JP3527903B2 - Image forming device - Google Patents

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 toner image on each of a plurality of image forming devices and directly or indirectly superimposing the toner images on a transfer paper via an intermediate transfer medium. In particular, although not intended to be limited to this, a plurality of photoconductors for multi-color recording such as magenta (M), cyan (C), yellow (Y) and black (K) for full-color recording are provided. Equipped with multiple developing devices, each toner image is formed on each photoconductor, and the transfer target (transfer paper or intermediate transfer medium) is conveyed or transferred along the array of photoconductors to transfer each color toner image to it. Color image forming apparatus.

[0002]

2. Description of the Related Art One form of this type of color image forming apparatus is disclosed in Japanese Unexamined Patent Publication No. 10-104898, and another form is disclosed in Japanese Unexamined Patent Publication No. 2001-134042. The color image forming apparatus disclosed in Japanese Unexamined Patent Publication No. 10-104898 has four sets of image forming units for forming toner images of magenta (M), cyan (C), yellow (Y) and black (K). And a direct transfer type full-color image forming apparatus using a plurality of image forming carriers, in which the toner images of the respective colors formed by them are directly and sequentially transferred onto a transfer paper conveyed by a transfer belt. JP-A-2001-
The color image forming apparatus disclosed in Japanese Patent No. 134042 is
Each of the colors formed by each image forming unit is provided with an intermediate transfer belt in addition to four sets of image forming units for forming toner images of magenta (M), cyan (C), yellow (Y) and black (K). This is an indirect transfer type full-color image forming apparatus using a plurality of image forming carriers, in which toner images are sequentially transferred onto an intermediate transfer belt and transferred onto a transfer paper.

There are several other types of color image forming apparatuses. For example, in Japanese Patent Laid-Open No. 9-50166, one photoconductor belt and four developing devices are provided, and an electrostatic latent image for recording a first color is formed on the photoconductor belt, and the electrostatic latent image is first developed. Image developed by a developing device and transferred to an intermediate transfer belt, then an electrostatic latent image for second color recording is formed, developed by a second developing device and transferred in advance on the intermediate transfer belt. Transfer onto the intermediate transfer belt, sequentially transfer the images of the third and fourth colors to the intermediate transfer belt in the same process, and transfer the overlap of the four-color image on the intermediate transfer belt to the transfer paper. An indirect transfer type full-color image forming apparatus using an image carrier is disclosed. In this image forming apparatus, in order to accurately align each color image with the intermediate transfer belt, a reference mark on the intermediate transfer belt is detected by a sensor at a predetermined position, and the image formation process of each color image is performed based on the mark detection. To control. Further, if the photosensitive belt portion in contact with the intermediate transfer belt is charged, an electrostatic attraction force is generated between them and a speed deviation occurs. Therefore, the intermediate transfer is performed at the time of detecting the reference mark that determines the image forming base point of the first color. The photoconductor belt portion in contact with the belt is controlled so as not to be charged.

On the other hand, Japanese Unexamined Patent Publication No. 5-134529, which discloses an image forming apparatus for monochromatic recording, detects the presence or absence of image writing which is not a background even during the image forming process of one sheet, up to the point where image writing is performed. It is disclosed that the driving of the developing means is suspended to shorten the driving time as much as possible, thereby extending the life of the developer and the apparatus.

[0005]

The above-described full-color image forming apparatus using a plurality of image-forming members is suitable for a machine having a high printing speed, and a full-color image forming device using a single image-forming member is not , Mainly suitable for high image quality machines.

However, with the recent spread of PCs (personal computers), the number of full-color image prints has increased rapidly, and it has become a great demand from the market to achieve both image quality and print speed. Therefore, it is difficult to increase the speed of a full-color image forming apparatus using a single image-forming member due to physical restrictions. Therefore, a full-color image forming apparatus using a plurality of image-forming members can achieve both high speed and high image quality. Is desired. A full-color image forming apparatus using a plurality of image-forming members is physically easy to achieve high speed, and thus high image quality is important.

Although there are various viewpoints in terms of high image quality, the technique which transfers the four colors without color misregistration is said to be the most difficult in a full-color image forming apparatus using a plurality of image forming members. This is because the transfer paper passes between the transfer nips of the four drums, but if the transfer speed fluctuates at this time, the color shift will occur immediately.

In addition, there is a demand for longer life of the device and its associated supplies, and in designing the equipment, the products are designed so as to take advantage of the characteristics of each equipment in consideration of the demands from these markets. .

In view of the above, in the conventional machine, as seen in the above-mentioned Japanese Patent Laid-Open No. 134529/1993, regarding the development drive, the presence or absence of an image is detected to shorten the drive time of the development means as much as possible. Control is performed so as to extend the life of the developer and the apparatus. However, as described in the text of the above-mentioned JP-A-5-134529,
In many cases, the rotation of the developing clutch is turned on / off, so that the photosensitive member tends to have uneven rotation. Therefore, in such a case, in the case of a full-color image forming apparatus using a plurality of image forming members, there is a fear of positional deviation due to uneven rotation.

Further, as described in the above-mentioned Japanese Patent Laid-Open No. 9-50166, when a photoconductor and a transfer belt have an adhesive force due to a frictional force or an electrostatic force, and there is a speed difference between the photoconductor and the transfer belt, one of them is generated. It acts to pull the other, and the positional relationship between the two shifts, resulting in color shift. Further, when the surface of the belt is cleaned, the adhesive force due to static electricity becomes large, and when toner is present between the photoconductor and the transfer belt, the adhesive force sharply decreases. It is written that, when a developing device comes into contact with an actually charged photoconductor, the adhesion between the photoconductor and the transfer belt is reduced by the background toner.

In FIG. 9, four photoconductor drums, four developing devices and one transfer belt are used, and each developing device is used as a system for transmitting the power of the electric motor by turning on the clutch at each color developing timing. In the full-color image forming process of the conventional image forming apparatus driven by connecting,
An example of the drive timing of an electric element is shown.

