JP2016180872A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To significantly reduce defects in formation of print images.SOLUTION: The present invention comprises: an intermediate transfer belt that conveys, while carrying, a developer image in a conveyance direction; a secondary transfer part that secondarily transfers the developer image from the intermediate transfer belt to a medium; a detection part that is arranged on the downstream side of the secondary transfer part in the conveyance direction and detects a developer on the intermediate transfer belt; and a control part that controls a secondary transfer voltage to be applied to the secondary transfer part. During a first mode of detecting a transfer residual developer on the intermediate transfer belt after secondary transfer, when the detection part detects a transfer residual developer as a developer on the intermediate transfer belt, the control part controls the secondary transfer voltage to be applied to the secondary transfer part on the basis of a result of the detection, and thereby reducing the transfer residual developer after the secondary transfer of the developer from the intermediate transfer belt to the medium to significantly reduce defects in formation of print images, irrespective of the electric resistance values of media to be used for the formation of print images.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an image forming apparatus, and is suitable for application to, for example, an intermediate transfer type color electrophotographic printer (hereinafter also referred to as a color printer).

  In the conventional image forming apparatus, an intermediate transfer belt is stretched between a driving roller, a driven roller, and a backup roller arranged below the four image forming units, and the four primary transfer rollers are interposed via the intermediate transfer belt. The secondary transfer roller is pressed against the backup roller via the intermediate transfer belt, and is pressed against the photosensitive drums of the four image forming units. As a result, the image forming apparatus sequentially superimposes the four color toner images on the photosensitive drums of the four image forming units on the outer surface of the intermediate transfer belt rotated together with the driving roller via the four primary transfer rollers. Primary transfer, transport to a secondary transfer position by a secondary transfer roller, and secondary transfer to a medium. Further, in the image forming apparatus, a density sensor is disposed opposite to the outer surface of the belt between a secondary transfer roller and a driven roller which are upstream of the secondary transfer position in the toner image conveyance direction by the intermediate transfer belt. Therefore, when correcting the toner density, the image forming apparatus sequentially arranges the four color density detection toner images on the photosensitive drums of the four image forming units on the outer surface of the intermediate transfer belt rotated together with the driving roller, and performs primary transfer. During the conveyance to the secondary transfer position, the toner density of each of the four color density detection toner images is detected via the density sensor. The image forming apparatus appropriately changes the control conditions of the four image forming units and the four primary transfer rollers according to the detection results of the toner densities for the four colors, and the photosensitive drums of the four image forming units. The toner density at the time of forming the toner image on the top is corrected (for example, see Patent Document 1).

JP 2014-25962 A (pages 6 to 11, FIGS. 1 to 4)

  By the way, in the conventional image forming apparatus, various media having different materials and thicknesses can be used for forming a print image. However, the electric resistance value (hereinafter also referred to as a medium resistance value) of the medium differs depending on the type (material, thickness, etc.) of the medium. For this reason, in the image forming apparatus, when the voltage value of the transfer voltage applied to the secondary transfer roller is constant regardless of the type of the medium when the print image is formed, the secondary image of the toner image is generated depending on the medium resistance value depending on the type of the medium. The transfer conditions may change, and the toner image may not be fully transferred from the intermediate transfer belt to the medium, and the toner may remain on the outer surface of the belt. Since the image forming apparatus does not detect the toner remaining on the outer surface of the belt after the secondary transfer of the toner image from the intermediate transfer belt to the medium, the voltage value of the transfer voltage applied to the secondary transfer roller is set to 2 It cannot be adjusted to reduce the toner remaining on the outer surface of the belt after the next transfer. Therefore, the conventional image forming apparatus has a problem that, when forming a print image, depending on the type of the medium, the toner image cannot be secondarily transferred from the intermediate transfer belt to the medium, and a print image formation failure occurs.

  The present invention has been made in consideration of the above points, and an object of the present invention is to propose an image forming apparatus capable of greatly reducing the formation failure of a printed image.

  In order to solve such a problem, in the present invention, an intermediate transfer belt that carries a developer image that has been primarily transferred and conveys the developer image in a predetermined conveyance direction, and secondary transfer of the developer image from the intermediate transfer belt to a medium 2 A secondary transfer unit, a detection unit that is disposed downstream of the secondary transfer unit in the transport direction and detects the developer on the intermediate transfer belt, and a control unit that controls a secondary transfer voltage applied to the secondary transfer unit In the first mode in which the control unit detects the residual transfer developer after the secondary transfer on the intermediate transfer belt, the detection unit detects the residual transfer developer as the developer on the intermediate transfer belt. Based on the detection result, the secondary transfer voltage applied to the secondary transfer portion is controlled.

  Therefore, according to the present invention, it is possible to reduce the residual transfer developer after the secondary transfer of the developer image from the intermediate transfer belt to the medium, regardless of which of the media having different electric resistance values is used for forming the print image.

  According to the present invention, an intermediate transfer belt that carries a developer image that has been primarily transferred and conveys the developer image in a predetermined conveyance direction, a secondary transfer unit that secondarily transfers the developer image from the intermediate transfer belt to a medium, A detection unit that is disposed downstream of the secondary transfer unit in the conveyance direction and detects the developer on the intermediate transfer belt, and a control unit that controls the secondary transfer voltage applied to the secondary transfer unit are provided and controlled. When the detection unit detects the transfer residual developer as the developer on the intermediate transfer belt in the first mode in which the detection unit detects the transfer residual developer after the secondary transfer on the intermediate transfer belt, the detection result On the basis of this, by controlling the secondary transfer voltage applied to the secondary transfer portion, any of the media having different electrical resistance values is used for forming the print image. Transfer residual developer after the next transfer can be reduced, Comb formation of printed image defects can be realized an image forming apparatus capable of greatly reduced.

1 is a schematic side view showing an internal configuration of a color printer according to the present invention. 2 is a block diagram illustrating a circuit configuration of a color printer. FIG. FIG. 6 is a schematic diagram for explaining a voltage adjustment toner image primarily transferred to an intermediate transfer belt. FIG. 5 is a schematic diagram for explaining transfer residual toner after secondary transfer of a voltage adjustment toner image on an intermediate transfer belt. FIG. 6 is a schematic diagram for explaining a voltage adjustment toner image secondarily transferred to a medium. It is a basic diagram which shows the relationship between the voltage value of a secondary transfer voltage, and the toner density of a transfer residual toner.

The best mode for carrying out the invention (hereinafter, also referred to as an embodiment) will be described below with reference to the drawings. The description will be given in the following order.
(1) Embodiment (2) Other embodiments

(1) Embodiment (1-1) Internal Configuration of Color Printer In FIG. 1, reference numeral 1 denotes an intermediate transfer type color printer according to the present invention as a whole. The color printer 1 forms a print image on the surface of a plurality of types of quadrangular media 2 such as plain paper or film. For example, the printer 1 is a substantially square box type whose right end surface in the drawing is the front surface 3A. A housing 3 is provided. Incidentally, in the following description, when the color printer 1 is viewed facing the front surface 3A of the printer housing 3, the direction above the color printer 1 indicated by the arrow a1 in the figure is also referred to as the printer upward direction, which is the opposite. Is also referred to as the downward direction of the printer, and when there is no need to distinguish these directions, they are collectively referred to as the upward and downward direction of the printer. Further, in the following description, the direction in front of the color printer 1 indicated by the arrow b1 in the figure when the color printer 1 is viewed facing the front surface 3A of the printer housing 3 is also referred to as the front direction of the printer. Is also referred to as the rear direction of the printer, and when there is no need to distinguish between these directions, they are also collectively referred to as the front-rear direction of the printer. Furthermore, in the following description, the left direction of the color printer 1 indicated by the arrow c1 in the figure when the color printer 1 is viewed facing the front surface 3A of the printer housing 3 is also referred to as the printer left direction. The opposite direction is also referred to as the right direction of the printer, and when it is not necessary to distinguish between these, they are also collectively referred to as the printer left-right direction. The printer housing 3 has, on the upper surface 3B, a medium delivery section 3BX that delivers the medium 2 on which the print image is formed, and a medium discharge port 3BY that ejects the medium 2 from the printer housing 3 to the medium delivery section 3BX. Is formed.

  In the printer casing 3, an image forming unit 5 for forming a print image on the surface of the medium 2 is disposed at the center, and the medium 2 is supplied to the image forming unit 5 at the lower end. A medium supply unit 6 is disposed for the purpose. The image forming unit 5 includes, for example, four first to fourth image forming units 10 to 13, a transfer unit 15, and a fixing unit 16. The first to fourth image forming units 10 to 13 use toners as developers of different colors of black (K), cyan (C), magenta (M), and yellow (Y) for forming a print image. The configuration is the same except for. That is, the first to fourth image forming units 10 to 13 are the first to fourth image carriers that are provided so as to be rotatable in one rotation direction indicated by an arrow d1 in the drawing around a shaft parallel to the horizontal direction of the printer. The surfaces of the fourth photosensitive drums 20 to 23 are charged to a predetermined potential by first to fourth charging rollers 24 to 27 as charging units, and then first to fourth LEDs (Light Emitting Diodes) as exposure units. An electrostatic latent image is formed by exposure with the heads 28 to 31, and the electrostatic latent image is developed with toner charged to a predetermined negative potential by first to fourth developing rollers 32 to 35 as developing units. Thus, black, yellow, magenta, and cyan toner images are formed as developer images.

