JPH11272025A - Image forming device - Google Patents

Abstract

(57) Abstract: In a tandem image forming apparatus having a plurality of image carriers and a sheet conveying belt arranged side by side, a multi-color image and a single-color image are formed without depending on the accuracy of control means such as a cam. Then, the position of the conveyor belt is switched to realize stable paper conveyance. In an image forming apparatus according to the present invention, a sheet transport belt (3) swings about a support shaft (8) located near a first rotary roller (5) as a rotation center, and contacts a first image carrier (1a-1d). Paper transport belt moving means 7, 8, 20 capable of positioning and holding at a paper transport position and a second paper transport position contacting only image carrier 1d closest to first rotating roller 5; Positioning means 11 for extending and positioning the paper transport belt at the first paper transport position;
And a control means (cam) 16 that swings to the paper transport position.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus capable of performing color printing, such as a color copying machine and a color printer, and more particularly, to a single-color and multi-color printing method in a single transport mode. The present invention relates to a tandem-type image forming apparatus that switches according to a road.

[0002]

2. Description of the Related Art In recent years, there has been an increasing demand for multicolor printing output in image forming apparatuses such as copying apparatuses and printers.
At the same time, higher speed is also required. In this case, a tandem type color image forming apparatus having multiple image forming units arranged side by side is required. However, it is not decided that multi-color printing is always performed, and generally, the frequency of printing in black is much higher. When printing in black is performed in a tandem type, the cost per sheet (running cost) is extremely high compared to an image forming apparatus dedicated to black. that is,
This is because the life of the image forming unit of the color not used is counted similarly to the image forming unit for black since the image forming unit is used in the same manner as in the multicolor printing.

[0003] In order to solve this problem, when printing in black is performed, the sheet conveying surface of the sheet conveying belt is partially separated from the image forming units other than black, and the image forming units for colors other than black are separated. There has been proposed a tandem type image forming apparatus which is not used (for example, Japanese Patent Application Laid-Open
146383, JP-A-9-146328).

Here, an example of a tandem-type image forming apparatus that switches between two types of printing methods, that is, a single-color printing mode and a multi-color printing mode by a single transport path will be described. FIGS. 4A and 4B are cross-sectional views showing a schematic configuration of an image forming section of a tandem type image forming apparatus, and FIG. 4A shows a state in which full-color printing is performed. ) Shows the state when black printing is performed.

As shown in FIGS. 4 (a) and 4 (b), the image forming section comprises four photosensitive drums (image carriers) 41a, 41b, 41
c, 42, and these photosensitive drums 41a,
Each of 41b, 41c, and 42 individually carries a predetermined color toner image. Further, these photoconductor drums 41a,
Opposite to 41b, 41c, and 42, there is provided a conveyor belt 43 that circulates and moves in a direction in which the photosensitive drums 41a, 41b, 41c, and 42 are arranged in parallel as indicated by an arrow H in the drawing. The transport belt 43 is made of an insulating material such as PET,
The photosensitive drum 41 is arranged in a flat loop shape in the horizontal direction and adsorbs paper (transfer material) on the outer peripheral surface of the upper circulating portion.
a, 41b, 41c, and 42, or circulates to bring the paper into contact with at least one of the photosensitive drums 42 or the other photosensitive drums 41a, 41b, and 41c.

A transfer brush 44 (44a, 44b, 4) for forming a transfer section corresponding to the four photosensitive drums 41a, 41b, 41c, 42 is provided inside the transport belt 43.
4c, 44d) are juxtaposed. The transfer brush 44 (transfer unit) applies a positive polarity charge to the transport belt 43,
Due to this electric field, each of the photosensitive drums 41a, 41b, 41
c, the toner image on the photosensitive drum is transferred to the sheet in contact with 42. On the downstream side in the vicinity of the transfer brush 44, a neutralization brush 45 (45a, 45b, 45c, 45d) is provided. The charge removing brush 45 removes the charge applied to the transport 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.