FIG. 10 shows a graph in which the surface position fluctuation in the moving direction of the transfer belt when one sheet of A3 is passed at the timing shown in FIG. 9 is measured. In the example shown in FIG. 10, a rapid position change is seen around 1200 ms. Also, a rapid position change is seen around 5300 ms. The former is synchronized with turning on the Y developing clutch. The latter is synchronized with the M and C developing clutches being off. About 1200
The position change of ms is during M image formation (exposure M), and is about 530
The position variation of 0 ms indicates that it occurs during image formation of Y and K (exposure Y and K). Therefore, at the conventional clutch on / off timing, each color appears as a color shift due to the above-described position variation.

When the developing clutch is turned on or off,
The transfer belt speed fluctuates, and the reason for this is described below. If the photoconductor and the transfer belt are driven with the developing clutch off (before the transfer paper enters the photoconductor / transfer belt pressure contact part), there is almost no toner on the photoconductor, so the surface state is used for transfer. When it comes into pressure contact with the belt surface, the linear velocity of the transfer belt is about 1% faster than the original speed because it is slightly pulled by the photoconductor. For reference, the linear velocity ratio between the photoconductor and the transfer belt of each company's tandem machine is shown below. The photoconductor is uniformly set faster than the transfer belt.

[0014]

Next, when the developing clutch is turned on at a predetermined timing, even if there is no image, the toner adheres to the photoconductor at the toner smear level. When the smeared toner enters the photosensitive member / transfer belt pressure contact portion, the slip becomes larger there than when there is no toner. The change in the amount of the transfer belt pulled by the photoconductor appears as a change in the transfer belt position. Therefore, the position change does not appear on the transfer belt immediately after the developing clutch is turned on, but the position change occurs when the background toner adheres to the photoconductor when it is turned on and enters the pressure contact portion. In the conventional example in which the control timing is shown in FIG. 9 and the transfer belt position fluctuation is shown in FIG. 10, the time from when the developing clutch is turned on until the position fluctuation appears on the transfer belt is about 230 ms. This corresponds to the moving time of the photosensitive member from the developing nip position of the photosensitive member to the pressure contact portion with the transfer belt + suction time of the developing clutch.

Further, conventionally, each transfer bias is synchronized with the movement of the transfer paper, and the transfer bias is turned on with reference to the timing of the registration clutch.
It is almost the same as the entry into the transfer member (entering the photoconductor nip), and the transfer biases are sequentially turned on. Further, the OFF state is almost the same as the time when the transfer sheet is removed from between the photoconductors / transfer members (photoconductor nip omission), and the transfer biases are sequentially turned off. Therefore, the conventional transfer bias on /
The off timing is performed during the image forming process.

FIGS. 11 to 13 are graphs showing changes in the transfer belt surface position when one sheet of A3 is passed at the conventional timing. FIG. 11 corresponds to the transfer belt position fluctuation shown in FIG. FIG. 12 shows the transfer position shift of each color caused by the transfer belt position change shown in FIG. The positional deviation amounts of M, C, Y, and K on FIG. 12 are
The transfer belt position fluctuations shown in FIG. 11 are extracted from the position fluctuations during the periods of the image forming processes M, C, Y, and K indicated by the white horizontal bars in FIG. FIG. 13 shows transfer position deviations (calculated values) of M, C, and Y with respect to the transfer position of black (K) shown in FIG.

The transfer belt position variation shown in FIG. 11 is as shown in FIG.
The measurement is performed by making the transfer bias application timing and the development clutch on / off timing the same as the conventional timing shown in FIG. Therefore, the waveforms should be almost the same. However, the waveform of belt position fluctuation (see FIG.
1) is greatly different from the conventional example shown in FIG.

The cause of this difference is the amount of the transfer unit used (characteristic change or deterioration due to use). That is, it is a change with time. The waveform in FIG. 11 is a measurement of the transfer unit that has undergone a drive test corresponding to long-term use during the durability test.

By comparing the waveform of FIG. 10 with the waveform of FIG. 11, the effect of the transfer bias application timing is initially (see FIG. 1).
0) has almost no effect, but it has been found that the running stability of the transfer belt is affected over time (FIG. 11).
The cause may be that the transfer bias amount is slightly different due to changes in the resistance values of the transfer bias applying member and the transfer belt over time. As a result, the adhesion between the transfer belt and the transfer bias applying member is increased, which is a load for driving the transfer belt, and it is considered that the on / off of the transfer bias impairs the stability of the transfer belt running. Figure 1
Speed increase from about 6000 ms to 8000 ms in 1 is also a problem. This is a phenomenon caused by the linear velocity ratio between the photoconductor and the transfer belt (the photoconductor is about 1% faster). In short, the speed of the transfer belt varies due to the application of the transfer bias and the linear velocity ratio.
In such a state, the speeds at which the respective colors are printed are different, so that the respective colors cannot be accurately matched. In order to accurately match the colors, the graph of the measurement result needs to be straight.

FIGS. 14 to 16 show waveforms of the transfer unit under the durability test when the paper is passed without applying the transfer bias. FIG. 14 corresponds to the transfer belt position variation shown in FIGS. 10 and 11. Figure 15
Shows the transfer position deviation of each color caused by the transfer belt position fluctuation shown in FIG. The positional deviation amounts of M, C, Y, and K in FIG. 15 are the periods of the image forming processes M, C, Y, and K indicated by the white horizontal bars in FIG. 14 of the transfer belt position variation illustrated in FIG. This is a variation of the position. FIG. 16 shows transfer position deviations (calculated values) of M, C, and Y with respect to the transfer position of black (K). There is almost no decrease in speed and color shift as seen in FIGS. 11 to 13. Therefore, it can be seen that as the number of times the transfer unit is used increases, the transfer bias position variation in FIG.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus capable of high-speed printing and having less transfer deviation of a toner image on a transfer body.

