JP3279155B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image forming apparatus which constantly and stably adsorbs a sheet on a sheet conveying path.

[0002]

2. Description of the Related Art Conventionally, there is a color image forming apparatus.
This color image forming apparatus is roughly classified into a single drum type and a multi-stage drum type (tandem type). Single drum type
For each page of the paper, toners of Y (yellow: yellow) toner, M (magenta: red dye) toner and C (cyan: greenish blue) toner, which are three primary colors of subtractive color mixing, Since printing (image formation) processing is performed individually for each toner in order to transfer a total of four kinds of toners, a total of four types of Bk (black: black) toners dedicated to printing, the printing process is performed on one page of paper. Will be repeated four times,
Therefore, it takes a long time for the printing process. On the contrary,
The tandem type includes a type in which four types of toners are sequentially superimposed and transferred on a sheet in one process, and a type in which the toner is temporarily superimposed and transferred on an intermediate transfer body once and then re-transferred to a sheet at once.
Each has almost four times the processing speed as compared with the single drum type. For this reason, in recent years, various tandem-type color image forming apparatuses have been put to practical use, in combination with the fact that the internal apparatuses have been made smaller and assembled (unitized) to be relatively inexpensive. .

FIG. 6 (a) shows an example of a tandem type color image forming apparatus in an external perspective view, and FIG. 6 (b) shows a side sectional view thereof. This tandem type color image forming apparatus is shown in FIG.
As shown in FIG. 1A, an opening / closing tray 2 is provided on the front surface (right side in the figure) of the apparatus main body 1, and a paper cassette 3 is detachably provided at a lower portion. A paper discharge tray 5 is formed on an upper surface of the upper cover 4, and sheets on which an image is discharged from the upper paper discharge port 6 are stacked. A power switch 7, a liquid crystal display device 8, a plurality of input keys 9, and the like are disposed on the front side of the upper cover 4.

When an image is formed, as shown in FIG. 1 (b), a sheet P loaded and stored in a sheet cassette 3 in the apparatus main body 1 is fed to a sheet feeding roller 11 placed above the sheet P. To the waiting section. Alternatively, when forming an image on one to several sheets of different sizes and qualities, the open / close tray 2
Is rotated to the front of the apparatus as shown by the arrow A in the figure to open it, and the auxiliary tray 2b folded inside is further opened and rotated to the front of the apparatus as shown by the arrow B in the figure. The sheet is placed on the sheet and fed to the standby unit by the sheet feeding roller 12. A standby roll pair 13 is provided in the standby unit. The standby roll pair 13 temporarily stops the sheet fed from the sheet cassette 3 or the opening / closing tray 2 and then conveys the sheet to the image forming unit along the conveying path indicated by the broken line in FIG. Start.

[0005] The image forming section includes a belt 14 for transporting a sheet.
Is stretched between the two rotating rollers 15a and 15b, and four image forming units 16 are opposed to the belt conveying surface.
(16-1, 16-2, 16-3, 16-4). The belt 14 circulates and rotates in a counterclockwise direction indicated by arrows C and D in the figure. The image forming unit 16 is configured by assembling a charger, an exposure head, a developing roller, a transfer device, a cleaner, and the like in a unit frame, and is arranged in series in a multi-stage manner in the conveying direction of the belt 14. These various devices assembled with the image forming unit are arranged around the photosensitive drum 17 when the image forming unit 16 is mounted on the apparatus main body as shown in the figure. A fixing device 1 is provided downstream of the image forming section in the sheet conveying direction.
8, a discharge roller 19 and a rear discharge port 21 are provided.

On the conveyed sheet, toner images are sequentially transferred for each color from four photosensitive drums 17 in an image forming section, and the toner images are fixed in a fixing section 18.
9 as indicated by the dashed arrow E in the figure.
From the aircraft. Alternatively, the discharge path is switched upward by a switching lever (not shown) or the like, and the discharge rollers 2
As shown by a dashed arrow F in FIG.

The density of printing (image forming) pixels (one dot) is 30 pixels per inch at a normal resolution.
It is 0 to 400 dots (12 to 16 dots per millimeter), but if the superposition of the four colors causes a misalignment of about one dot, patterns such as moiré fringes occur in the image and the quality of the image is greatly reduced. descend. Therefore, belt 1
While the paper conveyed by 4 is sequentially transferred with toner images for each color from the four photosensitive drums 17, it is necessary that the paper is reliably held on the belt 14 to maintain a stable state.
As a technique for this purpose, a paper pressing roller provided generally on the upstream side in the paper transport direction of a belt similar in structure to the belt 14 shown in FIG. 6B is disposed at an angle, and a bias voltage is applied to the paper pressing roller. (See the first embodiment of JP-A-7-199590).

FIG. 7A is a schematic diagram for explaining the method. As shown in FIG. 2A, this method is an insulating method which is stretched between two rotating rollers 23 and 24 by an urging roller 25 and circulates in a counterclockwise direction indicated by arrows E and F in the figure. The angle .theta. Between the horizontal line 36 and the line connecting the centers of the rollers (dashed line 35 in the figure) and the horizontal roller 36 with respect to the rotating roller 24 upstream in the transport direction. And a bias power supply 37 applies a suction bias to the paper pressing roller 32. By doing so, the electric field forming point of the paper pressing roller 32 and the rotating roller 24 on the transport belt 26 is close to each other, and the paper P is more easily attracted to the transport belt 26. Then, when performing image formation, the transport belt 26 includes the photosensitive drums 27a, 27b, 2 of the four image forming units.
The sheet P is conveyed in contact with each of 7c and 27d. The photosensitive drums 27a, 27b, 27c, and 27d are Y (yellow), M (magenta), C (cyan), and B, respectively.
It carries a k (black) toner image. The paper P is taken out one by one from a paper container 28 composed of a paper feed cassette or the like by a paper feed roller 29, fed to an image forming unit by a standby roll pair 31 at an image forming timing, and fed by a paper pressing roller 32. The photosensitive drums 27a, 27b, 27c, and 27d are attracted to the conveyor belt 26 and are corona chargers 33a, 33b, 33c, and 33d.
The toner images formed on the respective peripheral surfaces are sequentially transferred to the paper surface, toner images of respective colors are superimposed, and the fixing unit 34 thermally fixes the toner images on the paper surface.

FIG. 1B shows a second embodiment of the above-mentioned proposal, in which the rotating roller 24 on the upstream side of the conveyor belt 26 is moved downward and the downstream side is rotated in order to perform monochrome printing. The roller 23 is moved upward to incline the entire conveying belt 26, and the conveying belt 26 (that is, the paper P conveyed by the conveying belt 26)
Are brought into contact with only the photosensitive drum 27d carrying the toner image, and the other photosensitive drums 27a, 27b,
And 27c.

