JP5617664B2 - Recording medium conveying apparatus and image forming apparatus - Google Patents

Description

  The present invention includes a recording medium conveying apparatus that conveys a recording medium on which an image is formed by an image forming section that forms an image on a recording medium such as paper with a liquid recording agent, and the image forming section and the recording medium conveying apparatus. The present invention also relates to various image forming apparatuses such as a printer, a plotter, a printing apparatus, a copying apparatus, a digital multifunction peripheral, and a facsimile apparatus.

In the various image forming apparatuses as described above, an electrophotographic method, a wire dot method, an ink jet method, a thermal method, a thermal transfer method, an ink jet method, a stencil printing method, etc., depending on the image forming method in the image forming unit (means). Various methods are used.
In either case, generally, a recording medium represented by paper is supplied to the image forming unit, where an image such as a character, photograph, or figure is formed, and then the recording medium is conveyed in the paper discharge direction. For the recording medium conveying apparatus for that purpose, a conveying roller pair comprising a driving roller and a driven roller that rotates in contact with the driving roller is generally used.

However, when the image forming unit forms an image on a recording medium with a liquid recording agent (hereinafter referred to as “ink”) such as an inkjet method or a stencil printing method, the ink of the image formed in the image forming unit is It does not dry immediately and needs to be dried while being conveyed.
Therefore, for example, a spur roller (a kind of point contact roller) in which a plurality of spurs with star-shaped or gear-shaped protrusions formed on the outer periphery are arranged at intervals in the axial direction is used as the driven roller of the pair of transport rollers. A technique is employed in which the image surface side of the recording medium is regulated by a spur roller, and the driven roller and the image surface of the recording medium are brought into point contact to prevent rubbing of dirty ink.

For example, in Patent Document 1 (Japanese Patent Laid-Open No. 2006-35866), in an inkjet recording apparatus, a recording medium conveying unit that conveys a recording medium after image recording is supported by a conveying roll that supports the side opposite to the recording side of the recording medium. And a plurality of spurs that are held by the holding member so as to face the conveyance roll and are in contact with the recording side of the recording medium.
Then, the holding member is divided into a plurality of blocks in the width direction orthogonal to the conveyance direction of the recording medium, each of the blocks holds a plurality of spurs rotatably, and the spurs to be held are added in the direction of the conveyance roll. It is also described that the pressurizing force to be set can be set for each block, and the pressure contact pressure between the spur and the transport roll is set to be constant, thereby reducing the number of parts and assembly man-hours.

Further, in Patent Document 2 (Japanese Patent Laid-Open No. 2004-203526), in an ink jet printer, a first transport unit is disposed on the upstream side of the ink head, and a second transport unit is disposed on the downstream side. Each of the second conveying means is composed of a plurality of roller pairs composed of a driving roller and a driven roller arranged in a direction orthogonal to the conveying direction of the recording medium, and the driven roller of the second conveying means is composed of a star-shaped spur, The second conveying means sets the nipping pressure of the recording medium by the driving roller and the driven roller lower than that of the first conveying means, and other than the nipping pressure of the outermost roller pair in the direction orthogonal to the conveying direction. It is described that it is set higher than the holding pressure of the roller pair.
By doing so, even when some deformation occurs at the tip of the recording medium, the recording medium can be securely held without applying excessive pressure by the star-shaped spur, and the recording medium is transported in a stable state. It is also described that it can.

Further, Patent Document 3 (Japanese Patent Application Laid-Open No. 2009-137167) discloses an image forming apparatus including a recording head that forms an image by ejecting ink onto a sheet, and in the conveying direction downstream of the recording head in the sheet conveying direction. Is provided with a paper discharge transport means comprising a plurality of transport rollers arranged at intervals and a plurality of spurs facing each of the transport rollers, and the plurality of spurs are retracted from the transport path with the most downstream side in the transport direction as a fulcrum. It is described that the guide member is held so as to be rotatable in the direction, and can be stopped and held in a state where the guide member is rotated in the retracting direction.
Accordingly, it is described that, when an image is formed on a sheet with conspicuous traces of spurs, the number of spurs contacting the sheet can be reduced, so that the spurs can be made inconspicuous.

  However, in such an image forming apparatus, when the conveyance distance of the recording medium (paper) after image formation is long, a plurality of pairs of conveyance rolls (rollers) and spur rollers or blocks are required along the conveyance direction. Become. Further, when an ink jet method using water-based ink is used as the image forming means, the ink dries out the worst immediately after the image formation, so the contact pressure between the paper and the spur needs to be the lowest. Further, when transporting thick paper, a large transport force is required.

  In the prior art described in Patent Document 1, a plurality of recording medium conveying means including a conveying roll and a plurality of blocks holding a plurality of spurs facing the conveying roll are arranged along the conveying direction of the recording medium. In order to satisfy the conditions, it is necessary to considerably increase the number of spurs for each recording medium conveying means (the larger the number of spurs, the larger the contact area with the recording medium, so the contact pressure at each contact point is small. If each recording medium conveying means is configured in the same manner, the number of spurs in the entire apparatus becomes very large, so that there is a problem that it is not realistic in view of assembly and cost.

  In the prior art described in Patent Document 2, the second conveying unit sets the holding pressure of the recording medium by the driving roller and the driven roller to be lower than that of the first conveying unit, and is in a direction orthogonal to the conveying direction. It is necessary to set the pinching pressure of the outermost roller pair to be higher than the pinching pressure of the other roller pairs. Nipping pressure setting is required, which is not realistic. Furthermore, it becomes more difficult to perform the same holding pressure setting for a plurality of rollers arranged along the recording medium conveyance direction.

  On the other hand, if the adjustment of the holding pressure is to be dealt with by the contact area between the recording medium and the spur, the roller pair arranged immediately after the image forming unit where the lightest pressure is required from the ink drying speed in the ink jet method. As it goes to the downstream side, it is necessary to make the pressure further light, and there is a problem that the number of spurs as the whole apparatus becomes extremely large.

  According to the prior art described in Patent Document 3, in the state where the guide member is rotated in the retracting direction, only the transport roller on the most downstream side and the spur opposed thereto contribute to the transport of the recording medium. There is a problem that only a long-sized recording medium can be transported in the transport direction. Moreover, even if it comprises in this way, it does not lead to reducing the number of spurs.

  The present invention has been made in order to solve the above-described problems. An image forming apparatus including an image forming unit that forms an image on a recording medium using a liquid recording agent such as ink, and an image formed by the image forming unit. In a recording medium conveying apparatus that conveys a recording medium on which the recording medium is formed, even if the recording medium conveying path becomes long due to drying of ink, reverse paper discharge or double-sided image formation, the recording medium Can be reliably transported without fouling, and the pressure spring common to various point contact rollers can be used to reduce parts cost and assembly cost. An object of the present invention is to reduce the number of spurs of the spur roller.

In order to achieve the above object, a recording medium conveying apparatus according to the present invention comprises a recording medium conveying apparatus that conveys a recording medium on which an image is formed with a liquid recording agent in an image forming unit as follows.
The recording medium includes a driving roller that contacts the surface of the recording medium on which the current image is not formed and a driven roller that contacts the surface of the recording medium on which the current image is formed. The driven roller is pressed against the driving roller with a constant urging force. A plurality of pairs of conveyance rollers are arranged at intervals along the conveyance path of the recording medium.
The driven roller of each transport roller pair is a point contact roller, and point contact of the transport roller pair according to the transport time or transport distance of the recording medium on which the image is formed from the image forming unit to each transport roller pair. The contact area between the roller and the recording medium was reduced.

