JP2009069649A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To eliminate a means for bending a paper conveying path for a paper that is fed to a belt, regarding an image forming apparatus wherein the belt is separated from some of image carriers during a monochromatic image forming period. <P>SOLUTION: The image forming apparatus includes: the plurality of image carriers arrayed in one line; the belt extending along the image carriers; a plurality of support rolls including a driving roll arranged on a K-color image carrier side; a belt tilt-driving part for tilt-driving the belt so that the belt may come in contact with the plurality of image carriers in a color image forming mode, and the belt may come in contact with only the K-color image carrier among the plurality of image carriers and also the belt may be separated from other image carriers in a monochromatic image forming mode; and a paper pressing part, in the monochromatic image forming mode, for pressing the paper at a second position located on the downstream side of the first position in the belt conveying direction in the color image forming mode. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus.

  2. Description of the Related Art Conventionally, as an image forming apparatus represented by an electrophotographic copying machine, a printer, or the like, a plurality of image holding members that hold toner images of different colors are provided, and the toner images held by these plurality of image holding members are finally obtained. There is known a so-called tandem color image forming apparatus that transfers images onto paper.

In Patent Document 1, a plurality of photosensitive drums as image holding bodies corresponding to respective colors of K (black), C (cyan), M (magenta), and Y (yellow), and the photosensitive drums are opposed to each other. And an image forming apparatus provided with a belt for conveying paper. In this image forming apparatus, the belt is held by a drive roll and a driven roll, and the paper supplied from the supply roll is directed from the driven roll side to the drive roll side along the path through the photosensitive drum. Transport. The drive roll and the driven roll are supported by the belt unit frame. The belt unit frame is held so as to be tiltable about the rotation axis of the K-color photosensitive drum close to the drive roll side. In order to suppress the consumption by stopping the operation of the photosensitive drums of the other colors in the monochrome image formation with K color, the belt unit frame is in contact with all the photosensitive drums during the color image formation, and the belt unit frame during the monochrome image formation Rotates to a position in contact with only the K photosensitive drum.
JP-A-6-258914 (page 4-5, FIG. 1)

  When the belt unit frame is rotated, the position changes as the distance from the center increases, and the portion on the driven roll side of the belt moves greatly. In order to change the path of the sheet supplied from the supply roll to the belt in accordance with the position of the moving belt, it is conceivable to arrange a sheet guide member or the like that bends the path of the sheet between the supply roll and the belt. However, if the direction of the paper supplied from the supply roll is forcibly changed by a paper guide member or the like, the path distance from the supply roll to the photosensitive drum or the transfer roll varies significantly. Further, if the direction of the paper is changed in a limited space between the supply roll and the belt, the paper is strongly rubbed against the paper guide member, and the running noise increases. In addition, the load varies depending on the orientation of the sheet, and the moving speed of the belt or the like may vary.

  In view of the above circumstances, the present invention eliminates the need for a means for bending the conveyance path of the paper supplied to the belt in the image forming apparatus in which the belt is separated from a part of the image holding member during monochrome image formation. Objective.

The first image forming apparatus of the image forming apparatus of the present invention that achieves the above object includes a K color image holding body that holds a K color toner image arranged at one end, and is arranged in a line. A plurality of image carriers that hold toner images of different colors;
A belt that extends along the plurality of image carriers and conveys a sheet along a path along the plurality of image carriers;
A plurality of support rolls including a drive roll disposed on the K-color image carrier side, over which the belt is bridged and drives the belt;
In a color image forming mode for forming a color image composed of a plurality of color toner images, a plurality of transfer rolls facing each of the plurality of image carriers with the belt interposed therebetween, and the belt contacts the plurality of image carriers, In a monochrome image forming mode for forming a monochrome image composed of a K-color toner image, the belt contacts only the K-color image holding body among the plurality of image holding bodies and is separated from the other image holding bodies. A belt tilting drive section for tilting the belt;
The sheet supplied toward the belt is pressed against the belt, and in the monochrome image forming mode, at a second position downstream in the belt conveyance direction from the first position in the color image forming mode. And a sheet pressing portion for pressing the sheet.

  According to the first image forming apparatus of the present invention, in the monochrome image forming mode, the sheet is pressed down at the second position downstream of the position in the color image forming mode, and thus supplied toward the belt. There is no need to bend the paper transport path. In addition, a sheet guide member for bending the sheet conveyance path immediately before the belt is unnecessary, and traveling noise is reduced.

Here, in the first image forming apparatus of the present invention, the first position is a position where the belt is sandwiched between the support rolls arranged on the most upstream side in the transport direction of the support rolls. Because
The second position is a downstream side in the transport direction with respect to a supply path through which the sheet is supplied toward the belt and a position where the belt intersects, and the most upstream side in the transport direction of the image carrier. It is preferable that the image carrier is located on the upstream side in the transport direction with respect to the image carrier arranged in the above.

  Since the sheet first comes into contact with the belt and is pressed against the belt by the sheet pressing unit, fluctuations in the moving speed can be suppressed as compared with the configuration in which the sheet is abutted against the sheet pressing unit.

Further, in the first image forming apparatus of the present invention, the paper pressing unit is configured to charge the paper so that the paper is brought into close contact with the belt,
It is preferable that the charging roll includes a charging roll moving mechanism that moves the charging roll to the first position in the color image forming mode and moves the charging roll to the second position in the monochrome image forming mode.

  By moving the charging roll, a single charging roll can be used as a member for pressing the sheet at the first position and the second position.

Further, in the first image forming apparatus of the present invention, the sheet pressing unit includes a first roll for pressing the sheet at the first position;
In the monochrome image forming mode, it is preferable to include a second roll that presses the sheet that has passed through the side opposite to the belt of the first roll at the second position.

  By providing the first roll and the second roll, the roll moving mechanism is omitted and the reliability is improved, and the sheet is pressed by two rolls in a color image forming mode that requires high accuracy for image positioning. .

