JP2008107444A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus to relatively reduce the variation of the rotational speed of an intermediate transfer belt even though load varies on the intermediate transfer belt, and color shift and positional deviation in transfer are prevented over a long term with simple constitution. <P>SOLUTION: The image forming apparatus 1 has: a photoreceptor drum 11 with an electrostatic latent image formed thereon a rotary type developing device 14 supplying developer to the photoreceptor drum 11; an intermediate transfer part 20 having the intermediate transfer belt 21 to which a toner image is primarily transferred, and a plurality of rollers on which the intermediate transfer belt 21 is stretched; and a secondary transfer part 50 transferring the toner image on the intermediate transfer belt 21. The intermediate transfer part 20 has a drive roller 22 driven to rotate, and is provided with a braking member 90 for applying load to the rotation of a tension roller 23 positioned first in the upstream direction of the drive roller 22 in the rotating direction of the intermediate transfer belt 21 and driven for rotation. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a printer, a copying machine, and a facsimile. In particular, the present invention relates to an image forming apparatus having an intermediate transfer unit.

  2. Description of the Related Art Conventionally, an image forming apparatus employs a method in which an electrostatic latent image formed on an image carrier is developed as a toner image by a developing device, and the toner image is transferred to a transfer material, for example, paper to form an image. There is something. When a toner image is transferred to a transfer material, the toner image is not transferred directly from the image carrier to the transfer material, but is temporarily transferred to an endless intermediate transfer belt and then transferred from the intermediate transfer belt to the transfer material. There is an image forming apparatus that performs the next transfer. The intermediate transfer belt is stretched and rotated by a plurality of rollers.

  Such an image forming apparatus using an intermediate transfer belt is often seen in a full-color image forming apparatus. Specifically, the image forming apparatus forms a toner image formed on the image carrier for each color (for example, black, yellow, cyan, magenta, etc.), and transfers the toner image of each color to the intermediate transfer belt. Overlay on the belt. The full-color toner image formed on the intermediate transfer belt is transferred to the transfer material at the secondary transfer portion. In this way, image formation is performed.

  Here, when transferring from the image carrier to the intermediate transfer belt or from the intermediate transfer belt to the transfer material, there may be a positional shift of the toner image transfer. When this positional deviation occurs, the quality of the formed image is affected.

  One of the causes for the positional deviation of the transfer of the toner image is a fluctuation in the rotation speed of the intermediate transfer belt. Specifically, for example, in an image forming apparatus using a rotary developing device, one image carrier is usually provided. When a color image is formed, a toner image is formed on the image carrier for each color, and sequentially overlaid on the intermediate transfer belt. That is, if four colors of toner are used, it is necessary to rotate the intermediate transfer belt four times until the color toner image is transferred to the intermediate transfer belt.

  By the way, until the primary transfer to the intermediate transfer belt is completed, the secondary transfer roller and the belt cleaning device are basically not in contact with the intermediate transfer belt so as not to disturb the primary transfer. Yes. The secondary transfer roller is in contact with the intermediate transfer belt for secondary transfer from the intermediate transfer belt to the transfer material. The belt cleaning device is in contact with the intermediate transfer belt in order to clean toner remaining on the belt without being subjected to secondary transfer.

  The secondary transfer roller is brought into contact with the intermediate transfer belt in order to perform secondary transfer of the toner image on the intermediate transfer belt onto the transfer material when or before the completion of the primary transfer on the intermediate transfer belt. . The belt cleaning device is also brought into contact with the intermediate transfer belt in order to collect the residual toner after the secondary transfer. In this way, a load is applied to the intermediate transfer belt.

  When the secondary transfer is completed, the secondary transfer roller and the belt cleaning device are separated from the intermediate transfer belt so as not to hinder the next image formation. That is, the load on the intermediate transfer belt is removed.

  Due to such fluctuations in the load applied to the intermediate transfer belt, fluctuations occur in the speed at which the belt rotates. The image forming apparatus performs primary transfer and secondary transfer at a predetermined timing. However, if the belt rotational speed fluctuates, the toner image transfer position shifts.

As a solution to the above problem, the invention described in Patent Document 1 has been proposed. In Patent Document 1, a plurality of developing devices, a photoreceptor, an intermediate transfer belt, a transfer unit that performs secondary transfer, a belt cleaner, a belt cleaner contact / separation mechanism, and a drive shaft of the intermediate transfer belt are pressed against each other. A color image forming apparatus including a pressure contact member that applies a friction load to the rotation of the drive shaft is shown. (See claims 1 and 2 and FIG. 4). With this configuration, a friction load is applied to the rotation of the drive shaft, and the influence of the load fluctuation caused by the transfer roller is reduced. (Paragraphs 0076, 77). In addition, it is also described that the pressure contact member is configured to be able to contact and separate from the drive shaft (see claim 4, FIG. 9, etc.).
JP 9-311522 A

  As described above, the fluctuation of the load applied to the intermediate transfer belt affects the rotation speed of the intermediate transfer belt, and there is a problem that misalignment may occur during primary transfer and secondary transfer.

  Here, looking at the invention described in Patent Document 1, the invention described in Patent Document 1 certainly gives a frictional load to the rotation of the drive shaft by the pressure contact member. Become smaller. However, since the pressure contact member is brought into contact with the drive shaft, there is a problem that wear of the pressure contact member is fast, the possibility of deformation increases, and the frequency of component replacement increases.

