JP2010113280A - Transfer device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transfer device that secondarily transfers a stable toner image to various recording media by minimizing belt linear speed fluctuation when a recording medium rushes in an endless belt, while ensuring the stable conveyance of the endless belt. <P>SOLUTION: The transfer device includes: a drive transmission means that is disposed right in the upstream of a counter roller when viewed in the driven direction of the endless belt and that transmits rotation torque from a drive source to a first drive roller, which drives and runs the endless belt; a speed increase drive means that transmits rotation torque from the drive transmission means to a second drive roller, also serving as the counter roller; and a transmission torque limiting means. The speed increase drive means increases the endless belt peripheral speed of the second drive roller higher than the endless belt peripheral speed of the first drive roller. The transmission torque-limiting means prevents a rotation torque greater than a set torque from being transmitted to the second drive roller from the speed increase drive means. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a transfer apparatus for transferring an image on an intermediate transfer unit constituted by an endless belt to a recording medium, and a transfer apparatus having a mechanism for buffering an impact on the endless belt that occurs when the leading end of the recording medium enters. The present invention also relates to an image forming apparatus such as a copying machine, a printer, a facsimile, or a multifunction machine having at least two of these functions.

  As an image forming apparatus using a conventionally known intermediate transfer unit, a technique using an electrophotographic method, an ink jet method, or a so-called chemical set method is known. In an electrophotographic image forming apparatus, an electrostatic latent image formed on an image carrier such as a photoconductor disposed in an image forming unit is converted into a toner image by a developing device, and then the toner image is transferred to the photoconductor. And the intermediate transfer means such as an intermediate transfer belt, primary transfer is performed to the intermediate transfer means in the vicinity of the primary transfer nip. Thereafter, the toner image carried on the intermediate transfer unit is secondarily transferred to a recording medium such as a recording sheet by using a secondary transfer nip portion constituted by the intermediate transfer unit and a transfer roller. An image is formed by applying pressure and heat by a fixing device.

  In addition, in an ink jet type or chemical set type image forming apparatus, as described in Patent Document 1 and Patent Document 2, powder (intermediate) that can be dissolved or swelled by an ink liquid and can be peeled off from an intermediate transfer means. After applying and forming a layer (also referred to as a transfer medium) on the intermediate transfer unit, an intermediate image is formed by applying ink liquid ejected from the inkjet recording head to the powder layer in accordance with an image signal, Perform primary transfer. Thereafter, an image is formed by transferring the intermediate image carried on the intermediate transfer unit to a recording medium using a secondary transfer nip portion constituted by the intermediate transfer unit and a transfer roller. A technique for forming an intermediate image by applying the ink liquid described above directly onto an intermediate transfer means without using an intermediate transfer medium such as a powder layer has been developed.

  However, the thicker the recording medium conveyed to the secondary transfer nip portion of the image forming apparatus using the intermediate transfer means, the stronger the stiffness, or the stronger the curling of the recording medium, the more the leading edge of the recording medium is The impact generated at the time of collision or contact when entering the intermediate transfer means becomes large, and the impact is caused by the primary transfer of a toner image from an image carrier such as a photoconductor to the intermediate transfer means, or by inkjet When the intermediate image is primarily transferred from the recording head or the like to the intermediate transfer means, it causes a disturbance in the steady transfer linear velocity in the sub-scanning direction of the recording medium. This is a cause of color misregistration. Further, the resistance generated when the recording medium is caught in the secondary transfer nip portion also causes an action to reduce the belt linear velocity of the intermediate transfer means, and this action is also an image position called a shock jitter. It is a factor that causes misregistration and color misregistration.

  If there is a problem such as shock jitter due to the change in the belt linear velocity as described above, it is good to form only one image, but when forming multiple images, the previous page is secondary. The impact at the time of transfer propagates to the intermediate transfer means, and the toner image or intermediate image (hereinafter also simply referred to as an image) to be primarily transferred to the intermediate transfer means at the primary transfer portion of the next page is disturbed in the sub-scanning direction. As a result, such a disturbed image is secondarily transferred to the recording medium of the next page. Therefore, it is desirable that the rotational behavior of the intermediate transfer means be as constant as possible.

  Therefore, in Patent Document 3, in an electrophotographic image forming apparatus, by providing a variable unit that presses the back surface of the intermediate transfer belt, which is an intermediate transfer unit, when the recording medium enters the intermediate transfer belt by the variable unit. An invention is disclosed in which the drive locus or trajectory of the intermediate transfer means is changed so that the angle of entry of the recording medium becomes smaller, and the fluctuation in load on the intermediate transfer belt, which causes shock jitter, can be reduced.

  However, the invention disclosed in Patent Document 3 must be configured such that the driving path of the intermediate transfer belt can be changed by the variable means, so that stable belt conveyance cannot be performed, and consequently stable. This causes a problem that the toner image cannot be obtained. Even if it becomes possible to reduce the impact of the recording medium colliding with the intermediate transfer belt by reducing the angle of entry of the recording medium by changing the drive track, the recording medium can be It is impossible to cope with the impact or resistance at the time of being bitten by the belt, and as a result, it is not possible to sufficiently buffer the fluctuation of the belt linear velocity which is a cause of shock jitter.

  Also, in Patent Document 4, in an electrophotographic image forming apparatus, the intermediate transfer belt and the recording medium are first contacted with respect to the upstream side in the recording medium sub-scanning direction from the upstream side to the downstream side. In the region and on the inner periphery of the intermediate transfer belt, a bending restriction means for restricting the bending when the recording medium contacts the intermediate transfer belt is provided, and the bending restriction means prevents the intermediate transfer belt from being bent and deformed. An invention for preventing the occurrence of shock jitter due to bending deformation is disclosed.

  By providing such a deflection regulating means, it becomes possible to regulate the belt deflection when the recording medium first collides with the intermediate transfer belt. Even if the deflection regulating means is provided, the deflection regulating means is provided. And the intermediate transfer belt are in contact with each other, when the recording medium collides with or comes into contact with the intermediate transfer means, an additional frictional force due to the collision occurs between the two. In the invention disclosed in Patent Document 4, the roller disposed on the downstream side in the transport direction of the collision position of the intermediate transfer belt is configured as a driving roller that transmits the driving force from the driving source directly or indirectly. Therefore, this frictional force generates a torque in the direction to reduce the linear speed of the intermediate transfer belt with respect to the roller forming the above-described secondary transfer portion, and the generation of shock jitter is sufficiently effective. Cannot be prevented.

Japanese Patent No. 3996299 Japanese Patent No. 4086437 JP 2007-57715 A JP 2006-235266 A

  In light of the above problems, the object of the present invention is to provide a belt line that absorbs shock to the belt when the recording medium enters the endless belt while ensuring stable conveyance of the endless belt as an intermediate transfer unit. Providing a transfer device capable of secondary transfer of stable images to various recording media such as thick paper, high-rigidity recording media, or recording media with strong curl by reducing the speed fluctuation as much as possible In addition, an object of the present invention is to provide an image forming apparatus using the transfer device.

  According to the present invention, there is provided an endless belt that is stretched and driven by a plurality of rollers according to the present invention, the endless belt carrying an image to be transferred to a recording medium, and one of the plurality of rollers. And a transfer roller that is disposed opposite to the endless belt with the endless belt interposed therebetween and forms a transfer nip portion by pressing the endless belt with each other. In the transfer device in which the image carried on the endless belt is transferred to a recording medium conveyed to the transfer nip portion, the endless belt is disposed immediately upstream of the opposing roller when viewed in the driving direction of the endless belt. Drive transmission means for transmitting rotational torque from a drive source to a first drive roller for driving the belt to travel, and rotational torque distributed from the drive transmission means to the opposing roller The counter roller is configured as a second driving roller by transmitting rotational torque from the speed increasing driving means and the transmission torque limiting means, The speed increasing drive means is configured such that the peripheral speed at which the second drive roller drives the endless belt is at least the same speed as or faster than the peripheral speed at which the first drive roller drives the endless belt. The transmission torque limiting means is configured to prevent rotational torque from being transmitted to the second drive roller above a set torque, and the speed increasing drive transmission means rotates the second drive roller. This is solved by a transfer device characterized in that it is set to be equal to or less than the rotational torque to be caused.