[0023]

[Means for Solving the Problems] (1) A plurality of photoconductors (11M, C, Y, K) arranged in a predetermined direction, and a plurality of developing means (20M) each forming a toner image on each photoconductor. , C, Y, K),
Transfer target for receiving transfer of toner image on each photoconductor
A transfer belt (6 ) that conveys (P) along the arrangement of the photoconductors.
0), the transfer means for transferring the toner images on the photosensitive member to the transfer member (67M, C, Y, K ; 9M, C, Y, K) and an image forming apparatus having the plurality of developing means (20M, C, Y, K ) of all
The photoconductor (11M, C, Y, K) and the transfer belt (60)
After starting the drive, the transfer target (P) comes first.
The exposure timing of the photoconductor (11M)
Body from the development nip position the transfer belt (60) and of (11M)
Moving time of the photoconductor (11M) to the pressure contact portion and the developing means
To the system that transmits the power of the electric motor.
Before the time (230 ms) combined with the suction time of
An image forming apparatus, wherein driving is started by turning on a developing clutch .

For ease of understanding, in parentheses, symbols of corresponding elements or corresponding matters of the embodiments shown in the drawings and described later are added for reference. The same applies to the following.

In this image forming apparatus, the transferred material (P, 60) is driven along the arrangement of the image forming members (11M, C, Y, K) to be transferred.
Since the toner image on each image carrier is transferred onto the surface of (P, 60), one image carrier is used to form images for forming plural types of toner images on the transferred body (P, 60). It can be performed at an extremely high speed as compared with the case of using only. Load fluctuation caused by switching each developing means from off (stop) to on (drive),
The change in the adhesive force due to the entry of the background stain toner between the image forming member and the transferred member when the developing means is turned on is before the development timing of the image forming member where the transferred member reaches the earliest. Therefore, that is, before the entire image forming process, there is no change in the slip ratio or the linear velocity ratio between the image forming member and the transferred member due to the switching of the developing unit from OFF to ON, and there is no transfer deviation. You can get prints with less.

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION ( 1a ) The image forming apparatus according to ( 1 ) above, in which all of the plurality of developing units are simultaneously driven (FIG. 6). In the embodiment of the present invention, all the developing clutches are turned on about 800 ms before the start of the image forming process on the most upstream side. Since each developing means is switched from off to on at the same time, not only the control of switching on the developing means is simplified, but also load fluctuation due to the switching on of the developing means and the turning on of the developing means. Due to the background stain toner entering between the image carrier and the transfer target, the adhesive force changes at the same time, and before all the image forming processes, the image carrier during the image forming process. The constant value stability of the slip ratio or linear velocity ratio between the transfer target and the transfer target is high. That is, the effect of suppressing the transfer deviation of the toner image is high.

(2) A plurality of image forming members (11M, C, Y, K) arranged in a predetermined direction, and a plurality of developing means (20M, C) each forming a toner image on each image forming member. , Y, K) and the transfer target (P, 60) for receiving the transfer of the toner image on each image bearing member.
(61-64) means for driving along the arrangement of the image carrier
And an image forming apparatus having respective transfer means (67M, C, Y, K; 9M, C, Y, K) for transferring the toner image on each image forming body to the transfer receiving body. The image forming apparatus is characterized in that all the driving of (1) is stopped after the transfer end timing of the image forming carrier which the transfer target reaches last (FIG. 6).

Due to load fluctuations caused by switching each developing means from ON (driving) to OFF (stop), and due to the developing means being turned OFF, the area of the image bearing member which is free of the background stain toner is brought into pressure contact with the transferred material. During the image forming process, the developing means is turned on because the change in the adhesive force is after the developing timing of the image forming member through which the transferred material finally passes, that is, after the entire image forming process. There is no change in the slip ratio or the linear velocity ratio between the image bearing member and the transferred member due to switching off, and a print with less transfer deviation can be obtained.

( 2a ) The image forming apparatus according to ( 2 ) above, in which all the driving of the plurality of developing means are simultaneously stopped (FIG. 6). In the embodiment of the present invention, all the developing clutches are turned off about 50 ms after the end of the image forming process on the most downstream side. Since each developing means is switched from on to off at the same time,
Not only the control of switching off the developing means is simplified, but also the load fluctuation due to the switching off of the developing means and the fact that the background stain toner disappears and the adhesive force changes due to the turning off of the developing means. Since all the image forming processes are performed, the constant value stability of the slip ratio or the linear velocity ratio between the image bearing member and the transferred member during the image forming process is high. That is, the effect of suppressing the transfer deviation of the toner image is high.

( 3 ) Each of the transfer means (67M, C, Y, K; 9M, C,
The image forming apparatus according to any one of (1) to ( 2a ) above, in which all transfer bias application by (Y, K) is started before the transfer start timing of the most upstream transfer means (67M, 9M) (FIG. 8).

The most upstream change in the electrostatic adhesion between the image bearing member (11M, C, Y, K) and the transfer target (P, 60) due to the start (ON) of the transfer bias application is the most upstream. Since the transfer is completed before the transfer is started by the transfer means, even if the number of times the transfer target (60) is used is increased, the speed fluctuation of the transfer target (P, 60) is reduced, thereby reducing the color shift. That is, there is no change in the slip ratio or the linear velocity ratio between the image bearing member and the transferred member due to the switching of the transfer bias from OFF to ON after the most upstream transfer means has started the transfer, and the transfer deviation does not occur. You can get few prints.

(3a) The image forming apparatus according to ( 3 ) above, wherein the transfer bias application by each of the transfer means is simultaneously performed (FIG. 8). Since the transfer bias is applied to each transfer means at the same time, it is easy to control the transfer bias to be turned on. Even if the number of times the transfer target (60) is used increases, the constant value stability of the slip ratio or linear velocity ratio between the image bearing member and the transfer target during the image forming process is high. That is, the effect of suppressing the transfer deviation of the toner image is high.