  Further, when the pressure contact member is brought into contact with the drive shaft, there is a problem that the influence on the rotation speed of the intermediate transfer belt is large. That is, it is necessary to arrange and adjust the pressure contact member with high accuracy and manage it. In addition, if wear or the like of the pressure contact member occurs, there is a problem that the influence of load reduction due to the wear or the like directly appears on the intermediate transfer belt. Furthermore, since the wear of the pressure contact member is likely to occur, the rotation speed of the intermediate transfer belt is likely to be different from the initial setting from the early stage of using the image forming apparatus, and the rotation speed of the intermediate transfer belt becomes unstable. There is a possibility. As a result, it can be said that the invention of Patent Document 1 is likely to cause positional deviation in transfer.

  Further, Patent Document 1 describes that the pressure contact member is pressed against the cylindrical surface of the drive shaft. Therefore, in that case, there is a problem that the contact member requires a certain space. If it does so, it will become difficult to form an image forming apparatus compactly. Further, in Patent Document 1, a member that supports the pressure contact member is required, and further, the case where the pressure contact member is configured to be able to contact and separate is also described in Patent Document 1, and the structure of the image forming apparatus and the pressure contact member are described. There is also a problem that the installation becomes complicated.

  The present invention has been made in view of the above-described problems of the prior art, and even if a constant load is applied to the intermediate transfer belt and a load fluctuation occurs with respect to the intermediate transfer belt, the fluctuation of the rotation speed of the intermediate transfer belt is relatively detected. It is an object of the present invention to provide an image forming apparatus that can be reduced in size and has a simple configuration and no color shift or positional shift during transfer over a long period of time.

  In order to solve the above-mentioned problems, an invention according to claim 1 includes an image carrier on which an electrostatic latent image is formed, one or more developing devices that supply a developer to the image carrier and develop a toner image, An endless intermediate transfer belt to which the developed toner image is primarily transferred, an intermediate transfer portion having a plurality of rollers that stretch the intermediate transfer belt, and a toner image on the intermediate transfer belt for transferring to a transfer material In the image forming apparatus having the secondary transfer portion, the intermediate transfer portion has a driving roller that is driven and rotated, and all or a part of the other rollers are driven by the intermediate transfer belt. A rotating member that rotates and is provided with a brake member for applying a load to the rotation of the driven roller on the driven roller that is first positioned in the upstream direction of the driving roller when viewed from the rotating direction of the intermediate transfer belt; did.

  According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the brake member is provided at a roller shaft end portion of the driven roller.

  According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the driven roller provided with the brake member is urged by a urging member in a direction away from the driving roller. It was.

  According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, the outer diameter of the driven roller provided with the brake member is larger than the outer diameter of the driving roller. It was decided to

  According to the first aspect of the present invention, since the brake member for applying a constant load to the driven roller for stretching the intermediate transfer belt is provided, the contact of the secondary transfer roller and the belt cleaning device to the load of the entire intermediate transfer belt is provided. The load fluctuation due to separation can be made relatively small, and the fluctuation in the rotation speed of the intermediate transfer belt caused by the load fluctuation can be prevented. Therefore, it is possible to provide a high-quality image forming apparatus that does not cause positional deviation and color deviation in the transfer of the formed image.

  In addition, since the brake member is provided on the driven roller other than the drive roller for rotating the intermediate transfer belt, the brake member is less likely to be worn and deformed than when the brake member is provided on the drive roller. Accordingly, maintenance of the image forming apparatus is facilitated. In addition, when the brake member is provided on the driving roller, the influence on the rotational speed of the intermediate transfer belt is great. In the present invention, the brake member is provided on the driven roller. Therefore, the influence of the load reduction due to wear of the brake member or the like is less likely to affect the rotational speed of the intermediate transfer belt than when the brake member is provided on the driving roller. Accordingly, it is possible to provide an image forming apparatus in which the intermediate transfer belt rotates at a stable speed over a long period of time.

  According to the invention described in claim 2, in addition to the effect of the invention described in claim 1, the brake member is provided only at the end of the roller shaft of the driven roller, so that the configuration is very simple, and the brake member There is less space to install. Therefore, it is possible to provide a compact image forming apparatus while suppressing manufacturing costs.

  According to the invention described in claim 3, in addition to the effect of the invention described in claim 1 or 2, the driven roller provided with the brake member is biased in a certain direction, so that the tension of the intermediate transfer belt is kept constant. Can keep. Furthermore, even when the brake member is worn, it is possible to adopt a structure in which the driven roller is urged and pressed against the brake member, and it is possible to easily achieve a constant load to the driven roller at all times.

  According to the invention described in claim 4, in addition to the effects of the invention described in claims 1 to 3, it is possible to prevent the intermediate transfer belt from becoming hazy, and to further prevent positional deviation and color deviation during transfer. it can. In general, for example, a roller that stretches an intermediate transfer belt made of resin is better as the outer diameter is larger. This is because, when the state where the image forming apparatus is not used continues, a roller having a larger curvature with respect to the intermediate transfer belt, that is, a roller having a smaller outer diameter, is more likely to have a habit on the intermediate transfer belt. When the image forming apparatus is used with the intermediate transfer belt in a hazy state, positional deviation and color deviation may occur in transferring the formed image. Further, when the outer diameter of the driven roller is increased, inertia (inertial force) in rotation of the roller is increased, and the necessity of the brake member is increased. However, in the present invention, the brake member is provided. Therefore, according to the present invention, it is possible to prevent the intermediate transfer belt from becoming hazy while sufficiently responding to load fluctuations on the intermediate transfer belt, and it is possible to provide an image forming apparatus that is further free of transfer positional deviation and color deviation.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS. However, each element such as configuration and arrangement described in this embodiment does not limit the scope of the invention and is merely an illustrative example.