  Incidentally, the first to fourth image forming units 10 to 13 include, for example, a first image forming unit 10 that forms a black toner image along the rear direction of the printer, a second image forming unit 11 that forms a cyan toner image, The third image forming unit 12 for forming a magenta toner image and the fourth image forming unit 13 for forming a yellow toner image are arranged in this order. In addition, the first to fourth image forming units 10 to 13 are detachably mounted with first to fourth toner cartridges as developer supply units that store toners of corresponding colors, respectively. The first to fourth image forming units 10 to 13 dispose toner from the first to fourth toner cartridges to the first to fourth developing rollers 32 to 35 in the first to fourth image forming units 10 to 13. Supplying to places. Accordingly, the first to fourth image forming units 10 to 13 charge the toner supplied from the first to fourth toner cartridges by the first to fourth developing rollers 32 to 35 as described above, thereby first to fourth. By transferring to the electrostatic latent image on the four photosensitive drums 20 to 23, the electrostatic latent image is developed to form a toner image.

  The transfer unit 15 performs primary transfer by sequentially superimposing the four color toner images on the first to fourth photosensitive drums 20 to 23 on the outer surface of the endless intermediate transfer belt 41 by the primary transfer unit 40, A secondary transfer unit 42 secondarily transfers toner images of four colors from the outer surface of the belt to the surface of the medium 2. In the following description, the width from one opening to the other opening in the intermediate transfer belt 41 is also referred to as a belt width, and the direction along the belt width (that is, the direction from one opening to the other opening, and this) Is also referred to as the belt width direction. In this case, the transfer unit 15 has a belt driving roller 43 at a predetermined position that is obliquely below the rearmost fourth image forming unit 13 and is opposite to the one rotation direction around a shaft parallel to the printer horizontal direction. It is provided to be rotatable in the other rotation direction. In addition, the transfer unit 15 can rotate in a different rotational direction around a shaft parallel to the left-right direction of the printer at a predetermined position that is obliquely below the front of the first image forming unit 10 that is positioned at the foremost position. Is provided. Further, the transfer unit 15 has a backup roller 45 constituting the secondary transfer unit 42 at a predetermined position directly below the intermediate position between the belt driving roller 43 and the first driven roller 44 with a shaft parallel to the horizontal direction of the printer as a center. It is provided so as to be rotatable in the other rotation direction.

  Furthermore, the transfer unit 15 is provided at a predetermined position obliquely above the back-up roller 45 so that the second driven roller 46 can rotate in one rotation direction about a shaft parallel to the left-right direction of the printer. The transfer unit 15 includes a belt driving roller 43, a first driven roller 44, a backup roller 45, and a second driven roller 46. The intermediate transfer belt 41 has a belt width direction parallel to the printer left-right direction, and the rear side of the inverted triangle. It is stretched so as to form a substantially letter shape with a slanted concave surface. Here, the second driven roller 46 is in contact with the outer surface of the belt on which the above-described toner image of the intermediate transfer belt 41 and a toner image as a developer image described later are carried. The belt driving roller 43, the first driven roller 44, and the backup roller 45 are in contact with the inner surface of the belt, which is the back side of the outer surface of the belt on which the toner image and toner image of the intermediate transfer belt 41 are carried. Incidentally, in the transfer unit 15, for example, the arrangement positions of the belt driving roller 43, the backup roller 45, and the second driven roller 46 are fixed, but the first driven roller 44 is provided so as to be displaceable obliquely upward in the front direction. . The first driven roller 44 is urged so as to be displaced to the front side via a shaft by an urging portion (not shown) such as a compression coil spring. As a result, the transfer unit 15 is not slackened to the intermediate transfer belt 41 spanned by the belt driving roller 43, the first driven roller 44, the backup roller 45, and the second driven roller 46 by urging the first driven roller 44. Tension is applied.

  In addition, the transfer unit 15 includes four primary transfer rollers 47 to 50 constituting the primary transfer unit 40 between the belt driving roller 43 and the first driven roller 44, each centered on a shaft parallel to the horizontal direction of the printer. It can be rotated in other rotational directions and can be displaced in the vertical direction of the printer. The four primary transfer rollers 47 to 50 are each urged so as to be displaced upward through the shaft by an urging portion (not shown) such as a compression coil spring. Thus, the four primary transfer rollers 47 to 50 push the upper part of the surface to the lower part of the surface of the first to fourth photosensitive drums 20 to 23 facing each other via the intermediate transfer belt 41. Pressing with pressure. Further, the transfer unit 15 has a secondary transfer roller 51 that constitutes the secondary transfer unit 42 directly under the backup roller 45 so that the secondary transfer roller 51 can rotate in one rotation direction around a shaft parallel to the horizontal direction of the printer, and the vertical direction of the printer. It is provided so that it can be displaced. The secondary transfer roller 51 is biased so as to be displaced upward through the shaft by a biasing portion (not shown) such as a compression coil spring. As a result, the secondary transfer roller 51 presses the upper part of the surface against the lower part of the surface of the backup roller 45 through the intermediate transfer belt 41 with a predetermined pressing force.

  In the transfer unit 15, one end of the shaft of the belt driving roller 43 is mechanically connected to an output shaft of a unit driving motor (not shown) provided in the printer housing 3. Therefore, the transfer unit 15 rotates the belt driving roller 43 in the other rotation direction according to the operation of the unit driving motor, and rotates the intermediate transfer belt 41 together with the first driven roller 44 and the backup roller 45 in conjunction with the rotation. Can be rotated in the direction. The transfer unit 15 is electrically connected to a primary transfer power source (not shown) provided in the printer housing 3 at one end of each of the four primary transfer rollers 47 to 50. . As a result, the transfer unit 15 causes each of the four primary transfer rollers 47 to 50 to transfer toner from the primary transfer power source while the intermediate transfer belt 41 is rotated in the other rotation direction when a print image to be described later is formed. When a primary transfer voltage having a positive polarity different from the polarity of the potential is applied, four color toner images on the first to fourth photosensitive drums 20 to 23 are applied to the outer surface of the belt by the action of Coulomb force. Primary transfer can be performed in the order of cyan and black. Then, as the intermediate transfer belt 41 rotates, the transfer unit 15 moves to the secondary transfer portion 42 through the stretched position of the first driven roller 44 while the intermediate transfer belt 41 holds the four color toner images on the outer surface of the belt. Can be transported. Incidentally, in the transfer unit 15, the four contact positions on the outer surface of the intermediate transfer belt 41 with the lower portions of the surfaces of the first to fourth photosensitive drums 20 to 23 are respectively the primary transfer of the toner image and a toner image described later. Position. In the following description, the transport direction of a toner image carried on the outer surface of the belt by the intermediate transfer belt 41 or a toner image described later is indicated by a thick arrow in the drawing along the stretched shape of the intermediate transfer belt 41. Also called.

  The transfer unit 15 is electrically connected to one end of a shaft of a backup roller 45, for example, a secondary transfer power source, which will be described later, provided in the printer housing 3. Further, in the transfer unit 15, one end of the shaft of the secondary transfer roller 51 is grounded. As a result, the transfer unit 15 has a negative polarity equal to the polarity of the toner potential from the secondary transfer power source to the backup roller 45 in a state in which the intermediate transfer belt 41 is rotated in the other rotation direction when a print image to be described later is formed. When the secondary transfer voltage is applied, the secondary transfer voltage applied to the backup roller 45 and the electric field generated between the backup roller 45 and the secondary transfer roller 51 according to the secondary transfer voltage are applied to 4 on the outer surface of the belt. A color toner image can be secondarily transferred onto the surface of the medium 2. Incidentally, in the transfer unit 15, the contact position of the intermediate transfer belt 41 with the upper portion of the surface of the secondary transfer roller 51 on the outer surface of the intermediate transfer belt 41 becomes the secondary transfer position of a four-color toner image to the medium 2 and a toner image described later. . The transfer unit 15 has a plate-like cleaning blade 52 that is long in the left-right direction of the printer for removing toner adhering to the outer surface of the intermediate transfer belt 41 at the position where the belt driving roller 43 of the intermediate transfer belt 41 is stretched. A blade tip is pressed against the outer surface of the belt.

  The fixing unit 16 is provided with a heating roller 56 having a built-in heater 55 so as to be able to rotate in the other rotation direction, and in one rotation direction with the pressure roller 57 pressing the surface against the surface of the heating roller 56 with a predetermined pressing force. It is provided to be rotatable. Then, the fixing unit 16 heats and presses the four color toner images on the surface of the medium 2 while conveying the medium 2 with the heating roller 56 and the pressure roller 57 interposed therebetween, thereby fixing the color print image. Is formed. On the other hand, the medium supply unit 6 is provided so as to be attachable / detachable with respect to the printer housing 3, a medium cassette 60 in which a plurality of media 2 can be loaded, and a feeding roller 61 for feeding the medium 2 from the medium cassette 60. Is provided. The medium supply unit 6 also includes, for example, a pair of feed rollers 62 and a retard roller 63 that separate the two media 2 one by one when the two media 2 are fed from the medium cassette 60 by the feeding roller 61. Is also provided. In the printer housing 3, a medium supply transport unit 65 that forms a medium supply transport path for transporting the medium 2 fed from the medium cassette 60 to the image forming unit 5 is disposed at the front lower end. Yes. In the printer casing 3, a medium discharge transport unit 66 that forms a medium discharge transport path for transporting the medium 2 fed from the fixing unit 16 to the medium discharge port 3BY is disposed at the rear upper end. Yes.