It is desirable that the relationship between the conveyance time or conveyance distance of the recording medium and the contact area between the point contact roller and the recording medium is an inversely proportional relationship.
Each of the point contact rollers is constituted by a spur roller having a plurality of spurs, and the transport roller according to the transport time or transport distance of the recording medium on which the image is formed from the image forming unit to each transport roller pair. The number of spurs of the pair of spur rollers may be reduced, or the spur tooth thickness may be reduced.

  Each of the point contact rollers is composed of an abrasive roller in which abrasive grains are bonded to the outer surface of the roller at a uniform density, and the recording medium on which the image is formed from the image forming unit to each pair of conveying rollers is conveyed. Depending on the time or transport distance, the size of the abrasive grains in the abrasive roller of the transport roller pair may be reduced.

  Alternatively, each of the point contact rollers is composed of an abrasive roller in which abrasive grains of a uniform size are adhered to the outer surface of the roller, and the image from the image forming unit to each of the conveying roller pairs is formed. Depending on the conveyance time or conveyance distance of the recording medium, the density of abrasive grains in the abrasive roller of the conveyance roller pair may be sparse.

  Further, each point contact roller is constituted by a knurling roller having a knurled outer surface of the roller, and the conveyance time or conveyance of the recording medium on which the image is formed from the image forming unit to each of the conveyance roller pairs. Depending on the distance, the knurling pitch of the knurling roller of the pair of conveying rollers may be coarse.

In these recording medium conveying apparatuses, guide plates facing each other with a predetermined gap are formed so as to form a conveying path for the recording medium in a path between the pair of conveying rollers adjacent in the conveying direction of the recording medium. One or more point contacts are provided on the guide plate side that regulates the side of the recording medium on which the current image is formed among the guide plates facing each other so as to partially protrude from the guide plate into the gap. An idler roller should be installed.
In this case, the contact area between the point contact idler roller and the recording medium is reduced according to the transport time or transport distance of the recording medium on which the image is formed from the image forming unit to each point contact idler roller. Even better.

It is desirable that the relationship between the conveyance time or conveyance distance of the recording medium and the contact area between the point contact idler roller and the recording medium is an inversely proportional relationship.
Further, it is desirable that an amount of protrusion of each point contact idler roller from the guide plate into the gap is 1/2 or more of the gap interval and less than the gap.
Further, the point contact roller, which is the driven roller of the pair of transport rollers, also extends along the transport path of the recording medium of the guide plate that regulates the surface of the recording medium on which the current image is formed, among the guide plates facing each other. It may be arranged so as to protrude from the line in the direction within the gap by an amount that is 1/2 or more of the gap interval and less than the gap interval.

An image forming apparatus according to the present invention includes an image forming unit that forms an image on a recording medium with a liquid recording agent, a recording medium supply device that supplies the recording medium to the image forming unit, and any one of the recording medium conveying devices described above. It is characterized by having.
It is particularly effective that the image forming unit is an ink jet type image forming unit including one or more ink jet heads.

  The recording medium conveying apparatus according to the present invention and the image forming apparatus provided with the recording medium conveying apparatus are provided even if the conveying path for conveying the recording medium on which the image is formed by the liquid recording agent in the image forming unit in an undried state is long. Since the image surface can be reliably conveyed without being stained, and a pressure spring common to various point contact rollers can be used, the parts cost and the assembling cost can be reduced. In addition, when a spur roller is used as the point contact roller, the number of spurs can be reduced as the spur roller disposed on the downstream side in the transport direction, so the number of spurs used in the entire apparatus is reduced to reduce costs. be able to.

1 is a diagram illustrating a recording medium conveyance path of a first embodiment of an image forming apparatus to which a recording medium conveyance apparatus according to the present invention is applied. It is a top view which shows the structure of the switchback roller pair 74 in FIG. FIG. 7 is a plan view illustrating a configuration of a conveyance roller pair 75 in FIG. 1. FIG. 7 is a plan view illustrating a configuration of a conveyance roller pair 76 in FIG. 1. It is a top view which shows the structure of the conveyance roller pair 77 in FIG. FIG. 3 is an exploded view showing a spur roller 74c in FIG. 2 exploded in a thrust direction. FIG. 7 is an exploded view showing the spur roller 77c in FIG. 5 in a thrust direction. It is the figure which looked at each component of the spur roller 74c in FIG. 6 from the axial direction individually.

It is sectional drawing of the blade edge vicinity of a spur which shows an example of another method of changing the contact area with the recording medium of a spur roller. It is sectional drawing of the blade edge | tip vicinity of a spur which shows another example similarly. It is a top view of the drive roller and driven roller of the Example which used the abrasive roller as a point contact roller. It is a top view of the driven roller of the other Example which uses the abrasive roller as a point contact roller. It is a top view of the driven roller of the Example which uses the knurled roller as a point contact roller. It is a figure which shows the recording medium conveyance path | route of 2nd Example of the image forming apparatus to which the recording medium conveyance apparatus by this invention is applied. It is a figure which expands and shows a part of duplex unit 8 in FIG.

Hereinafter, embodiments for carrying out the present invention will be specifically described with reference to the drawings.
In each embodiment described here, the recording medium is referred to as “paper”, but includes plain paper, recording paper, recording sheet, transfer paper, and the like. In addition, the recording medium is not limited to paper, but a sheet or long sheet that can form an image with a liquid recording agent (generally referred to as ink) such as a sheet or film of resin or metal, cloth, leather, etc. But you can.
Image formation includes the formation of characters, photographs, graphics, etc. on a recording medium by recording, printing, printing, printing, or the like.

[First Embodiment of Image Forming Apparatus]
A recording medium conveyance path of a first embodiment of an image forming apparatus to which the recording medium conveyance apparatus according to the present invention is applied will be described with reference to FIG. The image forming apparatus 1 shown in FIG. 1 is an ink jet type image forming apparatus.
First, an outline of an image forming process in the image forming apparatus 1 will be described.

  A sheet as a recording medium is supplied to the image forming unit 5 from the first sheet feeding unit 2 or the external second sheet feeding unit 3 in the image forming apparatus 1, and an inkjet image is formed in the image forming unit 5. The image forming unit 5 includes four line-type inkjet heads 51 to 54 that use four color inks of black (K), cyan (C), magenta (M), and yellow (Y) as liquid recording agents, respectively. An inkjet image forming unit that can form a full color image.

  Each of the line-type inkjet heads 51 to 54 has a length corresponding to the maximum width orthogonal to the sheet conveyance direction, and can simultaneously form one line image over the entire width of the sheet, so that high-speed printing is possible. However, a serial type ink jet head in which ink nozzles are mounted on a carriage and an image is formed while moving in the width direction of the paper may be used.

  The post-image forming conveyance unit 7 that conveys the sheet on which the inkjet image is formed in the image forming unit 5 is a horizontal conveyance path A that is directly discharged to the left discharge outlet 9 and an image in the image forming unit 5. A conveyance path B branched from the conveyance path A after formation, and a conveyance path C and a conveyance path D for discharging the paper 10 conveyed by the conveyance path B through the switchback roller pair 74 and then discharging the paper to the discharge outlet 9. It has.

The conveyance path C also serves as a switchback path. When it is detected that the rear end of the sheet 10 has reached the position of the switchback sensor 73, the conveyance of the sheet 10 is temporarily stopped, and then the switchback roller pair 74 is turned on. The paper 10 is reversely rotated to reverse the transport direction of the paper 10 and is guided to the paper discharge outlet 9 through the transport path D. In addition, in order to form an image on the back side of the sheet 10 on which an image is formed on the front surface, a duplex unit 8 having a duplex conveyance path E that leads to the image forming unit 5 again is provided.
Even when the paper 10 passes through any of the transport paths C, D, and E, it is a transport path through which the paper 10 is transported by the switchback roller pair 74 of the transport unit 7 after image formation.
In this embodiment, a recording medium conveying apparatus is constituted by these conveying paths.

