JP2008064891A - Image forming apparatus and image forming method - Google Patents

Abstract

In an image forming apparatus for transferring a toner image from an intermediate transfer belt onto a recording medium, transfer unevenness and shock jitter are reduced in the image on the recording medium even when various recording media are used.
Toner images on photoreceptors 20Y, 20M, 20C, 20C, and 20K are sequentially transferred onto an intermediate transfer belt 14 to form a superimposed toner image, and a registration roller pair 4 and an intermediate transfer belt at a predetermined timing. The transfer paper 2 is sent out to a secondary transfer nip formed by the secondary transfer roller 5, the superimposed toner image is transferred onto the transfer paper 2, and the toner image transferred to the transfer paper is fixed by the fixing device 6. In the image forming apparatus,
After the leading edge of the transfer paper passes through the secondary transfer nip, the recording medium conveyance force of the registration roller pair is made smaller than the recording medium conveyance force before passing through the secondary transfer nip.
[Selection] Figure 1

Description

  The present invention relates to an image forming apparatus such as a copying machine, a facsimile, and a printer, and an image forming method.

  As an image forming apparatus for forming a color image, an apparatus using an intermediate transfer belt is widely known. In this apparatus, toner images formed on a plurality of photoconductors are sequentially transferred onto an intermediate transfer belt to form a superimposed toner image. Then, the superimposed toner image on the intermediate transfer belt is transferred onto a transfer sheet, which is a recording medium fed by a pair of registration rollers, at a transfer nip where the transfer roller contacts the intermediate transfer belt. At the transfer nip, the toner image is transferred onto the transfer paper, and at the same time, the transfer paper is sent out toward the fixing nip where the pressure member contacts the fixing member. At the fixing nip, the toner image on the transfer paper is fixed by heat and pressure, and at the same time, the transfer paper on which the toner image is fixed is sent out toward the paper discharge unit. In the image forming apparatus having such a configuration, the transfer paper is also sent out in the transfer nip and the fixing nip as described above. In the transfer nip, the transfer paper is sent out by the surface movement of the intermediate transfer belt that is rotationally driven by the drive roller, and in the fixing nip, the transfer paper is sent out by the rotational drive of either the fixing member or the pressure member. ing. In the image forming apparatus having such a configuration, the transfer paper is conveyed while being sandwiched between the registration roller pair and the transfer nip or the registration roller pair and the fixing nip via the transfer nip. That is, the transfer paper is simultaneously subjected to a conveying force from a plurality of locations.

In addition, there are various types of transfer paper used in the image forming apparatus, and characteristics such as thickness, surface friction coefficient, mass, and stiffness differ greatly from one another. Even if the conveying means is driven to give the same conveying force due to the change in the clamping pressure due to the difference in the thickness of the transfer paper or the difference in the friction coefficient, the conveying speed does not become constant. Also, depending on the thickness of the transfer paper and the difference in stiffness, even if the conveying means is driven so as to give the same conveying force, there are cases where the bending is increased and those which are decreased. In the apparatus that receives the conveying force simultaneously from the plurality of locations, a difference in the conveyance speed due to the characteristics of the transfer paper occurs at the plurality of locations, so that a large difference occurs in the speed relationship between the plurality of locations. Moreover, a big difference will be produced also in the bending method. As described above, in the apparatus that receives the conveying force simultaneously from a plurality of locations, the behavior in the conveying path varies greatly depending on the transfer paper. In other words, the transfer paper has different speed relationships at several locations, and there is almost no deflection, and the transfer paper stretches between the registration roller pair and the transfer nip, or the deflection is too large and slips at the transfer nip. I'll be relaxed. For this reason, it becomes difficult to stably transfer the transfer paper at a desired transfer speed at the transfer nip portion, and an abnormal image called black jitter and transfer unevenness may occur.

One method for generating black jitter is when the transfer paper conveyed between the registration roller pair and the transfer nip is less bent. If the transfer paper stretches due to the characteristics of the transfer paper or the speed relationship between the registration roller pair and the transfer nip, the transfer paper in the transfer nip portion is conveyed at the linear speed of the registration roller pair, and the intermediate transfer belt body However, it is driven to rotate at the linear speed of the registration roller pair together with the transfer paper. When the trailing edge of the transfer paper passes through the pair of registration rollers, the intermediate transfer belt is rotated again by the driving force of the driving unit that rotationally drives the intermediate transfer belt, but the driving force is applied to the intermediate transfer belt by the backlash of the driving unit. It is not transmitted immediately and stops for a moment. If the toner image is being transferred from the photosensitive member to the intermediate transfer belt during the stop, a shock jitter occurs in the image transferred to the intermediate transfer belt. The same thing occurs between the transfer nip and the fixing nip. When there is little bending between the transfer nip and the fixing nip, shock jitter is likely to occur on the transfer paper.

Transfer unevenness is also caused by the difference in transfer speed between the transfer sheet and the intermediate transfer belt at the transfer nip due to the difference in speed relationship between transfer sheets at multiple locations, and the transfer nip due to the amount of deflection before and after the transfer nip. Generated by slipping at the part.