  In the first image forming apparatus of the present invention, it is preferable that at least the second roll is a charging roll that causes the sheet to adhere to the belt by charging the sheet.

  If the second roll for pressing the paper in both the color image forming mode and the monochrome image forming mode is a charging roll, the paper can be brought into close contact with the belt in both modes.

The second image forming apparatus of the image forming apparatuses of the present invention that achieves the above object includes a K-color image holding body that holds a K-color toner image and is arranged in a line. A plurality of image holders for holding different color toner images,
A belt that extends along the plurality of image carriers and conveys a sheet along a path along the plurality of image carriers;
A plurality of support rolls including a drive roll disposed on the K-color image carrier side, over which the belt is bridged and drives the belt;
In a color image forming mode for forming a color image composed of a plurality of color toner images, a plurality of transfer rolls facing each of the plurality of image carriers with the belt interposed therebetween, and the belt contacts the plurality of image carriers, In a monochrome image forming mode for forming a monochrome image composed of a K-color toner image, the belt contacts only the K-color image holding body among the plurality of image holding bodies and is separated from the other image holding bodies. A belt tilting drive section for tilting the belt;
Supplying paper toward the belt, and having at least three supply rolls in contact with each other in a row in a direction crossing the paper supply direction, and in the color image forming mode, of the three image forming bodies, A paper supply unit that supplies paper from between two supply rolls arranged on the side and supplies paper from between two supply rolls arranged on the side away from the image carrier in the monochrome image forming mode. It is characterized by comprising.

  In the second image forming apparatus of the present invention, the paper supply position is adjusted to the inclination of the belt by selecting two of the three supply rolls responsible for paper supply in the color image formation mode and the monochrome image formation mode. Can be adjusted. This eliminates the need for a paper guide for bending the transport path of the paper supplied to the belt. In addition, it is possible to stabilize the approaching posture of the paper with respect to the belt and suppress the deviation of the images of the respective colors.

  In the first image forming apparatus of the present invention, one of the two supply rolls on both sides and the one supply roll in the center of the three supply rolls is made of metal, and the other The supply roll is preferably made of an elastic resin.

  Wear can be suppressed by making one of the supply rolls in contact with each other metal and the other made of resin.

  In the first image forming apparatus of the present invention, each of the three supply rolls rotates in a rotation direction opposite to the rotation direction in the color image formation mode in the monochrome image formation mode. It is preferable.

  By changing the rotation direction of the supply roll, the paper supply position can be changed without using a mechanism for separating the supply rolls from each other.

  Further, in the first image forming apparatus of the present invention, the three supply rolls are the first of the three supply rolls, and the two supply rolls in charge of paper supply in the color image forming mode are in contact with each other. The distance from the position 1 to the transfer roll disposed on the most upstream side in the transport direction on the path along the belt in the color image formation mode, and the monochrome image formation of the three supply rolls. It is preferable that the two supply rolls in charge of paper supply in the mode are arranged at positions where the distance from the second position where the two supply rolls contact each other to the transfer roll in the monochrome image forming mode is substantially equal.

  By arranging the three rolls in this way, the positioning accuracy of each color image can be increased.

  As described above, according to the present invention, an image forming apparatus that does not require a means for bending a conveyance path of a sheet supplied to a belt is realized.

  FIG. 1 is a diagram showing a schematic configuration of a printer which is a first embodiment of an image forming apparatus of the present invention.

  A printer 1 shown in FIG. 1 is a color image forming apparatus capable of forming either a color image or a monochrome image on a medium, and is different from each other in K (black), C (cyan), M (magenta), and Y (yellow). ) Four photosensitive drums 11k, 11c, 11m, and 11y that hold toner images of the respective colors, and a conveyance belt that extends along these photosensitive drums 11k, 11c, 11m, and 11y and conveys a sheet as a medium. 21. The photosensitive drums 11k, 11c, 11m, and 11y correspond to an example of the image holding member according to the present invention, and the conveyance belt 21 corresponds to an example of the belt according to the present invention. The photosensitive drums 11k, 11c, 11m, and 11y are incorporated in four image forming units 10k, 10c, 10m, and 10y that can be attached to and detached from the printer 1, respectively. The conveyor belt 21 is attached to the belt unit 20. Further, the printer 1 includes a paper container 51 for storing paper, a transport roll 54 for transporting paper, a registration roll 55 as a paper feed timing adjusting member for adjusting the transport timing of the paper, and the paper to the transport belt 21. Also provided are an adsorbing roll 71 to be in close contact, a fixing roll 58 for fixing the toner image transferred to the paper, a discharge roll 56 for discharging the paper on which the image is formed, and a paper discharge unit 52 for discharging the paper.

  The four image forming units 10k, 10c, 10m, and 10y all have the same structure, and differ only in the color of the accommodated toner. The image forming units 10k, 10c, 10m, and 10y of the respective colors will be described as representative of the K-color image forming unit 10k. The image forming unit 10k includes the K-color photosensitive drum 11k that holds the K-color toner image. In addition, the charging roller 12k for uniformly charging the surface of each photosensitive drum, the developer containing portion 13k containing the toner, and the toner conveyed from the developer containing portion 13k via the developer conveying portion 14k. A developing device 15k that develops an electrostatic latent image on the body drum 11k to form a toner image, a static elimination roll 16k that neutralizes the photoreceptor drum 11k after the toner image is transferred to a sheet, and a residual toner on the photoreceptor drum A cleaning blade 17k for removing the residual toner is provided. The photosensitive drum 11k, the charging roll 12k, the developer accommodating portion 13k, the developer conveying portion 14k, the developing device 15k, the charge removing roll 16k, and the cleaning blade 17k are supported by a photosensitive housing 18k as a unit casing. ing.