Here, a description will be given of the difference in purpose between when the paper is discharged through the transport path A and when the paper is discharged through the transport path C. FIG.
Paper that passes through the transport path A: Paper with a kilo-continuous amount of 210 kg paper or more Paper that passes through the transport path C: Paper with a kilo-continuous amount of less than 210 kg paper Since it cannot withstand, paper is discharged without reversing or double-sided printing.

A sheet of paper having a kilo-unit weight of less than 210 kg has low paper rigidity and can withstand bending conveyance, so that it is led to a conveyance path for performing reversal processing and double-sided printing.
Another object of the present invention is to discharge the ink after the ink is sufficiently dried in a state where the sheet is held by the pair of conveying rollers by passing through a long conveying path.

  The first sheet feeding means 2 in the image forming apparatus 1 includes two sets of sheet feeding trays 21 and 22, pickup rollers 21 a and 22 a, feed rollers 21 b and 22 b, reverse rollers 21 c and 22 c, and conveyance roller pairs 21 d and 22 d. It has. Further, a pre-registration conveyance unit 4 and a registration roller pair 13 are provided by conveyance roller pairs 11 and 12 each composed of a driving roller and a driven roller. These components constitute a recording medium supply device that supplies a recording medium (paper) to the image forming unit 5.

  Hereinafter, the paper transport path will be described in detail by taking as an example a case where paper is fed from the lower paper feed tray 22 in the first paper feed means 2. Note that the rotation direction of the roller and the conveyance direction of the sheet according to the following description are all in FIG.

(1) When printing on only one side of a paper of 210 kg or more, and ejecting the paper with the image side facing up The paper loaded on the paper feed tray 22 is transferred to a pickup roller 22a by a mechanism (not shown). The sheet is then brought into contact with pressure, and then paper feeding is started by the left rotation of the pickup roller 22a.
Thereafter, the sheet is separated into a single sheet by a feed roller 22b that rotates in the direction of feeding out the paper and a reverse roller 22c that rotates in the direction of pulling back the sheet, and is fed in the direction of the arrow, and consists of a driving roller and a driven roller. The sheet is conveyed upward (in the direction of the arrow) by a pair of conveyance rollers 22d and a similar pair of conveyance rollers 21d subsequent thereto.

  The sheet is further conveyed through the pre-registration conveyance unit 4 by conveyance roller pairs 11 and 12 each composed of a driving roller and a driven roller, and reaches the registration roller pair 13 in a stopped state. After the leading edge of the sheet abuts against the registration roller pair 13 to form a predetermined warp (deflection) and the skew is corrected, the sheet is re-conveyed by the registration roller pair 13 at a predetermined timing. Adsorbed to the endless wide belt 61.

The endless wide belt 61 is rotatably stretched by a driving roller 62 and three driven rollers 63, 64, 65, is given a predetermined tension by a tension roller 66, and is counterclockwise by a driving device (not shown). It is driven to rotate around.
A large number of holes are formed in the endless wide belt 61. By sucking air through the holes by a fan (not shown), the sheet can be conveyed while adsorbing the back surface thereof.

After the leading edge of the sheet transferred from the registration roller pair 13 to the endless wide belt 61 is detected by the sensor 67, black (K), cyan (C), The magenta (M) and yellow (Y) four-color line-type inkjet heads 51 to 54 are sequentially driven.
In this manner, ink is sequentially ejected from the nozzles at the tips of the four color line-type inkjet heads 51 to 54, thereby forming a full-color inkjet image on one surface of the paper.

In the meantime, the endless wide belt 61 is driven so that there is no speed fluctuation as much as possible. Actually, the speed fluctuation is detected by a detection device (not shown), and ink is ejected at an accurate timing according to the movement of the paper. Is called.
The sheet on which the inkjet image is formed is conveyed to the left in the horizontal direction as it is. However, based on the sheet thickness information of the sheet input by the operator in advance or automatically detected by the image forming apparatus 1, the kilo continuous amount of 210 kg sheet In the case of the above paper, the switching claw 71a of the conveyance unit 7 after image formation is moved to the position indicated by the dotted line, and is guided to the horizontal conveyance path A by the switching claw 71a.

  Then, the image surface is conveyed in a non-contact manner by a suction force by a roller 71c and a perforated endless belt 71b spanned between the rollers 71d provided in the conveyance path A and an air suction fan (not shown). Thereafter, the sheet is conveyed leftward by a pair of discharge rollers 79 including a driving roller 79 a and a driven roller 79 b, and is discharged out of the image forming apparatus 1 via a discharge outlet 9. A discharge tray (not shown) or a post-processing device such as a finisher is installed downstream of the discharge outlet 9.

(2) When printing on only one side of a sheet of less than 210 kg of kilo-continuous paper and ejecting it with the image side facing up After the sheet is fed and conveyed from the sheet feeding tray 22, a predetermined timing is set by the registration roller pair 13. This is the same as in the case of (1) described above until the image forming unit 5 forms an inkjet image while being re-conveyed and adsorbed and conveyed by the endless wide belt 61 of the non-contact conveying unit 6.

  When the paper thickness information of the paper input by the operator in advance or automatically detected by the image forming apparatus 1 is less than 210 kg paper, the position where the switching claw 71a of the post-image forming transport unit 7 is indicated by a solid line The sheet on which the inkjet image is formed is guided to the conveyance path B. Also in the transport path B, the paper 10 is sucked and transported by the endless wide belt 61.

  The conveyed sheet 10 is guided to the switching claws 68 and 72 at the position indicated by the solid line and reaches the conveyance path C. Thereafter, the sheet 10 is transported by the switchback roller pair 74 and the transport roller pairs 75 to 78 each consisting of a pair of rollers in the transport path C without being stopped, and passes through the rear part of the transport path A to the discharge roller pair 79. The paper is nipped and conveyed by the pair of paper discharge rollers 79 and is discharged from the paper discharge outlet 9. By discharging the sheet on which the image is formed by the image forming unit 5 through such a long conveyance path, the ink on the sheet can be discharged after being sufficiently dried.

Each pair of rollers constituting the switchback roller pair 74 and the conveying roller pairs 75 to 78 includes driving rollers 74a, 75a, 76a, 77a, 78a and driven rollers 74b, 75b, 76b, 77b, 78b. Among them, the driving rollers 74a, 75a, 76a, and 77a are controlled to rotate forward and backward by motors (not shown).
In this case, the drive rollers 74a, 75a, 76a, 77a are driven to rotate counterclockwise. The drive roller 78a is always driven to rotate clockwise by a motor (not shown).

(3) When printing on only one side of a sheet of less than 210 kg of paper and discharging the image side down After the sheet is fed and conveyed from the sheet feeding tray 22, a predetermined timing is set by the registration roller pair 13. The image forming unit 5 forms an ink jet image while being attracted to and transported by the endless wide belt 61 of the non-contact transport unit 6, and then the switching claws 68 and 72 located at the positions indicated by solid lines through the transport path B. The process up to the conveyance path C after being guided is the same as in the case of (2) described above.

If the paper thickness information of the paper input by the operator in advance or automatically detected by the image forming apparatus 1 is less than 210 kg paper, and the reverse discharge is set by the print instruction information, the switchback roller pair When the switchback sensor 73 detects the rear end of the sheet 10 that is nipped by the sheet 74 and conveyed downward (in the direction of the arrow), the switchback roller pair 74 and the conveyance roller pair of the conveyance unit 7 after image formation are triggered by the detection. The driving of 75 to 77 is stopped once, and the sheet is stopped at that position. At the same time, the switching claw 72 is moved to a position indicated by a dotted line by an actuator (not shown). At this time, the switching claw 68 remains at the position indicated by the solid line.