  According to a second aspect of the present invention, there is provided an endless belt that is stretched and driven to run on a plurality of rollers, the endless belt carrying an image to be transferred to a recording medium, and the plurality of the endless belts. A counter roller, which is one of the rollers, disposed opposite to the endless belt, and has a transfer roller that forms a transfer nip portion by pressing the endless belt with the counter roller. In the transfer device in which the image carried on the endless belt is transferred to a recording medium conveyed from the medium conveying means to the transfer nip portion, immediately before the upstream side of the opposing roller as viewed in the driving direction of the endless belt. A drive transmission means for transmitting rotational torque from a drive source to a first drive roller disposed and driving the endless belt, and transmitted to the first drive roller by the drive transmission means. Speed increasing drive means and transmission torque limiting means for transmitting rotational torque to the counter roller via the first drive roller, the counter roller from the speed increasing drive means and transmission torque limiting means It is also configured as a second driving roller by transmitting rotational torque, and the speed increasing driving means drives the peripheral speed at which the second driving roller drives the endless belt, and the first driving roller drives the endless belt. The transmission torque limiting means is configured to prevent rotational torque from being transmitted to the second drive roller at a set torque or higher. The set torque is set to be equal to or less than a rotational torque at which the acceleration drive transmission means attempts to rotate the second drive roller. To propose a location.

  According to a third aspect of the present invention, there is provided an endless belt that is stretched and driven to run on a plurality of rollers, the endless belt carrying an image to be transferred to a recording medium; A counter roller, which is one of the rollers, disposed opposite to the endless belt, and has a transfer roller that forms a transfer nip portion by pressing the endless belt with the counter roller. In the transfer device in which the image carried on the endless belt is transferred to a recording medium conveyed from the medium conveying means to the transfer nip portion, immediately before the upstream side of the opposing roller as viewed in the driving direction of the endless belt. A drive transmission means for transmitting rotational torque from a drive source to a first drive roller disposed and driving the endless belt; and the drive source for transmitting rotational torque to the first drive roller A second drive source and a second drive transmission means provided separately and independently from the drive transmission means, the second drive source and the second drive transmission means for transmitting rotational torque to the opposed roller, and the opposed roller A transmission torque limiting means configured to prevent the rotation torque from being transmitted when the rotation torque is not less than a set torque, and the counter roller transmits the rotation torque from the second drive source to the second drive transmission. The second drive roller and / or the second drive transmission means is a peripheral speed at which the second drive roller drives the endless belt. The first drive roller is configured to be at least the same speed as or faster than the circumferential speed at which the endless belt is driven, and the second drive source includes the second drive transmission means. The rotational torque transmitted to the second drive roller is set to be equal to or less than the rotational torque transmitted from the first drive source to the first drive roller, and the set torque is determined by the second drive roller. The circumferential speed for driving the endless belt is configured to be faster than the circumferential speed for driving the endless belt, and is transmitted from the second driving source to the second driving roller. The rotational torque transmitted from the first drive source to the first drive roller is set below the rotational torque from the drive source that drives the second drive roller, and the second drive roller Is configured such that the circumferential speed for driving the endless belt is higher than the circumferential speed for driving the endless belt by the first driving roller, and the rotation transmitted from the second driving source to the second driving roller. When the torque is less than or equal to the rotational torque transmitted from the first drive source to the first drive roller, and the peripheral speed at which the second drive roller drives the endless belt and the first drive roller drives the endless belt When the peripheral speed to drive is the same, the transfer apparatus characterized by setting below or equal to the rotational torque of the drive source which drives the second drive roller is proposed.

  In the present invention, it is effective that the first drive roller and the second drive roller have fixed axial positions with respect to each other and further have a fixed axial position with respect to the recording medium conveying means. It is.

  In the present invention, the recording medium front end contact position between the first driving roller and the second driving roller and where the recording medium conveyed by the recording medium conveying means first contacts the endless belt is set. And a bending restricting means disposed on a surface opposite to the surface on which the recording medium contacts the endless belt is further provided, and the bending restricting means is always in contact with the endless belt. Therefore, it is effective when the bending of the endless belt is restricted.

  The present invention also proposes an image forming apparatus comprising the above-described transfer device. The image forming apparatus proposed in the present invention is not limited to an image forming apparatus that uses an electrophotographic intermediate transfer unit, and even an ink jet type or chemical set type image forming apparatus is stretched around a plurality of rollers. Any image forming apparatus that employs an endless belt-shaped intermediate transfer unit that is driven to run in a heated state may be used.

  According to the present invention, in addition to the first driving roller configured to mainly drive the endless belt, slip torque or idling is performed so that the rotational torque from the drive source is transmitted and the rotational torque exceeding the set torque is not transmitted. A second drive roller that is also a counter roller that forms a transfer nip portion provided with a transmission torque limiting means configured to perform, and in addition, the peripheral speed at which the second drive roller drives the endless belt is Since one drive roller is configured to be at least the same speed or faster than the peripheral speed for driving the endless belt, the impact generated when the leading edge of the recording medium enters the transfer nip portion is endless. Even when applied to the belt, the set torque from the transmission torque limiting means is always applied to the endless belt via the second drive roller which is also a counter roller. Therefore, it is possible to reduce the belt linear velocity fluctuation due to the impact as much as possible without the need to variably configure the drive trajectory of the endless belt, and as a result, various recordings can be achieved while ensuring stable conveyance of the endless belt. Stable secondary transfer of an image to a medium is possible, the compatibility of the recording medium is improved, and a stable and high-quality image can be obtained.

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

  First, the generation principle of the conventional image forming apparatus and shock jitter will be described with reference to FIG. 11 in addition to FIGS. FIG. 8 is a cross-sectional view schematically showing a conventional electrophotographic image forming apparatus using an intermediate transfer unit, and FIG. 9 shows a shock jitter generated in a secondary transfer portion of the conventional image forming apparatus. It is sectional drawing which showed the behavior to perform roughly. FIG. 11 is a cross-sectional view schematically showing an ink jet type or chemical set type image forming apparatus, which will also be described later.

  In the electrophotographic image forming apparatus shown in FIG. 8, first to fourth four image forming units 20Y, 20M, 20C, and 20Bk are arranged in a housing (not shown), and each image forming unit is provided with each image forming unit. Are provided with photoreceptors 21Y, 21M, 21c, and 21Bk. A toner image of a different color is formed on each photoconductor. In the example shown in FIG. 8, a yellow toner image, a magenta toner image, and a cyan toner are formed on these photoconductors 21Y, 21M, 21c, and 21Bk. An image and a black toner image are formed.

  An endless belt-shaped intermediate transfer belt 53 configured as an intermediate transfer unit is disposed opposite to the first to fourth photoconductors 21Y, 21M, 21c, and 21Bk, and each of the photoconductors 21Y, 21M, 21c, and 21Bk is provided with the intermediate transfer means. The intermediate transfer belt 53 is disposed so as to contact the surface. The intermediate transfer belt 53, which is an intermediate transfer means, is generally stretched and driven to travel by being inscribed and / or circumscribed by a plurality of rollers. In the example shown in FIG. 8, the intermediate transfer belt 53 is wound around support rollers 54, 55, 56, and 57, and the roller 54, which is one of the support rollers inscribed therein, is driven by a driving device (not shown). In this case, the driving roller 54 is driven to rotate the inscribed driven roller 55 and the opposing roller 57 and the cleaning roller 56 that are in contact with each other. Is driven to rotate. The driven roller 55 is provided with a tension applying member such as a spring that applies a load in the direction of applying tension to the intermediate transfer belt 53, and the intermediate transfer belt 53 is moved at a predetermined tension by the action of the tension applying member. Configured to be stretched.

  Since each color toner image is formed on the photoconductors 21Y, 21M, 21c, and 21Bk and the respective toner images are transferred onto the intermediate transfer belt 53, the configuration is substantially the same. A configuration in which the toner image is transferred onto the intermediate transfer belt 53 without C and Bk) will be described below.

