JP3317466B2 - Color image forming equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rotationally driven image carrier and a plurality of electrostatic latent images sequentially formed on the carrier, each having a different color toner image. The present invention relates to a color image forming apparatus including a plurality of developing units for visualizing an image.

[0002]

2. Description of the Related Art A color image forming apparatus of the above-mentioned type is constructed as, for example, a color copying machine, a color facsimile or a color printer. In any case, different color toners are formed on an image carrier. Images are sequentially formed, and the toner images are superimposed on each other and transferred onto a transfer material directly or via an intermediate transfer member to obtain a color image. When the toner images of each color on the image carrier are transferred to the transfer material via the intermediate transfer body, the toner images of each color on the image carrier are sequentially transferred onto the intermediate transfer body such that they overlap each other. After a color image is once obtained on the intermediate transfer body, this is collectively transferred to a transfer material. When the toner image on the image carrier is directly transferred to the transfer material, the different color toner images sequentially formed on the image carrier are sequentially transferred onto the transfer material such that they overlap each other.

As described above, in each case, a color image in which toner images of different colors are superimposed on each other is formed on a transfer material. An electrostatic latent image for each color toner image is formed on an image carrier. When forming on the top, if the surface linear velocity of this image carrier fluctuates even slightly, corresponding to the speed fluctuation,
Because each electrostatic latent image expands and contracts, the toner images of each color transferred on the transfer material slightly shift from each other, thereby causing a color shift in the color image, which appears as uneven color and uneven density, Significantly degrades the quality of color images.

[0004] Each gear of the drive system for driving the image carrier may be slightly eccentric or its tooth profile may not be formed correctly as designed, thereby causing the image carrier to rotate during its rotation. This causes a speed fluctuation, and causes the above-described problem.

In view of this, the number of teeth of the gear train constituting the drive system of the image carrier is set so that the ratio of the number of teeth of the gears meshing with each other is an integer. An image forming apparatus has been proposed in which any electrostatic latent image starts to be formed from the same position on the image carrier so that the leading end of the electrostatic latent image is located at the same position on the image carrier (for example, And JP-A-1-307774. According to this configuration, the speed fluctuations of the image carriers that occur when forming the electrostatic latent images for the toner images of the respective colors can be aligned in the same pattern, and the occurrence of color misregistration can be effectively suppressed. Can be. That is, when each electrostatic latent image is formed, its electrostatic latent image slightly expands and contracts locally due to the speed fluctuation of the image carrier. The latent images can be aligned in the same state. If the toner images of each color formed from such an electrostatic latent image are superimposed and transferred to a transfer material, a high-quality color image without color shift can be obtained. In this way, eccentricity and the like for each gear constituting the drive system for the image carrier,
Even if there is a defective tooth profile, a color image without color shift can be obtained.

However, according to the study by the present inventor, it has become clear that the cause of the speed fluctuation in the image carrier is not only the eccentricity of the gear of the driving system and the defective tooth profile. That is, this type of color image forming apparatus is provided with an image forming element that rotates while being in contact with the image carrier, and when such an image forming element is attached in an eccentric state, for example, When the imaging element rotates, it exerts a periodically fluctuating external force on the surface of the image carrier, which causes a speed variation on the image carrier, and finally causes a color shift on the color image formed on the transfer material. This causes uneven color and uneven density.

The image forming element is manufactured so that the image forming element does not apply a fluctuating load to the image carrier when the image forming element rotates.
Further, if this is brought into contact with the image carrier, the occurrence of the above-mentioned color shift can be prevented. However, it is not only technically difficult to construct the image forming element in this way, but also the cost is increased. This is not a good solution.

[0008]

SUMMARY OF THE INVENTION The present invention has been made based on the above-described novel recognition, and an object of the present invention is to provide an image forming element which rotates while being in contact with an image carrier. Even if you apply an external force that fluctuates periodically,
It is an object of the present invention to provide a color image forming apparatus capable of effectively suppressing the occurrence of color shift in a color image due to this.

[0009]

According to the present invention, in order to achieve the above object, an image carrier which is driven to rotate and a plurality of electrostatic latent images sequentially formed on the carrier are provided in different colors. A plurality of developing units that visualize the toner images as toner images of different colors depending on the type of toner. Also starts to form from the same position on the image carrier, and in a state where the visible images sequentially formed on the image carrier are superimposed, directly or via an intermediate transfer body, is transferred onto a transfer material to obtain a color image. In the color image forming apparatus, the number of rotations per unit time of at least one image forming element that rotates while being in contact with the surface of the image carrier and exerts a periodically fluctuating external force on the surface of the image carrier. The ratio of the image carrier to the number of rotations per unit time is adjusted. The number of rotations per unit time is set so that the image forming element contacts the surface of the image carrier in order to remove toner remaining on the image carrier after transfer of the visible image. A color image forming apparatus characterized in that it is a cleaning brush that rotates while being in contact with the color image forming apparatus.

[0010]

[0011]

[0012]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a schematic sectional view showing the entire structure of a color copying machine as an example of a color image forming apparatus according to the present invention, FIG. 2 is an enlarged view of a part thereof, and FIG. 5 is a timing chart showing an operation example of a color copying machine.

The color copying machine shown in FIG. 1 has a color image reading section 1 and a color image recording section 2 located below the color image reading section 1. The contact glass 4 is fixed. An original 5 is placed on the upper surface of the contact glass 4, and the original 5 is pressed onto the contact glass 4 by a pressure plate (not shown).

An illumination lamp 6 is provided inside the main body case 3.
A color scanner 21 including first to third mirrors 7, 8, 9 and an imaging lens 10 is arranged. When the operator operates a print key on an operation unit (see FIG. 5) not shown in FIGS. 1 and 2, a print start signal is generated as shown in FIG. Is started. That is, after the generation of the print start signal, the scanner start signal shown in FIG. 3B is generated, whereby the scanner motor (see FIG. 5) not shown in FIGS. The illumination lamp 6 and the first mirror 7 shown in FIG. 1 and the second and third mirrors 8 and 9 respectively move to the left in FIG. 1 at a speed ratio of 2: 1.

