JPH09179372A - Image forming device - Google Patents

Abstract

(57) An object of the present invention is to provide an image forming apparatus that forms an image by always synchronizing relative image transfer positions in a multi-stage image transfer section. SOLUTION: Gears of the same arrangement of a drum drive system are formed by gears molded from the same mold. Color drum 5-
The drive system of the drive gears A1 to A3 of 1, 5-2 and 5-3 and the drive gear A4 of the black drum 5-4 is branched from the motor 38, and only the drive gear A4 is driven in the monochrome mode. It When returning to the full color mode, first, all the drive gears A1 to A4 rotate and the sensor 52 causes the protrusion 51 to move.
Is detected to recognize that the drive gears A1 to A3 have reached the reference position, the clutch gear 34 disengages the clutch, and the drive gear A1
~ A3 stops. Then only the drive gear A4 rotates,
The sensor 54 detects the protrusion 53, recognizes that the drive gear A4 has reached the reference position, and stops the motor 38. With this, the gears of the drive system are aligned with the reference position of the full color mode, and the transfer relative positions of the four color images are aligned.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for forming a multicolor image by arranging image carriers in a multi-stage manner.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus for forming a multicolor image by arranging image carriers (photosensitive drums) in multiple stages, the gears of the photosensitive drums are meshed with each other to form the photosensitive drums. There is a drum drive gear that drives each. Since there is a limit to the manufacturing accuracy of any member, a plurality of drum driving gears corresponding to the plurality of (3 or 4) photosensitive drums have mechanically generated shapes or dimensions. There is always an error. Therefore, it is unavoidable that the photosensitive drum driven by this has uneven rotation due to an error.

Such uneven rotation of the photosensitive drum appears as fluctuations in the moving speed of the peripheral surface of the photosensitive drum. From the photosensitive drums arranged side by side in a multi-stage manner, the respective toner images are transferred in an overlapping manner on one sheet of paper, but the toner images of the respective colors of the respective photosensitive drums are subjected to the respective rotation unevenness, that is, the peripheral surface. If the position shift occurs due to the fluctuation of the moving speed of, the unevenness occurs in the color registration which should be correct, and a good image cannot be obtained. In order to solve this problem, based on the fact that uneven rotation occurs periodically, the drum drive gears of the same molded product are used, these same positions are marked, and the positions are separated from each other. It is known that the combination of gears is set such that the relative positions of the marks of the drum driving gears also match when the image transfer positions of the photoconductor drums relatively match.

By doing so, the image transfer positions of the respective photosensitive drums corresponding to each other are synchronized with the positions of the marks of the drum driving gears, and since the respective drum driving gears are the same molded product, they are driven by them. The same rotation unevenness is generated on each of the photoconductor drums in synchronization with mutually corresponding image transfer positions. In other words, since the fluctuations in the moving speed of the peripheral surface with respect to the image transfer position of the photosensitive drum are synchronized with each other, the transfer for each color is performed at the same position on the paper. Therefore, the above error may appear as a partial expansion / contraction of the entire image when viewed finely, but it does not appear as an error of color superposition, so an image with good brightness and resolution can be obtained. It turns out that.

[0005]

By the way, in image formation, not only multicolor printing, but rather black one-color printing is in great demand. Therefore, many image forming apparatuses are capable of switching between a full-color mode for performing multicolor printing and a monochrome mode for performing monochrome printing. In this case, generally, even in the monochrome mode, a mechanical rotation is simply stopped by stopping the optical writing drive to the photoconductor drum corresponding to the color system so as to avoid the technically difficult method and realize the method easily. The drive is generally operated as it is. Therefore, the above-mentioned relative position of the drive gear that has been once aligned and set does not change.

However, when the color system mechanical drive is performed and the color system photoconductor drum rotates during the printing of black only, the photoconductor drum always has an initialization charging brush, a developing roller and a cleaning roller. Since the plates and the like are in sliding contact, this sliding contact consumes the color system members. Then, there is a problem that the life of the member is exhausted even though the color printing is not actually performed so much.

When the full color mode is switched to the monochrome mode, this problem can be solved for the time being by stopping both writing and rotation driving for the color system and driving only the black system. However, in this case, not only is there a great technical difficulty in switching the mechanical drive system, but also, as described above, the image transfer positions of the respective photoconductor drums corresponding to each other are adjusted. Even after the printing in the monochrome mode is completed, the relative position setting does not match between the driven black drum drive gear and the color drum drive gear stopped during that period. .