  In the printer housing 3, for example, a later-described control unit having a microprocessor configuration is provided for overall control of the color printer 1. The control unit is communicably connected to a host device such as an external personal computer via a predetermined interface (not shown) provided in the printer housing 3. Further, the printer casing 3 is provided with an operation panel, which will be described later, including a display unit and an operation unit, for example, at the front end portion of the upper surface 3B. Therefore, when the formation of a color print image (that is, printing) is instructed from the host device or the formation of the color print image (that is, printing) is instructed via the operation panel, the control unit responds accordingly. A print image forming process is executed. In addition to the color print image, the control unit is instructed to form (ie, print) a monochrome print image from the host device, or is instructed to form (ie, print) a monochrome print image via the operation panel. In response to this, a monochrome print image forming process can also be executed.

  That is, the control unit drives and controls each unit in the printer casing 3 when forming a color print image, thereby feeding out the medium 2 from the medium cassette 60 one by one and through the medium supply conveyance path. Carry to 5. At this time, the control unit drives and controls the first to fourth LED heads 28 to 31 based on the print data indicating the color print target image. As a result, the control unit forms four color toner images on the surfaces of the first to fourth photosensitive drums 20 to 23 in the first to fourth image forming units 10 to 13 as described above. Further, the controller applies a primary transfer voltage to each of the four primary transfer rollers 47 to 50 from the primary transfer power source while rotating the intermediate transfer belt 41 in the transfer unit 15, so that the belt outer surface of the intermediate transfer belt 41. The four color toner images on the first to fourth photosensitive drums 20 to 23 are sequentially superposed on each other to perform primary transfer, and the intermediate transfer belt 41 carries the four color toner images on the outer surface of the belt to perform the secondary transfer position. Transport to. Then, the control unit applies the secondary transfer voltage from the secondary transfer power source to the backup roller 45 in the transfer unit 15, thereby continuing the medium 2 conveyed to the image forming unit 5 through the medium supply conveyance path. The toner images of the four colors on the outer surface of the belt are secondarily transferred to the surface of the medium 2 while being conveyed to the fixing unit 16 side by being sandwiched between 41 and the secondary transfer roller 51. As a result, the control unit fixes the four color toner images on the surface of the medium 2 in the fixing unit 16 to form a color print image, and the medium 2 passes through the medium discharge conveyance path to the medium discharge port 3BY. It is conveyed and discharged to the medium delivery unit 3BX.

  In addition, when the monochrome print image is formed, the control unit feeds the media 2 one by one from the media cassette 60 and conveys the media 2 to the image forming unit 5 through the medium supply conveyance path. However, at this time, the control unit drives and controls only the first LED head 28 of the first image forming unit 10 for forming the black toner image based on the print data indicating the monochrome print target image. Accordingly, the control unit forms a black toner image on the surface of the first photosensitive drum 20 in the first image forming unit 10 as described above. The control unit applies a primary transfer voltage from the primary transfer power source to one primary transfer roller 47 while rotating the intermediate transfer belt 41 in the transfer unit 15, so that the first transfer voltage is applied to the outer surface of the intermediate transfer belt 41. The black toner image on the photosensitive drum 20 is primarily transferred, and the intermediate transfer belt 41 carries the black toner image on the outer surface of the belt and conveys it to the secondary transfer position. Then, the control unit applies the secondary transfer voltage from the secondary transfer power source to the backup roller 45 in the transfer unit 15, thereby continuing the medium 2 conveyed to the image forming unit 5 through the medium supply conveyance path. The black toner image on the outer surface of the belt is secondarily transferred onto the surface of the medium 2 while being transported to the fixing unit 16 side so as to be sandwiched between 41 and the secondary transfer roller 51. Thus, the control unit fixes the black toner image on the surface of the medium 2 in the fixing unit 16 to form a monochrome print image, and conveys the medium 2 to the medium discharge port 3BY through the medium discharge conveyance path. Then, it is discharged to the medium delivery unit 3BX.

  Incidentally, in the print data indicating the color print target image, if there is a portion expressed in black in the print target image, the portion expressed in black of the print target image in the color print image formed on the surface of the medium 2 Information indicating whether the black portion corresponding to is generated with only black toner or cyan, magenta or yellow toner is included. Therefore, when a color print image is formed on the surface of the medium 2, the control unit expresses the black portion of the print image as black as a single color generated only with the black toner or cyan according to the print data. , Black as a mixed color generated by magenta and yellow toners. The print data indicating the monochrome print target image includes information indicating that the black portion of the monochrome print image formed on the surface of the medium 2 is generated only with the black toner. Therefore, when a monochrome print image is formed on the surface of the medium 2, the control unit expresses the black portion of the print image as black as a single color generated only with black toner according to the print data.

  By the way, in the color printer 1, various media 2 having different materials and thicknesses can be used for forming a color or monochrome print image. However, the plurality of types of media 2 have different electric resistance values (hereinafter also referred to as medium resistance values) of the media 2 depending on the material, thickness, and the like. Therefore, the transfer unit 15 has a downstream side in the toner transport direction by the intermediate transfer belt 41 with respect to the arrangement position of the secondary transfer unit 42 and an upstream in the toner transport direction with respect to the contact position of the second driven roller 46 with respect to the outer surface of the belt. For example, a toner sensor 70 composed of a light emitting element and a light receiving element for detecting the amount of toner on the outer surface of the belt is disposed in a predetermined position on the side so as to face the central portion of the outer surface of the belt in the belt width direction without contact. ing. That is, in the transfer unit 15, the toner sensor 70 is opposed to a portion on the outer surface of the intermediate transfer belt 41 that is not in contact with any other part between the secondary transfer position and the contact position of the second driven roller 46. Are arranged. For example, the control unit uses the toner sensor 70 to adjust the value of the secondary transfer voltage applied to the backup roller 45 in accordance with the operation of the operation panel (that is, the operation unit) by the user. Adjustment processing is being executed. Further, the control unit uses the toner sensor 70 periodically and according to the operation of the operation panel (that is, the operation unit) by the user, toner of toner images formed on the surfaces of the first to fourth photosensitive drums 20 to 23. A toner density correction process for correcting the density is also executed.

(1-2) Secondary Transfer Voltage Adjustment Process and Toner Density Correction Process Next, the secondary transfer voltage adjustment process and the toner density correction process executed by the control unit 75 will be described in order with reference to FIG. In the control unit 75, for example, the operation unit 76A and the display unit 76B of the operation panel 76 described above are connected to an internal input / output unit (I / O) 75A. The control unit 75 is connected to the input / output unit 75A, for example, with the toner sensor 70 and the secondary transfer power source 77 described above, and the first to fourth LED heads 28 to 31 (not shown in FIG. 2) and 1 A next transfer power source (not shown in FIG. 2) and the like are also connected. Note that the shaft of the backup roller 45 of the secondary transfer unit 42 is electrically connected to the secondary transfer power source 77 as described above. For example, when forming a color or monochrome print image, the control unit 75 loads the medium 2 used for forming the print image into the medium cassette 60 by the user, and displays a print setting screen via the operation unit 76A of the operation panel 76. Is requested, print setting screen data stored in advance is read from the internal storage unit 75B. Further, the control unit 75 sends the print setting screen data to the display unit 76B of the operation panel 76, thereby displaying a print setting screen (not shown) based on the print setting screen data on the display unit 76B.

  The control unit 75 then designates the type of the medium 2 used for forming the print image at this time as the material, thickness, and the like on the print setting screen via the operation unit 76A by the user, and the medium size of the medium 2 Is specified, medium type information indicating the type of the medium 2 and medium size information indicating the medium size of the medium 2 are fetched from the operation unit 76A. In addition, when the type of the print image formed on the surface of the medium 2 is arbitrarily designated from monochrome and color on the print setting screen via the operation unit 76A by the user, the control unit 75 Image type information indicating the type of the print image is fetched from 76A. In addition, when the user is instructed to execute the secondary transfer voltage adjustment process on the print setting screen via the operation unit 76A, the control unit 75 responds to the first mode prior to the formation of the print image on the medium 2. The secondary transfer voltage adjustment mode is entered, and the secondary transfer voltage adjustment process is executed in the form of trial printing. In this case, if the type of the print image indicated by the image type information is monochrome, the control unit 75 controls the drive of each unit in the printer housing 3 in substantially the same manner as when the above-described monochrome print image is formed. Therefore, the control unit 75 feeds out one medium 2 from the medium cassette 60 and conveys it to the image forming unit 5 through the medium supply conveyance path.

  Further, the control unit 75 generates predetermined head control data for toner image formation according to the medium size indicated by the medium size information by the internal head control data generation unit 75C, and the first LED head 28 of the first image forming unit 10. To control the drive. As a result, the controller 75 exposes the first photosensitive drum 20 at the center in the drum longitudinal direction with the first LED head 28 with a substantially uniform amount of light along the circumferential direction of the drum without any gap, and is long in the circumferential direction of the drum. A belt-like electrostatic latent image is formed. Then, the control unit 75 develops the electrostatic latent image at the center of the surface of the first photosensitive drum 20 with the black toner by the first developing roller 32. As a result, the controller 75 generates a belt-like transfer voltage adjustment toner image (hereinafter also referred to as a voltage adjustment toner image) along the circumferential direction of the drum at the center of the surface of the first photosensitive drum 20. Is formed as a so-called solid image with 100%. Further, the controller 75 applies a primary transfer voltage from the primary transfer power source to one primary transfer roller 47 while rotating the intermediate transfer belt 41 in the transfer unit 15, and the voltage on the first photosensitive drum 20. The toner image for adjustment is primarily transferred to the center of the outer surface of the intermediate transfer belt 41 in the belt width direction with the toner image longitudinal direction parallel to the toner transport direction. The control unit 75 carries the voltage adjusting toner image on the outer surface of the belt by the intermediate transfer belt 41 and conveys it to the secondary transfer position. In the following description, in the voltage adjustment toner image, one end on the downstream side in the toner transport direction is also referred to as the front end of the toner image, and the other end on the upstream side in the toner transport direction is also referred to as the rear end of the toner image.