[0010]

However, the above-mentioned structure certainly contributes to strengthening of the electric field to the transport belt because the paper pressing roller is inclined upstream with respect to the upstream rotating roller. However, on the other hand, there is a drawback that the paper is guided in a direction away from the transport belt due to the rigidity of the paper.

FIGS. 8 (a) and 8 (b) are enlarged views of the configuration on the upstream side of the image forming section shown in FIGS. 7 (a) and 7 (b).
As shown in FIG. 3A, a line (dashed line 3 in FIG. 3) connecting the center of the above-described rotating roller 24 and the center of the paper pressing roller 32 is provided.
5), when the sheet pressing roller 32 is disposed at an angle θ of 60 to 80 degrees with respect to the horizontal line 36 and is inclined upstream, an image forming unit (see FIG. The direction of the sheet sent out to the left) is indicated by a broken line 3 perpendicular to a line (dashed line 35 in the figure) connecting the center of the rotating roller 24 and the center of the sheet pressing roller 32.
8 is an obliquely upper left direction. Therefore, even if the configuration is made so that the sheet is more appropriately attracted to the transport belt 26 by devising the position of application of the bias angle bias voltage,
On the other hand, since the direction in which the paper is fed onto the transport belt is the direction away from the transport belt as indicated by the above-mentioned broken line 38, the broken arrow 3 in the figure is opposed to the bias voltage attracting force.
As shown at 9, there is a possibility that the paper will be lifted from the transport belt 26 and transported. If the sheet is conveyed to the transfer section while floating, the suction becomes unstable, and the printing position shifts, or the leading edge of the sheet is caught in various places, causing problems such as sheet jam. This means that the transfer belt 26 is used for printing in one color black as shown in FIG.
The same applies when the upstream side is moved downward and the downstream side is moved upward. In this case, since the conveyance distance to the transfer portion of the black toner image is long, the floating paper becomes more unstable as shown by the dashed arrow 39 'in the figure, and the printing position is different depending on the page, and Easy to jam.

[0012] Since the adsorption of the paper to the transport belt is unstable as described above, the above-described configuration uses a dielectric belt as the transport belt to strongly attract the paper.
Further, a corona discharger is used as a transfer unit in order to obtain sufficient transferability with respect to a system load change due to an environmental change or the like caused by the dielectric property of the transport belt.

However, the corona discharger requires a relatively large current, and therefore has a problem that the power supply becomes large. In particular, when the processing speed is increased, the amount of ozone generated by corona discharge increases. Therefore, a processing apparatus for removing the ozone is required, which causes a problem that the apparatus is further increased in size and cost is increased. I have. Furthermore, in this configuration, since the dielectric belt and the paper are strongly charged,
The adsorption power is too strong, so a special device is required to forcibly remove electricity from the paper and dielectric belt when separating the paper on which images are formed from the dielectric belt. There is a problem that the price rises.

SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus in which the conveyance state of a sheet is always stable, the elimination of harmful ozone is easy, and the discharge of the conveyance belt is easy. is there.

[0015]

The construction of the image forming apparatus according to the present invention will be described below. First, the invention according to claim 1 is directed to a plurality of image carriers arranged in parallel, and a plurality of toner image forming units for individually forming toner images of a predetermined color on the plurality of image carriers. Means, a transport belt that adsorbs the transfer material on the outer peripheral surface and circulates to move the transfer material into contact with at least one of the plurality of image carriers, and the plurality of images inside the transport belt. A plurality of transfer units arranged to form a transfer unit corresponding to the carrier, and a transfer bias voltage having a predetermined polarity applied to transfer a toner image to a transfer material in contact with the image carrier; The first and second rotating rollers disposed outside the transfer portions at both ends of the transfer portion in the juxtaposition direction of the transfer portion and over which the transport belt is stretched, and press the first rotary roller via the transport belt. And transfer the transfer material with the transfer belt. An image forming apparatus having a suction auxiliary roller to assist the adsorption on the conveyor belt of the transfer material is assumed. The invention according to claim 1
In the image forming apparatus described above, the suction assisting roller is
Connecting the center of the loading auxiliary roller and the center of the first rotating roller.
Line and contact of the suction assist roller with the transport belt.
From the section toward the second rotating roller
The angle of intersection with the ridge will be less than 90 °
As described above, the first rotating roller is pushed through the transport belt.
Configured to press.

Then, for example, as described in claim 2,
Suction to apply suction bias voltage to suction assist roller
It may be configured to further include a bias voltage applying unit. Previous
The attraction bias voltage applying means may be, for example, as set forth in claim 3.
Thus, a voltage having the same polarity as the transfer bias voltage is
It is configured to apply the voltage to the wearing assist roller. Also, for example
As set forth in claim 4, closest to the second rotating roller.
The toner image forming means corresponding to the image carrier may include the image carrier.
A black toner image is formed on the toner carrier corresponding to another image carrier.
-The image forming means is configured to form a chromatic toner image.
You. And the first and second rotating rollers are, for example,
6. The transfer material according to claim 5, wherein the transfer material is the first rotation row.
Roller while being conveyed from the roller side to the second rotating roller side.
Move the conveyor belt so that the toner image is transferred to the copying material.
It is configured to rotate to move.

Next, the invention according to claim 6 is arranged side by side.
A plurality of image carriers; and
A plurality of toner image forming means for forming a color toner image;
The transfer material is adsorbed to the peripheral surface to reduce the number of the plurality of image carriers.
Circulating transfer to bring the transfer material into contact with one image carrier.
A moving conveyor belt, and the plurality of conveyor belts inside the conveyor belt.
The image bearing member is arranged to form a transfer portion corresponding to the image carrier.
Prescribed to transfer toner image to transfer material in contact with carrier
A plurality of transfer units to which a transfer bias voltage having a polarity is applied
Than the transfer portions at both ends in the direction of juxtaposition of the plurality of transfer portions.
A first and a first, which are disposed outside and around which the conveyor belt is stretched;
A second rotating roller and the first belt via the transport belt;
The transfer roller is arranged to always press the
And the transfer belt for the transfer material.
Image with suction assist roller that assists suction
A forming device is assumed.

In the image forming apparatus according to the present invention,
Therefore, for the image carrier closest to the second rotating roller,
The transfer belt so that the transfer material always contacts in the same posture.
In the transferable position, and the above described
Set the transfer belt at the transferable position or the transfer material
To the untransferable position separated from the image carrier
Belt moving means, and selectively moving the belt moving means
Control means for controlling, the suction assist roller,
The center of the suction assist roller and the center of the first rotating roller
And a line connecting the suction assist roller and the transport belt.
The conveyor belt moves from the contact portion toward the second rotating roller.
The angle of intersection with the heading line is determined by the control means
Angle not exceeding 90 ° regardless of the movement control of the moving means.
So that the first rotation row is
The belt moving means and the range of movement of the belt moving means.
Configured to be set.