An object of the present invention is to provide an image forming apparatus which forms an image by always synchronizing relative image transfer positions in a multi-stage image transfer section.

[0009]

The construction of the image forming apparatus according to the present invention will be described below. According to the present invention, a plurality of image carriers arranged in parallel, an image carrier gear fixed to each of the plurality of image carriers, and a drive unit provided correspondingly so as to mesh with the image carrier gears are transmitted. A plurality of driving gears, a plurality of toner image forming means for individually forming toner images of a predetermined color on the plurality of image carriers, and a transfer material on at least one image carrier of the plurality of image carriers. Conveying means for conveying the transfer material to bring it into contact with each other, and a plurality of transfer means for transferring the toner image to the transfer material which is arranged so as to correspond to the plurality of image carriers and constitutes a transfer portion and is in contact with the image carrier. And means,
The plurality of image carrier gears and the plurality of drive gears have the same shape and are processed by the same molding die and have a mark, respectively, and correspond to the distance between the plurality of image carriers based on the mark. And the image carrier is assembled so that the relative phases of the image carriers are the same.

In the image forming apparatus of the present invention, the transfer material is conveyed by the conveying means while performing only the image forming step related to the first image carrier of the plurality of image carriers.
First mode in which the transfer material is conveyed so as to contact only the image carrier, and the second mode in which the transfer material is conveyed so as to contact all the image carriers while executing the image forming process related to all the image carriers. Control means for switching control to the mode, first detection means for detecting a position of the drive gear corresponding to the first image carrier, which is associated with the mark, and a predetermined image other than the first image carrier. Second detection means for detecting the position of the drive gear corresponding to the carrier relative to the mark, and the first and second detections at least when the control means switches from the first mode to the second mode. And a relative phase correction means for driving a predetermined drive gear to correct the relative phase shift of the image carrier based on the detection result of the means.

Then, for example, as described in claim 2, the toner image forming means corresponding to the first image carrier is a means for forming a black toner image on the image carrier, and another image carrier. The toner image forming unit corresponding to is configured as a unit that forms a chromatic color toner image.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1A is a plan view showing the arrangement and engagement state of the photosensitive drum and the drum drive gear in one embodiment, and FIG. 1B is a side view thereof.
2 is a side view showing a drive system of an image forming apparatus including such a photosensitive drum and a drum drive gear.

First, the overall structure will be described with reference to FIG. The image forming apparatus (apparatus main body) shown in FIG. 2 is provided with a sheet conveying belt 4 (conveying means) substantially in the center thereof.
The paper conveyance belt 4 is stretched between the drive rotation roller 1 and the driven rotation roller 2, and the end portion on the upstream side in the paper conveyance direction is nipped by the driven roller 2 and the auxiliary roller 3 and circulates. Then, the sheet is brought into contact with the sheet conveying surface of the upper circulation portion of the sheet conveying belt 4 and the four photosensitive drums 5 (5
-1, 5-2, 5-3, 5-4) are provided. These photosensitive drums 5 (image-bearing members) are each a case 6
It is rotatably supported at the bottom of (6-1, 6-2, 6-3, 6-4). Directly above the photoconductor drum 5, an optical writing head 8 (8-
1, 8-2, 8-3, 8-4) are inserted and arranged by closing the upper lid member 7. The upper lid member 7 opens and closes around a support shaft 9 at the rear of the apparatus body.

Transfer brushes 11 (transfer means) are arranged so as to face the photoconductor drums 5 from the back surface of the paper transport belt 4, and form image forming portions for respective colors. The four casings 6 include Y (yellow: yellow) toner, which is the three primary colors of subtractive colors, from the casing 6-1 in the most upstream direction (right side in the figure) to the casing 6-4 in the most downstream direction. , M (magenta: red dye) toner, C (cyan: blue with greenish tint) toner, and Bk (black: black) toner dedicated to printing characters and the like, a total of 4 types of toner It is housed one by one. Although not shown in particular, around the photosensitive drum 5, a cleaner and an initialization charger are arranged on the left side of the optical writing head 8 and a developing roller is arranged on the right side thereof.