( 4 ) Each of the transfer means (67M, C, Y, K; 9M, C,
The image forming apparatus according to any one of (1) to (3a) above, in which all transfer bias application by Y, K) is stopped after the transfer end timing of the downstreammost transfer means (67K, 9K) (FIG. 8). .

The change in electrostatic adhesion between the image bearing member (11M, C, Y, K) and the transfer target (P, 60) due to the stop (off) of the transfer bias application is the most downstream change. Since the transfer is completed after the transfer by the transfer means, even if the number of times the transfer target (60) is used is increased, the speed fluctuation of the transfer target (P, 60) is reduced, thereby reducing the color misregistration. That is, there is no change in the slip ratio or the linear velocity ratio between the image bearing member and the transferred member due to switching of the transfer bias from ON to OFF by the transfer means at the most downstream side, and the transfer deviation occurs. You can get prints with less.

( 4a ) The image forming apparatus described in ( 4 ) above, wherein the application of the transfer bias by each of the transfer means is simultaneously stopped (FIG. 8). In the embodiment of the present invention, all transfer biases are turned off about 50 ms after the end of the image forming process on the most downstream side. Since the application of the transfer bias to each transfer means is stopped at the same time, the control of switching the transfer bias off can be simplified. Even if the number of times the transfer target (60) is used increases, the constant value stability of the slip ratio or linear velocity ratio between the image bearing member and the transfer target during the image forming process is high. That is, the effect of suppressing the transfer deviation of the toner image is high.

Further, by simultaneously starting and stopping the transfer bias for all transfer means, it is possible to simplify software and IO devices for controlling all transfer means.
Cost can also be reduced.

( 5 ) Color scanner (SCR), image forming apparatus (PT) according to any one of the above (1) to ( 4a )
R), and a color copying machine (FIG. 1) including an image processing device (40) for converting color image data generated by the color scanner into image data for image formation of the image forming device. According to this, in the color copying apparatus, the function and effect described in any one of the above (1) to ( 4a ) can be obtained.

( 6 ) Parallel bus for transferring image data
(Pb), image memory (MEM), image memory control means (IMAC) for writing image data on the parallel bus to the image memory and reading image data from the image memory on the parallel bus, and the color scanner The color copying apparatus of ( 5 ) above, further comprising image data control means (CDIC) for controlling the exchange of image data between the image processing means and the parallel bus.

For example, the image data control means (CDIC) sends the output image data of the color scanner processed by the image processing device (40) to the parallel bus (Pb), and the image memory control means (IMAC) outputs the parallel bus ( The image data of Pb) can be written in the image memory (MEM). Then, the image memory control means (IMAC) reads the image data of the image memory (MEM) onto the parallel bus (Pb), and the image data control means (CDIC) reads the RGB image data of the parallel bus (Pb) from the image processing device (40 ) To the image forming apparatus (PTR) for printout. Therefore, image data can be accumulated and stored in the image memory. Further, image editing can be performed by using reading and writing with respect to the image memory (MEM).

Other objects and features of the present invention will become apparent from the following description of embodiments with reference to the drawings.

[0041]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment FIG. 1 shows the appearance of a multi-function copying machine according to one embodiment of the present invention. The multi-function copying machine is roughly composed of an automatic document feeder ADF, an operation board OPB, an SCR, and a color printer PTR. The on-board multi-function controller includes a personal computer PC and a switch P.
BX is connected, and the exchange PBX is connected to a telephone line (facsimile communication line). Printer PTR
The printed paper of is ejected onto the paper ejection tray 8.

FIG. 2 shows the configuration of the color printer PTR. The printer of this embodiment is a laser printer.
This laser printer PTR is a magenta (M), cyan
Four sets of toner image forming units for forming images of (C), yellow (Y) and black (black: K) are arranged along the moving direction of the transfer paper (from the lower right to the upper left in the figure). The levers are arranged in this order. That is, it is a four-drum type full-color image forming apparatus.

These magenta (M), cyan (C), yellow
The (Y) and black (K) toner image forming units respectively include photoconductor units 10M, 10C, 10Y and 10K having photoconductor drums 11M, 11C, 11Y and 11K, and developing units 20M, 20C, 20Y and 20K. Is equipped with. Further, the respective toner image forming portions are arranged such that the rotation axes of the photoconductor drums 11M, 11C, 11Y and 11K in the respective photoconductor units are parallel to the horizontal x-axis and the transfer paper moving direction (y, 45 on the z-plane with respect to the y-axis
It is set so that a predetermined pitch is arranged on the left upward line). As the photoconductor drum of each photoconductor unit, a photoconductor drum having an organic photoconductor (OPC) layer on the surface and having a diameter of 30 mm was used.

In addition to the toner image forming section, the laser printer PTR carries an optical writing unit 2 by laser scanning, paper feed cassettes 3, 4, a pair of registration rollers 5, and a transfer paper carrying each toner. A transfer belt unit 6 as a belt device having a transfer / transport belt 60 as a transfer / transport member for transporting the transfer position of the image forming unit, a fixing unit 7 of a belt fixing system, a discharge tray 8 and the like are provided. . The laser printer also includes a manual feed tray, a toner replenishing container, a waste toner bottle, a double-sided / reversing unit, a power supply unit, and the like, which are not shown.

The optical writing unit 2 is provided with a light source, a polygon mirror, an f-θ lens, a reflection mirror, etc., and supplies a laser beam to the surface of each photoconductor drum 11M, 11C, 11Y and 11K based on image data. Irradiate while swinging and scanning in the x direction. Further, the alternate long and short dash line in FIG. 2 indicates the transfer paper conveyance path. The transfer paper fed from the paper feed cassettes 3 and 4 is conveyed by the conveyance rollers while being guided by a conveyance guide (not shown), and is then sent to the registration roller pair 5. The transfer paper sent to the transfer / transport belt 60 at a predetermined timing by the registration roller pair 5 is transferred / transferred to the transfer / transport belt 60.
And is conveyed so as to pass through the transfer position of each toner image forming unit.