At this time, the light from the illumination lamp 6 illuminates the original 5, and the reflected light images thereof are first to third mirrors 7, 8, and 9.
, And passes through the imaging lens 10 such as a CCD
An image is formed on a color sensor 11 composed of a photoelectric conversion element such as the one shown in FIG. In this way, the color image information of the original 5 is read for each of the blue, green and red color separation lights, and these are converted into electric signals (color separation image signals). Then, based on the intensity levels of these color-separated image signals, the image processing unit performs color conversion processing,
Black, cyan, magenta and yellow color image data are obtained. Reading of such image data is performed for each of black, cyan, magenta, and yellow, as described later. This means that four first to fourth scanner start signals are shown in FIG. 3B.

On the other hand, the color image recording section 2 converts the above-described black, cyan, magenta and yellow color image data into optical signals, and respectively corresponds to a black toner image, a cyan toner image, a magenta toner image and a yellow toner image. A toner image was obtained as described below, and
A full-color image is formed. In this example,
As described later, a black toner image, a cyan toner image,
Although a visible image is formed in the order of the magenta toner image and the yellow toner image, the formation order of the toner images can be appropriately selected and set.

In FIG. 1, a writing optical unit 13 provided in a main body case 12 of the color image forming section 2 is provided.
Has a laser 14, from which a laser beam L light-modulated corresponding to each of the above-described color image data is emitted, and the laser beam is reflected by a polygon mirror (rotating polygon mirror) 16. . This polygon mirror 16
Has a plurality of reflecting mirrors, is rotationally driven by a motor (hereinafter, referred to as a polygon motor) 15, and has a laser beam L.
Is reflected by the reflecting mirror of the polygon mirror 16, and f
The light passes through the / θ lens 17, is reflected by the reflection mirror 18, and emerges from the case 19 of the writing optical unit 13. The laser beam L emitted from the case 19 in this manner is applied to the drum-shaped photosensitive member 2 which is an example of an image carrier that is driven to rotate.
Exposure of the 0 surface.

Here, a more specific configuration of the color image recording unit 2 will be clarified while describing details of the image forming operation. First, when the copy operation is started by operating the print key as described above, the scanner motor is activated by the first scanner start signal, and the illumination lamp 6 and the mirror 7 of the color scanner 21 are operated, as described above.
Documents 8 and 9 move forward, and original 5 is illuminated and scanned. As a result, the color image information of the original 5 is read. At this time, first, in this example, black color image data is obtained. With the start of the copying operation, the color image reading section 1 starts reading black image data at a predetermined timing. Illumination lamp 6 after going forward
And the mirrors 7, 8, and 9 move back and return to the home position shown in FIG.

On the other hand, the photosensitive member 20 is driven to rotate in a counterclockwise direction (the direction of arrow A) in FIGS. 1 and 2 by a driving device described later, and the surface of the photosensitive member 20 is fixed by a charging roller 22 as an example of a charging unit. Is uniformly charged. A laser beam L light-modulated based on the black image data obtained as described above is emitted from the laser 14 of the writing optical unit 13, and the laser beam L is emitted from the photoconductor 20 already charged by the charging roller 22. The surface is exposed as described above, and an electrostatic latent image corresponding to the black image data is formed on the photoconductor. “Image data writing” shown in FIG. 3C means formation of this electrostatic latent image, and “Bk data” indicates formation of an electrostatic latent image corresponding to black image data. In the following description, when it is necessary to distinguish this electrostatic latent image from other latent images, it will be referred to as a black latent image.

As shown in FIG. 2, four developing units 23Bk, 23Y, 23M and 23 are provided around the photosensitive member 20.
C is provided. These developing units visualize the electrostatic latent image formed on the photoconductor 20 as a black toner image, a yellow toner image, a magenta toner image, and a cyan toner image, respectively, as described later. In the following description, when it is necessary to distinguish these developing units, they will be referred to as a black developing unit 23Bk, a yellow developing unit 23Y, a magenta developing unit 23M, and a cyan developing unit 23C.

As shown in FIG. 2, the black developing device 23Bk includes a developing case 24Bk containing a developer (not shown), a developing sleeve 25Bk that is driven to rotate against the photosensitive member 20, and a developing case 24Bk. And a fixed magnet (not shown) provided inside the developing sleeve 25Bk for stirring the developer therein and supplying the developer to the developing sleeve 25Bk. The case 24Bk contains a black developer.

Here, a powdery two-component developer having a black toner and a carrier is used as the developer, but a one-component developer containing no carrier may be used. Such a developer is carried on the developing sleeve 25Bk by the magnetic force of the fixed magnet, and is conveyed by the rotation of the sleeve 25Bk. The black electrostatic latent image is visualized as a black toner image by the black toner of the developer carried on the developing sleeve 25Bk in the developing area 70Bk which is the area where the developing sleeve 25Bk and the photoconductor 20 face each other. You. Immediately before the leading end of the black latent image in the rotation direction of the photoconductor 20 reaches the developing area 70Bk, the developing sleeve 2
5Bk starts to rotate and turns the black latent image into a black toner image as described above. After the rear end of the black latent image in the rotation direction of the photoconductor 20 has passed through the developing area 70Bk, the electrostatic latent image for the next cyan toner image described later reaches the developing area 70Bk of the black developing device 23Bk. Before the development, the developing sleeve 25Bk rotates in the reverse direction to cut off the developer on the surface of the developing sleeve 25Bk, thereby bringing the developing operation into a non-operation state. 3E shows the operating state of the developing sleeve 25Bk of the black developing device 23Bk described above, and “Bk developing” indicates that the black latent image can be used as a black toner image as described above. It shows that it is visualized.

The other developing units 23Y, 23M, and 23C are configured in the same manner as the black developing unit 23Bk, except that each developing case contains a developer having a yellow toner, a magenta toner, and a cyan toner, respectively. The operation during the development is the same as that of the black developing device 23Bk. Therefore, parts corresponding to the respective elements of the black developing device 23Bk are denoted by Y, M, and C instead of Bk of the reference numerals assigned to the black developing device, and the description thereof is omitted. When one of the four developing units is performing the developing operation, the other developing unit does not perform the developing operation.

