JP5561612B2 - Image forming apparatus - Google Patents

Description

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

  In this type of image forming apparatus, if a sudden speed change occurs in the intermediate transfer belt, which is a belt image carrier that is endlessly moved while being stretched by a plurality of stretching rollers, the latent image carrier may transfer to the primary transfer unit. As a result, the image transferred onto the intermediate transfer belt expands and contracts. For this reason, in the image transferred from the latent image carrier onto the intermediate transfer belt, light and shade are generated in a portion that should have a constant image density. Further, in a multi-color image forming apparatus that sequentially superimposes and transfers images of different colors on the intermediate transfer belt, color shift occurs due to the speed fluctuation of the intermediate transfer belt.

  The sudden change in the speed of the intermediate transfer belt described above is caused by passing a sheet as a transfer material through a secondary transfer nip formed by a secondary transfer roller and a counter roller facing the secondary transfer roller via the intermediate transfer belt. Occurs when paper is used.

  More specifically, as shown in FIG. 24, the leading edge of the sheet S enters the secondary transfer nip formed by the secondary transfer roller 133 and the secondary transfer counter roller 116 via the intermediate transfer belt 110, thereby The next transfer nip is expanded by the thickness of the sheet S. When the secondary transfer nip is expanded by the thickness of the paper S, a load is suddenly applied to the driving of the secondary transfer counter roller 116, and the rotation of the secondary transfer counter roller 116 is temporarily delayed. As a result, the belt amount fed from the driving roller 114 around which the upstream end of the secondary transfer nip upstream stretch surface is wound is larger than the belt amount fed by the secondary transfer counter roller 116. As a result, the stretch surface on the upstream side of the secondary transfer nip becomes loose.

  When the intermediate transfer belt 110 is slackened due to the load fluctuation caused by the transfer paper S entering the secondary transfer nip as described above, the driving roller 114, the driven roller 115, and the secondary transfer counter roller 116 stretch the tension. A speed fluctuation occurs in the intermediate transfer belt 110 that is laid and rotating. For this reason, if an image is transferred from the photosensitive drum 104 to the intermediate transfer belt 110 at the primary transfer portion at this time, the image quality deterioration as described above occurs due to the speed fluctuation.

  In the image forming apparatus described in Patent Document 1, the intermediate transfer belt is bent inward on the stretched surface on the upstream side of the secondary transfer nip of the intermediate transfer belt which becomes loose when the paper enters the secondary transfer nip. Thus, a tension roller that is urged by a spring from the outside is provided. When the tension on the secondary transfer nip upstream stretch surface of the intermediate transfer belt decreases, the tension roller is displaced inward by the spring biasing force, and the tension on the secondary transfer nip upstream stretch surface is increased. Thereby, when the sheet is passed through the secondary transfer nip, it is possible to suppress the occurrence of the speed fluctuation due to the decrease in the tension of the transfer surface upstream of the secondary transfer nip.

  However, in the image forming apparatus described in Patent Document 1, the tension roller is not displaced when the sheet enters the transfer nip, and the tension on the upstream surface of the secondary transfer nip is not increased. That is, after the paper enters the secondary transfer nip and the tension on the secondary transfer nip upstream stretch surface of the intermediate transfer belt is reduced, the tension roller is displaced and the secondary transfer nip upstream stretch surface The tension of is increased. For this reason, immediately after the sheet enters the secondary transfer nip, the stretched surface on the upstream side of the secondary transfer nip becomes loose, and as described above, the intermediate transfer belt 110 fluctuates in speed. At this time, if the image is transferred from the photosensitive drum 104 to the intermediate transfer belt 110 at the primary transfer portion, the image quality deterioration as described above occurs due to the speed fluctuation.

  Further, in the image forming apparatus described in Patent Document 1, in order to reduce the size of the apparatus, the intermediate transfer belt is stretched by being bent inward by 90 ° or more on the stretching surface on the downstream side of the secondary transfer nip. For this reason, local stress is generated at a position where the intermediate transfer belt is bent inward by 90 ° or more, and there is a problem that it is difficult to obtain durability of the intermediate transfer belt due to this local stress.

  Further, the intermediate transfer type image forming apparatus in which the toner image carrying belt is an intermediate transfer belt has been described so far. However, when transferring the toner image on the intermediate transfer belt to a sheet for image quality improvement, image transfer and image transfer are performed. The same problem may occur in the transfer section even in an image forming apparatus of a simultaneous transfer fixing system that performs fixing at the same time.

  Further, even in a direct transfer type image forming apparatus in which the toner image carrying belt is a photosensitive belt and the toner image on the photosensitive belt is directly transferred to a sheet by the transfer portion, the same problem may occur in the transfer portion. . In this case, when the sheet enters the transfer portion, the speed fluctuation of the photosensitive belt that has been driven at a constant speed until then occurs. Due to the speed fluctuation of the photosensitive belt, a deviation occurs between the exposure light irradiation timing for forming the latent image and the timing when the surface of the photosensitive belt passes the exposure position, and the positional deviation of the latent image formed on the photosensitive belt is shifted. A malfunction that occurs may occur.

  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 capable of suppressing the speed fluctuation of the belt image carrier when the transfer material enters the transfer nip.

In order to achieve the above object, the invention of claim 1 is directed to a loop-shaped belt image carrier that is endlessly moved while being stretched by a plurality of tension rollers, and the plurality of tension belts via the belt image carrier. A transfer roller that faces one of the gantry rollers and abuts against the front surface, which is the outer surface of the loop of the belt image carrier, to form a transfer nip, is provided to the transfer material sandwiched in the transfer nip. An image forming apparatus comprising: a transfer unit that transfers an image carried on the front surface; and an area upstream of the transfer nip of the belt image carrier in the belt image carrier moving direction in the vicinity of the transfer roller. The contact member that contacts the contact member, and the contact member and the transfer roller are supported, and the tension of the belt image carrier increases in accordance with the displacement of the transfer roller when the transfer material enters the transfer nip. Displaced in the direction Possess the interlocking means that the interlocking means regulates the transfer roller supporting member supporting the transfer roller, and the contact member supporting member supporting the contact member, the distance between each of the support member restrainer It is characterized by comprising a member .
According to a second aspect of the present invention, in the image forming apparatus according to the first aspect , a distance between the transfer roller support member and the contact member support member can be adjusted by the restriction member. It is.
According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect , the abutting member is moved against the belt image carrier by gravity applied to the abutting member itself or the abutting member supporting member. In this way, the loop abuts from the inside to the outside.
The invention of claim 4 is the image forming apparatus according to claim 1 or 2, urges for urging said contact member so as to abut against the outer loop inside against the belt image carrier It has the means.
The invention of claim 5, claim 1, in the image forming apparatus 3 or 4, adjusting the position of the contact member with respect to the belt image bearing member in accordance with the thickness of the transfer material It is characterized by.
According to a sixth aspect of the present invention, in the image forming apparatus according to the fifth aspect , the image forming apparatus further comprises a transfer material thickness detecting means for detecting the thickness of the transfer material, and the thickness is detected by the transfer material detecting means. The position of the abutting member with respect to the belt image carrier is adjusted.
The invention of claim 7 is the image forming apparatus according to claim 1, 2, 3, 4 or 5, provided in the vicinity of the transfer nip, a heating means for heating the belt image carrier or a transfer material And the toner image on the belt image carrier is transferred to the transfer material and fixed at the transfer nip at the same time.

  In the present invention, the abutting member is displaced in a direction in which the tension of the tension surface on the upstream side of the transfer nip of the belt image carrier is increased in conjunction with the displacement of the transfer roller when the transfer material enters the transfer nip. As a result, immediately after the transfer material enters the transfer nip, the tension on the upstream surface of the transfer nip is increased by the contact member, and a decrease in the tension on the upstream surface of the transfer nip can be suppressed. Therefore, it is possible to suppress the speed fluctuation of the belt image carrier that occurs due to the decrease in the tension of the tension surface on the upstream side of the transfer nip immediately after the transfer material enters the transfer nip.