Photoreceptor drum 11M of each toner image forming section,
The toner images formed on 11C, 11Y and 11K are
The transfer paper, which is carried and transferred by the transfer / conveyance belt 60, is transferred to the fixing unit 7 by superposing the toner images of respective colors, that is, the transfer paper on which the color image is formed. When passing through the fixing unit 7, the toner image is fixed on the transfer paper. The transfer paper on which the toner image is fixed is discharged onto the paper discharge tray 8.

That is, the transfer is a direct transfer system in which the toner image is directly transferred onto the transfer paper. The photosensitive drums 11M, 11C, 11Y and 11K have a linear velocity (about 125 mm / se) which is about 1% faster than the transfer / conveying belt 60.
It is driven by c). That is, the linear velocity ratio (photoreceptor speed / transfer belt speed × 100%) is about 101%.

FIG. 3 shows an outline of the toner image forming portion for yellow Y among the toner image forming portions. The other toner image forming portions have the same structure as that of the yellow Y. In FIG. 3, the yellow Y toner image forming unit includes the photoconductor unit 10Y and the developing unit 20Y as described above. The photoconductor unit 10Y irradiates the photoconductor drum 11Y, a brush roller 12Y for applying a lubricant to the photoconductor drum surface, a swingable blade 13Y for cleaning the photoconductor drum surface, and a light for the photoconductor drum surface. A charge eliminating lamp (not shown), a non-contact type charging roller 15Y for uniformly charging the surface of the photosensitive drum, and the like are provided.

In the photoconductor unit 10Y having the above-mentioned structure, the optical writing unit 2 modulates the polygons modulated on the basis of print data on the surface of the photoconductor drum 11Y uniformly charged by the charging roller 15Y to which an AC voltage is applied. When the laser beam L deflected by the mirror is emitted while being scanned, an electrostatic latent image is formed on the surface of the photoconductor drum 11Y. The electrostatic latent image on the photoconductor drum 11Y is developed by a developing unit 20Y described later to become a yellow Y toner image. At the transfer position Pt where the transfer paper P on the transfer / transport belt 60 passes, the toner image on the photosensitive drum 11Y is transferred to the transfer paper P. After the toner image has been transferred, the surface of the photoconductor drum 11Y is coated with a predetermined amount of lubricant by the brush roller 12Y, cleaned by the blade 13Y, and discharged by the light emitted from the discharge lamp. To prepare the electrostatic latent image of.

The developing unit 20Y contains a two-component developer containing a magnetic carrier and a negatively charged toner. Then, the developing roller 22Y disposed so as to be partially exposed from the opening of the developing case 1Y on the side of the photosensitive drum,
Transport screws 23Y, 24Y, doctor blade 25
Y, toner concentration sensor 26Y, powder pump 27Y and the like are provided. The developer contained in the developing case 21Y is
It is frictionally charged by being stirred and conveyed by the conveying screws 23Y and 24Y. Then, a part of the developer is carried on the surface of the developing roller 22Y. The doctor blade 25Y uniformly regulates the layer thickness of the developer on the surface of the developing roller 22Y,
The toner in the developer on the surface of the developing roller 22Y is transferred to the photoconductor drum 11Y, whereby a toner image corresponding to the electrostatic latent image appears on the photoconductor drum 11Y. Development case 2
The toner density of the developer in 1Y is the toner density sensor 26Y.
Detected by. When the density is insufficient, the powder pump 27Y is driven to replenish the toner.

Magenta images in the four photoconductor drums,
Photosensitive drum 11 for forming a cyan image and a yellow image
M, 11C and 11Y are decelerated by one stage via a power transmission system and a speed reducer (not shown) by one electric motor (color drum motor; color drum M: not shown) for driving a color drum, not shown. Driven. The photoconductor drum 11K for forming a black image is the one for driving the black drum.
The electric motor (K drum motor: not shown) is driven by one-stage deceleration via a power transmission system and a speed reducer (not shown). Further, the transfer / conveying belt 60 includes a transfer driving roller 62K via a power transmission system using the K drum motor.
Is driven to move rotationally. Therefore, the K drum motor drives the K photoconductor drum 11K and the transfer / conveyance belt 60, and the color drum motor drives the M, C, Y photoconductor drums 11M, 11C, 11Y.

Further, the K developing device 20K includes a fixing unit 7
Is driven by an electric motor (not shown) that drives a power transmission system and a clutch (not shown). M, C,
The Y developing devices 20M, 20C and 20Y are the registration rollers 5
Is driven by an electric motor (not shown) via a power transmission system and a clutch (not shown). Developing device 20
M, 20C, 20Y, and 20K are not constantly driven, and are transmitted by the clutch so that they can be driven at a predetermined timing.

FIG. 4 shows the rough structure of the transfer belt unit 6 in a little more detail. The transfer conveyance belt 60 of the transfer belt unit 6 is a high resistance endless single layer belt having a volume resistivity of 10 ⁹ to 10 ¹¹ Ωcm, and its material is PV.
DF (polyvinylidene fluoride). The transfer / conveyance belt 60 includes a pair of photosensitive drums 11M,
Four grounded stretching rollers 61 to 11 are provided so as to pass through the respective transfer positions in contact with and facing 11C, 11Y and 11K.
It is hung around 64. Of these tension rollers,
A power supply 65 is provided at the inlet roller 61 on the upstream side in the transfer paper moving direction.
The electrostatic attraction roller 65 to which a predetermined voltage is applied from a is disposed so as to face each other. These two rollers 61, 6
The transfer paper (P) that has passed between 5 is the transfer conveyance belt 60.
It is electrostatically adsorbed on top. The exit roller 62 on the downstream side in the transfer paper moving direction is a drive roller that frictionally drives the transfer / conveyance belt 60, and is connected to a drive source (not shown).
Further, a bias roller 66, to which a predetermined cleaning voltage is applied from a power source 66a, is arranged so as to come into contact with the outer peripheral surface of the transfer / conveying belt 60 stretched between the stretching rollers 63 and 64. The bias roller 66 removes foreign matter such as toner attached to the transfer / conveyance belt 60.

