JP3502699B2 - Color electrophotographic equipment - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used in copying machines, printers, and the like, and a toner image of each color is sequentially formed on an image carrier, while a toner image of each color is superposed on an intermediate transfer member to form a full-color image. The present invention relates to a color electrophotographic apparatus that forms a sheet and transfers a full-color image onto a transfer paper.

[0002]

2. Description of the Related Art Conventionally, a color electrophotographic apparatus having an electrophotographic image forming apparatus uses one photoconductor belt and one intermediate transfer belt, and BK (black), C ( Cyan), M (magenta),
A toner image of Y (yellow) is formed, and these toner images are transferred onto a transfer paper using a transfer roller to obtain a full color print.

[0003]

However, in the above-mentioned conventional color electrophotographic apparatus, it is important to accurately position the image of each color, and the photoconductor belt and the intermediate transfer belt are correctly and at a constant speed. Although it needs to be driven, both belts are in contact with each other at the primary transfer portion where the toner is transferred from the photoconductor belt to the intermediate transfer belt, and therefore frictional force and adhesive force due to static electricity are generated, resulting in a minute speed difference between the belts. In some cases, there is a problem in that one of the belts works to pull the other and the positional relationship between the two belts is displaced. In particular, when the surface of the belt is cleaned, the adhesive force due to static electricity increases, which affects color misregistration. This electrostatic adhesion force is abruptly reduced due to the gap created by the presence of toner even if a small amount of toner is present between the belts. In fact, on the charged photoconductor belt, when the developing device comes into contact, a small amount of toner called "background stain toner" adheres to the area other than the image area, which is sufficient to reduce the electrostatic adhesion force between the belts. Work.

The image formation for each color is started by detecting a reference mark provided on the intermediate transfer belt, and the optical writing is started by detecting this mark. Therefore, when the mark of the first color is detected, both the photoconductor belt and the intermediate transfer belt are mechanically contacted at the primary transfer section while both are cleaned and no toner is attached. Is given, the marks are detected in a state in which they are electrically closely attached.

On the other hand, the photosensitive belt and the intermediate transfer belt are
The primary transfer unit is driven so that the speeds are almost equal,
Due to variations in the outer diameter of the drive roller of each belt, a slight speed difference occurs. Since the drive of the intermediate transfer belt is transmitted from the photoconductor belt side, when the rotation of the intermediate transfer belt is slower than the photoconductor belt, it is pulled by the photoconductor belt and precedes the movement of the photoconductor belt. However, when it is faster than the photoconductor belt, it receives the force returned by the photoconductor,
It will move later than the photoreceptor.

When a mark on the intermediate transfer belt is detected in such a state, it is detected that the positional relationship between the two belts is deviated at the time of detecting the mark, but when the image surface reaches the primary transfer portion, the image or the background is detected. The dirty toner enters the primary transfer portion, the adhesion between the belts is weakened, and the misregistration returns to the normal state, so that the image is not transferred to the correct position and misalignment occurs. For the second and subsequent colors, when the mark is detected, the image or background toner is already present in the primary transfer portion, and the shift between the transfer belts does not occur. Therefore, an image in which the first color is displaced from the second and subsequent colors is obtained.

As described above, the adhesive force between the two belts becomes different between when the mark of the first color is detected and when the marks of the second and subsequent colors are detected, and the marks are detected in a state where the positional relationship between the two belts is different. However, there is a problem that color shift occurs. Therefore, the present invention solves the above-mentioned problems of the related art, and an image carrier (photoreceptor belt) and an intermediate transfer member (intermediate transfer belt) are detected at the time of detecting the mark of the first color and at the time of detecting the marks of the second and subsequent colors. The positional relationship with
An object of the present invention is to provide a color electrophotographic apparatus having a low cost and a simple structure capable of preventing color misregistration from occurring.