  First, the outline of the image forming apparatus 1 in the embodiment of the present invention will be described with reference to FIG. FIG. 1 is a schematic cross-sectional view for explaining a schematic configuration of an image forming apparatus 1 according to an embodiment of the present invention.

  The image forming apparatus 1 according to the present embodiment includes an image forming unit 10, an intermediate transfer unit 20, a paper feeding unit 30, a paper transport unit 40, a secondary transfer unit 50, a fixing device 60, a toner supply unit 70, and the like. . The details will be described below.

  The image forming unit 10 cleans a photosensitive drum 11 as an image carrier, a charging roller 12 for uniformly charging the surface of the photosensitive drum 11, and toner and deposits remaining on the surface of the photosensitive drum 11. Drum cleaning device 13, rotary developing device 14 that develops the electrostatic latent image formed on the photosensitive drum 11 with toner of each color, image information sent from an external computer, etc. The drum unit 11 includes a laser unit 15 for scanning exposure.

  The photosensitive drum 11 has an electrostatic latent image formed on the surface thereof, and is rotatably provided in the approximate center of the image forming apparatus 1 (the direction of rotation is indicated by an arrow). The rotation shaft (not shown) is provided so as to extend perpendicular to the paper surface of FIG. The photosensitive drum 11 is formed to have a photosensitive layer such as amorphous silicon or an OPC photosensitive member.

  The charging roller 12 is provided on the top of the photosensitive drum 11. The charging roller 12 is in contact with the photosensitive drum 11 to uniformly charge the surface of the photosensitive drum 11 and is driven to rotate in a predetermined direction. A cleaner 12 a for cleaning the charged product adhering to the charging roller 12 is provided above the charging roller 12.

  The drum cleaning device 13 is provided on the right side of the photosensitive drum 11 in FIG. 1, and cleans toner and deposits remaining on the surface of the photosensitive drum 11.

  The rotary developing device 14 is provided adjacent to the photosensitive drum 11 on the left side in FIG. The rotary developing device 14 includes a rotating frame 14a and four developing devices 14B, 14Y, 14C, and 14M that are provided corresponding to the four color toners and supported by the rotating frame 14a. And rotated by a drive mechanism including a gear. The rotary developing device 14 has a cylindrical shape that is rotatable around an axis. The rotation axis of the rotary developing device 14 passes through the center of the rotation frame 14 a, and the axial direction thereof is parallel to the axial direction of the rotation axis of the photosensitive drum 11.

  As shown in FIG. 1, the rotating frame 14 a has four sections that are equally divided into four in the circumferential direction by a partition frame 14 d that extends radially from the center of the rotating shaft. In each section, developing units 14B, 14Y, 14C, and 14M corresponding to four toner colors of magenta, cyan, yellow, and black are arranged, and the developing units 14B, 14Y, 14C, and 14M have the same configuration. is there. When the rotary developing device 14 rotates, the developing rollers 14b, 14y, 14c, and 14m in each section face the photosensitive drum 11 with a predetermined gap.

  The laser unit 15 scans and exposes the photosensitive drum 11 based on image information sent from an external computer or the like, and is provided above the rotary developing device 14. Laser light 15L is emitted from the laser unit 15 based on the image information, and a reflection mirror 15a is provided on the optical path of the laser light 15L. The laser beam 15L is reflected by the reflecting mirror 15a and irradiated on the surface of the photosensitive drum 11 (laser beam 15L is shown by a two-dot chain line). The internal configuration of the laser unit 15 includes a laser light source, a polygon mirror, a polygon mirror driving motor, and the like (not shown).

  The intermediate transfer unit 20 includes an intermediate transfer belt 21 to which toner images of respective colors formed on the photosensitive drum 11 are sequentially transferred, a driving roller 22 for stretching and rotating the intermediate transfer belt 21, a tension roller 23, The photosensitive drum 11 is composed of primary transfer rollers 24 and 25 adjacent to each other via the intermediate transfer belt 21, a belt cleaning device 26 for cleaning the intermediate transfer belt 21, and the like, details of which will be described later.

  The paper feed unit 30 includes a paper feed cassette 31, a manual feed tray 32, and the like. A paper feed cassette 31 having a placement plate 33 on which the paper P is placed is provided at the bottom of the apparatus. In addition, the paper feed unit 30 includes a pickup roller 34 at the upper right portion of the paper feed cassette 31 and a roller pair at the right side of the pickup roller 34 in order to send the paper P on the loading plate 33 to the paper transport path one by one. And a double feed prevention roller 35. Further, a manual feed tray 32 is provided on the right side surface of the apparatus so that paper can be separately fed. The manual feed tray 32 is also provided with a pickup roller 36 for feeding the paper P one by one to the paper transport path.