Here, "C developing sleeve", "M developing sleeve", and "Y" in (f), (g) and (h) of FIG.
"Developing sleeve" indicates the developing sleeves 25C, 25M, and 25Y of the cyan developing device 23C, the magenta developing device 23M, and the yellow developing device 23Y, and "C developing", "M developing", and "Y developing" respectively. Rotate to perform the developing operation.

As described above, the three developing devices 23Y and 23
M and 23C are set in the development inactive state, and the black developing device 23
By operating only Bk, the black latent image formed on the photoconductor 20 is visualized as a black toner image. This black toner image is transferred to the surface of an intermediate transfer belt 27 which is an example of an intermediate transfer member. You.

The intermediate transfer belt 27 is configured as an endless belt wrapped around a driving roller 28, a transfer bias roller 29, and a driven roller 30, and a belt cleaning blade around the belt cleaning blade, which is an example of an intermediate transfer member cleaning element. A belt cleaning device 32 having a transfer roller 31 and a transfer roller 33 are provided.
The belt cleaning blade 31 and the belt cleaning blade 31 can be freely moved toward and away from the intermediate transfer belt 27 by a contacting / separating device (see FIG. 5) composed of, for example, a solenoid not shown in FIGS. Further, the transfer bias roller 29 and the driven roller 30 are also located at a position where the intermediate transfer belt 27 is brought into contact with the photoconductor 20 as shown in FIGS. It is operable between a retracted position where the intermediate transfer belt 27 is retracted and the intermediate transfer belt 27 is separated from the photoconductor 20. Belt cleaning device 32
Belt cleaning blade 31 and transfer roller 33
The contact timing of the intermediate transfer belt 27 with the intermediate transfer belt 27 and the timing of the intermediate transfer belt 27
These are as shown in (l), (k) and (j) of FIG. 3, respectively. When the belt cleaning device 32 has a cleaning element other than the belt cleaning blade 31, for example, a fur brush, the fur brush is also moved toward and away from the intermediate transfer belt 27 together with the belt cleaning blade 31.

The black toner image formed on the photoreceptor 20 as described above is transferred to the intermediate transfer belt 27.
During this transfer, the intermediate transfer belt 27 abuts on the photoconductor 20 and is driven to rotate in the direction of arrow B (FIG. 2) at the same surface linear speed as the surface of the photoconductor 20, but the belt cleaning blade 31 and the transfer roller 33 Is separated from the intermediate transfer belt 27. Hereinafter, the direction B of the intermediate transfer belt 27
Is referred to as forward movement as necessary, and rotation in the opposite direction is referred to as backward movement. The transfer of the toner image from the photoconductor 20 to the intermediate transfer belt 27 is referred to as “intermediate transfer”, and a contact portion between the photoconductor 20 and the intermediate transfer belt 27 where the intermediate transfer is performed is defined as an intermediate transfer unit 34. I will call it. Such an intermediate transfer is performed by applying to the transfer bias roller 29 a bias voltage having a polarity opposite to the charging polarity of the toner on the photoconductor 20. When the black toner image on the photoconductor 20 passes through the intermediate transfer section 34, the toner image is intermediately transferred to the surface of the intermediate transfer belt 27 by the action of the bias voltage.
“Bk transfer” in FIG. 3I indicates the intermediate transfer of this black toner image.

The toner remaining on the surface of the photoconductor 20 that has passed through the intermediate transfer unit 34 is cleaned by an image carrier cleaning device (hereinafter, referred to as a photoconductor cleaning device according to the configuration of this embodiment) 35. The illustrated photoconductor cleaning device 35 includes a cleaning brush 36, which is an example of a cleaning member, and a cleaning blade 37, which come into contact with the photoconductor 20 to clean and remove toner remaining on the surface thereof. The surface of the photoconductor 20 from which the residual toner has been cleaned is subjected to a charge removing operation by a charge removing lamp 38 which is an example of a charge removing device, and is initialized.

Next, the illumination lamp 6 and the mirrors 7, 8, and 9 of the color scanner 21 move forward again by the second scanner signal (FIG. 3B), and the same illumination scanning as described above is performed. Done. At this time, in this example, cyan color image data is obtained, and a laser beam L light-modulated based on the cyan image data is emitted from the laser 14. This laser beam is charged by the charging roller 22 and exposes the surface of the photoconductor 20 which continues to rotate counterclockwise to form an electrostatic latent image corresponding to cyan image data on the surface. “C data” in FIG. 3C indicates the formation of this electrostatic latent image. Hereinafter, such an electrostatic latent image will be referred to as a cyan latent image as necessary. The cyan latent image is exactly the same as the black latent image,
The image is visualized as a cyan toner image by 3C.

The developing sleeve 25C of the cyan developing unit 23C
After the rear end of the previous black latent image has passed through the developing area 70C where the sleeve 25C and the photoconductor 20 are opposed, and before the leading end of the cyan latent image reaches this developing area. Then, the developing operation is started by starting the rotation, whereby the visualization of the cyan latent image is executed.
After the rear end of the cyan latent image has passed through the developing area 70C and before the electrostatic latent image for the next magenta toner image arrives at the developing area 70C, the cyan developing device 23C does not perform development. The state is the same as in the case of the black developing device 23Bk.

The cyan toner image formed on the photoreceptor 20 as described above is superimposed on the already transferred black toner image in the same manner as in the case of the black toner image, and is subjected to intermediate transfer. The intermediate transfer is performed on the belt 27 (“C transfer” in FIG. 3I). The surface of the photoreceptor after the intermediate transfer of the cyan toner image is cleaned by the photoreceptor cleaning device 35 and subjected to the charge removing operation by the charge removing lamp 38 is exactly the same as the case of the black toner image.

Then, exactly as described above,
Magenta color image data is obtained, and the photosensitive member 20 is exposed by a laser beam modulated based on the magenta color image data to form an electrostatic latent image (magenta latent image) on the photosensitive member 20 (FIG. 3C). "M data"). The magenta latent image is visualized as a magenta toner image by a magenta developing device 23M, and is superimposed on a black toner image and a cyan toner image on the intermediate transfer member 27 and is intermediately transferred (“M transfer” in FIG. 3 (i)). )).