  As described above, when the conveyance force is simultaneously received from a plurality of locations, it is difficult to stabilize the conveyance behavior corresponding to all the transfer sheets, and the abnormal image may be generated.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an image forming apparatus for transferring a toner image from an intermediate transfer belt onto a recording medium, even if various recording media are used. It is an object to provide an image forming apparatus and an image forming method capable of reducing uneven transfer and shock jitter in the upper image.

In order to achieve the above object, an invention according to claim 1 includes an image carrier carrying a toner image, an intermediate transfer member onto which the toner image of the image carrier is intermediately transferred, and the image transferred onto the intermediate transfer member. Transfer means for transferring a toner image to a recording medium, a registration roller driven to send the recording medium to the transfer means at a predetermined timing, and a fixing means for fixing the toner image transferred to the recording medium. In the image forming apparatus, after the leading edge of the recording medium passes through the transfer nip formed by the transfer means and the intermediate transfer member, the recording medium conveying force of the registration roller pair is recorded before passing through the transfer nip. Means for reducing the medium conveying force is provided.
According to a second aspect of the present invention, there is provided an image carrier that carries a toner image, an intermediate transfer member on which the toner image of the image carrier is intermediately transferred, and a toner image transferred to the intermediate transfer member on a recording medium. An image forming apparatus comprising: a transfer unit that transfers; a registration roller that is driven to send the recording medium to the transfer unit at a predetermined timing; and a fixing unit that fixes the toner image transferred to the recording medium. After the leading edge of the recording medium passes through the fixing nip formed by the fixing means, means for reducing the recording medium conveying force of the registration roller pair to be smaller than the recording medium conveying force before passing through the fixing nip is provided. It is characterized by this.
According to a third aspect of the present invention, in the image forming apparatus of the second aspect, after the leading edge of the recording medium passes through the transfer nip, the recording medium conveying force of the registration roller pair is increased before passing through the transfer nip. A means for reducing the recording medium conveying force is provided.
According to a fourth aspect of the present invention, in the image forming apparatus according to the first, second, or third aspect, a transfer prenip is formed at an upstream portion of the transfer nip with respect to the conveyance direction of the recording medium.
According to a fifth aspect of the present invention, in the image forming apparatus according to the first, second, third, or fourth aspect, the recording medium conveying force of the recording medium conveying means positioned upstream from the registration roller pair in the conveying direction of the recording medium. Further, at the same timing when the recording medium conveying force of the registration roller pair is reduced, a means for making the recording medium conveying force smaller than the previous recording medium conveying force is provided.
According to a sixth aspect of the present invention, in the image forming apparatus of the first, second, third, fourth or fifth aspect, the registration roller pair is separated as a means for reducing the recording medium conveying force of the registration roller pair. It is characterized by that.
According to a seventh aspect of the present invention, in the image forming apparatus according to the first, second, third, fourth or fifth aspect, as a means for reducing the recording medium conveying force of the registration roller pair, pressurization for pressing the registration roller pair It is configured to move relatively in the separation direction by a distance equal to or less than the free length of the spring.
According to an eighth aspect of the present invention, in the image forming apparatus of the first, second, third, fourth, or fifth aspect, as a means for reducing the recording medium conveying force of the registration roller pair, drive transmission to the registration roller pair is performed. It is characterized by being configured to cut.
According to a ninth aspect of the present invention, in the image forming apparatus of the first, second, third, fourth, fifth, sixth, seventh, or eighth aspect, the transfer is performed upstream of the registration roller pair in the conveyance direction of the recording medium. Means is provided for removing paper dust from the transfer medium without exerting a conveying force on the medium.
According to a tenth aspect of the present invention, there is provided an image carrier that carries a toner image, an intermediate transfer member on which the toner image of the image carrier is intermediately transferred, and a toner image transferred to the intermediate transfer member on a recording medium. Image formation in an image forming apparatus comprising: transfer means for transferring; registration rollers driven to feed the recording medium to the transfer means at a predetermined timing; and fixing means for fixing the toner image transferred to the recording medium In the method, after the leading end of the recording medium passes through the transfer nip formed by the transfer means and the intermediate transfer member, the recording medium conveying force of the registration roller pair is set to the recording medium before passing through the transfer nip. It is characterized by being smaller than the conveying force.

  According to these inventions, after the leading edge of the recording medium passes through the transfer nip and is sent out by the surface movement of the intermediate transfer belt, the recording medium conveying force by the registration roller pair is reduced, and a plurality of recording media are provided. Reduce one of the conveying forces simultaneously received from the location. Accordingly, the recording medium is easily conveyed at the surface moving speed of the intermediate transfer member, which is another conveying force received simultaneously from a plurality of locations. That is, by reducing the recording medium conveyance force by the registration roller pair at the above timing, the force that has affected the recording medium conveyance speed and conveyance behavior in the transfer nip is reduced. As a result, even when various recording media are used, it is possible to stabilize the conveyance speed and conveyance behavior of the recording medium at the transfer nip portion compared to the conventional case, and abnormal images such as transfer unevenness and shock jitter at the transfer nip portion. Generation can be reduced.