  The paper transport unit 40 is for transporting the paper P in the image forming apparatus 1. The sheet conveying section 40 is a sheet for discharging the image-formed sheet P from the sheet feeding section 30 to a later-described secondary transfer roller 51 and a secondary transfer roller 51 through the fixing device 60. The second conveyance path 42 that reaches the discharge port 47 and the sheet P that has once passed through the fixing device 60 pass through the secondary transfer roller 51 again, so that the second conveyance path 42 is moved from the middle of the second conveyance path 42 to the middle of the first conveyance path 41. It is composed of a reverse conveyance path 43 provided so as to be connected. Note that the paper transport direction is indicated by arrows.

  The first transport path 41 is provided with a curved portion 44 for reversing the transport direction while transporting the paper P sent out from the paper feed cassette 31 upward. In addition, at the upper part of the curved portion 44, the conveyance path from the manual feed tray 32 joins. In front of the secondary transfer roller 51, a registration roller pair 45 for controlling the conveyance timing of the paper P is disposed. A plurality of conveyance roller pairs 46 are provided in the conveyance path in which these elements are provided. A guide plate (not shown) for guiding the paper P is also provided as appropriate.

  The second transport path 42 is provided with a plurality of transport roller pairs 46. A guide plate (not shown) for guiding the paper P is also provided as appropriate.

  The reverse conveyance path 43 is a conveyance path used for double-sided printing. The reverse conveyance path 43 joins the upstream side of the registration roller pair 45 in the sheet conveyance direction from the portion where the branching claw 48 provided in the middle of the second conveyance path 42 and downstream of the fixing device 60 in the sheet conveyance direction. It is provided to do. The reverse conveyance path 43 is provided so as to pass above the sheet feeding cassette 31 and below the secondary transfer roller 51 and the second conveyance path 42. The reverse conveyance path 43 is also provided with a plurality of conveyance roller pairs 46, and a guide plate (not shown) for guiding the paper P is also provided as appropriate.

  The secondary transfer unit 50 includes a secondary transfer roller 51 and a driving roller 22. The secondary transfer roller 51 is for transferring the image transferred to the intermediate transfer belt 21 onto the paper P conveyed so as to be sandwiched between the secondary transfer roller 51 and the intermediate transfer belt 21. Therefore, the secondary transfer roller is supported so that the secondary transfer roller 51 can rotate and be in contact with and away from the intermediate transfer belt so that a nip is formed via the drive roller 22 and the intermediate transfer belt 21. A voltage is applied to the secondary transfer roller 51 so that the toner is transferred onto the paper P at a predetermined timing by a voltage applying means (not shown).

  The fixing device 60 is for melting and fixing the toner transferred onto the paper P, and is provided in the middle of the second transport path 42 and below the rotary developing device 14. The fixing device 60 includes a heating roller 61 having a built-in heater and a pressure roller 62 that presses against the heating roller 61. Heat and pressure is fixed to the paper P.

  The toner supply unit 70 includes a toner container 71, a toner supply device 72, and the like. The toner container 71 is a part that stores toner to be supplied to the developing devices 14B, 14Y, 14C, and 14M of the rotary developing device 14, and is provided above the photosensitive drum 11 and the intermediate transfer belt 21. Although the toner containers 71 are not visible in FIG. 1, four toner containers 71 are arranged side by side in the direction perpendicular to the paper surface of FIG. The toners of magenta, cyan, yellow, and black are accommodated.

  The toner supply device 72 is for supplying the toner of each color stored in the toner container 71 to the corresponding developing devices 14B, 14Y, 14C, and 14M, and above the photosensitive drum 11, the laser unit. 15 is arranged in a space between the toner container 71 and the toner container 71 so as to move up and down. The toner supply device 72 has a thin tip, and when it moves downward, the tip is inserted into the developing devices 14B, 14Y, 14C, and 14M to supply toner.

  Next, an image forming operation will be briefly described. The image forming apparatus 1 executes an image forming operation based on the input image data as follows.

  First, the photosensitive drum 11 is charged by the charging roller 12. Thereafter, scanning exposure corresponding to image data is performed on the photosensitive drum 11 by the laser unit 15, and an electrostatic latent image is formed on the photosensitive drum 11. Next, the rotary developing device 14 is rotated so that the corresponding color developing devices 14B, 14Y, 14C, and 14M are opposed to the photosensitive drum 11. In this state, the electrostatic latent image on the photosensitive drum 11 is developed with the corresponding color toner. The developed toner image is transferred to the intermediate transfer belt 21. The above operation is sequentially repeated for each color, and a full-color toner image is formed on the intermediate transfer belt 21. For example, when a black single-color image is formed, the above operation may be performed once. The toner remaining on the photosensitive drum 11 after the transfer is cleaned by the drum cleaning device 13.

  On the other hand, in the paper feeding unit 30, one sheet P is taken out from the paper feeding cassette 31 or the manual feed tray 32 by the pickup roller 34 and the like and conveyed to the registration roller pair 45. Thereafter, the sheet P is conveyed from the registration roller pair 45 in time with the image formation on the intermediate transfer belt 21 and guided to the secondary transfer roller 51. The secondary transfer roller 51 abuts on the intermediate transfer belt 21 and applies a predetermined voltage to the secondary transfer roller 51, and the toner image formed on the intermediate transfer belt 21 is transferred onto the paper P. The sheet P is guided to the fixing device 60 by the second conveyance path 42, and the toner image is fixed on the sheet P by the fixing device 60. In the case of single-sided printing, the paper is sequentially discharged from the paper discharge port 47 through the branch claw 48, and the paper P on which the image has been formed is received on the discharge tray 49.