Subsequently, in the same manner as described above, yellow color image data is obtained, and the photosensitive member 20 is exposed by a laser beam light-modulated based on the color image data.
An electrostatic latent image (yellow latent image) is formed on the photoconductor 20 (see FIG. 3).
(“Y data” in (c)). Then, this yellow latent image is visualized as a yellow toner image by the yellow developing unit 23Y, and the yellow latent image is intermediately transferred onto the intermediate transfer belt 27 while being superimposed on the three color toner images (FIG. 3).
(I) “Y transfer”).

As described above, on the intermediate transfer belt 27, intermediately transferred toner images of different colors are sequentially superimposed, and a full-color image composed of toner images of four colors is formed on the surface thereof. The intermediate transfer belt 2
7 executes the following operation for intermediate transfer of each toner image.

As described above, the black toner image on the photosensitive member 20 is first intermediately transferred onto the intermediate transfer belt 27.
After the completion of the intermediate transfer of the black toner image, the transfer bias roller 29 and the driven roller 30 move rightward in FIGS. 1 and 2 to separate the intermediate transfer belt 27 from the photoconductor 20 ((j in FIG. 3). )reference). The intermediate transfer belt 27 stops rotating in the direction of arrow B, that is, the forward movement, and simultaneously returns at high speed in the direction of arrow C.
It moves backward at a high speed in the direction of arrow C opposite to the direction of arrow B (see (i) of FIG. 3). By this return operation, the leading end of the black toner image on the intermediate transfer belt 27 (the leading end when the intermediate transfer belt 27 is viewed in the rotation direction of the arrow B) passes through a portion corresponding to the intermediate transfer unit 34. The intermediate transfer belt 27 stops and waits at a distance from the substantial portion by a predetermined distance.

Next, when the leading end of the cyan toner image on the photosensitive member 20 reaches a predetermined position before the portion corresponding to the intermediate transfer section 34, the intermediate transfer belt 27 starts to move forward in the direction of arrow B again. The intermediate transfer belt 27 is
1 and 2 as shown in FIGS. 1 and 2 (FIG. 3).
(I) and (j)). In this way, the cyan toner image is intermediately transferred onto the intermediate transfer belt 27.
In this case, the rotation of the intermediate transfer belt 27 and the timing of contact with the photoconductor 20 are performed so that the cyan toner image is accurately superimposed on the black toner image that has already been intermediately transferred onto the intermediate transfer belt 27. Is controlled.

Subsequently, exactly as described above,
The rotation of the intermediate transfer belt 27 and the operation of contacting and separating from the photoconductor 20 are controlled, so that the magenta toner image and the yellow toner image formed on the photoconductor 20 are sequentially intermediate-transferred onto the intermediate transfer belt 27. In this way, 4
A full-color image in which the color toner images are superimposed is obtained. After the fourth color yellow toner image is intermediately transferred to the intermediate transfer belt 27, the intermediate transfer belt 27 does not return but continues to move in the direction of arrow B at the same speed.

On the other hand, the plurality of paper feed units 40 and 4 shown in FIG.
A transfer material 43 made of transfer paper having different sizes is stored in one paper feed tray, and a transfer material 43 such as OHP paper or thick paper is stored in another paper feed unit 42. The transfer material 43 of the size or the material designated by the operation unit is supplied to one of the paper feeding units 40, 41, and 42.
From the intermediate transfer belt 27 and the transfer roller 33 at a predetermined timing by the rotation of the registration roller 44 by the rotation of the registration roller. Sent to. At this time, the transfer roller 33 moves the intermediate transfer belt 2 via the transfer material 43 by the operation of the above-described contact / separation device.
7 is pressed against and abuts on the intermediate transfer belt 2 by the action of the bias voltage applied to the transfer roller 33.
The superimposed full-color images of the four colors on 7 are collectively transferred onto the transfer material 43. Following the intermediate transfer from the photoconductor 20 to the intermediate transfer belt 27, the transfer material 43
The final transfer is performed.

The transfer material 43 to which the four color superimposed toner images have been collectively transferred from the intermediate transfer belt 27 is conveyed to a fixing device 47 by a conveying device 46, and a fixing roller 47a and a pressure roller 47b controlled to a predetermined temperature. The toner image is fixed on the transfer material by the action of heat and pressure. The transfer material that has passed through the fixing device 47 is discharged out of the apparatus and stacked on a copy tray 48.

On the other hand, the cleaning blade 31 of the belt cleaning device 32 comes into pressure contact with the intermediate transfer belt 27 at a predetermined timing after the yellow toner image of the final color is intermediately transferred from the photosensitive member 20 to the intermediate transfer belt 27, and
The toner remaining on the intermediate transfer belt 27 after the color superimposed toner image is finally transferred to the transfer material 43 is cleaned and removed. After the completion of the cleaning operation, the belt cleaning blade 31 separates from the intermediate transfer belt 27 at a predetermined timing. Such a contact / separation operation may be performed such that the entire belt cleaning device 32 approaches or separates from the intermediate transfer belt 27,
Only the belt cleaning blade 31 may be moved toward and away from the intermediate transfer belt 27.

At the time of repeat copying, following the above-described step of forming the fourth color yellow toner image in the first sheet copying operation, the color image reading unit 1 performs the second sheet copying operation at a predetermined timing. The operation and the formation of the toner image on the photoconductor 20 are executed. After the four-color superimposed full-color image on the intermediate transfer belt 27 is finally transferred collectively to the first transfer material 43, the second sheet is transferred to the area of the intermediate transfer belt 27 cleaned by the belt cleaning device 32. Control is performed so that the black toner image is intermediately transferred, and thereafter, the same operation as the copying operation for the first sheet is performed.

