JP3584938B2 - Image forming device - Google Patents

Description

  The present invention relates to an image forming apparatus such as a printer and a copying machine, and more particularly, to an image forming apparatus having a transfer unit that transfers a toner image to a recording material.

  2. Description of the Related Art In recent years, so-called full-color tandem machines have been proposed for image forming apparatuses such as printers, copiers, and facsimile machines for the purpose of forming a color image at high speed and high image quality. As a typical example of this tandem machine, four image forming units of yellow (Y), magenta (M), cyan (C) and black (K) are arranged in parallel with each other, and each of these image forming units The toner images of each color of yellow, magenta, cyan, and black sequentially formed on the intermediate transfer belt, which is an intermediate transfer member, are temporarily transferred multiple times (primary transfer), and then the recording material ( And a full-color or black-and-white (monochrome) image is formed by transferring (secondary transfer) all at once onto a sheet of paper and fixing the toner image formed on the recording material.

  Here, as a conventional technique, a secondary transfer roll is opposed to an intermediate transfer belt, and a toner image is transferred from the intermediate transfer belt to a recording material at a secondary transfer unit where the secondary transfer roll is disposed. Is widely adopted. However, when the secondary transfer roll is brought into contact with the intermediate transfer belt and secondary transfer is performed on the conveyed recording material, when the thin paper coated paper or the like is conveyed, the recording material is wound around the secondary transfer roll. In some cases, it caused troubles such as jams. Therefore, in order to maintain good releasability of the recording material from the intermediate transfer belt and stabilize the transportability of the recording material to the fixing device, for example, a transfer in which the recording material is conveyed in a secondary transfer unit of a tandem machine. A technique has been proposed in which a belt is pressed against an intermediate transfer belt, and a transfer belt is pressed against the intermediate transfer belt using a roll that stretches the transfer belt as a transfer roll in the secondary transfer unit (for example, And Patent Document 1.). In such a technique, for example, a recording material is electrostatically attracted to a transfer belt and transferred / transported, and the recording material is separated from the transfer belt at a tension roll position where the curvature is small, for example, with thin paper coated paper. It is possible to prevent the occurrence of troubles of peeling off.

  Although not a tandem machine, the toner image formed on the rotating photosensitive drum is transferred to a recording material conveyed to a transfer conveyance belt stretched by a driving roll and a driven roll, and the toner image is transferred. There has been proposed an image forming apparatus using a transfer belt device that conveys the recorded recording material to the downstream side by the transfer conveyance belt (for example, see Patent Document 2).

JP-A-10-319741 (page 4-6, FIG. 2) JP-A-6-59581 (page 4-5, FIG. 2)

  Here, in a so-called intermediate transfer system in which a toner image is once carried on an intermediate transfer belt, in order to transfer a toner image to a recording material (paper) at the time of secondary transfer, a secondary transfer roll and an opposing roll are used. It is necessary to position a backup roll (a roll disposed inside the intermediate transfer belt in the secondary transfer section) with high accuracy. This is because, if a positional accuracy shift occurs between the transfer roll and the facing portion (backup roll or carrier), there is a possibility that troubles such as poor transfer and poor parallelism may be caused.

  Therefore, for example, as in the technique disclosed in Patent Document 1, when the transfer belt is pressed against the intermediate transfer belt using a roll that stretches the transfer belt as the transfer roll in the secondary transfer unit, This transfer roll needs to be positioned with high accuracy with respect to the backup roll. Further, for example, even when a so-called paper transport method as disclosed in Patent Document 2 is adopted, when a transfer roll or the like is disposed in a transfer unit for transferring a toner image to a recording material, the toner image is excellent. In order to transfer the toner image onto the transfer roller, accurate positioning between the transfer roll and the opposite toner image carrier is required.

Here, it is preferable that the transfer belt is configured to be able to contact and separate from the carrier, since the driving load of the carrier can be minimized. At this time, the conveyed recording material is conveyed on the transfer belt in a state where the surface on which the toner image is not transferred is in contact with the transfer belt. Therefore, when the transfer belt driving mechanism is provided on the upstream side in the conveyance direction of the recording material, the conveyance surface of the transfer belt may be loosened, and the conveyance of the recording material may not be performed properly.
When the transfer belt is configured to be able to contact and separate from the carrier, it is preferable that the contact and separation mechanism be simple, and that the transfer belt be more reliably contacted with the carrier with a stable pressure. Is preferred. Further, for example, when a conveyance unit for conveying the recording material transferred from the transfer belt to a further downstream side (for example, a fixing device) is provided, a transfer belt driving mechanism and a transfer belt contact / separation mechanism should be considered. At this time, it is necessary to consider a good transfer performance with the transfer means.

SUMMARY OF THE INVENTION The present invention has been made to solve the above technical problems, and an object of the present invention is to provide an apparatus having improved transfer performance to a recording material.
Another object of the present invention is to obtain good conveyance performance even when the recording material is conveyed downstream of the sheet conveyance direction via a transfer belt after the transfer, for example.