  As described above, according to the present invention, there is an excellent effect that the speed fluctuation of the belt image carrier when the transfer material enters the transfer nip can be suppressed.

1 is a schematic configuration diagram of an image forming apparatus according to an embodiment. 1 is a schematic configuration diagram of a conventional image forming apparatus. The figure which shows the speed fluctuation | variation of a middle transfer drive roller and a driven roller. FIG. 6 is a schematic diagram of a sheet on which a toner image in which positional deviation has occurred is transferred. (A) A diagram showing the transmission of force when the paper enters the pre-nip portion, (b) an enlarged explanatory view near the secondary transfer nip when the paper enters the pre-nip portion, (c) the paper enters the pre-nip portion. The graph explaining the speed fluctuation when entering. (A) A diagram showing the transmission of force when the paper enters the main nip, (b) an enlarged view of the vicinity of the secondary transfer nip when the paper enters the main nip, and (c) the paper is in the main nip. The graph explaining the speed fluctuation | variation at the time of entering a part. Explanatory drawing of the mechanism in which both the intermediate transfer drive roller and the entrance roller decelerate due to the entry of the main nip portion of the paper. (A) The figure which showed transmission of force when the pre-nip area | region of an intermediate transfer belt returns, (b) The expansion explanatory view of the secondary transfer nip vicinity when the pre-nip area | region of an intermediate transfer belt returns, (c) Intermediate transfer belt The graph explaining the speed fluctuation | variation by returning the pre-nip area | region of. 6 is a graph showing a relationship between displacement of a tension roller and a secondary transfer roller and speed fluctuations of a middle transfer driving roller and a driven roller. The figure which shows an example of a conventional structure. The figure which shows the other example of a conventional structure. 1 is a schematic configuration diagram of a main part of an image forming apparatus according to Configuration Example 1. FIG. FIG. 5 is a detailed view of the operation of the mechanism according to Configuration Example 1; FIG. 5 is a schematic configuration diagram of a main part of an image forming apparatus according to Configuration Example 2. The graph which shows the simulation result of the relationship between the elapsed time from the time of paper rushing, and a driven roller linear velocity fluctuation rate. FIG. 10 is an enlarged view of the vicinity of a secondary transfer unit of an image forming apparatus according to Configuration Example 3. The control circuit diagram of a cam position switching mechanism. The flowchart of mode switching. The flowchart of the control which changes the amount of abutting to a pressing roller support member with paper thickness. The block diagram in the case of performing paper thickness detection. FIG. 6 is an operation flowchart when the mode is switched by detecting the thickness of a sheet. FIG. 10 is a schematic configuration diagram of an image forming apparatus having a transfer fixing device according to Configuration Example 5. FIG. 10 is a schematic configuration diagram of an image forming apparatus having a transfer fixing device of another configuration according to Configuration Example 5. FIG. 6 is a schematic diagram illustrating a state in which the tension state of the intermediate transfer belt is changed when the transfer material enters the secondary transfer nip.

Hereinafter, an embodiment of an image forming apparatus to which the present invention is applied will be described.
FIG. 1 is a schematic configuration diagram of an image forming apparatus according to the present embodiment. The image forming apparatus includes four process units 100Y, 100C, 100M, and 100Bk for forming yellow (Y), cyan (C), magenta (M), and black (Bk) toner images. Further, a sheet conveyance path composed of a plurality of guide plates for conveying the recording sheet in the apparatus, a registration roller pair 9, a fixing device 15, an optical writing unit (not shown), a transfer unit 50, and the like are also provided.

  The image forming apparatus according to the present embodiment has a so-called tandem configuration in which four process units 100Y, 100C, 100M, and 100Bk are arranged along an endless moving direction with respect to an intermediate transfer belt 2 described later.

  The process units 100Y, 100C, 100M, and 100Bk for the respective colors share a common support as a unit with the photosensitive drums 1Y, 1C, 1M, and 1Bk as latent image carriers and various devices disposed around the photosensitive drums 1Y, 1C, 1M, and 1Bk. It is supported by the body and is detachable from the printer unit main body. The configuration is the same except that the colors of the toners used are different.

  Taking the Y process unit 100Y as an example, a charging device 103Y, a developing device 101Y, a drum cleaning device 102Y, and the like are provided around a photosensitive drum 1Y as a toner image carrier. The photosensitive drum 1Y of the process unit 100Y is driven to rotate counterclockwise in the drawing by a driving unit (not shown). The charging device 103Y uniformly charges the peripheral surface of the rotationally driven photosensitive drum 1Y to the same polarity as the charging polarity of the toner. An optical writing unit (not shown) drives a laser diode based on image information, and irradiates the rotating charged photosensitive drum 1Y while deflecting the laser light in the direction of the rotation axis, respectively. Perform optical scanning processing. Thereby, an electrostatic latent image based on the Y image information is formed on the photosensitive drum 1Y. As the photosensitive drum 1Y, a drum-like member is used in which a photosensitive layer is formed by applying a photosensitive organic photosensitive material on a base tube made of aluminum or the like. However, an endless belt may be used.

  The developing device 101Y develops the electrostatic latent image on the photosensitive drum 1Y using a two-component developer (hereinafter simply referred to as a developer) containing a magnetic carrier (not shown) and non-magnetic Y toner. Instead of the two-component developer, a type that develops with a one-component developer not containing a magnetic carrier may be used.

  The Y toner image formed on the photosensitive drum 1Y by development is transferred to the front surface of the intermediate transfer belt 2 at a Y primary transfer nip described later. The transfer residual toner adhering to the photosensitive drum 1Y after the Y toner image is transferred in this way is removed from the surface of the photosensitive drum 1Y by the drum cleaning device 102Y. Prior to this cleaning, the surface of the photosensitive drum 1Y is discharged by receiving light from a discharge lamp (not shown).

  Although the Y process unit 100Y has been described, M, C, and Bk toner images are similarly formed on the surfaces of the photosensitive drums 1M, 1C, and 1Bk in the M, C, and Bk process units.

  A transfer unit 50 is disposed below the four process units 100Y, 100C, 100M, and 100Bk. The transfer unit 50 has an intermediate transfer belt 2 as a toner image carrying belt. The intermediate transfer belt 2 is stretched by stretching rollers such as a medium transfer driving roller 3, a secondary transfer counter roller 5, a tension roller 6, a driven roller 7, and an entrance roller 4. The intermediate transfer belt 2 is endlessly moved in the clockwise direction in the figure by the rotational drive of the intermediate transfer driving roller 3 while being in contact with the photosensitive drums 1Y, 1C, 1M, and 1Bk. As a result, primary transfer nips for Y, C, M, and Bk where the photosensitive drums 1Y, 1C, 1M, and 1Bk and the intermediate transfer belt 2 are in contact with each other are formed.

  In the vicinity of the primary transfer nips for Y, C, M, and Bk, the intermediate transfer belt 2 is moved to the photosensitive drums 1Y, 1C, 1M, and 1Bk by primary transfer rollers 54Y, 54C, 54M, and 54Bk disposed inside the belt loop. It is pushing toward. A primary transfer bias is applied to the primary transfer rollers 54Y, 54C, 54M, and 54Bk by a power source (not shown). As a result, a primary transfer electric field for electrostatically moving the toner images on the photosensitive drums 1Y, 1C, 1M, and 1Bk toward the intermediate transfer belt 2 is formed in the primary transfer nips for Y, C, M, and Bk. ing.

  In the drawing, toner images are sequentially formed at the primary transfer nips on the front surface of the intermediate transfer belt 2 that sequentially passes through the primary transfer nips for Y, C, M, and Bk with endless movement in the clockwise direction. Overlaid and primary transferred. By this primary transfer of superposition, a four-color superposed toner image (hereinafter referred to as a four-color toner image) is formed on the front surface of the intermediate transfer belt 2.