  On the other hand, in the case of double-sided printing, the paper P that has passed through the fixing device 60 is switched back on the second conveyance path 42 downstream of the branching claw 48 in the paper conveyance direction. be introduced. Thereafter, the paper P that is turned upside down is returned to the upstream side of the registration roller pair 45 in the first transport path 41 again. Then, the toner image is transferred from the secondary transfer roller 51 in time with the back side of the paper P. Thereafter, the paper is discharged from the paper discharge port 47.

  Next, the configuration of the intermediate transfer unit 20 according to the embodiment of the present invention will be described with reference to FIG. 1 using FIG. FIG. 2 is a perspective view of the belt unit 80 according to the embodiment of the present invention as seen from the upper right front. For convenience of explanation, the intermediate transfer belt 21 is not shown in FIG.

  The intermediate transfer unit 20 includes a belt unit 80 in which members such as a drive roller 22, a tension roller 23, primary transfer rollers 24 and 25, a drive transmission gear 27, and springs 28a and 28b as biasing units are supported as a unit. have.

  The belt unit 80 is provided in the image forming apparatus 1, and is provided below the photosensitive drum 11 and the toner container 71 and above the first conveyance path 41 in the image forming apparatus. (See FIG. 1). If the belt unit 80 is installed in the image forming apparatus after the belt unit 80 is provided with each member such as the driving roller 22, the image forming apparatus 1 can be easily assembled and manufactured, and the intermediate transfer unit can be easily maintained.

  Next, each member supported by the belt unit 80 will be described.

  As shown in FIG. 2, in the belt unit 80, the driving roller 22 is rotatably supported at the left end of the belt unit 80 in FIG. A drive transmission gear 27 for transmitting the drive from a motor (not shown) is connected to the roller shaft end 22a of the drive roller 22. Accordingly, the drive roller 22 is driven to rotate by driving from the drive transmission gear 27.

  On the other hand, referring to FIG. 1, the drive roller 22 is positioned below the photosensitive drum 11 and just above the secondary transfer roller 51 in the image forming apparatus. The drive roller 22 forms a nip with the secondary transfer roller 51 via the intermediate transfer belt 21.

  As shown in FIG. 2, the tension roller 23 is rotatably supported by the belt unit 80 at the right end thereof. A spring 28a for urging the tension roller 23 is supported on the left side of the tension roller 23 so as to be accommodated in the belt unit 80 in a pair (front side and back side in FIG. 2). ing. The urging direction of the spring 28a is a direction away from the drive roller 22 (the urging direction is indicated by a broken line).

  On the other hand, referring to FIG. 1, the tension roller 23 is provided on the right side in the image forming apparatus 1 in FIG. 1, and the height position thereof is arranged to be substantially the same as that of the photosensitive drum 11.

  As shown in FIG. 2, the primary transfer rollers 24 and 25 are rotatably supported on the upper surface of the belt unit 80 and on the diagonally upper right side of the drive roller 22. Both ends of the primary transfer rollers 24 and 25 are connected by a connecting member 83 so that the positional relationship between the interval and the height is maintained constant. Further, a pair of springs 28b is supported below the primary transfer rollers 23 and 24 so as to be housed in the belt unit 80 (a front side and a back side in FIG. 2). In FIG. 2, the rear spring 28b is invisible. The spring 28b urges the connecting member 83, that is, the primary transfer rollers 23 and 24 upward (the urging direction is indicated by a broken line).

  On the other hand, referring to FIG. 1, the primary transfer rollers 24 and 25 are disposed below the photosensitive drum 11 and adjacent to the photosensitive drum 11. Since the primary transfer rollers 24 and 25 are biased upward by the spring 28b as described above, a predetermined range of the intermediate transfer belt 21 between the primary transfer roller 24 and the primary transfer roller 25 is photosensitive. It contacts the body drum 11. That is, the photosensitive drum 11 and the intermediate transfer belt 21 form a nip, and the toner image is transferred from the photosensitive drum 11 to the surface of the intermediate transfer belt 21 within the predetermined range.

  As described above, the belt unit 80 supports a plurality of rollers such as the driving roller 22, the tension roller 23, and the primary transfer rollers 24 and 25. Further, the plurality of rollers are supported so that their respective axial directions are parallel to each other. Then, the intermediate transfer belt 21 is wound around the plurality of rollers that are rotatably supported. As shown in FIG. 2, the tension roller 23 and the primary transfer rollers 24 and 25 are urged by springs 28a and 28b as urging members, so that a constant tension is applied to the intermediate transfer belt 21. Then, the intermediate transfer belt 21 is stretched (see FIG. 1).

  When the drive is transmitted to the drive roller 22 and the drive roller 22 rotates, the stretched intermediate transfer belt 21 rotates. The tension roller 23 and the primary transfer rollers 24 and 25 are driven to rotate via the intermediate transfer belt 21. In short, the intermediate transfer belt 21 rotates as the driving roller 22 rotates.

  A belt cleaning device that is not provided in the belt unit 80 but forms the intermediate transfer portion 20 will be described. Referring to FIG. 1, the belt cleaning device 26 is provided on the left side of the drive roller 22 in FIG. The belt cleaning device 26 is configured to be able to contact and separate from the intermediate transfer belt 21 and cleans the intermediate transfer belt 21 at a predetermined timing. The belt cleaning device 26 includes a brush or a roller that is in sliding contact with the surface of the intermediate transfer belt 21. With this roller or the like, the belt cleaning device 26 scrapes off the deposits on the intermediate transfer belt 21.