  As described above, according to the present invention, in an image forming apparatus that transfers a toner image from an intermediate transfer belt onto a recording medium, even if various recording media are used, transfer unevenness and shock jitter are reduced in the image on the recording medium. There is an excellent effect of being able to.

Hereinafter, as an image forming apparatus to which the present invention is applied, an embodiment of an electrophotographic color printer (hereinafter simply referred to as a printer) will be described.
First, the basic configuration of the printer will be described. FIG. 1 is a schematic configuration diagram of the printer. In the figure, a transfer belt unit 10 having an intermediate transfer belt 14 and four process units for generating toner images of yellow, magenta, cyan, and black (hereinafter referred to as Y, M, C, and K) are provided. ing. These four process units use different colors of Y, M, C, and K toners as image forming substances, but the other configurations are the same and are replaced when the lifetime is reached. For example, a process unit for generating a Y toner image includes a drum-shaped photoconductor 20Y as a latent image carrier, a drum cleaning device 40Y, a charge eliminating device (not shown), a charging device 30Y, a developing device 50Y, and the like. Yes. The process unit, which is an image forming unit, can be attached to and detached from the printer main body, so that consumable parts can be replaced at a time. Further, a toner bottle 9Y filled with toner is provided, and a predetermined replenishment amount is replenished to the developing device 50Y by a conveyance path (not shown).

  The charging device 30Y uniformly charges the surface of the photoreceptor 20Y that is rotated clockwise in the drawing by a driving unit (not shown). The uniformly charged surface of the photoreceptor 20 </ b> Y is exposed and scanned by the laser beam L to carry a Y electrostatic latent image. The electrostatic latent image of Y is developed into a Y toner image by a developing device 50Y using a Y developer containing Y toner and a magnetic carrier. Then, intermediate transfer is performed on an intermediate transfer belt 14 described later. The drum cleaning device 40Y removes toner remaining on the surface of the photoreceptor 20Y after the intermediate transfer process. The static eliminator neutralizes residual charges on the photoreceptor 20Y after cleaning. By this charge removal, the surface of the photoreceptor 20Y is initialized and prepared for the next image formation. In the other color process units as well, (M, C, K) toner images are formed on the photoreceptors (20M, C, K) in the same manner, and are intermediately transferred onto the intermediate transfer belt.

  The developing device 50Y has a developing roll disposed so as to be partially exposed from the opening of the casing. Further, it also has two conveying screws, a doctor blade, a toner concentration sensor (hereinafter referred to as a T sensor) and the like arranged in parallel to each other.

  A Y developer (not shown) containing a magnetic carrier and Y toner is accommodated in the casing of the developing device 50Y. This Y developer is triboelectrically charged while being agitated and conveyed by two conveying screws, and is then carried on the surface of the developing roll. Then, after the layer thickness is regulated by the doctor blade, it is transported to the developing region facing the Y photoconductor 20Y, where Y toner is attached to the electrostatic latent image on the photoconductor 20Y. By this adhesion, a Y toner image is formed on the photoreceptor 20Y. In the developing device 50Y, the Y developer that has consumed Y toner by the development is returned to the casing as the developing roll rotates.

  In FIG. 1 shown above, an optical writing unit 8 is disposed below the process unit. The optical writing unit 8 serving as a latent image forming unit irradiates each of the photoconductors 20Y, 20M, 20C, and 20K in the process unit with a laser beam L emitted based on the image information. By this exposure, electrostatic latent images for Y, M, C, and K are formed on the photoreceptors 20Y, 20M, 20C, and 20K. The optical writing unit 8 irradiates the photosensitive member through a plurality of optical lenses and mirrors while scanning the laser light (L) emitted from the light source with a polygon mirror rotated by a motor.

  On the lower side of the optical writing unit 8 in the figure, paper storage means having a paper storage cassette 1 and a paper feed roller 3 incorporated therein are disposed. The paper storage cassette 1 stores a plurality of transfer papers 2 as sheet-like recording media, and a paper feed roller 3 is brought into contact with the uppermost transfer paper 2. When the paper feed roller 3 is rotated counterclockwise in the drawing by a driving means (not shown), the uppermost transfer paper 2 is sent out toward the paper feed conveyance path. In this paper feed conveyance path, relay rollers 91 and 93 for conveying the transfer paper 2 and a double-sided roller 92 for conveying the transfer paper 2 sent out from the double-sided paper reversing unit provided on the left side of the printer are provided. ing.

  A registration roller pair 4 is disposed near the end of the paper feed conveyance path. The registration roller pair 4 rotates both rollers so as to sandwich the transfer paper 2, but temporarily stops rotating immediately after sandwiching. Then, the transfer paper 2 is sent out toward a secondary transfer nip described later at an appropriate timing.