With such a purpose, an image processing apparatus to which the present invention is applied is configured to transfer a toner image carried on the carrier to a recording material and to contact the carrier with the toner image. A transfer belt configured to be separable, and a drive shaft that is provided downstream of the transfer belt in the recording material conveyance direction to drive the transfer belt, and is a central axis when the transfer belt comes into contact with and separates from the carrier. When the transfer belt is provided on the upstream side of the transfer belt in the recording material conveyance direction to stretch the transfer belt, and when the transfer belt comes into contact with the carrier, the driven roller is pressed toward the carrier, includes a swing arm to forcibly release the pressing force against the carrier driven roller by rotating the conveyor belt allowed to convey the recording material conveyed further to the downstream side of the transfer belt, and the transfer base Drive shaft provided in the preparative conveyor belt side is characterized in that is displaceable relative to the position of the conveyor belt.

In this case, if the conveyance belt conveys the recording material after the transfer of the toner image from the downstream side of the transfer belt to the fixing unit, the conveyance belt is in a favorable state with respect to the fixing unit on the downstream side. This is preferable in that the recording material after transfer can be conveyed. Further, the transfer belt is driven by a drive roll having a drive shaft as an axis, and is stretched by a driven roll made of a rubber roll and the drive roll. Further, the drive roll may be characterized by being made of a metal member such as SUS. Further, the transfer belt can be characterized as an endless annular belt having a volume resistivity of 10 ⁶ to 10 ¹⁰ Ω · cm.

  From another viewpoint, the image processing apparatus to which the present invention is applied includes a carrier on which a toner image is carried, and a toner image carried on the carrier, which is transferred to a recording material. A transfer belt configured to be detachable from the drive belt, and a drive shaft provided downstream of the transfer belt in the recording material conveyance direction to drive the transfer belt and to be a central axis when the transfer belt comes into contact with and separates from the carrier. And an oscillating arm that pivots around the fulcrum to separate the transfer belt from the carrier.

Here, if the driven roll further includes a coil spring acting on the swing arm to press the driven roll toward the carrier, for example, the transfer belt and the pressing belt determined by the pressing force determined by the coil spring. This is preferable in that the driven roll can be pressed against the carrier.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to further improve the transfer performance to a recording material, and the conveyance performance of a recording material.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
-Embodiment 1-
FIG. 1 is a diagram illustrating an image forming apparatus to which the exemplary embodiment is applied. The image forming apparatus shown in FIG. 1 is an intermediate transfer type image forming apparatus employing a so-called tandem type, and includes a plurality of image forming units 10 (10Y, 10M) on which toner images of respective color components are formed by an electrophotographic method. , 10C, 10K), an intermediate transfer belt 15 serving as a carrier for sequentially transferring (primary transfer) and holding each color component toner image formed by each image forming unit 10, and a superimposition transferred onto the intermediate transfer belt 15 The image forming apparatus includes a secondary transfer unit 20 that collectively transfers (secondarily transfers) a toner image to a sheet P, which is a recording material (transfer material), and a fixing unit 30 that fixes the image that is secondarily transferred onto the sheet P. In addition, a control unit 40 that controls the operation of each device (each unit) is provided.

  In the present embodiment, each image forming unit 10 (10Y, 10M, 10C, 10K) has a charger 12 for charging the photosensitive drum 11 around the photosensitive drum 11 rotating in the direction of arrow A. A laser exposure device 13 for writing an electrostatic latent image on the photoconductor drum 11 (an exposure beam is indicated by reference numeral Bm in the figure); , A primary transfer roll 16 for transferring each color component toner image formed on the photosensitive drum 11 to the intermediate transfer belt 15, and a drum cleaner 17 for removing residual toner on the photosensitive drum 11 , Etc. are sequentially arranged. These image forming units 10 are arranged substantially linearly in the order of yellow (Y color), magenta (M color), cyan (C color), and black (K color) from the upstream side of the intermediate transfer belt 15. I have.

The intermediate transfer belt 15 which is an intermediate transfer member (toner image carrier) is made of a resin such as polyimide or polyamide containing an appropriate amount of a conductive agent such as carbon black, and has a volume resistivity of 10 ⁶ to 10 ⁶ . It is formed so as to have a resistance of 10 ¹⁴ Ω · cm, and is formed of a film-shaped endless belt having a thickness of, for example, about 0.1 mm. The intermediate transfer belt 15 is circulated (rotated) at a predetermined speed in a direction B shown in the figure by various rolls. The various rolls include a drive roll 31 driven by a motor (not shown) having excellent constant speed to circulate and drive the intermediate transfer belt 15, and an intermediate roll extending substantially linearly along the arrangement direction of the photosensitive drums 11. A support roll 32 that supports the transfer belt 15, a tension roll 33 that applies a constant tension to the intermediate transfer belt 15 and functions as a correction roll that prevents meandering of the intermediate transfer belt 15, and a backup that is provided in the secondary transfer unit 20. The cleaning unit includes a roll 25 and a cleaning backup roll 34 provided in a cleaning unit that scrapes residual toner on the intermediate transfer belt 15.