  A secondary transfer roller 8 serving as an abutting member is disposed below the intermediate transfer belt 2 in the drawing, and a portion of the intermediate transfer belt 2 that is wound around the secondary transfer counter roller 5 is contacted from the belt front surface. A secondary transfer nip is formed in contact therewith. Thus, a secondary transfer nip is formed in which the front surface of the intermediate transfer belt 2 and the secondary transfer roller 8 are in contact with each other. The shaft center of the secondary transfer roller 8 is located upstream of the shaft center of the secondary transfer counter roller 5 in the paper transport direction. In this embodiment, the secondary transfer roller 8 is driven to rotate counterclockwise in the figure by a motor (not shown). Note that the secondary transfer roller 8 may be rotated around the intermediate transfer belt 2.

  A secondary transfer bias having the same polarity as the toner is applied to the secondary transfer counter roller 5 in the belt loop by a power source (not shown). On the other hand, the secondary transfer roller 8 outside the belt loop is grounded. Thereby, a secondary transfer electric field is formed in the secondary transfer nip.

  A registration roller pair 9 is disposed on the right side of the secondary transfer nip in the drawing. In parallel with the image formation, the paper feed roller 18 is rotated to feed out the paper 19 as a transfer material from the paper feed cassette 20, separated one by one by the separation roller 17, put into the paper transport path, and transported by the transport roller 16. Then it stops against the registration roller pair 9. Alternatively, the paper on the manual feed portion is fed out, put into the paper conveyance path, and abutted against the registration roller pair 9 and stopped.

  The sheet 19 sandwiched between the registration rollers is sent to the secondary transfer nip at a timing that can be synchronized with the four-color toner image on the intermediate transfer belt 2. In the secondary transfer nip, the four-color toner images on the intermediate transfer belt 2 are collectively transferred to a sheet as a transfer material by the influence of the secondary transfer electric field and the nip pressure, and a full color image is formed in combination with the white color of the sheet.

  On the front surface of the intermediate transfer belt 2 that has passed through the secondary transfer nip, untransferred toner that has not been transferred to the paper at the secondary transfer nip adheres. This untransferred toner is cleaned by a belt cleaning device (not shown) that contacts the intermediate transfer belt 2.

  The sheet 19 that has passed through the secondary transfer nip is fed toward the fixing device 15 by the conveyance force between the intermediate transfer belt 2 and the conveyance belt 11. The fixing device 15 is configured by pressing the pressure roller 12 against a fixing belt 13 a stretched between a fixing roller 13 and a heating roller 14. The fixing belt 13a is heated by an IH coil (not shown) in the heating roller 14, and is heated to a temperature necessary for image fixing. On the other hand, the pressure roller 12 also incorporates a heater (not shown) and is used for preheating during standby. The unfixed image on the paper is fixed on the paper 19 by applying heat and pressure at the nip portion between the fixing belt 13 a and the pressure roller 12. The heater of the fixing device 15 does not have to use an IH coil, and may be a system constituted by a pair of heat rollers.

  The fixing device 15 applies heat and pressure to fix the transferred image, and then the paper is discharged to a paper discharge tray (not shown). Alternatively, the image is again guided to the transfer position by a double-side reversing mechanism (not shown), and an image is recorded and fixed on the back surface, and then discharged to a paper discharge tray.

  The secondary transfer roller 8 that is in contact with the intermediate transfer belt 2 to form a secondary transfer nip includes a metal cored bar and an elastic member such as rubber coated on the peripheral surface thereof. In the secondary transfer nip, the portion of the intermediate transfer belt 2 that is wound around the secondary transfer counter roller 5 bites into the elastic member on the surface of the secondary transfer roller 8. Thereby, a wide secondary transfer nip is formed.

  Next, problems of the intermediate transfer belt 2 of the conventional image forming apparatus will be described. FIG. 2 is a schematic configuration diagram of a conventional image forming apparatus, and the basic configuration is substantially the same as that of the image forming apparatus of the present embodiment, and thus description thereof is omitted.

When the sheet 19 enters the secondary transfer nip portion, the intermediate transfer driving roller 3 that stretches a region (hereinafter referred to as a primary transfer region) that contacts the photosensitive drums 1Y, 1C, 1M, and 1Bk of the intermediate transfer belt 2 The driven roller 7 undergoes speed fluctuation as shown in FIG. Such a phenomenon is particularly noticeable when a thick paper is passed (in this example, a continuous weight of 220 [kg] paper, a basis weight of 256 [g / m ² ] paper or more is assumed).

  On the other hand, the photosensitive drums 1Y, 1C, 1M, and 1Bk are rotationally driven at substantially the same speed even when the leading edge of the sheet enters the secondary transfer nip, so that the photosensitive drums 1Y, 1C, 1M, and 1Bk and the intermediate transfer belt are driven. A speed difference occurs between the two. Due to this speed difference, a transfer position shift occurs in the primary transfer nip.

  FIG. 4 is an explanatory diagram schematically showing a sheet 19 on which a toner image having a transfer position shift as described above is transferred as a final image when a single color image is formed.

  A toner image including a transfer position shift in the primary transfer nip that occurs when the leading edge of the sheet enters the secondary transfer nip is defined on the sheet 19 at a position L from the leading edge of the sheet, where L is the distance from the primary transfer nip to the secondary transfer nip. Transfer or transfer / fixing. For this reason, as shown in FIG. 4, the final image on the paper 19 to be ejected is a local area I2 that is lighter in color than the normal image portion I1 or a portion I3 that is darker than the normal image portion I1. The image has a typical density unevenness.

  Note that, when images of a plurality of colors are formed, the distances from the primary transfer nip to the secondary transfer nip are different for each color, so that images having different distances L from the leading edge of the paper to the density unevenness are output for each color.

  Thus, in order to prevent the transfer position shift in the primary transfer nip that occurs when the secondary transfer nip enters the leading edge of the paper, the speed fluctuations of the intermediate transfer driving roller 3 and the driven roller 7 when the secondary transfer nip enters the leading edge of the paper. It is necessary to suppress it. The mechanism by which the speed fluctuations of the intermediate transfer driving roller 3 and the driven roller 7 occur will be described below.

  In the image forming apparatus according to the present embodiment, as shown in FIG. 1, the axial center of the secondary transfer roller 8 is located upstream of the axial center of the secondary transfer counter roller 5 in the sheet conveyance direction. For this reason, the nip where the outer peripheral surface of the intermediate transfer belt 2 contacts the secondary transfer roller 8 has the following two nip portions. That is, the inner peripheral surface of the intermediate transfer belt 2 is in a secondary transfer nip (hereinafter referred to as a main nip portion) that is in contact with the secondary transfer counter roller 5 and upstream of the secondary transfer nip in the sheet conveying direction. The inner peripheral surface of the intermediate transfer belt 2 has a nip portion that is not in contact with the secondary transfer counter roller 5 (hereinafter referred to as a pre-nip portion).

  As described above, since the image forming apparatus of the present embodiment has the main nip portion and the pre-nip portion, the speed fluctuations of the intermediate transfer driving roller 3 and the driven roller 7 are roughly divided into the following three fluctuations. ing.

<(1) Speed fluctuation due to the leading edge of the paper 19 entering the prenip>
FIG. 5 is an explanatory diagram of speed fluctuation that occurs when the leading edge of the paper 19 enters the pre-nip portion. When the leading edge of the sheet enters the pre-nip portion, a stretch region (hereinafter referred to as pre-nip region T3) between the secondary transfer counter roller 5 and the entrance roller 4 which is a stretch surface on the upstream side of the transfer nip of the intermediate transfer belt 2 is pushed inward. It is. When the pre-nip region T3 of the intermediate transfer belt 2 is pushed inward, the portion of the pre-nip region T3 on the upstream side in the moving direction of the intermediate transfer belt from the contact portion with the front end of the sheet is intermediate transfer as shown in FIG. Pulled in the belt moving direction. As a result, as shown in FIG. 5B, the inlet roller 4 is subjected to a pulling force I2 in the same direction as the intermediate transfer belt moving direction, and the inlet roller 4 is subjected to a torque E2 in the same direction as the rotational direction. As a result, the entrance roller 4 is accelerated.