  Above the process unit in the figure, there is disposed a transfer belt unit 10 that allows the intermediate transfer belt 14 as an endless moving body to move endlessly while stretching. The transfer belt unit 10 which is a transfer means and is an endless moving body unit includes a secondary transfer roller 5 and a belt cleaning device 13 in addition to the intermediate transfer belt 14. Further, four primary transfer rollers 12Y, 12M, 12C, and 12K, a secondary transfer backup roller 15, a cleaning backup roller 16, a tension roller 17 and the like are also provided. The intermediate transfer belt 14 is endlessly moved counterclockwise in the figure by the rotational drive of the secondary transfer backup roller 15 while being stretched around these seven rollers. The primary transfer rollers 12Y, 12M, 12C, and 12K hold the intermediate transfer belt 14 that is moved endlessly in this manner between the photoreceptors 20Y, 20M, 20C, and 20K, thereby forming primary transfer nips. . In these methods, a transfer bias having a polarity opposite to that of the toner (for example, plus) is applied to the back surface of the intermediate transfer belt 14 (inner surface of the loop). All the rollers except the primary transfer rollers 12Y, 12M, 12C, and 12K are electrically grounded. The intermediate transfer belt 14 sequentially passes through the primary transfer nips for Y, M, C, and K along with the endless movement thereof, and Y, M, and C on the photoreceptors 20Y, 20M, 20C, and 20K. , K toner images are superimposed and primarily transferred. As a result, a four-color superimposed toner image (hereinafter referred to as a four-color toner image) is formed on the intermediate transfer belt 14.

  The secondary transfer backup roller 15 sandwiches the intermediate transfer belt 14 between the secondary transfer roller 5 and forms a secondary transfer nip. The visible four-color toner image formed on the intermediate transfer belt 14 is transferred to the transfer paper 2 at the secondary transfer nip. Then, combined with the white color of the transfer paper 2, a full color toner image is obtained. Untransferred toner that has not been transferred to the transfer paper 2 adheres to the intermediate transfer belt 14 after passing through the secondary transfer nip. This is cleaned by the cleaning device 13. The transfer paper 2 on which the four-color toner images are collectively transferred at the secondary transfer nip is sent to the fixing device 6 via the post-transfer conveyance path.

  Next, the fixing device 6 will be described. FIG. 2 is a schematic configuration diagram illustrating an example of a fixing device, which includes a fixing belt 51, a fixing roller 57, a heating roller 58 as a fixing member, and a pressure roller 52 as a pressure member. The fixing roller 57 and the pressure roller 52 are rollers having silicon rubber on a metal core. The heating roller 58 is a hollow roller made of metal such as aluminum or iron and has a built-in heating means such as a halogen lamp 59, and the fixing belt 51 is heated from the inside through the heating roller by this radiant heat. . The fixing belt 51 has a silicone rubber layer and a release layer on a polyimide or nickel base material. The tension roller 53 is in contact with the front surface of the fixing belt 51 and applies tension to the fixing belt 51 by biasing means such as a spring. Further, a thermistor 64 that detects the temperature of the surface of the fixing belt is provided. The fixing belt 51 is heated to a temperature at which the unfixed toner image on the recording medium 2 is softened or melted by the heating roller 58. The pressure roller 52 as a pressure member is pressed against the fixing roller 57 via the fixing belt 51 to form a fixing nip. In the pressure roller 52, the driving force of the paper feed drive motor is transmitted by the paper feed drive unit, and the pressure roller 52 is rotationally driven. As the pressure roller 52 rotates, the fixing belt 51 rotates. The transfer paper 2 fed into the fixing device 6 is sandwiched between the fixing nips so that the unfixed toner image carrying surface is in close contact with the fixing belt 51. Then, the toner in the toner image is softened by the influence of heating and pressurization, and the full color image is fixed. Thereafter, the paper is discharged out of the apparatus by the paper discharge roller 7.

  Further, it can be used as a facsimile by connecting a telephone line (not shown) to the printer. Further, by providing a scanner for this print, it can be a copier.

Next, the characteristic part of the printer of this embodiment will be described. In the printer having the above configuration, the leading edge of the transfer paper 2 conveyed from the registration roller pair 4 passes through the secondary transfer nip formed by the secondary transfer roller 5 and the intermediate transfer belt 14 or is added to the fixing belt 51. After passing through the fixing nip formed by the pressure roller 52, a registration driving clutch (not shown) connected to the driving side registration roller of the registration roller pair 4 is disconnected. As a result, the conveying force at the registration roller pair 4 is eliminated. In this way, by eliminating the conveying force by the registration roller pair 4, one of the conveying forces that the transfer paper 2 receives simultaneously from a plurality of locations is reduced. For this reason, the transfer paper 2 is easily transported at the surface moving speed of the intermediate belt 14 which is another transport force received simultaneously from a plurality of locations. That is, by removing the transport force by the registration roller pair 4 at the above timing, the factors affecting the transport speed and transport behavior of the transfer paper 2 in the secondary transfer nip are reduced. As a result, even when the transfer paper 2 having various characteristics is used, the transfer speed and transfer behavior of the transfer paper 2 at the secondary transfer nip portion can be stabilized as compared with the conventional transfer paper. The occurrence of abnormal images can be reduced.