  Here, as shown in FIG. 3, the voltage adjusting toner image 80 has a predetermined toner image length L1 in the toner image longitudinal direction that is slightly shorter than the medium length L2 in the medium conveyance direction when the medium 2 is conveyed. The length is selected. Further, the voltage adjustment toner image 80 has a toner image width W1 which is a length along the toner image width direction orthogonal to the longitudinal direction of the toner image, and a medium width W2 in a direction orthogonal to the medium conveyance direction when the medium 2 is conveyed. The width is selected to be a predetermined width that faces the toner sensor 70 when the intermediate transfer belt 41 conveys the toner sensor 70 to the arrangement position. For example, a so-called A4 size medium 2 having a long side length of 297 [mm] and a short side length of 210 [mm] is used for forming a print image, and the medium 2 has one short side. When transported in a posture toward the medium transport direction (that is, the short side is perpendicular to the medium transport direction and the long side is parallel to the medium transport direction), the voltage adjustment toner image 80 has a toner image length L1. Is selected to be a length of about 280 [mm] slightly shorter than the length of the long side of the medium 2 (that is, the medium length L2 during conveyance). Further, the toner image 80 for voltage adjustment is selected so that the toner image width W1 is about 50 mm which is narrower than the length of the short side of the medium 2 (that is, the medium width W2 during conveyance). Incidentally, in the following description, one end positioned on the downstream side in the medium transport direction when the medium 2 is transported is also referred to as a medium front end, and the other end positioned on the upstream side in the medium transport direction is also referred to as a medium rear end.

  When the control unit conveys the voltage adjustment toner image 80 to the secondary transfer position by the intermediate transfer belt 41, the polarity of the potential of the toner as the voltage adjustment toner image 80 from the secondary transfer power source 77 to the backup roller 45 is the same. Apply a secondary transfer voltage of negative polarity. As a result, the control unit 75 continues the conveyance of the medium 2 conveyed to the image forming unit 5 via the medium supply conveyance path by the intermediate transfer belt 41 and the secondary transfer roller 51, and the belt outer surface on the surface of the medium 2. The upper voltage adjustment toner image 80 is secondarily transferred so as to repel the backup roller 45. At this time, however, the control unit 75 controls the secondary transfer power source 77 while the voltage adjusting toner image 80 passes through the secondary transfer position, so that the secondary transfer voltage is transferred from the secondary transfer power source 77 to the backup roller 45. For example, the voltage value is sequentially increased stepwise and applied. For example, when the A4 size medium 2 is used to form a print image and the control unit 75 forms a voltage adjustment toner image 80 having a toner image length L1 of about 280 [mm], the voltage adjustment toner While the portion of the image 80 from the front end position of the toner image to a position of about 20 mm toward the rear end side of the toner image passes through the secondary transfer position, the secondary transfer power source 77 applies −800 [ A secondary transfer voltage having a voltage value of about V] is applied. Thereafter, the control unit 75 supplies a voltage value from the secondary transfer power source 77 to the backup roller 45 every time a portion having a length of about 20 [mm] sequentially passes through the secondary transfer position in the voltage adjustment toner image 80. A secondary transfer voltage increased by −200 [V] is applied. Then, the control unit 75 finally uses the secondary transfer power source 77 while the voltage adjustment toner image 80 has a length of about 20 [mm] at the rear end of the toner image passing through the secondary transfer position. A secondary transfer voltage having a voltage value of about −3600 [V] is applied to the backup roller 45. As a result, the control unit 75 sets the voltage adjustment toner image 80 from the belt outer surface of the intermediate transfer belt 41 to, for example, a position inside the surface of the medium 2 by a length L3 of about 10 mm from the front end of the medium as the front end of the toner image. Further, a position inside the toner image rear end by a length L4 of about 7 [mm] from the rear end of the medium is set as the rear end of the toner image (that is, from the position on the surface of the medium 2 about 10 [mm] from the front end of the medium to the rear end of the medium Secondary transfer is performed up to an inner position of about 7 mm.

  As shown in FIGS. 4 and 5, the control unit 75 changes the voltage value of the secondary transfer voltage applied from the secondary transfer power source 77 to the backup roller 45 in a stepwise manner, so that the intermediate transfer belt can be changed. The amount of toner 80A secondarily transferred from the outer surface of the belt 41 to the surface of the medium 2 as a voltage adjusting toner image 80 is partially changed. Therefore, the control unit 75 sets the toner 80 </ b> B (hereinafter also referred to as transfer residual toner) 80 </ b> B that remains on the outer surface of the intermediate transfer belt 41 without being fully transferred to the surface of the medium 2 as the voltage adjustment toner image 80. The intermediate transfer belt 41 conveys the toner image to a position facing the toner sensor 70 downstream of the secondary transfer position in the toner conveyance direction (hereinafter also referred to as a sensor facing position). In the following description, the portion of the transfer residual toner 80B on the outer surface of the intermediate transfer belt 41 that has passed through the secondary transfer position when the voltage value of the secondary transfer voltage applied to the backup roller 45 is sequentially changed. (In other words, in the above example, each portion of 20 [mm] along the toner conveyance direction) is also referred to as a transfer voltage change portion. The controller 75 controls the driving of the toner sensor 70 when the intermediate transfer belt 41 transports the untransferred toner 80B to the downstream side in the toner transport direction from the secondary transfer position. Thus, the toner sensor 70 emits detection light from the light emitting element and irradiates the central portion of the outer surface of the intermediate transfer belt 41 (that is, the transfer residual toner 80B carried on the central portion of the outer surface of the belt). Further, the toner sensor 70 receives reflected light obtained by reflecting the detection light at the central portion of the outer surface of the intermediate transfer belt 41 (that is, the residual toner 80B) by the light receiving element, and the amount of the received reflected light. A photoelectric signal having a signal level corresponding to the signal level is sent to the control unit 75 as a toner detection signal.

  Here, the amount of light reflected by the light receiving element of the toner sensor 70 varies depending on the toner concentration of the toner on the outer surface of the intermediate transfer belt 41. Therefore, when the light receiving element of the toner sensor 70 receives the reflected light, it outputs a toner detection signal having a signal level corresponding to the toner density of the toner carried on the outer surface of the intermediate transfer belt 41 as the amount of the reflected light. It is sent to the control unit 75. For example, the control unit 75 stores in advance a data table (not shown) that indicates various signal levels that can be taken by the toner detection signal and the toner density corresponding to the signal level in the storage unit 75B. Yes. Accordingly, at this time, the control unit 75 determines the sensor based on the distance from the secondary transfer position to the sensor facing position on the outer surface of the belt and the toner transport speed of the toner by the intermediate transfer belt 41 (that is, the rotational speed of the intermediate transfer belt 41). It is detected that a plurality of transfer voltage changing portions of the residual transfer toner 80B have sequentially reached the facing position. Further, whenever the control unit 75 detects that the transfer voltage change portion of the transfer residual toner 80B has reached the sensor facing position, the control unit 75 performs the transfer based on the signal level of the toner detection signal and the data table in the storage unit 75B. The toner density at the voltage change portion is detected. Further, the control unit 75 sets the secondary transfer voltage applied to the backup roller 45 to the toner density detected for each transfer voltage change portion of the transfer residual toner 80B when the transfer voltage change portion passes the secondary transfer position. Associate voltage values. As a result, the control unit 75 determines the secondary transfer voltage that has the lowest toner concentration in the residual transfer toner 80B from the toner concentration in each transfer voltage change portion in the residual transfer toner 80B and the voltage value of the secondary transfer voltage. A voltage value (hereinafter also referred to as a first voltage value) is detected. That is, the control unit 75 can transfer the largest amount of toner from the outer surface of the intermediate transfer belt 41 to the surface of the medium 2 as the voltage adjusting toner image 80 (that is, the amount of the residual toner 80B on the outer surface of the belt is maximized). The first voltage value of the secondary transfer voltage is detected.

  Here, FIG. 6 shows the relationship between the toner concentration (that is, the amount of toner) of the residual transfer toner 80B and the voltage value of the secondary transfer voltage. The vertical axis represents the toner concentration of the residual transfer toner 80B, and the horizontal axis represents the secondary. It shows as a characteristic curve of the graph as the voltage value of the transfer voltage. According to FIG. 6, in the color printer 1, when the voltage adjusting toner image 80 is secondarily transferred from the outer surface of the intermediate transfer belt 41 to the surface of the medium 2, the voltage of the secondary transfer voltage applied to the backup roller 45. It can be seen that when the value is relatively small, the toner density of the untransferred toner 80B on the outer surface of the belt is relatively high. This is because the electric field generated in the secondary transfer portion 42 for secondary transfer of the voltage adjusting toner image 80 on the intermediate transfer belt 41 to the surface of the medium 2 is relatively weak, and therefore the amount is relatively large on the outer surface of the belt. This is probably because the toner remained on the surface of the medium 2 without being transferred. Further, according to FIG. 6, in the color printer 1, when the voltage value of the secondary transfer voltage applied to the backup roller 45 is gradually increased, the toner concentration of the transfer residual toner 80B on the outer surface of the belt is gradually decreased accordingly. I understand that This can increase the amount of toner transferred from the outer surface of the belt to the surface of the medium 2 as a result of increasing the voltage value of the secondary transfer rolling pressure. Probably because it was obtained. However, it can be seen from FIG. 6 that in the color printer 1, when the voltage value of the secondary transfer voltage applied to the backup roller 45 is increased to some extent, the toner concentration of the transfer residual toner 80B on the outer surface of the belt increases again. This is because the electric field generated in the secondary transfer portion 42 is too strong, and an air discharge occurs between the intermediate transfer belt 41 and the medium 2 in the vicinity of the secondary transfer position. This is considered to be because the toner remained on the outer surface of the belt without being transferred to the surface of the medium 2 so as to be attracted to the backup roller 45 because the toner was reversed.