A standby roll pair 12 is disposed on the upstream side of the sheet conveying belt 4, and the upstream side thereof branches laterally and downwardly, and in the lateral direction, a sheet feeding roller 13, a separating member 14, and a plurality of sheets. An openable paper tray 15 on which the paper P is placed is arranged. Further, a transport path 16 formed of two guide plates is disposed below, and a paper cassette 17 is also detachably mounted upstream (downward) thereof for accommodating a large number of sheets. . A paper feed roller 18 is arranged above the paper feed end.

A fixing device 19, a paper discharge roll 21, and a switching lever 22 are provided downstream of the paper transport belt 4. The switching lever 22 guides the paper to the upper discharge path 23 when it is in the lower position as shown in FIG.
When the sheet is rotated upward, the sheet is guided to the sheet discharge port 24 that opens on the rear surface of the apparatus. The downstream side of the discharge path 23 communicates with the upper discharge port 26 via the discharge roll pair 25. A paper output tray 27 is provided in front of the upper paper output port 26 (at the rear of the upper lid member 7).
Are formed.

The photosensitive drum 5 (5-1, 5-2, 5)
-3, 5-4), as shown in FIG. 1 (a), drum gears 31-1, 31-2, 31-3 and 31- are attached to the respective ends.
4 is provided integrally with the photosensitive drum 5. And
The drum drive gears 32-1 (A1), 32-- are attached to the drum gears 31-1, 31-2, 31-3, and 31-4.
2 (A2), 32-3 (A3) and 32-4 (A4) are in mesh with each other. Also, these drum drive gears A
Small gears of reduction gears B1, B2, B3, and B4 in which a large-diameter gear and a small-diameter gear are integrally formed are meshed with 1, A2, A3, and A4.

The above-mentioned drum driving gears A1, A2, A3 and A4 are gears of the same shape molded by the same mold, and as shown in FIG. 1 (b), they are at the same position (the same position of the mold). ), The same mark 33 (33-1, 33-2,
33-3, 33-4) are engraved. In this case, if the mold is not a single-mold mold but a multi-mold mold that molds a plurality of products (gears) with the same specifications at once, even if the design specifications are the same, However, if the mold positions of the multiple molds are different, a subtle difference occurs due to a mechanical error in the mold raising, and thus the drive transmission characteristics of the drum drive gears as products also differ. In this case, good multicolor printing cannot be performed if it is used as it is for driving a photosensitive drum that requires precision in a multistage image forming unit. Therefore,
In the present embodiment, products formed from molds at the same position of the mold have the same shape. With this, even if there are eccentricities and shape errors in the plurality of drum drive gears molded from the mold at the same position of the mold in this way,
Since the positions and amounts of the eccentricity and the shape error are all the same, the gear meshing should be set so that the same position of each drum drive gear corresponds to the transfer position of each photosensitive drum to be synchronized. For example, deviations (positional deviations) due to eccentricity and shape errors of the drum drive gears at the transfer positions of the photoconductor drums all occur in the same state, and as a result, there is no deviation in the mutual transfer positions of the respective colors to be superimposed. Does not occur.

Drum drive gears A1, A shown in FIG. 1 (b)
2, Marks 33-1, 33-2, 3 in A3 and A4
As described above, the positions of 3-3 and 33-4 are set at the transfer positions of the four photoconductor drums 5 (5-1, 5-2, 5-3, 5-4) that should be relatively synchronized. In order to correspond respectively, the arrangement in the case where the drum drive gears A1, A2, A3, and A4 are in mesh with the drum gears 31-1, 31-2, 31-3, and 31-4, respectively, is shown.

Further, the use of the above-mentioned gears having the same shape is not limited to the drum driving gears A1, A2, A3 and A4, but the drum gears 31-1, 31-2, 3-2.
The same applies to 1-3 and 31-4, and the same applies to the reduction gears B1, B2, B3, and B4.