  The photosensitive drums 11k, 11c, 11m, and 11y for each color are arranged in a row with the photosensitive drum 11k for K color as one end of the row. A C-color photosensitive drum 11c is disposed adjacent to the K-color photosensitive drum 11k.

  The printer 1 includes a control unit 31 that controls the operation of each unit of the printer, an image processing unit 32 that processes image information, a writing drive circuit 33, and a laser beam L on the photosensitive drums 11k, 11c, 11m, and 11y. And a latent image forming device 34 for forming an electrostatic latent image on each photoconductor drum. Whether the control unit 31 forms a monochrome image composed of a K-color toner image in the monochrome image formation mode based on image information supplied from an external image information transmission device (not shown) or operation information from an operation unit (not shown). Or whether to form an image in the color image forming mode.

  The control unit 31 irradiates the four photosensitive drums 11k, 11c, 11m, and 11y with laser beams Lk, Lc, Lm, and Ly in the color image forming mode. On the other hand, in the monochrome image forming mode, in order to suppress the consumption and power consumption of the image forming units 10c, 10m, and 10y, only the K-color photosensitive drum 11k is irradiated with the laser light Lk, and an image other than the K-color image. The operations of the forming units 10c, 10m, and 10y are stopped.

  The belt unit 20 includes, in addition to the transport belt 21, a pair of support rolls 22 and 23 around which the transport belt 21 is stretched, a unit frame 24 that rotatably supports the support rolls 22 and 23, and toner attached to the transport belt 21. A waste toner storage unit 25 and a paper guide unit 26 for guiding the movement of the paper during duplex printing. The two support rolls 22 and 23 include a drive roll 22 and a driven roll 23 that drive the conveyance belt 21. Hereinafter, the support roll 22 is also referred to as a drive roll 22, and the support roll 23 is also referred to as a driven roll 23. The driving roll 22 is disposed on the K color photosensitive drum 11k side, and the driven roll 23 is disposed on the Y color photosensitive drum 11y side. The conveyor belt 21 circulates and moves in the direction indicated by the arrow D12 by the drive roll 22, and conveys the sheet along a path along the photosensitive drums 11y, 11m, 11c, and 11k. The direction in which the paper is conveyed from the driven roll 23 side to the drive roll 22 side on the photosensitive drums 11y, 11m, 11c, and 11k side in the circulating belt 21 is defined as a conveyance direction D12. That is, the driven roll 23 is disposed on the most upstream side in the transport direction D12.

  Also attached to the unit frame 24 are transfer rolls 40k, 40c, 40m, and 40y for transferring toner images formed on the respective photosensitive drums. Each of the transfer rolls 40k, 40c, 40m, and 40y is formed of a conductive resin material. The transfer rolls 40k, 40c, 40m, and 40y are arranged in a line, and are provided at positions facing the corresponding photosensitive drums 11k, 11c, 11m, and 11y with the conveyance belt 21 interposed therebetween. The K color transfer roll 40k is disposed at one end of the row and is disposed on the most downstream side in the transport direction D12 of the transport belt 21. The C-color transfer roll 40c as the adjacent transfer roll is disposed adjacent to the K-color transfer roll 40k. A Y-color transfer roll 40y is disposed on the most upstream side in the transport direction D12 of the transport belt 21. The transfer rolls 40k, 40c, 40m, and 40y are urged so as to press the conveyor belt 21 against the photosensitive drums 11k, 11c, 11m, and 11y that the conveyor belt 21 contacts. A backup roll 45 is provided between the driven roll 23 and the Y color transfer roll 40y. The backup roll 45 is disposed at a position in contact with the conveyance belt 21.

  Further, the unit frame 24 is provided with a suction roll 71 for bringing the paper into close contact with the transport belt 21 upstream of the Y-color photosensitive drum 11y and the Y-color transfer roll 40y on the most upstream side in the transport direction D12. ing. The suction roll 71 is made to adsorb to the transport belt 21 by charging the paper. The suction roll 71 corresponds to an example of the charging roll referred to in the present invention. The suction roll 71 is provided on the side of the photosensitive drums 11 k to 11 y with respect to the conveyance belt 21, and is provided movably along the conveyance belt 21. Details of the moving mechanism of the suction roll 71 will be described later.

  The printer 1 shown in FIG. 1 has an image forming apparatus main body U1 and an opening / closing member U2 that can be opened and closed by rotating about a rotation axis R provided at the lower end of the image forming apparatus main body U1.

  FIG. 2 is a diagram illustrating a state in which the opening / closing member of the printer illustrated in FIG. 1 is opened.

  The opening / closing member U2 is supported by the image forming apparatus body U1 so as to be movable between a closed position shown in FIG. 1 and an open position shown in FIG. The belt unit 20 is mounted on the opening / closing member U2 side, and in the open position shown in FIG. 2, the conveyance belt 21 and the image forming units 10k, 10c, 10m, and 10y inside the printer 1 are exposed to the outside of the printer 1, and the parts Replacement and removal of jammed paper becomes possible. In the closed position shown in FIG. 1, the opening / closing member U2 is fixed to the image forming apparatus body U1, and an image forming operation can be executed.

  FIG. 3 is a perspective view showing an opening / closing member and a belt unit of the printer shown in FIG. FIG. 3 shows a state where the opening / closing member U2 is removed from the image forming apparatus main body U1.