Further, as the transfer electric field forming means for forming a transfer electric field at each transfer position, the photosensitive drums 11M, 1M
Transfer bias applying members 67M, 67C, 67Y and 67K are provided so as to come into contact with the back surface of the transfer / conveying belt 60 that forms a contact facing portion that contacts and faces 1C, 11Y and 11K. This transfer bias applying member 67
M, 67C, 67Y and 67K are fixed brushes made of Myra, and transfer bias is applied from the transfer bias power sources 9M, 9C, 9Y and 9K. By the transfer bias applied by the transfer bias applying member, transfer charge is applied to the transfer / transport belt 60, and a transfer electric field having a predetermined strength is formed between the transfer / transport belt 60 and the surface of the photosensitive drum at each transfer position. .

FIG. 5 shows an electric system of the copying machine shown in FIG. Original scanner SCR for optically reading originals
In the reading unit 44, the light reflected by the lamp with respect to the original is condensed on the light receiving element by the mirror and the lens. The light receiving element (CCD in this embodiment) is in the sensor board unit SBU (hereinafter simply referred to as SBU), and the image signal converted into an electric signal in the CCD is
After being converted into a digital signal, that is, read image data on the SBU, it is output from the SBU to the image processing 40.

The system controller 46 and the process controller 31 are connected to the parallel bus Pb and the serial bus S.
Communicate with each other via b. The image processing 40 internally performs data format conversion for a data interface between the parallel bus Pb and the serial bus Sb.

The read image data from the SBU is transferred to the image processing 40, and the image processing causes signal deterioration due to quantization into an optical system and a digital signal (scan system signal deterioration: read image data due to scanner characteristics. -Distortion of the image data), the image data is transferred to the copying function controller MFC and written in the memory module MEM (hereinafter simply referred to as the memory MEM or MEM). Alternatively, a process for printer output is applied to the printer PTR.

That is, the image processing 40 includes a job of storing the read image data in the memory MEM and reusing it.
Video data control VDC without storing in memory MEM
(Hereinafter, simply referred to as VDC), and the image is output by the laser printer PTR. As an example of storing in the memory MEM, when copying a plurality of originals, the reading unit 44 is operated only once, the read image data is stored in the memory MEM, and the stored data is read out multiple times. is there. As an example where the memory MEM is not used, when one original is copied, only the read image data may be processed as it is for printer output, and therefore it is not necessary to write to the memory MEM.

First, when the memory MEM is not used, the image processing 40 performs image reading correction on the read image data, and then performs image quality processing for conversion into area gradation. The image data after the image quality processing is transferred to VDC. For the signal converted into the area gradation, the post-processing regarding the dot arrangement and the pulse control for reproducing the dots are performed by VDC, and the reproduced image is formed on the transfer paper in the image forming unit 35 of the laser printer PTR. To do.

In the case where additional processing such as rotation in the image direction and image composition is carried out when the image data is stored in the memory MEM and is read from the memory MEM, the image data subjected to the image reading correction is passed through the parallel bus Pb. It is sent to the image memory access control IMAC (hereinafter simply referred to as IMAC). Here, based on the control of the system controller 46, the access control of the image data and the memory MEM, the external personal computer PC
It expands print data (hereinafter simply referred to as a PC) (character code / character bit conversion) and compresses / expands image data for effective use of memory. The data sent to the IMAC is stored in the MEM after data compression, and the stored data is read out as necessary. The read data is decompressed, restored to the original image data, and returned from the IMAC to the image processing 40 via the parallel bus Pb.

When the process is returned to the image processing 40, image quality processing is performed there and pulse control by VDC is performed to form a visible image (toner image) on the transfer paper in the image forming unit 35.

The FAX transmission function, which is one of the composite functions,
Image processing of image data read by the document scanner SCR 40
Image reading correction is performed in the FAX control unit FCU (hereinafter simply referred to as FCU) via the parallel bus Pb.
Transfer to. The FCU converts data to a telephone line PN (hereinafter simply referred to as PN) which is a public line communication network, and then P
Send to N as FAX data. FAX reception is PN
The line data from is converted into image data by the FCU, and transferred to the image processing 40 via the parallel bus Pb and the color data interface control CDIC (hereinafter simply referred to as CDIC). In this case, no special image quality processing is performed, dot rearrangement and pulse control are performed in VDC, and the image forming unit 35 forms a visible image on the transfer paper.

In a situation where a plurality of jobs, such as a copy function, a FAX transmission / reception function and a printer output function, operate in parallel, the reading unit 44 and the image forming unit 35.
And the allocation of the parallel bus Pb usage right to the job,
System controller 46 and process controller 31
Control with.

The process controller 31 controls the flow of image data, the system controller 46 controls the entire system, and manages the activation of each resource. For the function selection of this digital multi-function copying machine, the operation contents OPB are selected and input to set the processing contents such as the copy function and the FAX function.

The printer engine 34 shown in FIG.
Includes an electric device such as a motor, a solenoid, a charger, a heater, a lamp, and an electric sensor, which are incorporated in the printing mechanism shown in FIG. 1, that is, an image forming mechanism, and an electric circuit (driver) and a detection circuit (signal processing circuit) for driving them. It is a mechanism driving electric system, and the operation of these electric circuits is controlled by the process controller 31, and the detection signal (operating state) of the electric sensor is read by the process controller 31.