The small-diameter gear of the drive-side reduction gear C1 meshes with the large-diameter gear of the reduction gear B1.
For the large diameter gears 2 and B3, one reduction gear C2 on the drive side
The small-diameter gear of is engaged. The large-diameter gears of the reduction gears C1 and C2 mesh with one clutch gear 34. The clutch gear 34 is engaged with a drum drive motor 38 via idle gears 35, 36 and 37.
The above reduction gears C1 and C2 are also gears of the same shape,
Therefore, from the drum drive motor 38 to the idle gear 3
The drive characteristics seen from the rotation reference position transmitted to the downstream side via the reduction gears C1 and C2 by the drive force transmitted to the clutch gear 34 via 7, 36 and 35 are the same. Therefore, again from the reduction gear C1 to the reduction gear B
1. Rotational characteristics transmitted to the photosensitive drum 5-1 via the drum driving gear A1, and the reduction gear C2 to the reduction gear B
2, rotation characteristics transmitted to the photoconductor drum 5-2 via the drum drive gear A2, and the photoconductor drum 5 via the reduction gear C2, the reduction gear B3, and the drum drive gear A3.
The rotation characteristics transmitted to -3 are also the same when viewed from the rotation reference position.

On the other hand, a reduction gear C is provided between the reduction gear B4 corresponding to the photosensitive drum 5-4 and the drum drive motor 38.
4 is interposed, the large-diameter gear meshes with the motor shaft gear, and the small-diameter gear meshes with the large-diameter gear of the reduction gear B4. In this drive system, from reduction gear C4 to reduction gear B4,
The rotation characteristic transmitted to the photoconductor drum 5-4 via the drum drive gear A4 is the rotation transmitted from the reduction gear C1 or the reduction gear C2 to the photoconductor drum 5-1, 5-2 or 5-3. Idle gear 3 so that it has the same characteristics
Gear ratios between 7, 36 and 35 are set.

The gear of the drive rotation roller 1 for driving the paper transport belt 4 is connected to the drive shaft of the transport drive motor 65 via two idle gears 61 and 62 and two reduction gears 63 and 64. . Then, the pressure roller 19-1 of the fixing device 19 causes the idle gear 61 to move through the reduction gear 46.
It is connected to. As a result, the paper transport belt 4 and the fixing device 19 are simultaneously driven by the transport drive motor 65.

In such a structure, the image forming apparatus has a monochrome mode (first mode) for printing one color of black and a full color mode (second mode) for multicolor printing of full color.

FIGS. 3A and 3B are views for explaining the switching mechanism for printing in the full-color mode and for printing in the monochrome mode. Switching of the central portion of the image forming apparatus described above. The mechanism is enlarged and shown. Then, (a) of the same figure shows the state when printing in the full-color mode, and (b) of the same figure shows the state when printing in the monochrome mode.

As shown in FIGS. 1 (a) and 1 (b), a movable arm 41 extends between the upper circulation portion 4a and the lower circulation portion 4b of the sheet conveyance belt 4 in parallel with the conveyance direction. Are arranged. The movable arm 41 has a fixed support roller 42 at one end and a movable support roller 43 at the other end.

The fixed support roller 42 is rotatably fixed to a frame 45 of the apparatus main body by a support shaft 44. The fixed support roller 42 is provided in the vicinity of the upstream side of the image forming portion formed by the most downstream photosensitive drum 5-4 and the transfer brush 11. On the other hand, the movable support roller 43 on the free end side of the movable arm 41 is the uppermost photosensitive drum 5-.
The sheet conveying belt 4 is supported by abutting the inner peripheral surface of the sheet conveying belt 4 at a position between the image forming portion formed by 1 and the transfer brush 11 and the driven rotation roller 2.

A cam engaging portion 46 is provided below the movable arm 41.
Are formed so as to project laterally, and this cam engaging portion 46
On the other hand, the cam 47 is slidably in contact. Cam 47
Selectively 90 in the forward or reverse direction about the fulcrum 48.
The movable arm 41 is swung up and down as shown by a double-headed arrow A in the figure.

FIG. 7A shows the state when the cam 47 is rotated 90 degrees counterclockwise. At this time, the contact point of the cam 47 with the cam engaging portion 46 is the farthest point from the fulcrum 48, and the movable arm 41 is pushed up by the cam 47 and pivots (swings) in the upward direction to the upper position. It is localized. As a result, the movable arm 41 stretches the paper transport belt 4 (upper circulation portion 4a) between the drive rotation roller 1, the fixed support roller 42, and the movable support roller 43 so that all four photosensitive drums 5 are contacted. They are brought into contact with each other and moved to a transferable position with all four photosensitive drums 5.

