sheet;
A second conveying member that is located downstream of the first conveying member with respect to the conveying direction of the sheet and conveys the sheet conveyed by the first conveying member;
Separating means provided between the first conveying member and the second conveying member, for separating the sheet from the first conveying member;
Detecting means for detecting a sheet between the first conveying member and the second conveying member;
An image forming apparatus comprising: a control unit configured to increase a relative speed of the second conveyance member with respect to the first conveyance member based on the looseness of the sheet detected by the detection unit. The detecting means detects looseness of the sheet toward the side where the separating means is provided with respect to the sheet conveying path by the first conveying member and the second conveying member. The image forming apparatus according to claim 1. The detecting means detects the looseness of the sheet to the side opposite to the side where the separating means is provided with respect to the sheet conveying path by the first conveying member and the second conveying member. The image forming apparatus according to claim 1, wherein: The control means increases the sheet conveyance speed by the second conveyance member with respect to the sheet conveyance speed by the first conveyance member, thereby the second conveyance unit with respect to the first conveyance member. The image forming apparatus according to claim 1, wherein the relative speed of the conveying member is increased. The control means lowers the sheet conveyance speed by the first conveyance member with respect to the sheet conveyance speed by the second conveyance member, so that the second conveyance relative to the first conveyance member is reduced. The image forming apparatus according to claim 1, wherein the relative speed of the conveying member is increased. The said control means raises the relative speed of the said 2nd conveyance member with respect to the said 1st conveyance member by stopping conveyance of the sheet | seat by the said 1st conveyance member. The image forming apparatus according to claim 3. The control means increases the relative speed of the second transport member with respect to the first transport member, and then passes the second transport relative to the first transport member after elapse of a recovery time when the looseness of the sheet is eliminated. The image forming apparatus according to claim 1, wherein the relative speed of the conveying member is returned. The control means acquires information specifying the rigidity of the sheet, and makes the relative speed of the second conveying member variable with respect to the first conveying member according to the rigidity of the sheet. The image forming apparatus according to any one of claims 1 to 7. A third transport member located upstream of the first transport member with respect to the transport direction of the sheet,
The detecting means for detecting a sheet between the first conveying member and the second conveying member constitutes a first detecting means, and the first conveying member and the third conveying member A second detecting means for detecting a sheet in between,
The control means makes the relative speed of the first transport member relative to the third transport member variable based on the looseness of the sheet detected by the first detection means and the second detection means. The image forming apparatus according to claim 1, wherein a relative speed of the second transport member with respect to the first transport member is variable.

Images