FIG. 6 shows the operation timing of the image forming element under the image forming process control of the process controller 31. The difference from the conventional example shown in FIG. 9 is that development M, C, Y, K
It is the on / off timing of the clutch. The transfer paper P is in contact with the photosensitive member of the color M / transfer pressure contact in synchronization with the turning on of the transfer M bias with reference to the on-timing of the registration clutch (the rising edge of the signal shown in FIG. 6) that connects the registration roller 5 to the power transmission system. Enter the department. Further, conventionally, as shown in FIG. 9, the developing M and C clutches are turned on at substantially the same time, but the other colors are sequentially turned on and the same is applied to the off state. Therefore, the conventional clutch on / off timing is performed during the image forming process.
However, in the present embodiment, as shown in FIG. 6, the on / off timing of the developing clutch is set to a time outside the image forming process.

FIG. 10 is a graph showing changes in the transfer belt surface position when one sheet of A3 is passed at the conventional timing.
7 and FIG. 7 shows the timing A shown in FIG. 6 of the present embodiment.
3 is a graph showing a change in the transfer belt surface position when one sheet of No. 3 is passed.

The position variation shown in FIG. 7 is the tangential direction of the peripheral surface of the photosensitive drum with respect to the virtual transfer position when the surface of the transfer paper comes into contact with each point on the peripheral surface of the photosensitive drum at the same linear velocity. Of the actual transfer position.

In the conventional example shown in FIG. 10, about 120
A sudden position change is seen around 0 ms. Also about 530
A rapid position change is seen near 0 ms. The former is synchronized with turning on the Y developing clutch. The latter is synchronized with the M and C developing clutches being off. In the upper area of FIGS. 6 to 10, horizontal bars of M, C, Y, and K are drawn as an image forming process. The period with a horizontal bar is the image forming process period for each color.

The graphs of FIGS. 7 and 10 also include a rectangular wave indicating the on / off state of the registration clutch. The high level region of the rectangular wave is on (driving) and the low level region is off (stopping). In the conventional example shown in FIG. 10, about 1200 ms
It is shown that the position variation of (1) occurs during M image formation, and the position variation of about 5300 ms occurs during Y, K image formation.

In FIG. 7 showing the first embodiment of the present invention, it can be seen that no abrupt position change occurs during the image forming process. Therefore, at the conventional timing, each color appears as a color shift due to the above-described position variation. On the other hand, at the timing of the present invention, no rapid position change is observed, so it can be seen that the color shift is at a level at which it is hardly noticeable.

Photosensitive drum 11 with the developing clutch off.
When M, 11C, 11Y and 11K and the transfer / conveying belt 60 are driven (the transfer paper P is still the photosensitive drum 11M).
/ Before entering the transfer conveyance belt pressure contact portion), the photoconductor 11
Since there is almost no toner on M, 11C, 11Y, and 11K, when the transfer belt 60 is pressed against the surface of the transfer belt in that surface state, the transfer / conveying belt 60 has a linear velocity of about 1% faster than the photosensitive drums 11M, 11C, 11Y, and 11K. It has been pulled a little by and it is faster than it should be. Next, when the developing clutch is turned on at a predetermined timing, even if there is no image, the toner adheres to the photoconductor at the toner level of the background stain. When the smeared toner enters the photosensitive member / transfer belt pressure contact portion, the slip at the pressure contact portion becomes larger than that in the state where there is no toner. In short, the amount pulled by the photoconductor changes. The change in the amount of the transfer belt pulled by the photoconductor appears as a change in the transfer belt position. Therefore, the position change does not appear on the transfer belt immediately after the developing clutch is turned on, but the position change occurs when the background toner adheres to the photoconductor when it is turned on and enters the pressure contact portion. In this example, the time is about 230 ms. This can be read from FIG. 10 because the waveform does not change abruptly immediately after the developing clutch is turned on or off and the waveform changes after about 230 ms.

All image forming processes M, C, Y, shown in FIG.
The positional deviation is stable at about 0.10 mm in the entire section of K, so that the color deviation is small.

-Second Embodiment-Hardware and image data processing of the second embodiment, and
The outline of image forming control is the same as that of the above-described first embodiment. However, the second embodiment is different from the first embodiment in the on / off timing control of the transfer bias by the process controller 31.

FIG. 8 shows the operation timing of the image forming element under the image forming process control of the process controller 31 of the second embodiment. The difference from the conventional example shown in FIG.
These are the on / off timings of the C, Y, K clutches and the on / off timings of the transfer M, C, Y, K biases. The on / off timing of each color developing clutch is the same as in the first embodiment shown in FIG.

As described above, application of the transfer bias for each color (ON) while the transfer unit is used less frequently.
Although the toner image transfer position deviation due to / stop (OFF) does not appear so much (FIG. 10), the toner image transfer position deviation due to ON / OFF of each color transfer bias becomes remarkable as the number of times the transfer unit is used increases (FIG. 10). 11 to 13).

Therefore, in the second embodiment, as shown in FIG. 8, the on / off timing of the transfer bias is set to a time outside the image forming process. That is, the transfer biases of all colors are turned on almost at the same time as the start of the image forming process on the most upstream side (M). Further, the transfer bias for all colors is turned off at the transfer bias off timing on the most downstream side (K), and at least it does not affect the image forming process. In this embodiment, all transfer biases are turned off about 50 ms after the end of the image forming process on the most downstream side (K).

In the second embodiment, as described above, the all-color developing clutch and all-color transfer bias are turned on before the start of the all-color image forming process, and after the all-color image forming process is completed.
Since the all-color development clutch and all-color transfer bias are turned off, even if the number of times the transfer unit is used increases, the same slip conditions will be maintained in the photoconductor / transfer belt pressure portion during the image formation process for all colors. Therefore, the transfer belt runs stably. As a result, the color misregistration caused by the change in the transfer belt position is significantly reduced. At the same time, the software for controlling the transfer bias and the device for turning on / off the transfer bias can be simplified, which can reduce the load on the software designer and the device cost.