As described above, the illustrated color copier is
The rotatable photoconductor 20 and a plurality of electrostatic latent images (a black latent image, a cyan latent image, a magenta latent image, and a yellow latent image) sequentially formed on the photoconductor 20 are separated from each other by different colors. A plurality of developing units (black developing unit 23Bk, cyan developing unit 23C, and a plurality of developing units) that visualize as toner images (black toner image, cyan toner image, magenta toner image, and yellow toner image) of different colors depending on the toner.
The magenta developing device 23M and the yellow developing device 23Y) are provided, and the visible images (toner images) sequentially formed on the photoconductor 20 are transferred onto the transfer material 43 via the intermediate transfer belt 27 in an overlapping state. Thus, a full-color image is obtained on the transfer material 43.

When the respective visible images sequentially formed on the photosensitive member 20 are directly transferred onto a transfer material in a state of being superimposed, for example,
The transfer material may be clamped on a holding body such as a holding drum, and the visible images on the photoreceptor may be transferred onto the transfer material while sequentially superimposing them, and a color image may be formed on the transfer material. In this case, no intermediate transfer member is required.

FIG. 4 shows an example of a driving system for driving the photosensitive member 20 to rotate.
Drive motor 49 consisting of a brushless motor controlled by L
And a first intermediate gear 51 meshing with the motor shaft gear 50
A second intermediate gear 52 that is concentric with the gear 51 and rotates integrally therewith; a third intermediate gear 53 that meshes with the second intermediate gear 52;
And a photoreceptor shaft gear 55 fixed to the photoreceptor 20.
It is driven to rotate counterclockwise, that is, in the direction of arrow A, via a gear train consisting of 1, 52, 53 and 55.

Here, if each of the above-mentioned gears is mounted eccentrically or if there is a tooth profile defect, even if the drive motor 49 rotates at a constant speed, a small amount of A speed fluctuation occurs, and correspondingly, each electrostatic latent image formed on the photoconductor 20 slightly expands and contracts. Therefore, when such electrostatic latent images are visualized as toner images of different colors, and these are intermediate-transferred onto the intermediate transfer belt 27, a color shift may occur in the full-color image.

Therefore, in this example, as is known per se,
The number of each tooth is set so that the gear ratio of the meshing gears constituting the gear train described above is an integer. Here, the ratio of the number of teeth is the ratio of the number of teeth of the large-diameter gear and the small-diameter gear of the gear pair that mesh with each other. That is, when considering a large gear and a small gear that mesh with each other, this is a value obtained by dividing the number of teeth of the large gear by the number of teeth of the small gear. When the number of teeth of both gears is equal to each other, the ratio of the number of teeth is 1 It is. All such tooth ratios are set to integers.

With this configuration, the photosensitive member 2
When 0 makes one rotation, each gear 50, 51, 52, 53,
The total number of revolutions of 55 is always an integral number. In this embodiment, in addition to the above configuration, the leading ends of the respective electrostatic latent images (black latent image, cyan latent image, magenta latent image, and yellow latent image) for the toner images of the respective colors are located at the same position on the photoconductor 20. As described above, each electrostatic latent image is configured to start to be formed from the same position on the photoconductor 20. For example, assuming that a black latent image is formed from a fixed start position on the photoreceptor 20 indicated by a reference symbol W in FIG. 4, other cyan latent images, magenta latent images, and yellow latent images are also formed at the start positions. W, whereby the leading end of each latent image when viewed in the rotation direction of the photoconductor 20 always coincides with the start position W.

With the above configuration, when the photosensitive member 20 rotates, the driving gears 50, 51, 52,
Based on the eccentricity of 53 and 55 and the defective tooth shape,
When the speed fluctuation occurs, the speed fluctuation pattern is made uniform when forming the electrostatic latent images for the toner images of the respective colors on the photoconductor 20. Thereby, the transfer material 43
, The occurrence of color misregistration in the four-color superposed toner image, that is, the full-color image, can be effectively suppressed.

In this example, when the length of the transfer material 43 used in the feed direction (transfer material size) is reduced, more specifically, the A4 size transfer material 43 is laterally fed and a full-color image is formed on its surface. When forming or using a transfer material having a smaller length in the feeding direction, each of the electrostatic latent images (black latent image, cyan latent image, magenta latent image or yellow latent image) is formed. When a large-sized full-color image is formed on the surface of the photosensitive member 20 by using a transfer material having a large length in the feeding direction such as a double letter size, the photosensitive member 20 is formed by two rotations. While rotating, each electrostatic latent image is formed. That is, each electrostatic latent image is formed each time the photoconductor 20 makes one or more rotations. In each case, the gears 50, 51, It is possible to prevent the occurrence of color misregistration in the full-color image due to the speed variation of the photoconductor due to the eccentricity of the 52, 53, and 55 and the defective tooth profile, and a high-quality full-color image can be formed on the transfer material 43. FIG. 3 is a timing chart when a copying operation is performed by laterally feeding an A4 size transfer material.

In the example shown in FIG. 4, the rotation speed is reduced to 1/12 from the motor shaft gear 50 to the first intermediate gear 51, and further reduced to 1/2 from the second intermediate gear 52 to the third intermediate gear 53.
And the speed from the third intermediate gear 53 to the photoreceptor shaft gear 55 is further reduced to 1/2, and further reduced to 1/48 in total.
More specifically, the number of teeth of the motor shaft gear 50 is 11,
The number of teeth of the first intermediate gear 51 is set to 132, the number of teeth of the second intermediate gear 52 is set to 20, the number of teeth of the third intermediate gear 53 is set to 40, and the number of teeth of the photoreceptor shaft gear 55 is set to 80. In this way, the gear ratios of the gears meshing with each other are all set to integers.