  The photoconductor 21 is driven to rotate counterclockwise. At this time, the surface of the photoconductor 21 is irradiated with light from a static eliminator (not shown) to initialize the surface potential. The initialized photoreceptor surface is uniformly charged to a predetermined polarity by the charging device 22. The charged surface is irradiated with a light-modulated laser beam L emitted from an exposure apparatus (not shown), and an electrostatic latent image corresponding to the writing information is formed on the surface of the photoreceptor 21. In the present embodiment, an exposure apparatus including a laser writing apparatus that emits a laser beam L is used. However, an exposure apparatus having an LED array and an image forming unit may be used. The electrostatic latent image formed on the photoreceptor 21 is visualized as a toner image when it passes through the developing device 23.

  On the other hand, a primary transfer roller 52 is disposed inside the intermediate transfer belt 53 so as to face the photoconductor 21 with the belt interposed therebetween, and the primary transfer roller 52 contacts the back surface of the intermediate transfer belt 53. Thus, an appropriate primary transfer nip portion between the photosensitive member 21 and the intermediate transfer belt 53 is formed.

  A transfer voltage having a polarity opposite to the toner charging polarity of the toner image formed on the photosensitive member 21 is applied to the primary transfer roller 52. As a result, a transfer electric field is formed between the photosensitive member 21 and the intermediate transfer belt 53, and the toner image on the photosensitive member 21 is electrostatically transferred onto the intermediate transfer belt 53 that is rotationally driven in synchronization with the photosensitive member 21. Primary transfer.

  As described above, the yellow toner image, the magenta toner image, the cyan toner image, and the black toner image are respectively formed on the photoconductors 21Y, 21M, 21C, and 21Bk, and the toner images of the respective colors are conveyed on the intermediate transfer belt 53. A full color image is formed by sequentially superimposing on the intermediate transfer belt 53 from the upstream side in the direction.

  On the other hand, as shown in FIG. 8, a recording medium storage unit 1 in which recording media such as recording paper and sheets are stacked and stored is disposed in the lower part of the apparatus body. The stacked recording media are separated from the stacked bundle of recording media by the frictional conveying force generated by the rotation of the pickup roller 3, and then the feeding force fed in the conveying direction by the paper feed roller 4 is supplied. Although loaded, the sheet feed reverse roller 5 that rotates with a predetermined torque in the opposite direction to the sheet feed roller 4 is reliably separated and conveyed one by one, and further, the conveyance drive roller 6 and the conveyance driven It is conveyed through the roller 7. When the leading edge of the recording medium passes through the conveyance driving roller 6 and the conveyance driven roller 7, the recording medium is conveyed while the conveyance direction is regulated by the lower conveyance guide plate 8 and the upper conveyance guide plate 9, and passes through the registration sensor 10. . When the leading end of the recording medium passes through the registration sensor 10, the time required for the recording medium to reach the registration roller pair 11, 12 that has not yet started to rotate is calculated, and a predetermined conveyance is performed based on the calculation result. Control is performed to stop the amount after the conveyance drive roller 6 is rotationally driven. By being conveyed by this predetermined amount, the recording medium is curved so as to swell with respect to the recording medium conveyance path indicated by a two-dot chain line in the drawing after abutting against the stopped pair of registration rollers 11 and 12. This is commonly referred to as forming a loop. The recording medium in which the loop is formed makes uniform contact with the registration roller pairs 11 and 12 by the restoring force to return to its own plane, and the recording medium is registered.

  The registered recording medium is driven by the registration roller pairs 11 and 12 and the conveyance driving roller 6 at the timing of the images sequentially transferred to the intermediate transfer belt 53 by the image forming units 20Y, 20M, 20C, and 20Bk. Thus, the secondary transfer roller 58 and the counter roller 57 are guided and conveyed between the lower secondary pre-transfer guide plate 14 and the upper secondary pre-transfer guide plate 15, and a spring provided on the transfer roller 58 or the like. By the action of the urging means, the image is secondarily transferred at the secondary transfer nip portion formed by pressing the intermediate transfer belt 53 with a predetermined transfer pressure. The recording medium subjected to the secondary transfer is further transported, fixed to the recording medium by receiving heat and pressure by a fixing roller pair 59 disposed on the downstream side in the recording medium transport direction, and discharged from the image forming apparatus. Thus, the image forming operation is completed.

  Next, an example of a conventional image forming apparatus using an intermediate transfer unit in an ink jet method or a chemical set method will be described with reference to FIG. FIG. 11 is a schematic cross-sectional view showing an ink jet type or chemical set type image forming apparatus using an intermediate transfer unit. Note that components having the same functions as those used in the electrophotographic image forming apparatus of FIG. 8 described above are denoted by the same reference numerals, and description thereof will be omitted as necessary.

  In the ink jet type image forming apparatus using the intermediate transfer unit as shown in FIG. 11, the intermediate transfer belt 53 as the intermediate transfer unit is configured as an endless belt. In the image forming apparatus shown in FIG. It is stretched between 54, 55 and 57. Further, a roller 54 that is one of these supporting rollers inscribed in the intermediate transfer belt 53 is configured as a drive roller that is driven by a drive device (not shown), and the intermediate transfer is performed by the rotational drive of the drive roller 54. The belt 53 is driven to run clockwise as indicated by an arrow in the figure, and is configured to carry and convey an intermediate transfer medium (to be described later) and an intermediate image formed on the intermediate transfer medium.

  In the image forming apparatus shown in FIG. 11, first, an application amount of an intermediate transfer medium (not shown) in the intermediate transfer medium container 88 is controlled by an application amount control blade 89, and passes through an application auxiliary roller 80 and an application roller 81. Then, it is applied in layers on the surface of the intermediate transfer belt 53. This intermediate transfer medium is a powder that can be dissolved or swelled by an ink liquid and can be peeled off from the intermediate transfer means. In the illustrated image forming apparatus, an intermediate transfer medium is used, but it is also possible to apply ink directly to the intermediate transfer belt 53 without using the intermediate transfer medium. In this case, the intermediate transfer medium itself is not required in addition to the intermediate transfer medium container 88, the coating amount control blade 89, the coating auxiliary roller 80, and the coating roller 81.

  Next, ink droplets corresponding to the image signal are ejected by the ink jet recording head 100 and are primarily transferred as an intermediate image onto the intermediate transfer belt 53 via the intermediate transfer medium. On the other hand, the recording medium accommodated in the recording medium accommodating portion 1 such as a paper feed tray is separated one by one by the paper feed rollers 97, 98, 99, 95, and 96 and is registered up to the registration roller pairs 11 and 12. Be transported. The image formed by the ink droplets, which is an intermediate image formed on the intermediate transfer belt 53, and the intermediate transfer medium of the image portion are transferred to the recording medium conveyed to the pair of registration rollers 11 and 12 as described above by the electrophotographic method. Similar to the image forming apparatus, the timing of the intermediate image is measured, and the secondary transfer roller 58 and the counter roller 57 are predetermined by a biasing means (not shown) such as a spring provided on the transfer roller 58. Secondary transfer is performed at the secondary transfer nip portion formed by pressing the intermediate transfer belt 53 with the transfer pressure of the transfer pressure, and is further conveyed and discharged from the discharge portion such as a discharge tray by the discharge rollers 93 and 94. The paper is discharged.

  Further, after the image formed by the ink droplets formed on the intermediate transfer belt 53 and the intermediate transfer medium of the image portion are transferred to the recording medium, the intermediate transfer remaining on the surface of the intermediate transfer belt 53 The medium is cleaned by a cleaning roller 122 and cleaning blades 123 and 124 as necessary, and thereafter, the intermediate transfer medium is applied again.

  Here, FIG. 9 shows a schematic enlarged cross-sectional view of the secondary transfer portion of the image forming apparatus as shown in FIG. 8 or FIG. 11. The behavior in which shock jitter occurs at the next transfer portion will be described.

  As shown in FIG. 9A, the leading end of the recording medium first contacts the intermediate transfer belt 53 at the recording medium leading end contact position 18 in the prenip region located upstream of the secondary transfer nip region in the intermediate transfer belt conveyance direction. When contact is made (when the pre-nip enters), the intermediate transfer belt 53 is pushed inward and bent from the initial stretched state before the recording medium is secondarily transferred, and this bending action causes the recording of the intermediate transfer belt 53 to be recorded. A situation occurs in which the belt linear velocity on the upstream side as viewed in the driving direction with respect to the medium front end contact position 18 becomes faster. As a result, the image forming unit 20Y, 20M, 20C, 20Bk or the primary transfer portion that performs the primary transfer of the next page by the ink jet recording head 100 causes a positional deviation of the image to be formed. A streak-like image in which the pixel density in the sub-scanning direction of the recording medium becomes coarse appears at the time of secondary transfer of the next page.