And, for example, as described in claim 7,
Suction to apply suction bias voltage to suction assist roller
It may be configured to further include a bias voltage applying unit. Previous
The attraction bias voltage applying means may be, for example, as set forth in claim 8.
Thus, a voltage having the same polarity as the transfer bias voltage is
It is configured to apply the voltage to the wearing assist roller. In addition, the suction
The arrival bias voltage applying means may be, for example, as set forth in claim 9.
And applying a suction bias voltage to the suction assist roller.
The transfer of the belt moving means by the control means is not possible.
It is performed according to the movement control to the position. In addition,
In this case as well, for example, the second
Toner image corresponding to the image carrier closest to the rotating roller
Forming means for forming a black toner image on the image carrier;
The toner image forming means corresponding to the image carrier is a chromatic toner.
It is configured to form an image. In addition, the first and second
The rotating roller of, for example, as described in claim 11, the
The transfer material is moved from the first rotating roller side to the second rotating roller.
The toner image is transferred to the transfer material while being conveyed to the side
So that the conveyor belt rotates to move
Constitute.

[0020]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1A is a cross-sectional view of a main part (image forming unit) of an image forming apparatus according to an embodiment, and shows a state where full-color printing (recording) is performed. FIG. 2B is an enlarged view of the paper carrying section.

As shown in FIG. 1A, the image forming unit comprises four photosensitive drums (image carriers) 41a and 41b, which are arranged in series and in multiple stages as indicated by a dashed line in FIG. ,
41c and 42 are provided. These photosensitive drums 4
1a, 41b, 41c and 42 are made of an organic photoconductor such as OPC, which uniformly covers the surface of the metal roller, or an inorganic photoconductor such as Se or a-Si. The photoreceptor drums 41 (41a, 41b, 41c) and 42 respectively carry a predetermined color toner image developed on the peripheral surface thereof in accordance with the electrostatic latent image and rotate.

Opposite to these photosensitive drums 41 and 42, there is provided a transfer belt 43 that circulates and moves in a direction in which the photosensitive drums 41 and 42 are arranged side by side as indicated by the arrow H in the figure. The transfer belt 43 is formed by adding carbon black to a fluororesin (tetrafluoroethylene copolymer (ETFE)) to adjust the resistance, thereby controlling the transfer resistance to 10 ¹¹ to 10.
It is composed of a 150 μm thick film member having a volume resistivity of ¹⁴ Ω · cm. This transport transfer belt 43
Are arranged in a flat loop shape in the horizontal direction, adsorb a sheet (transfer material) on the outer peripheral surface of the upper circulation portion, and
1a, 41b, 41c, and at least one of the photosensitive drums 42 or the photosensitive drum 42 and another photosensitive drum 4
The paper circulates to contact the papers 1a, 41b and 41c. Thus, the sheet is transported to the transfer position by the transport transfer belt 43, and the toner images on the photosensitive drums 41 and 42 are transferred. If the volume resistivity of the transfer belt 43 is lower than 10 ¹¹ Ω · cm, the paper P is less likely to be electrostatically attracted to the transfer belt 43. This is presumably because the electric charge stays on the rear surface of the transfer belt 43 and does not run off.

Abuts against the inside of the transfer belt 43,
The transfer brushes 44 (44a, 44b, 44c, 4c, 4c) correspond to the four photosensitive drums 41a, 41b, 41c, and 42, respectively.
4d) are juxtaposed. These transfer brushes 44 (transfer means) are formed by forming a woven fabric made of a pile of conductive rayon, nylon, acrylic, or the like as a fiber material, forming the brush shape, and attaching the woven fabric to a metal or plastic substrate. Although not shown, a transfer power supply for outputting a constant current of positive polarity is connected to the transfer brushes 44. The current flowing through the transfer brush 44 varies depending on the feed speed and width of the transfer belt 43, but it has been experimentally found that several μA is usually sufficient. These transfer brushes 44 are opposed to the photoconductor drums 41 and 42, and are arranged so as to sandwich the transfer belt 43 between the photoconductor drums and form a transfer portion. The above-described positive charge is applied to the sheet from the transfer brush 44 via the transfer belt 43, and the electric field generated by the charge causes the photosensitive drum 41 (41a, 41b, 41c) to be charged.
Alternatively, the negative toner image on the photoconductor drum is transferred to the paper in contact with 42.

As described above, the transfer belt 43 has a semiconductive resistance, and the transfer charger is configured as a transfer brush 44 which is in contact with the transfer belt. Even if the resistance between the base and the ground is reduced, the transfer load resistance is less than that, so that the transfer current flows in the direction of the paper. Therefore, even in such a case, a sufficient transfer electric field can be obtained. That is, the image forming apparatus can be used in all environments from a dry state to a high humidity state.

Downstream in the vicinity of the transfer brush 44, static elimination brushes 45 (45a, 45b, 45c, 45d) are provided. The charge removing brush 45 removes the charge applied to the transfer belt 43 at the transfer unit. This stabilizes the transfer potential of the downstream transfer section or the first transfer section in the next print mode.

The flat ends of the transfer belt 43 are stretched (held from the inside) at both ends of the transfer portions in the direction in which the transfer portions are arranged and outside the transfer portions, and the transfer transfer belt 43 is driven. Rotating roller 46 (first rotating roll) is disposed on the upstream side (right side in the drawing) in the transport direction, and a driving rotating roller 47 (second rotating roll)
Is disposed on the downstream side in the transport direction. The driven rotary roller 46 and the drive rotary roller 47 are connected to support shafts 46-1 and 47.
-1 (roller supporting means), the frame 5 of the apparatus main body
2 are respectively fixed in position. The driven rotation roller 46 and the drive rotation roller 47 rotate in the counterclockwise direction in the drawing, respectively. As a result, the transfer belt 43 described above circulates, and the paper P (transfer material) is driven from the driven rotary roller 46 (first rotary roll) side to the drive rotary roller 47.
The toner image is transferred while being conveyed to the (second rotating roll) side.

A tension roller 48 (belt tension means) is disposed near the drive roller 47 in contact with the inner peripheral side of the lower circulation portion of the transfer belt 43. The tension roller 48 is rotatably provided at the tip of a key-shaped arm 49, and the arm 49 has a rear end at a fulcrum 5.
1 rotatably supports the frame 52 of the apparatus main body. Central part of arm 49 and frame 5 of device main body
A tension spring 53 is engaged between the two, and the tension spring 53
The arm 49 is urged downward in the figure. As a result, the tension roller 48 urges and supports the lower portion of the transport transfer belt 43 so as to constantly pull it downward (to push it outward). Thereby, the transfer belt 43
, And the entire transfer belt 43 is stretched between the driven rotary roller 46 and the drive rotary roller 47 with a predetermined tension.