  Next, based on FIG. 3, the brake member 90 which concerns on embodiment of this invention is demonstrated. FIG. 3A is a perspective view of the brake member 90 according to the embodiment of the present invention. FIG. 4B is a side view of the brake member 90 according to the embodiment of the present invention. (C) is an enlarged perspective view of the side end portion of the tension roller 23 in the belt unit 80 for explaining the attachment of the brake member 90 according to the embodiment of the present invention. For convenience of explanation, the illustration of the intermediate transfer belt 21 is omitted in FIG.

  The brake member 90 constantly applies a load due to friction to a roller that stretches the intermediate transfer belt 21, and loads the belt cleaning device 26 and the secondary transfer roller 51 against the intermediate transfer belt 21 by pressing against or separating from the intermediate transfer belt 21. This is to relatively reduce the influence of fluctuation. That is, if the load on the intermediate transfer belt 21 varies, the rotational speed of the intermediate transfer belt 21 is affected. Therefore, fluctuations in the rotational speed of the intermediate transfer belt 21 cause positional deviation during transfer.

  Specifically, in the present embodiment, the brake member 90 is provided on the tension roller 23. The tension roller 23 is a driven roller that is first positioned in the upstream direction of the driving roller 22 when viewed from the rotation direction of the intermediate transfer belt 21 (see FIG. 1).

  In the present embodiment, the specific shape of the brake member 90 is a substantially C-shaped cross section as shown in FIGS. 3 (a) and 3 (b). In other words, a part of a cylindrical member is cut in a direction parallel to the axial direction. The brake member 90 may be cylindrical.

  Examples of the material used for the brake member 90 include high-density microcell urethane foam. The material of the brake member 90 is not limited to this, and can be appropriately selected in consideration of heat resistance, shape stability, shape followability, and the like.

  Next, the attachment of the brake member 90 will be described. As shown in FIG. 3C, the brake member 90 in the present embodiment is provided at the shaft end portion 91 of the tension roller 23. Then, the shaft end 91 is fitted to the bearing 92 for rotatably supporting the tension roller 23 while the brake member 90 is mounted around the shaft end 91 (the mounting order is shown by a one-dot chain line). . FIG. 3C shows only one shaft end 91 of the tension roller 23 for convenience of explanation, but the brake member 90 is similarly provided at the shaft end 91 of the other tension roller 23. The shaft end 91 is pivotally supported by the bearing 92.

  As described above, the brake member 90 is simple in processing and mounting, is inexpensive, and requires less space than a conventional case where a blade or the like is provided. Therefore, the image forming apparatus 1 according to the present embodiment is low in cost and meets the demand for downsizing of the image forming apparatus 1.

  The tension roller 23, which is a driven roller provided with the brake member 90, is biased by a spring 28 a that is a biasing member in a direction away from the driving roller 22. As a result, the brake member 90 is pressed against the shaft end 91, and the tension roller 23 is constantly loaded by the brake member 90. Further, even if the brake member 90 is worn, there is no gap between the shaft end portion 91 and the brake member 90, and a stable load can be applied to the tension roller 23 for a long period of time.

  3C, in the image forming apparatus 1 according to the present embodiment, the outer diameter of the tension roller 23 provided with the brake member 90 is larger than the outer diameter of the driving roller 22. . If the state where the image forming apparatus 1 is not used continues, a roller having a larger curvature with respect to the intermediate transfer belt 21, that is, a roller having a smaller outer diameter, is more likely to become addictive to the intermediate transfer belt 21. Therefore, the habit of the intermediate transfer belt 21 can be prevented. Accordingly, it is possible to prevent positional deviation and color deviation during transfer due to the habit of the intermediate transfer belt 24. Further, when the outer diameter of the driven roller is increased, the inertia (inertial force) in rotation of the roller is increased and the necessity of the brake member is increased. However, in the present embodiment, the brake member 90 is provided as described above. . Therefore, the image forming apparatus 1 can prevent the intermediate transfer belt from becoming hazy while sufficiently dealing with the load fluctuation on the intermediate transfer belt.

  Here, in the image forming apparatus 1 according to the present embodiment, a transfer operation in the case where color images are continuously formed will be described (see FIG. 1).

  First, when image formation of the first sheet is started by inputting image data to be formed in the image forming apparatus 1, a toner image is developed on the photosensitive drum 11, and the toner image is transferred to the intermediate transfer belt. As described above, it is transferred to 21. Since the primary transfer rollers 24 and 25 and the photosensitive drum 11 are disposed to face each other, a certain area of the intermediate transfer belt 21 stretched around the primary transfer rollers 24 and 25 is pressed against the photosensitive drum 11. ing. The transfer from the photosensitive drum 11 to the intermediate transfer belt 21 is performed by applying a predetermined voltage to the primary transfer rollers 24 and 25 at a predetermined timing in a certain region in pressure contact. In this way, primary transfer from the photosensitive drum 11 as an image carrier to the intermediate transfer belt 21 is performed.

  In the case of forming a color image, the image forming apparatus 1 according to the present embodiment employs the rotary developing device 14. Therefore, in order to form one color image, a maximum of four primary transfers are performed. The Hereinafter, it is assumed that four primary transfers are performed unless otherwise specified.