[0008]

The gist of the present invention resides in that in claim 1, a developing device, an image carrier and an intermediate transfer member are provided, and a reference mark provided on the intermediate transfer member is detected. In synchronism with the above, the toner images of the respective colors sequentially formed on the image carrier by the developing device are sequentially transferred onto the intermediate transfer member by the primary transfer unit so that the toner images are formed on the intermediate transfer member. In a color electrophotographic apparatus of a type in which a full-color image is transferred onto a transfer paper by a secondary transfer unit, a portion of the image carrier that is located in the primary transfer unit at the time of detecting the reference mark of the first color. Is controlled so as not to be charged, and in the second aspect, after the entire fixed length in the non-charged portion of the image carrier passes the position of the primary transfer portion, the reference mark of the first color Control to detect In addition, in claim 3, when the reference mark of the first color is detected, the intermediate transfer bias applied to the intermediate transfer member in the primary transfer portion is controlled to be turned off. In No. 4, the image bearing in the portion where the intermediate transfer bias is turned off is performed.
The control is performed so that the reference mark of the first color is detected after the entire fixed length of the holding body has passed the position of the primary transfer portion. This is to control so that a part of the surface of the image carrier in a ready state detects the reference mark of the first color after passing through the primary transfer portion.

[0009]

Therefore, according to the first aspect of the invention, when the reference mark of the first color is detected, the portion of the image carrier which is positioned in the primary transfer portion is controlled so as not to be charged, so that the intermediate portion between the image carrier and The electrostatic adhesion with the transfer body is lost,
As in the case of being charged, the electrostatic transfer force prevents the intermediate transfer body from being displaced with respect to the image carrier and the color shift from occurring. Also, for the second and subsequent colors, since the toner developed as an image or the minute toner that adheres to the outside of the image adheres to the image carrier,
Electrostatic adhesion is weakened.

[0010] According to claim 2, non of the image bearing member
By controlling so that the reference mark of the first color is detected after the entire fixed length in the charged portion has passed the primary transfer position, it is possible to reliably prevent the electrostatic adhesion force from being generated. According to a third aspect of the present invention, the intermediate transfer bias applied to the intermediate transfer member in the primary transfer section is controlled to be turned off at the time of detecting the reference mark of the first color. Has the effect of. Further, in claim 4, the image carrier is provided in a portion of the primary transfer portion where the intermediate transfer bias is turned off.
By controlling so as to detect the reference mark of the first color after the entire body of a fixed length has passed through the primary transfer portion, the same effect as in claim 2 is obtained. Further, in claim 5, a small amount of toner adheres to the entire surface of the image carrier, which is ready for development by operating the developing device, even if there is no image. By controlling so as to detect the reference mark of the first color after passing through the primary transfer portion, the portion acts as a lubricating oil between the image bearing member and the intermediate transfer member so that the electrostatic adhesion force is increased. Significantly reduced,
Eliminates misalignment of the intermediate transfer member.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, a photosensitive belt 1 which is an image carrier
Are supported by the photoconductor drive roller 2 and the photoconductor driven roller 41. A developing device in which four color developing units of C (cyan) 4a, M (magenta) 4b, Y (yellow) 4c, and BK (black) 4d are arranged in a circle in contact with the photosensitive belt 1. A developing device 4, an intermediate transfer belt 5, a photoconductor cleaning device 10, and a charging roller 9 are arranged, and an electrostatic latent image is formed on the belt 1 by being exposed by the optical writing device 3. The intermediate transfer belt 5 is supported by an intermediate transfer belt drive roller 6 and a driven roller 45, and the transfer roller 8,
An intermediate transfer cleaning device 11 is arranged in contact with the intermediate transfer cleaning device 11, and a belt reference position detection sensor 7 for detecting the reference mark 30 (see FIG. 2) on the belt 5 is arranged in close proximity to the transfer roller 8. abutment forms a secondary transfer portion
It is Further, two backup rollers 43 and 44 are arranged in the primary transfer portion D with which the photosensitive belt 1 abuts. Transfer is performed by the transfer paper passing through the contact portion between the transfer roller 8 and the intermediate transfer belt 5, and a fixing device 12 including a pair of rollers is provided on the downstream side of the transfer roller on the transfer path of the transfer paper. It is arranged.

Further, the photosensitive belt 1 and the intermediate transfer belt 5
As shown in FIG. 2, the drive configuration of the drive motor 20 uses the toothed belt 21 and the pulleys 22 and 23 to rotate the drive motor 20.
The speed is reduced to the same rotation speed as the predetermined rotation speed of the photoconductor belt drive roller 2 and transmitted to the photoconductor belt drive roller 2 via the couplings 24a and 24b. The intermediate transfer belt 5 is driven by transmitting the rotation of the photoconductor belt driving roller 2 using the toothed belt 25 and the pulleys 26 and 27,
The rotation direction is reversed by the gears 28 and 29. The couplings 24a and 24b in the figure are shown in a separated state, and these 24a and 24b are connected during rotation transmission.
The reason for driving directly by coupling is that if a gear or the like is used, uneven rotation due to precision occurs. Since each belt needs to be replaced depending on its life, each belt is configured to be attachable to and detachable from the drive unit.