As described above, when the rotation of the driving side registration roller is turned on / off using an electromagnetic clutch, the arrangement of the registration roller pair 4 is not changed, and a part of the drive transmission path from the driving source to the registration driving roller is not changed. To cut. Therefore, the conveying force that the registration roller pair 4 applies to the transfer paper 4 can be reduced without changing the arrangement of the registration roller pair 4. Further, although the registration roller pair 4 does not have a conveyance force, the registration roller pair 4 can hold the vicinity of the rear end of the transfer paper 2 to perform stable transfer paper conveyance.

  Further, at the same timing as when the registration driving clutch is disengaged, the relay rollers 91 and 93, the double-sided roller 92, and the driving clutch for the paper feeding roller 3 provided on the upstream side of the paper feeding conveyance path from the registration roller pair 4. (Neither shown). As a result, the conveying force with respect to the transfer sheet 2 is also eliminated on the upstream side of the sheet feeding conveyance path from the registration roller pair 4. This further reduces the factors that affect the transfer speed and transfer behavior of the transfer paper in the secondary transfer nip, stabilizes the transfer speed, and reduces the occurrence of abnormal images such as transfer unevenness and shock jitter.

Further, the drive clutches of the paper feed roller 3 and the relay rollers 91 and 93 are engaged in accordance with the timing of the next toner image formation, and the next transfer paper 2 is transported from the paper feed cassette 1 into the transport path. Then, when the leading edge of the next transfer paper 2 reaches the registration roller pair 4, it is detected by a sensor (not shown), and the transfer paper 2 is again intermediated with the secondary transfer roller 5 by the registration roller pair 4 while taking a timing with this detection signal. It is conveyed to the secondary transfer nip of the transfer belt 14.

  Further, as shown in FIG. 1, this printer has a short conveying path length from the registration roller pair 4 through the secondary transfer nip to the fixing nip from the viewpoint of downsizing of the apparatus. Therefore, if the conveyance force of the registration roller pair 4 is lost immediately after passing through the secondary transfer nip, the conveyance may not be stable. Therefore, as described above, after the leading edge of the transfer paper 2 passes through the fixing nip and receives the conveying force by the fixing device 6, the conveying force by the registration roller pair 4 may be reduced. In this way, the transfer paper 2 is easily transported at the surface moving speed of the intermediate transfer belt 14 by reducing one of the transport forces received simultaneously from a plurality of locations. That is, by eliminating the conveyance force by the registration roller pair 4 at the above timing, the factors affecting the conveyance speed and conveyance behavior of the transfer paper 2 in the secondary transfer nip are reduced. As a result, even when various recording media are used, the transfer speed and transfer behavior of the transfer paper 2 at the secondary transfer nip can be stabilized compared to the conventional case, and abnormal images such as transfer unevenness and shock jitter are generated. Can be reduced.

  Further, in the case where the transfer force of the registration roller pair 4 is eliminated or reduced after the transfer paper 2 passes through the secondary transfer nip, the deflection amount of the transfer paper 2 between the registration roller pair 4 and the secondary transfer nip. May not be kept constant, and the posture of the transfer paper 2 at the entrance of the secondary transfer nip may vary. This change in the posture of the transfer paper 2 at the entrance of the secondary transfer nip can cause image defects such as abnormal discharge before transfer. Therefore, in addition to the secondary transfer nip, the secondary transfer roller 5 and the intermediate transfer belt 14 form a secondary transfer prenip on the upstream side thereof. FIG. 4 is an enlarged view of the secondary transfer portion. In addition to the secondary transfer nip formed by the secondary transfer roller 5 itself being in contact with the intermediate transfer belt 14 while being compressed, the intermediate transfer belt 14 is wound around the secondary transfer roller 5 on the upstream side thereof. A secondary transfer prenip is formed. In the secondary transfer prenip, as shown in FIG. 4, two roller tangent lines of the transfer counter roller 15 and the secondary transfer roller 5 are stretched between the secondary transfer backup roller 15 and the tension roller (entrance roller) 17. The transfer belt 14 is formed so as to have an angle that enters the inside of the transfer belt 14 (so as not to be parallel). In this manner, the transfer paper 2 and the toner are mechanically brought into contact with the upstream portion of the secondary transfer nip by the intermediate transfer belt 14 and the secondary transfer roller 5 and the posture of the transfer paper 2 can be corrected. By having a secondary transfer prenip that can be generated, image defects due to variations in the posture of the transfer paper 2 are prevented.