  The opening / closing member U2 has an attachment hole U2h for attachment to the image forming apparatus main body U1. The unit frame 24, the waste toner container 25, and the paper guide 26 constituting the belt unit 20 are fixed and integrated with each other. The drive roll 22 and the driven roll 23 (see FIG. 1) are rotatably held at both upper and lower ends of the unit frame 24. The rotating shaft 22a of the drive roll 22 passes through the unit frame 24 and protrudes at both ends. Hereinafter, the direction in which the drive roll 22 extends is the left-right direction. One end of the rotation shaft 22a is provided with a gear 22p for transmitting a rotational force from a drive gear 65 (see FIG. 4) provided in the image forming apparatus main body U1. A protrusion 25a protruding left and right is provided on the side of the driven roll 23 of the waste toner container 25, and enters a notch U2b formed in the opening / closing member U2. The unit frame 24 is movable along the notch U2b on the driven roll 23 side. The suction roll 71 provided in the unit frame 24 constitutes a paper pressing unit 70 that presses the paper toward the transport belt 21. In addition to the suction roll 71, the sheet pressing unit 70 of this embodiment includes a solenoid 72 and a link member 73 as a moving mechanism that moves the suction roll 71.

  FIG. 4 is a perspective view showing a support frame of the printer shown in FIG. FIG. 4 shows a support frame U1F that supports the structure of the image forming apparatus main body U1 together with the image forming units 10k, 10c, 10m, and 10y.

  The image forming units 10k, 10c, 10m, and 10y are mounted in a row on the support frame U1F. A rotation axis R is provided at the lower end of the support frame U1F. The rotation shaft R is fitted into the mounting hole U2h of the opening / closing member U2 (FIG. 3), so that the opening / closing member U2 is rotatably supported by the support frame U1F. A bearing U1H into which the rotating shaft 22a of the drive roll 22 is fitted is formed along the hole on both sides of the support frame U1F. The drive roll 22 is engaged with the gear 22p on the outside of the bearing U1H. A driving gear 65 that transmits a driving force to the motor 66 and a motor 66 that rotationally drives the driving gear 65 are provided.

  When the opening / closing member U2 of FIG. 3 is moved to the closed position (see FIG. 1) while being attached to the support frame U1F of FIG. 4, the support frame U1F, that is, the image forming apparatus main body U1 and the opening / closing member U2 are fixed and integrated with each other. Become. At this time, the rotating shaft 22a of the drive roll 22 is fitted into the bearing U1H. As a result, at the closed position shown in FIG. 1, the belt unit 20 including the unit frame 24 is supported by the image forming apparatus body U <b> 1 around the rotation shaft 22 a of the drive roll 22. In the closed position, the drive gear 65 (FIG. 4) is engaged with the gear 22 p (FIG. 3), and the drive force from the motor 66 is transmitted to the drive roll 22.

  The support frame U1F is provided with two cams 61a and 61b at a position between the M-color image forming unit 10m and the Y-color image forming unit 10y, and a motor 62 that rotationally drives the cams 61a and 61b. Is provided. The cams 61a and 61b are abutted against the portion of the unit frame 24 on the driven roll 23 side at the closed position (FIG. 1). The motor 62 is provided with a sensor (not shown) that detects the rotation angle of the cams 61a and 61b, and rotates the cams 61a and 61b by a predetermined range of angles in accordance with the control of the control unit 31 (FIG. 1). A spring (not shown) that presses the belt unit 20 toward the image forming units 10y, 10m, 10c, and 10k is provided between the belt unit 20 and the opening / closing member U2. When the cams 61 a and 61 b rotate at the closed position, the belt unit 20 tilts about the rotation shaft 22 a of the drive roll 22. By the tilting of the belt unit 20, the transport belt 21 is also tilted about the rotation shaft 22 a of the drive roll 22. The belt unit 20 including the unit frame 24 and the cams 61a and 61b correspond to an example of a belt tilting drive unit referred to in the present invention.

  Next, details of the suction roll 71 and its drive mechanism described with reference to FIG. 3 will be described.

  FIG. 5 is a front view showing the appearance of the unit frame shown in FIG. FIG. 5 shows the left and right ends of the unit frame and the components attached to the unit frame. 6 is a view showing a side surface of the unit frame shown in FIG. 5, and FIG. 7 is an enlarged perspective view in which the solenoid and the link member shown in FIG. 6 are enlarged. FIG. 8 is an enlarged perspective view showing the state of the suction roll in the monochrome image forming mode.

  As shown in FIGS. 5 to 7, the rotation shaft 71 a of the suction roll 71 penetrates through an arcuate guide hole 24 h formed in the unit frame 24 and is attached to the link member 73 on the left and right outer sides of the unit frame 24. . A solenoid 72 is connected to the opposite side of the link member 73 across the rotation shaft 73p. When the solenoid 72 performs a suction operation according to the control of the control unit 31, the link member 73 rotates about the rotation shaft 73p, and the suction roll 71 moves along the guide hole 24h in the first position S1 shown in FIGS. Move to. Conversely, when the solenoid 72 performs the pushing operation, the suction roll 71 moves to the second position S2 shown in FIG. 5 to 7, the suction roll 71 sandwiches the conveyance belt 21 between the suction roll 71 and the driven roll 23. At the second position S <b> 2 shown in FIG. 8, the suction roll 71 is connected to the backup roll 45. The conveying belt 21 is sandwiched between them. The setting of the second position S2 will be described later.

  FIG. 9 is a diagram illustrating a state of the image forming unit, the belt unit, and the cam in the color image forming mode. FIG. 10 is a diagram illustrating a state of the image forming unit, the belt unit, and the cam in the monochrome image forming mode. 9 and 10 show the positional relationship between the image forming units 10k, 10c, 10m, and 10y and the belt unit 20 when the opening / closing member U2 is closed (see FIG. 1).

  The belt unit 20 supports the drive roll 22 and the driven roll 23 rotatably, and at the same time, is supported so as to be tiltable about the rotation shaft 22 a of the drive roll 22. The belt unit 20 tilts between the color mode position shown in FIG. 9 and the monochrome mode position shown in FIG. 10 as the cams 61a and 61b rotate. Along with this, the conveyor belt 21 also tilts about the rotation shaft 22 a of the drive roll 22.