  Therefore, in the color printer 1, by optimizing the strength of the electric field generated in the secondary transfer unit 42, toner is transferred from the belt outer surface of the intermediate transfer belt 41 to the surface of the medium 2 without leaving the belt outer surface. I know you get. By the way, in the color printer 1, the strength of the electric field generated in the secondary transfer unit 42 is the voltage value of the secondary transfer voltage applied to the backup roller 45, the backup roller 45, the intermediate transfer belt 41, and the secondary transfer roller 51. It is determined by each electric resistance value and the medium resistance value of the medium 2. Therefore, in the color printer 1, for example, the voltage value of the secondary transfer voltage can be appropriately selected according to the electric resistance values of the backup roller 45, the intermediate transfer belt 41, and the secondary transfer roller 51 and the medium resistance value of the medium 2. For example, the strength of the electric field generated in the secondary transfer part 42 can be optimized. In the color printer 1, the electrical resistance values of the backup roller 45, the intermediate transfer belt 41, and the secondary transfer roller 51, which are part of the elements that determine the strength of the electric field generated in the secondary transfer unit 42 as described above. Can be assumed to some extent from the physical properties of the backup roller 45, the intermediate transfer belt 41 and the secondary transfer roller 51. However, in the color printer 1, the medium resistance value, which is a part of the element that determines the strength of the electric field generated by the secondary transfer unit 42, varies depending on what medium 2 is used by the user to form a print image. It's hard to predict.

  Therefore, the control unit 75 does not know the medium resistance value of the medium 2 but for adjusting the voltage while sequentially changing the voltage value of the secondary transfer voltage in the form of trial printing on the surface of the medium 2 actually used for forming the print image. The toner image 80 is secondarily transferred, and the strength of the electric field generated in the secondary transfer portion 42 is optimized from various voltage values of the secondary transfer voltage at that time, so that the toner density of the residual transfer toner 80B (ie, the toner density 80B) The first voltage value that can most reduce the amount of residual toner 80B) is detected. The control unit 75 can then secondary-transfer the voltage adjusting toner image 80 from the outer surface of the intermediate transfer belt 41 to the surface of the medium 2 most efficiently (that is, by reducing the amount of the residual toner 80B most). When the first voltage value of the secondary transfer voltage is detected, the detected first voltage value, the above-described medium type information, and image type information are stored in the storage unit 75B in association with each other. As a result, the control unit 75 ends the secondary transfer voltage adjustment process and notifies the user to that effect, for example, via the display unit 76B. When the user who has received the notification continues to instruct execution of print image formation on the print setting screen, for example, the control unit 75 executes monochrome print image formation processing in the same manner as described above. In one image forming unit 10, a black toner image is formed and primarily transferred onto the outer surface of the intermediate transfer belt 41. Then, when the toner image is conveyed to the secondary transfer position by the intermediate transfer belt 41, the control unit 75 reads the first voltage value from the storage unit 75B and controls the secondary transfer power source 77 to control the secondary transfer power source 77. The secondary transfer voltage of the first voltage value is applied from the power source 77 to the backup roller 45, and the toner image is secondarily transferred from the outer surface of the intermediate transfer belt 41 to the surface of the medium 2. In addition, the control unit 75 fixes the toner image on the surface of the medium 2 to form a monochrome print image.

  On the other hand, when the control unit 75 executes the secondary transfer voltage adjustment process, if the type of the print image indicated by the image type information is color, each unit in the printer housing 3 is configured to form the above-described color print image. The drive control is performed in substantially the same manner. However, as described above, in a color print image, a black portion is expressed by black as a single color generated by only black toner, and is expressed by black as a mixed color generated by cyan, magenta, and yellow toner. There is a case. Therefore, the control unit 75 sequentially feeds, for example, two media 2 from the medium cassette 60 and conveys them to the image forming unit 5 through the medium supply conveyance path. In addition, the control unit 75 generates the same head control data as described above by the head control data generation unit 75C. Then, the control unit 75 sends head control data from the head control data generation unit 75C to the first LED head 28 of the first image forming unit 10 for trial printing on the first medium 2, and then the second sheet. For trial printing on the medium 2, the head control data generation unit 75C sends the head control data to the second to fourth LED heads 29 to 31 of the remaining second to fourth image forming units 11 to 13. As a result, the control unit 75 forms a black voltage adjustment toner image 80 on the surface of the first photosensitive drum 20 in the first image forming unit 10 as described above, and the voltage adjustment toner image 80 alone is intermediate. The primary transfer is performed on the belt outer surface of the transfer belt 41 and the transfer belt 41 is conveyed to the secondary transfer position. The control unit 75 continues to use cyan, magenta, and yellow on the surfaces of the second to fourth photosensitive drums 21 to 23 in the second to fourth image forming units 11 to 13 as in the case of the first image forming unit 10. Each of the voltage adjustment toner images is formed as a solid image with a toner density of 100 [%], and these three color voltage adjustment toner images are superimposed on the belt outer surface of the intermediate transfer belt 41 in order for primary transfer. These are also conveyed to the secondary transfer position.

  When the control unit 75 conveys the black voltage adjusting toner image 80 to the secondary transfer position by the intermediate transfer belt 41, the voltage of the secondary transfer voltage applied to the backup roller 45 from the secondary transfer power source 77 as described above. The black voltage adjusting toner image 80 is secondarily transferred from the outer surface of the intermediate transfer belt 41 to the surface of the first medium 2 while sequentially changing the value. In addition, the control unit 75 conveys the untransferred toner 80B by the intermediate transfer belt 41 to the downstream side in the toner conveying direction from the secondary transfer position, so that the transfer remaining toner 80B of the transfer remaining toner 80B is used using the toner sensor 70 as described above. Along with the toner concentration, the first voltage value of the secondary transfer voltage that can minimize the toner concentration is detected. In addition, when the control unit 75 conveys the voltage adjustment toner images for the three colors, which are sequentially overlapped by the intermediate transfer belt 41, to the secondary transfer position, the secondary transfer power source is the same as in the case of the black voltage adjustment toner image 80. While the secondary transfer voltage applied from 77 to the backup roller 45 is sequentially changed, the voltage adjustment toner image for three colors from the outer surface of the intermediate transfer belt 41 is applied to the surface of the second medium 2 as a secondary. Transcript. In addition, the control unit 75 uses the toner sensor 70 in the same manner as described above to transfer the transfer residual toner at this time to the downstream side in the toner transfer direction from the secondary transfer position by the intermediate transfer belt 41. Along with the toner density of the toner, a voltage value of a secondary transfer voltage (hereinafter also referred to as a second voltage value) that can minimize the toner density is detected.

  In this way, the control unit 75 detects the first voltage value of the secondary transfer voltage based on the black voltage adjusting toner image 80, and also detects the secondary voltage based on the voltage adjusting toner images for three colors. When the second voltage value of the transfer voltage is detected, the storage unit 75B stores the first voltage value and the second voltage value in association with the above-described medium type information and image type information. As a result, the control unit 75 ends the secondary transfer voltage adjustment process and notifies the user to that effect, for example, via the display unit 76B. When the user who has received the notification continues to instruct execution of print image formation on the print setting screen, for example, the control unit 75 executes color print image formation processing as described above. However, for example, when the first voltage value and the second voltage value match, the control unit 75 supplies the secondary transfer voltage of the first voltage value from the secondary transfer power source 77 in the backup roller 45 in forming a color print image. Then, four color toner images are secondarily transferred from the outer surface of the intermediate transfer belt 41 to the surface of the medium 2. In contrast, for example, when the first voltage value and the second voltage value are different, the control unit 75 obtains an average voltage value that is an average value of the first voltage value and the second voltage value, and performs color printing. In the image formation, a secondary transfer voltage of the average voltage value is applied to the backup roller 45 from the secondary transfer power source 77, and the four color toner images are secondarily transferred from the outer surface of the intermediate transfer belt 41 to the surface of the medium 2. Let

  When the first voltage value and the second voltage value are different, the control unit 75 does not simply obtain the average voltage value and use it as the voltage value of the secondary transfer voltage, for example, analyze the print data, The first voltage value and the second voltage value can be properly used according to the analysis result. That is, the control unit 75 stores the first voltage value and the second voltage value in the storage unit 75B with information that can be distinguished from each other. In addition, the control unit 75 analyzes the print data when forming a color print image. As a result, when the black portion generated by only the black toner and the black portion generated by the cyan, magenta, and yellow toner are mixed in the color print image, the control unit 75 performs the first voltage value and the second voltage. An average voltage value that is an average value of the values is obtained, and the obtained average voltage value is set as a voltage value of the secondary transfer voltage applied from the secondary transfer power source 77 to the backup roller 45 in the formation of a color print image. On the other hand, the control unit 75 applies the first voltage value from the secondary transfer power source 77 to the backup roller 45 in forming the color print image when only the black portion generated by the black toner exists in the color print image. The secondary transfer voltage is set to a voltage value. Further, when there is only a black portion generated by cyan, magenta, and yellow toners in the color print image, the control unit 75 sets the second voltage value from the secondary transfer power source 77 to the backup roller 45 in forming the color print image. It can also be a voltage value of a secondary transfer voltage to be applied. In the following description, since the monochrome is designated as the type of print image, the first voltage value stored in the storage unit 75B by executing the secondary transfer voltage adjustment process and the color as the type of print image are designated. Accordingly, the first voltage value and the second voltage value stored in the storage unit 75B by executing the secondary transfer voltage adjustment process are collectively referred to as an optimum voltage value as appropriate.