Thereafter, at a predetermined timing, the drive rollers 74a, 75a, 76a, and 77a of the switchback roller pair 74 and the conveyance roller pairs 75 to 77 are reversely driven clockwise. As a result, the sheet is switched back and guided by the switching claw 72, merges with the conveyance path C via the conveyance path D, and is conveyed upward (in the direction of the arrow) by the conveyance roller pair 78 in which the driving roller 78a rotates clockwise. Then, the paper is sandwiched and conveyed by the pair of paper discharge rollers 79 via the rear portion of the conveyance path A, and is discharged from the paper discharge outlet 9 with the image surface facing down.
In this case, when the sheets on which images of a plurality of pages are sequentially formed are stacked and discharged, the image surface is facing downward, so the page order is aligned, and it is necessary to rearrange after removing the sheets. Disappear. The point that the ink on the paper can be discharged after being sufficiently dried is the same as in the case of (2).

Here, the merging position X of the conveyance path D to the conveyance path C is set downstream of the conveyance roller pair 77 that holds the maximum size of the length in the sheet conveyance direction when the sheet 10 is stopped due to switching back. Has been.
Therefore, the sheet after the switchback is smoothly conveyed by the switchback roller pair 74 and the conveyance roller pairs 75 to 78.

(4) When double-sided printing is performed on a sheet of less than 210 kg paper, the sheet is fed and conveyed from the sheet feeding tray 22 and then re-conveyed by the registration roller pair 13 at a predetermined timing. An inkjet image is formed in the image forming unit 5 while being adsorbed and conveyed by the endless wide belt 61, and then guided to the switching claw 68 and 72 at a position indicated by a solid line through the conveyance path B until reaching the conveyance path C. This is the same as (2) above.

Even if the paper thickness information of the paper input by the operator in advance or automatically detected by the image forming apparatus 1 is less than 210 kg of continuous paper and duplex printing is set by the print instruction information, ) When the sheet 10 on which the image is formed enters the conveyance path C from the conveyance path B through the switchback roller pair 74, the drive rollers 75a, 76a, 77a of the conveyance roller pair 75, 76, 77 are Turn the paper counterclockwise and load the paper.

  Thereafter, when the switchback sensor 73 detects the trailing edge of the paper 10, the switchback roller pair 74 and the conveying roller pairs 75, 76, and 77 are driven to be triggered by this, and the paper 10 is stopped. At the same time, the switching claw 68 is moved to a position indicated by a dotted line by an actuator (not shown). At this time, the switching claw 72 remains at the position indicated by the solid line.

  Then, the switchback roller pair 74 and the conveyance roller pairs 75, 76, 77 are driven in reverse at a predetermined timing, the paper 10 is switched back, guided by the switching claw 68, and conveyed to the duplex conveyance path E by the duplex unit 8. The The double-sided conveyance path E is provided with a pair of double-sided conveyance rollers 81, 82, and 83 each consisting of a pair of driving rollers 81a, 82a, and 83a and driven rollers 81b, 82b, and 83b that are driven clockwise.

  Thereafter, the sheet 10 is conveyed in the direction of the arrow by the duplex conveying rollers 81 to 83 on the duplex conveying path E, and is returned to the pre-registration conveying unit 4. Then, the leading end abuts against the registration roller pair 13 to form a predetermined warp (deflection), and the skew is corrected. Thereafter, the image is re-conveyed by the registration roller pair 13 at a predetermined timing, and an image is formed on the back surface by the image forming unit 5 while the front side is adsorbed and conveyed by the endless wide belt 61 of the non-contact conveying unit 6. .

Thereafter, the sheet is again conveyed along the conveyance path B and the conveyance path C, and is discharged from the discharge outlet 9 by the discharge roller pair 79 through the rear part of the transfer path A. At this time, the switching claw 68 has returned to the position indicated by the solid line, and in the transport path C after backside printing, the switchback roller pair 74 transports the paper without stopping it to ensure the productivity of double-sided printing. doing.
In this case, since the front surface on which the image is formed at the front of the paper is discharged downward, the page order is aligned and discharged through the conveyance path C. Therefore, the ink on the back surface on which the image is formed later The paper can be discharged after it is sufficiently dried.

[Point contact roller]
Hereinafter, the point contact roller employed in this embodiment will be described in detail.
In this embodiment, the switchback roller pair 74, the conveyance roller pairs 75 to 78 on the conveyance path C downstream in the conveyance direction, the paper discharge roller pair 79, and the duplex conveyance roller pairs 81 to 83 on the duplex conveyance path E. , The driving rollers 74a to 79a and 81a to 83a are in contact with the side of the paper on which the current image is not formed, and the driven rollers 74b to 79b and 81b to 83b are the surfaces on which the current image of the paper is formed. The sheet is conveyed while contacting the side and holding the sheet.

Therefore, point driven rollers that are substantially point-contacted with the paper are employed as the driven rollers 74b to 79b and 81b to 83b that are in contact with the surface of the paper on which the current image is formed.
The point contact roller makes point contact with the image surface where the ink on the paper is insufficiently dried, thereby minimizing the contact area between the point protrusion on the point contact roller side and the ink attached to the paper. .

  As a result, the ink on the image surface of the paper is less likely to adhere to the point contact roller, and the ink adhering to the point protrusion of the point contact roller is not noticeable even when retransferred to the paper. That is, the point contact roller is used for the purpose of preventing the image formed on the paper from being deteriorated. Examples of the point contact roller include a spur roller (star roller), an abrasive roller, and a knurled roller. The abrasive roller is a roller in which a large number of abrasive particles (ceramic, glass, etc.) are bonded to the outer surface of the roller.

As described above, a plurality of pairs of conveyance rollers are arranged at intervals along the conveyance path of the sheet on which the image is formed, and the point contact roller as a driven roller is fixed to the drive roller by a spring described later. It is made to press with the energizing force of.
The closer to the image forming unit 5, the undried ink of the image formed on the paper, and it dries as it is conveyed (as time passes). For this reason, the conveyance roller pair close to the image forming unit 5 needs to reduce the contact pressure at each contact point between the point contact roller and the sheet, but it is necessary to ensure a predetermined conveyance force.

In order to transport the paper, a transport force of a predetermined amount or more is required regardless of the position in the transport direction, but in order to prevent contamination due to ink adhesion or rubbing, each pair of contact points is close to the transport roller pair close to the image forming unit 5. It is necessary to reduce the contact pressure at. Therefore, according to the present invention, the total contact area (contact area at each contact point × number of contact points) between the point contact roller of the pair of transport rollers close to the image forming unit 5 and the sheet is increased to ensure the transport force. .
On the other hand, since the ink is dried away from the image forming unit 5, the contact pressure at each contact point can be increased at a position far from the image forming unit 5, and as a result, in order to ensure a predetermined conveying force, The contact area between the point contact roller and the paper can be reduced (the number of contact points can be reduced).

Therefore, in the present invention, the conveyance time (including the stop time at the switchback roller pair 74) or conveyance of the sheet on which the image is formed from the image forming unit 5 to each conveyance roller pair (including the switchback roller pair 74). In accordance with the distance (conveying speed × conveying time), the contact area between the point contact roller of the carrying roller pair and the paper is reduced (the number of contact points is reduced).
It is desirable that the relationship between the sheet conveyance time or conveyance distance and the contact area between the point contact roller and the sheet is an inversely proportional relationship.

