JP2001100541A - Tandem color image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tandem color image forming device capable of being miniaturized, preventing the floating of paper, easily separating the paper from a carrying belt and reducing the distortion of the carrying belt caused by a creep phenomenon. SOLUTION: Both ends of the carrying belt 57 are supported by an upstream side rotating roller 58 and a downstream side rotating roller 59 functioning also as a transfer device and the depth thereof is small. Since the paper fed from a pair of standby rollers 71 is directly carried in the first transfer part consisting of a most upstream photoreceptor drum 62a and the roller 58, the floating of the paper before transfer is prevented. The paper is easily separated from the belt 57 by steep bend due to the large curvature of the roller 59 and the attracting force of the drum 62d at the rear end of the belt 57. As for the paper being carried in a fixing part 79 from the belt 57, the floating of the paper is prevented because a turning restraining member 86 is turned downward as necessary and the paper is pressed by a spur pulley at the edge of the member 86. Then, fixing heat is transmitted to the belt 57 through respective members 87, 88, 89 and 61 so as to remove the distortion.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic tandem type color image forming apparatus in which image forming units are arranged in a multistage manner.

[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 one page of paper, each of M (magenta: red dye) toner, C (cyan: greenish blue) toner, and Y (yellow: yellow) toner, which are three subtractive primary colors, and K dedicated to printing black parts and characters
Since printing (image formation) processing is individually performed for each toner in order to transfer a total of four types of toners (black) toner in a superimposed manner, the printing process is repeated four times for one page of paper. Therefore, it takes a long time for the printing process.

[0003] On the other hand, the tandem type has four steps in one process.
There are two types: a type in which the toner of the type is sequentially superimposed on the sheet, and a type in which the toner is sequentially superimposed on the intermediate transfer body, and then transferred once to the sheet. Each has almost four times the processing speed as compared with the single drum type. For this reason, in recent years, internal devices have been reduced in size and assembled into units (unitized).
As a result, various color image forming apparatuses having a tandem configuration have been put to practical use.

FIG. 5 is a side sectional view showing an example of such a tandem type color image forming apparatus. The tandem type color image forming apparatus 1 includes an upper cover 2 at an upper portion of the apparatus main body, and a paper cassette 3 detachable from the front (right side in the figure) at a lower portion. Placed and contained. Further, an openable / closable paper feed tray 4 is provided on the front surface. A power switch (not shown), a liquid crystal display device, a plurality of input keys, and the like are arranged on a front upper surface 5 of the apparatus main body, and the rear cover 2 is arranged substantially entirely behind the power switch. The upper cover 2 has an upper discharge tray 6 formed at the rear thereof together with the upper surface of the rear of the apparatus main body, and opens and closes vertically using a hinge (not shown) at the rear (left side in the figure) as a fulcrum.

[0005] Inside the main body of the apparatus, a conveyor belt 7 formed in a flat loop shape in the front and rear direction is arranged substantially at the center with the conveyance surface horizontal. The conveyor belt 7 includes a driving roller 8
, And is driven by the drive roller 8 to circulate in the counterclockwise direction in the figure. The four photosensitive drums 11 (1)
1a, 11b, 11c, 11d) are arranged. A peripheral surface of the photosensitive drum 11 is surrounded in a clockwise direction to surround a cleaner, an initialization charger, and an optical writing head 12 (hereinafter, referred to as an optical writing head).
Various devices such as a developing device 13, a developing roller 14, a transfer charging roller 15 and the like are provided, and various devices around the photoreceptor drum 11a are shown. I have.

[0006] In each of these image forming sections, the optical writing head 12 faces the photosensitive drum 11 and forms a recording section there. The developing device 13 includes magenta (M), cyan (C), and yellow (Y) in order from the developing device 13 on the upstream side (right side in the drawing) to the developing device 13 on the downstream side (left side in the drawing). And black (K) non-magnetic toner are accommodated therein, and the developing roller 14 is rotatably supported in the lower opening. The developing roller 14 is in pressure contact with the photosensitive drum 11 to form a developing section there. Also,
The transfer charging roller 15 is connected to a transfer power supply unit (not shown), and is in pressure contact with the lower surface of the photosensitive drum 11 via the conveyor belt 7, thereby forming a transfer unit.

At the upstream end of the transport belt 7 in the paper transport direction, an auxiliary suction roller 16 presses the driven roller 9 via the transport belt 7 to form a paper carry-in portion. The suction assist roller 16 is connected to a bias power supply (not shown) and supplies a positive polarity voltage to the conveyance belt 7 to assist the conveyance belt 7 to adsorb a sheet.

A standby roller pair 17 and a paper sensor 18 are disposed upstream of the paper carry-in section, and the upstream thereof is branched laterally and downwardly.
1, and the above-mentioned openable / closable paper feed tray 4 are provided. Further, a feed path 22 composed of two guide plates is formed below, and a pair of conveying rollers 23 is disposed at an upstream (lower) end of the feed path 22. positioned. Above the paper feed end of the paper feed cassette 3, a paper feed roller 24 having a half-moon cross section is disposed.

On the other hand, a paper separating claw 25 is disposed on the downstream side of the transport belt 7 in the paper transport direction in contact with the belt end, and a fixing unit 26 is disposed downstream thereof. Fixing unit 26
Is a fixing roller pair including a heat roller and a pressure roller in a heat insulating housing, a fixing portion separating claw that presses against the heat roller,
It is composed of a roller cleaner, an oil application roller, a temperature sensor and the like.

Downstream of the fixing section 26, a pair of paper discharge rollers 2 is provided.
7 and a switching flap 28 are arranged, and a downstream side thereof forms a paper discharge path 29 which is inverted from the upper side to the front side.
The terminal end of the opening 9 is opened as an upper discharge opening above the rear part of the upper discharge tray 6, and a discharge roller pair 31 is disposed in the opening. Immediately below the switching flap 28, a rear discharge port 32 that opens to the outside is formed.