A movable arm 55 (oscillating member) is provided between the upper circulating portion and the lower circulating portion of the transfer belt 43 and extends parallel to the conveying direction. Movable arm 55
Has a fixed support roller 56 at one end and a movable support roller 57 at the other end.

The fixed support roller 56 is rotatably fixed to the frame 52 of the apparatus main body by a support shaft 59. The fixed support roller 56 includes a driving rotary roller 47.
The transfer brush 44d (transfer unit) closest to the (second rotation roller) is provided near the driven rotation roller 46 (first rotation roller). The fixed support roller 56 is in contact with the inner peripheral surface of the transfer belt 43 so that the photosensitive drum 42 (image carrier) closest to the driving rotary roller 47 always contacts the transfer belt 43. The transfer belt 43 is held at a transferable position so that the paper (transfer material) always contacts the drum 42 in the same posture.

The movable arm 55 has the above-mentioned movable support roller 57 on its free end side.
Abuts against the inner peripheral surface of the transfer belt 43 at a position between the transfer brush 44a (transfer means) closest to the driven rotation roller 46 (first rotation roller) and the driven rotation roller 46, thereby causing the transfer belt 43 to move. I support it.

The movable arm 55 has an end on the movable support roller 57 side centered on the support shaft 59 as shown by a double-headed arrow J in the drawing (a direction intersecting the surface of the transfer belt 43).
Then, the transfer belt 43 is moved via the movable support roller 57. The movable arm 55, the fixed support roller 56, and the movable support roller 57 constitute a belt moving unit. The movable arm 55
The three transfer brushes 44a, 44b, and 44c other than the transfer brush 44d among the four transfer brushes 44 are integrally attached to the movable arm 5.
5 is moved by the same distance in the same direction in accordance with the moving transfer belt 43 in accordance with the swing of the belt 5.

A cam engaging portion 61 is formed at a lower portion of the movable arm 55 so as to protrude laterally, and a cam 63 (control means) slidably abuts the cam engaging portion 61. ing. The cam 63 rotates 90 degrees in both the forward and reverse directions about the fulcrum 62, and selectively controls the movement of the movable arm 55 to position the movable arm 55.

FIGS. 7A and 7B show a state in which the cam 63 has rotated 90 degrees in the counterclockwise direction. At this time, the contact point of the cam 63 with the cam engaging portion 61 is a point farthest from the fulcrum 62, and the movable arm 55 is pushed up by the cam 63, rotates upward, and is located at the upper position. .
Accordingly, the movable arm 55 moves the transfer belt 43 to the photosensitive drum 41 other than the photosensitive drum 42 which is always in the transferable position via the movable support roller 57 by the movement control by the cam 63. It has been moved to the transferable position.

In such a movement of the transfer belt 43, as shown in FIG. 1 (b), the paper introducing portion 43 'between the driven rotary roller 46 and the movable support roller 57 of the transfer belt 43 is directed slightly upward and to the left. The image forming portion between the movable support roller 57 and the fixed support roller 56 tilts and moves only in a horizontal state similarly to the position between the fixed support roller 56 and the drive rotation roller 47, and the position of the driven rotation roller 46 does not move. .
A pressing roller 54 (a suction auxiliary roller) that opposes the driven rotating roller 46 and presses the driven rotating roller 46.
Is arranged. The driven rotation roller 46 is formed of a metal roller, while the pressing roller 54 is formed of a conductive rubber roll.

The pressing roller 54 is driven by the driven rotary roller 4.
A line 58 (a dashed line in the figure) connecting the center of the holding roller 54 and the center of the pressing roller 54 forms an angle δ smaller than 90 degrees with respect to the conveyance surface of the paper introduction portion 43 ′ of the conveyance transfer belt 43 on the downstream side. It is arranged at an angle. Thus, the holding roller 5
The sheet 4 is inclined with respect to the sheet introduction section 43 ′ in the direction of pressing the sheet, so that the sheet nipped by the pressing roller 54 and the transfer belt 43 and conveyed to the image forming section has a leading end. Is extruded in the direction in which the transfer belt 43 bites, and adheres well to the transfer belt 43. The pressing roller 54 is applied with a bias voltage described later in detail. The press roller 54 conveys the sheet in cooperation with the transfer belt 43 while assisting the adsorption of the sheet onto the transfer belt 43 by the bias voltage and the above-described sheet pressing.

FIG. 2 is a side sectional view of an image forming apparatus (tandem type color image forming apparatus) having such an image forming section therein. The appearance of the image forming apparatus 70 is shown in FIG.
This is almost the same as that shown in (a), and includes an opening / closing tray 72 on the front of the apparatus (right side in the figure) and a paper cassette 73 at the bottom.
Is detachably provided. In addition, the upper lid 74 of the device includes:
A paper discharge tray 75 is formed on the upper surface, and sheets on which images formed on the paper are discharged from the upper paper discharge port 76 are stacked thereon. Although not shown in the figure, a power switch, a display device, a plurality of input keys, and the like are provided on the front side of the upper lid 74.

As shown in the drawing, the inside of the image forming apparatus is substantially in the center, and the above-described image forming section, that is, four photosensitive drums 41 (41a, 41b, 41c) and 4
2, a transfer belt 43 opposed thereto, a driven rotary roller 46 that holds and drives the transfer belt 43, a drive rotary roller 47,
From the rear surface of the transfer belt 43, the photosensitive drums 41 and 4
A transfer arm 44 and a movable arm 55 whose front portion swings up and down by a cam 63 are disposed opposite to the transfer brush 44. Various devices in four image forming units 77 (77a, 77b, 77c, 77d), which will be described in detail later, are arranged so as to surround the four photosensitive drums 41 and 42, respectively.

On the upstream side (right side in the drawing) of the image forming section in the sheet transport direction, a standby roll pair 81 and a sheet detection sensor 82 are arranged. In the horizontal direction, a paper feed roller 83, a separating member 84, and the above-described opening / closing tray 72 are provided. Further, a transport path 85 formed from two guide plates is provided below,
Upstream thereof, the above-mentioned paper cassette 73 stores a large number of sheets P
And feed the paper feed end. A paper feed roller 86 is disposed above the paper feed end. Then, a fixing device 87, a paper discharge roller 88,
A switching lever 89 is provided. The fixing device 87 includes a pressure contact roller, a heat generation roller,
It is composed of a peripheral surface cleaner, an oil application roller, a thermistor, and the like, and heat-fixes the toner image transferred onto the paper to the paper surface. The switching lever 89 guides the sheet to an upper discharge path 91 when it is at a lower position as shown in the figure, and a discharge port 92 that opens the sheet to the rear surface of the apparatus when it is rotated upward.
Guide to Downstream of the discharge path 91 is a discharge roll pair 9
3 and communicate with the upper discharge port 76.