At both ends of the transfer section in the juxtaposition direction, outside the transfer sections, the flat ends of the transfer belt 43 are stretched, and a driving rotary roller 46 for driving the transfer belt 43 is provided downstream in the transfer direction. The driven rotary roller 47 is disposed on the upstream side in the transport direction. The driven rotation roller 47 is formed of a metal roller. The driving rotary roller 46 and the driven rotary roller 47
Are fixed to the frame 52 of the apparatus main body by support shafts 46-1 and 47-1 (roller support means), respectively. The driving rotation roller 46 and the driven rotation roller 47 rotate in the counterclockwise direction in the drawing, respectively. As a result, the transport belt 43 is circulated so that the toner image is transferred onto the paper while the paper P (transfer material) is transported from the driven rotary roller 47 side to the drive rotary roller 46 side.

The tension roller 48 contacts the inner peripheral side of the lower circulating portion of the conveyor belt 43, and the driving roller 4
It is arranged close to 6. The tension roller 48 is rotatably provided at the tip of a key-shaped arm 49.
Reference numeral 9 denotes a rear end rotatably supported by a frame 52 of the apparatus main body by a fulcrum 51. A tension spring 53 is engaged between the center of the arm 49 and the frame 52 of the apparatus main body, and the tension spring 53 urges the arm 49 downward in the figure. As a result, the tension roller 48 urges and supports the lower circulating portion of the conveyor belt 43 so as to always pull it downward (to push it outward). by this,
The deflection of the transport belt 43 is absorbed, and the entire transport belt 43 is driven by a driven rotary roller 47 and a drive rotary roller 46 with a predetermined tension.
It is stretched between. A movable arm 55 is disposed between the upper circulation part and the lower circulation part of the conveyor belt 43 and extends in parallel with the conveyance direction. The 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 is provided near the driven rotation roller 47 of the transfer brush 44 d closest to the drive rotation roller 46. The fixed support roller 56 comes into contact with the inner peripheral surface of the transport belt 43 so that the photosensitive drum 42 closest to the driving rotary roller 46 always contacts the transport belt 43, and thereby the sheet is applied to the photosensitive drum 42. The transfer belt 43 is held at a transferable position so that the transfer belt 43 is always brought into contact with the same posture. The movable arm 55 is provided with the above-described movable support roller 57 on its free end side. The movable support roller 57 is located at a position between the transfer brush 44 a closest to the driven rotary roller 47 and the driven rotary roller 47. The transport belt 43 is supported in contact with the inner peripheral surface of the transport belt 43.

The movable arm 55 pivots (oscillates) in the vertical direction (the direction crossing the surface of the conveyor belt 43) as shown by a double-headed arrow J in FIG. Move), and move the transport belt 43 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. In addition, the movable arm 55 includes
Transfer brush 44d among the four transfer brushes 44 described above
The other three transfer brushes 44a, 44b, 44c except for
Are attached integrally, and move by the same distance in the same direction in accordance with the movement of the transport belt 43 as the movable arm 55 swings.

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 contacts 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.

FIG. The state where the cam 63 is rotated 90 degrees in the counterclockwise direction is shown. At this time, the cam 63
Is located farthest from the fulcrum 62, and the movable arm 55 is pushed upward by the cam 63, turns upward, and is located at the upper position. As a result, the movable arm 55 is controlled by the cam 63 to move via the movable support roller 57 to the photosensitive drums 41 a and 41 a, other than the photosensitive drum 42, which are always in the transferable position.
The transfer belt 43 is moved to a transferable position with respect to 41b and 41c. FIG. 6B shows a state in which the cam 63 has been rotated 90 degrees clockwise from the position shown in FIG. 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 43 to a transfer-impossible position with respect to the other photosensitive drums 41a, 41b, and 41c except for the photosensitive drum 42 by the movement control by the cam 63.

In any of the above movements, the position of the driven rotary roller 47 does not move. Further, a pressing roller 54 that opposes the driven rotating roller 47 and presses the driven rotating roller 47 is provided.
Is formed of a conductive rubber roller, and a bias voltage (not shown) is applied thereto. The holding roller 54 holds the sheet with the conveyance belt 43 and conveys the sheet while assisting the adsorption of the sheet to the conveyance belt 43. The driven rotation roller 47 and the pressing roller 54 form a paper carry-in port to the image forming section.