  Next, as shown in FIG. 9B, when the leading end of the recording medium reaches the secondary transfer nip portion and is bitten by the secondary transfer nip portion (at the time of the main nip), the recording medium becomes a spring or the like. A force acts to push down the transfer roller 58 pressed against the intermediate transfer belt 53 by the thickness of the recording medium by the biasing means, and the secondary transfer nip portion of the intermediate transfer belt 53 is resisted by this force. A situation occurs in which the upstream line speed becomes slow. As a result, the image forming units 20Y, 20M, 20C, and 20Bk or the primary transfer portion that performs the primary transfer by the ink jet recording head 100 causes a positional deviation of the image to be formed. A streak-like image having a dense pixel density in the sub-scanning direction appears at the time of secondary transfer of the next page.

  Further, as shown in FIG. 9C, the recording medium collided with the intermediate transfer belt 53 as shown in FIG. 9A after the leading end of the recording medium passed through the secondary transfer nip region. The intermediate transfer belt 53 that has been bent inward so far tries to return to the state where it is stretched straight by its own tension, so that this restoring force or operation causes the secondary transfer nip portion of the intermediate transfer belt 53 to be restored. A situation occurs in which the upstream line speed becomes slow. As a result, the image forming unit 20Y, 20M, 20C, 20Bk or the primary transfer portion that performs the primary transfer by the ink jet recording head 100 causes a positional deviation of the image to be formed. As a result, a streak-like image having a high pixel density appears at the time of secondary transfer of the next page.

  Finally, when the above-described rushing operation of the recording medium is completed and normal secondary transfer to the recording medium is performed as shown in FIG. 9D, the intermediate transfer belt 53, the transfer roller 58, and the opposite Since the roller 57 is driven in a normal steady running state, the belt linear velocity does not vary.

  FIG. 10 is a graph schematically showing changes in the belt linear velocity at the primary transfer portion during the recording medium entering operation, with the belt linear velocity on the vertical axis and the elapsed time on the horizontal axis. As can be seen from FIG. 10, the first peak drawn in the direction of increasing the belt linear velocity is the belt line at the pre-nip when the recording medium collides with the recording medium tip contact position 18 shown in FIG. 9A. As described above, the recording medium comes into contact with the intermediate transfer belt 53 and pushes the intermediate transfer belt 53 to the inside of the normal belt driving track or path so that the primary transfer portion of the intermediate transfer belt 53 The line speed is increased. The second peak in the direction of reducing the next belt linear velocity is the belt linear velocity behavior at the time of the main nip when the recording medium shown in FIG. 9B enters the secondary transfer nip portion, as described above. In addition, the linear speed of the primary transfer portion of the intermediate transfer belt 53 is reduced by the resistance generated when the recording medium is caught in the secondary transfer nip. Further, the third peak in the direction of reducing the next belt linear velocity is due to the belt return behavior shown in FIG. 9C, and as described above, the secondary transfer roller 58 has a thickness of the recording medium. After being pushed down by a certain amount, the belt linear velocity is decelerated due to the restoring force of the intermediate transfer belt 53 pushed inward to return to the original stretched state.

  The defect in image density caused by the belt linear velocity fluctuation as described above is generally called a shock jitter. In order to obtain a good image, this shock jitter must be prevented. A mechanism provided in the transfer device to prevent this shock jitter is the main component of the present invention, and its configuration and operation will be described below.

  The configuration of the first embodiment of the present invention for preventing the shock jitter as described above is shown in FIGS. FIG. 1 is a cross-sectional view schematically showing an example of an electrophotographic image forming apparatus to which the first embodiment of the present invention is applied, and FIG. 2 is a view around the secondary transfer portion of the first embodiment. It is the perspective view which showed the structure schematically. Here, it should be noted that FIG. 2 corresponds to a perspective view seen from the back side of the diagram shown in FIG. 1 in order to illustrate the motor 70, the gear 61, and the like not shown in FIG. Also, the outer diameters of the rollers in the figure are the same for convenience in order to briefly explain the shaft torque, the peripheral speed, the belt conveyance speed, etc., and to deepen the understanding of the invention. Therefore, as shown in this figure, it should be understood that the present invention is not limited only to rollers having the same outer diameter. Further, the configuration of the present invention will be described below. In this case, the same reference numerals are assigned to the same components as those in the conventional technology, and the description thereof is omitted.

  Similar to the example of the conventional image forming apparatus described above, in the present invention, the intermediate transfer belt 53 as an intermediate transfer unit is stretched around a plurality of support rollers 54, 55, 56, and 57. Here, the driving roller 54 for driving the intermediate transfer belt 53 is disposed immediately upstream of the counter roller 57 when viewed in the driving direction of the intermediate transfer belt 53. Further, as is apparent from the perspective view of FIG. 2, the shaft of the first drive roller 54 is provided with a gear 61 that is a drive transmission means configured integrally with the shaft. The gear 61 is motively connected to a motor 70 that is a drive source via a pinion 72, and is configured such that rotational torque is transmitted from the motor 70 to the first drive roller 54. As a result, the first drive roller is directly driven to rotate by the rotational torque of the motor 70, and the intermediate transfer belt 53 that is in frictional contact with the first drive roller 54 is also driven. At the same time, the gear 61 is integrally formed with a pulley 62 which is one component of the speed increasing drive transmission means, and the pulley 62 is also rotationally driven by distributing the rotational torque of the motor 70.

Here, the pulley 62 is configured to be able to rotate a pulley 64 that is motively connected to the counter roller 57 via the timing belt 63, and the pulley 62, the timing belt 63, and the pulley 64 are used to increase speed drive transmission. Means are configured. In the present embodiment, the pulley 64 is formed integrally with a torque limiter 65 that is a transmission torque limiting means, and the torque limiter 65 is motively connected to the opposing roller 57, but the set torque T _L When the above shaft load torque is generated, the shaft is configured to idle or slip with respect to the drive shaft of the facing roller 57. Accordingly, the counter roller 57 shown in FIGS. 1 and 2 is configured as the second drive roller 57 by transmitting the rotational torque from the speed increasing drive transmission means and the transmission torque limiting means, while the torque limiter 65 is configured. Rotational torque is transmitted up to the set torque _TL , but no further rotational torque is transmitted.

Further, the gear ratio between the pulley 62 and the pulley 64, the peripheral velocity V ₂ of the second driving roller 57 drives the intermediate transfer belt 53, the peripheral velocity V ₁ of the first driving roller 54 drives the intermediate transfer belt 53 At least the same speed or a slight speed can be set. That is, in the speed increasing drive transmission means in the present invention, the gear ratio is set so that the relationship of V ₂ ≧ V ₁ is established. The concept of the speed increasing drive transmission means in the present invention includes a peripheral speed V _{1 at} which the first drive roller 54 drives the intermediate transfer belt 53, and a peripheral speed V at which the second drive roller 57 drives the intermediate transfer belt 53. _The case where ₂ becomes the same speed is also included.

Here, when the first drive roller 54 directly connected from the gear 61 serving as drive transmission means rotates the intermediate transfer belt 53 using the rotational torque transmitted from the motor 70, the intermediate transfer belt 53 is stretched. The second drive roller 57 is subjected to torque for rotating the second drive roller 57 via the intermediate transfer belt 53. Therefore, although the second drive roller 57 depends on the winding angle of the intermediate transfer belt 53 and the surface friction coefficient of both of them, the contact surface does not slip unless a considerable rotational torque load is applied to the second drive roller. Therefore, the rotational torque at which the intermediate transfer belt 53 tries to rotate the second driving roller 57 is substantially equal to the rotational torque of the first driving roller 54. Thus, the axial torque T ₁ applied from the first drive roller 54 is applied via the intermediate transfer belt 53.