  In the color image forming mode, the belt unit 20 is tilted to the position shown in FIG. 9, and the conveyance belt 21 is in contact with all of the four photosensitive drums 11k, 11c, 11m, and 11y. In the monochrome image forming mode, the belt unit 20 is tilted to the position shown in FIG. 10, and the conveying belt 21 is brought into contact with only the K-color photosensitive drum 11k and is separated from the other photosensitive drums 11c, 11m, and 11y. Become.

  Further, the suction roll 71 moves to the first position S1 in the color image forming mode shown in FIG. 9, and in the monochrome image forming mode shown in FIG. 10, the second roller on the downstream side in the transport direction D12 from the first position. To position S2. The second position S2 described above is downstream in the transport direction D12 from the position S3 where the transport belt 21 intersects the supply path Q1 through which the paper is supplied from the registration roll 55 toward the transport belt 21, and the transport is performed. It is set on the upstream side in the transport direction D12 relative to the Y-color photosensitive drum 11y disposed on the most upstream side in the direction D12.

  Here, returning to FIG. 1, the operation of the printer 1 will be described.

  When image information of a color image is transmitted to the printer 1 from, for example, an external image information transmission device (not shown) or the like, and the control unit 31 determines that an image is formed in the color image formation mode, the image processing unit 32 controls the control unit 31. Is converted into image information for forming a latent image of each color and output to the writing drive circuit 33. The writing drive circuit 33 outputs a drive signal to the latent image forming device 34 according to the image information. The latent image forming device 34 irradiates the photosensitive drums 11k, 11c, 11m, and 11y with laser beams Ly, Lm, Lc, and Lk corresponding to the drive signals.

  The photosensitive drums 11k, 11c, 11m, and 11y rotate in the direction indicated by the arrow D11, are charged by the charging roll 12k, and scanned by the laser beams Ly, Lc, Lm, and Ly, so that electrostatic latent images corresponding to image information are obtained. An image is formed. The electrostatic latent image is developed with toner to form a toner image.

  On the other hand, the paper P taken out from the paper container 51 is transported by the transport roll 54 and sent out from the registration roll 55 at a timing corresponding to the toner image formation on the photosensitive drums 11k, 11c, 11m, and 11y. The sheet is sent out along the supply path Q1 toward the conveyor belt 21 and, after contacting the conveyor belt 21, is pressed against the conveyor belt 21 and charged by the suction roll 71 at the first position. Adsorb to. The paper is sandwiched between the photosensitive drums 11k, 11c, 11m, and 11y and the transfer belt 21 between the corresponding transfer rolls 40k, 40c, 40m, and 40y, and the transfer belts Y, M, and Y. , C, K in this order. During this time, the toner images of the respective colors formed on the photosensitive drums 11k, 11c, 11m, and 11y are transferred onto the paper by the transfer rolls 40k, 40c, 40m, and 40y. The toner transferred to the paper is heated and pressed by the fixing roll 58 and fixed on the paper. In this way, a color image is formed on the paper and is discharged to the paper discharge unit 52 by the discharge roll 56. When images are formed on both sides of the paper, the discharge roll 56 reverses, the paper is conveyed via the back of the belt unit 20, and image formation is performed again with the front and back reversed.

  When the printer 1 operates in the monochrome image forming mode, only the K-color image forming unit 10k necessary for image formation among the four image forming units 10k, 10c, 10m, and 10y is used to reduce power consumption and consumption. The image forming units 10c, 10m, and 10y other than the K color stop operating. At this time, if the conveying belt 21 comes into contact with the stopped photosensitive drums 11c, 11m, and 11y, scratches are caused by rubbing. In order to prevent sliding between the photosensitive drums 11c, 11m, and 11y and the conveyor belt 21 that are stopped, in the monochrome image forming mode, the cams 61a and 61b (see FIG. 10) rotate and the unit frame 24 is positioned as shown in FIG. Tilt to. Due to the tilt of the unit frame 24, the conveying belt 21 contacts only the K-color photosensitive drum 11k, and is separated from the other photosensitive drums 11k with a sufficient clearance. Further, the suction roll 71 moves from the first position Q1 (see FIG. 9) to the second position Q2 (see FIG. 10) under the control of the control unit 31. In the monochrome image forming mode shown in FIG. 10, the sheet fed from the registration roll 55 toward the conveyance belt 21 along the supply path Q1 is conveyed to the conveyance belt 21 at a position S3 where the supply path Q1 and the conveyance belt 21 intersect. After making contact with a posture having a gentle angle that does not affect the moving speed of the belt 21, the belt 21 is pressed against the conveyance belt 21 by the adsorption roll 71 at the second position S <b> 2 and is charged and adsorbed to the conveyance belt 21. . The sheet adsorbed to the conveyance belt 21 passes between the photosensitive drum 11k and the corresponding transfer roll 40k while being sandwiched between the photosensitive drum 11k and the conveyance belt 21. During this time, the K-color toner image formed on the photosensitive drum 11k is transferred onto the paper by the transfer roll 40k. In this way, in the monochrome image forming mode, a monochrome image of K color is formed on the paper.

  Next, a second embodiment of the present invention will be described. In the following description of the second embodiment, the same reference numerals are given to the same elements as those in the embodiments described so far, and differences from the above-described embodiments will be described.

  FIG. 11 is a perspective view showing an opening / closing member and a belt unit of the printer according to the second embodiment of the present invention.

  In the printer of the second embodiment, a sheet pressing unit 270 that presses the sheet supplied toward the conveyance belt 21 against the conveyance belt 21 has two rolls, a suppression roll 271 and an adsorption roll 272. The holding roll 271 in this embodiment does not have a sheet charging function.

  The holding roll 271 is disposed at the first position S1 that sandwiches the conveyance belt 21 between the follower roll 23, and the suction roll 272 is disposed at the second position S2 described with reference to FIG. Yes. The holding roll 271 corresponds to an example of the first roll according to the present invention, and the suction roll 272 corresponds to an example of the second roll according to the present invention. In the present embodiment, the positions of the holding roll 271 and the suction roll 272 are fixed with respect to the unit frame 24, and the sheet pressing portion 270 is different from the first embodiment in that no drive mechanism is provided. Other points in the second embodiment are the same as those in the first embodiment.