A cleaner bottle 94 is detachably provided between the image forming section and the sheet cassette 73. this,
A blade scraper 95 is provided above the cleaner bottle 94.
Is attached, and its tip is in contact with the surface of the lower circulation portion of the transfer belt 43. Blade scraper 95
Removes the toner remaining on the surface of the transfer belt 43 to clean the transfer belt 43, and stores the scraped unnecessary toner in the cleaner bottle 94.

FIG. 3 shows the image forming unit 77 (77
a, 77b, 77c, 77d). Image forming unit 77 (77a, 77b, 77c, 77d)
Have the same configuration except that the color of the toner contained therein is different. In the figure, one developing unit 7
7 shows the entire contents, and others are partially omitted.
As shown in the figure, the image forming unit 77 includes a cleaner 101, a charger 102, and a developing device 103. The developing device 103 (toner image forming means) forms a container, holds a developing roller 104 rotatably at a lower opening thereof, and stores a toner 105 therein. The developing device 103 of the image forming unit 77d corresponding to the photosensitive drum 42 (image carrier) closest to the driving rotary roller 47 (second rotary roller) shown in FIGS. Are stored in the image forming units 77a, 77b, and 77c corresponding to the other photosensitive drums 41.
M (magenta) and C (cyan) color toners are stored respectively.

A toner stirring member 106 is provided below the inside of the developing device 103.
Rotates as indicated by the two-dot chain line in FIG.
The toner is fed to the lower supply roller 107 while stirring the toner. The supply roller 107 is made of a sponge member, is pressed against the developing roller 104,
The toner 105 is supplied to the peripheral surface of the developing roller 104 so as to be rubbed. A blade spring 108 in the form of a leaf spring is in contact with the circumferential surface of the developing roller 104 in the rotation direction.
In addition to enhancing the adhesion to the toner layer 04, the toner layer to be attached is suppressed to a certain thickness.

Each of the devices incorporated in the above-described image forming unit 77 has a gear or an electrode (not shown), and is engaged with a drive mechanism and a power supply electrode of the device main body by being mounted on the device main body. Driven.

An exposure head 109 fixed to the upper cover 74 shown in FIG. 2 is provided between the charger 102 and the developing roller 104 as the upper cover 74 is closed.
As shown by 1, the robot descends along an arc-shaped trajectory and is located at the image forming position. The upper cover 74 is opened and the exposure head 109 is opened.
Is raised, the image forming unit 77 (77a, 77
b, 77c, 77d) can be individually taken out of the machine in a straight line direction inclined obliquely rightward and upward as indicated by a two-dot chain line 202 in the figure. As described above, when the image forming unit 77 is taken out, the protective cover 203 rotates clockwise to cover and protect the photosensitive drum 42.

Next, the operation of the image forming process of the image forming apparatus according to the present embodiment having the above configuration will be described with reference to FIGS. 1 to 3 again. First, when the power is turned on to the image forming apparatus 70 (see FIG. 2), the number of sheets and other designations are input by a key, and when full-color printing (image formation) is designated, the cam 6 is driven by a driving mechanism (not shown).
3 is rotated by 90 degrees in the counterclockwise direction, whereby the movable arm 55 is rotated upward, whereby the movable support roller 57 is moved upward, and the transfer belt 43 is moved.
To all four photosensitive drums 41 (41a, 41b, 4
1c) and 42 (see FIG. 1 (a)).

Subsequently, the sheet feeding roller 86 is moved to the sheet cassette 73.
Is fed to the standby roll pair 81 via the transport path 85. Alternatively, the paper feed roller 83 feeds the paper placed on the open / close tray 72 to the standby roll pair 81. The fed paper P is detected by a paper detection sensor 82.
Is detected. The standby roll pair 81 stops rotating, and the paper P
Is made to abut on the holding portion to stand by.

The driving rotary roller 47 starts rotating in the counterclockwise direction, and the driven rotary roller 46 is driven to start rotating in the same counterclockwise direction. As a result, the transport transfer belt 43 has four photosensitive drums 42 and 41 whose upper circulation portion
1A and 3A, the whole circulates in the direction from right to left as indicated by the arrow H in FIG. 1A and FIG.

At the same time, the image forming units 77a and 77a
7b, 77c and 77d are sequentially driven in accordance with the print timing, and the photosensitive drums 41a,
41b, 41c and 42 are sequentially driven to rotate clockwise. Then, each image forming unit 77 (FIG. 3)
The exposure head 109 corresponding to (refer to (1)) is sequentially driven.
By this driving, the charging brush 102 is moved to the photosensitive drum 41.
And a uniform charge on the peripheral surfaces of the exposure head 10 and the exposure head 10.
Reference numeral 9 forms an electrostatic latent image on the photosensitive drum peripheral surface by exposing the photosensitive drum peripheral surface in accordance with an image signal. The developing roller 104 transfers the toner 105 to a low potential portion of the electrostatic latent image to form (develop) a toner image on the peripheral surface of the photoconductor drum.

When the leading edge of the toner image on the peripheral surface of the photosensitive drum 41a at the most upstream position is rotated and conveyed to a point facing the transfer belt 43, the print start position of the paper P coincides with the point. Thus, the standby roll pair 81 starts rotating and feeds the paper P to the paper carry-in port of the image forming unit.
The press roller 54 and the driven rotary roller 46 pinch the fed sheet P together with the transfer belt 43, and
4 transports the paper P while pressing the leading end of the paper P into the transport transfer belt 43 by pressing the leading end of the paper P to the downstream side by an inclined arrangement of an angle δ. The leading end of the paper P is sequentially sent out by being pinched by the driven rotation roller 46 and the pressing roller 54 and, even after leaving the pinching portion, is stably attracted to the transfer belt 43 so that the photosensitive drum 41 a and the transfer brush 44 a
And is conveyed to the most upstream transfer section formed by. At this time, the angle formed by the transfer belt 43 (paper introduction part 43 ′) stretched between the driven rotation roll 46 and the movable support roll 57 with the horizontal line is about 15 °, and the paper P is transferred to the transfer part. The entry is reliably performed along the transfer belt 43 without any obstacle. Thereafter, electrostatic attraction occurs due to the electric field of the transfer unit between the transfer belt 43 and the sheet. Thereafter, the sheet is sequentially sent along the transfer belt 43 to the next transfer unit.

While the paper P is being conveyed in this manner, the paper P is applied to each of the photosensitive drums 41 and 42 by an electric field formed between the photosensitive drums 41 and 42 by applying a voltage from each of the transfer brushes 44a, 44b, 44c and 44d. And 42 are sequentially transferred onto the paper.

The paper P to which the four color toner images have been transferred is separated from the transfer belt 43 by the separation claws 205 (see FIG. 2), and is carried into the fixing device 87. After the toner image is thermally fixed by the fixing device 87 on the paper P,
As a result, the toner image is discharged from the rear paper outlet 92 with the toner image facing upward, or from the upper paper outlet 76 with the toner image facing downward.