Also, in this example, (b), (c),
The scanner start signal shown in (d), the timing of starting formation of each electrostatic latent image on the photoconductor 20, that is, the signal of image data writing start timing, and the transfer reference as a reference for starting the forward movement of the intermediate transfer belt 27. All of the signals are controlled to occur based on the same reference signal. That is, FIG. 5 is a block diagram of a main part of the above-described color copying machine. In FIG. 5, the polygon synchronization detector indicated by reference numeral 56 is the polygon mirror 16 shown in FIG.
When rotating, the detector periodically detects a laser beam reflected by each of the reflecting mirrors, for example, a photo sensor.A polygon synchronization detection pulse signal generated by this detector is used as a reference, and a scanner signal and , And an image data write start timing signal and a transfer reference signal are respectively generated. Further, as can be seen from FIG. 3, when the count number of the polygon synchronization detection pulse signal becomes P from the generation of the scanner start signal, each electrostatic latent image starts to be formed on the photoconductor 20, and then the polygon synchronization detection is performed. When the pulse signal count reaches t ₀ , the rotation of the intermediate transfer belt 27 starts. At the start of rotation of the intermediate transfer belt, the leading end of each toner image has reached a certain position before the intermediate transfer unit 34,
At a predetermined timing slightly after that point, the intermediate transfer belt 27 is brought into contact with the photoconductor 20 to execute the intermediate transfer ((j) in FIG. 3).

By performing the above-described control, the toner images of four colors can be superimposed and transferred at the same position on the intermediate transfer belt 27, and the displacement of the toner images can be prevented.

Further, the intermediate transfer belt 27 is driven by a stepping motor for driving the intermediate transfer belt (not shown), and the forward movement, the backward movement, and the speed pattern when the respective toner images are intermediately transferred to the intermediate transfer belt 27. As shown in FIG. 3 (i), the rotation is performed by the forward and reverse rotations of the same number of pulses of the stepping motor and the operation of the same pattern. Thereby, the driving roller 2 of the intermediate transfer belt 27
8 and the gears (not shown) constituting the drive system thereof are eccentric or the gears have defective tooth shapes, the color misregistration caused by these is eliminated by the four-color toner on the intermediate transfer belt 27. It is possible to prevent a full-color image composed of images from being generated.

As described above, by taking various measures, it is possible to suppress the occurrence of color misregistration in the full-color image formed on the transfer material. As a result, it has become clear that the occurrence of color misregistration cannot be completely prevented only by the measures described above.
That is, in this type of color image forming apparatus, during the image forming operation, it rotates while abutting on the surface of the rotating image carrier, and exerts a periodically varying external force on the surface of the image carrier. An image element is provided. In the color copying machine shown in FIGS. 1 and 2, the cleaning brush 36 provided in the above-described photoconductor cleaning device 35 and the charging roller 22 constitute this image forming element. I have. These image forming elements exert a periodic fluctuating load on the photoconductor 20, and an example of these elements will be described more specifically.

FIG. 6 shows the details of the photoconductor cleaning device 35. The cleaning brush 36 is rotatably supported by a casing 57 of the photoconductor cleaning device 35.
7 is fixed to the casing 57, and the front edge portion thereof is in pressure contact with the surface of the photoconductor 20. The cleaning brush 36 has a central shaft 58 and a fur brush 59 provided on the surface thereof. The cleaning brush 36 is entirely formed in a roller shape, and is driven by a driving device (not shown) with respect to the rotation direction of the photoconductor 20. It is rotationally driven in the counter direction, that is, counterclockwise in FIG. At this time, the fur brush 59 is generally called a bite,
The portion pressed against the photoconductor 20 is deformed by the reaction force from the photoconductor 20. The fur brush 59 is made of a conductive material or a medium resistor (a material having a resistance value of 10 ¹² Ω or less in a part of the fur brush from the central axis 58 to the photosensitive member 20). In FIG. 6, hatching indicating the cross section of each element is omitted for convenience.

The cleaning brush 36 is provided with a bias roller 60 which rotates in the counter direction with respect to the rotation thereof, ie, in the counterclockwise direction in FIG.
9 is in contact with a predetermined amount. The bias roller 60 is made of a conductor, and a bias voltage having a polarity opposite to the charged polarity of the residual toner T on the photoreceptor to be cleaned, that is, a positive polarity in this example, is applied to the roller 60 by a power supply 61, whereby the cleaning is performed. A bias voltage having the same polarity is also applied to the brush 36. Bias roller 6
The applied voltage to 0 is, for example, about + 50V.

The photoconductor cleaning device 35 has a pre-cleaning static eliminator 62 disposed upstream of the cleaning brush 36 in the rotation direction of the photoconductor 20, and the residual toner T on the photoconductor 20 is removed by this static eliminator. By the operation of 62, the toner is uniformly charged to a predetermined polarity, in this example, a negative polarity. Such a toner T is applied to the rotating cleaning brush 3.
6, the photosensitive drum 20 is scraped off from the surface of the photosensitive drum 20, and is electrostatically attracted to the cleaning brush 36 by the action of the bias voltage applied to the brush 36. The residual toner T thus attracted is further electrostatically attracted to the bias roller 60, and the toner is subsequently removed from the surface of the bias roller 60 by the toner removing blade 63 pressed against the bias roller 60. The toner is discharged and conveyed to the outside of the photoconductor cleaning device 35 by a toner discharge device including a collection coil 64.

As described above, the cleaning brush 36
Rotates while constantly contacting the surface of the photoconductor 20 during the formation of an electrostatic latent image on the photoconductor 20, in order to remove toner remaining on the photoconductor 20 after the transfer of the visible image. During the formation of the electrostatic latent image on the photoconductor 20, the photoconductor 20 is always in contact with the photoconductor 20 and rotates (see (m) in FIG. 3).

FIG. 7 is an enlarged view of the charging roller 22. The charging roller 22 exemplified here has a metal core shaft 6.
5, an elastic layer 66 fixed therearound, and a carbon-dispersed urethane rubber layer 67 laminated on the outer periphery thereof.
When the pressure toward the photoconductor 20 is released from both ends of the core shaft 65, the urethane rubber layer 67 comes into pressure contact with the surface of the photoconductor 20 and is rotated by the rotation of the photoconductor 20. As described above, the charging roller 22 is rotatably supported. At this time, a voltage of a predetermined polarity, for example, a negative polarity is applied to the charging roller 22 by the power supply 68. Is charged to a predetermined polarity.