[Example in which the point contact roller is a spur roller]
First, an embodiment in which a spur roller is used as the point contact roller will be described. That is, the switchback roller pair 74 and the driven rollers 74 b to 78 b of the conveyance roller pair 75 to 78, the driven roller 79 b of the paper discharge roller pair 79, and the double-sided conveyance of the duplex unit 8 in the post-image forming conveyance unit 7 in FIG. In this embodiment, spur rollers that are point contact rollers are used as the driven rollers 81b, 82b, and 83b of the roller pairs 81 to 83, respectively.

In this embodiment, after the image formation in the image forming unit 5, first, the non-contact conveyance unit 6 performs conveyance that does not contact the image surface side of the paper. Thereafter, the paper is nipped and conveyed for the first time by the switchback roller pair 74, but in consideration of undried ink, low-pressure conveyance by the point contact roller (driven roller 74b) is performed here.
As shown in FIG. 2, the drive roller 74a of the switchback roller pair 74 has a configuration in which a roll-shaped rubber layer 26 is formed on the outer periphery of a metal shaft-shaped metal core 25, and the rubber layer 26 is spaced in the thrust direction. Is divided into 6 pieces.

  On the other hand, the driven roller 74b is constituted by a spur roller 74c divided into six parts in the thrust direction corresponding to the rubber layer 26 of the drive roller 74a. Each spur roller 74c is held at both ends in the axial direction by a pair of bearings 31, and each bearing 31 is urged toward the driving roller 74a by a spring 32 having the same spring characteristics. Each bearing 31 is regulated in the thrust direction and radial direction by a bearing support 33. All the bearing support portions 33 are fixed to a common connecting rod 34.

  Each spur roller 74c has a deformed shaft 37 in which a flange 35 is integrally formed by a mold, a flange 36 on the opposite side, and the same plate-shaped spur 38 as shown in FIG. It is composed of seven identical spacers 39 inserted between the seven spurs 38 and the adjacent spurs 38 respectively.

  As shown in FIG. 8, the deformed shaft 37 has a shape in which a part of the cylindrical shaft in the radial direction is chamfered in a planar shape, and the deformed shaft 37 penetrates the flange 36, the spur 38, and the spacer 39. A deformed hole H having the same shape is formed. Then, by fitting the deformed shaft 37 and the spur 38 with the deformed hole H, both are positioned in the radial direction. The spacer 39 and the flange 36 may form a perfect hole instead of the deformed hole H.

As shown in FIG. 8, the spur 38 is a star-shaped or gear-shaped point contact plate in which a large number of small protrusions are radially formed on the outer periphery.
At the time of assembly, from the state shown in FIG. 6, seven spurs 38 and six spacers 39 are sequentially inserted into the deformed shaft 37 with the flange 35 integrated, and the bearings 31 are fitted to both ends in the thrust direction. As a result, the bearings 31 are supported by the bearing support portions 33 fixed to the connecting rods 34 to restrict the position in the thrust direction.
The transport roller pairs 75, 76, 77 on the downstream side in the paper transport direction from the switchback roller pair 74 are configured as shown in FIGS. 3, 4, and 5, respectively. The configuration of the switchback roller pair 74 described in FIG. Therefore, in FIG. 3, FIG. 4, and FIG. 5, the parts corresponding to FIG.

Each of the driving rollers 75a, 76a, 77a of the conveying roller pair 75, 76, 77 has the same configuration as that of the driving roller 74a of the switchback roller pair 74, and has a roll shape on the outer peripheral portion of the metal shaft-shaped cored bar 25. The rubber layer 26 is formed by being divided into six parts at intervals in the thrust direction.
On the other hand, the driven rollers 75b, 76b, and 77b are similarly composed of spur rollers 75c, 76c, and 77c that are each divided into six in the thrust direction.

  Each spur roller 75c, 76c, 77c is held at both ends in the axial direction by a pair of bearings 31, and each bearing 31 is urged by a spring 32 toward the drive rollers 75a, 76a, 77a. Each bearing 31 is regulated in the thrust direction and radial direction by a bearing support 33. All the bearing support portions 33 are fixed to a common connecting rod 34.

As shown in FIG. 3, each spur roller 75c has six spurs and five spacers interposed therebetween. As shown in FIG. 4, each spur roller 76c has five spurs and four spacers interposed therebetween.
As shown in FIG. 5 and an exploded view of the spur roller 77c in FIG. 7, the spur roller 77c has four spurs and three spacers interposed therebetween.
In this manner, the number of spurs 38 in the spur roller that constitutes the driven roller is reduced as the pair of transport rollers is arranged on the downstream side in the paper transport direction. Other configurations are the same as the driven roller 74b and the spur roller 74c of the switchback roller pair 74, and thus the description thereof is omitted.

In other words, the total number of spurs 38 of the driven rollers of the transport roller pairs sequentially arranged in the paper transport path differs depending on the installation position. As a result, the contact area of the driven roller with the paper is different.
That is, in the embodiment of the present invention, an image is formed from the position of the yellow line type ink jet head of the image forming unit 5 in FIG. 1 which is the final image forming unit to the pair of conveying rollers provided on the downstream side in the sheet conveying direction. The conveyance time or conveyance distance of the sheet and the number of spurs 38 of the driven rollers of the conveyance roller pair, that is, the contact area with the sheet are in an inversely proportional relationship (the contact pressure at the contact point with the sheet is proportional). I have to.

  The paper on which the image is formed by the inkjet image forming unit dries the ink according to the elapsed time after the image formation. Therefore, when the paper is nipped and conveyed by a pair of conveyance rollers after image formation, nipping conveyance at a light pressure as much as possible is required immediately after the image formation by the inkjet head, and the pressure increases as the time after image formation elapses. Can be held and conveyed.

  The pair of transport rollers arranged on the downstream side in the sheet transport direction from the image forming unit 5 increases the transport distance until the sheet reaches after the image is formed, and therefore the sheet transport time becomes longer. As described above, the number of spurs of the driven roller is decreased in inverse proportion to the sheet conveyance time or conveyance distance, thereby reducing the contact area with the sheet and increasing (proportional) the contact pressure at the contact point with the sheet. I am doing so.

Therefore, the switchback roller pair 74 and the driven rollers 74b, 75b, 76b, and 77b of the pair of transport rollers 75 to 77 shown in FIGS. 75c, 76c and 77c are pressed against the drive roller side by the same urging force by the spring 32 having the same urging characteristic.
Even if each spur roller is pressed toward the driving roller with the same urging force, the smaller the number of spurs 38, the smaller the contact area with the paper, so the contact pressure at each contact point with the paper, that is, the pressure per unit area Becomes bigger. Thereby, a necessary conveying force can be obtained.

  In this way, all the same parts are used for the configuration of the switchback roller pair 74 and the conveyance roller pairs 75 to 77, and only the number of spurs of the spur rollers 74c, 75c, 76c, and 77c is changed. It is possible to provide a simple function, and the productivity and assemblability of parts are good, and it is possible to implement at low cost.

  Further, a driven roller 78b of the conveyance roller pair 78, a driven roller 79b of the paper discharge roller pair 79, and driven rollers 81b, 82b, 83b of the double-sided conveyance roller pairs 81, 82, 83 provided in the duplex unit 8 are also provided. It is comprised by the spur roller etc. which were similarly divided | segmented into plurality (six division in this example) by the same components as each driven roller mentioned above by FIGS. Then, the number of spurs in each spur roller is changed according to the transport time or transport distance until the sheet on which the image is formed arrives from the image final forming unit.