Next, black printing (black-color image forming processing) will be described. FIG. 4A is a diagram showing a state of the image forming unit when performing black printing, and FIG. 4B is an enlarged view of the paper carrying unit. FIG. 4A shows a state in which the cam 63 is rotated 90 degrees clockwise from the position shown in FIG. 1A. At this time, the contact point of the cam 63 with the cam engaging portion 61 is the closest point from the fulcrum 62, and the movable arm 55 is rotated downward and located at the lower position. As a result, the movable arm 55 moves the transport belt 4 with respect to the other photosensitive drums 41 (41a, 41b, 41c) except for the photosensitive drum 42 by the movement control by the cam 63.
3 is moved to a non-transferable position. That is, the rotation of the movable arm 55 causes the movable support roller 57 to move downward as indicated by the arrow K in the drawing, so that the transport belt 43 is directly supported by the fixed support roller 56 and the drive rotation roller 46. , A gap M is formed between itself and the lower surface of the conveyor belt 43 to separate from the conveyor belt 43. In this case as well, the position of the driven rotary roller 46 does not move.

As described above, the conveyor belt 43 maintains the contact state with the photosensitive drum 42 between the driving rotary roller 47 and the fixed support roller 56 in the same state as in the case of full color printing on the one hand, and the fixed state on the other. Between the support roller 56 and the driven rotation roller 46, the remaining photosensitive drums 41 (41
a, 41b, 41c).

Subsequently, the paper P is fed by the paper feed roller 86 or the paper feed roller 83, the paper is detected by the paper detection sensor 82, the paper P is waited by the standby roll pair 81, and the driven rotation roller 46 and the drive rotation roller 47 are used. Conveyor belt 4
The circulating movement of No. 3 is the same as in the above-described full-color printing.

Then, together with this, the image forming unit 7
7d is driven, and the other image forming units 77a, 77b
And 77c pause. The rotation drive of the photosensitive drum 42 corresponding to the image forming unit 77d, the application of charge to the photosensitive drum 42 by the charging brush 102, the exposure head 109
The formation of the electrostatic latent image on the peripheral surface of the photosensitive drum by the printer and the toner image formation of the electrostatic latent image by the developing roller 104 are the same as in the above-described full-color printing.

At the timing when the leading end of the black toner image on the peripheral surface of the photosensitive drum 42 is rotated and conveyed to a point facing the conveyor belt 43, the printing start position of the paper P coincides with the point. The standby roll pair 81 starts rotating and feeds the sheet P to the sheet inlet of the image forming unit.

Also in this case, the pressing roller 54 and the driven rotary roller 46 hold the fed sheet P together with the transfer belt 43, and the pressing roller 54 is inclined to the downstream side at an angle δ not exceeding 90 degrees. Then, the sheet P is conveyed while pressing the leading end of the sheet P against the transfer belt 43.

Subsequently, the paper P by the transport belt 43
, Transfer of the black toner image onto the paper surface by the transfer brush 44d, separation of the sheet P from the conveyance belt 43 by the separation claw 205, heat fixing of the toner image by the fixing device 87, and rear discharge by the discharge roller 88 The discharge of the paper P from the paper outlet 92 or the upper paper outlet 76 is the same as in the above-described full-color printing.

When the paper P is transported by the transport belt 43, the movable support roller 57 is separated from the transport belt 43, so that the transport belt 43 does not bend between the fixed support roller 56 and the driven rotary roller 46. Form a plane. As a result, the paper P is driven
Is transported while being stably held on the transport belt 43 over a relatively long distance from the transport belt 43 to the fixed support roller 56.

As described above, in the case of both full-color printing and black printing, the portion between the fixed support roller 56 and the driven rotary roller 46 of the conveyor belt 43 only swings up and down, and black printing is performed. Conveyor belt 43 for transfer unit
Is constant because the positions of both the driving rotary roller 47 and the fixed support roller 56 are immobile. Further, the paper carry-in entrance to the image forming unit is constant because the positions of the driven rotation roller 46 and the pressing roller 54 are not moved. The posture of the paper P discharged from the image forming unit and carried into the fixing device 87 is constant because the positions of the photosensitive drum 42, the driving rotation roller 47, and the fixed support roller 56 are not moved.

As described above, since the attitude of the conveyor belt 43 with respect to the transfer section for performing black printing is always constant, the transfer timing and the transfer brush in the transfer section for printing black toner in both full-color printing and black printing. There is no need to change the voltage control or the like of 44d, and in any case, the processing can be performed by the same control method. Also, since the paper entrance of the image forming unit with respect to the paper feeding unit such as the paper cassette and the standby roll pair is always constant, the position of the paper cassette and the position of the standby roll pair are required for both full-color printing and black printing. It is not necessary to change the position corresponding to the paper inlet which fluctuates up and down as in the related art. In addition, since the orientation of the paper P discharged from the image forming unit is always constant, the guide path to be conveyed to the fixing device is changed according to the paper discharge attitude in both full color printing and black printing. This eliminates the need for this, and this also makes it possible to constitute a simple mechanism as a whole.

In the above embodiment, the black toner image forming unit 77d, that is, the photosensitive drum 42 carrying the black toner image is arranged at the most downstream side of the conveyance path of the image forming section. Is not limited to this.
2 is disposed at the most upstream side of the transport path, and accordingly, the fixed support roller 56 is disposed upstream of the transport path, the movable support roller 57 is disposed downstream of the transport path, and the movable arm 55 is disposed accordingly. The movable arm may be configured to swing up and down on the left side with the right side of the figure as a fixed support shaft, contrary to the above-described embodiment.

Although the pressing roller 54 is a fixed position roll, the inclination angle with respect to the transfer belt 43 in black printing and full-color printing may be changed so that the paper feeding direction is optimal for each printing mode.
For example, at the time of black printing, the position is the same as that in the above-described embodiment, and at the time of full-color printing, the paper introduction portion of the transport transfer belt is slightly obliquely upward, so that the biting angle with respect to the transport transfer belt is made slightly shallow. It may be.

By the way, the transfer belt 43 is
The paper P must be sufficiently electrostatically attracted and conveyed so as not to be affected by a slight load fluctuation or the like acting on the paper P. Thus, the paper P is transferred to the transfer belt 4.
In this embodiment, as described above, 10 ¹¹ Ω · cm
The above resistance propensity is given. Then, the pressing roller 5 is pressed so that the sheet P is easily attracted to the transfer belt 43.
4 is disposed in a posture inclined to the downstream side.

In full-color printing, the transport distance is short to the Y (yellow) transfer section where the paper P is transported first, so that there is no possibility that the transport attitude of the paper P will be distorted due to external force applied to the transport attitude. The sheet P is sufficiently attracted to the transfer belt 43 by receiving the charge for transfer in the first step.
(Yellow) as long as it can be conveyed correctly to the transfer portion. Therefore, in the case of full-color printing, it is not necessary to control the paper transporting attitude further than that as long as the above-described pressing roller 54 presses the paper against the surface of the transporting transfer belt to guide the attitude to assist suction.