  Incidentally, the untransferred toner 80B on the outer surface of the intermediate transfer belt 41 is used to detect the toner density, and is then transported by the intermediate transfer belt 41 to the position where the cleaning blade 52 is disposed. It is removed from the belt outer surface. Therefore, in the color printer 1, although the transfer residual toner 80B is transported to the downstream side in the toner transport direction from the secondary transfer position by the intermediate transfer belt 41, the transfer residual toner 80B hinders the formation of a monochrome or color print image. There is nothing. In this way, the control unit 75 detects the optimum voltage value of the secondary transfer voltage that is optimum for the secondary transfer in the form of trial printing prior to the formation of a color or monochrome print image. Then, the control unit 75 uses the secondary transfer voltage of the detected optimum voltage value for secondary transfer of the toner image from the intermediate transfer belt 41 to the medium 2 in the formation of a color or monochrome print image. Regardless of whether the medium 2 having a different medium resistance value is used for forming a color or monochrome print image, after the secondary transfer of the toner image from the intermediate transfer belt 41 to the medium 2, the belt is secondarily transferred to the surface of the medium 2 on the belt outer surface. It is possible to reduce the transfer residual toner that cannot be transferred.

  When the control unit 75 executes the secondary transfer voltage adjustment process and stores the optimum voltage value of the secondary transfer voltage in the storage unit 75B, the user thereafter instructs the execution of the secondary transfer voltage adjustment process again. Until then, the latest optimum voltage value stored in the storage unit 75B is continuously used as the voltage value of the secondary transfer voltage applied from the secondary transfer power supply 77 to the backup roller 45 in the formation of the print image. When the execution of the secondary transfer voltage adjustment process is instructed again by the control unit 75 and the user, the process proceeds to the secondary transfer voltage adjustment mode to execute the secondary transfer voltage adjustment process. Whether there is an optimum voltage value associated with the same medium type information and image type information among the optimum voltage values already stored in the storage unit 75B based on the medium type information and the image type information. Is detected. As a result, the control unit 75 includes the same medium type information and image type information as the medium type information and image type information input by the user at this time, among the optimum voltage values already stored in the storage unit 75B. If there is no associated optimum voltage value, the same processing as described above is executed, and the optimum voltage value of the secondary transfer voltage is newly detected and stored in the storage unit 75B. On the other hand, the control unit 75 includes the medium type information and the image type information that are the same as the medium type information and the image type information input by the user in the optimum voltage value already stored in the storage unit 75B. If there is an optimum voltage value associated with, the optimum voltage value is set to be used for secondary transfer, and the secondary transfer voltage adjustment processing is terminated.

  The control unit 75 can distinguish the first voltage value and the second voltage value from the storage unit 75B by executing the secondary transfer voltage adjustment process by specifying the color as the type of print image as described above. When such information is added and stored, the first voltage value can be used for the subsequent formation of a monochrome print image. That is, when the user designates monochrome as the type of print image and the execution of the secondary transfer voltage adjustment process is instructed, the control unit 75 shifts to the secondary transfer voltage adjustment mode and performs the secondary transfer voltage adjustment process. In this case, based on the medium type information input by the user, the first voltage value already stored in the storage unit 75B corresponds to the image type information indicating either monochrome or color. It is detected whether there is a first voltage value associated with the same medium type information regardless of whether it is attached. As a result, the control unit 75 includes the first voltage associated with the same medium type information as the medium type information input by the user in the first voltage value already stored in the storage unit 75B. If there is no value, the same processing as described above is executed, and the first voltage value of the secondary transfer voltage is newly detected and stored in the storage unit 75B. On the other hand, the control unit 75 associates the first voltage value already stored in the storage unit 75B with the same medium type information as the medium type information input by the user at this time. If there is a voltage value, the first voltage value is set to be used for secondary transfer, and the secondary transfer voltage adjustment processing is terminated.

  Incidentally, in addition to the above configuration, the control unit 75 detects, for example, that a medium cassette 60 has been inserted into and removed from the printer housing 3 with a predetermined sensor. When the control unit 75 detects that the medium cassette 60 has been inserted into or removed from the printer housing 3, for example, the type of the medium 2 in the medium cassette 60 is indicated to the user via the display unit 76 B of the operation panel 76. Inquire whether or not it has been changed to a different one. As a result, when the user is notified through the operation unit 76A of the operation panel 76 that the type of the medium 2 has not been changed, the control unit 75 instructs the execution of the secondary transfer voltage adjustment process. If the fact that the type of the medium 2 has been changed is notified, the user is instructed to execute the secondary transfer voltage adjustment process via the display unit 76B of the operation panel 76, for example. You can also encourage them.

  For example, the control unit 75 automatically shifts to the toner density correction mode, which is the second mode, every time the number of media 2 on which a print image is formed reaches a predetermined predetermined number. Execute the process. The control unit 75 also shifts to the toner density correction mode and executes the toner density correction process when the user instructs execution of the toner correction process via the operation unit 76A of the operation panel 76 at an arbitrary timing. In this case, the control unit 75 controls driving of the first to fourth image forming units 10 to 13 and the transfer unit 15. The control unit 75 generates first to fourth head control data for forming a predetermined toner image by the head control data generation unit 75C, and the first to fourth LED heads of the first to fourth image forming units 10 to 13. 28 to 31 for driving control. As a result, the control unit 75 exposes the center portion of the surface of the first to fourth photosensitive drums 20 to 23 with, for example, a predetermined amount of light by the first to fourth LED heads 28 to 31 and forms a rectangular electrostatic latent image. Form. Then, the control unit 75 develops the electrostatic latent image at the center of the surface of the first to fourth photosensitive drums 20 to 23 with the toner of black, cyan, magenta, and yellow by the first to fourth developing rollers 32. As a result, the control unit 75 forms a square toner image at a desired toner density such as 100 [%] at the center of the surface of the first to fourth photosensitive drums 20 to 23. Further, the control unit 75 applies primary transfer voltages to the four primary transfer rollers 47 to 50 from the primary transfer power source while rotating the intermediate transfer belt 41 in the transfer unit 15, so that the belt of the intermediate transfer belt 41 is applied. A toner image for correcting the toner density of a patch pattern (hereinafter, referred to as a toner image for patch density) in which four color toner images on the first to fourth photosensitive drums 20 to 23 are arranged in order along the toner transport direction at the center of the outer surface in the belt width direction. Is also referred to as a density correction toner image). Then, the controller 75 carries the density correction toner image on the outer surface of the belt by the intermediate transfer belt 41 and conveys it to the secondary transfer position.

  However, when the density transfer toner image is conveyed to the secondary transfer position by the intermediate transfer belt 41, the control unit 75 reduces the movement of the toner as the density correction toner image from the intermediate transfer belt 41 to the secondary transfer roller 51. The secondary transfer voltage having a predetermined voltage value with a positive polarity opposite to the polarity of the potential of the toner as the density correction toner image is transferred from the secondary transfer power source 77 to the backup roller 45 by performing the toner movement reduction process. Apply. As a result, the control unit 75 draws the density correction toner image held on the outer surface of the belt by the intermediate transfer belt 41 to the backup roller 45 by the secondary transfer voltage having a positive polarity applied to the backup roller 45. Pass the secondary transfer position. In this way, the control unit 75 transfers the secondary transfer unit 42 (that is, the backup roller 45 to which a secondary transfer voltage having a positive polarity opposite to the polarity of the toner) is applied to the secondary transfer roller 51 to the density correction toner. It functions as an adhesion preventing unit that prevents the toner as an image from moving and adhering, and thus the toner image for density correction carried on the outer surface of the belt by the intermediate transfer belt 41 does not reduce the amount of toner. It can be transported to a sensor facing position that is downstream of the secondary transfer position in the toner transport direction.