  A voltage having a polarity opposite to the charging polarity of the toner is applied to each of the primary transfer rolls 16 provided inside the intermediate transfer belt 15 which is opposed to each of the photosensitive drums 11 and extends substantially linearly. As a result, the toner images on the respective photosensitive drums 11 are sequentially electrostatically attracted to the intermediate transfer belt 15, and a superimposed toner image is formed on the intermediate transfer belt 15.

  The secondary transfer unit 20 includes a secondary transfer conveyance belt (secondary transfer belt) 21 disposed on the toner image bearing surface side of the intermediate transfer belt 15 and a backup roll 25 as an opposing roll. The backup roll 25 is a tube of EPDM and NBR blended rubber in which carbon is dispersed on the surface, and is made of EPDM rubber. The surface of the backup roll 25 is formed to have a surface resistivity of 7 to 10 logΩ / □ and a roll diameter of 28 mm. Is set to, for example, 70 degrees (Asker C). The backup roll 25 is disposed on the back side of the intermediate transfer belt 15 and forms a counter electrode of the secondary transfer conveyance belt 21. A metal power supply roll 26 for stably applying the secondary transfer bias is in contact with the backup roll 25. Are located.

On the other hand, a secondary transfer conveyance belt (secondary transfer belt) 21 is stretched by a driven roll (transfer roll) 23 as a first roll and a drive roll 22 as a second roll, for example, a volume resistivity. Is a semiconductive endless annular belt of 10 ⁶ to 10 ¹⁰ Ω · cm, and a material having a 100% elongation modulus of 3.8 MPa is used. The secondary transfer conveyance belt 21 is conveyed at a predetermined speed by a drive roll 22 made of, for example, SUS, and given a predetermined tension by a driven roll 23 made of, for example, a rubber roll and the drive roll 22.

  The driven roll 23 is disposed in pressure contact with the backup roll 25 with the secondary transfer conveyance belt 21 and the intermediate transfer belt 15 interposed therebetween, and performs secondary transfer on the sheet P conveyed on the secondary transfer conveyance belt 21. It functions as a secondary transfer roll. Further, by changing the pressure state between the backup roll 25 and the driven roll 23, the contact state of the secondary transfer member can be changed, and alignment adjustment and image parallelism adjustment can be performed. The diameter of the drive roll 22 is so small that it does not wind around the secondary transfer conveyance belt 21 even when thin paper coated paper is conveyed. Further, a cleaner 27 made of a rubber plate-like member that scrapes off the toner on the secondary transfer conveyance belt 21 is provided on the secondary transfer conveyance belt 21 in the vicinity of the upstream side of the secondary transfer portion that contacts the intermediate transfer belt 15. It is configured to abut.

  A belt cleaner 35 that removes residual toner and paper dust on the intermediate transfer belt 15 after the secondary transfer and cleans the surface of the intermediate transfer belt 15 is provided downstream of the secondary transfer unit 20 in the intermediate transfer belt 15. Are provided so as to be able to freely come and go. On the other hand, on the upstream side of the yellow image forming unit 10Y, a reference sensor (home position sensor) for generating a reference signal serving as a reference for setting an image forming timing in each image forming unit 10 (10Y, 10M, 10C, 10K). ) 42, and an image density sensor 43 for adjusting image quality is provided downstream of the black image forming unit 10K. The reference sensor 42 generates a reference signal by recognizing a predetermined mark provided on the intermediate transfer belt 15, and in accordance with an instruction from the control unit 40 based on the recognition of the reference signal, each image forming unit 10 ( 10Y, 10M, 10C, and 10K) are configured to start image formation.

  Further, in the present embodiment, as a paper transport system, a paper tray 50 for storing the paper P, a paper feed roll 51 for taking out and transporting the paper P stacked on the paper tray 50 at a predetermined timing, a paper feed roll 51 The transport roll 52 transports the paper P fed by the transport roll 52, the transport chute 53 that transports the paper P transported by the transport roll 52 to the secondary transfer unit 20, and transports the paper P after the secondary transfer by the secondary transfer transport belt 21 The transport belt 55 transports the sheet P to be fixed to the fixing unit 30.

  Next, a basic image forming process of the image forming apparatus according to the present embodiment will be described. Image data output from an image reading device (IIT) not shown or a personal computer (PC) not shown is input to the image forming apparatus shown in FIG. In the image forming apparatus, after an image processing device (IPS) (not shown) performs predetermined image processing, an image forming operation is performed by the image forming unit 10 or the like. The image processing device (IPS) performs predetermined image processing such as shading correction, position shift correction, lightness / color space conversion, gamma correction, frame erasing, color editing, and moving editing on the input reflectance data. Is done. The image data subjected to the image processing is converted into four color material gradation data of yellow (Y), magenta (M), cyan (C), and black (K), and is output to the laser exposure device 13. .

  The laser exposure device 13 irradiates the photosensitive drum 11 of each of the image forming units 10Y, 10M, 10C, and 10K with an exposure beam Bm emitted from, for example, a semiconductor laser according to the input color material gradation data. I have. In the photoconductor drums 11 of the image forming units 10Y, 10M, 10C, and 10K, after the surface is charged by the charger 12, the surface is scanned and exposed by the laser exposure device 13 to form an electrostatic latent image. The formed electrostatic latent image is developed as a toner image of each color of yellow (Y), magenta (M), cyan (C), and black (K) in each of the image forming units 10Y, 10M, 10C, and 10K. Is done.