In the loop of the conveyor belt 7, a rotating arm 33 is disposed between the upper circulation section and the lower circulation section of the conveyor belt 7 and extends in parallel with the sheet conveyance direction. The rotating arm 33 has a fixed support roller 34 at one end and a movable support roller 35 at the other end.

The fixed support roller 34 is rotatably fixed to and supported by a frame of the apparatus main body via a support shaft 36. The fixed support roller 34 is provided closest to the driving roller 8, that is, near the upstream side of the transfer charging roller 15 in the most downstream transfer section. The fixed support roller 34 is disposed in contact with the inner peripheral surface of the transport belt 7 so that the photoreceptor drum 11d at the most downstream and the transport belt 7 are always in contact.

The rotating arm 33 is supported coaxially with the support shaft 36 of the fixed support roller 34, and its free end (right side in the drawing) is centered on the support shaft 36 by a cam mechanism (not shown). Rotate up and down. The above-mentioned movable support roller 35 located at its free end is located closest to the driven roller 9, that is, at the position between the transfer charging roller 15 and the driven roller 9 in the most upstream transfer section, on the inner peripheral surface of the transport belt 7. The transfer belt 7 is supported in contact with the transfer belt 7. While the transfer charging roller 15 facing the photoreceptor drum 11d is fixed in position to the frame of the apparatus main body, the other three transfer charging rollers 15 are supported by a rotating arm 33, It is configured to move up and down with rotation.

The transport belt 7 is provided with a tension roller 37 which presses against the back surface of the lower circulation portion. The tension roller 37 pushes the lower circulation portion of the conveyor belt 7 downward by a rotating member 39 which is biased downward by a biasing member 38. Thereby, the transport belt 7
, And the entire conveyor belt 7 is stretched between the driving roller 8 and the driven roller 9 with a predetermined tension.

Between the conveyor belt 7 and the paper cassette 3,
A cleaner bottle 41 is provided detachably. A blade scraper 42 is attached to the upper portion of the cleaner bottle 41, and the tip of the blade scraper 42 contacts the surface of the lower circulation portion of the conveyor belt 7. Blade scraper 42
Removes the toner remaining on the surface of the transport belt 7 to clean the transport belt 7, and stores the scraped unnecessary toner in the cleaner bottle 41.

FIG. 6A is a diagram showing a state when printing (printing) a color image by the above-described color image forming apparatus, and FIG. 6B is a diagram showing a state when printing a monochrome image. FIG. 5A and 5B, the same components as those shown in FIG. 5 are denoted by the same reference numerals as in FIG. FIG. 6A shows a state in which the whole is set to the full-color printing mode.
The upper circulating portion of the conveyor belt 7 is supported between the movable support roller 35 and the drive roller 8 and contacts the four photosensitive drums 11a to 11d, as in the case of
Four transfer charging rollers 15 are pressed against the photosensitive drum 11 from the back surface.

On the other hand, when the rotating arm 33 is rotated downward from the position shown in FIG. 6A, as shown in FIG. 6B, the movable support roller 35 and the upstream The individual transfer charging rollers 15 move downward and separate from the transport belt 7. Thus, the upper circulation portion of the transport belt 7 is supported between the driving roller 8, the fixed support roller 34, and the driven roller 9. That is, the transport belt 7 is separated from the remaining three photosensitive drums 11a to 11c which are in contact with only the photosensitive drum 11d.

The operation when the color image forming apparatus 1 having the above-described structure forms an image will be briefly described again with reference to FIGS. 5 and 6A and 6B. First, power is supplied to the apparatus main body of the tandem-type color image forming apparatus 1, and the type of paper to be used, the number of sheets, the print mode, the paper feed mode, and other designations are input as keys or signals from a host device to be connected. Then, the apparatus main body starts printing (printing).
The following is a printing process when the full-color printing mode shown in FIG. 6A is selected.

First, the paper feed roller 24 makes one rotation to take out the uppermost one of the sheets stored in the sheet cassette 3, and transfers this sheet to the standby roller pair via the transport roller pair 23 and the feed path 22. To 17. Or, the paper feed roller 19
Feeds the uppermost sheet placed on the open / close sheet feed tray 4 to the standby roller pair 17 in cooperation with the separating member 21.

The standby roller pair 17 temporarily stops rotating,
The advance of the sheet is stopped by abutting the leading end of the sheet against the holding portion of the roller pair, the skew of the sheet is corrected, and the transfer timing is waited. The drive roller 8 rotates counterclockwise to start the circulating movement of the transport belt 7. The four image forming units are sequentially driven in accordance with the printing timing, and the photosensitive drum 11 rotates clockwise.

An initialization charger applies a uniform high negative charge to the peripheral surface of the photosensitive drum 11 to initialize the photosensitive drum 11. The optical writing head 12 performs exposure according to an image signal on the peripheral surface of the photosensitive drum 11 to record an electrostatic latent image including a high negative potential portion by the above initialization and a low negative potential portion whose potential has been attenuated by the exposure. I do. Developing roller 14
Transfers the toner in the developing unit 13 to the low potential portion of the electrostatic latent image to form a toner image on the peripheral surface of the photoconductor drum 11 (reversal development).

At the timing when the leading end of the magenta toner image on the peripheral surface of the photosensitive drum 11a of the image forming unit at the uppermost stream in the sheet conveying direction is rotated and conveyed to the transfer unit which is the part facing the conveyor belt 7, The standby roller pair 17 starts rotating and feeds the paper toward the transport belt 7 so that the printing start position of the paper coincides with the transfer unit. Suction assist roller 16
Presses the paper against the conveyor belt 7 while applying a charging voltage to the conveyor belt 7 to assist the suction. The paper is electrostatically attracted to the transport belt 7 and transported downstream.