  FIG. 12 is a diagram illustrating a state of the image forming unit, the belt unit, and the cam in the color image forming mode in the second embodiment. FIG. 13 is a diagram illustrating a state of the image forming unit, the belt unit, and the cam in the monochrome image forming mode in the second embodiment.

  In the color image forming mode, the belt unit 20 is tilted to the position shown in FIG. 11, and the conveyance belt 21 is brought into contact with all four photosensitive drums 11k, 11c, 11m, and 11y. In the color image forming mode, the paper is supplied from the registration roll 55 toward the transport belt 21 along the supply path Q1. After the sheet comes into contact with the conveyance belt 21, the sheet is pressed against the conveyance belt 21 by the holding roll 271 at the first position. Next, the suction roller 272 in the second position is pressed against the transport belt 21 and charged, and is in close contact with the transport belt 21. In the color image forming mode, the sheet is pressed against the transport belt 21 by two rolls including a suppression roll 271 and a suction roll 272.

  On the other hand, in the monochrome image forming mode, the belt unit 20 is tilted to the position shown in FIG. 13, and the conveying belt 21 is brought into contact only with the K-color photosensitive drum 11k and separated from the other photosensitive drums 11c, 11m, and 11y. It becomes a state. In the monochrome image forming mode, the sheet fed from the registration roll 55 toward the transport belt 21 along the supply path Q1 passes through the side of the restraining roll 271 opposite to the transport belt 21. The sheet is gently brought into contact with the conveyance belt 21 at a position S3 where the supply path Q1 and the conveyance belt 21 intersect, and then pressed against the conveyance belt 21 and charged by the suction roll 272 in the second position. Close contact with.

  Next, a third embodiment of the present invention will be described. In the following description of the third embodiment, the same reference numerals are given to the same elements as those in the embodiments described so far, and differences from the above-described embodiments will be described.

  FIG. 14 is a diagram showing a schematic configuration of a printer according to the third embodiment of the present invention.

  The printer 3 shown in FIG. 14 supplies three registration rolls 381, 382, 383 (hereinafter referred to as registration rolls 381, 382) that are in contact with each other in a line in a direction intersecting with the paper supply direction. , And a path switching member 391 that switches a supply path for supplying paper to the three registration rolls 381 to 383. The suction roll 371 is fixed at a first position where the belt is sandwiched between the suction roll 371 and the driven roll 23, and no moving mechanism is provided. The registration rolls 381, 382, and 383 correspond to an example of the supply roll of the present invention. The printer of the third embodiment is different from the first embodiment in these points. Other points in the third embodiment are the same as those in the first embodiment.

  FIG. 15 is a perspective view showing the appearance of the registration roll unit of the printer shown in FIG.

  A registration roll unit 380 shown in FIG. 15 is a unit that supplies paper toward the transport belt 21, and is attached to a lower portion in the support frame U1F shown in FIG. The registration roll unit 380 corresponds to an example of a paper supply unit according to the present invention. The three registration rolls 381 to 383 are rotatably supported by the unit frame 384 of the registration roll unit 380. Among the three registration rolls 381 to 383, two supply rolls 381 and 382 on the side of the photosensitive drums 11k to 11y are in charge of paper supply in the color image forming mode, and from the photosensitive drums 11k to 11y in the monochrome image forming mode. Two supply rolls 382 and 383 on the remote side are in charge of paper supply. Of the three registration rolls 381 to 383, two registration rolls 381 and 383 on both sides are made of metal, and the central registration roll 382 is made of a resin having elasticity such as rubber. The registration rolls 381 and 383 on both sides are pressed against the central registration roll 382 with such a strength that the sheet sandwiched between the registration rolls 382 and the central registration roll 382 does not escape. The central registration roll 382 is rotationally driven by a motor 387 via a clutch 385 and a belt 386. The motor 387 can rotate forward and backward according to the control of the control unit 31 (see FIG. 14). The two registration rolls 381 and 383 on both sides are driven rolls and rotate in the opposite direction to the central registration roll 382 as the central registration roll 382 rotates. The unit frame 384 is also provided with a transport roll 54 that transports paper toward the registration rolls 381 to 383. Under the registration rolls 381 to 383, a guide member and a path switching member for guiding the sheet conveyed by the conveyance roll 54 to the registration rolls 381 to 383 are provided.

  16 is a perspective view showing an internal structure of the registration roll unit shown in FIG. 15, and FIG. 17 is a side view of the structure shown in FIG.

  As shown in FIG. 16, below the registration rolls 381 to 383, a path switching member 391 that switches the conveyance path of the sheet conveyed from the conveyance roll 54, and a sheet whose path has been switched by the path switching member 391 is used as a registration roll. Three guide members 393, 394, and 395 are provided for directing. The path switching member 391 is rotatably supported by the unit frame 384. A solenoid 392 is connected to the rotation shaft of the path switching member 391 via a link member. When the solenoid 392 operates according to the control of the control unit 31 (see FIG. 31), the path switching member 391 rotates and switches the path. As shown in FIG. 17, the path switching member 391 is guided between the guide members 393 and 394, and is connected to the two registration rollers 381 and 382 arranged on the photosensitive drums 11 k to 11 y side among the three registration rollers 381 to 383. Switching between the transport path for transporting toward the two registration rollers 382 and 383 that are guided between the guide members 393 and 395 and disposed on the side away from the photosensitive drums 11k to 11y. Do. Of the three guide members 393 to 395, the center guide member 394 has a bifurcated end on the registration rolls 381 to 383 side, and this end extends larger than the diameter of the center registration roll. . For this reason, the paper supplied toward the registration rolls 381 to 383 avoids the resin registration roll 382 which is easily worn at the center, and first contacts one of the metal registration rolls 381 and 383 on both sides. And sandwiched between the registration rolls 382.