  In the first image formation, the toner images are sequentially transferred to the intermediate transfer belt 21, and the toner image of the fourth color is transferred to the intermediate transfer belt during the primary transfer or after the completion of the primary transfer. Therefore, the secondary transfer roller 51 and the belt cleaning device 26 that have been in the retracted state are pressed against each other. At this time, the load on the intermediate transfer belt 21 increases and the load varies. The transfer material is transferred from the registration roller 45 toward a nip portion between the intermediate transfer belt 21 and the secondary transfer roller 51 so as to overlap with a predetermined timing, that is, a full-color toner image formed on the intermediate transfer belt 21. The paper P is conveyed. A predetermined voltage is applied to the secondary transfer roller, and the toner image on the intermediate transfer belt 21 is transferred onto the paper P. Thereafter, as described above, the toner image is fixed through the fixing device.

  Here, when the secondary transfer roller 51 and the belt cleaning device that are in the retracted state are pressed against each other, the load on the intermediate transfer belt 21 increases, the rotational speed of the intermediate transfer belt 21 decreases, or the intermediate transfer belt 21 It may be bent. Further, when the sheet P passes through the nip between the secondary transfer roller and the intermediate transfer belt 21, the load on the intermediate transfer belt 21 further increases. In particular, when the thick sheet P is used for image formation, the load on the intermediate transfer belt 21 is increased. The increase in load cannot be ignored.

  However, since the tension roller 23 is provided with a brake member 90 and a constant load is always applied to the tension roller 23, the load on the intermediate transfer belt 21 by the secondary transfer roller 51, the belt cleaning device, and the paper P. Even if fluctuations occur, the influence can be made relatively small. Accordingly, fluctuations in the rotational speed of the belt can be reduced, and no transfer position deviation occurs in the secondary transfer.

  Note that a brake member 90 is provided on the tension roller 23 that is first positioned upstream of the driving roller 22 in view of the rotational direction of the intermediate transfer belt 21 in order to cope with load fluctuations. When such a brake member 90 is provided, the rotational speed of the intermediate transfer belt 21 is inevitably reduced at that portion. This may cause the belt to bend, but in the present embodiment, the drive roller 22 pulls the intermediate transfer belt 21 between the drive roller 22 and the tension roller 23, and the intermediate transfer belt 21 is kept from being bent. Is done. Therefore, the brake member 90 does not affect the secondary transfer.

  The image forming apparatus 1 according to the present embodiment can start the primary transfer of the next image, that is, the second image, during the secondary transfer. By doing so, it is possible to increase the productivity of image formation.

  Here, if the secondary transfer roller 51 and the belt cleaning device 26 are kept in pressure contact with the intermediate transfer belt 21 in the primary transfer of the second image, the primary transfer is hindered. Therefore, the secondary transfer roller 51 and the belt cleaning device 26 are separated from the intermediate transfer belt 21 so as not to interfere. At this time, the load on the intermediate transfer belt 21 is reduced. Further, the separation may be performed during the primary transfer of the first color toner image of the second image in the image forming apparatus 1 of the present embodiment.

  As a result, the load on the intermediate transfer belt 21 is reduced, so that the rotation speed of the intermediate transfer belt 21 is increased and the intermediate transfer belt 21 is bent, and the first color toner image of the second image is affected. There is a possibility that positional deviation occurs in the transfer.

  However, in the image forming apparatus 1 according to the present embodiment, the tension roller 23 is provided with the brake member 90, and a constant load is constantly applied to the tension roller 23. Therefore, the secondary transfer roller 51, the belt cleaning device, and the like. Even if the load on the intermediate transfer belt 21 varies due to the separation of the belt 26, the influence can be relatively reduced. Therefore, fluctuations in the rotational speed of the intermediate transfer belt 21 can be reduced. That is, even in the primary transfer of the second image, no transfer positional deviation occurs.

  The above situation is the same for a single color image or a color image that does not use four color toners, and a high-quality image forming apparatus that does not cause misalignment of transfer can be provided.

  Thus, a photosensitive drum 11 as an image carrier on which an electrostatic latent image is formed, a rotary developing device 14 for supplying a developer to the image carrier and developing a toner image, and developed toner An endless intermediate transfer belt 21 on which an image is primarily transferred, and an intermediate transfer unit 20 having a plurality of rollers such as a drive roller 22, a tension roller 23, and primary transfer rollers 24 and 25 that stretch the intermediate transfer belt 21. In the image forming apparatus 1 having the secondary transfer unit 50 for transferring the toner image on the intermediate transfer belt 21 to the paper P as a transfer material, the intermediate transfer unit 20 drives and rotates a driving roller 22 that rotates. The tension roller 23 and all or part of the primary transfer rollers 24 and 25 are driven to rotate via the intermediate transfer belt 21, and the tension roller 23 is rotated in the direction of rotation of the intermediate transfer belt 21. Thus, if the tension roller 23, which is a driven roller first positioned in the upstream direction of the driving roller 22, is provided with a brake member 90 for applying a load to the rotation of the driven roller, the entire intermediate transfer belt 21 is provided. The load fluctuation due to the contact and separation of the secondary transfer roller 51 and the belt cleaning device 26 with respect to the load can be made relatively small, and the fluctuation of the rotation speed of the intermediate transfer belt 21 caused by the load fluctuation can be prevented. Therefore, it is possible to provide a high-quality image forming apparatus 1 that does not cause positional deviation or color deviation in the transfer of the formed image.