  Further, as indicated by an arrow F (2) in FIG. 5A, the force I2 pulling in the same direction as the moving direction of the intermediate transfer belt is transmitted to the intermediate transfer driving roller 3 via the intermediate transfer belt 2, and the intermediate transfer belt 3 is rotated. Torque in the same direction as the rotation direction is applied to the drive roller 3, and the intermediate transfer drive roller 3 is accelerated as shown by a thick line in FIG. Finally, as shown by an arrow F (2) in FIG. 5A, a force I2 pulling in the same direction as the intermediate transfer belt moving direction is transmitted to the driven roller 7 via the intermediate transfer belt 2. The As a result, the driven roller 7 is accelerated as indicated by the thick line in FIG.

  Further, a portion of the pre-nip region T3 of the intermediate transfer belt 2 on the downstream side in the intermediate transfer belt moving direction is pulled in the direction opposite to the intermediate transfer belt moving direction. As a result, as shown in FIG. 5B, the secondary transfer counter roller 5 is subjected to a pulling force I1 in the direction opposite to the intermediate transfer belt moving direction, and the secondary transfer counter roller 5 has a rotational direction. A reverse torque E1 is applied. Thereby, the secondary transfer counter roller 5 is decelerated.

  Further, the force I1 pulling in the direction opposite to the moving direction of the intermediate transfer belt is transmitted to the tension roller 6 and the driven roller 7 via the intermediate transfer belt 2 as indicated by an arrow F (1) in FIG. The Considering the transmission path, the force I2 pulling in the same direction as the intermediate transfer belt moving direction is transmitted to the driven roller 7 and the driven roller 7 is accelerated before the driven roller 7 is accelerated by the force I1 pulling in the direction opposite to the intermediate transfer belt moving direction. 7 should slow down. However, looking at FIG. 5C, the driven roller 7 is not decelerated by the force I1 pulling in the direction opposite to the moving direction of the intermediate transfer belt. In this embodiment, since the secondary transfer roller 8 is driven by a motor different from the intermediate transfer roller 3, the secondary transfer roller 8 is pulled in the direction opposite to the moving direction of the intermediate transfer belt by the rotational driving force of the secondary transfer roller 8. This is probably because the force I1 has disappeared.

  As shown in FIG. 5B, the intermediate transfer driving roller 3 is accelerated by the force I2 pulled in the intermediate transfer belt moving direction, whereby the primary transfer region T1 of the intermediate transfer belt 2 is accelerated. As a result, as shown in FIG. 4, a portion I2 having a lighter color than the portion I1 of the normal image is generated.

<(2) Speed fluctuation caused by the leading edge of the paper 19 entering the nip portion>
FIG. 6 is an explanatory diagram of speed fluctuations that occur when the leading edge of the sheet enters the main nip portion that is the secondary transfer nip.

  The speed fluctuation due to the leading edge of the sheet 19 entering the main nip portion is caused by the secondary transfer counter roller 5 being pushed by the leading edge of the sheet 19 pushing down the secondary transfer roller 8 when the leading edge of the sheet 19 enters the main nip portion. Is a decrease that decelerates.

  Here, the mechanism by which the secondary transfer counter roller 5 decelerates will be described with reference to FIG. As shown in FIG. 7, in order for the leading end of the sheet 19 to enter the main nip portion, the leading end of the sheet 19 needs to push down the secondary transfer roller 8 by an amount corresponding to the thickness of the sheet 19.

  As shown in FIG. 7, the secondary transfer roller 8 is urged in the direction of arrow A in the figure by the urging coil spring 10b. In order to push down the secondary transfer roller 8, the force (arrow B in the figure) that the leading edge of the paper 19 pushes down the secondary transfer roller 8 needs to exceed the urging force of the urging coil spring 10b. The force B that pushes down the leading edge of the sheet 19 is a conveying force that conveys the leading edge of the sheet to the right side in the figure, and the conveying force is the rotational driving force C of the secondary transfer counter roller 5. That is, when the leading edge of the sheet 19 comes into contact with the secondary transfer roller 8, the leading edge of the sheet pushes down the secondary transfer roller 8 to the secondary transfer counter roller 5 in addition to the torque for transporting the intermediate transfer belt 2. The torque required for this is generated. As a result, as shown in FIG. 6B, the rotational load (arrow D1 in the figure) of the secondary transfer counter roller 5 increases, and the secondary transfer counter roller 5 decelerates.

  On the other hand, the entrance roller 4 is also decelerated similarly to the secondary transfer counter roller 5. This is because when the leading edge of the sheet 19 enters the main nip portion, the sheet 19 does not advance until the leading edge of the sheet 19 pushes down the secondary transfer roller 8, so that the belt travels due to the frictional force between the intermediate transfer belt 2 and the sheet. A load J2 is generated. The belt running load J2 causes a torque D2 in the direction opposite to the rotation direction to act on the entrance roller 4, and the entrance roller 4 is similarly decelerated.

  The belt running load J2 is transmitted to the intermediate transfer driving roller 3 through the intermediate transfer belt 2 as shown by an arrow (3) in FIG. The belt traveling load transmitted to the intermediate transfer driving roller 3 is canceled out by the driving force of the motor that rotationally drives the intermediate transfer driving roller 3, so that the driven roller upstream of the intermediate transfer driving roller 3 in the intermediate transfer belt moving direction. 7 is not transmitted.

  When the secondary transfer counter roller 5 decelerates, a stretch region (hereinafter referred to as a tension control region T2) between the secondary transfer counter roller 5 and the driven roller 7 which is a stretch surface on the downstream side of the transfer nip of the intermediate transfer belt 2 is intermediate transfer. Pulled in the direction opposite to the belt moving direction, and a force J1 in the direction opposite to the intermediate transfer belt moving direction is transmitted to the tension roller 6 and the driven roller 7 as shown by an arrow F (4) in FIG. The

  When the force J1 pulling in the direction opposite to the direction of movement of the intermediate transfer belt is transmitted to the driven roller 7, the driven roller 7 is decelerated as shown by the bold line in FIG. As the driven roller 7 decelerates, the primary transfer region T1 of the intermediate transfer belt 2 is pulled in the direction opposite to the direction of movement of the intermediate transfer belt, and torque in the direction opposite to the rotation direction is applied to the intermediate transfer drive roller 3. As a result, the intermediate transfer driving roller 3 is decelerated as indicated by the thick line in FIG.

  As described above, the driven roller 7 and the intermediate transfer driving roller 3 are decelerated. As a result, the primary transfer region T1 of the intermediate transfer belt 2 is decelerated, and the portion I3 that is darker than the normal image portion I1 as shown in FIG. Will occur.

<(3) Speed fluctuation due to return of the pre-nip region T3 of the intermediate transfer belt 2 after the leading edge of the sheet has entered the nip portion>
FIG. 8 is an explanatory diagram of fluctuation due to the return of the pre-nip region T3 of the intermediate transfer belt 2 after the leading edge of the sheet has entered the main nip portion.

  As shown in FIG. 8B, when the leading edge of the sheet pushes down the secondary transfer roller 8 and enters the main nip portion, the pre-nip region T3 of the intermediate transfer belt 2 that has been pushed inward by the leading edge of the sheet 19 until now is formed. Return to the original. As a result, a phenomenon opposite to the above <(1) Speed fluctuation caused by the leading edge of the paper 19 entering the pre-nip portion> occurs.

  That is, a force G1 that pushes the intermediate transfer belt 2 in the same direction as the intermediate transfer belt movement direction is generated on the downstream side in the intermediate transfer belt movement direction from the position where the front end of the sheet in the pre-nip region T3 pressed the intermediate transfer belt 2. .

  On the other hand, a force G2 that pushes the intermediate transfer belt 2 in the direction opposite to the intermediate transfer belt movement direction is generated on the upstream side in the intermediate transfer belt movement direction from the position where the front end of the sheet in the prenip region T3 pressed the intermediate transfer belt 2. To do.