  FIG. 18 is a diagram illustrating the states of the photosensitive drum, the conveyance belt, and the registration roll unit in the color image forming mode of the printer illustrated in FIG. 14, and FIG. 19 is a diagram illustrating the state in the monochrome image forming mode.

  With reference to FIGS. 18 and 19, the arrangement of the three registration rolls 381 to 383 will be described in more detail.

  The three registration rollers 381 to 383 have a distance from the first contact position S11 where the two supply rolls 381 and 382 in charge of paper supply in the color image forming mode shown in FIG. 18 contact each other to the Y color transfer roll 40y. , A position where the distance from the second contact position S12 where the two supply rolls 382 and 383 in charge of paper supply contact each other to the Y color transfer roll 40y in the monochrome image forming mode shown in FIG. 19 is substantially equal. Is arranged. For this reason, it is possible to suppress the shift of the position where the image is formed on the paper in the color image formation mode and the monochrome image formation mode.

  In the color image forming mode shown in FIG. 18, the conveyance belt 21 is in contact with all of the four photosensitive drums 11k, 11c, 11m, and 11y. The driven roll 23 side of the conveyor belt 21 moves to the photosensitive drum 11y side. By driving the solenoid 392, the path switching member 391 switches the conveyance path to the side passing through the registration roll 381 on the photosensitive drum 11y side. Further, the central registration roll 381 is driven by the motor 387 and rotates in the rotation direction indicated by the arrow D31, and the two registration rolls 381 and 383 on both sides rotate in the rotation direction opposite to the central registration roll 382. The sheet conveyed from the conveyance roll 54 (see FIG. 15) is guided to the registration roll 381 on the photosensitive drum 11y side by the path switching member 391 and the guide members 393 and 394. The sheet that has come into contact with the registration roll 381 is sandwiched between the two registration rolls 381 and 382 on the photosensitive drum 11y side, and is supplied toward the transport belt 21 from the first contact position S11. The sheet in contact with the conveyance belt 21 is charged by the suction roll 371 and pressed against the conveyance belt 21 to be in close contact with the conveyance belt 21. The paper is transported in the transport direction D21 by the transport belt 21.

  In the monochrome image forming mode shown in FIG. 19, the conveyance belt 21 is brought into contact only with the K-color photosensitive drum 11k and is separated from the other photosensitive drums 11c, 11m, and 11y. The side of the driven roll 23 in the conveyor belt 21 moves to the side away from the photosensitive drum 11y. The path switching member 391 switches the conveyance path to the side passing through the registration roll 383 on the side away from the photosensitive drum 11y. Further, the central registration roll 381 is driven by the motor 387, and the three registration rolls 381 to 383 rotate in the rotation direction indicated by the arrow D32 that is opposite to the color image forming mode. The sheet conveyed from the conveyance roll 54 (see FIG. 15) is guided to the registration roll 383 on the side away from the photosensitive drum 11y by the path switching member 391 and the guide members 393 and 395. The sheet in contact with the registration roll 383 is sandwiched between the two registration rolls 382 and 383 on the side away from the photosensitive drum 11y, and is supplied toward the conveying belt 21 from the second contact position S12. The sheet in contact with the conveyance belt 21 is charged by the suction roll 371 and pressed against the conveyance belt 21 to be in close contact with the conveyance belt 21. The paper is transported in the transport direction D21 by the transport belt 21.

  The paper supply position is adjusted in accordance with the inclination of the conveyance belt 21, and the paper is supplied to the conveyance belt 21 in an approach posture in which fluctuation is suppressed.

  In the above-described embodiment, the belt unit 20 including the unit frame 24 is described as being supported by the image forming apparatus main body U1 around the rotation shaft 22a of the drive roll 22, but the present invention is not limited thereto. For example, the center at which the belt tilts may be on the rotation axis of the K-color transfer roll, or may be on the rotation axis of the K-color photosensitive drum.

  In the embodiment described above, the example in which the sheet pressing unit 270 includes two rolls, that is, the suppressing roll 271 and the suction roll 272 has been described. However, the present invention is not limited to this example. The part may have two adsorption rolls.

  In the above-described third embodiment, the two registration rolls 381 and 383 on both sides are made of metal and the central registration roll 382 is made of resin. However, the present invention is not limited to this. For example, the registration rolls on both sides may be made of an elastic resin and the central registration roll may be made of metal.

  In the third embodiment described above, the three registration rollers 381 to 383 have a distance from the first contact position S11 to the Y color transfer roll 40y and from the second contact position S12 to the Y color transfer roll 40y. However, the present invention is not limited to this, for example, the three registration rolls are arranged at positions where the above two distances are not equal, Depending on the difference between these two distances, the timing for forming an image on the image holding member may be adjusted by the image processing unit 32 or the write drive circuit 33 (FIG. 14).