  The toner images formed on the photosensitive drums 11 of the image forming units 10Y, 10M, 10C, and 10K are transferred onto the intermediate transfer belt 15 at a primary transfer section where the respective photosensitive drums 11 and the intermediate transfer belt 15 abut. Transcribed. More specifically, in the primary transfer section, a voltage having a polarity opposite to the charge polarity of the toner is applied to the base material of the intermediate transfer belt 15 by the primary transfer roll 16, and the unfixed toner image is transferred to the surface of the intermediate transfer belt 15. And the primary transfer is performed. The unfixed toner image primary-transferred in this way is conveyed to the secondary transfer unit 20 as the intermediate transfer belt 15 rotates.

  On the other hand, in the paper transport system, the paper supply roll 51 rotates in synchronization with the timing of image formation, and paper P of a predetermined size is supplied from the paper tray 50. The paper P supplied by the paper feed roll 51 is transported by the transport roll 52, and reaches the secondary transfer unit 20 via the transport chute 53. Before reaching the secondary transfer unit 20, the transport chute 53 rises in conjunction with the raising operation (advance operation) of the secondary transfer transport belt 21 to form a transport path to the secondary transfer unit 20. ing. The sheet P is temporarily stopped, and the registration roll (not shown) is rotated in accordance with the movement timing of the intermediate transfer belt 15 carrying the toner image as described above, so that the position of the sheet P and the position of the toner image are changed. Is adjusted.

  In the secondary transfer section 20, the driven roll 23 is connected to the backup roll 25 with the semiconductive secondary transfer conveyance belt 21 and the intermediate transfer belt 15 sandwiched therebetween in accordance with the timing of the secondary transfer to the paper P. Is pressed. At this time, the sheet P conveyed in a timely manner is sandwiched between the intermediate transfer belt 15 and the secondary transfer conveyance belt 21. At this time, when a voltage (regular transfer bias) having the same polarity as the charge polarity of the toner is applied to the power supply roll 26, a transfer electric field is formed as a counter electrode on the secondary transfer conveyance belt 21, and the driven roll 23 is backed up. At the secondary transfer position pressed by the roll 25, the unfixed toner image carried on the intermediate transfer belt 15 is electrostatically transferred onto the paper P.

  Thereafter, the sheet P on which the toner image has been electrostatically transferred is conveyed as it is while being separated from the intermediate transfer belt 15 by the secondary transfer conveyance belt 21, and is provided downstream of the secondary transfer conveyance belt 21 in the sheet conveyance direction. Transport belt 55. The transport belt 55 transports the paper P to the fixing unit 30 in accordance with the optimal transport speed in the fixing unit 30. The unfixed toner image on the sheet P undergoes a fixing process by heat and pressure by the fixing unit 30 and is fixed on the sheet P, and the sheet P on which the fixed image is formed is removed by an ejection roll (not shown). Is discharged to the outside. On the other hand, after the transfer to the paper P is completed, the residual toner remaining on the intermediate transfer belt 15 is conveyed to the cleaning unit with the rotation of the intermediate transfer belt 15, and the intermediate toner is transferred by the cleaning backup roll 34 and the belt cleaner 35. It is removed from the transfer belt 15.

Next, the mechanism of the secondary transfer unit 20 according to the present embodiment will be described.
FIG. 2 is an explanatory view showing the mechanism of the secondary transfer unit 20. As shown in FIG. 2, the secondary transfer unit 20 changes the pressing force of the driven roll 23 against the backup roll 25 shown in FIG. And a transfer belt unit 80 for separating and abutting the secondary transfer conveyance belt 21 from the intermediate transfer belt 15.

  The backup roll unit 70 moves the driven roll 23 in the transfer belt unit 80 up and down by different amounts at both ends of IN (rear side, rear side) / OUT (front side, front side), and thereby the driven roll 23 By adjusting the pressing force between the secondary transfer unit 20 and the backup roll 25, the amounts of these bites in the secondary transfer unit 20 can be adjusted. By adjusting the bite amount by IN / OUT, the image parallelism can be adjusted. In order to realize such a function, as shown in FIG. 2, the backup roll unit 70 is provided at both ends of the IN / OUT of the apparatus, and each of the frames 71 and IN / OUT which move up and down in different phases. Positioning pins 72 provided on the frame 71 for adjusting the bite amount between the backup roll 25 and the driven roll 23 by IN / OUT, and the IN / OUT frame 71 provided on each of the IN / OUT are moved up and down by IN / OUT. The eccentric cam 73 for adjusting the nip width (bite-in amount, pressure contact amount), a rotating shaft 74 for rotating the eccentric cam 73, a motor 75 as a driving source, and a driving gear of the motor 75 mesh with the rotating shaft 74. A gear 76 for transmitting the driving force, a coil spring 77 for urging the frame 71 against the eccentric cam 73 at both ends thereof, And a encoder 78 for detecting the reference position and the rotation amount.