  The force G2 for pushing the intermediate transfer belt 2 in the direction opposite to the moving direction of the intermediate transfer belt is driven by the entrance roller 4 or the intermediate transfer via the intermediate transfer belt 2 as shown by an arrow F (6) in FIG. It is transmitted to the roller 3. A force G2 that pushes the entrance roller 4 in a direction opposite to the moving direction of the intermediate transfer belt is generated, and a torque H1 in the direction opposite to the entrance roller rotation direction is generated in the entrance roller 4 as shown in FIG. The roller 4 decelerates. Similarly, torque in the direction opposite to the rotation direction of the intermediate transfer drive roller is generated in the intermediate transfer drive roller 3, and the speed of the intermediate transfer drive roller 3 decreases as shown by the thick line in FIG. 8C.

  On the other hand, the force G1 for pushing the intermediate transfer belt 2 in the same direction as the moving direction of the intermediate transfer belt is indicated by an arrow F (5) in FIG. Or to the tension roller 6 or the driven roller 7. When a force G1 that pushes the intermediate transfer belt 2 in the direction opposite to the direction of movement of the intermediate transfer belt is transmitted to the secondary transfer counter roller 5, as shown in FIG. Torque H2 in the same direction is generated, and the secondary transfer counter roller 5 is accelerated. Similarly, a torque in the same direction as the driven roller rotation direction is generated in the driven roller 7, and the speed of the driven roller 7 increases as shown by a thick line in FIG. 8C.

  FIG. 9 is experimental data on the relationship between the speed fluctuations of the driven roller 7 and the intermediate transfer driving roller 3 and the displacements of the tension roller 6 and the secondary transfer roller 8.

  As shown in FIG. 9, the tension roller 6 suddenly starts almost simultaneously with the start of the above-described <(2) Speed fluctuation due to the leading edge of the paper 19 entering the nip portion>. It can be seen that the intermediate transfer belt starts to be displaced outward. This means that the tension roller 6 is pushed down to the outside of the intermediate transfer belt due to an increase in belt tension (tension) between the secondary transfer counter roller 5 and the driven roller 7 of the intermediate transfer belt 2.

  If the tension roller 6 is not provided, there is no relaxation of the belt tension due to the tension roller 6 being pushed down to the outer side of the intermediate transfer belt. Accordingly, the deceleration of the driven roller 7 is increased.

  It can also be seen that the secondary transfer roller 8 starts to be displaced outward (downward in the drawing) almost simultaneously with the tension roller 6 starting to be displaced outwardly of the intermediate transfer belt. Therefore, if the belt tension in the tension control region T2 can be weakened in conjunction with the displacement of the secondary transfer roller 8, the load torque for decelerating the secondary transfer counter roller 5 can hardly be transmitted to the driven roller 7, and the driven roller 7 In addition, a decrease in the speed of the intermediate transfer driving roller 3 can be suppressed, and a decrease in the speed of the primary transfer region T1 of the intermediate transfer belt 2 can be suppressed.

  Here, as shown in FIG. 10, a pressing roller 41 is installed outside the intermediate transfer belt near the downstream side in the intermediate transfer belt moving direction from the secondary transfer nip, and a cleaning device 60 for cleaning the intermediate transfer belt 2. Is located downstream of the pressing roller 41 in the direction of movement of the intermediate transfer belt, the pressing roller 41 comes into pressure contact with the transfer residual toner 70 on the intermediate transfer belt 2 before being removed by the cleaning device 60. For this reason, a part of the transfer residual toner 70 is transferred from the intermediate transfer belt 2 to the pressing roller 41, and the pressing roller 41 may become dirty or the toner may be scattered. It is not preferable to do so.

  Further, as shown in FIG. 11, when the pressing roller 41 is installed inside the intermediate transfer belt near the downstream side in the intermediate transfer belt moving direction from the secondary transfer nip, before the sheet 19 enters the secondary transfer nip. The pressing roller 41 bites into the intermediate transfer belt 2 from the inner side to the outer side by a predetermined amount (solid line in the figure), but after the sheet 19 enters the secondary transfer nip, the pressing roller 41 moves to the intermediate transfer belt 2. Retreat inward (dotted line in the figure). Therefore, the contact pressure and contact angle of the cleaning blade 51 with respect to the intermediate transfer belt 2 change before and after the sheet 19 enters the secondary transfer nip. Although it is sufficient if there is a margin in the cleaning performance of the cleaning device 60, there is a possibility that cleaning failure may occur due to the entry of the sheet 19 into the secondary transfer nip.

[Configuration example 1]
FIG. 12 is an overall configuration diagram of this configuration example, in which the pressing roller 41 is disposed inside the intermediate transfer belt in the vicinity of the upstream side of the secondary transfer nip so as to abut on the outer side from the inner side of the intermediate transfer belt. .

  The secondary transfer unit 10 that rotatably supports the secondary transfer roller 8 is rotatable with respect to the apparatus main body about the secondary transfer unit rotation fulcrum 43 by an eccentric cam 48 that is rotatably provided on the apparatus main body. Is provided. Further, the secondary transfer unit 10 includes a tension spring support point 46 provided below the secondary transfer unit and a tension spring support point 45 provided on the apparatus main body side above the tension spring support point 46. The pulling force of the tension spring 44 supported at both ends urges a force to rotate the secondary transfer unit 10 counterclockwise in the drawing around the secondary transfer unit rotation fulcrum 43.

  When the sheet enters, the pressing roller 41 is displaced to the outside of the intermediate transfer belt by its own weight in conjunction with the vertical downward displacement of the secondary transfer unit, thereby generating an acceleration force in the primary transfer region T1 of the intermediate transfer belt 2. Thus, the load force (main nip entry fluctuation) generated when the secondary transfer nip enters the leading edge of the paper is to be offset.

  On the other hand, when the sheet 19 leaves the secondary transfer nip, the pressing roller 41 is displaced inward of the intermediate transfer belt in conjunction with the vertical upward displacement of the secondary transfer unit, so that the primary transfer of the intermediate transfer belt 2 is performed. In the region T1, a force opposite to the load force generated when the sheet 19 comes out of the secondary transfer nip is generated to suppress the load force.

  With this mechanism, it is possible to solve problems such as a change in cleaning performance in which the pressing roller 41 is contaminated with toner remaining after transfer or toner is scattered, and a transfer position shift in the primary transfer nip caused by a speed variation of the intermediate transfer belt 2 is achieved. Can be obtained.

FIG. 13 is a detailed view of the operation of this mechanism.
The pressing roller support member 47 supports the pressing roller 41 at one end on the upstream side in the intermediate transfer belt movement direction, and the other end on the downstream side in the intermediate transfer belt movement direction rotates around the rotation axis of the entrance roller 4. It is provided as follows.

  As a regulating member that regulates the distance between the secondary transfer unit 10 and the pressing roller support member 47, a cam 32 is fixed and installed on the secondary transfer unit side, and the cam 32 contacts the pressing roller support member 47. As a result, the secondary transfer unit 10 can no longer approach the pressing roller support member 47, and the distance between the two is regulated. In this embodiment, the cam 32 is provided in the secondary transfer unit 10, but the cam 32 may be provided in the pressing roller support member 47.

<When the secondary transfer part is not pressurized>
When the secondary transfer nip is not pressed, the secondary transfer unit 10 is pushed downward by the eccentric cam 48 and rotated clockwise around the secondary transfer unit rotation fulcrum 43 as shown in FIG. Thus, by separating the secondary transfer roller 8 from the intermediate transfer belt 2, the pressing roller support member 47 rotates in the clockwise direction in the drawing by its own weight or the weight of the pressing roller 41 around the axis of the entrance roller 4. Then, the pressing roller 41 bites and presses the intermediate transfer belt 2 from the inner side to the outer side by a predetermined amount.