1 is a diagram illustrating a schematic configuration of a printer according to a first embodiment of the present invention. It is a figure which shows the state which the opening-and-closing member of the printer shown in FIG. 1 opened. FIG. 2 is a perspective view showing an opening / closing member and a belt unit of the printer shown in FIG. 1. It is a perspective view which shows the support frame of the printer shown in FIG. It is a front view which shows the external appearance of the unit frame shown in FIG. It is a figure which shows the side surface of the unit frame shown in FIG. It is the expansion perspective view which expanded the part of the solenoid and link member shown in FIG. It is an expansion perspective view which shows the adsorption | suction roll in the position of a monochrome image formation mode. It is a figure which shows the state of the image formation unit, belt unit, and cam in color image formation mode. It is a figure which shows the state of the image formation unit in a monochrome image formation mode, a belt unit, and a cam. It is a perspective view which shows the opening-and-closing member and belt unit of the printer of 2nd Embodiment of this invention. It is a figure which shows the state of the image formation unit in the color image formation mode in 2nd Embodiment, a belt unit, and a cam. It is a figure which shows the state of the image formation unit in the monochrome image formation mode in 2nd Embodiment, a belt unit, and a cam. It is a figure which shows schematic structure of the printer of 3rd Embodiment of this invention. It is a perspective view which shows the external appearance of the registration roll unit of the printer shown in FIG. It is a perspective view which shows the internal structure of the registration roll unit shown in FIG. It is a side view which shows the internal structure of the registration roll unit shown in FIG. FIG. 15 is a diagram illustrating states of the photosensitive drum, the conveyance belt, and the registration roll unit in the color image forming mode of the printer illustrated in FIG. 14. FIG. 4 is a diagram illustrating a state of a photosensitive drum, a conveyance belt, and a registration roll unit in a monochrome image forming mode.

Explanation of symbols

1,3 Printer (image forming device)
11c, 11m, 11y Photosensitive drum (image carrier)
11k K color photosensitive drum (K color image carrier)
20 Belt unit 21 Conveyor belt (belt)
22 Drive roll (support roll)
22a Rotating shaft 23 Follower roll (support roll)
61a, 61b cam 24 unit frame (belt tilt drive unit together with 61a, 61b)
40k K color transfer roll (transfer roll)
40c, 40m, 40y Transfer roll (transfer roll)
55 Registration Roll 70 Paper Pressing Unit 71,272,371 Adsorption Roll 72 Solenoid 73 Link Member (Movement Mechanism Together with 72)
380 Registration roll unit (paper supply unit)
381, 382, 383 Registration roll 391 Route switching member 393, 394, 395 Guide member

Claims (9)

A plurality of image holding members for holding different color toner images arranged in a line, including a K color image holding member for holding a K color toner image disposed at one end;
A belt that extends along the plurality of image carriers and conveys a sheet along a path along the plurality of image carriers;
A plurality of support rolls including a drive roll disposed on the K-color image holding body side, on which the belt is bridged and drives the belt;
In a color image forming mode for forming a color image composed of a plurality of color toner images, a plurality of transfer rolls facing each of the plurality of image carriers with the belt interposed therebetween, and the belt contacts the plurality of image carriers. In a monochrome image forming mode in which a monochrome image composed of a K color toner image is formed, the belt contacts only the K color image holding body among the plurality of image holding bodies and is separated from the other image holding bodies. A belt tilting drive section for tilting the belt;
The sheet supplied toward the belt is pressed against the belt, and in the monochrome image forming mode, at a second position downstream of the first position in the color image forming mode in the conveying direction of the belt. An image forming apparatus comprising: a sheet pressing portion that presses a sheet. The first position is a position where the belt is sandwiched between the support rolls arranged on the most upstream side in the transport direction of the support rolls,
The second position is the downstream side in the transport direction with respect to the supply path through which the paper is supplied toward the belt and the position where the belt intersects, and the most upstream side in the transport direction of the image carrier. The image forming apparatus according to claim 1, wherein the image forming apparatus is located on the upstream side in the transport direction with respect to the image holding member disposed in the image forming apparatus. A charging roll that causes the sheet pressing portion to adhere the sheet to the belt by charging the sheet;
The charging roll is provided with a charging roll moving mechanism that moves the charging roll to the first position in the color image forming mode and moves to the second position in the monochrome image forming mode. The image forming apparatus according to claim 1. A first roll that holds the paper in the first position;
2. The monochrome image forming mode, further comprising: a second roll that presses a sheet that has passed through a side opposite to the belt of the first roll at the second position. 3. The image forming apparatus according to 1 or 2.   The image forming apparatus according to claim 4, wherein at least the second roll is a charging roll that causes the paper to adhere to the belt by charging the paper. A plurality of image holding members for holding different color toner images arranged in a line, including a K color image holding member for holding a K color toner image disposed at one end;
A belt that extends along the plurality of image carriers and conveys a sheet along a path along the plurality of image carriers;
A plurality of support rolls including a drive roll disposed on the K-color image holding body side, on which the belt is bridged and drives the belt;
In a color image forming mode for forming a color image composed of a plurality of color toner images, a plurality of transfer rolls facing each of the plurality of image carriers with the belt interposed therebetween, and the belt contacts the plurality of image carriers. In a monochrome image forming mode in which a monochrome image composed of a K color toner image is formed, the belt contacts only the K color image holding body among the plurality of image holding bodies and is separated from the other image holding bodies. A belt tilting drive section for tilting the belt;
Supplying paper toward the belt, and having at least three supply rolls in contact with each other in a row in a direction intersecting with the paper supply direction, and in the color image forming mode, of the image supply body among the three supply rolls. A paper supply unit that supplies paper from between two supply rolls arranged on the side and supplies paper from between two supply rolls arranged on the side away from the image carrier in the monochrome image forming mode An image forming apparatus comprising:   Of the three supply rolls, one of the two supply rolls on both sides and the one supply roll in the center is made of metal, and the other supply roll is made of an elastic resin. The image forming apparatus according to claim 6.   8. The image formation according to claim 6, wherein each of the three supply rolls rotates in a rotation direction opposite to a rotation direction in the color image formation mode in the monochrome image formation mode. apparatus.   The three supply rolls start from the first position where two of the three supply rolls in charge of paper supply in the color image forming mode are in contact with each other, in the color image forming mode. And a distance to the transfer roll disposed on the most upstream side in the transport direction on the path along the path, and two of the three supply rolls are in charge of supplying paper in the monochrome image forming mode. 9. The image forming apparatus according to claim 6, wherein the image forming apparatus is disposed at a position where a distance from the second position in contact with the transfer roll in the monochrome image forming mode is substantially equal. 10. .

Images