  In addition, since the brake member 90 is provided on the tension roller 23 which is a driven roller other than the drive roller 22 for rotating the intermediate transfer belt 21, the brake member 90 is worn compared to the case where the brake member 90 is provided on the drive roller 22. It becomes difficult to deform. Accordingly, maintenance of the image forming apparatus 1 is facilitated. Further, when the brake member 90 is provided on the driving roller 22, the influence on the rotational speed of the intermediate transfer belt 21 becomes large. In the present invention, the brake member 90 is provided on the tension roller 23. Therefore, the effect of the load reduction due to wear of the brake member 90 or the like is less likely to affect the rotational speed of the intermediate transfer belt 21 than when the brake member 90 is provided on the drive roller 22. Accordingly, it is possible to provide the image forming apparatus 1 in which the intermediate transfer belt 21 rotates at a stable speed over a long period of time.

  In the image forming apparatus 1, if the brake member 90 is provided at the roller shaft end portion 91 of the tension roller 23, the brake member 90 is provided only at the roller shaft end portion 91 of the tension roller 23. The configuration is very simple and the space for installing the brake member is small. Therefore, it is possible to provide a compact image forming apparatus that is easy to assemble and that reduces manufacturing costs.

  Further, in the image forming apparatus 1, if the tension roller 23 provided with the brake member 90 is biased by the spring 28 a that is a biasing member in a direction away from the driving roller 22, the tension of the intermediate transfer belt 21. Can be kept constant. Furthermore, even when the brake member 90 is worn, it is possible to adopt a structure in which the tension roller 23 is urged and pressed against the brake member 90, and a constant load can always be easily applied to the tension roller.

  Further, if the outer diameter of the driven roller (tension roller 23) provided with the brake member 90 is larger than the outer diameter of the driving roller 22, it is possible to prevent the intermediate transfer belt 21 from becoming hazy and further transfer. It is possible to prevent positional misalignment and color misalignment. In general, the larger the outer diameter, the better the roller that stretches the intermediate transfer belt 21 made of resin, for example. This is because, when the state where the image forming apparatus is not used continues, a roller having a larger curvature than the intermediate transfer belt 21, that is, a roller having a smaller outer diameter, is more likely to have a habit on the intermediate transfer belt 21. When the image forming apparatus 1 is used with the intermediate transfer belt 21 having a habit, positional deviation and color deviation may occur in transferring the formed image. Further, when the outer diameter of the driven roller (tension roller 23) is increased, the inertia (inertial force) in the rotation of the roller increases and the necessity of the brake member 90 increases. In the present invention, the brake member 90 is provided. It is. Accordingly, it is possible to prevent the intermediate transfer belt 21 from becoming hazy while sufficiently responding to the load fluctuation on the intermediate transfer belt 21, and to provide the image forming apparatus 1 that is further free of transfer positional deviation and color deviation.

  Although the embodiments of the present invention have been described above, the scope of the present invention is not limited to these embodiments, and various modifications can be made without departing from the spirit of the invention. For example, the image forming apparatus 1 according to the present embodiment has been described with respect to the case where the rotary developing device 14 is used. In addition, the tension roller 23 is described as the first roller positioned upstream of the driving roller 22 when viewed from the rotational direction of the intermediate transfer belt 21. However, the tension roller 23 may be applied to other driven rollers as necessary. .

  The present invention is applicable to an image forming apparatus having an intermediate transfer belt stretched by a roller.

1 is a schematic cross-sectional view for explaining a schematic configuration of an image forming apparatus according to an embodiment of the present invention. It is the perspective view which looked at the belt unit which concerns on embodiment of this invention from the upper right front. (A) is a perspective view of a brake member concerning an embodiment of the present invention. (B) is a side view of the brake member concerning the embodiment of the present invention. (C) is an enlarged perspective view of the side end portion of the tension roller 23 in the belt unit for explaining the attachment of the brake member according to the embodiment of the present invention.

Explanation of symbols

1 Image forming apparatus 11 Photosensitive drum (image carrier)
14 Rotary developer (Developer)
20 Intermediate transfer portion 21 Intermediate transfer belt 22 Drive roller 23 Tension roller 24 Primary transfer roller 25 Primary transfer roller 28a Spring (biasing member)
50 Secondary transfer portion 51 Secondary transfer roller 90 Brake member 91 Shaft end portion 92 Bearing

Claims (4)

An image carrier on which an electrostatic latent image is formed, one or a plurality of developing devices for supplying a developer to the image carrier to develop a toner image, and an endless shape on which the developed toner image is primarily transferred In an image forming apparatus having an intermediate transfer belt and an intermediate transfer portion having a plurality of rollers for stretching the intermediate transfer belt, and a secondary transfer portion for transferring a toner image on the intermediate transfer belt to a transfer material,
The intermediate transfer unit has a driving roller that is driven and rotated, and all or a part of the other rollers are driven and rotated via the intermediate transfer belt,
An image forming apparatus, wherein a brake member for applying a load to the rotation of the driven roller is provided on the driven roller first positioned upstream of the drive roller as viewed from the rotation direction of the intermediate transfer belt.   The image forming apparatus according to claim 1, wherein the brake member is provided at a roller shaft end portion of the driven roller.   The image forming apparatus according to claim 1, wherein the driven roller provided with the brake member is urged by a urging member in a direction away from the driving roller.   The image forming apparatus according to claim 1, wherein an outer diameter of the driven roller provided with the brake member is larger than an outer diameter of the driving roller.

Images