Incidentally, in both the first and second embodiments,
It is a full-color copying machine that has a combined function of 4-drum system + direct transfer belt system, but it is a 4-drum system in which toner images of respective colors are transferred onto the intermediate transfer belt in a superimposed manner, and then transferred to transfer paper all at once. The present invention may or may not be applied to the intermediate transfer method.

[0080]

EFFECTS OF THE INVENTION The transferred material (P, 60) is formed on the image carrier (11M, C, Y,
The toner image on each image forming carrier is transferred onto the surface of the transfer target (P, 60) by driving along the arrangement of (K), so that multiple types of toner images are transferred to the transfer target (P, 60). The image formation to be performed can be performed at an extremely high speed as compared with the case where only one image carrier is used. Each developing means is off (stopped) to on (driven)
Load fluctuation due to switching to the
As a result, background toner enters between the image carrier and the transfer target.
The change in the adhesive force caused by the
Since it is before the development timing of the image carrier,
Before the whole image forming process, the developing means is turned on.
Image carrier and transfer target
There is no change in the slip ratio or linear velocity ratio during
A print with less unevenness can be obtained.

[Brief description of drawings]

FIG. 1 is a front view of a full-color image forming apparatus having a composite function according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing an outline of an image forming mechanism of the printer PTR shown in FIG.

FIG. 3 is an enlarged cross-sectional view showing a configuration of a photosensitive unit 10Y for yellow Y image formation and a developing device 20Y for yellow Y shown in FIG.

FIG. 4 is an enlarged view of the transfer / conveyance unit 6 shown in FIG.

5 is a block diagram showing an outline of an electric system of the full-color image forming apparatus shown in FIG.

6 is a time chart showing the drive timing of the image forming functional elements shown in FIG. 2 under the color print process control of the process controller 31 shown in FIG.

7 is a graph in which the surface position variation of the transfer / conveying belt 60 shown in FIG. 2 in the moving direction is measured during the image forming process and before and after the image forming process.

FIG. 8 is a time chart showing the driving timing of the image forming functional elements under the color print process control of the process controller according to the second embodiment of the present invention.

FIG. 9 shows a conventional color print process control,
6 is a time chart showing drive timings of image forming functional elements.

FIG. 10 is a graph in which the surface position variation in the moving direction of the conventional transfer / transport belt is measured during the image forming process and before and after the image forming process.

FIG. 11 is a graph showing a change in the surface position of the transfer / transport belt in the moving direction during the image forming process and before and after the image forming process when the number of times the transfer unit is used is increased.

FIG. 12 is a graph showing the positional deviation of each color extracted based on the positional deviation shown in FIG.

FIG. 13 is a graph showing the positional shift of each MCY color with respect to the K color calculated based on the positional shift of each color shown in FIG.

FIG. 14 is a surface of a transfer conveyance belt in a moving direction during, before, and after an image forming process when all transfer biases are turned off when the number of times the transfer unit is used is increased. It is a graph which measured position variation.

FIG. 15 is a graph showing the positional deviation of each color extracted based on the positional deviation shown in FIG.

16 is a graph showing the positional shift of each MCY color with respect to the K color calculated based on the positional shift of each color shown in FIG.

[Explanation of symbols]

PC: Personal computer PN: Public communication line PBX: Exchanger ADF: Automatic document feeder SCR: Document scanner OPB: Operation unit PTR: Printer 2: Optical writing unit 3, 4: Rest cassette 5: Pair of registration rollers 6: Transfer belt unit 7: Fixing unit 8: Paper ejection tray 10M, 10C, 10Y, 10K: photoconductor unit 11M, 11C, 11Y, 11K: Photosensitive drum 20M, 20C, 20Y, 20K: Developing device 60: Transfer / Conveyor Belt

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI G03G 15/16 G03G 15/08 507H (72) Inventor Yuzo Katsumata 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Company (72) Inventor Mineyo Takahashi 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Company (56) References JP-A-11-174862 (JP, A) JP-A-10- 221914 (JP, A) JP 63-151970 (JP, A) JP 63-49165 (JP, A) JP 2002-23449 (JP, A) JP 2001-282071 (JP, A) JP 2002-6716 (JP, A) JP-A-1-96669 (JP, A) Actual development Sho 63-195350 (JP, U) (58) Fields investigated (Int.Cl. ⁷ , DB name) G03G 15/01 -15/01 117

Claims (4)

(57) [Claims] 1. A plurality of photosensitive elements arranged in a predetermined direction, a plurality of developing means, each forming a toner image on the photosensitive member, a transfer member for receiving the toner image on the photoreceptor A transfer belt for carrying along the arrangement of the photoconductors ,
In the image forming apparatus having each transfer means for transferring the toner image on each photoconductor to the transfer body, all of the plurality of developing means are connected to the photoconductor and the
After starting the transfer belt drive,
The exposure timing of the photoconductor
From the development nip position of the body to the pressure contact part with the transfer belt
Of the moving time of the photosensitive member and the developing means to move the electric motor.
The suction time of the developing clutch connected to the force transmission system
Turn on the development clutch before the combined time
The image forming apparatus is characterized in that the driving is started thereby . 2. A plurality of image forming members arranged in a predetermined direction, a plurality of developing means for forming a toner image on each image forming member, and a transfer of the toner image on each image forming member. in the image forming apparatus having a means for driving the transfer object along the arrangement of the imaging bearing member, and the transfer means for transferring the toner images on the imaging bearing member to a transfer member for receiving the All of the driving of a plurality of developing means
After the final transfer timing of the image bearing member
An image forming apparatus characterized by being stopped . Wherein all the transfer bias application by the respective transfer means, initiates the transfer start timing earlier transfer means the most upstream image forming apparatus according to claim 1 or 2. Wherein said all transfer bias application according to the transfer means, and stops the timing after the end transcription of the most downstream of the transfer means, the image forming apparatus according to claim 1 or 2.