  Further, a fur brush 90 for removing paper dust is disposed in the paper feed conveyance path upstream of the pair of registration rollers 4 so as to touch the image transfer surface of the transfer paper 2, and the paper dust on the image transfer surface of the transfer paper 2. Remove. The fur brush 90 does not have a conveying force with respect to the transfer paper 2 and does not affect the behavior of the transfer paper 2. Further, by disposing in the paper feed conveyance path upstream from the registration roller pair, when the registration roller pair contacts and conveys the transfer paper 2, between the registration roller pair 4 and the secondary transfer nip. There is no possibility that the transfer state of the transfer paper 2 will be affected, and it is possible to prevent the registration roller from being stained with paper dust.

  Next, another specific means for reducing the conveying force at the registration roller pair 4 will be described. FIG. 3 is an enlarged view of the driving means for the registration roller pair 4. The registration roller pair 4 includes a registration driving roller 41 and a registration driven roller 42. The registration driven roller 42 is in pressure contact with the registration driving roller 41 by a registration roller pressing spring 43. The registration driven unit 46 including the registration driven roller 42 and the registration roller pressure spring 43 is configured to be rotatable with the registration movable fulcrum shaft 45 as a fulcrum. The distance between the axes of the registration driving roller 41 and the registration driven roller 42 can be controlled.

The leading edge of the transfer sheet 2 conveyed from the registration roller pair 4 passes through the secondary transfer nip formed by the secondary transfer roller 5 and the intermediate transfer belt 14 or the fixing belt 51. After passing through the fixing nip formed by the pressure roller 52, the driven roller contact / separation cam 44 rotates to increase the distance between the axes of the registration roller pair 4. As described above, when the registration roller pair 4 is separated, the distance between the axes of the registration roller pair 4 is not less than the free length of the registration roller pressure spring 43 or the maximum movement in the pressing direction of the registration driven roller 42 is possible. The driven roller contact / separation cam 44 is rotated until the distance is exceeded. As a result, the conveying force at the registration roller pair 4 is eliminated. In this way, by eliminating the conveyance force by the resist roller pair 4, the conveyance speed of the transfer paper 2 in the secondary transfer nip and the factors affecting the conveyance behavior are reduced to stabilize the conveyance speed, and abnormal images such as uneven transfer and shock jitter are generated. Preventing the occurrence of

As described above, by moving the registration driven roller 42 side, the registration roller pair 4 can be separated with a simple configuration without a gear train or belt for driving.

Further, although the registration roller pair 4 is not separated, the pressure applied to the transfer paper 2 may be reduced. In this case, the driven roller contact / separation is within a range in which the distance between the axes of the registration roller pair 4 is kept below the free length of the registration roller pressure spring 43 or below the maximum movable distance of the registration driven roller 42 in the pressure direction. The cam 44 is rotated. As a result, the conveying force at the registration roller pair 4 is reduced. In this way, by reducing the conveyance force by the registration roller pair 4, the conveyance speed of the transfer paper 2 in the secondary transfer nip and factors affecting the conveyance behavior are reduced, the conveyance speed is stabilized, and the abnormality in the secondary transfer nip portion is abnormal. Prevent image generation. Moreover, since the impact at the time of contact / separation is smaller than the complete separation, problems such as shock jitter due to the impact can be suppressed. Furthermore, although the conveyance force is small, the transfer roller 2 can be stably conveyed by holding the vicinity of the rear end of the transfer sheet 2 with the registration roller pair 4.

  Further, as described above, the registration roller pair 4 is not immediately after passing through the secondary transfer nip, but after the leading edge of the transfer paper 2 has passed through the fixing nip and has been fed by the fixing device 6 to be fed out. The conveyance force by may be reduced. Alternatively, the conveyance force by the registration roller pair 4 may be reduced to some extent immediately after passing through the secondary transfer nip, and the conveyance force may be reduced stepwise so as to be further reduced after passing through the fixing nip. By finely adjusting the way to reduce the transport force, the transport speed and transport behavior of the transfer paper 2 at the secondary transfer nip can be stabilized more efficiently, and abnormal images such as uneven transfer and shock jitter can be generated. Can be reduced.

  Further, as described above, the relay rollers 91 and 93, the duplex rollers 92 provided on the upstream side of the conveyance path with respect to the registration roller pair 4 at the same timing as changing the inter-axis distance of the registration roller pair 4; The conveying force of the paper feed roller 3 etc. is reduced. FIG. 5 shows a block diagram of the means for changing the distance between the axes of the relay roller 93 to reduce the conveying force. This eliminates the transport force applied to the transfer paper 2 in the upstream portion of the registration roller pair 4, reduces the transport speed of the transfer paper 2 in the secondary transfer nip and the factors that affect the transport behavior, stabilizes the transport speed, The occurrence of an abnormal image called shock jitter can be further reduced.

Further, in these cases in which the registration driven roller 42 moves, after the trailing edge of the transfer sheet 2 passes through the registration roller pair 4, the leading edge of the next transfer sheet 2 hits the registration roller pair 4. The registration driven roller 42 is returned to a position where a normal pressure can be applied during transfer paper transfer.