<At the time of pressurizing the secondary transfer section (before entering the paper)>
When the secondary transfer nip is pressed, as shown in FIG. 13B, the pressing of the secondary transfer unit 10 by the eccentric cam 48 is released, and the secondary transfer unit 10 is subjected to the secondary transfer by the tension force of the tension spring 44. The secondary transfer roller 8 is brought into contact with the intermediate transfer belt 2 by rotating counterclockwise in the figure around the unit rotation fulcrum 43. Further, as described above, when the secondary transfer unit 10 rotates, the cam 32 abuts against the pressing roller support member 47 and the pressing roller support member 47 is pushed up by the cam 32, and the pressing roller support member 47 becomes the entrance roller. 4 rotates around the axis 4 in the counterclockwise direction in the figure, and the pressing roller 41 retracts a predetermined amount inside the intermediate transfer belt.

<After entering the paper>
When the secondary transfer nip enters the leading edge of the sheet, as shown in FIG. 13C, the cam 32 is pushed down together with the secondary transfer unit 10 by an amount corresponding to the sheet thickness. As a result, the pressing roller support member 47 rotates around the axis of the entrance roller 4 in the clockwise direction in the figure by its own weight or the weight of the pressing roller 41, and the pressing roller 41 moves the intermediate transfer belt 2 from the inner side to the outer side. And the intermediate transfer belt 2 is pulled.

  With such a configuration, the pressing roller 41 can pull the intermediate transfer belt 2 by a predetermined amount toward the outer side of the intermediate transfer belt 2 at the timing of entering the secondary transfer nip at the leading edge of the sheet. In the primary transfer region T1, it is possible to cancel a load force generated when the secondary transfer nip enters the leading edge of the sheet.

  Further, there is no need to provide a sensor for detecting a change in the tension of the intermediate transfer belt 2 or use an actuator to displace the pressing roller 41, and the secondary transfer unit 10 and the pressing roller 41 are independent of each other. Since it is supported by the support member, the operability when the secondary transfer unit 10 is pulled out from the apparatus main body to the front side in the drawing and taken out of the apparatus is improved.

In this mechanism, when printing on thick paper of 300 [g / m ² ] or more, if the sheet 19 is sandwiched between the secondary transfer roller 8 and the intermediate transfer belt 2 at the secondary transfer nip, it is pressed against the cam 32. It is designed to be separated from the roller support member 47. At this time, the secondary transfer unit 10 is pulled upward by the pulling force of the tension spring 44, so that the secondary transfer roller 8 is pressed against the intermediate transfer belt 2 and good transfer can be performed at the secondary transfer nip. Nip pressure is generated.

On the other hand, when printing paper less than 300 [g / m ² ] paper, when the paper 19 is sandwiched between the secondary transfer roller 8 and the intermediate transfer belt 2 at the secondary transfer nip, the cam 32 and the pressing roller support member 47 is not separated, and the nip pressure of the secondary transfer nip is reduced by the contact force between the cam 32 and the roller support member 47. Therefore, in order to suppress such a decrease in the nip pressure, it is necessary to increase the tensile force of the tension spring 44 correspondingly. However, even if the nip pressure is decreased, it is not always necessary to increase the tension force of the tension spring 44 as long as the transfer image is not greatly affected.

[Configuration example 2]
FIG. 14 is an overall configuration diagram in Configuration Example 2. In this configuration example, in addition to the configuration of the configuration example 1, a tension spring 52 that applies a tension force that rotates the pressing roller support member 47 clockwise around the axis of the entrance roller 4 is a pressing roller. It is attached to the other end side of the support member 47. Accordingly, the pressing roller 41 presses the intermediate transfer belt 2 from the inside to the outside by not only the weight of the pressing roller 41 and the pressing roller support member 47 but also the tensile force of the tension spring 52.

  When the pressing roller 41 is pressed against the intermediate transfer belt 2 only by the weight of the pressing roller 41 or the pressing roller support member 47 as in the configuration example 1, in order to set a larger pressing force, the pressing roller 41 It is necessary to increase the volume or to provide a stay on the pressing roller support member 47 separately. On the other hand, if the configuration is such that the pressing roller 41 is pressed against the intermediate transfer belt 2 using the tension force of the tension spring 52 as in this configuration example, it can be freely set by setting the spring constant and spring displacement of the tension spring 52. Since the pressing force can be set, the above-described problems are eliminated.

  Since the operation in this configuration example is the same as that in configuration example 1, the description of the operation is omitted.

<Suppression effect by simulation>
FIG. 15 shows a comparison of the speed fluctuation of the driven roller after the sheet 19 enters the secondary transfer nip between the conventional apparatus and the apparatus of this configuration example. The calculation conditions are such that the cam 32 and the pressing roller support member 47 are separated from each other after the sheet 19 enters the secondary transfer nip, and the secondary transfer unit between the conventional apparatus and the apparatus of this configuration example is designed. It is assumed that the tension force of the tension spring 44 pulling up 10 is the same. FIG. 15 shows the result when a sheet 19 having a basis weight of 359 [g / m ² ] is passed. Even when such a thick sheet enters the secondary transfer nip, the apparatus of this configuration example uses the conventional apparatus. In comparison, a speed fluctuation suppressing effect of about 60 [%] can be obtained.

[Configuration example 3]
In the configuration example 1 and the configuration example 2, the cam 32 and the pressing roller support member 47 are designed to be separated after entering the secondary transfer nip of the sheet 19 when printing thick paper of 300 [g / m ² ] or more. It is. For this reason, when printing on paper thinner than that, the cam 32 and the roller support member 47 are not separated even after the paper 19 enters the secondary transfer nip, and the nip pressure in the secondary transfer nip decreases. Transfer performance may be impaired.

  FIG. 16 is an overall view of a configuration in Configuration Example 3. In this configuration example, the cam 32 fixed to the secondary transfer unit 10 as a regulating member that regulates the distance between the secondary transfer unit 10 and the pressing roller support member 47 in the configuration example 1 and the configuration example 2 is provided. The eccentric transfer cam 33 is provided so as to be rotatable with respect to the secondary transfer unit 10. The position of the eccentric cam 33 is controlled by a motor (not shown) so that a plurality of abutting amounts against the pressing roller support member 47 can be set.

  In this configuration example, mode 1 is a mode in which the eccentric cam 33 is not abutted against the pressing roller support member 47, and mode 2 is a mode in which the eccentric cam 32 is abutted against the pressing roller support member 47 by a predetermined amount. Provided.

Mode 1 is used, for example, when printing on plain paper or thin paper of less than 300 [g / m ² ] paper. As a result, the speed fluctuation of the intermediate transfer belt 2 when the sheet 19 enters the secondary transfer nip is relatively smaller than when thick paper is used, and when printing on plain paper or thin paper that is less likely to cause density unevenness due to transfer position deviation in the primary transfer nip. When printing is performed in the state of mode 1, the eccentric cam 33 and the pressing roller support member 47 are not always in contact with each other, so that the transfer can be performed without reducing the nip pressure of the secondary transfer nip.

On the other hand, mode 2 is used when printing thick paper of 300 [g / m ² ] or more, for example. Before the sheet 19 enters the secondary transfer nip, the eccentric cam 33 and the pressing roller support member 47 come into contact with each other, so that the nip pressure in the secondary transfer nip decreases. However, since the eccentric cam 33 and the pressing roller support member 47 are designed to be separated from each other after the sheet 19 enters the secondary transfer nip, it decreases before the sheet 19 enters the secondary transfer nip. Further, the nip pressure of the secondary transfer nip returns to the same level as when the mode 1 is executed, and the image can be transferred from the intermediate transfer belt 2 to the sheet 19 with a predetermined nip pressure.

That is, in this configuration example, when using plain paper or thin paper (less than 300 [g / m ² ] paper) in which the speed fluctuation of the intermediate transfer belt 2 is small when the paper 19 enters the secondary transfer nip, the eccentric cam 33 is used. Mode 1 is executed in which the paper is not pressed against the pressing roller support member 47, and thick paper (300 [g / m ² ] paper or more) having a large speed fluctuation of the intermediate transfer belt 2 when the paper 19 enters the secondary transfer nip is used. In this case, mode 2 in which the eccentric cam 33 is abutted against the pressing roller support member 47 is executed, and the transfer can be selected with a predetermined nip pressure while suppressing the load fluctuation.