As described above, the charging roller 22 is also connected to the photosensitive member 20.
Rotates while contacting the surface of the photoconductor 20, and charges the surface of the photoconductor 20 before forming an electrostatic latent image. In the present example, the charging roller 22 rotates while contacting the surface of the photoconductor 20 during the formation of the electrostatic latent image on the photoconductor 20 (see (m) in FIG. 3).

The cleaning brush 36 and the charging roller 22 constituting an image forming element which rotates while being in contact with the photosensitive member 20
Is formed as described above, but when these elements are mounted in an eccentric state, the photosensitive member 20
To the external force that fluctuates periodically. Therefore, when each of the electrostatic latent images of the black latent image, the cyan latent image, the magenta latent image, and the yellow latent image is formed on the photosensitive member 20 as described above, the photosensitive member 20 is subjected to a variable load applied thereto. , A periodic speed fluctuation occurs, and this causes a slight expansion and contraction of each electrostatic latent image. Therefore, if these electrostatic latent images are visualized as toner images while leaving them unattended, and then these toner images are sequentially transferred to the intermediate transfer belt 27, a full-color image composed of the superposed toner images is obtained. Color misregistration occurs in the image, which causes color unevenness and density unevenness, and significantly degrades the image quality.

Therefore, in the illustrated color copying machine, the above-described image forming element, that is, the cleaning brush 3 is used.
6 and at least one of the charging rollers 22, in this example, the unit time of each of the photoconductors 20 such that the ratio of the number of rotations per unit time to the number of rotations per unit time of the photoconductor 20 is an integer. The number of revolutions per hit is set. For this reason,
The total number of rotations of the charging roller 22 and the cleaning brush 36 when the photoconductor 20 makes one rotation is an integer number of times. That is, as shown in FIG. 6, it is assumed that the photoconductor 20 and the cleaning brush 36 are in contact with each other at a position indicated by a symbol X at a certain point in time. When the body 20 has just made one rotation, the photoconductor 20 and the cleaning brush 36 again contact each other at the initial X position. The relationship between the charging roller 22 and the photoconductor 20 is the same.

In addition to the above configuration, any one of the electrostatic latent images (black latent image, cyan latent image, magenta latent image, and yellow latent image) is located at the same position on the photosensitive member 20 as described above. The electrostatic latent image is also configured to start to be formed from the same position on the photoconductor 20. With these configurations, when forming each electrostatic latent image, the pattern of the variable load applied by the cleaning brush 36 and the charging roller 22 applied to the photoconductor 20 becomes the same. Therefore, the pattern of the speed fluctuation of the photoconductor 20 based on the fluctuation load becomes the same when each electrostatic latent image is formed. For this reason, each electrostatic latent image is transferred to the photoconductor 20.
When the electrostatic latent image is formed during one rotation of the photoreceptor 20 and each electrostatic latent image is formed while the photoconductor 20 is rotated a plurality of times, even if the respective electrostatic latent images slightly expand or contract, The state is the same for all electrostatic latent images. Therefore, when these electrostatic latent images are visualized as toner images, respectively, and they are intermediately transferred onto the intermediate transfer belt 27, no color shift occurs in the full-color image. Thus, the quality of the full-color image formed on the transfer material 43 can be improved. The same applies to the case where a method of directly transferring each toner image from the photoconductor 20 to the transfer material without using the intermediate transfer belt 27 is adopted.

Here, in order to understand the present invention, experimental examples performed by the present inventors will be described below.

In this experimental example, the diameter of the photosensitive member 20 was 12
0 mm, and the linear velocity V on the surface is theoretically V = 180.
(Mm / sec). At this time, the rotation speed n (rp) of the photoconductor 20 per unit time (per minute)
m) is {180 (mm / sec) x 60 (sec / mm)} / {120 (mm) x
π｝ = 28.648 (rpm). Therefore, the number of rotations of the drive motor 49 per unit time shown in FIG.
Then, 26.648 (rpm) × 48 = 1375.10 (rpm).

FIGS. 8 and 9 are graphs showing how the rotation speed of the photosensitive member 20 varies with the rotation of the cleaning brush 36. FIG. That is, it is an actual measurement graph showing the speed fluctuation of the photoconductor 20 due to the rotation of the fur brush 36 without considering the speed fluctuation of the photoconductor 20 due to the rotation of the charging roller 22. Here, the charging roller 22 and the intermediate transfer belt 27 described above are separated from the surface of the photoconductor 20,
In addition, the operations of the developing units 23Bk, 23C, 23M, and 23Y are stopped, and only the cleaning brush 36 and the cleaning blade 37 of the photoconductor cleaning device 35 are pressed against the photoconductor 20 as described above, and the photoconductor 20 is driven to rotate. . Then, the photoconductor 20 was rotated twice to form each of the electrostatic latent images (black latent image, cyan latent image, magenta latent image, and yellow latent image) on the photoconductor 20. One electrostatic latent image is formed by rotating the photoconductor 20 twice. At that time, as described above, all the electrostatic latent images started to be formed from the same position W (FIG. 5) of the photoconductor 20. 8 and 9, the time at which the formation of each electrostatic latent image on the photosensitive member 20 is started is set to “zero”. Bk, C, M, and Y in FIGS. 8 and 9 indicate the photosensitive member 20 when a black latent image, a cyan latent image, a magenta latent image, and a yellow latent image are formed on the photosensitive member 20, respectively.
Shows the speed. FIG. 8 shows the cleaning brush 36.
Is set to 178.93 rpm, and FIG. 9 shows measurement data when the number of revolutions N is set to 171.89 rpm.

Since the number of rotations n of the photoconductor 20 per unit time is 28.648 rpm as described above, FIG.
In the example shown in FIG. 2, the cleaning brush 36 and the photoconductor 20
The ratio of the number of rotations per unit time of N / n is N / n = 178.93 (rpm) /28.648 (rpm) = 1
2.492, and the value of the ratio is not an integer.
n is shifted by about 1/2 cycle.