FIG. 5 is a side sectional view showing a schematic configuration of an image forming apparatus (tandem type color image forming apparatus) having the image forming section shown in FIG. 4 therein. This image forming apparatus 70
Has an opening / closing tray 72 on the front surface (right side in the figure) of the apparatus and a detachable paper cassette 73 at the bottom. Also,
A paper discharge tray 75 is formed on an upper surface of the upper cover 74 of the apparatus, and sheets on which images formed on the paper discharged from an upper paper discharge port 76 are stacked. 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.

The inside of the image forming apparatus is substantially in the center of the image forming section, that is, the four photosensitive drums 41a and 41a.
1b, 41c, 42, and a conveying belt 43 facing the same,
The photoreceptor drum 4 is held by the driving rotary roller 46, the driven rotary roller 47,
The transfer brush 44 and the movable arm 55 whose front portion swings up and down by a cam 63 are disposed opposite to the transfer brushes 1a, 41b, 41c and 42. The four photoconductor drums 41a, 41b, 41c, 42 are wrapped around the four image forming units 77a, 77b, 77, respectively.
c, 77d Various devices (charging device, exposure head, developing device,
Cleaner, etc.).

A pair of standby rolls 81 and a paper detection sensor 82 are disposed on the upstream side (right side in the drawing) of the image forming section in the paper conveyance direction. Is a sheet feed roller 83, a separating member 84, and the above-described opening / closing tray 7
2 are provided. Further, a conveyance path 85 formed of two guide plates is provided below, and the paper cassette 73 stores a large number of papers P and looks up at the paper feed end upstream thereof. . A paper feed roller 86 is disposed above the paper feed end. Then, downstream of the image forming section in the sheet conveying direction, a fixing device 87, a sheet discharging roller 88, a switching lever 8
9 are provided. The fixing device 87 includes a pressure contact roller, a heating roller, a peripheral cleaning device, an oil application roller, a thermistor, and the like, which are assembled in a heat-insulating housing, and thermally fixes the toner image transferred onto the paper to the paper surface. . The switching lever 89 guides the sheet to the upper discharge path 91 when it is at the lower position as shown in the figure, and moves the sheet to the discharge port 92 that opens to the rear surface of the apparatus when it is rotated upward. invite. The downstream side of the discharge path 91 communicates with the upper discharge port 76 via a discharge roll pair 93.

[0017]

An example of a conventional tandem type color image forming apparatus has been described above. However, in the above-mentioned prior art, a cam 63 is used as a movement control means for the conveyor belt 43 as shown in FIG. ing. Then, the cam engaging portion 61
When the contact point is located farthest from the fulcrum 62, the transport belt 43 for multicolor printing is pushed up by the cam 63 and rotates upward, and is localized at the upper position as shown in FIG. . Further, when the cam 63 rotates 90 degrees from the above position and the contact point of the cam engaging portion 61 becomes a point closest to the fulcrum 62, the transport belt 43 rotates downward and as shown in FIG. Is located in the lower position.

However, in the above configuration, the cam 63
The position of the conveyor belt 43 is determined by the positional accuracy of the photosensitive drums 41a, 41a, 4b.
1b and 41c, the conveying belt 4
3 must be cut into the photosensitive drums 41a, 41b, and 41c more than necessary, and it is difficult to stably convey the paper. When a plurality of cams 63 exist in the axial direction,
If an error occurs in the outer shape accuracy and position accuracy of each cam 63,
The conveyance belt 43 is not kept parallel, causing a problem such as a deviation of the belt, which greatly affects the service life.

The life of the conveyor belt 43 is shorter than that of the machine main body, and the conveyor belt 43 needs to be replaced at least several times.
In the case of an inexpensive machine, it is necessary for the user to replace the machine, and therefore, the transport belt 43 needs to be configured to be replaceable.