However, in the present embodiment, two printing modes are provided so that black printing is also performed. For black printing,
As shown in FIGS. 4A and 4B, the sheet P is transported a relatively long distance from the loading section by the pressing roller 54 and the driven rotating roller 46 to the transfer section for forming a black toner image. Therefore, it is difficult to say that there is no possibility that the conveyance posture of the paper P becomes unstable. In the present embodiment, in the case of this black printing, a suction bias voltage is further applied to the pressing roller 54 so that the sheet is positively electrostatically attracted to the transfer belt.

FIG. 5 is a diagram schematically showing the configuration of such a paper carry-in section for positively electrostatically adsorbing paper.
In this figure, the same parts as those shown in FIGS. 1 to 4 are denoted by the same reference numerals as in FIGS. The driven rotating roller 46 shown in the figure is a grounded metal roller, while the pressing roller 54 is a rubber roller whose resistance is adjusted by carbon black. This press roller 5
For example, CR rubber that exhibits a resistance of 10 ⁶ Ω when a voltage of 500 V is applied to the shaft and the roller surface is used as 4.
The transfer brush 44 (4 in FIG. 1A) is
4a, 44b, 44c and 44d) as a positive voltage having the same polarity as the voltage Vt applied, for example, +2.0
A voltage of KV is applied from the bias power supply 206. Thus, the sheet P can be positively electrostatically attracted to the transfer belt 43. Then, the sheet P can be transported without causing a positional shift to a black print transfer portion located downstream of the relatively long transport path.

Here, the reason why the polarity of the bias voltage applied to the pressing roller 54 is the same as the polarity of the voltage applied to the transfer brush 44 will be described. The leading end of the sheet P is positioned at the first transfer position (the photosensitive drum 41a and the transfer brush 44).
(point opposite to a), when the paper P is sandwiched between the pressing roller 54 and the driven rotary roller 46, the paper P has a sufficiently large resistance in a normal environment or a low humidity environment. . However, when the humidity is high, the resistance decreases due to moisture absorption. Therefore, when the applied electric field increases, current flows. Therefore, the pressing roller 5
If the bias voltage applied to the transfer brush 4 is a voltage having a polarity opposite to that of the transfer brush 44, the absolute value of the potential difference from the transfer position to the suction position by the pressing roller is the sum of the absolute values of the respective applied voltages. As a result, the current flowing to the transfer brush 44 by the transfer power supply flows to the bias power supply side through the paper P, and an electric field required for transfer is not formed. Therefore, the toner image formed on the photosensitive drum is not formed. Cannot be transferred to paper.

In order to prevent this, in this embodiment, the bias voltage applied to the pressing roller 54 has the same polarity as the transfer voltage applied to the transfer brush 44. More preferably, the bias voltage is the voltage Vt of the transfer power supply.
When the voltage is substantially the same as that described above, no potential difference occurs, and therefore, no current leakage or leakage occurs. Therefore, as described above, sufficient transfer can be obtained by suction conveyance without causing a shift in the conveyance posture of the sheet.

As described above, the transfer and transfer belt has 10 ¹¹ to 1
In addition to having a volume specific resistance of 0 ¹⁴ Ω · cm, as a transfer material (paper) suction means, a grounded conductive roller (drive rotating roller) and a voltage-applied conductive roller (pressing roller) are used. By using a pair of rollers and applying a voltage of the same polarity as the transfer brush to the transfer material suction surface side of the transfer belt, the transfer material suction transfer can be realized with a small power supply and a simple configuration. Further, there is no generation of ozone, and sufficient transfer can be obtained even when the environment changes from drying to high humidity.

In the full-color printing, as described above, it is not necessary to particularly assist the suction, and as shown in FIG.
A switch 207 is provided between the bias power supply 20 and the input terminal of the switch 207 as shown by a double-headed arrow Q in the figure.
The switch 207 is switched to ground for full-color printing, and is switched to the bias power source 206 only for black printing.
In this way, unlike a configuration in which a bias voltage is constantly applied, a power-saving type transport mechanism that always performs stable paper suction without increasing the load on the power supply can be constructed.

[0071]

As described above, according to the present invention,
Since the angle formed by the press roller with respect to the transfer belt is set so that the paper cuts into the belt, the paper is always transported along the transfer belt in both black printing and full-color printing. The posture is always stable, and a good image can be obtained. In addition, the frequency of occurrence of problems such as paper jams is reduced, and the work efficiency of image formation is improved.
In addition, the transfer belt has a volume resistivity of 10 ¹¹ to 10 ¹⁴ Ω · cm and a voltage of the same polarity as that of the transfer brush is applied to the sheet suction at the sheet loading section. As a result, the transfer is facilitated with a small current, so that it is possible to realize a compact recording apparatus suitable for environmental protection without ozone generation.

[Brief description of the drawings]

FIG. 1A is a side view of a main part (image forming unit) of an image forming apparatus according to an embodiment, in which full-color printing (recording) is performed, and FIG. FIG.

FIG. 2 is a side sectional view of an image forming apparatus (tandem type color image forming apparatus) including the image forming unit of FIG. 1 therein.

FIG. 3 is an enlarged view of the image forming unit shown in FIG. 2;

FIGS. 4A and 4B are diagrams showing a state in which the image forming unit shown in FIG. 1 performs black printing.

5 is a diagram illustrating an example of a further configuration of a sheet carry-in unit that positively electrostatically attracts a sheet in the image forming unit in FIG. 1;

6A is an external perspective view showing an example of a tandem type color image forming apparatus, and FIG. 6B is a side sectional view thereof.

7A and 7B are diagrams schematically showing a configuration of a conventional tandem type image forming unit.