  Each of the eccentric cams 73 provided on the IN / OUT is fixed to the rotating shaft 74 so that the phase is shifted in the circumferential direction by the angle thereof. 71 are configured to have different extrusion amounts. That is, in the image forming apparatus to which the present embodiment is applied, by controlling the rotation angle of the rotating shaft 74 based on the instruction of the control unit 40 shown in FIG. The pushing amount of a certain driven roll 23 is adjusted. As a result, the bite amount between the driven roll 23 and the backup roll 25 can be adjusted with the intermediate transfer belt 15 and the secondary transfer conveyance belt 21 interposed therebetween. By adjusting the bite amount, the image parallelism can be changed by changing the nip pressure distribution of the secondary transfer. In the present embodiment, an adjustment of ± 0.6 mm is possible as an IN / OUT biting adjustment range in the secondary transfer unit 20. In addition, as an adjustment method, besides a method of adjusting the value by continuously changing the value, it is also possible to prepare a plurality of steps in advance and to adjust the value in a stepwise manner.

  It is effective that the IN / OUT biting adjustment in the transfer nip is performed when the unit of the secondary transfer unit 20 is replaced or each belt unit is replaced. The control unit 40 automatically prints out a sample whose condition has been changed with respect to the bite amount of the secondary transfer when the IN / OUT difference is, for example, −A, 0, and + A (mm) when these units are replaced. Then, the sample is read by, for example, a scanner or the like, and the image parallelism is measured. After that, the control unit 40 may rotate the motor 75 based on the measurement result and adjust the IN / OUT biting amount so as to have the most preferable value. The parallelism of this image is determined by the length L1 (mm) of the IN side of the paper P and the length of the OUT side when the same length image is formed by IN / OUT of the image formed on the printed paper. The difference from L2 (mm) is represented by ΔL (mm).

  On the other hand, in the transfer belt unit 80, the secondary transfer conveyance belt 21 can be brought into contact with or separated from the intermediate transfer belt 15 by moving the shaft of the driven roll 23 up and down about the drive roll 22. For this purpose, as shown in FIG. 2, the transfer belt unit 80 rotates about a fulcrum 81 provided at both ends of the IN / OUT, and the other end different from the end 82 a is connected to the shaft of the driven roll 23 (the driven (A shaft), a retracting cam 83, IN, which is an eccentric cam that abuts a tip portion 82a of each swing arm 82 provided on IN / OUT and swings the swing arm 82. A rotary shaft 84 for simultaneously rotating the retract cams 83 at both ends of / OUT, a drive gear 85 that rotates by receiving a driving force from a motor (not shown), a reference position for the retract cam 83, An encoder 86 for detecting the amount of rotation and a coil spring 87 for bringing the swing arm 82 into contact with the retract cam 83 are provided. Further, a positioning member 88 is provided at both ends of the IN / OUT and engages with the positioning pin 72 to position the driven roll 23.

  Each retract cam 83 of IN / OUT in the transfer belt unit 80 is fixed to the rotating shaft 84 so that the radius does not change between IN / OUT depending on the angle. For example, the retract cam 83 is rotated, for example, 180 degrees from a state in which the secondary transfer conveyance belt 21 is in contact with the intermediate transfer belt 15 shown in FIG. Is lifted upward by the retract cam 83, the other end different from the end 82a pivots downward via the fulcrum 81. Thereby, the secondary transfer conveyance belt 21 can be separated (retracted) from the intermediate transfer belt 15. Further, by further rotating by a predetermined angle (for example, 180 degrees), the driven roll 23 can be advanced, and the secondary transfer conveyance belt 21 can be brought into contact with the intermediate transfer belt 15 (contact).

  FIG. 3 is a perspective view of the transfer belt unit 80 as viewed from below. On the shaft 84 provided below the transport chute 53, together with the retract cam 83 described above, a chute push-up cam 56, which is an eccentric cam that rotates in the opposite phase to the retract cam 83, is provided on the IN side and the OUT side. Have been. A chute spring 57 is provided near the chute lifting cam 56. When the retracting cam 83 rotates by the rotation of the rotating shaft 84 and the positioning member 88 (the driven roll 23) rises, the transport chute 53 is also pushed up by the rotation of the chute pushing up cam 56 in synchronization with this movement. Thus, the paper P can be smoothly transported during the secondary transfer.

  FIG. 4 is a diagram for explaining the mechanism of the transfer belt unit 80 in more detail. The secondary transfer conveyance belt 21 is stretched by a driving roll 22 and a driven roll 23, and a positioning member 88 is connected to a driven shaft 23 a of the driven roll 23, and a driving source 22 is connected to the driving shaft 22 a of the driving roll 22. Is connected via a gear 92. On the drive shaft 22a side of the drive roll 22, a bracket 93 in which a bearing (not shown) for supporting the drive roll 22 and a drive device (such as a motor 91 and a gear 92) are integrated is provided. The motor 91 is fixed to a bracket 93, and the bracket 93 is connected to the frame 90 side (including a block member connected to the frame 90) by a screw 95 through an elongated hole 94. For the screw 95, a predetermined gap is ensured even when the screw cutting is interrupted in the middle, and the screw 95 is not fastened beyond a certain displacement, for example, a shoulder screw is used. Then, the bracket 93 is fastened to the frame 90 side by a long hole 94 provided in the bracket 93 so as to be slidable in the S direction shown in FIG. Incidentally, for example, an oil-containing resin washer or the like may be provided between the screw 95 and the bracket 93 to further ensure free sliding. Further, in order to eliminate the play of the gap generated due to the sliding, it is effective to urge with a leaf spring or the like.