However, when the user sets the detachable transport belt 43 at a predetermined position in the machine body, the cam 63
5 is a position where the transport belt 43 is pushed upward as shown in FIG. 5, there is a problem that operability is hindered because a large resistance force is received from the cam 63.

The present invention has been made in view of the above circumstances, and does not depend on the accuracy of a control means such as a cam for controlling the movement of the sheet conveying belt, and determines the position of the conveying belt between the multi-color and black-only modes. It is a first object of the present invention to provide a tandem-type image forming apparatus capable of performing switching, realizing stable paper conveyance, and ensuring a long service life without causing adverse effects such as belt deviation. Also,
It is a second object of the present invention to provide an image forming apparatus with good operability when attaching and detaching a conveyor belt.

[0022]

In order to achieve the above object, according to the first aspect of the present invention, a plurality of image carriers arranged side by side and a predetermined color toner are individually placed on the plurality of image carriers. A plurality of toner image forming means for forming, a paper transport belt circulating to adsorb a transfer material on an outer peripheral surface and bring the transfer material into contact with at least one of the plurality of image carriers, and the paper A plurality of transfer units disposed inside the conveyor belt to form a transfer unit corresponding to the plurality of image carriers, and a plurality of transfer units configured to transfer a toner image to the transfer material being in contact with the image carriers; In the image forming apparatus provided with first and second rotating rollers which are disposed outside the transfer units at both ends in the juxtaposition direction of the transfer unit and are wound around the paper transfer belt, the paper transfer belt is A spindle located near the first rotating roller A sheet transporter that swings as a center of rotation and can be positioned and held between a first sheet transport position that contacts each of the image carriers and a second sheet transport position that contacts only the image carrier closest to the first rotating roller. Belt moving means, positioning means for extending and positioning the paper transport belt moving means to the first paper transport position, and pressing the paper transport belt moving means to the second paper transport position by contacting and pressing the positioning means. And a control means for swinging.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the image forming apparatus further includes a detachable sheet conveying belt moving unit, and after the image forming operation is completed, the control unit controls the sheet conveying belt. The moving means is controlled so as to be positioned at the first sheet transport position.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration, operation and operation of the present invention will be described below in detail with reference to the illustrated embodiment. FIG.
1A and 1B are cross-sectional views illustrating a schematic configuration of an image forming unit of a tandem-type image forming apparatus according to the present invention, and FIG. 1A illustrates a state where full-color printing is performed; (B) shows a state when black printing is performed. still,
The overall configuration of the image forming apparatus is substantially the same as that of the image forming apparatus shown in FIG. 5, and a toner image forming means disposed around each photoreceptor serving as an image carrier, and paper (transfer material) feeding And a paper discharge unit, a fixing device, and the like, but these are not shown.

As shown in FIGS. 1A and 1B, the image forming section includes four photosensitive drums 1a, 1b, 1c and 1d, which are image carriers, arranged in series and in multiple stages. ing. Although not shown, these photosensitive drums 1
A, 1b, 1c, and 1d are provided around the photosensitive drum, respectively, to uniformly charge the surface of the photosensitive drum, and the charged photosensitive drum surface is subjected to optical writing by laser light, LED light, or the like to form an electrostatic latent image. And a toner image forming means including a developing device for developing an electrostatic latent image formed on the photosensitive drum with toner of each color and visualizing the electrostatic latent image formed on the photosensitive drum. Toner image (for example, yellow (Y),
Magenta (M), cyan (C), and black (K) toner images. Further, these photosensitive drums 1a,
1b, 1c and 1d, these photosensitive drums 1
A paper transport belt 3 that circulates and moves in the direction indicated by the arrow A in the drawings a, 1b, 1c, and 1d is provided. The paper transport belt 3 is made of an insulating or high-resistance material, and is arranged in a flat loop shape in the horizontal direction. The paper circulates to contact at least one photosensitive drum of the drums 1a, 1b, 1c, 1d.