  In this embodiment, the spur roller of the driven roller 78b has five spurs, the spur roller of the driven roller 79b has seven spurs, the spur roller of the driven roller 81b in the duplex unit has five spurs, and the spur roller of the driven roller 82b. Has four spurs and the spur roller of the driven roller 83b has three spurs.

  In terms of the conveyance distance, the distance between “switchback roller pair 74 to conveyance roller pair 75”, the distance between “switchback roller pair 74 to conveyance roller pair 78 during reverse rotation”, and “switchback roller pair during reverse rotation”. 74 to the double-sided conveyance roller pair 81 "is substantially the same from the conveyance path necessary for feeding the minimum paper, but when switching back by reverse rotation of the switchback roller pair 74, a control for temporarily stopping the paper is entered. Therefore, it takes time, so that the ink dries more when it reaches the roller pair immediately after that.

Therefore, the number of spurs of the spur roller in the driven roller 78b of the transport roller pair 78 and the driven roller 81b of the double-sided transport roller pair 81 is 5 as compared to the number of spur rollers of the driven roller 75b of the transport roller pair 75. Can be reduced.
Further, the number of spurs of the spur roller in the driven roller 79b of the discharge roller pair 79 is as large as seven because there is a condition that the sheet is transported through the horizontal transport path A immediately after image formation.

As a method of changing the contact area of the spur roller with the paper, as described above, there is also a method of changing the contact area with the paper by changing the tooth tip thickness of each spur, in addition to changing the number of spurs in each spur roller.
FIG. 9 shows an example in which a spur 38 having the same thickness is used to form a slope 38b that thins the tooth tip toward the outer periphery by etching (= dissolving processing, chemical cutting, etc.) of the tooth tip portion 38a. Show. For example, as shown in FIG. 9, by changing the angle of the slope 38b, the tooth tip thickness can be changed to change the contact area with the paper. Alternatively, it is possible to change the thickness of the tooth tip simply by changing the etching amount of the tooth tip portion 38a while keeping the angle of the inclined surface 38b constant.
According to these methods, all spurs can be punched from a metal plate having the same thickness, but an etching process is required.

  9A shows a driven roller of a pair of conveyance rollers (for example, FIG. 9) arranged at a position relatively close to the image forming unit 5 in FIG. 1 on the downstream side in the sheet conveyance direction (paper conveyance time and conveyance distance is short). 1 is a cross-sectional view of the vicinity of the tooth tip portion of the spur 38 of the spur roller constituting the spur roller 74b), and the slope angle θ1 of the slope 38b formed on the tooth tip portion 38a by etching is small and the tooth tip thickness is as thick as W1. ing.

  (B) of the figure is a follower roller of a pair of conveyance rollers (for example, FIG. 1) arranged at a position relatively far from the image forming unit 5 in FIG. 1 on the downstream side in the sheet conveyance direction (paper conveyance time and conveyance distance is long). 77b) is a cross-sectional view of the vicinity of the tip portion of the spur 38 of the spur roller constituting the spur roller, and the inclination angle θ2 of the slope 38b formed in the tooth tip portion 38a by etching is large (θ2> θ1), and the tip thickness W2 thereof. Is as thin as W2 = (4/7) × W1.

  FIG. 10 shows an example in which a spur 38 having a different plate thickness is used and the tooth contact thickness (same as the plate thickness) is changed to change the contact area with the paper. According to this method, a plurality of types of metal plates having different thicknesses are required as spur materials, but etching is not necessary. Further, since a material with a thin plate thickness can be used, the material cost can be reduced.

FIG. 10A shows a spur roller that constitutes a driven roller (for example, 74b in FIG. 1) of a pair of conveyance rollers arranged at a position relatively close to the downstream side in the sheet conveyance direction from the image forming unit 5 in FIG. It is the spur 38, and the tooth tip thickness W1 of the tooth tip portion 38a due to the plate thickness is thick.
(B) of the figure is a spur of a spur roller constituting a driven roller (for example, 77b in FIG. 1) of a pair of conveyance rollers disposed at a relatively far position downstream of the image forming unit 5 in FIG. The tooth tip thickness W2 of the tooth tip portion 38a due to the plate thickness is as thin as W2 = (4/7) × W1.

[Example in which the point contact roller is an abrasive roller]
As another embodiment of the present invention, an embodiment in which the point contact rollers used as the respective driven rollers 74b to 79b and 81b to 83b of each of the conveying roller pairs shown in FIG. Will be explained by.
As described above, the abrasive roller is a roller in which a large number of abrasive particles (ceramic, glass, etc.) are bonded to the outer surface of the roller.

For example, the driven rollers 74b and 77b shown in FIGS. 11 and 12 are each composed of six abrasive roller 74d and 77d, and each of the abrasive rollers 74d and 77d has a metal, resin or rubber on the outer periphery of the shaft 41. Etc., and a large number of abrasive grains (any one of 43a to 43c) made of ceramic or glass are bonded to the outer surface of the roll portion.
In order to change the contact area with the paper according to the arrangement position (paper transport time or transport distance) on the downstream side in the paper transport direction from the image forming unit 5 shown in FIG. 1, in the example shown in FIG. The size of the abrasive grains in the grain roller is changed.

In FIG. 11, a driven roller 74b of a switchback roller pair 74, which is a pair of transport rollers disposed at a position relatively close to the downstream side in the paper transport direction from the image forming unit 5 (paper transport time and transport distance is short), is configured. In each abrasive roller 74d, relatively large abrasive grains 43a (contact area D) are adhered to the outer surface of the roll portion 42 with a substantially uniform density.
On the other hand, each of the abrasive rollers 77d constituting the driven roller 77b of the pair of transport rollers 77 disposed at a position where the paper transport time and transport distance are long is relatively far from the image forming unit 5 on the downstream side in the paper transport direction. Relatively small abrasive grains 43b (for example, contact area (4/7) × D) are bonded to the outer surface of the roll portion 42 at the same substantially uniform density as the abrasive roller 74d.

The drive roller 74a of the switchback roller pair 74 in FIG. 11 also has a configuration in which a roll-shaped rubber layer 26 is formed on the outer peripheral portion of the metal shaft-shaped cored bar 25 as described with reference to FIG. Is divided into six parts at intervals in the thrust direction. The drive rollers of the other transport roller pairs have the same configuration.
And if the abrasive roller which comprises each driven roller 74b-79b, 81b-83b in FIG. 1 is set to 74d-79d and 81d-83d, the magnitude | size (contact area) of the abrasive grain will be made into the following order.
74d = 79d>75d> 76d = 78d = 81d> 77d = 82d> 83d

FIG. 12 shows an embodiment in which the density of the abrasive grains in the abrasive roller is changed in order to change the contact area with the paper according to the arrangement position on the downstream side in the paper conveyance direction from the image forming unit 5 shown in FIG. An example is shown.
In FIG. 12, a driven roller 74b of a switchback roller pair 74, which is a pair of transport rollers, is disposed at a position relatively close to the downstream side in the paper transport direction from the image forming unit 5 (paper transport time and transport distance is short). In each abrasive roller 74d, a large number of abrasive particles 43c having a substantially uniform particle size are bonded to the outer surface of the roll portion 42 at a relatively high density.