On the other hand, the second drive roller 57 has a torque limiter 65 which is a speed increasing drive transmission means and a transmission torque limiting means as another means for transmitting the rotational torque, and the rotational torque T ₂ transmitted from these is as follows. driven pulley 62 and a pulley 64 the second driving roller 57 is an intermediate transfer the peripheral speed V ₂ for driving the belt 53 first drive roller 54 is an intermediate transfer belt 53 by the gear ratio of the constituting the speed increasing drive transmission means In the case where it is configured to be slightly faster than the peripheral speed V ₁ to be driven, it is smaller than the shaft torque T ₁ transmitted to the first drive roller 54 by the increased speed because of the inversely proportional relationship. It has become. That is, the second driving roller 57, while the rotational torque T ₁ from the axial direction via the intermediate transfer belt 53 is transferred, a small rotation torque T ₂ than the rotational torque T ₁ from the axial outer side of the opposite It is transmitted via the speed increasing drive transmission means and the transmission torque limiting means 65. In the case where the first driving roller 54 and the second driving roller 57 is driven at the same peripheral speed by a speed increasing drive transmission means, the rotational torque T ₁ and T ₂ as described above, the same value.

Therefore, if the set torque T _L of the torque limiter 65 is set to be equal to or less than the rotational torque T _{2 at} which the speed increasing drive transmission means tries to rotate the second drive roller 57, the speed increasing drive transmission is set. In a normal traveling drive state in which the peripheral speed V ₂ is driven faster than the peripheral speed V ₁ by the means, the rotational torque T ₁ greater than the set torque _TL is transmitted to the torque limiter 65 from the second drive roller 57 side. Thus, since the torque limiter 65 slips or slips, even if the second drive roller 57 that is also the opposing roller tries to rotate slightly faster than the first drive roller 54, the speed difference is absorbed or converged. It will be configured to be able to.

In the case where the speed increasing drive transmission means peripheral velocity V ₁ and the peripheral velocity V ₂ is set to be driven at the same peripheral speed, and, setting torque T _L is equal to or less than the rotational torque T ₂ in the case, the speed difference between the rollers 54 and 57 in the circumferential speed of the intermediate transfer belt 53 does not occur, also, the torque limiter 65 in the axial direction of the large torque T ₁ than the set torque T _L is the second driving roller 57 Therefore, the torque limiter 65 normally slips or slips. Further, when the peripheral speed V ₁ and the peripheral speed V ₂ are set to be driven at the same peripheral speed by the speed increasing drive transmission means, the set torque T _L is set similarly to the rotational torque T _2. in the case, it takes the torque limiter 65 from the axial direction to an axially outer same rotational torque T ₁ to T ₂ is the second drive roller 57 and the set torque T _L, the torque limiter 65 is never idle or slipping. However, since there is no speed difference between the rollers 54 and 57 at the peripheral speed of the intermediate transfer belt 53, it is not necessary to absorb the speed difference in the normal running of the intermediate transfer belt 53, and the speed difference is not in the normal running state. The resulting problem does not occur.

Here, when the recording medium enters the intermediate transfer belt 53, for example, as described above, the recording medium collides with the intermediate transfer belt 53 to bend the intermediate transfer belt 53, or to the secondary transfer nip portion. Even if an attempt is made to change the belt linear velocity of the intermediate transfer belt 53 due to the resistance caused by the biting of the intermediate transfer belt 53, the speed increasing drive transmission means and the torque limiter 65 are applied from the outside in the axial direction of the second drive roller 57 which is also a counter roller. Since at least the rotational torque _TL is transmitted through the second transfer roller 57, the rotational driving force of the second drive roller 57 when the recording medium enters the secondary transfer nip can be secured. The intermediate transfer belt 53 always has a tension that prevents the intermediate transfer belt 53 from acting, and a resistance and a restoring force against the intermediate transfer belt 53. It is possible to reduce external factors that try to disturb the original belt linear velocity of the transfer belt 53.

  The principle of preventing the occurrence of shock jitter in the transfer apparatus of the present invention configured as described above will be described below with reference to FIG. 3 depicting the behavior of each moment when the recording medium is conveyed to the secondary transfer nip portion as in FIG. This will be described in more detail.

In FIG. 3A, as in FIG. 9A, when the leading end of the recording medium enters the intermediate transfer belt 53, the recording medium bends the intermediate transfer belt at the recording medium leading end contact position 18 in the pre-nip region. It is sectional drawing which shows the behavior of the moment which is going to do. The torque T _f shown in this figure is a value obtained by converting a force for bending the intermediate transfer belt 53 into a rotational torque on the second drive roller 57 when the leading end of the recording medium enters the intermediate transfer belt 53. It is. The rotational torque transmitted from the axial direction to the second drive roller 57 at the moment shown in FIG. 3A from the axial direction via the intermediate transfer belt 53 is from the first drive roller 54 via the intermediate transfer belt 53 as described above. The value obtained by subtracting the above-mentioned torque T _f from the transmitted rotational torque T ₁ , as described above, the second drive roller 57 passes from the outside in the axial direction via the speed increasing transmission means and the torque limiter 65. At least for the set torque T _L , the rotational torque for rotating the second drive roller 57 is transmitted, so that the tension that prevents the force to bend the intermediate transfer belt 53 acts on the intermediate transfer belt 53, It is possible to reduce an external factor that tends to disturb the original belt linear velocity of the intermediate transfer belt 53. Incidentally, contrary to the conditions described above, than the circumferential speed V ₁ of the first driving roller 54 conveys the intermediate transfer belt 53, the peripheral velocity V ₂ of the second driving roller 57 to convey the intermediate transfer belt 53 is set smaller In this case, when the second drive roller 57 rotates at the set torque _TL when the recording medium enters, the intermediate transfer belt 53 is always loosened, resulting in unstable belt conveyance. It cannot be adopted. Therefore, the speed increasing transmission drive means, the above peripheral speed V _2, the circumferential velocity V ₁ and whether at least the same speed, or must be configured to be able to accelerate. As will be apparent to those skilled in the art, when the torque _Tf is larger than the set torque _TL of the torque limiter 65, the torque limiter 65 slips or slips due to the action of the torque _Tf . The torque limiter setting torque _TL needs to be larger than the value of the torque _Tf .

Next, as shown in FIG. 3 (b), when the leading end of the recording medium is caught in the secondary transfer nip, a force acts to push down the transfer roller 58 by the thickness of the recording medium. The second drive roller 57, which is also the opposing roller, tries to decelerate. As described above, the second drive roller 57 is at least set torque from the outside in the axial direction via the speed increasing transmission means and the torque limiter 65. The _TL component is configured to transmit a rotational torque for rotating the second drive roller 57, so that the function of preventing the conveyance speed of the intermediate transfer belt 53 from being delayed always works. It will be. Therefore, the linear speed of the intermediate transfer belt 53 on the upstream side of the secondary transfer nip is prevented from being delayed. As a result, the image is transferred to the intermediate transfer belt 53 by the image forming units 20Y, 20M, 20C, and 20Bk in the primary transfer nip. The toner image is prevented from being misaligned, and a streak-like image having a dense pixel density in the sub-scanning direction on the recording medium is minimized.

Further, as shown in FIG. 3C, when the leading end of the recording medium passes through the secondary transfer nip, the intermediate transfer belt 53 that has been bent inward so far returns to a straight state again. The second drive roller 57 is also decelerated by the force, but as described above, the second drive roller 57 is at least set torque via the speed increasing transmission means and the torque limiter 65 from the outside in the axial direction. since T _L component is the rotational torque to rotate the second driving roller 57 is transmitted, so that the effect of preventing the belt linear speed of the intermediate transfer belt 53 to try Okureyo acts constantly. Accordingly, the linear speed of the intermediate transfer belt 53 on the upstream side of the secondary transfer nip is prevented from being delayed. As a result, the primary transfer is performed to the intermediate transfer belt 53 by the image forming units 20Y, 20M, 20C, and 20Bk in the primary transfer nip. The toner image is prevented from being misaligned, and a streak-like image having a dense pixel density in the sub-scanning direction on the recording medium is minimized.