Inside the paper transport belt 3, the above-mentioned 4
Transfer brushes (transfer means) 9a, 9b, 9 for forming transfer portions corresponding to the individual photosensitive drums 1a, 1b, 1c, 1d
c, 9d are arranged side by side, and these transfer brushes 9a, 9b,
9c and 9d apply transfer charges to the sheet transport belt 3, and the electric field causes the respective photosensitive drums 1a, 1b, 1
The toner image on the photosensitive drum is transferred to the paper in contact with c and 1d. Each of the transfer brushes 9a, 9b, 9c,
A configuration may be adopted in which a neutralization brush or the like is disposed near the downstream side of the paper transporting direction 9d to remove the charge applied to the paper transport belt 3 at each transfer unit. The photosensitive drums 1a, 1b, 1c, and 1d after the transfer are configured to remove residual toner and the like by a cleaner (not shown).

At both ends of the transfer section in the juxtaposition direction outside the transfer sections, the flat ends of the sheet transfer belt 3 are stretched over the both ends, and a driving rotary roller 5 (the first rotation roller 5) for driving the sheet transfer belt 3 is provided. One rotating roller) is disposed on the downstream side in the transport direction (left side in the drawing), and the driven rotary roller 4 (second rotary roller) is disposed on the upstream side in the transport direction. Also,
The support shaft 5a of the drive rotation roller 5 is supported on both side surfaces (not shown) of the transfer case 2 and is connected to drive means such as a motor via a drive mechanism such as a gear. On the other hand, a support shaft 4a of the driven rotary roller 4 is supported so as to be movable in the horizontal direction with respect to both side surfaces (not shown) of the transfer case 2 and a pressing spring 6a.
The paper transport belt 3 is stretched between the driving rotary roller 5 and the driven rotary roller 4 with a predetermined tension. And the driving roller 5
Is rotated in the counterclockwise direction in the figure, the paper transport belt 3 is circulated, and the paper fed from the paper feed unit (not shown) to the driven rotary roller 4 side is transported to the drive rotary roller 5 side. , Each photosensitive drum 1a, 1b, 1c, 1d
The toner image is transferred onto the sheet from (or the most downstream photosensitive drum 1d).

A movable arm 7 is disposed on the inner peripheral side of the paper transport belt 3, and the movable arm 7 has a movable support roller 20 on its free end side. At a position between the transfer brush 9 a closest to the rotating roller 4 and the driven rotating roller 4, the sheet abuts on the inner peripheral surface of the sheet carrying belt 3 to support the sheet carrying belt 3. The movable arm 7 is provided with the driving rotary roller 5.
(The first rotating roller) is rotated (swinged) up and down about the support shaft 8 located near the (first rotating roller), and
The upper circulating section of the sheet conveying belt 3 is moved through the position 0.
That is, the movable arm 7, the fixed support shaft 8, and the movable support roller 20 constitute a paper transport belt moving unit, and the upper circulation portion of the paper transport belt 3 has the support shaft 8 of the movable arm 7 as the rotation center. Each of the photosensitive drums 1 is moved upward through the movable support roller 20 by the upward swing.
a, 1b, 1c, 1d, a first paper transport position that contacts
The upper circulating portion of the paper transport belt 3 is supported by the support shaft 8 of the movable arm 7.
Is moved downward via the movable support roller 20 by the downward swing about the rotation center, and the driving rotary roller 5 (first
(The rotating roller) is located at the second sheet transport position in contact with only the photosensitive drum 1d closest to the photosensitive drum 1d.

Further, the four transfer brushes 9a, 9b, 9c and 9d are integrally attached to the movable arm 7, and correspond to the paper transport belt 3 which moves with the swing of the movable arm 7. They move in the same direction by approximately the same distance. However,
The transfer brush 9d, which is the most downstream in the paper transport direction, hardly moves because it is located near the support shaft 8 of the movable arm 7, and the contact with the paper transport belt 3 is maintained at all times, but the other transfer brushes 9a, 9b , 9c are in contact with the paper transport belt 3 at the first paper transport position in FIG. 1A, and are out of contact with the paper transport belt 3 at the second paper transport position in FIG. 1B.