The sheet is first conveyed to the first transfer section formed by the photosensitive drum 11a and the transfer charging roller 15. The transfer charging roller 15 applies a transfer current output from a transfer bias power supply (not shown) to the sheet via the transport belt 7. As a result, the magenta toner image on the photosensitive drum 11 is transferred to the paper.

Subsequently, the cyan toner image on the photosensitive drum 11b of the second transfer portion from the upstream in the sheet transport direction is transferred by the transfer charging roller 15, and the yellow toner image on the photosensitive drum 11c of the third transfer portion is further transferred. The image is transferred by the transfer charging roller 15, and the black toner image on the photosensitive drum 11 d in the lowermost transfer portion is transferred by the transfer charging roller 15.

The paper on which the toner images of the four colors are superimposed and transferred is separated from the conveyor belt 7 by the paper separating claw 25,
The sheet is carried into the fixing unit 26. The paper is applied heat and pressure by the fixing unit 26 to fix the toner image on the paper surface, and is carried out by being sandwiched by a pair of paper discharge rollers 27. Switching flap 2
When the roller 8 is rotated to the lower position shown in FIG. 5, it is guided by the upper discharge path 29, is further turned forward from above, and the toner image surface is turned downward by the discharge roller pair 31. The paper is discharged onto the upper paper discharge tray 6 in a face-down state. On the other hand, when the switching flap 28 is rotating upward, the switching flap 28 is guided in the lateral direction, and is discharged from the rear discharge port 32 to the outside of the apparatus in a face-up state in which the toner image surface faces upward.

In the monochrome print mode shown in FIG.
By rotating the rotating arm 33 downward, the three image forming units on the upstream side are excluded from image formation, and only the black toner image is formed by the photosensitive drum 11d and the transfer charging roller 15 of the most downstream image forming unit. Is transferred to the paper. Except for this point, the other processing operations and their timings are not much different from those in the above-described full-color printing mode, and thus the description is omitted.

[0027]

As described above, in the conventional tandem-type color image forming apparatus 1, as shown in FIGS. 5 and 6 (a) and 6 (b), The downstream end supported by the drive roller 8 is disposed so as to protrude outside the transfer portion facing the most downstream photosensitive drum 11d, and the upstream end supported by the driven roller 9 of the transport belt 7. The portion is disposed so as to protrude outward from the transfer portion facing the most upstream photosensitive drum 11a.
In other words, the upper circulating portion of the transport belt 7 that contributes to image formation is located outside the area where the four transfer portions are arranged, respectively. This has caused a problem of an increase in the size of the apparatus main body, and there has been a problem that it has not been possible to cope with a demand for a smaller apparatus in recent years, which has been strongly demanded by the market.

FIGS. 7 (a), 7 (b) and 7 (c) are views for explaining further problems in the tandem type color image forming apparatus, and FIG. 7 (a) shows a circle A in FIG. 6 (a). 7 (b) is an enlarged view of a portion surrounded by a circle B in FIG. 6 (a), and FIG. 7 (c) is a drive roller 8 and a fixing device 26 of FIG. It is an enlarged view of the vicinity.

In the case of the full-color printing mode shown in FIG. 6A, the paper is driven by the driven roller 9 and the suction assisting roller 1.
6 and the photosensitive drum 1
While being transported to the most upstream transfer portion formed by the transfer roller 1a and the transfer charging roller 15, as shown in FIG. 7A, the transport belt 7 maintained at the full-color print mode position by the movable support roller 35 is used. Is formed in a slightly convex shape, so that the leading end 43-1 of the paper 43 rises from the conveyor belt 7 before entering the transfer portion, and the photosensitive drum 11a
There is also a problem that a problem that paper jam occurs due to collision with the sheet often occurs.

Further, since the conveying belt 7 maintains the force of attracting the sheet 43 even after passing through the lowermost transfer section, as shown in FIG. Leading edge 43-1 of paper 43 to be separated from transport belt 7
5 slips through the paper separating claw 25 shown in FIG. 5 while adsorbed on the conveyor belt 7 and moves downward along the circumference of the drive roller 8 having a smaller curvature (larger arc) than the other rollers. And the problem often arises that fixing becomes impossible.

Further, since the conveyance speed of the fixing unit 26 is set to be slightly lower than the conveyance speed of the conveyance belt 7, a long length conventionally used for an advertisement called a POP (Point of Purchase: point of purchase) is conventionally used. When printing on normal paper, the size of normal paper is 297 × 420 mm in A3 size, while that of long paper is 297 × 900 mm. Therefore, when printing on long paper using a color image forming apparatus for plain paper, ,
As shown in FIG. 7C, the portion of the paper 43 mainly behind the central portion is formed between the conveyance belt end portion 7-1 and the fixing portion 26, and originally has the shape of the guide portion 46 as shown by the broken line 45. However, since the feed amount from the rear is slightly large as described above, it rises upward as shown by an arrow C in order to find an escape place, and touches the fixing cover 26-1 and the like to fix the unfixed image. There is also a problem that image defects occur due to rubbing.

The photosensitive drums 11 of the respective image forming units for forming toner images of the respective colors on the paper are arranged and arranged in a straight line from upstream to downstream in the paper transport direction. 7 is also stretched so that the upper circulation portion supported by several rollers and contributing to image transfer is straight. On the other hand, the conveying belt 7 is rotated by a biasing member 38 via a rotating member 39 by a biasing member 38 in order to correct the slack caused by the change in the attitude of moving up and down in the full-color printing mode and the monochrome printing mode and maintain the tension properly. The lower circulating portion is constantly pushed downward by the tension roller 37 which is urged, and is stretched.