Finally, after the above-described moments in FIGS. 3A to 3C have elapsed as shown in FIG. 3D, the intermediate transfer belt 53, the second drive roller 57 that is also a counter roller, and the transfer roller 58 is returned to the running state of the normal, therefore, the torque limiter 65 is again idle to slip since receiving the rotational torque T ₁ of the the first driving roller 54 via the intermediate transfer belt 53 from the second driving roller 57 side Will do. In FIG. 9, the belt linear velocity behavior when the present invention is implemented is indicated by a broken line, and as is apparent from FIG. 9, the first to third peaks that attempt to disturb the belt linear velocity decrease. You can see what is going on.

  FIG. 4 is a diagram schematically showing various variations of the present invention. An arrow indicated by a thick solid line in the figure indicates torque or action to be transmitted or generated. For example, on the intermediate transfer belt 53 in the figure, an arrow pointing to the lower left side indicates an intermediate transfer belt 53. Indicates the torque to drive the belt with the driving force from the drive source, and the arrow pointing upward on the right side disturbs the linear velocity of the intermediate transfer belt 53 when the recording medium enters the intermediate transfer belt 53. Expresses the action to be done.

  FIG. 4A corresponds to the first embodiment described above. In the first embodiment, the driving force from the motor 70 that is the driving source is first received by the gear 61 that is the driving transmission means, and the first driving roller 54 is directly transmitted with the rotational torque from the gear 61. The drive transmission means 61 further distributes the rotational torque to the speed increase drive transmission means so that the speed increase drive transmission means can transmit the rotational torque to the second drive roller 57 via the torque limiter 65. Composed.

  As shown in FIG. 4A, unlike the embodiment shown in FIG. 2, the torque limiter 65 and the acceleration drive transmission means can be interchanged. FIG. 5 is a cross-sectional view schematically showing an embodiment in which the torque limiter 65 and the speed increasing drive transmission means are interchanged. In FIG. 5, it can be seen that the torque limiter 65 is installed between the pulley 62 and the gear 61. Even if the torque limiter 65 is arranged in this way, it is possible to obtain the same effect as that of the embodiment shown in FIG.

  As a modification of the first embodiment shown in FIG. 4A, a second embodiment is shown in FIG. In the embodiment shown in FIG. 4B, the driving force from the motor 70 as the driving source is received by the gear 61 as the driving transmission means, and the driving force is directly transmitted to the first driving roller 54. Although it is the same as that of 1st embodiment, the acceleration drive transmission means and the torque limiter 65 are comprised by the shaft end part on the opposite side to the gear 61 transmitting rotational torque to the 1st drive roller 54. The point is different. In other words, the rotational drive transmission means and the torque limiter 65 are transmitted with the rotational torque not via the drive transmission means 61 but via the first drive roller 54. In the case of the second embodiment, the torque limiter 65 that is a transmission torque limiting means may be provided between the first drive roller 54 and the speed increasing drive transmission means, as in the first embodiment. You may provide between the 2nd drive roller 57 and the speed increase drive transmission means.

  Even if configured in this way, the speed increase drive transmission means and the torque limiter 65 acting on the second drive roller 57 can detect the linear speed fluctuation of the intermediate transfer belt 53 caused by the recording medium hitting the intermediate transfer belt 53. By preventing as much as possible, the first drive roller 54 can obtain the same effect as in the first embodiment without being directly affected by the linear speed fluctuation of the intermediate transfer belt 53 that occurs downstream in the conveyance direction of the first drive roller 54. Can do. 4B, the main roller for driving the intermediate transfer belt 53 is only the first drive roller 54 even when the recording medium enters the secondary transfer nip portion. Since the first drive roller 54 is not directly affected by the linear speed fluctuation of the intermediate transfer belt 53 that occurs on the downstream side in the conveyance direction of the first drive roller 54, it is possible to provide a stable belt running and is effective. It is.

As a further modification, a third embodiment is shown in FIG. In the embodiment shown in FIG. 4 (c), the driving source (first driving source) and the driving transmission means (first driving transmission means) for driving the first driving roller 54 are independent of the opposing rollers. A drive source (second drive source) and drive transmission means (second drive transmission means) for driving a certain second drive roller 57 are provided. However, as in the first and second embodiments, the peripheral speed V _{2 at} which the second drive roller 57 drives the intermediate transfer belt 53 is the peripheral speed V at which the first drive roller 54 drives the intermediate transfer belt 53. The second drive source and / or the drive transmission means are configured to be at least as fast as or faster than _1, and the second drive source transmits to the second drive roller 57 via the second drive transmission means. The rotational torque T ₂ is set to be equal to or less than the rotational torque T ₁ transmitted from the first drive source to the first drive roller 54. Further, the torque limiter 65 is a transmission torque limiting means is again in the set torque T _L or more, it is set so as not to transmit the rotational torque from the second drive source to the second driving roller 57, the set torque T _L Is set equal to or less than the rotational torque T ₂ transmitted from the second drive transmission means to the second drive roller 57. In the third embodiment, as shown in FIG. 4C, even if the torque limiter 65 and the drive transmission means are interchanged, that is, the driving force from the second drive source is used as the torque limiter 65 and the second drive. The same effect can be obtained regardless of the transmission means.

In such a configuration, the running drive state of the normal of the intermediate transfer belt 53 in a case where the peripheral velocity V ₂ is driven faster than the circumferential speed V _1, the torque limiter 65 which is powered connected to the second driving roller 57 , has been idle or slipping by the rotational torque T ₁ which is transmitted via the intermediate transfer belt 53 from the first driving roller 54, it is configured to converge the conveying speed difference between the intermediate belt 53 that occurs between the rollers Can do. However, in this case, the rotational torque T ₁ of the first driving roller 54 rotating torque T ₂ of the second driving roller 57 is a case identical, and, if the same setting torque T _L is also the rotational torque T ₂ are The difference in speed between the two rollers cannot be absorbed by the slipping or slipping of the torque limiter 65 and cannot be employed. Accordingly, the peripheral velocity V ₂ is driven faster than the peripheral velocity V _1, and, in the case the rotational torque T ₁ of the first driving roller 54 and the rotational torque T ₂ of the second drive roller is the same, set torque T _L Must be set at a rotational torque T ₂ or less from the drive source that drives the second drive roller 57. When the circumferential speed V ₂ is driven faster than the circumferential speed V ₁ and the rotational torque T ₂ of the second drive roller is equal to or less than the rotational torque T ₁ of the first drive roller 54, and the circumferential speed V ₂ is the circumferential speed. In the same case as V ₁ , the torque limiter 65 is idling or slipping due to the rotational torque T ₁ transmitted from the first drive roller 54 via the intermediate transfer belt 53, or travels in synchronization with the intermediate transfer belt 53. Driven.

Even in such a configuration, the second drive roller 57 is separately provided with respect to an impact that attempts to change the belt linear velocity of the intermediate transfer belt 53 by the recording medium entering the secondary transfer nip portion. Since at least the rotational torque _TL is transmitted among the rotational torques from the second drive source provided in the recording medium, the rotational drive force of the second drive roller 57 is ensured when the recording medium enters the secondary transfer nip portion. As a result, the same effects as those of the first embodiment and the second embodiment can be obtained.

  When configured as in the third embodiment, unlike the first and second embodiments, the speed-increasing drive transmission means can be omitted, so the drive source for driving the first drive roller 54 and the second drive roller 57 Each of the internal angular velocity fluctuations with the second drive source for driving the motor is prevented from being buffered to the drive rollers. Therefore, for example, the influence of load fluctuation or the like exerted on the secondary transfer nip portion by the recording medium is not transmitted to the first drive roller, so that it is possible to provide stable running of the intermediate transfer belt 53. It is effective.