  FIG. 17 is a control circuit diagram of the eccentric cam position switching mechanism 28 that switches the position of the eccentric cam 33. As shown in FIG. 17, when a command from a CPU (not shown) is input to the microprocessor 26 in the drive command unit 25, the microprocessor 26 displaces the pressing roller 41 stored in the memory 27 in advance. The drive voltage value corresponding to the amount is taken out and sent to the drive driver 29 of the eccentric cam position switching mechanism 28 to rotate the motor 30.

  FIG. 18 shows a flowchart of mode switching between mode 1 and mode 2 in this configuration example. In this configuration example, it is normally set so that the printing process is performed using the mode 1, and when the mode switching is OFF, the mode 1 in which the eccentric cam 33 is not pressed against the pressing roller support member 47 is executed. When mode switching is ON, mode 2 in which the eccentric cam 33 is pressed against the pressing roller support member 47 is executed.

  If mode switching ON is selected when a print job is input (YES in S1), mode switching is ON and mode 2 is executed, and a command is transmitted from the CPU of the printer body to the drive command unit 25 and the cam position switching mechanism 28. When the secondary transfer unit 10 is pressed, the eccentric cam 33 is pressed against the pressing roller support member 47 (S2). After such an operation is executed, printing is started (S3), printing processing is performed (S4), and when printing is completed (YES in S5), mode switching is turned off, mode 1 is executed, and the pressing roller support member After the eccentric cam 33 is separated from 47 (S6), a series of control is completed. The mode switching setting can be set by a button operation on the printer body or a print setting on the computer.

[Configuration Example 4]
In this configuration example, as shown in Table 1, a plurality of abutting amounts of the eccentric cam 33 to the pressing roller support member 47 can be set by a plurality of paper thicknesses.

  FIG. 19 shows a flowchart of control in this configuration example. In the present configuration example, the medium cardboard mode and the super cardboard mode can be further set in mode 2, and the displacement position of the eccentric cam 33 corresponding to each of the medium cardboard mode and the super cardboard mode can be set. The printing is started after the operation of switching the position of the eccentric cam 33 is performed.

  If mode switching ON is selected when a print job is input (YES in S1), mode switching is ON and mode 2 is executed. Next, when the ultra-thick paper mode is selected in mode 2 (YES in S3), the super-thick paper mode is executed, and a command is transmitted from the CPU of the printer body to the drive command unit 25 and the cam position switching mechanism 28, When the secondary transfer unit 10 is pressed, the eccentric cam 33 is pressed against the pressing roller support member 47 by the amount of contact shown in Table 1 (S4). On the other hand, if the ultra-thick paper mode is not selected in mode 2 (NO in S3), the medium-thick paper mode is executed, and a command is transmitted from the CPU of the printer body to the drive command unit 25 and the cam position switching mechanism 28. When the next transfer unit 10 is pressurized, the eccentric cam 33 is pressed against the pressing roller support member 47 by the amount of contact shown in Table 1 (S9). After such an operation is executed, printing is started (YES in S5), printing processing is performed (S6), and when printing is completed (YES in S7), mode switching is turned off, mode 1 is executed, and the pressing roller After the eccentric cam 33 is separated from the support member 47 (S8), a series of control is completed. The mode switching setting can be set by a button operation on the printer body or a print setting on the computer.

  As the sheet 19 becomes thicker in proportion to the thickness of the sheet 19, the lowering amount of the secondary transfer unit 10 when the sheet 19 enters the secondary transfer nip increases. Therefore, as the sheet 19 becomes thicker, the eccentric cam 33 and the pressing roller support member after the sheet 19 enters the secondary transfer nip even if the amount of the eccentric cam 33 hitting the pressing roller support member 47 is large. 47 can be separated from each other, so that a decrease in the nip pressure of the secondary transfer nip can be suppressed.

  With such a configuration, even in the medium-thick paper mode, it is possible to perform transfer with a predetermined nip pressure while obtaining a load fluctuation suppressing effect due to cam abutment.

  Here, when the mode is selected by scanning by the user, there is a possibility that the mode selection is wrong. Therefore, the position switching operation may be performed after detecting the thickness of the sheet 19 actually conveyed.

  FIG. 20 shows a configuration diagram when paper thickness detection is performed. A thickness detection sensor 46 is arranged upstream of the resist portion so that the thickness is detected before the resist is started. FIG. 21 shows a flowchart of the operation at that time.

  When a print job is input and the sheet 19 is fed to the registration unit (S1), the thickness detection sensor 46 detects the sheet thickness. When the sheet thickness exceeds a predetermined threshold (YES in S2), mode switching is turned on and mode 2 is executed, and a command is transmitted from the CPU of the printer body to the drive command unit 25 and the cam position switching mechanism 28. When the next transfer unit 10 is pressurized, the eccentric cam 33 is pressed against the pressing roller support member 47 (S3). After such an operation is executed, printing is started (S4), printing processing is performed (S5), and when printing is completed (YES in S6), mode switching is turned off, mode 1 is executed, and the pressing roller support member After the eccentric cam 33 is separated from 47 (S7), a series of control is completed. When detecting the sheet thickness by the thickness detection sensor 46, a table having a plurality of displacement amounts of the eccentric cam 33 according to the sheet thickness is set as described above, and these displacement amounts are set as threshold values. Various modes may be executed.

[Configuration Example 5]
In Configuration Example 5, a method of applying the present invention to an image forming apparatus having a transfer fixing device that transfers a toner image on an intermediate transfer belt to a sheet 19 and also fixes the toner image will be described.

  FIG. 22 is a schematic configuration diagram of an image forming apparatus having a transfer fixing device. As shown in FIG. 22, a heating device 21 serving as a heating unit that heats the sheet 19 is provided near the secondary transfer nip and upstream of the secondary transfer nip in the sheet conveyance direction. The heating device 21 is heated to a temperature sufficient to fix the toner on the paper 19, and the transfer and fixing are simultaneously performed in the secondary transfer nip.

  FIG. 23 is a schematic configuration diagram of an image forming apparatus having a transfer fixing device of another configuration. As shown in FIG. 23, the intermediate transfer belt 2 is heated near the secondary transfer nip and downstream of the intermediate transfer drive roller 3 in the intermediate transfer belt movement direction and upstream of the pressing roller 41 in the intermediate transfer belt movement direction. A heating device 22 is provided as a heating means. The intermediate transfer belt 2 is heated by the heating device 22, the toner on the intermediate transfer belt 2 is melted, and transfer and fixing are simultaneously performed in the secondary transfer nip.

  Also in the image forming apparatus having the transfer fixing device as shown in FIGS. 22 and 23, the behavior of each roller, the intermediate transfer belt 2, the paper 19, and the like when the paper 19 enters the secondary transfer nip is a configuration example. The same as in the case of the configuration example 1 to 4. Therefore, the configuration shown in Configuration Example 1 to Configuration Example 4 can be applied to an image forming apparatus having a transfer fixing device as shown in FIGS. 22 and 23 as it is. Further, at that time, the details of the operation are the same as those of the configuration example 1 to the configuration example 4, and thus the description thereof is omitted here.