(Embodiment 1) A cam engaging member 11 that rotates about a support shaft 12 is attached to both sides of the transfer case 2 on which the paper transport belt 3 is mounted.
One end 13 of the cam engaging member 11 is engaged with an elongated hole 10 opened on a side surface of the movable arm 7. The other end 14 of the cam engaging member 11 slidably abuts a cam 16 which is supported by a frame (not shown) on the apparatus main body side via a support shaft 17 and which is rotated by a driving means (not shown). It has become. Note that a part of the cam engaging member 11 and the transfer case 2 are connected to a spring 15
And acts to move the swing end side of the movable arm 7 upward. Further, the cam 16 rotates about the support shaft 17, contacts the cam engaging member 11, and presses, thereby selectively controlling the movement of the movable arm 7 via the cam engaging member 11, and Second of arm 7
It functions as a control unit that performs positioning to the paper transport position.

Here, in FIG. 1A, a point 16a closest to the support shaft 17 of the cam 16 faces the cam engaging member 11, and the cam 16 is not in contact with the cam engaging member 11. Is shown. In this case, the spring 15 pivotally moves the movable arm 7 via the cam engaging member 11 in the upward direction. FIG. 2 shows an exploded view of a main part of the paper conveying belt moving means. As shown in FIG. 2, the transfer case 2 is provided with a hole 19 for regulating the rotation range of the cam engaging member 11. A positioning projection 13a provided at one end 13 of the cam engaging member 11 abuts on an upper portion 19a of a hole 19 provided in the transfer case 2, and the movable arm 7
The upward position of is restricted. That is, the cam engaging member 11 has a function as a positioning means, and thus, via the movable support roller 20 of the movable arm 7, the photosensitive drum 1a other than the photosensitive drum 1d which is always in the transferable position. , 1b, 1c, the paper transport belt 3 and the transfer brushes 9a, 9b, 9c are moved to the transferable position and positioned at the first paper transport position.

In FIG. 1B, the support shaft 1 of the cam 16 is shown.
The point 16b farthest from 7 faces the cam engaging member 11 side, and shows a state in which the cam 16 is in contact with the cam engaging member 11 and pressurized. In this case, since the cam engaging member 11 is rotated counterclockwise by the pressure of the cam 16, the swinging end of the movable arm 7 is rotated (swinged) downward to move the movable support roller 20 to the paper. It is moved in a direction away from the conveyor belt 3. The movable support roller 20 of the movable arm 7
Is moved to a position where it does not contact the conveyor belt 3,
The paper transport belt 3 and the transfer brushes 9a, 9b, 9c are moved to the non-transferable positions with respect to the other photosensitive drums 1a, 1b, 1c except for the photosensitive drum 1d on the support shaft 8 side of the movable arm 7. , At the second sheet transport position.

In the present invention, the position of the cam 16 is such that the photosensitive drums 1a, 1b, 1c, 1
Although arranged on the side opposite to d, the same effect can be expected when it is arranged in the same direction as the photosensitive drum.
When the cam is disposed in the same direction as the photoconductor drum, the cam is the end 1 of the cam engaging member 11 on the opposite side to FIG.
Contact 3

(Embodiment 2) In the image forming apparatus having the structure shown in FIG. 1, after the image forming operation is completed, the cam 16 is rotated to the state shown in FIG.
Is controlled so as not to be in contact with the cam engaging member 11, the swinging end of the movable arm 7 moves upward, and the paper transport belt 3 is positioned at the above-described first paper transport position. The paper transport belt 3 and the paper transport belt moving means move the transfer case 2 together with the arrow 18 as shown in FIG.
In this direction. In this case, since the cam 16 pivotally supported on the apparatus main body side does not contact the cam contact member 11, the transfer case 2 can be smoothly attached to and detached from the apparatus main body. And operability during maintenance are improved.