During a printing stop or a halt period of the apparatus main body, a roller having a large curvature in the stretched state by the urging force is provided by a roller supporting portion of the driving roller 8 or the driven roller 9 in which the curvature of the conveyor belt 7 becomes large. Rolling for a long time causes the transport belt 7 to deform as time passes, resulting in a roller habit called creep phenomenon. When the conveyance belt 7 is driven at the start of printing an image, the roller habit appears as a distortion accompanied by a change in the shape of the straight line in the upper circulating portion of the conveyor belt 7 formed as the straight line, and as a result, There is also a problem that color shift occurs when toner images of four colors of M, C, Y, and K are superimposed and transferred.

FIGS. 8 (a) and 8 (b) are diagrams for explaining a problem caused by the above-mentioned roller habit. As shown in FIG.
Assuming that the length between the positions P0 and P1 of the conveyance belt 7 when there is no distortion between the position P0 and the position P1 is L0, the rotation of the conveyance belt 7 causes the position P0 and the position P1 as shown in FIG.
When the distortion 47 enters between them, the length of the conveyor belt 7 between the positions P0 and P1 becomes “L0 + α”.

Therefore, even if the paper is conveyed by the configuration based on the flatness of the conveyor belt 7 and the toner image is transferred in the transfer section as in the conventional case, the transfer belt 7 having the distortion 47 has Even if the drive roller 8 rotates accurately and stably as described above, the transport belt 7 where the distortion 47 is generated is transferred to the downstream transfer portion, for example, the photosensitive drum 11d and the transfer charging roller shown in FIG. When the sheet passes through the transfer section 48 with the transfer belt 15, the position of the conveyor belt 7 fluctuates, resulting in color misregistration.

The above-described distortion 47 of the conveyor belt 7 occurs from the time of shipment from the factory until it reaches the user, or even when it is at the user's hand, in a state of suspension of use for a long time. In addition, the driven roller 9 is also affected by the deformation of the conveyor belt 7 due to the distortion 47, and the rotation thereof becomes irregular, and this rotation unevenness appears on the paper surface as an image blur, which also causes a reduction in image quality. There was one.

The object of the present invention is to solve the above-mentioned conventional situation,
It can respond to the downsizing of equipment, eliminates the problem of paper lifting entering the uppermost transfer section, facilitates separation of paper from the end of the transport belt, and raises the paper between the transport belt and the fixing section. It is an object of the present invention to provide a tandem-type color image forming apparatus which prevents the problem of color misregistration caused by the distortion of the conveying belt due to the roller tendency.

[0038]

The construction of a tandem type color image forming apparatus according to the present invention will be described below. First,
A tandem-type color image forming apparatus according to claim 1, wherein a plurality of image carriers are arranged in parallel, and a plurality of toner image forming means for individually forming a predetermined color toner image on the plurality of image carriers. And the at least one of the plurality of image carriers is arranged at an upstream rotating roller and a downstream rotating roller disposed corresponding to the image carriers at both ends in the juxtaposition direction, and the transfer material is attracted to the outer peripheral surface by adsorbing the transfer material on the outer peripheral surface. A transport belt that circulates so as to sequentially contact the transfer material with a plurality of image carriers, and an image carrier via the transport belt to form a transfer unit corresponding to the plurality of image carriers inside the transport belt. And a plurality of transfer rotating rollers to which a transfer bias is supplied for transferring a toner image to the transfer material being in contact with the image carrier while being in contact with the image carrier, wherein the upstream rotating roller and the downstream rotating roller are provided. Roller is the above-mentioned transfer rotating roller function Configured to combine.

Next, in a tandem type color image forming apparatus according to the present invention, a plurality of image carriers are juxtaposed and a predetermined color toner image is formed on each of the plurality of image carriers. A plurality of toner image forming means, and at least an outer rotating surface and a downstream rotating roller disposed corresponding to the image carriers at both ends in the direction in which the plurality of image carriers are arranged in parallel, and transferred to the outer peripheral surface; A conveyance belt that circulates to adsorb the material and sequentially contacts the transfer material to the plurality of image carriers, and a transfer unit configured to correspond to the plurality of image carriers inside the conveyance belt. A plurality of transfer units that are pressed against the image carrier via a transport belt and that are supplied with a transfer bias to transfer a toner image to the transfer material that is in contact with the image carrier, the transport belt includes: The upstream rotation roller and the downstream rotation Configured so as not to protrude to both end portions than over la.

Further, according to a third aspect of the present invention, there is provided a tandem type color image forming apparatus, wherein a plurality of image carriers are juxtaposed, and a plurality of image carriers each forming a predetermined color toner image on the plurality of image carriers. A toner image forming means, and a transport belt that is circulated and moved around a plurality of rollers to attract the transfer material to the outer peripheral surface and sequentially contact the transfer material with the plurality of image carriers.
A toner image is transferred to the transfer material that is in pressure contact with the image carrier via the transport belt to form a transfer unit corresponding to the plurality of image carriers inside the transport belt and is in contact with the image carrier. And a plurality of transfer means to which a transfer bias is supplied in order to make a line connecting the plurality of transfer portions non-linear so as to be convex outside the circulating movement path of the transport belt. Be composed.

[0041]

Embodiments of the present invention will be described below with reference to the drawings. Note that, in the following description, the above-described image bearing member includes, for example, the photosensitive drum 62 and the like.
The toner image forming means includes, for example, a developing device 66, a developing roller 67, and the like, and the transferring means includes, for example, an upstream rotating roller 58, a downstream rotating roller 59, a transfer rotating roller 68, and the like.

FIG. 1 is a side sectional view showing the internal configuration of a tandem type color image forming apparatus according to one embodiment.
In the tandem type color image forming apparatus 50 shown in FIG.
The structure and function of the front upper surface 55 and the upper paper discharge tray 56 are the same as those of the upper cover 2, the paper cassette 3, the openable paper feed tray 4, the front upper surface 5, and the upper paper discharge tray 6 shown in FIG. Is the same as

In this embodiment, a slightly flat loop-shaped transport belt 57 is disposed at the center of the apparatus body of the tandem-type color image forming apparatus 50 at substantially the center. The conveyor belt 57 is made of a sheet member made of a fluorine-based material having excellent durability and transferability, and is fixed in shape by heat of 80 degrees due to a heat cycle. It has the property that it can be shrunk by the heat of and returned to its original shape.