In the movable arm 41, the three photoconductive drums 5 on the upstream side of the above-mentioned four transfer brushes 11 are provided.
Three transfer brushes 11 corresponding to 1, 5-2 and 5-3
Are integrally attached, and move in the same direction and by the same distance in correspondence with the moving paper transport belt 4 as the movable arm 41 swings. As a result, when the paper transport belt 4 is rotated upward as shown in FIG. 3A, the three transfer brushes 11 are connected to the three photoconductor drums 5-1, 5-2 and 5-3. , Face the transferable position. On the other hand, the transfer brush 11 corresponding to the most downstream photosensitive drum 5-4 is fixed to the frame 45 of the apparatus main body. This transfer brush 1
The reference numeral 1 always makes sliding contact with a portion of the sheet conveying belt 4 stretched between the drive rotation roller 1 and the fixed support roller 42, which are also fixed to the frame 45 of the main body of the apparatus, so that the photosensitive member is placed at the transferable position. It faces the drum 5-4. As a result, in the full-color mode, all four photoconductor drums 5 that transfer four color toners are set to a transferable state.

A tension roller 51 is arranged near the inner surface of the lower circulation portion of the paper transport belt 4 and closer to the drive rotation roller 1. The tension roller 51 is rotatably provided at the tip of a key-shaped arm 52, and
The rear end of 2 is rotatably supported by a frame 45 of the apparatus main body by a fulcrum 53. A pulling spring 54 is engaged between the central portion of the arm 52 and the frame 45 of the apparatus main body, and the pulling spring 54 biases the arm 52 in the downward direction of the drawing. As a result, the tension roller 51 supports the lower circulation portion of the sheet conveying belt 4 while always urging it so as to pull it downward, absorbs the bending of the sheet conveying belt 4, and drives and rotates the entire sheet conveying belt 4 with a predetermined tension. It is stretched between the roller 1 and the driven rotation roller 2. As a result, even when the sheet conveyance belt 4 is moved to the upper or lower position by the rotation of the movable arm 41, the sheet conveyance belt 4 is
It is always stretched and supported.

Referring again to FIG. 2, when the main body of the apparatus is turned on and full-color printing is designated, the switching mechanism is switched to the full-color mode transport state shown in FIG. 3 (a). When the number of sheets and other designations are input here, the sheet feed roller 18 feeds the sheet placed and accommodated in the sheet cassette 17 to the standby roll pair 12 through the conveyance path 16. Alternatively, the paper feed roller 13 feeds the paper P placed on the openable paper tray 15 to the standby roll pair 12. The fed paper P comes into contact with the standby roll pair 12 that is temporarily stopped, stops, and stands by for re-conveyance.

Then, the drive rotation roller 1 starts to rotate in the counterclockwise direction, and the driven rotation roller 2 is driven to start to rotate in the counterclockwise direction as well. Then, the sheet conveying belt 4 comes into contact with the four photoconductor drums 5 and the whole is circularly moved counterclockwise. In response to this, the photosensitive drum 5 is driven and rotated. The initialization charger applies a uniform charge to the peripheral surface of the photosensitive drum 5, and the optical writing head 8
The charged peripheral surface of the photosensitive drum is exposed in accordance with an image signal to form an electrostatic latent image on the peripheral surface of the photosensitive drum. Then, the developing roller transfers the toner to the low potential portion of the electrostatic latent image to form (develop) a toner image on the peripheral surface of the photosensitive drum.

At the timing when the leading edge of the toner image on the peripheral surface of the photosensitive drum 5 is rotationally conveyed to the point of opposition to the sheet conveyance belt 4, the print start position of the sheet P coincides with the point of opposition. The standby roll pair 12 starts rotating to start feeding the paper P. Paper P reaching the belt feed port
Is nipped and conveyed by the driven rotation roller 2 and the auxiliary roller 3 together with the sheet conveyance belt 4.

The paper P is the photosensitive drum 5 and the transfer brush 1.
While the toner image is sequentially transferred on the paper surface for each color by the electric field formed between the two, even after the trailing edge is released from the nip between the driven rotation roller 2 and the auxiliary roller 3, the transfer of the charge in the transfer portion causes It is electrostatically adsorbed well on the conveyor belt 4 and conveyed.