[0035]

As described above, in the image forming apparatus according to the first aspect, the sheet conveying belt is preliminarily stretched and positioned at the first sheet conveying position in contact with each photoconductor (image carrier) by the positioning means. A mechanism that uses control means such as a cam that presses against the positioning means only when the paper conveyance belt is positioned at the second paper conveyance position that contacts only the photoconductor on the downstream side in the paper conveyance direction. By
The belt position can be switched between multi-color and black without depending on the accuracy of the control means such as cams, achieving stable paper conveyance and long life without any adverse effects such as deviation of the paper conveyance belt. Image forming apparatus capable of ensuring image quality can be provided.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the image forming apparatus further includes a detachable sheet conveying belt moving unit, and after the image forming operation is completed, the control unit controls the sheet forming unit. Since the transport belt moving means is controlled to be positioned at the first paper transport position, when the paper transport belt moving means is positioned at the first paper transport position, the control means such as the cam is positioned by the positioning means. , The paper transport belt and the paper transport belt moving means can be easily attached and detached,
An image forming apparatus with good operability can be provided.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of the configuration of an image forming unit of a tandem-type image forming apparatus according to the present invention, in which (a) is a schematic cross-sectional view of the image forming unit showing a state when performing full-color printing; FIG. 3B is a schematic cross-sectional view of the image forming unit showing a state where black printing is performed.

FIG. 2 is an exploded perspective view of a main part of a configuration example of a sheet conveying belt moving unit in an exploded state.

FIG. 3 is an explanatory diagram of a method of attaching and detaching a transfer case including a sheet conveying belt moving unit.

4A and 4B are diagrams illustrating a configuration example of an image forming unit of a conventional tandem-type image forming apparatus, wherein FIG. 4A is a schematic cross-sectional view of the image forming unit illustrating a state where full-color printing is performed;
FIG. 3B is a schematic cross-sectional view of the image forming unit showing a state where black printing is performed.

FIG. 5 is a side sectional view illustrating a schematic configuration example of an image forming apparatus including the image forming unit illustrated in FIG. 4 therein.

[Explanation of symbols]

 1a, 1b, 1c, 1d: photosensitive drum (image carrier) 2: transfer case 3: paper transport belt 4: driven rotary roller (second rotary roller) 5: drive rotary roller (first rotary roller) 6 : Pressing spring 7: Movable arm (paper transport belt moving means) 8: Support shaft of movable arm 9a, 9b, 9c, 9d: Transfer brush (transfer means) 10: Slot 11: Cam engaging member (positioning means) 12: Support shaft of the cam engaging member 15: Spring 16: Cam (control means) 17: Support shaft of the cam 18: Direction of attaching / detaching the transfer case 19: Hole for regulating the rotation range of the cam engaging member 20: Movable support roller

Claims (2)

[Claims] A plurality of image carriers arranged side by side; a plurality of toner image forming means for individually forming a predetermined color toner on the plurality of image carriers; and a transfer material adsorbed on an outer peripheral surface. A paper transport belt circulating to contact the transfer material with at least one image carrier of the plurality of image carriers, and a transfer unit inside the paper transport belt corresponding to the plurality of image carriers. A plurality of transfer means for transferring a toner image to the transfer material in contact with the image carrier; and a plurality of transfer units provided outside the transfer units at both ends in the direction in which the plurality of transfer units are arranged in parallel. A first and a second around which the paper transport belt is stretched
An image forming apparatus including a first roller and a second roller, wherein the sheet transport belt swings around a support shaft located near the first rotary roller as a center of rotation, and a first sheet transport position in contact with each of the image carriers. Paper transport belt moving means capable of being positioned and held at a second paper transport position contacting only the image carrier closest to the first rotating roller; and stretching the paper transport belt movable means to the first paper transport position. An image forming apparatus comprising: a positioning unit that performs additional positioning; and a control unit that swings the paper transport belt moving unit to a second paper transport position by applying pressure while contacting the positioning unit. 2. The image forming apparatus according to claim 1, further comprising: a detachable paper transport belt moving means, wherein after the image forming operation is completed, said control means causes said paper transport belt moving means to move to said first position. An image forming apparatus controlled to be positioned at a sheet transport position.