  When the density transfer toner image is conveyed to the sensor facing position by the intermediate transfer belt 41, the control unit 75 controls the drive of the toner sensor 70 in the same manner as described above. As a result, the control unit 75 controls the sensor facing position based on the distance from the secondary transfer position to the sensor facing position on the outer surface of the belt and the toner transport speed of the toner by the intermediate transfer belt 41 (that is, the rotational speed of the intermediate transfer belt 41). Then, it is detected that the four color toner images constituting the density correction toner image have successively arrived. Further, each time the toner images sequentially reach the sensor facing position, the controller 75 determines the toner image based on the signal level of the toner detection signal given from the light receiving element of the toner sensor 70 and the data table in the storage unit 75B. The toner density is detected. The control unit 75 assumes the toner density detected for each of the four color toner images constituting the density correction toner image when the toner image is formed on the surface of the first to fourth photosensitive drums 20 to 23. For example, the control conditions at the time of toner image formation for the first to fourth image forming units 10 to 13 are appropriately corrected according to the comparison result. As a result, the control unit 75 does not change the first to the first even if the charging characteristics of the toner change depending on the usage environment (ambient temperature, humidity, etc.) of the color printer 1 and the usage status (use period, execution of continuous printing, etc.). 4 A toner image can be formed on the surfaces of the photosensitive drums 20 to 23 with a desired toner density corrected. Incidentally, the toner image for density correction on the outer surface of the intermediate transfer belt 41 is also used to detect the toner density, and is then conveyed to the position where the cleaning blade 52 is disposed by the intermediate transfer belt 41, so that the cleaning blade 52 Remove from the belt outer surface. Therefore, in the color printer 1, the density correction toner image is transported downstream of the secondary transfer position in the toner transport direction by the intermediate transfer belt 41 to detect the toner density, but the density correction toner image is monochrome or color. The formation of the printed image is not hindered.

(1-3) Operation and Effect of Embodiment In the above configuration, in the color printer 1, in the transfer unit 15, the toner sensor 70 is disposed downstream of the secondary transfer position of the intermediate transfer belt 41 in the toner transport direction. And placed opposite to each other without contact. Then, the control unit 75 of the color printer 1 shifts to the secondary transfer voltage adjustment mode and executes the secondary transfer voltage adjustment process in the form of trial printing prior to the formation of the print image on the medium 2, thereby the first image. The voltage adjusting toner images formed by the forming unit 10 and the second to fourth image forming units 11 to 13 are primarily transferred to the belt outer surface of the intermediate transfer belt 41 and conveyed to the secondary transfer position. The control unit 75 of the color printer 1 sequentially changes the voltage value of the secondary transfer voltage applied from the secondary transfer power source 77 to the backup roller 45 of the secondary transfer unit 42 from the outer surface of the intermediate transfer belt 41. The toner image for voltage adjustment is secondarily transferred to the surface of the medium 2 and the transfer residual toner on the outer surface of the belt is transported by the intermediate transfer belt 41 to a sensor facing position downstream in the toner transport direction from the secondary transfer position. . The control unit 75 of the color printer 1 detects the toner concentration (that is, the amount of toner) of the transfer residual toner on the outer surface of the intermediate transfer belt 41 via the toner sensor 70, and based on the detection result, the print image The voltage value of the secondary transfer voltage applied from the secondary transfer power source 77 to the backup roller 45 of the secondary transfer unit 42 is controlled. According to the above configuration, the color printer 1 performs the secondary transfer of the toner image from the intermediate transfer belt 41 to the medium 2 regardless of whether the medium 2 having a different medium resistance value is used for forming a color or monochrome print image. Thereafter, the residual toner remaining on the outer surface of the belt without being fully transferred to the surface of the medium 2 can be reduced. As a result, the color printer 1 almost certainly prevents the formation of defects such as blurring in the printed image formed on the surface of the medium 2 and so-called dust that a plurality of spots on the surface are exposed in minute dots. Thus, it is possible to greatly reduce the formation failure of the printed image.

  By the way, in the conventional image forming apparatus, the density sensor is arranged upstream of the secondary transfer position of the intermediate transfer belt in the toner conveyance direction. For this reason, in the conventional image forming apparatus, even if the density sensor is used to detect the toner density of the residual toner on the outer surface of the intermediate transfer belt as in the present embodiment, the secondary transfer is performed by the intermediate transfer belt. When the subsequent transfer residual toner is transported downstream of the secondary transfer position in the toner transport direction, the toner density cannot be detected because it is removed from the outer surface of the belt by the cleaning blade. Further, the conventional image forming apparatus is provided with a mechanism for bringing the cleaning blade into contact with the outer surface of the intermediate transfer belt so that the transfer residual toner is transported downstream of the secondary transfer position in the toner transport direction by the intermediate transfer belt. In this case, if the cleaning blade is separated from the outer surface of the belt, it can be conveyed to the position where the density sensor is disposed without removing the transfer residual toner from the outer surface of the belt by the cleaning blade. However, in the conventional image forming apparatus, when the transfer residual toner passes through the primary transfer position, it adheres to the surface of the photosensitive drum and changes the toner concentration (that is, the amount of toner). It cannot be detected accurately. On the other hand, in the color printer 1 according to the present embodiment, the toner sensor 70 is provided between the secondary transfer position on the belt outer surface of the intermediate transfer belt 41 and the contact position of the second driven roller 46 on the downstream side in the toner transport direction. It was arranged to face the part where no other parts are in contact. Accordingly, the color printer 1 uses the intermediate transfer belt 41 to transfer toner remaining on the outer surface of the belt to the toner sensor 70 on the downstream side in the toner transport direction from the secondary transfer position without reducing the toner density (that is, the amount of toner). It can be conveyed to the arrangement position. Therefore, the color printer 1 can accurately detect the toner concentration of the transfer residual toner on the outer surface of the intermediate transfer belt using the toner sensor 70.

  When the control unit 75 of the color printer 1 shifts to the toner density correction mode and executes the toner density correction process, the density correction toner images formed by the first to fourth image forming units 10 to 13 are transferred to the intermediate transfer belt. The primary transfer is performed on the outer surface of the belt 41 and conveyed to the secondary transfer position. Then, the control unit 75 of the color printer 1 applies a secondary transfer voltage having a voltage value opposite to the polarity of the toner potential from the secondary transfer power source 77 to the backup roller 45 of the secondary transfer unit 42. As a result, the color printer 1 causes the secondary transfer unit 42 to function as an adhesion preventing unit, so that the density correction toner image carried on the outer surface of the intermediate transfer belt 41 does not adhere to the secondary transfer roller 51 at all. With this toner density, it can pass through the secondary transfer position and be transported to the sensor facing position on the downstream side in the toner transport direction. Therefore, the color printer 1 can accurately detect the toner density of the density correction toner image by using the toner sensor 70 used for the toner density detection in the secondary transfer voltage adjustment process also in the toner density correction process. In this way, the color printer 1 can accurately detect both the toner density of the voltage adjustment toner image and the toner density of the density correction toner image with a simple configuration using one toner sensor 70.

(2) Other embodiments (2-1) Other embodiments 1
In the above-described embodiment, the case where the voltage value of the secondary transfer voltage applied from the secondary transfer power source 77 to the backup roller 45 is changed stepwise during the secondary transfer voltage adjustment processing has been described. However, the present invention is not limited to this, and the voltage value of the secondary transfer voltage applied to the backup roller 45 from the secondary transfer power supply 77 may be linearly changed during the secondary transfer voltage adjustment processing. In the present invention, when the voltage value of the secondary transfer voltage applied from the secondary transfer power source 77 to the backup roller 45 is changed stepwise, the voltage value at the start of application, the voltage value at the end of application, and the change of the voltage value. Can be set to various voltage values different from the above-described −800 [V], −3600 [V], and −200 [V]. Furthermore, according to the present invention, when the voltage value of the secondary transfer voltage applied from the secondary transfer power source 77 to the backup roller 45 is changed stepwise or linearly, the voltage value is not gradually increased but gradually decreased. You can also. The present invention can achieve the same effects as those of the above-described embodiments even with these various configurations.

(2-2) Other embodiment 2
In the above-described embodiment, the case where the secondary transfer voltage is applied to the backup roller 45 from the secondary transfer power source 77 has been described. However, the present invention is not limited to this, and the secondary transfer voltage may be applied to the secondary transfer roller 51 from the secondary transfer power source 77 by grounding the backup roller 45. Incidentally, in the present invention, when the secondary transfer voltage is applied from the secondary transfer power source 77 to the secondary transfer roller 51, the toner is charged with a negative polarity. At the time of formation), a secondary transfer voltage having a positive polarity is applied from the secondary transfer power source 77 to the secondary transfer roller 51, and a negative polarity is applied from the secondary transfer power source 77 to the secondary transfer roller 51 during the toner density correction process. By applying the secondary transfer voltage, similarly to the above-described embodiment, the intermediate transfer belt 41 transports the transfer residual toner and the density correction toner image downstream of the secondary transfer position in the toner transport direction. can do. Therefore, the present invention can obtain the same effects as those of the above-described embodiment even with such a configuration.

(2-3) Other Embodiment 3
Further, in the above-described embodiment, during the toner density correction process, the control unit 75 performs the toner movement reduction process, and the secondary transfer having the polarity opposite to the polarity of the toner potential is transferred from the secondary transfer power source 77 to the backup roller 45. The case where the voltage is applied to cause the secondary transfer unit 42 to function as an adhesion preventing unit that prevents the toner as the density correction toner image from moving and adhering to the secondary transfer roller 51 has been described. However, the present invention is not limited to this, and a contact / contact portion that supports the secondary transfer roller 51 so as to be detachable from the outer surface of the intermediate transfer belt 41 is provided, and the controller 75 moves the toner during the toner density correction process. The secondary transfer voltage is not applied from the secondary transfer power source 77 to the backup roller 45 by performing the reduction process, and the separation contact portion is driven and controlled to separate the secondary transfer roller 51 from the outer surface of the intermediate transfer belt 41. Thus, the secondary transfer unit 42 may function as an adhesion preventing unit that prevents the toner as the density correction toner image from moving and adhering to the secondary transfer roller 51. The present invention can obtain the same effects as those of the above-described embodiment even with such a configuration.

