JP2004102039A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To decrease the color slurring quantity within an image or between images formed on an intermediate transfer belt. <P>SOLUTION: The rotational frequency of a polygon motor 35 is varied and controlled according to a belt thickness and the start of horizontal scan exposure and exposure timing are modulated to decrease the color slurring quantity generated owing to thickness unevenness distributed over the entire circumference of an intermediate transfer belt 8. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electrophotographic image forming apparatus that develops a latent image formed on a photoreceptor with toner, and transfers and fixes the toner on a transfer material to perform recording.
[0002]
In particular, it is used in an image recording apparatus having functions such as a copying machine and a printer, and in an image forming apparatus used as an output device such as a multifunction machine and a work station which also have such functions.
[0003]
[Prior art]
A plurality of electrophotographic process units in which a charging device and a developing device are arranged around a photoreceptor are juxtaposed in the device, and an optical image is formed on the photoreceptor surface in each process unit by an exposure device using a laser, LED light, or the like. A latent image is formed on the surface of the photoreceptor by visualizing the latent image, the latent image is visualized using a toner by a developing device, and then the toner is sequentially transferred to an intermediate transfer belt. In recent years, an image forming apparatus for forming an image has been put to practical use.
[0004]
FIG. 3 shows an example of a conventional color printing apparatus. This apparatus is a color electrophotographic copying machine that forms an image by superimposing toners of four colors of magenta, cyan, yellow, and black.
[0005]
Reference numerals 10Y, 10M, 10C, and 10K denote yellow, magenta, cyan, and black image forming units, respectively, and reference numeral 8 denotes an intermediate transfer belt.
[0006]
In each of the image forming units 10Y, 10M, 10C, and 10K, a charger 14, an exposure device 15, a developing unit 16, a transfer unit 17, and a cleaner 18 are arranged around the photosensitive drum 13, and the photosensitive drum 13 is formed by an electrophotographic process. A toner image of each color is formed on the surface.
[0007]
A toner image corresponding to each color is formed on each of the photosensitive drums 13C, 13M, 13Y, and 13K by an image information signal sent from the document reading device 12 or an output device (not shown) such as a computer. Each color toner is successively multiplex-transferred onto the intermediate transfer belt 8 made of a driven conductive sheet material, and a color image is formed on the intermediate transfer belt 8.
[0008]
After the transfer material stored in the cassette 1 is fed by the feed roller 2, the transfer material is transported by the transport rollers 3 to 6 and reaches the registration roller 7. The transfer material is sent out toward the intermediate transfer belt 8 in synchronization with the image on the intermediate transfer belt 8 after correcting the skew or the like by the registration roller 7.
The transfer material sent out from the registration roller 7 joins with the intermediate transfer belt 8 in the secondary transfer section 9, and collective transfer of the four-color toner from the intermediate transfer belt 8 to the transfer material is performed.
[0009]
The transfer material on which the transfer of the four-color toner images has been completed reaches the fixing roller pair 19 through the transport unit. The fixing roller pair 19 is heated by a heater (not shown), and the toner of each color is melted by heat and fixed on a transfer material to complete a color image.
[0010]
The transfer material on which the toner image has been fixed on the surface by the fixing roller pair 19 is directly discharged outside the apparatus.
[0011]
[Problems to be solved by the invention]
However, in the conventional example, the following two problems were significant when driving the belt member.
[0012]
Due to the belt driving roller and the problem such as geometrical shape deviation between the driving roller and the driven roller, the belt body speed changes successively. Therefore, in an image sequentially formed on the belt body, the belt body moving direction, so-called, There has been a problem with image quality such that a position shift occurs between the respective color images in the sub-scanning direction on the transfer material, and the color shift of an image formed on the transfer material deteriorates.
[0013]
These main factors are considered as follows.
[0014]
(1) The driving speed of the driving roller having a radius r driven at a constant angular speed ω and the belt speed V defined by the belt thickness h are represented as follows.
[0015]
V = (r + h / 2) · ω (1)
When the eccentricity Δr is superimposed on the driving roller, the fluctuation ΔV of the belt body moving speed V defined by the driving roller is expressed as follows.
[0016]
_{ΔV ω = Δr ω · ω (} 2)
ω: angular velocity (driving roller rotation cycle)
The speed variation [Delta] V _omega of the drive roller cycle, the respective color images produces a positional displacement of the drive roller cycle.
[0017]
{Circle around (2)} Changes in the belt moving speed defined by the belt driving roller also occur due to fluctuations in the thickness direction over the entire circumference of the belt, and as a result, each color on the transfer material collectively transferred from the belt is changed. As the image quality is degraded such that the image deviates from the ideal position, the image varies between a plurality of transfer materials, and the reproducibility of the repetitive position between the transfer materials is deteriorated.
[0018]
This is because if the belt thickness h wound on a drive roller having a radius r driven at a constant angular velocity ω has a thickness variation Δh over the entire circumferential length, the belt body moving speed defined by the drive roller The variation ΔV _L of V is expressed as follows.
[0019]
ΔV _L = Δh _L · ω (3)
L: Belt full-peripheral period diagram schematically showing the relationship between the belt linear velocity fluctuation defined by the belt driving roller and the positional deviation relationship of the image formed by the belt ideal case and the case including the above problem. 4, as shown in FIG.