  Further, the roller shaft positions of the first drive roller 54 and the second drive roller 57 are fixed with respect to each other, and the registration roller pairs 11 and 12 which are recording medium conveying means for conveying the recording medium to the secondary transfer nip portion. If the shaft position is fixed with respect to the roller shaft, the roller shaft is fixed regardless of the collision energy applied to the intermediate transfer belt 53 by the leading end of the recording medium. It is effective because it becomes possible to provide. If the axial positions of the first drive roller 54 and the second drive roller 57 and the registration roller pair 11 and 12 are not fixed, for example, the first drive roller 54 and the second drive roller 57 are intermediate. When the axial position of the transfer belt 53 is movable to apply tension, or when the axial positions of the registration roller pairs 11 and 12 are movable to apply conveyance force to the recording medium, the recording medium and the intermediate transfer belt are used. Each time the contact state with the roller 53 changes from FIG. 3A to FIG. 3D, each roller shaft fluctuates, and accordingly, the absolute position of the intermediate transfer belt 53 in the drive track moves. This also causes a change in the belt conveyance speed, and as a result, the intermediate transfer belt position is changed with respect to the toner image or the intermediate image formed in the primary transfer portion. . In order to prevent this reliably, the roller shaft positions of the first drive roller 54 and the second drive roller 57 are fixed with respect to each other as described above, and the recording medium is conveyed to the secondary transfer nip portion. It is more effective if the shaft positions are fixed with respect to the roller shafts of the registration roller pairs 11 and 12 as medium conveying means. In order to achieve the fixing of the respective shaft positions, the roller shafts of the first drive roller 54 and the second drive roller 57 and the roller shafts of the registration roller pairs 11 and 12 are connected to, for example, a housing of the image forming apparatus main body (not shown). This can be achieved by attaching it to the body in a fixed position.

  FIG. 6 is a sectional view and perspective view schematically showing a fourth embodiment of the present invention. In the fourth embodiment shown in FIG. 6, the deflection regulating means 30 is configured such that the recording medium conveyed from the registration roller pair 11, 12 between the first driving roller and the second driving roller is first applied to the endless belt. It is arranged in a region including the recording medium tip contact position 18 that is in contact with the surface opposite to the surface on which the recording medium contacts the intermediate transfer belt 53 (in the illustrated example, the inner peripheral surface of the intermediate transfer belt 53). Has been placed. The bending restricting means 30 includes a belt sliding contact material 31 and a belt sliding contact holding member 32, and the recording medium collides with the intermediate transfer belt 53 by always contacting the intermediate transfer belt 53. However, the intermediate transfer belt 53 is provided so as to be able to regulate the bending thereof. In the perspective view of FIG. 6, the recording medium tip contact position 18 is indicated by a two-dot chain line.

Here, even when the leading end of the recording medium conveyed to the secondary transfer nip collides with the intermediate transfer belt 53, the intermediate transfer belt 53 is prevented from being bent inward by the bending restricting means 30. However, even if the deflection regulating means 30 is provided, the deflection regulating means 30 and the intermediate transfer belt 53 are always in contact with each other, so that when the recording medium collides with the intermediate transfer belt 53, the collision is caused between the two. The resulting additional frictional force is generated. This frictional force, tension or the transport direction component of the intermediate transfer belt 53, because that can be a rotational torque T _b which acts on the opposite roller 57 as a factor disturbing the belt linear speed, than provided by the deflection restricting means 30 Not enough to reduce the occurrence of shock jitter.

  Therefore, as shown in FIG. 6, in addition to the deflection regulating means 30, a mechanism for preventing the linear speed fluctuation of the intermediate transfer belt 53 as described in the first to third embodiments is added. In addition to being able to prevent the action of bending the belt when the recording medium enters the intermediate transfer belt 53, it is possible to further prevent the occurrence of shock jitter, resulting in stable and high quality. A more effective configuration can be obtained for obtaining an image.

  The bend restricting means 30 is always provided in contact with the inner peripheral surface of the intermediate transfer belt 53 so that the intermediate transfer belt 53 is not bent when the recording medium first collides with the intermediate transfer belt 53. Therefore, it is necessary to have a rigidity that does not cause the intermediate transfer belt 53 to bend. Further, the inner transfer belt 53 is less worn on the inner peripheral surface, and the frictional resistance with the intermediate transfer belt 53 is less. Is desirable. The bending restricting means 30 is a structure (metal, resin, ceramic, etc., which is firmly supported by the image forming apparatus or the transfer apparatus via the belt sliding contact material holding member 32, but it has a predetermined Young's modulus or more. The belt sliding contact material 31 may be bonded, coated, plated, or the like, or may be attached with a fastening member such as a screw, a crimping tool, a rivet, or a snap pin. Alternatively, the belt sliding contact material 31 can be formed of the same material as the belt sliding contact holding member 32.

  Further, the above-described bending restricting means 30 is arranged in parallel with the intermediate transfer belt 53 in a state where the intermediate transfer belt 53 is stretched around a plurality of rollers without contacting the recording medium, that is, the recording. It is preferable that the medium is arranged so as to be parallel to the drive track in a state where no contact is made with the intermediate transfer belt 53. With this configuration, when the recording medium comes into contact with the intermediate transfer belt 53, the intermediate transfer belt 53 does not lift up against the deflection regulating means 30 parallel to the recording medium, and does not float. Since the endless belt is held by the area, stable belt traveling is possible.

FIG. 7 is a diagram showing a behavior in which shock jitter is prevented according to the fourth embodiment of the present invention. As is apparent from FIG. 7A, the recording medium conveyed to the secondary transfer nip portion. The intermediate transfer belt 53 does not bend even if the leading end of the belt collides with the intermediate transfer belt 53. Therefore, the rotational torque _Tf generated by the bending of the intermediate transfer belt 53 as shown in FIG. 3A does not occur, but the second driving roller 57 that is also the opposing roller generates due to the collision behavior. rotational torque T _b to be Midaso the linear speed of the intermediate transfer belt 53 is caused by the frictional force. However, as described above, the second drive roller 57 rotates to rotate the second drive roller 57 from the outside in the axial direction through the speed increasing transmission means and the torque limiter 65 at least for the set torque T _L. Since the torque is transmitted, the intermediate transfer belt 53 acts to prevent the force caused by this frictional force to disturb the belt linear velocity of the intermediate transfer belt 53, and the original belt linear velocity of the intermediate transfer belt 53 is reduced. It becomes possible to reduce the external factor which tries to disturb. Accordingly, this action prevents the intermediate transfer belt 53 from being displaced in the toner image primarily transferred to the intermediate transfer belt 53 at the primary transfer portion upstream of the driving direction at 20Y, 20M, 20C, and 20Bk. A streak-like image in which the pixel density in the sub-scanning direction on the recording medium is coarser is further less likely to occur.

  Further, as shown in FIG. 7B and FIG. 7C, even after the recording medium is caught in the secondary transfer nip portion, the intermediate transfer belt 53 is caused by the presence of the bending restricting means 30. Because of the straight state, streak-like image shock jitter is less likely to occur.

  The mechanism for buffering the impact when the recording medium enters the intermediate transfer belt, which is a preferred embodiment of the present invention, has been described above, but the present invention can be applied to other embodiments than the above-described embodiment. For example, in the above-described embodiment, the electrophotographic toner image shock jitter prevention mechanism has been mainly described. However, an inkjet type or chemical set type intermediate image using an intermediate transfer unit as shown in FIG. In addition, the effects of the present invention can be exhibited by adopting the same configuration for the drive roller 54 and the opposing roller 57. Also, an endless belt conveying device that conveys a recording medium in the sub-scanning direction for performing transfer, writing, printing, etc. in the image forming apparatus, and a driving roller that drives the endless belt by winding the endless belt around the roller; Even an endless belt conveyance device that forms a nip portion with a conveyance roller that applies pressure from the outside can be applied as a mechanism for buffering a rush impact that occurs when a recording medium passes.