The sheet P on which the four color toner images of Y (yellow), M (magenta), C (cyan), and Bk (black) are transferred in this manner from the conveyor belt 4 by a separating claw (not shown). It is separated and carried into the fixing device 19.
The fixing device 19 is composed of a pressure contact roller, a heat generating roller, a peripheral surface cleaner, an oil applying roller, a thermistor, etc. which are assembled in a heat insulating casing, and heat-fixes the toner image transferred onto the paper P on the paper surface. While carrying the paper P.

The paper P, on which the toner image is heat-fixed by the fixing device 19, is moved by the paper ejection roll 21 from the rear paper ejection port 24 with the toner image upward or from the upper paper ejection port 26 with the toner image downward. The sheet is discharged to the outside of the machine and is stacked on a sheet discharge tray 27 formed behind the upper lid member 7.

As shown in FIG. 1 (b), the drum drive gears A1, A2, A3 and A4 are marked with marks 33-1,
Based on 33-2, 33-3, and 33-4, four photoconductor drums 5 (5-1, 5-2, 5-3, 5-4) are prepared in advance.
Of the drum drive gears A1, A2, A3, and A4 are meshed with the drum gears 31-1, 31-2, 31-3, and 31-4 so as to correspond to the transfer positions of the drum drive motors. The drive characteristics of the reduction gears B1, B2, B3, and B4 for transmitting the drive of No. 38 are similarly unified, and the drive is transmitted by the reduction gears C1, C2, and C3 so that the relative positions match at the same timing. It is set. Therefore, in the above-described full-color printing, the transfer positions of the four color toner images transferred in an overlapping manner do not shift.

On the other hand, when printing is performed in the monochrome mode, as shown in FIG. 3 (b), the cam 47 rotates 90 degrees clockwise from the position shown in FIG. 3 (a). At this time the cam 47
The point of contact with the cam engaging portion 46 is the closest point from the fulcrum 48, and the movable arm 41 rotates downward about the fulcrum 44 and is localized at the lower position. This movable arm 41
By the rotation of, the movable supporting roller 43 descends and is released from the contact with the sheet conveying belt 4. As a result, the upper circulation portion 4a of the sheet conveying belt 4 is stationary in position between the drive rotation roller 1 and the fixed support roller 42 and remains in contact with the photosensitive drum 5-4, and the fixed support roller 42 And the driven rotation roller 2 move obliquely downward to the upstream side in the paper transport direction, and are separated from the three upstream photosensitive drums 5-1, 5-2, and 5-3.

As described above, only the photosensitive drum 5-4 for forming an image of black toner, the transfer brush 11 corresponding to the photosensitive drum 5-4, and the portion of the conveyor belt 4 corresponding to the image forming portion (transfer portion) can be transferred. Maintained at. Then, the clutch of the clutch gear 34 is disengaged, the drive transmission from the drum drive motor 38 to the reduction gears C1 and C2 is interrupted, and only the photoconductor drum 5-4 is drive-transmitted to perform monochrome mode printing.

The sheet conveying belt 4 for the transfer portion for forming a black toner image is located between the drive rotation roller 1 and the fixed support roller 42, which are fixed in position on the frame 45 of the apparatus main body, and has a belt posture. Since it is always constant, it is not necessary to change the transfer timing in the transfer portion that forms the black toner image, the voltage control of the transfer brush 11 or the like in both the full color mode and the monochrome mode. Control such as optical writing by information can be performed by the same control method.

By the way, the respective drive systems of the photoconductor drums 5-1 to 5-3 corresponding to the color image are connected by the gears of the same shape via the clutch gear 34. Therefore, the relative position of the drum drive gears A1, A2, and A3 does not deviate at any time. However, when the monochrome mode printing is performed as described above, during this period, the drum drive gears A1, A2, and A3 stop rotating, and only the drum drive gear A4 rotates. Therefore, a relative position corresponding to the transfer position is displaced between the color image transfer part and the black image transfer part. Therefore, if the printer returns to the full-color mode and prints in the full-color mode, the correct printing cannot be performed.

In this embodiment, when the monochrome mode is restored to the full-color mode, the relative positions of the drum driving gears are automatically reset so that the transfer positions of the four colors are not displaced. This will be described below.