As described above, in the present embodiment, the intermediate transfer belt 2 that is a loop-shaped belt image carrier that is endlessly moved while being stretched by a plurality of stretching rollers, and the plurality of stretching rollers via the intermediate transfer belt 2. A secondary transfer roller 8, which is a transfer roller that faces the front surface of the intermediate transfer belt 2 and forms a secondary transfer nip that is a transfer nip in contact with the front surface that is the outer surface of the loop of the intermediate transfer belt 2, is provided. In an image forming apparatus provided with a secondary transfer unit 10 as a transfer means for transferring an image carried on the front surface onto a sheet 19 as a transfer material sandwiched in a nip, in the vicinity of a secondary transfer roller 8. The pressing roller 41, which is a contact member that is in contact with a region upstream of the secondary transfer nip of the intermediate transfer belt 2 in the intermediate transfer belt moving direction, and the pressing roller 41 and the secondary transfer roller 8 are Lifting and has an interlocking means for displacing the abutting roller 41 pressed in conjunction with the secondary transfer roller displacement of the secondary transfer nip inrush of sheet 19 in the direction in which the tension of the intermediate transfer belt 2 increases. As a result, the pressing roller 41 is moved in the direction of increasing the tension on the upstream surface of the secondary transfer nip of the intermediate transfer belt 2 in conjunction with the displacement of the secondary transfer roller 8 when the sheet 19 enters the secondary transfer nip. Since the sheet 19 can be displaced, it is possible to suppress a decrease in the tension of the stretch surface on the upstream side of the secondary transfer nip of the intermediate transfer belt 2 when the sheet 19 enters the secondary transfer nip. Therefore, it is possible to suppress the speed fluctuation of the intermediate transfer belt 2 caused by the decrease in the tension of the stretch surface on the upstream side of the secondary transfer nip of the intermediate transfer belt 2 when the sheet 19 enters the secondary transfer nip.
The front Symbol interlocking means, a secondary transfer unit 10 is a transfer roller supporting member for supporting the secondary transfer roller 8, a pressing roller supporting member 47 which is the contact member supporting member for supporting the abutting roller 41 press In addition to the cam 32 that is a regulating member that regulates the distance between the support members, the degree of freedom in layout is improved as compared with the case where the interlocking unit is constituted by a single support member. The operability when the secondary transfer unit 10 supporting the secondary transfer roller 8 is pulled out of the apparatus can be improved.
Further, according to the present embodiment, the distance between the secondary transfer unit 10 and the pressing roller support member 47 can be adjusted by the eccentric cam 33 serving as the restricting member. The contact position of the pressing roller 41 with respect to the intermediate transfer belt 2 can be adjusted while ensuring the interlocking with the pressing roller 41. Therefore, since the tension of the tension surface on the upstream side of the secondary transfer nip of the intermediate transfer belt 2 can be controlled more appropriately, the speed fluctuation of the intermediate transfer belt 2 can be effectively suppressed.
Further, according to the present embodiment, the pressing roller 41 abuts against the intermediate transfer belt 2 from the inner side of the loop to the outer side due to the gravity applied to the pressing roller itself and the pressing roller support member 47, thereby performing the secondary transfer. When controlling the tension of the stretched surface on the upstream side of the secondary transfer nip by the pressing roller 41 interlocked with the roller 8, it is more likely that the pressing roller 41 is interlocked while receiving a predetermined contact pressure. The control effect is increased. Further, since it is not necessary to use a separate component for bringing the pressing roller 41 into contact with the intermediate transfer belt 2, it is possible to reduce the size and cost of the apparatus.
Further, according to the present embodiment, the secondary transfer is achieved by including the tension spring 52 that is an urging unit that urges the pressing roller 41 so as to contact the intermediate transfer belt 2 from the inner side to the outer side of the loop. When controlling the tension of the stretched surface on the upstream side of the secondary transfer nip by the pressing roller 41 interlocked with the roller 8, it is more likely that the pressing roller 41 is interlocked while receiving a predetermined contact pressure. The control effect is increased. In addition, a predetermined contact pressure can be applied to the intermediate transfer belt 2 without being restricted by the layout.
Further, according to the present embodiment, the position of the pressing roller 41 with respect to the intermediate transfer belt 2 is adjusted according to the thickness of the paper 19, so that when the paper 19 enters the secondary transfer nip according to the paper thickness, The load torque generated at the time of removal changes, and the load torque increases as the sheet 19 becomes thicker. Therefore, when the sheet 19 is thick, the position of the pressing roller 41 is further increased so that the contact pressure increases. Since it can be installed on the outside, the effect of suppressing the load torque can be obtained even on cardboard.
In addition, according to the present embodiment, the thickness detection sensor 46 that is a transfer material thickness detection unit that detects the thickness of the paper 19 is provided, and an intermediate position is determined according to the thickness detected by the thickness detection sensor 46. By adjusting the position of the pressing roller 41 with respect to the transfer belt 2, it is possible to prevent the user from setting the paper thickness by mistake and to set the position of the pressing roller 41 according to the paper thickness.
In addition, according to the present embodiment, the heating device 21 or 22 is provided in the vicinity of the secondary transfer nip, and is a heating unit that heats the intermediate transfer belt 2 or the sheet 19. Even in the case of an image forming apparatus having a transfer fixing device configured to transfer and fix the toner image on the paper 19 at the same time, the same effects as described above can be obtained by adopting the above-described configuration.

DESCRIPTION OF SYMBOLS 1 Photoconductor drum 2 Intermediate transfer belt 3 Intermediate transfer drive roller 4 Entrance roller 5 Secondary transfer counter roller 6 Tension roller 7 Driven roller 8 Secondary transfer roller 9 Registration roller pair 10 Secondary transfer unit 10b Energizing coil spring 11 Conveying belt 12 Pressure roller 13 Fixing roller 13a Fixing belt 14 Heating roller 15 Fixing device 16 Conveying roller 17 Separating roller 18 Paper feeding roller 19 Paper 20 Paper feeding cassette 21 Heating device 22 Heating device 25 Driving command unit 26 Microprocessor 27 Memory 28 Eccentric cam Position switching mechanism 29 Drive driver 30 Motor 32 Cam 32 Eccentric cam 33 Eccentric cam 41 Pushing roller 43 Secondary transfer unit rotation fulcrum 44 Tension spring 45 Tension spring spring support point 46 Tension spring spring support point 46 Thickness detection sensor 7 Pressing roller support member 48 Eccentric cam 50 Transfer unit 51 Cleaning blade 52 Tension spring 54 Primary transfer roller 60 Cleaning device 70 Transfer residual toner 100 Process unit 101 Developing device 102 Drum cleaning device 103 Charging device 104 Photosensitive drum 110 Intermediate transfer Belt 114 Drive roller 116 Opposite roller

JP-A-2005-338884

Claims (7)

A loop-shaped belt image carrier that is endlessly moved while being stretched by a plurality of stretching rollers;
There is provided a transfer roller that faces one of the plurality of stretching rollers through the belt image carrier and abuts against a front surface that is an outer surface of the loop of the belt image carrier to form a transfer nip. An image forming apparatus comprising: a transfer unit that transfers an image carried on the front surface to a transfer material sandwiched in the transfer nip;
A contact member that contacts a region upstream of the transfer nip of the belt image carrier in the belt image carrier moving direction in the vicinity of the transfer roller;
Interlocking means for supporting the contact member and the transfer roller and displacing the contact member in a direction in which the tension of the belt image carrier increases in conjunction with displacement of the transfer roller when the transfer material enters the transfer nip. I have a,
The interlocking means includes a transfer roller support member that supports the transfer roller, a contact member support member that supports the contact member, and a regulating member that regulates a distance between the support members. An image forming apparatus. The image forming apparatus according to claim 1 .
An image forming apparatus, wherein a distance between the transfer roller support member and the contact member support member is adjustable by the restriction member. The image forming apparatus according to claim 1 or 2 ,
The image forming apparatus according to claim 1, wherein the abutting member abuts the belt image carrier from the inside to the outside of the loop by gravity applied to the abutting member itself or the abutting member support member. The image forming apparatus according to claim 1 or 2,
An image forming apparatus, comprising: an urging unit that urges the abutting member to abut against the belt image carrier from the inside to the outside of the loop. Claims 1, 3 or in the image forming apparatus 4,
An image forming apparatus, wherein the position of the contact member with respect to the belt image carrier is adjusted according to the thickness of the transfer material. The image forming apparatus according to claim 5 .
Equipped with transfer material thickness detection means to detect the thickness of the transfer material,
An image forming apparatus, wherein the position of the contact member with respect to the belt image carrier is adjusted in accordance with the thickness detected by the transfer material detecting means. Claims 1,2,3, it was 4 or the image forming apparatus 5,
Provided in the vicinity of the transfer nip, having a heating means for heating the belt image carrier or transfer material, and configured to fix the toner image on the belt image carrier at the transfer nip at the same time as transferring to the transfer material. An image forming apparatus.

Images