1 is a cross-sectional view schematically showing an electrophotographic image forming apparatus to which a transfer device of the present invention is applied. FIG. 2 is a perspective view schematically showing a configuration around a secondary transfer portion of the image forming apparatus shown in FIG. 1. FIG. 6 is a diagram illustrating a behavior in which shock jitter is prevented according to the present invention, and FIG. 6A is a diagram illustrating a behavior due to a pre-nip entry at a moment when the leading end of the recording medium first contacts the intermediate transfer belt, and FIG. FIG. 8 is a diagram showing the behavior of the main nip entry at the moment when the leading end of the recording medium is caught in the secondary transfer nip, and (c) is a belt after the recording medium is caught in the secondary transfer part. FIG. 4D is a diagram illustrating a return behavior, and FIG. 4D is a diagram illustrating a steady state in which the fluctuation of the intermediate transfer belt is finished when the recording medium enters. It is a figure which shows typically the various variations of the structure of the rotational torque transmission path | route in the transfer apparatus of this invention, (a) is 1st embodiment, (b) is 2nd embodiment, (c) is 1st. Three embodiments are shown. FIG. 5 is a cross-sectional view schematically showing an example of an embodiment in which the speed increasing drive transmission unit and the transmission torque limiting unit in FIG. It is sectional drawing and perspective view which show a part of transfer apparatus of 4th embodiment of this invention roughly. FIG. 10 is a diagram illustrating a behavior in which shock jitter is prevented according to a fourth embodiment of the present invention, and (a) is a diagram illustrating a behavior due to a pre-nip entry at a moment when a leading end of a recording medium first contacts an intermediate transfer belt. And (b) is a diagram showing the behavior due to the entry of the nip at the moment when the leading end of the recording medium is caught in the secondary transfer nip, and (c) is the drawing showing that the recording medium is caught in the secondary transfer nip. FIG. 4D is a diagram illustrating a belt return behavior after being laid, and FIG. 4D is a diagram illustrating a steady state in which a change of the intermediate transfer belt is finished when a recording medium enters. FIG. 11 is a cross-sectional view schematically showing an electrophotographic image forming apparatus using a conventional intermediate transfer unit. FIG. 9A is a cross-sectional view schematically showing a behavior in which a shock jitter occurs in a secondary transfer portion of a conventional image forming apparatus, and FIG. 10A is a pre-nip at a moment when a leading end of a recording medium first contacts an intermediate transfer belt. FIG. 4B is a diagram illustrating the behavior due to rushing, and FIG. 5B is a diagram illustrating the behavior due to the nip rushing at the moment when the leading end of the recording medium is caught in the secondary transfer nip portion, and FIG. FIG. 6D is a diagram illustrating a belt return behavior after being bitten by a secondary transfer portion, and FIG. 6D is a diagram illustrating a steady state in which a behavioral change of the intermediate transfer belt is finished when a recording medium enters. FIG. 6 is a graph schematically showing fluctuations in the intermediate transfer belt linear velocity at the primary transfer portion that occur when the recording medium passes through the secondary transfer nip portion. FIG. 6 is a cross-sectional view schematically showing an ink jet type or chemical set type image forming apparatus using a conventional intermediate transfer unit.

Explanation of symbols

20Y, 20M, 20C, 20BK Image forming unit 21Y, 21M, 21C, 20BK Photoconductor 30 Deflection regulating means 54 First drive roller 57 Second drive roller (opposing roller)
61 Drive Transmission Means 62 Pulley 63 Timing Belt 64 Pulley 65 Transmission Torque Limiting Means 70 Drive Source 100 Inkjet Recording Head

Claims (6)

An endless belt that is stretched and driven by a plurality of rollers, and carries an image to be transferred to a recording medium; and
A transfer roller disposed opposite to the opposing roller, one of the plurality of rollers, with the endless belt interposed therebetween, and forming a transfer nip portion by pressing the endless belt with the opposing roller. And
In the transfer device in which the image carried on the endless belt is transferred to the recording medium conveyed from the recording medium conveying means to the transfer nip portion,
Drive transmission means that is disposed immediately upstream of the opposed roller as viewed in the driving direction of the endless belt, and that transmits a rotational torque from a driving source to a first drive roller that travels and drives the endless belt;
A speed increasing drive means for transmitting the rotational torque distributed from the drive transmission means to the counter roller and a transmission torque limiting means;
The counter roller is also configured as a second drive roller by transmitting rotational torque from the speed increasing drive means and transmission torque limiting means,
The speed-increasing drive means can increase the peripheral speed at which the second drive roller drives the endless belt at least the same speed as the peripheral speed at which the first drive roller drives the endless belt, or can increase the peripheral speed. Configured,
The transmission torque limiting means is configured to prevent rotational torque from being transmitted to the second drive roller above a set torque,
The transfer device according to claim 1, wherein the set torque is set to be equal to or less than a rotational torque at which the speed-increasing drive transmission means attempts to rotate the second drive roller. An endless belt that is stretched and driven by a plurality of rollers, and carries an image to be transferred to a recording medium; and
A transfer roller disposed opposite to the opposing roller, one of the plurality of rollers, with the endless belt interposed therebetween, and forming a transfer nip portion by pressing the endless belt with the opposing roller. And
In the transfer device in which the image carried on the endless belt is transferred to the recording medium conveyed from the recording medium conveying means to the transfer nip portion,
Drive transmission means that is disposed immediately upstream of the opposed roller as viewed in the driving direction of the endless belt, and that transmits a rotational torque from a driving source to a first drive roller that travels and drives the endless belt;
A speed increasing drive means and a transmission torque limiting means for transmitting the rotational torque transmitted to the first drive roller by the drive transmission means to the opposing roller via the first drive roller;
The counter roller is also configured as a second drive roller by transmitting rotational torque from the speed increasing drive means and transmission torque limiting means,
The speed-increasing drive means can increase the peripheral speed at which the second drive roller drives the endless belt at least the same speed as the peripheral speed at which the first drive roller drives the endless belt, or can increase the peripheral speed. Configured,
The transmission torque limiting means is configured to prevent rotational torque from being transmitted to the second drive roller above a set torque,
The transfer device according to claim 1, wherein the set torque is set to be equal to or less than a rotational torque at which the acceleration drive transmission means attempts to rotate the second drive roller. An endless belt that is stretched and driven by a plurality of rollers, and carries an image to be transferred to a recording medium; and
A transfer roller disposed opposite to the opposing roller, one of the plurality of rollers, with the endless belt interposed therebetween, and forming a transfer nip portion by pressing the endless belt with the opposing roller. And
In the transfer device in which the image carried on the endless belt is transferred to the recording medium conveyed from the recording medium conveying means to the transfer nip portion,
Drive transmission means that is disposed immediately upstream of the opposed roller as viewed in the driving direction of the endless belt, and that transmits a rotational torque from a driving source to a first drive roller that travels and drives the endless belt;
A second drive source and second drive transmission means provided separately from the drive source and drive transmission means for transmitting rotational torque to the first drive roller, wherein the second drive source and second drive transmission means are configured to transmit rotational torque to the opposing roller; A drive source and second drive transmission means;
A transmission torque limiting means configured to prevent the rotational torque transmitted to the opposing roller from being transmitted above a set torque;
The counter roller is also configured as a second drive roller by transmitting rotational torque from the second drive source from the second drive transmission means and transmission torque limiting means,
The second drive source and / or the second drive transmission means is configured such that the peripheral speed at which the second drive roller drives the endless belt is at least the same speed as the peripheral speed at which the first drive roller drives the endless belt, Or configured to be accelerated,
The rotational torque transmitted from the second drive source to the second drive roller via the second drive transmission means is set to be equal to or less than the rotational torque transmitted from the first drive source to the first drive roller. And
The set torque is a case where the second driving roller is configured to increase a circumferential speed at which the second driving roller drives the endless belt, and a speed at which the first driving roller drives the endless belt; and When the rotational torque transmitted from the two drive sources to the second drive roller is the same as the rotational torque transmitted from the first drive source to the first drive roller, the rotation from the drive source that drives the second drive roller Set below torque,
The circumferential speed at which the second drive roller drives the endless belt is configured to be faster than the circumferential speed at which the first drive roller drives the endless belt, and is transmitted from the second drive source to the second drive roller. When the rotational torque is less than or equal to the rotational torque transmitted from the first drive source to the first drive roller, and the peripheral speed at which the second drive roller drives the endless belt and the first drive roller When the peripheral speed for driving the endless belt is the same, the transfer device is set to be equal to or less than the rotational torque of the drive source for driving the second drive roller.   The first drive roller and the second drive roller are fixed in axial position with respect to each other, and further fixed in axial position with respect to the recording medium conveying means. 4. The transfer device according to any one of 3 above. Between the first drive roller and the second drive roller, the recording medium conveyed by the recording medium conveying means is disposed in a region including a recording medium front end contact position where the recording medium first contacts the endless belt, And the bending control means arrange | positioned at the surface on the opposite side to the surface where the said recording medium contacts the said endless belt is further provided,
5. The transfer device according to claim 1, wherein the bending of the endless belt is regulated by the bending regulating means always contacting the endless belt. 6.   An image forming apparatus comprising the transfer device according to claim 1.

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