As shown in FIG. 1 (b), the drum drive gears A1, A2, A3 and A4 have marks 33 at the same position.
(33-1, 33-2, 33-3, 33-4) are engraved. Then, in the initial setting corresponding to the full color mode, the drum drive gears A1, A2, A3 and A4 are set.
Is its mark 33-1, 33-2, 33-3 and 33-
4, the drum gears 31-1, 31-2, and 3-4 are arranged so as to correspond to the transfer positions of the photosensitive drum 5 to be synchronized, respectively.
31-3 and 31-4 are in mesh with each other at optimum positions.
Further, as described above, the relative positions of the drum drive gears A1, A2, and A3 do not shift and always match.
Therefore, if adjustment is made so that the relative position of any one of the drum drive gears A1, A2, or A3 and the drum drive gear A4 is adjusted, the transfer positions of all four drum drive gears A1 to A4 are compared. The relative positions will match.

In the present embodiment, the drum drive gear A3
Positioning is performed by (32-3) and the drum drive gear A4 (32-4). First, the drum drive gear A3 is provided with a positioning protrusion 51 fixed to the outside in the diametrical direction at a position corresponding to the mark 33-3. Then, the sensor 52 is fixed to the frame 45 of the apparatus body at a position where the protrusion 51 should be detected. The positions of the drum drive gears A1 to A3 when the sensor 52 detects the protrusion 51 are set as the reference position (initial setting position) in the full color mode.

On the other hand, the drum drive gear A4 is provided with a positioning projection 53 projecting outward in the diametrical direction at a proper position. Then, when the drum drive gear A4 is at the reference position (initial setting position) in the full color mode, the sensor 54 is fixed to the frame 45 of the apparatus main body at a position where the protruding piece 53 should be detected.

As described above, when the monochrome mode ends and the color mode returns to the full-color mode, first, the drive control unit (not shown) engages the clutch of the clutch gear 34 and drives the drum drive motor 38 to drive the drum. The drive gears A1 to A4 are rotated. Then, the sensor 52 is the protrusion 5.
When 1 is detected, driving is stopped once. As a result, the reference positions of the drum drive gears A1 to A3 are set.

Next, the clutch of the clutch gear 34 is disengaged, and the drum drive motor 38 is driven again. This allows
Only the drum drive gear A4 rotates. And sensor 5
When 4 detects the protrusion 53, the drive of the drum drive motor 38 is stopped. As a result, the drum drive gear A4 is
Set to the reference position. That is, four drum drive gears A
All of 1 to A4 are set to the reference position, and the relative position corresponding to the transfer position is the same in all image forming units. As a result, printing in the full car mode can be performed.

As described with reference to FIG. 2, the rotation characteristics transmitted to the photosensitive drum 5-4 are the same as those of the photosensitive drum 5-1.
Although the gear ratio between the idle gears 37, 36 and 35 is set so as to be the same as the rotation characteristic transmitted to 5-2 or 5-3, the relative position may shift after a long period of use. May occur. Therefore, as described above, the reference position may be reset not only when the monochrome mode ends but also when a certain operating time elapses.

Further, although the projecting piece 51 of the drum drive gear A3 is arranged at a position corresponding to the mark 33-3, the mark 33 is provided.
(33-1, 33-2, 33-3, 33-4) is for initializing the relative position between the drum drive gear and the photoconductor drum, and is always a position that coincides with the mark 33-3. It is not necessary to dispose the projecting piece 51 in. The projecting piece 51 and the sensor 52 may be arranged at a detectable position in the initial setting position of the drum drive gear.

[0051]

As described above, according to the present invention,
Since the reference position of each gear related to the drum drive can be automatically reset, fluctuations in the transfer position of the photoconductor drum due to uneven rotation of each gear related to the drum drive and uneven rotation due to uneven meshing accuracy can be automatically performed. It is possible to restore the correct position, and therefore, even in an apparatus having a switching between the monochrome mode and the color mode, it is possible to maintain the initial setting state of the drive system gear and always perform stable image formation. Similarly, since the reference position of each gear related to drum driving can be automatically reset, the monochrome driving system and the color driving system which are triggered by the switching mechanism between the monochrome mode and the color mode during the long-term use period are generated. Relative displacement of the system can be automatically corrected, and therefore stable image formation can be always performed even in long-term use.