As described above, according to the present embodiment, after the leading edge of the transfer paper 2 passes through the secondary transfer nip, the conveyance force at the registration roller pair 4 is reduced. In this way, by reducing the conveying force by the registration roller pair 4, one influence of the conveying force that the transfer paper 2 receives simultaneously from a plurality of locations is reduced. Accordingly, the transfer paper 2 is easily transported at the surface moving speed of the intermediate belt 14 which is another transport force received simultaneously from a plurality of locations. That is, by removing the transport force by the registration roller pair 4 at the above timing, the factors affecting the transport speed and transport behavior of the transfer paper 2 in the secondary transfer nip are reduced. As a result, even when various types of transfer paper 2 are used, the transfer speed and transfer behavior of the transfer paper at the secondary transfer nip can be stabilized compared to the conventional case, and abnormal images such as transfer unevenness and shock jitter are generated. Can be reduced.
Further, after the leading edge of the transfer paper 2 passes through the secondary transfer nip, the conveying force at the registration roller pair 4 may be reduced. If the conveyance path length from the registration roller pair 4 through the secondary transfer nip to the fixing nip is short, the conveyance may not be stable if the conveyance force of the registration roller pair 4 is lost immediately after passing through the secondary transfer nip. . Therefore, after the leading edge of the transfer paper 2 passes through the fixing nip and receives a conveying force by the fixing device 6, the conveying force by the registration roller pair 4 is reduced. In this way, by reducing one of the conveyance forces that the transfer paper 2 receives simultaneously from a plurality of locations, the same effect as described above can be obtained, and the conveyance speed and conveyance behavior of the transfer paper 2 at the secondary transfer nip portion can be reduced. It can be stabilized, and the occurrence of abnormal images such as uneven transfer and shock jitter can be reduced.
Alternatively, the conveyance force by the registration roller pair 4 may be reduced to some extent immediately after passing through the secondary transfer nip, and the conveyance force may be reduced stepwise so as to be further reduced after passing through the fixing nip. By finely adjusting the manner of reducing the transport force, the transport speed and transport behavior of the transfer paper 2 at the transfer nip portion can be more efficiently stabilized.
Further, a secondary transfer prenip is formed in the upstream portion of the secondary transfer nip. In the case where the transfer force of the registration roller pair is eliminated or reduced after the transfer paper 2 passes through the secondary transfer nip, the amount of deflection of the transfer paper 2 between the registration roller pair 4 and the secondary transfer nip is small. There is a possibility that the posture of the transfer paper 2 at the entrance of the secondary transfer nip may fluctuate without being kept constant. This change in the posture of the transfer paper 2 at the entrance of the secondary transfer nip can cause image defects such as abnormal discharge before transfer. Therefore, the secondary transfer roller 5 and the intermediate transfer belt 11 correct the posture of the transfer paper 2 by forming a secondary transfer prenip on the upstream side in addition to the secondary transfer nip. Prevent image defects due to posture changes.
Further, at the same timing when the conveyance force of the registration roller pair 4 is reduced, the conveyance force of the conveyance means provided on the upstream side of the conveyance path from the registration roller pair 4 is reduced. As a result, the transport speed of the recording medium in the secondary transfer nip and the factors affecting the transport behavior are further reduced to stabilize the transport speed.
Further, as a means for reducing the conveying force of the registration roller pair 4, the registration roller pair 4 is configured to be separated. Thereby, almost no conveyance force for the transfer paper 2 can be eliminated.
Further, as a means for reducing the conveying force of the registration roller pair 4, the registration roller pair 4 is moved in the separation direction by a distance equal to or less than the free length of the pressure spring for pressing the registration roller pair. As a result, the pressure applied to the transfer paper 2 is reduced and the conveying force is reduced. Moreover, since the impact at the time of contact / separation is smaller than the complete separation, problems such as shock jitter due to the impact can be suppressed. Further, although the conveyance force is small, the registration roller pair 4 holds the vicinity of the rear end of the transfer paper 2 and can stably convey the transfer paper.
Further, the mechanism for moving the registration roller pair is performed by the movement of the registration driven roller 42. In this way, by moving the registration driven roller 42 side, the registration roller pair 4 can be separated with a simple configuration without a gear train or belt for driving.
Further, as a means for reducing the conveying force of the registration roller pair 4, the drive transmission of the registration roller pair 4 is cut off. As described above, if the drive transmission means is used, the conveying force applied to the transfer paper 4 by the registration roller pair 4 can be reduced without changing the arrangement of the registration roller pair 4. Further, although there is no conveyance force, the registration roller pair 4 can hold the vicinity of the rear end of the transfer paper 2 to perform stable transfer paper conveyance.
Further, a fur brush 90 for removing paper dust is disposed in the conveyance path upstream of the registration roller pair 4 so as to touch the image transfer surface of the transfer paper 2, and the paper dust on the image transfer surface of the transfer paper 2 is removed. To do. As a result, the registration roller pair 4 can be prevented from being stained with paper dust. The fur brush 90 does not have a conveying force with respect to the transfer paper 2 and there is no possibility of affecting the transfer state of the transfer paper 2 between the pair of registration rollers 4 and the secondary transfer nip.