FIGS. 8A and 8B are diagrams schematically showing a configuration of a pressing roller of a conventional tandem type image forming unit.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Tandem-type color image forming apparatus 2 Opening / closing tray 2b Auxiliary tray 3 Paper cassette 4 Top lid 5 Discharge tray 6 Upper discharge port 7 Power switch 8 Liquid crystal display 9 Input key P Paper 11 Paper feed roller 12 Paper feed roller 13 Standby roll Pair 14 Conveyor belt 15a, 15b Rotary roller 16 (16-1, 16-2, 16-3, 16-4) Developing unit 17 Photoconductor drum 18 Fixing device 19 Discharge roller 21 Rear discharge port 22 Discharge roller 23 , 24 rotating roller 25 urging roller 26 transport belt 27a, 27b, 27c, 27d photoreceptor drum 28 container 29 paper feed roller 31 standby roll pair 32 paper press roller 33a, 33b, 33c, 33d corona charger 34 fixing unit 35 roller Connecting the center of the roller 36 horizontal line 37 bias power supply 38 connecting the center of the roller Line perpendicular to the line 39 Paper direction 41a, 41b, 41c, 42 Photoconductor drum (image carrier) 43 Conveyance transfer belt 43 'Paper introduction part of conveyance transfer belt 44 (44a, 44b, 44c, 44d) Transfer brush 45 ( 45a, 45b, 45c, 45d) Static elimination brush 46 Driving rotating roller (first rotating roller) 47 Driving rotating roller (second rotating roller) 48 Tension roller 49 Key-shaped arm 51 Support point 52 Frame of main body device 53 Pulling spring 54 holding roller 55 movable arm (oscillating member) 56 fixed support roller 57 movable support roller 58 center line of roller 59 support shaft 61 cam engaging portion 62 fulcrum 63 cam 70 image forming apparatus 72 opening and closing tray 73 paper cassette 74 top cover 75 discharge Paper tray 76 Upper discharge port 77 (77a, 77b, 77c, 77d) Image forming unit 81 Standby roll pair 82 Paper detection sensor 83 Paper feed roller 84 Separation member 85 Transport path 86 Paper feed roller 87 Fixer 88 Paper discharge roller 89 Switching lever 91 Discharge path 92 Rear discharge port 93 Paper discharge roll pair 94 Cleaner Bottle 95 Blade scraper 101 Cleaner 102 Charger 103 Developing device 103 Developing device 104 Developing roller 105 Toner 106 Toner stirring member 107 Supply roller 108 Doctor blade 109 Exposure head 203 Protective lid 205 Separating claw 206 Bias power supply 207 Switch

Continuation of front page (72) Inventor Tetsuya Abe 2-229 Sakuragaoka, Higashiyamato-shi, Tokyo Casio Electronics Co., Ltd. (56) References JP-A-8-328395 (JP, A) (58) Fields investigated ( Int.Cl. ⁷ , DB name) G03G 15/16 G03G 15/01 114

Claims (11)

(57) [Claims] 1. A plurality of image carriers arranged in parallel, a plurality of toner image forming means for individually forming toner images of a predetermined color on the plurality of image carriers, and a transfer material adsorbed on an outer peripheral surface. A transport belt that circulates to contact the transfer material with at least one image carrier of the plurality of image carriers, and a transfer unit inside the transport belt corresponding to the plurality of image carriers. A plurality of transfer means arranged to apply a transfer bias voltage having a predetermined polarity to transfer a toner image to a transfer material being in contact with the image carrier; First and second rotating rollers disposed outside the transfer section and around which the transfer belt is stretched, and the transfer material disposed to press the first rotation roller via the transfer belt to transfer the transfer material The transfer material is held between the belt and the transfer belt. An image forming apparatus comprising: a suction assisting roller for assisting suction on a belt; wherein the suction assisting roller includes a line connecting a center of the suction assisting roller and a center of the first rotating roller; The crossing angle of a line from the contact portion with the conveyor belt toward the second rotating roller is 90 degrees.
An image forming apparatus, wherein the first rotating roller is pressed via the transport belt so as to form an angle smaller than゜. 2. The image forming apparatus according to claim 1, further comprising an attraction bias voltage applying unit that applies an attraction bias voltage to the attraction assist roller. 3. The image forming apparatus according to claim 2, wherein the attraction bias voltage applying unit applies a voltage having the same polarity as the transfer bias voltage to the attraction assist roller. 4. A toner image forming unit corresponding to an image carrier closest to the second rotating roller forms a black toner image on the image carrier, and a toner image forming unit corresponding to another image carrier is 4. The image forming apparatus according to claim 1, wherein a chromatic toner image is formed. 5. The first and second rotating rollers are configured to transfer a toner image to the transfer material while the transfer material is conveyed from the first rotating roller to the second rotating roller. Rotating the conveyor belt to move it.
The image forming apparatus according to 1, 2, 3, or 4 . 6. A plurality of image carriers which are arranged in parallel, and said plurality of image carriers are provided.
A plurality of individual toner images each having a predetermined color formed on an image carrier
The toner image forming means, and adsorbing the transfer material
Transferring to at least one image carrier of a plurality of image carriers
A conveyor belt circulating to contact the material,
A transfer unit corresponding to the plurality of image carriers inside the belt
The transfer material that is provided to constitute the
-A transfer bias voltage of a predetermined polarity is applied to transfer the image.
A plurality of transfer means to be added, and a method of juxtaposing the plurality of transfer portions
The transfer belt disposed outside the transfer portion at both ends
First and second rotating rollers on which
To constantly press the first rotating roller via a belt
When the transfer material is disposed and nipped and transported by the transport belt,
In particular, a suction aid for assisting suction of the transfer material onto the transport belt.
In the image forming apparatus provided with an auxiliary roller, the transfer belt is held at a transferable position so that the transfer material always comes into contact with the image carrier closest to the second rotating roller in the same posture, and the other image forming device is used for other images. A belt moving means for moving the conveyor belt to a transferable position or a non-transferable position separated from the image carrier so that the transfer material is not in contact with the carrier; and selectively moving the belt moving means. and a control means for controlling the said suction auxiliary roller, the transfer from the contact portion of the line connecting the centers of the first rotation roller of the adsorber auxiliary rollers, and the conveyor belt of the suction auxiliary roller the intersection angle between the line belt toward the second rotating roller direction, wherein
As an angle not exceeding regardless 90 ° to the movement control of the belt moving means by the control means, and sets the movement range of the belt moving means together when pressing the first rotating roller via the conveying belt Image characterized by the following:
Forming equipment . 7. A suction bias voltage is applied to said suction assist roller.
A suction bias voltage applying means for applying pressure.
7. The image forming apparatus according to claim 6, wherein: 8. The attraction bias voltage applying means,
A voltage having the same polarity as the transfer bias voltage is applied to the suction assist roller.
8. The image forming apparatus according to claim 7, wherein the voltage is applied to the image forming apparatus.
Place. 9. The attraction bias voltage applying means shifts the application of the attraction bias voltage to the attraction auxiliary roller to the transfer impossible position of the belt moving means by the control means.
9. The image forming apparatus according to claim 7, wherein the control is performed in accordance with dynamic control . 10. An image bearing closest to said second rotating roller.
The toner image forming means corresponding to the body has a black color on the image carrier.
Forms a toner image and forms a toner image corresponding to another image carrier
Forming means for forming a chromatic toner image;
10. The image forming apparatus according to claim 6, 7, 8, or 9. 11. The apparatus according to claim 11, wherein said first and second rotating rollers are
The recording material is moved from the first rotating roller side to the second rotating row.
The toner image is transferred to the transfer material
Rotating to move the conveyor belt so that
Item 13. The image forming apparatus according to Item 6, 7, 8, 9 or 10.