  As described above, the drive shaft 22a, which is the shaft of the drive roll 22, has a degree of freedom in the direction in which the secondary transfer conveyance belt 21 is stretched, that is, the S direction, which is the paper conveyance direction, and is configured to be slidable. ing. At this time, since the slidable bracket 93 is fixed to the motor 91 and the driving device including the motor 91 and the gear 92 is integrally disposed, the slidable bracket 93 is driven in accordance with the sliding of the driving shaft 22a. The device also slides. Thereby, even in the state of being slid in the S direction, the driving roll 22 can be smoothly rotated, and smooth belt driving can be performed.

  In the positioning member 88, a bearing 89 is press-fitted at a predetermined position, and the driven shaft 23a of the driven roll 23 is inserted into the bearing 89. The end of the transport chute 53 (the side near the secondary transfer unit 20) is rotatably attached to the driven shaft 23a. With this configuration, the secondary transfer / conveyance belt 21 and the conveyance chute 53 are bent in a “C” shape from the bearing 89, and the bearing 89 and the driven shaft 23 a allow the positioning member 88 to swing. Have been. Thus, when the positioning member 88 is fitted to the positioning pin 72, the positioning member 88 can be displaced in synchronization with the displacement of the positioning pin 72. Since the positioning member 88 swings and the transport chute 53 is configured to be rotatable at the bearing 89, the degree of freedom with respect to the transport chute 53 is ensured, and unnecessary distortion or the like is generated with respect to the transport chute 53. I will not let you. As a result of securing a predetermined escape against the distortion or the like, the positioning of the transport chute 53 can be performed smoothly.

  The transfer belt unit 80 has IN / OUT plates 96 connected to the drive shaft 22a of the drive roll 22 and the driven shaft 23a of the driven roll 23. The plate 96 is bent from the plate center 96a. It is possible. When the secondary transfer conveyance belt 21 is stretched, the secondary transfer conveyance belt 21 is hung on the driving roll 22 and the driven roll 23 in a state where the plate 96 is bent from the plate center 96a. Thereafter, by extending the plate 96 at the plate center 96a, the secondary transfer conveyance belt 21 can be stretched with a constant tension.

Next, the retract / contact operation of the secondary transfer / conveyance belt 21 will be described.
FIG. 5 shows a state in which the secondary transfer conveyance belt 21 is retracted (separated) from the intermediate transfer belt 15 and the backup roll 25 shown in FIG. 1, and FIG. The side (contact) is shown.
In the retracted state as shown in FIG. 5, the tip 82 a of the swing arm 82 is pushed up by the retract cam 83 that rotates about the rotary shaft 84, and the secondary transfer conveyance belt 21, the driven roll 23, and the positioning member 88 Rotate around the drive shaft 22a. At this time, the positioning member 88 is separated from the positioning pin 72 of the backup roll unit 70.

  Thereafter, the toner image is carried on the intermediate transfer belt 15 by the image forming process as shown in FIG. 1, and before the toner image is conveyed to the secondary transfer unit 20, the paper P Before the transfer to the transfer section 20, the secondary transfer and transfer belt 21 contacts the intermediate transfer belt 15. In this operation, as shown in FIG. 6, the rotation shaft 84 rotates, for example, by 180 degrees, and the rotation of the rotation shaft 84 causes the retract cam 83 to rotate. Rotate counterclockwise (counterclockwise) as center. At this time, the urging of the retract cam 83 against the tip end portion 82a of the swing arm 82 is gradually removed, and the force (here, the pulling force) of the coil spring 87 causes the secondary transfer conveyance belt 21 to move around the drive shaft 22a. Rotate counterclockwise (counterclockwise). After the bias of the retract cam 83 is completely removed from the swing arm 82, the positioning member 88 is engaged with the positioning pin 72 by the force of the coil spring 87. In a state where the positioning member 88 is engaged with the positioning pin 72, the driven roll 23 shown in FIG. 1 is interposed between the intermediate transfer belt 15 and the secondary transfer conveyance belt 21 with the backup roll 25 at a predetermined pressure. Pressed.

  On the other hand, when the driven roll 23 moves upward, the rotation of the rotary shaft 84 causes the chute lifting cam 56 to rotate, and the conveyance chute 53 also rotates around the bearing 89. Due to the elevation of the positioning member 88, the side of the transport chute 53 close to the secondary transfer position (downstream in the transport direction, right side in the drawing) rises, but the side far from the secondary transfer position of the transport chute 53 (upstream in the transport direction) , Left side of the figure) is adjusted to an appropriate height by the chute push-up cam 56. As a result, the chute surface of the transport chute 53 and the paper transport surface of the secondary transfer transport belt 21 are slightly bent at the bearing 89 at the portion of the bearing 89 to form a paper transport path. In general, when performing the secondary transfer, the transport chute 53 needs to be positioned with high accuracy in order to keep the posture of the sheet P favorable. In the present embodiment, the position can be accurately determined by pushing up by the chute pushing up cam 56.