The transport belt 57 is supported at its upstream end (right side in the drawing) in the upper region contributing to image formation by an upstream rotating roller 58, and similarly in the upper region downstream in the sheet transport direction. The left end of the left side of the figure is supported by the downstream side rotation roller 59, and the lower side of the lower side rotation roller 5
9 is driven by being pressed against the drive roller 61,
It circulates in the counterclockwise direction in the figure.

The four photosensitive drums 62 (62a, 62b, 62c, 6)
2d) is arranged. Surrounding the peripheral surface of the photosensitive drum 62 clockwise (hereinafter, the photosensitive drum 62
a), a cleaner 63, an initialization charger 64, an optical writing head 65,
Developing device 66, developing roller 67, and upstream rotating roller 5
Eight devices are provided.

In place of the upstream rotating roller 58, a downstream rotating roller 59 is disposed on the most downstream photosensitive drum 62d, and a transfer rotating roller 68 is disposed on the two intermediate photosensitive drums 62b and 62c. Is arranged. The photosensitive drum 62, the cleaner 63, the initialization charger 64, and the developing device 6
6. The functions of the developing roller 67 are the same as those of the cleaner, the initializing charger, the developing device 13, and the developing roller 14 described with reference to FIG. The functions of the transfer roller 58 and the transfer roller 59 shown in FIG. 5 are the same as those of the transfer roller 15 shown in FIG. 5 except that the upstream roller 58 and the downstream roller 59 also serve as the conveyor belt support roller. The same is true. That is, as in the case of FIG. 5, the recording unit, the developing unit, and the transfer unit are respectively formed at predetermined positions.

The photosensitive drum 62, cleaner 63, initialization charger 64, developing device 66, developing roller 67
Is integrally mounted on the unit frame as an image forming unit, and is configured to be detachable from the apparatus main body. The optical writing head 65 is supported on the back surface of the upper lid 52 via a support member 69, moves in an upward and downward arc along with the opening and closing of the upper lid 52, and moves down by closing the upper lid 52. The photosensitive drum 62 is positioned above the photosensitive drum 62. The developing device 66 has an upstream side in the sheet transport direction (right side in the figure).
5, the magenta (M), cyan (C), yellow (Y), and black (K) non-magnetic toners are stored in order from the developing device 66 on the downstream side (left side in the figure). Is the same as

However, as described above, both ends of the upper circulating portion of the conveyor belt 57 are supported by the upstream rotation roller 58 and the downstream rotation roller 59 also serving as the transfer rotation roller, and the other ends are further provided. There are no rollers such as the drive roller 8 and the driven roller 9 shown in FIG.

On the upstream side of the transport belt 57 of the tandem type color image forming apparatus 50, a standby roller pair 71, a paper sensor 72, and a lateral and downward branch, and a paper feed roller 73 in the lateral direction. Handling member 74, feed path 7 in the downward direction
5, a transport roller pair 76 and a paper feed roller 77 are provided. These standby roller pair 71, sheet sensor 72, paper feed roller 73, separating member 74, feed path 75, transport roller pair 7
The configuration and function of the paper feed roller 6 and the paper feed roller 77 are as follows: the standby roller pair 17, the paper sensor 18, the paper feed roller 19, the separating member 21, the feed path 22, the transport roller of the tandem type color image forming apparatus 1 shown in FIG. The configuration and function of the pair 23 and the paper feed roller 24 are the same.

A guide plate 78 is disposed downstream of the transport belt 57 in the paper transport direction, and a fixing section 79 is disposed downstream of the guide plate 78. Fixing section 79 and fixing section 79
The configuration and function of the discharge roller pair 81, the switching flap 82, the rear discharge port 83, the discharge path 84, and the discharge roller pair 85 arranged downstream from the tandem type color image forming apparatus shown in FIG. 1, a fixing unit 26, a discharge roller pair 27,
A switching flap 28, a rear discharge port 32, a discharge path 29,
The configuration and function of the discharge roller pair 31 are the same.

However, in this embodiment, a rotation suppressing member 86 is provided on the outer wall on the upstream side of the fixing section 79. Rotation restraining member 8
6 is provided with a spur-shaped pulley at the tip, and is rotated by a drive mechanism (not shown) such as a solenoid between a broken line position and a solid line position as shown by a double-headed arrow D in the figure. It is arranged so as to swing up and down following the suppressed movement of the paper.

The heat generating roller 87 of the fixing section 79 includes
A heat conduction belt 89 is connected via a heat conduction roller 88. The heat conduction belt 89 rotates around a support shaft 91 at the end of the heat conduction roller 88 as a fulcrum between a standby position indicated by a broken line 89 ′ and a contact position with the drive roller 61 indicated by a solid line.

By rotating to the contact position with the drive roller 61 shown by the solid line, the fixing heat of the heat generating roller 87 can be transmitted to the transport belt 57 through the drive roller 61 as heat of 50 to 60 degrees. . At this time, the transport belt 57
Is controlled so that the heat generating roller 87 is controlled by a temperature thermistor (not shown) to an appropriate temperature in the range of 50 to 60 degrees of the contraction temperature of the conveyor belt 57. At this time, the conduction temperature can be controlled by appropriately bringing the heat conduction belt 89 into and out of contact with the drive roller 61.

By reducing the creep phenomenon by contracting the transport belt 57 by the heat controlled in this way, it is possible to reduce the distortion due to the roller habit (creep phenomenon) generated on the transport belt 57 during a long stop period. it can.