1 is a schematic configuration diagram illustrating a printer according to an embodiment. FIG. 2 is a schematic configuration diagram illustrating a fixing device of the printer. FIG. 3 is an enlarged view of a driving unit for a registration roller pair of the printer. The enlarged view of the secondary transfer part of the printer. FIG. 4 is an enlarged view of a registration roller pair and a relay roller driving unit of the printer.

Explanation of symbols

1: Paper feed cassette 2: Transfer paper 3: Paper feed roller 4: Registration roller pair 5: Secondary transfer roller 6: Fixing device 7: Paper discharge roller 8: Optical writing unit 9Y, M, C, K: Toner bottle 10 : Transfer belt unit
12Y, M, C, K: primary transfer roller 13: belt cleaning device 14: intermediate transfer belt 15: secondary transfer backup roller (transfer driving roller)
16: Cleaning backup roller 17: Tension roller (entrance roller)
20Y, M, C, K: Photoconductors 30Y, M, C, K: Charging devices 40Y, M, C, K: Drum cleaning device 41: Registration drive roller 42: Registration driven roller 43: Registration roller pressure spring 44: Follower roller contact / separation cam 45: Registration movable fulcrum shaft 46: Registration driven unit 50Y, M, C, K: Developer 51: Fixing belt 52: Pressure roller (fixing drive roller)
57: Fixing roller 59: Heating roller 64: Thermistor 90: Fur brush 91: Relay roller 92: Reversing roller 93: Relay roller

Claims (10)

An image carrier that carries a toner image, an intermediate transfer member on which the toner image of the image carrier is intermediately transferred, a transfer unit that transfers the toner image transferred to the intermediate transfer member to a recording medium, and the transfer unit An image forming apparatus comprising: a registration roller that is driven to send the recording medium at a predetermined timing; and a fixing unit that fixes the toner image transferred to the recording medium.
After the leading edge of the recording medium passes through the transfer nip formed by the transfer means and the intermediate transfer member, the recording medium conveying force of the registration roller pair is set to be greater than the recording medium conveying force before passing through the transfer nip. An image forming apparatus comprising a means for reducing the size. An image carrier that carries a toner image, an intermediate transfer member on which the toner image of the image carrier is intermediately transferred, a transfer unit that transfers the toner image transferred to the intermediate transfer member to a recording medium, and the transfer unit In an image forming apparatus comprising: a registration roller that is driven to send a recording medium at a predetermined timing; and a fixing unit that fixes a toner image transferred to the recording medium.
Provided is a means for making the recording medium conveyance force of the registration roller pair smaller than the recording medium conveyance force before passing through the fixing nip after the leading edge of the recording medium has passed through the fixing nip formed by the fixing unit. An image forming apparatus.   3. The image forming apparatus according to claim 2, wherein after the leading edge of the recording medium passes through the transfer nip, the recording medium conveying force of the registration roller pair is made smaller than the recording medium conveying force before passing through the transfer nip. An image forming apparatus comprising a means.   4. The image forming apparatus according to claim 1, wherein a transfer prenip is formed at an upstream portion of the transfer nip with respect to a conveyance direction of the recording medium.   5. The image forming apparatus according to claim 1, wherein a recording medium conveying force of a recording medium conveying unit located upstream of the registration roller pair with respect to a conveying direction of the recording medium is a recording medium conveying of the registration roller pair. An image forming apparatus, characterized in that means for reducing the recording medium conveying force is provided at the same timing as when the force is reduced.   6. The image forming apparatus according to claim 1, wherein the registration roller pair is configured to be separated as means for reducing a recording medium conveying force of the registration roller pair. . 6. The image forming apparatus according to claim 1, wherein the registration roller pair is separated by a distance equal to or less than a free length of a pressure spring that pressurizes the registration roller pair as means for reducing the recording medium conveying force of the registration roller pair. An image forming apparatus configured to move relatively in a direction. 6. The image forming apparatus according to claim 1, wherein as a means for reducing a recording medium conveying force of the registration roller pair, drive transmission to the registration roller pair is cut off. Image forming apparatus. 9. The image forming apparatus according to claim 1, wherein no conveying force is exerted on the transfer medium upstream of the pair of registration rollers in the conveying direction of the recording medium. An image forming apparatus comprising means for removing paper dust from a transfer medium. An image carrier that carries a toner image, an intermediate transfer member on which the toner image of the image carrier is intermediately transferred, a transfer unit that transfers the toner image transferred to the intermediate transfer member to a recording medium, and the transfer unit In the image forming method in the image forming apparatus, the image forming apparatus includes: a registration roller that is driven to send the recording medium at a predetermined timing; and a fixing unit that fixes the toner image transferred to the recording medium.
After the leading edge of the recording medium passes through the transfer nip formed by the transfer means and the intermediate transfer member, the recording medium conveyance force of the registration roller pair is greater than the recording medium conveyance force before passing through the transfer nip. An image forming method characterized in that the image forming method is also reduced.

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