For this reason, as shown by C and Y in FIG.
Photoconductor 20 for forming cyan latent image and yellow latent image
Are substantially the same, and as shown by Bk and M in the figure, the speed fluctuation patterns of the photosensitive member 20 when forming the black latent image and the magenta latent image are also substantially the same. , And the speed fluctuation pattern of the photoconductor 20 when forming the cyan and yellow latent images, that is, the curves C and Y, and the pattern of the speed fluctuation of the photoconductor 20 when forming the black and magenta latent images, that is, the curves Bk and M. , And the patterns are completely different from each other. Therefore, if these electrostatic latent images are visualized as toner images, and these are superimposed on the intermediate transfer belt 27 and intermediately transferred, it is apparent that significant color misregistration occurs in the full-color image. is there. This clearly indicates a defect of the conventional image forming apparatus.

On the other hand, in the case of FIG. 9, the number of rotations N of the cleaning brush 36 per unit time is 171.89.
8, and the number of rotations n of the photoconductor 20 per unit time is 28.648 rpm as in the case of FIG. 8, so that the ratio N / n between them is N / n = 171.89 (rpm ) /28.648 (rpm) = 6.
00, and the value of the ratio is an integer. That is, the rotational speeds n and N of the cleaning brush 36 and the photoconductor 20 are determined according to the present invention. In this case, as can be seen from the curves Bk, C, M, and Y in FIG. The speed variation of the surface linear velocity of the photoconductor 20 when forming each electrostatic latent image shows almost the same pattern. Accordingly, if each of these electrostatic latent images is visualized as a toner image and these are intermediately transferred onto the intermediate transfer belt 27 to obtain a full-color image, no color shift occurs in the image. Thus, a high-quality full-color image can be obtained on the transfer material.

Also in the case of the charging roller 22, color shift of a full-color image due to a fluctuating load applied to the photosensitive member 20 can be prevented in exactly the same manner. For example, when the diameter of the photoconductor 20 is 120 mm, the diameter of the charging roller 22 is 30 mm.
mm and the ratio of the number of rotations of the charging roller 22 and the photoconductor 20 per unit time may be an integer.

In the embodiment described above, the ratio of the number of rotations of the charging roller 22 and the cleaning brush 36 per unit time to the same number of rotations of the photosensitive member 20 is an integer. The effect of suppressing the occurrence of color misregistration can be achieved even if only the ratio of the rotation speed per unit time of one of the cleaning brush 36 and the photoconductor 20 to the rotation speed per unit time is an integer. Can be expected. When an element other than the cleaning brush 36 and the charging roller 22 is used as an image forming element which rotates while being in contact with the surface of the photoreceptor and exerts a periodically varying external force on the surface of the photoreceptor, the rotation per unit time is used. The number can also be set as described above. In short, the value of the ratio of the number of rotations per unit time of at least one of the image forming elements to the number of rotations per unit time of the image carrier may be set to an integer.

At this time, as shown in the illustrated embodiment, when the cleaning brush 36 that contacts the photosensitive member 20 is used,
Since a bias voltage is applied to the cleaning brush 36 as described above, the cleaning brush 3
6 and the photoconductor 20 have an electrostatic attraction force,
Due to the electrostatic force, the magnitude of the fluctuating load applied to the photoconductor 20 by the fur brush 36 is amplified. Therefore, when the present invention is applied to the fur brush 36 to which the bias voltage is applied as described above, color shift of a full-color image can be particularly effectively suppressed.

The present invention relates to a so-called analog type color image forming apparatus using an image forming optical system for forming an image of a document directly on a photoreceptor instead of a laser as an exposure means for the photoreceptor. The invention can also be applied to a color image forming apparatus using a dielectric instead of a photoreceptor, or a color image forming apparatus using an image carrier formed of a belt. Further, the number of colors of the toner images sequentially formed on the image carrier may be two or more. Therefore, the present invention can be applied to a color image forming apparatus having at least two developing units. Similarly, the present invention can be applied to a color image forming apparatus such as a color facsimile and a color printer.

[0075]

According to the present invention, the image forming element which comes into contact with the surface of the image carrier applies a variable load to the image carrier during its rotation, thereby causing a speed variation on the image carrier. Even if it occurs, it is possible to effectively suppress the color shift caused by the color shift from being applied to the color image, and it is possible to obtain a high-quality color image.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a color copying machine as an example of a color image forming apparatus according to the present invention.

FIG. 2 is a partially enlarged view of FIG.

FIG. 3 is a timing chart showing an operation example of the color copying machine shown in FIG.

FIG. 4 is an explanatory diagram illustrating an example of a drive system that rotationally drives a photoconductor.

FIG. 5 is a control block diagram of the color copying machine shown in FIG.

FIG. 6 is an enlarged view of the photoconductor cleaning device.

FIG. 7 is an enlarged view of a charging roller.

FIG. 8 is a graph showing speed fluctuations of the photoconductor when forming each electrostatic latent image, and is a diagram for clarifying a conventional defect.

FIG. 9 is a graph showing speed fluctuations of the photoconductor when forming each electrostatic latent image, and is a diagram for clarifying the effect of one embodiment of the present invention.

[Explanation of symbols]

 23Bk developing unit 23C developing unit 23M developing unit 23Y developing unit 36 cleaning brush 43 transfer material T toner W position

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) G03G 15/01-15/01 117 G03G 21/10 G03G 15/02-15/02 103

Claims (1)

(57) [Claims] 1. An image carrier that is driven to rotate and a plurality of electrostatic latent images sequentially formed on the carrier are visualized as toner images of different colors by toners of different colors. A plurality of developing devices are provided, and all the electrostatic latent images are started to be formed from the same position on the image carrier so that the leading end of each electrostatic latent image is located at the same position on the image carrier. In a color image forming apparatus that obtains a color image by transferring a visible image formed sequentially on a body directly or through an intermediate transfer body onto a transfer material, in contact with the surface of the image carrier, The ratio of the number of rotations of the at least one image forming element per unit time to the number of rotations of the image carrier per unit time, which rotates while applying an external force that periodically fluctuates on the surface of the image carrier. The number of rotations per unit time so that the value of Wherein the image forming element is a cleaning brush which rotates while being in contact with the surface of the image carrier in order to remove toner remaining on the image carrier after transfer of the visible image. Image forming device.