FIGS. 2A and 2B show four image forming units, the optical writing head 65, and the four photosensitive drums 62 of the tandem type color image forming apparatus 50, respectively. FIG. 2A is a view showing only the transport belt 57, and FIG. 2A is a view similar to that of FIG.
FIG. 2B shows a state of the full-color printing mode in which the upper circulation portion is in contact with the four photosensitive drums 62. FIG.
7 shows a state of the monochrome print mode in which the upper circulation section 7 is separated from the three photosensitive drums 62 on the upstream side. 2 (a) and 2 (b), the same components as those shown in FIG. 1 are denoted by the same reference numerals as in FIG.

As shown in FIG. 2A, the transport belt 57
As shown in FIG. 1, both ends of the upper circulating section are supported by an upstream rotating roller 58 and a downstream rotating roller 59 also serving as a transfer rotating roller, and the upstream end of the upper circulating section is the most upstream transfer section. And the downstream end forms the most downstream transfer portion. Further, there are no rollers such as the drive roller 8 and the driven roller 9 shown in FIG.

As a result, the front and rear dimensions of the apparatus body of the tandem type color image forming apparatus 50 can be reduced by the amount that the conveyor belt 57 does not protrude outside the transfer sections at both ends of the upstream and downstream sides. It is possible to reduce the size more than before.

Also in this example, a rotary arm 92 is provided to set the full-color print mode shown in FIG. 2A and the monochrome print mode shown in FIG. 2B.
In the rotary arm 92 in this example, the downstream rotation roller 59 also serves as the fixed support roller 34 shown in FIG. 5, and the upstream rotation roller 58 also serves as the movable support roller 35 shown in FIG. .

The upper belt supporting portion of the rotating arm 92 has the above-mentioned upstream rotating roller 58 and downstream rotating roller 59, and two transfer rotating rollers 68 between the upstream rotating roller 58 and the downstream rotating roller 59. Three idle rollers 9
3 are alternately arranged to support the transport belt 57 from below in a shape that forms a large arc 94 in a non-linear shape that is convex outwardly of the circulation movement path of the transport belt 57 as a whole. .

Incidentally, instead of the above idle roller 93,
Although not particularly shown, the sliding guide is connected to the upstream rotating roller 5.
8 and the transfer roller 68 on the upstream side, between the transfer roller 68 on the upstream side and the transfer roller 68 on the downstream side, and between the transfer roller 68 on the downstream side and the downstream roller 59. .

In any case, the transport belt 5
By supporting the upper circulation portion 7 in a shape that draws a convex arc upward, even if distortion occurs due to the creep phenomenon in the transport belt 57, it can be absorbed in shape, and the distortion appears as a change in the shape of the transport surface. As a result, the adverse effect on the formed image due to the distortion can be reduced.

As shown in FIG. 2B, when the rotation arm 92 is rotated downward about the rotation axis of the downstream rotation roller 59 as shown in FIG. The circulating portions are three photosensitive drums 62a-
Only the transfer portion formed by the downstream rotation roller 59 and the photosensitive drum 62d becomes effective, and is in the monochrome print mode.

Both the printing operation in the monochrome printing mode and the printing operation in the full-color printing mode shown in FIG. 5A are the same as those described with reference to FIGS. 5 and 6A and 6B. It is. However, in this example,
In addition to the miniaturization of the apparatus main body and the reduction of distortion due to the creep phenomenon, various inventions for further solving the conventional problems have been added. Hereinafter, this will be described.

FIGS. 3 (a), 3 (b) and 3 (c) are diagrams for explaining an operation state in which no trouble occurs in each section of the tandem type color image forming apparatus 50. FIG. 3 (a) is an enlarged view of a portion surrounded by a circle E, FIG. 3 (b) is an enlarged view of a portion surrounded by a circle F in FIG. 2 (a), and FIG.
FIG. 3 is an enlarged view of the vicinity of the fixing unit 79.

In the case of the full-color print mode shown in FIG. 2A, as shown in FIG. 7A, the uppermost stream from the sheet carry-in portion formed by the driven roller 9 and the auxiliary suction roller 16 is provided. As shown in FIG. 3A, there is no extra section up to the transfer section and no convex portion formed at the boundary between the extra section and the image forming section, and as shown in FIG. Since the first transfer portion formed by the rotation roller 58 also serves as the paper carry-in portion of the conveyor belt 57, the paper is transferred along the paper entry path 95 indicated by a two-dot chain line in FIG. And is directly carried into a first transfer portion formed by the upstream rotation roller 58. Then, the transfer of the toner image by the photosensitive drum 62a and the upstream rotation roller 58 is started at the image formation start position of the sheet. Therefore, the leading end of the incoming paper is transport belt 57
There is no room for the leading edge of the sheet to float during the first transfer after the sheet is placed on the photosensitive drum 62a, so that the leading edge of the sheet may hit the photosensitive drum 62a or the lower part of the image forming unit, causing a paper jam. The occurrence is eliminated.

Further, as shown in FIG. 3B, the sheet on which the transfer of the toner image at the most downstream transfer portion by the photosensitive drum 62d and the downstream rotation roller 59 has been completed is conveyed by the transfer portion as it is. Since the belt 57 serves as a sheet discharge unit, the end of the conveying belt 57 formed by the downstream rotation roller 59 has a large curvature and the photosensitive drum 62d.
The sheet is easily peeled off from the conveyor belt 57 by the attraction force due to the electric field, and the sheet discharge path 9 indicated by a two-dot chain line in FIG.
It is discharged stably along 6. This eliminates the problem that the sheet discharged from the final transfer section is wound around the transport belt that is reversed and not returned to the fixing section.

Further, as shown in FIG. 3 (c), the paper 9 on which the transfer of the toner image has been
7 is carried into the fixing unit 79, for example, the paper 97
In the case of a long sheet such as an OP sheet, if necessary, the rotation suppressing member 86 is rotated from the standby position indicated by the broken line 86 'in the drawing to the lower pressing position indicated by the solid line, thereby forming a spur shape. The pulley 86-1 presses down the sheet 97 to prevent the occurrence of such a problem that the sheet 43 shown in FIG. 7 (c) rises and rubs the unfixed image surface against the surrounding members, resulting in a defective image. can do.