  Here, in the present embodiment, when the positioning member 88 is engaged with the positioning pin 72, a predetermined play is given to the positioning member 88 by the bearing 89. Since the predetermined degree of freedom is provided as described above, when engaging with the positioning pin 72, unnecessary tension is not applied to the transport chute 53, and the precision of the transport chute 53 can be kept good. it can. Further, since the positioning member 88 is given a predetermined degree of freedom, it is possible to keep the flat surface of the secondary transfer conveyance belt 21. In particular, in the present embodiment, the image parallelism is changed by changing the nip pressure distribution of the secondary transfer. However, since the flat surface of the secondary transfer conveyance belt 21 is maintained, the image defect due to the twist and the parallelism are reduced. The occurrence of defects and the like can be suppressed.

  Further, in the present embodiment, as described with reference to FIG. 4, a bracket 93 in which a bearing (not shown) supporting the driving roll 22 and a driving device (a motor 91, a gear 92, and the like) are integrated, It is fastened to the frame 90 side so that it can slide in the S direction. When the positioning member 88 is engaged with the positioning pin 72 as shown in FIG. 6, the bracket 93 can move a predetermined amount in the S direction. If such a degree of freedom is not given to the bracket 93 and the bracket 93 is completely fixed to the frame 90 side, it is difficult to keep the flat surface of the secondary transfer conveyance belt 21 and the drive shaft 22a of the gear 92 The accuracy cannot be maintained during the engagement. In such a case, the transport performance of the paper P and the secondary transfer performance are adversely affected, and a good image cannot be obtained. In the present embodiment, the driving device is integrated with the bracket 93, and the paper conveyance direction is free when the secondary transfer conveyance belt 21 is positioned in contact with the intermediate transfer belt 15. This suppresses the occurrence of image defects and the like.

  As described in detail above, according to the present embodiment, in the method of performing transfer to the sheet P and transporting the sheet using the secondary transfer transport belt 21, the secondary transfer as the first positioning unit is performed. The driven roll (transfer roll) 23 is positioned with respect to the driven shaft 23 a at both ends in the vicinity of the unit 20. The positioning of the drive roll 22 with respect to the drive shaft 22a was performed. At this time, the positioning in the mechanism section on the downstream side in the sheet conveyance direction is performed only in the vertical direction, and the bracket 93 including the mechanism section is in a free state in the sheet conveyance direction. Thereby, the driven roll (transfer roll) 23 of the secondary transfer unit 20 and the backup roll 25 are reliably brought into contact with each other without depending on the dimensional variation of the belt transfer device including various mechanisms constituting the secondary transfer conveyance belt 21. And a good image can be obtained.

  Further, since the driving device including the motor 91 and the gear 92 is integrated, the meshing accuracy of the gear 92 becomes constant, and a good image can be obtained. Furthermore, according to the present embodiment, even when the image parallelism is performed by changing the pressure contact force between the backup roll 25 and the driven roll (secondary transfer roll) 23, that is, the secondary transfer nip pressure distribution. In addition, it is possible to suppress the occurrence of image defects, parallelism defects, and the like due to twisting of the belt and the like.

  In the present embodiment, an image forming apparatus using a secondary transfer belt system has been described as an example, but the present invention can also be applied to primary transfer and black and white image transfer. That is, the present embodiment effectively functions also for an image forming apparatus using a so-called paper transport method, which does not perform transfer to an intermediate transfer member. For example, when transferring a toner image formed on an image carrier such as a photosensitive drum to a recording material conveyed by a transfer belt, the transfer portion is provided with a retract / advance mechanism, and the transfer belt is moved in the paper conveyance direction. Thus, the positioning can be performed with a predetermined degree of freedom. According to this configuration, the positioning in the transfer portion can be reliably performed without depending on the variation in dimensions, and a good image can be obtained.

-Embodiment 2-
This embodiment is substantially the same as Embodiment 1, except that the drive roll 22 in the transfer belt unit 80 can be moved in the vertical direction (vertical direction) in addition to the paper transport direction (horizontal direction). It is connected to the 90 side. In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and the detailed description thereof will be omitted.

  FIG. 7 is a view for explaining a mechanism for connecting the transfer belt unit 80 to the frame 90 in the present embodiment. Here, FIG. 7A is a front view of the bracket 97 viewed from the secondary transfer / transport belt 21 side, FIG. 7B is a sectional view taken along the line VIIb-VIIb of FIG. 7A, and FIG. It is the top view which looked at 97 from the upper side. In the present embodiment, the drive shaft 22a of the drive roll 22 (not shown) is disposed so as to pass through an elongated hole 97a provided to open downward on the side surface of the bracket 97 having an L-shaped cross section. ing. The second embodiment is characterized in that the drive shaft 22a, the drive roll 22 to which the drive shaft 22a is attached, and the gear 92 (not shown) are movable in the vertical direction (vertical direction). Different from the first mode. The motor 91 is attached to the bracket 93 (not shown) described in the first embodiment, and is not attached to the bracket 97. A restricting member 98 fixed to the frame 90 by screws 99 and restricting the movement of the bracket 97 is attached to the bracket 97. The regulating member 98 is arranged with a small gap with respect to the bracket 97, and regulates the movement of the bracket 97 in the vertical direction (vertical direction), but allows the movement in the horizontal direction. Has become. The bracket 97 is provided, for example, on the IN / OUT side of the device.