On the other hand, each abrasive roller 77d constituting the driven roller 77b of the conveyance roller pair 77 disposed at a position relatively far away from the image forming unit 5 in the paper conveyance direction (paper conveyance time and conveyance distance is long) A large number of abrasive grains 43c having the same particle diameter as described above are bonded to the outer surface of the roll portion 42 at a relatively low density (for example, 4/7 of the abrasive density of the abrasive roller 74d).
And if the abrasive roller which comprises each driven roller 74b-79b, 81b-83b in FIG. 1 is set to 74d-79d and 81d-83d, the abrasive-grain density will be made into the following order.
74d = 79d>75d> 76d = 78d = 81d> 77d = 82d> 83d

Also in these examples in which an abrasive roller is used as the point contact roller, the structures of the abrasive roller bearing, the biasing spring, the bearing support, the common connecting rod and the like have been described with reference to FIGS. As in the embodiment using the spur roller, the assembling property can be improved. In addition, since the abrasive roller of any driven roller is pressed against the drive roller side with the same biasing force by the spring having the same biasing characteristic, the same spring can be used.
Even if each abrasive roller is pressed to the driving roller side with the same urging force, the contact area with the paper is smaller when the abrasive particle is smaller or the abrasive density is lower. The pressure per unit area increases. Thereby, even if the contact area is small, a necessary conveying force can be obtained.

[Example in which the point contact roller is a knurled roller]
As still another embodiment of the present invention, an embodiment in which the point contact rollers used as the driven rollers 74b to 79b and 81b to 83b of the respective transport roller pairs shown in FIG. 1 are knurled rollers will be described with reference to FIG. .
As shown in FIG. 13, each of the driven rollers 74b and 77b includes six knurling rollers 74e and 77e.

The knurled rollers 74e and 77e are formed with a roll 46 made of metal, resin, or the like on the outer periphery of the shaft 45, and on the outer surface of the roll 46 are uniformly inclined at 45 ° with respect to the axial direction. Knurls 47 with parallel grooves of pitch are provided.
In FIG. 13, the driven roller 74b of the switchback roller pair 74, which is a pair of transport rollers, is disposed at a position relatively close to the downstream side in the paper transport direction from the image forming unit 5 (paper transport time and transport distance is short). Each knurling roller 74e is provided with knurling 47 on the outer surface of the roller portion 46 at a relatively fine pitch (close interval).

On the other hand, each knurling roller 77e constituting the driven roller 77b of the conveyance roller pair 77 disposed at a position relatively far from the image forming unit 5 in the paper conveyance direction (long paper conveyance time and conveyance distance) Knurls 47 are applied to the outer surface of the portion 46 at a relatively coarse pitch (coarse spacing: for example, an interval 7/4 times that of the knurling roller 74e).
When the knurling rollers constituting the driven rollers 74b to 79b and 81b to 83b in FIG. 1 are 74e to 79ed and 81e to 83e, the pitch of the knurling 47 is set in the following order.
74e = 79e>75e> 76e = 78e = 81e> 77e = 82e> 83e

Also in this embodiment in which a knurling roller is used as the point contact roller, the structure of the knurling roller bearing, the spring for biasing, the bearing support portion, and the common connecting rod is the same as that of the spur roller described with reference to FIGS. The assembling property can be improved in the same manner as in the embodiment to be used. Since all the knurled rollers of the driven rollers are pressed against the drive roller side with the same urging force by the spring having the same urging characteristic, the same spring can be used.

  Even if each knurling roller is pressed to the driving roller side with the same urging force, the contact area with the paper becomes smaller when the pitch of the knurling is coarser, so the contact pressure at the contact point with the paper, that is, the pressure per unit area is growing. Thereby, even if the contact area is small, a necessary conveying force can be obtained.

[Second Embodiment of Image Forming Apparatus]
A recording medium conveyance path of a second embodiment of the image forming apparatus to which the recording medium conveyance apparatus according to the present invention is applied will be described with reference to FIGS. The image forming apparatus 1 ′ shown in FIG. 14 is also an ink jet type image forming apparatus similar to the image forming apparatus 1 shown in FIG. 1, and parts corresponding to those in FIG. Is omitted.

  Although not shown in FIG. 1, in such an image forming apparatus, the image forming unit 5 faces each other with a predetermined gap so as to form a transport path through which the paper on which the inkjet image is formed is transported. A guide plate is provided. As a technique for preventing paper contamination due to rubbing between the guide plate and the image surface, there is a technique in which a point contact idler roller is installed in a path between each pair of conveyance rollers that nipping and conveying the sheet.

  In the image forming apparatus 1 ′ shown in FIG. 14, the transport path downstream of the perforated endless belt 71 b of the transport path A, the transport paths C and D, and the double-sided transport path E are parallel to each other with a predetermined gap. A guide plate G is provided so as to oppose the plate. Then, the transport roller pair 74 in the transport path C, D from the switchback roller pair 74 to the transport roller pair 78 and the transport path from the switchback roller pair 74 to the duplex transport roller pair 83 in the duplex transport path E One or more guide plates G that pass between each of the guide plates G that face each other on the guide plate side that restricts the surface of the recording medium on which the current image is formed are projected into the gap. (1 to 3 in this embodiment) point contact idler rollers Y are arranged.

  In this embodiment, the driven rollers 74b of the switchback roller pair 74, the driven roller pairs 75 to 78 and the driven rollers 75b to 79b of the paper discharge roller pair 79, and the driven rollers 81b to 83b of the duplex conveying roller pairs 81 to 83 are used. Is a point contact roller such as a spur roller, an abrasive roller, or a knurling roller, and the point contact according to the conveyance time or conveyance distance of the paper on which the image is formed from the image forming unit 5 to each point contact roller. The contact pressure between the roller and the sheet is reduced (preferably inversely proportional), and the contact pressure at the contact point with the sheet is increased (proportional).

Further, in this embodiment, each point contact idler roller Y is also a point contact roller such as a spur roller, an abrasive roller, or a knurling roller, and an image from the image forming unit 5 to each point contact idler roller Y is displayed. The contact pressure at the contact point with the paper increases (proportional) so that the contact area between the point contact idler roller and the paper decreases (preferably inversely proportional) according to the transport time or transport distance of the formed paper. Like to do.

  Further, as shown in an enlarged view of a part of the duplex unit 8 in FIG. 15, the protrusion amount Z1 of the point contact idler roller Y from the guide plate G on the side facing the image surface of the sheet into the gap S is expressed as a gap. If the gap Z is not less than 1/2 of the S interval Z and of course less than the gap interval Z (Z> Z1 ≧ Z / 2), the image surface of the paper is prevented from coming into contact with the guide plate G, and the rubbing stain is ensured. Can be prevented. The protrusion amount Z1 is most preferably in the range of 1/2 to 2/3 of the gap Z of the gap S.

The desirable range of the projection amount Z1 of the point contact idler roller Y from the guide plate G on the side facing the image surface of the paper is a value derived by the inventor from the development process. It can be reliably separated from the opposing guide plate G.
The protruding amount Z1 is not limited to the point contact idler roller Y provided in the duplex unit 8, but is the same for all the point contact idler rollers Y provided in each transport path.

  Further, the point contact rollers which are the driven rollers 74b to 79b and 81b to 83b of each of the conveying roller pairs (including the switchback roller pair 74, the paper discharge roller pair 79, and the duplex conveying roller pairs 81 to 83) shown in FIG. All or a part of the guide plate G facing each other in the direction of the gap S from the extension line along the recording medium conveyance path of the guide plate that regulates the surface of the recording medium on which the current image is formed. If it is arranged so that it protrudes by an amount that is 1/2 or more of the gap Z of the gap S and less than the gap Z, it is possible to more reliably prevent the image surface of the paper from contacting the guide plate G.

The image forming apparatus according to the above-described embodiment includes a full-color ink jet image forming unit provided with four color line-type ink jet heads, but includes a full-color ink jet image forming unit provided with a serial ink jet head. Alternatively, a two-color or single-color ink jet image forming unit may be provided. In these, water-based ink is mainly used as a liquid recording agent.
In addition, the present invention can also be applied to those provided with a stencil type image forming unit or an offset type image forming unit that mainly uses oil-based ink as a liquid recording agent.