Finally, FIG.
In the following, a description will be given of a tension roller whose description is omitted. FIGS. 4A and 4B are diagrams showing an operation state of the tension roller, and FIG. 4C is a diagram for explaining a torque applied to the tension roller in accordance with the operation. As shown in FIG. 7A, an oil damper 98 is directly connected to the rotation shaft of the upstream rotation roller 58 that forms the most upstream transfer section together with the photosensitive drum 62a. A rotary arm 99 made of an elastic member is disposed on the oil damper 98, and a tension roller 101 is disposed at the tip of the rotary arm 99. A spiral spring 103 is interposed between the portion near the tension roller 101 of the rotating arm 99 and the frame 102 of the transport belt mechanism.

In FIG. 9A, the transport belt 57 is
When the circulating movement is started in the printing rotation direction shown by the arrow G in the figure by being driven by the drive roller 61 shown in FIG. 2, the upstream rotation roller 58 starts rotating in the counterclockwise direction shown by the arrow H in the figure. A torque that causes the oil damper 98 to rotate in the same rotational direction is generated, and this torque urges the rotating arm 99 to rotate counterclockwise against the urging force of the helical spring 103. As a result, the tension roller 101 moves the lower circulation portion 57-1 of the transport belt 57.
Is pushed downward as indicated by the arrow J in the figure to tension the transport belt 57.

When the conveyor belt 57 stops, the torque generated by the oil damper 98 is lost as shown in FIG. 3C, and the urging force of the pulling spiral spring 103 causes the oil spring 98 to lose its torque as shown in FIG. The tension roller 101 is pulled upward against its own weight, so that the lower circulating portion 5 of the transport belt 57 is moved.
Release the pressure on 7-1. Thereby, the transport belt 5
The tension applied to 7 becomes zero.

Therefore, in the engagement relationship between the transport belt 57 and the upstream rotary roller 58 and the downstream rotary roller 59 at both ends during the long-term stop period, the transport belt 57
Is applied only by its own weight, which is an extremely weak force, so that the transfer belt 57 is hardly distorted by the creep phenomenon.

[0072]

As described above in detail, according to the present invention, both ends of the upper circulating portion of the conveyor belt are supported by the upstream rotating roller and the downstream rotating roller also serving as the transfer rotating roller, respectively. Conventional drive rollers and driven rollers that protrude outside the transfer section are not required, and therefore the front and rear dimensions of the apparatus main body are reduced by the amount that the conveyor belt does not protrude outside the transfer sections at both ends of the upstream and downstream sides. Accordingly, it is possible to contribute to promotion of further miniaturization of the image forming apparatus.

Further, since the upper circulating portion of the conveyor belt is supported in a shape that draws a convex arc upward, even if the conveyor belt is distorted due to the creep phenomenon, it can be absorbed in shape, whereby the distortion is reduced. It is difficult to appear as a change in the shape of the image, and the adverse effect on the formed image due to the distortion can be reduced.

Further, since the conveying belt can be heated as required by using the heat source of the fixing section, the distortion of the conveying belt due to the creep phenomenon can be reduced. It is possible to stabilize the positional accuracy at the time of the initial operation and form a high-quality image from the time of the initial drive.

Further, since the first transfer portion formed by the most upstream photosensitive drum and the upstream side rotating roller also serves as the sheet carry-in portion of the conveyor belt, the sheet is directly transferred to the first transfer portion along the sheet entry path. There is no room for the leading edge of the paper to be lifted during the first transfer performed after being loaded and placed on the transport belt, so that the leading edge of the paper hits the lower part of the photosensitive drum or the image forming unit and the paper jam occurs. Is eliminated.

Further, since the most downstream transfer portion formed by the photosensitive drum and the downstream rotating roller directly serves as the sheet discharging portion of the transport belt, the edge of the transport belt formed by the downstream rotating roller has a large curvature and is exposed to light. The paper can be easily peeled off from the transport belt by the suction force of the electric field of the body drum, so that the paper discharged from the final transfer section is not wound around the transport belt which is turned over and returned to the fixing section. Is eliminated.

Further, a rotation suppressing member provided with a spur-shaped pulley is provided in the vicinity of the paper carry-in section of the fixing unit, and the sheet is held down by the spur-shaped pulley as necessary. Even in the case of paper, it is possible to prevent the occurrence of a defect that causes a defect due to rubbing of an unfixed image due to the lifting of the paper.

Further, since the tension roller is rotated by using the torque generated by the oil damper directly connected to the upstream rotating roller shaft to apply tension to the transport belt, the tension applied to the transport belt becomes zero when the operation of the apparatus main body is stopped. become,
Thereby, the distortion of the transport belt due to the creep phenomenon is remarkably reduced, and therefore, the blurring of the transferred image due to the distortion of the transport belt can be reduced, and high-quality image formation can be maintained.

[Brief description of the drawings]

FIG. 1 is a side sectional view showing an internal configuration of a tandem type color image forming apparatus according to an embodiment.

FIGS. 2A and 2B are diagrams illustrating only an image forming unit, an optical writing head, and a transport belt of a tandem-type color image forming apparatus, in which FIG. 2A illustrates a state of a full-color print mode, and FIG. It is a figure showing the state of.

3A and 3B are diagrams illustrating an operation state in which a failure does not occur in each unit of the tandem type color image forming apparatus, and FIG.
2A is an enlarged view of a portion surrounded by a circle E in FIG. 2A, FIG. 2B is an enlarged view of a portion surrounded by a circle F in FIG. 2A, and FIG. It is an enlarged view.