In this way, both belts 1 and 5 are driven by one drive motor 20. Driving with a single motor is cheaper and more convenient at the same time for making the waveform of the rotation unevenness constant. In the above structure, the photoconductor belt 1 is uniformly charged by the charging roller 9 to be charged, and the electrostatic latent image is formed on the photoconductor belt 1 by the optical writing device 3. Then, the developing device 4 is set to 90
Each color is developed by rotating it by °. The toner images formed on the photoconductor belt 1 are formed on four sheets by sequentially changing the colors from the first color to the fourth color, and these toner images are superimposed on the surface of the intermediate transfer belt 5 from the first color to the fourth color. It is transcribed while matching. The full-color image thus formed on the intermediate transfer belt 5 is transferred onto the transfer paper by the transfer roller 8 and the fixed full-color image is obtained by passing the transfer paper between the rollers of the fixing device 12. .

Next, details of the image forming operation will be described.
In order to align and superimpose images on the intermediate transfer belt 5, first, the reference mark 30 on the intermediate transfer belt 5 is detected by the belt position detection sensor 7 shown in FIG. The image formation is started in synchronization with this detection timing,
Images are superimposed on the same section on the intermediate transfer belt 5.

As shown in FIG. 3, the photosensitive belt 1 is given a negative charge by the charging roller 9 and passes through the developing portion of the developing device 4, and the photosensitive belt 1 and the intermediate transfer belt 5 are connected.
Reach the primary transfer portion D where they contact. The backup roller 43 of the primary transfer portion D is grounded, and a positive primary transfer bias is applied to the backup roller 43 from a power source 46 for primary transfer. Here, the positional relationship between the belts 1 and 5 at the time of detecting the reference mark 30 of the first color by the belt reference position detection sensor 7 (hereinafter simply referred to as “mark detection”) and at the time of detecting the mark of the second color and thereafter. The control shown in the time chart of FIG. 4 is performed in order to prevent the occurrence of color misalignment due to the shift. In the figure, for image formation, the drive motor 20 is turned on, the charging bias is x time (fixed length) , and the primary transfer bias is the sum of A, B, and C times shown in FIG.
After turning off for a certain length of time (a certain length of time ) , the photosensitive belt 1 and the intermediate transfer belt 5 rotate for a certain period of time including these x time and y time until a stable state where uniform image formation can be achieved, and then the mark At the same time as the detection, the optical writing of the image is started.

Thereafter, the development of the first color is started after a lapse of B time from the movement of the photosensitive belt 1 from the exposure position to the developing position, and further, the photosensitive belt 1 is moved from the developing position to the transfer position of the primary transfer portion D. The primary transfer of the first color is started after the lapse of C time to move to. Further, the color of the developing device 4 is changed between the development of the first color and the development of the second color. As described above, at the time of mark detection, the charging of the portion of the photosensitive belt 1 that reaches the primary transfer portion D, that is, the charge before (A + B + C) time, that is, y time, is turned off before the mark detection, and the x before that is turned off. By turning off the charging time, the photosensitive belt 1 and the transfer belt 5 at the time of mark detection
Prevents misalignment by eliminating electrical contact. Similarly, when the mark is detected, the primary transfer bias is turned off, and the time y before that is turned off to turn off the primary transfer bias to eliminate electrical contact between the photosensitive belt 1 and the transfer belt 5 at the time of mark detection.

Therefore, when the mark of the first color is detected, there is no toner on both belts 1 and 5, but since the adhesion force due to static electricity does not become large, both belts 1 and 5 are detected at the time of mark detection and at the time of transfer. There is no misalignment between them. The distance length on the intermediate transfer belt 5 corresponding to the time length indicated by x and y is preferably 30 mm to 50 mm.
Further, in another embodiment, as shown in FIG. 5, the development is started from a position C or more before the detection of the mark of the first color so that the background toner reaches the primary transfer portion D when the mark is detected. Control. As a result, a small amount of toner adheres to the entire surface of the photoconductor belt 1 even if there is no image, and this toner acts as a lubricating oil between the photoconductor belt 1 and the intermediate transfer belt 5. Since the electrostatic adhesion force is remarkably reduced, the positional deviation of the intermediate transfer belt 5 does not occur between the mark detection and the transfer.