In short, an image forming apparatus that includes an image forming unit that forms an image on a recording medium with a liquid recording agent, and a recording that transports the recording medium with the liquid recording agent formed in the image forming unit in an undried state. The present invention can be applied to all medium conveyance devices.
The image forming apparatus may be a printer, a plotter, a printing apparatus, a copying apparatus, a digital multifunction peripheral, a facsimile machine, or the like.
Furthermore, the above-described embodiments can be appropriately combined and implemented within a range that does not contradict each other.

  The present invention relates to various image forming apparatuses such as a printer, a plotter, a printing apparatus, a copying apparatus, a digital multifunction peripheral, and a facsimile apparatus, and in particular, an image forming section provided with an image forming section that forms an image on a recording medium such as paper with a liquid recording agent. The present invention can be applied to the apparatus and a recording medium conveying apparatus that conveys a recording medium on which an image is formed by the image forming unit.

1: Image forming apparatus 2: First sheet feeding unit 3: Second sheet feeding unit 4: Pre-registration conveyance unit 5: Image forming unit 6: Non-contact conveyance unit 7: Post-image formation conveyance unit 8: Duplex unit 9: Ejection Paper exit 10: Paper 11, 12: Transport roller pair 13: Registration roller pair 21, 22: Paper feed tray 21a, 22a: Pickup roller 21b, 22b: Feed roller 21c, 22c: Reverse roller 21d, 22d: Transport roller pair 25 : Metal core of drive roller 26: Rubber layer of drive roller 31: Bearing 32: Spring 33: Bearing support 34: Connecting rod 35 and 36: Flange 37: Deformed shaft 38: Spur 39: Spacer H: Deformed hole

41: Abrasive roller shaft 42: Abrasive roller rolls 43a, 43b, 43c: Abrasive grains 45: Knurled roller shaft 46: Knurled roller roll 47: Knurled 51-54: Black, cyan, magenta, yellow Line-type inkjet head 61: endless wide belt 62: driving rollers 63, 64, 65: driven roller 66: tension roller 67: sensor 68: switching claw 71a: switching claw 71b: perforated endless belt 71c, 71d: roller 72: Switching claw 73: Switchback sensor 74: Switchback roller pair 75-78: Transport roller pair

74b to 79b: driven roller (point contact roller) 74c to 77c: spur roller 74d, 77d: abrasive roller 74e, 77e: knurling roller 79: paper discharge roller pair 74a-79a: driving roller 81-83: double-sided conveyance roller pair 81a to 83a: driving roller
81b to 83b: driven roller (point contact roller)
A, B, C, D: Conveying path E: Double-sided conveying path X: Merge position G: Guide plate S: Gap Y: Point contact idler roller
Z: Gap interval Z1: Projection amount of point contact idler roller from guide plate

JP 2006-35866 A JP 2004-203526 A JP 2009-137167 A

Claims (14)

A recording medium conveying apparatus for conveying a recording medium on which an image is formed with a liquid recording agent in an image forming unit,
The driving roller is in contact with the surface of the recording medium on which the current image is not formed and a driven roller in contact with the surface on which the current image is formed, and the driven roller presses the driving roller with a constant urging force. A plurality of pairs of transport rollers are disposed at intervals along the transport path of the recording medium,
The driven roller of each pair of transport rollers is a point contact roller;
The contact area between the point contact roller of the transport roller pair and the recording medium decreases according to the transport time or transport distance of the recording medium on which the image is formed from the image forming unit to each of the transport roller pairs. A recording medium transporting device characterized in that it is configured as described above.   2. The recording medium conveyance device according to claim 1, wherein a relationship between a conveyance time or a conveyance distance of the recording medium and a contact area between the point contact roller and the recording medium is an inversely proportional relationship. In the recording medium conveying apparatus according to claim 1 or 2,
Each point contact roller is constituted by a spur roller having a plurality of spurs,
According to the transport time or transport distance of the recording medium on which the image is formed from the image forming unit to each of the transport roller pairs, the number of spurs that the spur roller of the transport roller pair has decreases. A recording medium conveying apparatus characterized by the above. In the recording medium conveying apparatus according to claim 1 or 2,
Each point contact roller is constituted by a spur roller having a plurality of spurs,
According to the conveyance time or conveyance distance of the recording medium on which the image is formed from the image forming unit to each conveyance roller pair, the spur tooth thickness of the spur roller of the conveyance roller pair is reduced. A recording medium transporting device characterized by the above. In the recording medium conveying apparatus according to claim 1 or 2,
Each of the point contact rollers is composed of an abrasive roller in which abrasive particles are bonded to the outer surface of the roller with a uniform density,
The size of the abrasive grains in the abrasive roller of the pair of conveying rollers is reduced according to the conveying time or conveying distance of the recording medium on which the image is formed from the image forming unit to each of the conveying roller pairs. A recording medium transporting device characterized by the above. In the recording medium conveying apparatus according to claim 1 or 2,
Each of the point contact rollers is composed of an abrasive roller in which abrasive particles of a uniform size are bonded to the outer surface of the roller,
The density of the abrasive grains in the abrasive roller of the pair of conveyance rollers is made sparse according to the conveyance time or conveyance distance of the recording medium on which the image is formed from the image forming unit to each of the conveyance roller pairs. A recording medium transporting device characterized by the above. In the recording medium conveying apparatus according to claim 1 or 2,
Each of the point contact rollers is constituted by a knurling roller in which knurling is applied to the outer surface of the roller,
According to the conveyance time or conveyance distance of the recording medium on which the image is formed from the image forming unit to each conveyance roller pair, the knurling pitch of the knurling roller of the conveyance roller pair is made coarse. A recording medium conveying apparatus. In the recording medium conveyance device according to any one of claims 1 to 7,
Providing guide plates facing each other with a predetermined gap so as to form a transport path for the recording medium in a path between the pair of transport rollers adjacent in the transport direction of the recording medium;
One or more point contact idler rollers projecting partially from the guide plate into the gap on the guide plate side that restricts the surface of the recording medium on which the current image is formed among the guide plates facing each other. A recording medium conveying apparatus characterized by comprising: The recording medium conveying apparatus according to claim 8,
The contact area between the point contact idler roller and the recording medium decreases according to the transport time or transport distance of the recording medium on which the image is formed from the image forming unit to each point contact idler roller. A recording medium carrying device.   The recording medium conveying apparatus according to claim 9, wherein a relationship between a conveying time or a conveying distance of the recording medium and a contact area between the point contact idler roller and the recording medium is an inversely proportional relationship. In the recording medium conveyance device according to any one of claims 8 to 10,
The recording medium transporting apparatus according to claim 1, wherein an amount of protrusion of each point contact idler roller from the guide plate into the gap is ½ or more of the gap interval and less than the gap. In the recording medium conveyance device according to any one of claims 8 to 11,
The point contact roller, which is the driven roller of the pair of transport rollers, is along the transport path of the recording medium of the guide plate that regulates the surface of the recording medium on which the current image is formed, among the guide plates facing each other. A recording medium transporting apparatus, wherein the recording medium transporting apparatus is disposed so as to protrude by an amount less than or equal to ½ or more of the gap interval in a direction within the gap from an extended line.   An image forming unit that forms an image on a recording medium with a liquid recording agent, a recording medium supply device that supplies the recording medium to the image forming unit, and a recording medium conveyance device according to any one of claims 1 to 12. An image forming apparatus comprising:   The image forming apparatus according to claim 13, wherein the image forming unit is an ink jet type image forming unit including one or more ink jet heads.