FIGS. 4A and 4B are diagrams illustrating an operation state of a tension roller, and FIG. 4C is a diagram illustrating a torque applied to the tension roller according to the operation;

FIG. 5 is a side sectional view showing an example of a conventional tandem type color image forming apparatus.

FIG. 6A is a diagram illustrating a state when a color image is printed by a conventional tandem-type color image forming apparatus, and FIG. 6B is a diagram illustrating a state when a monochrome image is printed.

FIGS. 7A, 7B, and 7C are diagrams illustrating further problems in the conventional tandem-type color image forming apparatus.

FIGS. 8A and 8B are diagrams for explaining a problem due to a roller habit of a transport belt in a conventional tandem type color image forming apparatus.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Tandem-type color image forming apparatus 2 Top cover 3 Paper cassette 4 Openable / closable paper feed tray 5 Front upper surface 6 Upper discharge tray 7 Conveyor belt 8 Drive roller 9 Follower roller 11 (11a, 11b, 11c, 11d) Photoconductor drum 12 Optical writing Head 13 Developing device 14 Developing roller 15 Transfer charging roller 16 Suction assist roller 17 Standby roller pair 18 Paper sensor 19 Feed roller 21 Separation member 22 Feed path 23 Transport roller pair 24 Feed roller 25 Paper separation claw 26 Fixing unit 27 Discharge Paper roller pair 28 switching flap 29 paper discharge path 31 paper discharge roller pair 32 rear paper discharge port 33 rotating arm 34 fixed support roller 35 movable support roller 36 support shaft 37 tension roller 38 urging member 39 rotating member 41 cleaner bottle 42 Blade scraper 43 Paper 43-1 Tip 44, 45 Dashed line 46 Guide part 47 Distortion 48 Transfer part 50 Tandem type color image forming apparatus 52 Top lid 53 Paper cassette 54 Openable paper feed tray 55 Front upper surface 56 Upper paper discharge tray 57 Transport belt 57-1 Lower circulation part 58 Upstream rotation Roller 59 Downstream rotating roller 61 Drive roller 62 (62a, 62b, 62c, 62d) Photoconductor drum 63 Cleaner 64 Initializing charger 65 Optical writing head 66 Developing device 67 Developing roller 68 Transfer rotating roller 69 Support member 71 Standby roller pair 72 paper sensor 73 paper feed roller 74 separating member 75 feed path 76 transport roller pair 77 paper feed roller 78 guide plate 79 fixing unit 81 paper discharge roller pair 82 switching flap 83 rear paper discharge port 84 paper discharge path 85 paper discharge roller pair 86 Rotation suppressing member 86-1 Spur-shaped pulley 87 Heat roller 88 thermally conductive roller 89 thermally conductive belt 91 supporting shaft 92 rotating arm 93 idle rollers 94 arc 95 sheet entrance path 96 paper discharge path 97 Paper 98 oil damper 99 swing arm 101 tension roller 102 frame 103 pulling the helical spring

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Akiyoshi Furusawa 2-229 Sakuragaoka, Higashiyamato-shi, Tokyo Casio Computer Co., Ltd. Tokyo Office (72) Inventor Masakazu Suzuki 2-229 Sakuragaoka, Higashiyamato-shi, Tokyo Casio Computer Co., Ltd. Tokyo Office (72) Inventor Hiroshi Ikemoto 2-229 Sakuragaoka, Higashiyamato-shi, Tokyo Casio Computer Co., Ltd. Tokyo Office F-term (reference) 2H030 AB02 AD01 AD05 AD16 BB02 BB23 BB44 BB46 BB54 2H032 AA05 AA15 BA01 BA05 BA11 BA18 BA21 BA23 BA30 CA02 DA12 DA16 DA17

Claims (3)

[Claims] A plurality of image carriers arranged side by side; a plurality of toner image forming means for individually forming a predetermined color toner image on the plurality of image carriers; The transfer material is at least stretched over the upstream rotation roller and the downstream rotation roller disposed corresponding to the image carriers at both ends in the installation direction, and the transfer material is attracted to the outer peripheral surface and the transfer material is applied to the plurality of image carriers. A transport belt that circulates so as to make sequential contact, and is pressed against the image carrier via the transport belt to form a transfer unit corresponding to the plurality of image carriers inside the transport belt; A plurality of transfer rotating rollers to which a transfer bias is supplied to transfer the toner image to the transfer material in contact with the transfer material, wherein the upstream rotating roller and the downstream rotating roller also have the transfer rotating roller function. Is characterized by Tandem type color image forming apparatus. 2. A plurality of image carriers arranged side by side; a plurality of toner image forming means for individually forming a predetermined color toner image on the plurality of image carriers; The transfer material is at least stretched over the upstream rotation roller and the downstream rotation roller disposed corresponding to the image carriers at both ends in the installation direction, and the transfer material is attracted to the outer peripheral surface and the transfer material is applied to the plurality of image carriers. A transport belt that circulates so as to make sequential contact, and is pressed against the image carrier via the transport belt to form a transfer unit corresponding to the plurality of image carriers inside the transport belt; A plurality of transfer units to which a transfer bias is supplied to transfer the toner image onto the transfer material in contact with the transfer belt, wherein the transport belt is closer to both ends than the upstream rotation roller and the downstream rotation roller. It does not protrude. Tandem type color image forming apparatus. 3. A plurality of image carriers arranged side by side; a plurality of toner image forming means for individually forming a predetermined color toner image on the plurality of image carriers; A transfer belt that adsorbs the transfer material on its surface and circulates so as to sequentially contact the transfer material with the plurality of image carriers; and a transfer unit inside the transfer belt corresponding to the plurality of image carriers. A plurality of transfer units that are pressed against the image carrier via the transport belt to supply a transfer bias to transfer the toner image onto the transfer material that is in contact with the image carrier. A tandem-type color image forming apparatus, wherein a line connecting the transfer portions is formed in a non-linear shape convex outside the circulation movement path of the transport belt.