(2-4) Other Embodiment 4
Further, in the above-described embodiment, when the secondary transfer voltage adjustment process is executed in a state where the color is designated as the type of print image, the black voltage adjustment toner image is independently provided on the outer surface of the intermediate transfer belt 41. The primary transfer is performed, and the voltage adjustment toner images for three colors of cyan, magenta, and yellow are sequentially superimposed to perform the primary transfer, and the toner density of each of the residual toner after the secondary transfer of the voltage adjustment toner image is set. The case of detection was described. However, the present invention is not limited to this, and when the secondary transfer voltage adjustment process is executed in a state where the color is specified as the type of print image, any of black, cyan, magenta, and yellow is applied to the outer surface of the intermediate transfer belt 41. Alternatively, only the voltage adjustment toner image of one color may be primarily transferred, and the toner density may be detected for the transfer residual toner after the secondary transfer of the voltage adjustment toner image. Further, according to the present invention, when the secondary transfer voltage adjustment process is executed in a state where the color is designated as the type of print image, the belt outer surface of the intermediate transfer belt 41 has a voltage of at least two colors of black, cyan, magenta, and yellow. The toner images for adjustment may be superposed in order to perform primary transfer, and the toner density of the transfer residual toner after the secondary transfer of the voltage adjustment toner image may be detected.

  In the present invention, for example, a toner amount sensor for detecting the amount of toner contained in each of the toner cartridges of the first to fourth image forming units 10 to 13 is provided, and the color is designated as the type of the print image. When the secondary transfer voltage adjustment process is executed in the above state, if a predetermined amount or more of black toner is stored in the toner cartridge of the first image forming unit 10, the black voltage adjustment is performed on the belt outer surface of the intermediate transfer belt 41. Primary transfer of only the toner image for black or primary transfer of the black voltage adjustment toner image alone, and primary adjustment by sequentially superimposing voltage adjustment toner images for three colors of cyan, magenta and yellow. The toner density may be detected for each transfer residual toner after the transfer and after the secondary transfer of these voltage adjusting toner images. In the present invention, when the secondary transfer voltage adjustment process is executed in a state where the color is designated as the type of print image, the amount of black toner contained in the toner cartridge of the first image forming unit 10 is a predetermined amount. If the number of the toner images is smaller than that, the voltage adjustment toner images for three colors of cyan, magenta, and yellow are sequentially superimposed on the outer surface of the intermediate transfer belt 41 to perform primary transfer, and after the secondary transfer of the voltage adjustment toner image. The toner density may be detected for the remaining transfer toner. Furthermore, according to the present invention, when the secondary transfer voltage adjustment process is executed in a state where the color is designated as the type of print image, a toner image for voltage adjustment is formed using only toner stored in a predetermined amount or more in the toner cartridge. Then, the voltage adjustment toner image formed on the belt outer surface of the intermediate transfer belt 41 is subjected to primary transfer alone or sequentially in order, and the transfer residual toner after the secondary transfer of the voltage adjustment toner image is toner. The concentration may be detected. The present invention can achieve the same effects as those of the above-described embodiments even with these various configurations.

(2-5) Other Embodiment 5
Further, in the above-described embodiment, the case has been described in which the control unit 75 is instructed to execute the secondary transfer voltage adjustment process or the toner density correction process via the operation panel 76. However, the present invention is not limited to this, and a secondary transfer voltage adjustment process or toner density correction is performed by the control unit 75 from a host device such as a personal computer that is mounted with a printer driver and is communicably connected to the color printer 1. You may instruct | indicate execution of a process.

(2-6) Other embodiment 6
Further, in the above-described embodiment, the case where the image forming apparatus according to the present invention is applied to the color printer 1 having the intermediate transfer type image forming unit 5 described above with reference to FIGS. 1 to 6 has been described. However, the present invention is not limited to this, and is widely applied to image forming apparatuses having various configurations such as an MFP (Multi-Function Peripheral) having an intermediate transfer type image forming unit, a facsimile, a multifunction peripheral, and a copying machine. Can be applied.

(2-7) Other Embodiment 7
Further, in the above-described embodiment, the belt driving roller 43 and the first driven roller described above with reference to FIGS. 1 to 6 are used as the intermediate transfer belt that carries the primary transferred developer image and conveys it in a predetermined conveying direction. The case where the intermediate transfer belt 41 stretched around the roller 44, the backup roller 45, and the second driven roller 46 is applied has been described. However, the present invention is not limited to this, and other intermediate configurations such as an intermediate transfer belt stretched around the belt driving roller 43, the first driven roller 44, and the backup roller 45 so as to form a substantially inverted triangle. The transfer belt can be widely applied.

(2-8) Other embodiment 8
Further, in the above-described embodiment, the secondary transfer unit that secondary-transfers the developer image from the intermediate transfer belt to the medium is a second transfer unit including the backup roller 45 and the secondary transfer roller 51 described above with reference to FIGS. The case where the next transfer portion 42 is applied has been described. However, the present invention is not limited to this, and a secondary transfer unit including a backup roller that is grounded and a secondary transfer roller that is electrically connected to a secondary transfer power source, a backup roller, a predetermined roller, and a tension roller. A secondary transfer unit composed of a secondary transfer belt that is rotatably stretched on a frame block, a tension block on which an intermediate transfer belt 41 is stretched, and a secondary transfer roller or a secondary transfer belt. Other secondary transfer portions having various configurations such as a transfer portion can be widely applied.

(2-9) Other Embodiment 9
Further, in the above-described embodiment, the toner sensor 70 described above with reference to FIGS. 1 to 6 is used as a detection unit that is disposed downstream of the secondary transfer unit in the transport direction and detects the developer on the intermediate transfer belt. The case where it applies is described. However, the present invention is not limited to this, and various other configurations of detection units such as an imaging unit can be widely applied.

(2-10) Other Embodiment 10
Further, in the above-described embodiment, the case where the control unit 75 having the microprocessor configuration described above with reference to FIGS. 1 to 6 is applied as the control unit for controlling the secondary transfer voltage applied to the secondary transfer unit. However, the present invention is not limited to this, and a wide variety of other control units such as a CPU (Central Processing Unit), a DSP (Digital Signal Processor), and a control unit having an external storage unit are widely applied. can do.

(2-11) Other Embodiment 11
Furthermore, in the above-described embodiment, the case where the backup roller 45 described above with reference to FIGS. 1 to 6 is applied as the first roller on which the intermediate transfer belt is stretched has been described. However, the present invention is not limited to this, and various other configurations of the first roller such as a grounded backup roller can be widely applied.

(2-12) Other Embodiment 12
Further, in the above-described embodiment, the secondary roller described above with reference to FIGS. 1 to 6 is provided as the second roller that is detachably attached to the intermediate transfer belt and is pressed against the first roller via the intermediate transfer belt. The case where the transfer roller 51 is applied has been described. However, the present invention is not limited to this, and a secondary transfer roller that is electrically connected to a secondary transfer power source, or a second transfer roller that is detachably attached to the intermediate transfer belt 41 via a predetermined contact portion. The second roller having various other configurations such as the next transfer roller can be widely applied.

  The present invention can be used for an image forming apparatus such as a color printer, an MFP, a facsimile, a multifunction peripheral, and a copying machine having an intermediate transfer type image forming section.

  DESCRIPTION OF SYMBOLS 1 ... Color printer, 41 ... Intermediate transfer belt, 42 ... Secondary transfer part, 45 ... Backup roller, 51 ... Secondary transfer roller, 70 ... Toner sensor, 75 ... Control part, 75B ... Storage unit 76... Operation panel 77. Secondary transfer power source 80. Voltage adjusting toner image 80 B Transfer residual toner

Claims (5)

An intermediate transfer belt that carries the primary transferred developer image and conveys it in a predetermined conveying direction;
A secondary transfer portion for secondary transfer of the developer image from the intermediate transfer belt to a medium;
A detection unit that is disposed downstream of the secondary transfer unit in the transport direction and detects the developer on the intermediate transfer belt;
A control unit for controlling a secondary transfer voltage applied to the secondary transfer unit,
The controller is
In the first mode in which the residual transfer developer after secondary transfer on the intermediate transfer belt is detected, if the residual transfer developer is detected as the developer on the intermediate transfer belt by the detection unit, the detection is performed. An image forming apparatus that controls the secondary transfer voltage applied to the secondary transfer unit based on a result. The controller is
Development that reduces the movement of the developer image on the intermediate transfer belt in the second mode in which the developer density of the developer image is corrected based on the detection result of the developer on the intermediate transfer belt by the detection unit. The image forming apparatus according to claim 1, wherein an agent movement reduction process is performed. The controller is
In the second mode, the developer that applies a voltage having a polarity opposite to a polarity of a voltage applied to the secondary transfer unit when the developer image is secondarily transferred from the intermediate transfer belt to the medium. The image forming apparatus according to claim 2, wherein a movement reduction process is performed. The secondary transfer portion is
A first roller on which the intermediate transfer belt is stretched;
A second roller provided so as to be detachable from the intermediate transfer belt and pressed against the first roller via the intermediate transfer belt;
The controller is
The image forming apparatus according to claim 2, wherein in the second mode, the developer movement reduction process for separating the second roller from the intermediate transfer belt is performed. The detector is
The secondary transfer unit on the downstream side in the transport direction from the secondary transfer unit and on the downstream side in the transport direction from the secondary transfer unit among the plurality of rollers on which the intermediate transfer belt is stretched The image forming apparatus according to claim 1, wherein the image forming apparatus is disposed on an upstream side in the transport direction with respect to the roller closest to.

Images