[0018]

As described above, according to the first aspect of the present invention, when the reference mark of the first color is detected, the portion of the image carrier which will be located in the primary transfer portion is controlled so as not to be charged. Therefore, it is possible to prevent the position of the intermediate transfer body from being displaced with respect to the image carrier and the color shift caused by the electrostatic force of adhesion between the image carrier and the intermediate transfer body. . Further, in the second and subsequent colors, since the toner developed as an image or the minute toner that adheres to the outside of the image adheres to the image carrier, the electrostatic adhesion force is weakened and the color shift does not occur.

According to a second aspect of the present invention, the reference mark of the first color is detected after the entire fixed length in the non-charged portion of the image carrier has passed the position of the primary transfer portion. By controlling to 1, it is possible to sufficiently remove the deviation caused by the electrostatic adhesion force, and it is possible to reliably prevent the color deviation. Further, according to claim 3, the intermediate transfer bias applied to the intermediate transfer member in the primary transfer portion is controlled to be turned off at the time when the reference mark of the first color is detected. Has the same effect. According to a fourth aspect of the present invention, the image carrier has a constant length in a portion where the intermediate transfer bias is turned off.
Since the control is performed so as to detect the reference mark of the first color after the entire length has passed the position of the primary transfer portion, the same effect as that of the second aspect is achieved. Further, according to claim 5, a part of the surface of the image carrier in which the developing device is in operation and ready for development detects the first color reference mark after passing through the primary transfer portion. Therefore, even if there is no image, a small amount of toner adheres to the entire surface of the image bearing member, and the lubricant acts between the image bearing member and the intermediate transfer member to cause electrostatic adhesion. Therefore, it is possible to prevent positional deviation and color misregistration of the intermediate transfer member by significantly reducing

[Brief description of drawings]

FIG. 1 is an overall schematic configuration diagram showing a color electrophotographic apparatus of an embodiment of the present invention.

FIG. 2 is a perspective view showing a drive mechanism for an image carrier and an intermediate transfer member.

FIG. 3 is an explanatory diagram showing the operation of the image carrier.

FIG. 4 is a time chart showing the operation timing of each unit.

FIG. 5 is a time chart when the developing device is first operated.

[Explanation of symbols]

1 Image carrier 4 Developing device 5 Intermediate transfer body 30 standard mark

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tomonori Yabuta, 10-3 Kitamura, Tottori City, Tottori Prefecture, Ricoh Microelectronics Co., Ltd. (56) Areas (Int.Cl. ⁷ , DB name) G03G 15/01-15/01 117 G03G 15/16

Claims (5)

(57) [Claims] 1. A developing device, an image carrier, and an intermediate transfer member, which are sequentially formed on the image carrier by the developing device in synchronization with the detection of a reference mark provided on the intermediate transfer member. A color electronic system in which toner images of respective colors are transferred to the intermediate transfer member in sequence by the primary transfer unit, and the full-color image formed on the intermediate transfer member is transferred to the transfer paper by the secondary transfer unit. In the photographic device, at the time of detecting the reference mark of the first color, the color electrophotographic device is controlled so that the portion of the image carrier positioned in the primary transfer portion is not charged. 2. A constant in an uncharged portion of the image carrier.
After the entire length of the sheet has passed the position of the primary transfer section,
The color electrophotographic apparatus according to claim 1, wherein the color electrophotographic apparatus is controlled so as to detect the first color reference mark. 3. The intermediate transfer bias applied to the intermediate transfer member in the primary transfer portion is controlled to be turned off at the time when the reference mark of the first color is detected. Color electrophotographic device. 4. In the portion where the intermediate transfer bias is turned off
4. The color electrophotographic apparatus according to claim 3, wherein control is performed so that the reference mark of the first color is detected after the entire fixed length of the image carrier in the image carrier passes the position of the primary transfer portion. . 5. A developing device, an image carrier, and an intermediate transfer member.
Prepared and synchronized with detection of reference mark provided on this intermediate transfer member
And sequentially formed on the image carrier by the developing device.
The toner image of each color is transferred by the primary transfer unit to the intermediate transfer.
The colors are transferred one after another onto the body and formed on the intermediate transfer body.
The full-color image on the transfer paper by the secondary transfer unit.
In the color electrophotographic apparatus of the method, a part of the surface of the image carrier in a state where the developing device is activated and ready to be developed detects the reference mark of the first color after passing through the primary transfer portion. control feature and be Luca color electrophotographic apparatus to be.