[Brief description of the drawings]

FIG. 1A is a plan view showing the arrangement and engagement of a photosensitive drum and a drum drive gear according to an embodiment, and FIG. 1B is a side view thereof.

FIG. 2 is a side view showing a drive system of an image forming apparatus including the photosensitive drum and the drum drive gear of FIG.

3A and 3B are enlarged views of a switching mechanism in a central portion of the image forming apparatus, FIG. 3A is a diagram showing a state when printing in a full color mode, and FIG. 3B is a state showing a state when printing in a monochrome mode. FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Drive rotation roller 2 Followed rotation roller 3 Auxiliary roller 4 Paper conveyance belt (conveyance means) 5 (5-1, 5-2, 5-3, 5-4) Photoconductor drum 6 (6-1, 6-2, 6-3, 6-4) Case 7 Upper lid member 8 (8-1, 8-2, 8-3, 8-4) Optical writing head 9 Spindle 11 Transfer brush (transfer means) 12 Standby roll pair 13 Supply Paper roller 14 Separation member 15 Openable paper tray 16 Conveyance path 17 Paper cassette 18 Paper feed roller 19 Fixer 19-1 Pressure contact roller 21 Paper ejection roll 22 Switching lever 23 Ejection path 24 Paper ejection port 25 Paper ejection roll pair 26 Upper ejection Paper mouth 27 Paper ejection trays 31-1, 31-2, 31-3, 31-4 Drum gears 32-1 (A1), 32-2 (A2), 32-3 (A
3), 32-4 (A4) drum drive gear B1, B2, B3, B4, C1, C2, C4 reduction gear 33 (33-1, 33-2, 33-3, 33-4) mark 34 clutch gear 35 , 36, 37 Idle gear 38 Drum drive motor 41 Movable arm 42 Fixed support roller 43 Movable support roller 44 Support shaft 45 Frame 46 Cam engagement part 47 Cam 48 Support point 51, 53 Sensor 52, 54 Projection piece

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[Procedure amendment]

[Submission date] March 1, 1996

[Procedure amendment 1]

[Document name to be amended] Drawing

[Correction target item name] Figure 3

[Correction method] Change

[Correction contents]

[Figure 3]

Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI Technical display location G03G 21/00 380 G03G 21/00 372

Claims (2)

[Claims] 1. A plurality of image carriers arranged in parallel, an image carrier gear fixed to each of the plurality of image carriers, and a drive device provided corresponding to each of the image carrier gears so as to mesh with each other. A plurality of driving gears for transmitting, a plurality of toner image forming means for individually forming toner images of a predetermined color on the plurality of image carriers, and a transfer material for at least one of the plurality of image carriers And a plurality of transporting means for transporting the transfer material to bring the transfer material into contact with each other, and a plurality of transfer means for transferring the toner image to the transfer material in contact with the image carrier, the transfer means being arranged so as to correspond to the plurality of image carriers. A plurality of image carrier gears and a plurality of drive gears, which have the same shape processed by the same molding die and are marked, and the plurality of image carriers are based on the marks. Corresponding to the distance between the bodies, the relative phase of the image carrier is In the image forming apparatus assembled so as to be the same, the transfer material is conveyed by the conveying means while the image forming step related to the first image carrier of the plurality of image carriers is executed. A first mode in which the transfer material is conveyed so as to contact only the carrier, and a second mode in which the transfer material is conveyed so as to contact all the image carriers while executing the image forming process related to all the image carriers. Control means for controlling switching to the first image carrier, first detecting means for detecting a position of the drive gear corresponding to the first image carrier, the position being associated with the mark, and a predetermined image carrier other than the first image carrier. Second detection means for detecting a position of the drive gear corresponding to the mark, and at least when the control means switches from the first mode to the second mode. Detection result An image forming apparatus comprising: a relative phase correction unit that drives a predetermined drive gear to correct the shift of the relative phase of the image carrier based on the above. 2. A toner image forming unit corresponding to the first image carrier is a unit for forming a black toner image on the image carrier, and a toner image forming unit corresponding to another image carrier is provided. The image forming apparatus according to claim 1, which is means for forming a colored toner image.