  By adopting such a configuration, the drive shaft 22a, which is the shaft of the drive roll 22, has a degree of freedom in the direction in which the secondary transfer conveyance belt 21 is stretched by the bracket 97, that is, in the S direction, which is the paper conveyance direction. In addition, the slots 97a provided in the bracket 97 provide a degree of freedom in the vertical direction, that is, the V direction which is a direction orthogonal to the surface of the sheet to be conveyed. At this time, the motor 91 is fixed to the bracket 93, but transmits the driving force via the gear 92, and slides (moves in the horizontal direction) or moves up and down (moves in the vertical direction) of the drive shaft 22a. Does not hinder the movement of Even when the driving roll 22 is moved in the S direction or the V direction shown in FIG. 7, the driving roll 22 can be smoothly rotated by maintaining the meshing by the gear 92, and further smooth belt driving is performed. Becomes possible. In particular, when the driven roll (transfer roll) 23 is configured to be able to move up and down by IN / OUT as in this embodiment, the secondary transfer conveyance belt 21 is twisted only by allowing horizontal movement. It is effective to arrange the drive roll 22 so as to be movable in the horizontal direction and the vertical direction, since the drive roll 22 is likely to be in a closed state. Note that the bracket 93 shown in the first embodiment may be replaced with the bracket 97 shown in the second embodiment, and a driving device including the motor 91 and the gear 92 may be integrally formed so as to be vertically movable.

  Examples of applications of the present invention include image forming apparatuses such as printers, facsimile machines, and copiers.

1 is a diagram illustrating an image forming apparatus to which the exemplary embodiment is applied. FIG. 4 is an explanatory diagram illustrating a mechanism of a secondary transfer unit. FIG. 4 is a perspective view of the transfer belt unit as viewed from below. FIG. 4 is a diagram for further detailing a mechanism of the transfer belt unit. FIG. 5 is a diagram illustrating a state in which the secondary transfer conveyance belt is retracted (separated) from the intermediate transfer belt and the backup roll. FIG. 5 is a diagram illustrating a state in which the secondary transfer conveyance belt is in contact (contact) with the intermediate transfer belt side. (a)-(c) is a figure which shows the mechanism for connecting a transfer belt unit to a flame | frame in Embodiment 2. FIG.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 10 ... Image forming unit, 11 ... Photoreceptor drum, 15 ... Intermediate transfer belt, 16 ... Primary transfer roll, 20 ... Secondary transfer part, 21 ... Secondary transfer conveyance belt, 22 ... Drive roll, 23 ... Driving roll (transfer Roll: 25, backup roll, 53: transport chute, 56: chute lifting cam, 57: chute spring, 70: backup roll unit, 72: positioning pin, 80: transfer belt unit, 81: fulcrum, 82: swing Arm, 83: Retract cam, 84: Rotating shaft, 87: Coil spring, 88: Positioning member, 89: Bearing, 91: Motor, 92: Gear, 93: Bracket, 94: Slot, 95: Screw, 96: Plate , 97: bracket, 97a: elongated hole, 98: regulating member, 99: screw

Claims (6)

A carrier on which the toner image is carried;
A transfer belt configured to transfer the toner image carried by the carrier to a recording material, and to be configured to be able to contact and separate from the carrier.
A drive shaft that is provided on the downstream side of the transfer belt in the recording material conveyance direction and drives the transfer belt, and is a central axis when the transfer belt comes into contact with and separates from the carrier.
Along with stretching the transfer belt provided on the recording material conveyance direction upstream side of the transfer belt, and when the transfer belt abuts on the carrier, a driven roll pressed toward the carrier,
A swing arm that forcibly releases the pressing force of the driven roll against the carrier by rotating about a fulcrum,
A conveyance belt that conveys the recording material conveyed by the transfer belt further downstream from the transfer belt ,
The image forming apparatus according to claim 1, wherein the drive shaft provided on the transfer belt side of the transfer belt is displaceable with respect to a position of the transfer belt. The image forming apparatus according to claim 1 , wherein the conveyance belt conveys the recording material after the transfer of the toner image from a downstream side of the transfer belt to a fixing unit.   The image forming apparatus according to claim 1, wherein the transfer belt is driven by a drive roll having the drive shaft as an axis, and is stretched by a driven roll made of a rubber roll and the drive roll.   The image forming apparatus according to claim 3, wherein the drive roll is made of SUS. The image forming apparatus according to claim 1, wherein the transfer belt is an endless annular belt having a volume resistivity of 10 ⁶ to 10 ¹⁰ Ω · cm. The image forming apparatus according to claim 1, further comprising a coil spring acting on the swing arm to press the driven roll toward the carrier .

Images