[0020]
In addition to showing the exposure timing by each exposure device, the horizontal axis represents the time t on the moving speed of the belt body, the vertical axis represents the belt line moving speed v, and the color scanning lines formed on the belt body are moved in the main scanning direction. This is shown in parallel, and shows how data is written in chronological order.
[0021]
In an ideal case, the transfer belt speed moves at a constant speed V as shown in FIG. A case is shown in which a transfer time difference corresponding to the installation interval of the image forming apparatus for each color of YMCK is given on the transfer belt moving at a constant speed, and writing is given one by one in the main scanning direction at equal intervals in the sub-scanning direction. As a result, it can be seen that the scanning lines of each of the YMCK colors are written at regular intervals in the sub-scanning direction without deviation.
[0022]
On the other hand, FIG. 5 shows a case where the speed of the belt body changes due to the belt thickness and the drive roller eccentricity. The fine AC component fluctuation in the belt speed fluctuation indicated by the solid line corresponds to the above-mentioned (1) the drive roller eccentricity period, and the large undulation component indicated by the broken line corresponds to the (2) belt speed unevenness period. Have fluctuations.
[0023]
In this case, even if the scanning lines are formed by the respective color image forming apparatuses at equal intervals in the sub-scanning direction, the sub-scanning intervals of the scanning lines become uneven by the speed variation of the belt body, and the state occurs for each color. A color shift between the YMCK colors occurs.
[0024]
The results of trial calculations as specific quantities are shown. When an intermediate transfer belt having a total length of 2000 mm has a thickness unevenness with an amplitude of about 5 μm, an eccentricity of the drive roller diameter is set to 10 μm, and a process speed is set to about 400 mm / s, the accumulation of images on the belt when the belt rotates around the belt. The displacement is at most about 100 μm. The result is shown in FIG. FIG. 7 shows an example of the accumulated positional deviation amount of each color and the color deviation amount generated between the respective colors when the image formation of each color is performed in a state where the accumulated positional deviation is present. Even when an image is formed using a belt having an amplitude of only about 5 μm, the maximum color shift amount on the paper is close to 100 μm. This amount is the ideal case for everything else, and in fact various factors are added to it, so if high quality image quality is required, a single element of 100 μm unit Is no longer acceptable.
[0025]
Accordingly, an object of the present invention is to solve the above problem (2) and to provide an image forming apparatus capable of achieving improvement in image quality. (Problem (1) can solve the color misregistration problem between images, for example, by making the transfer distance of each color image and the outer circumference of the belt drive roller equal or an integer ratio).
[0026]
Means and Action for Solving the Problems
SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a color image forming apparatus with less color shift by providing the following configurations (1) to (10).
[0027]
(1) An image is formed on a main body using one or more exposure devices and one or more parallel electrophotographic process units and a belt body, and a toner image is transferred onto a transfer material. In an image forming apparatus that performs a process of fixing a toner image to a transfer material by applying a desired amount of heat and pressure to the transfer material using
A belt body and one drive roller for driving the belt;
At least one driven roller including means for stretching the belt body,
A criterion defining the start of the thickness profile of the stretched belt body,
An image forming apparatus, wherein a scanning speed and an exposure timing of an exposure device are changed so as to cancel an image shift caused by a speed variation caused by a thickness profile of the belt.
[0028]
(2) The image forming apparatus according to (1), wherein the exposure device is a rotary polygon mirror.
[0029]
(3) The image forming apparatus according to (1), wherein the number of rotations of the exposure device is changed so as to cancel a position shift in the sub-scanning direction due to a variation in thickness of the belt member.
[0030]
(4) In response to changing the rotation speed of the exposure device so as to cancel the displacement in the sub-scanning direction due to the thickness variation of the belt member, the main scanning synchronization reference signal of the exposure device is displaced in the main scanning direction. The image forming apparatus according to (3), wherein the image forming apparatus is changed so as to cancel out.
[0031]
(5) The exposure timing of the exposure device in the main scanning direction is modulated to change the main scanning magnification in response to the rotation speed of the exposure device being changed so as to cancel the positional deviation in the sub-scanning direction due to the thickness variation of the belt member. The image forming apparatus according to the above (3), wherein the correction has been performed.
[0032]
(6) The image forming apparatus according to (1), wherein the belt body is an intermediate transfer belt.
[0033]
(7) The image forming apparatus according to (1), wherein the belt body is a transfer / transport belt.
[0034]
(8) The image forming apparatus according to (1), wherein the belt body is a photosensitive belt.
[0035]
(9) The image according to (1), wherein the thickness profile of the belt is measured using a displacement measuring device installed in an image forming apparatus, and is fed back as information for controlling the rotation speed of the exposure device. Forming equipment.
[0036]
(10) The image forming apparatus according to (1), wherein the speed profile of the belt is measured by using a speed measuring device installed in the image forming apparatus, and is fed back as information for controlling the rotation speed of the exposure device. apparatus.
[0037]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described based on examples with reference to the drawings.
[0038]
[Example 1]
The overall configuration of the apparatus is the same as that of the conventional example, and a description thereof will be omitted.
[0039]
FIG. 1 shows an extracted main part configuration. The laser light emitted from the laser light emitting device 31 is reflected by the polygon motor unit 35, passes through the optical lens, and forms a latent image on the drum 13. A so-called BD detection device 32 is provided to specify the start position of the scanning line at this time. A toner image is formed by an electrophotographic process function unit (not shown), and is transferred onto an intermediate transfer belt 8 that is driven to rotate in a direction indicated by an arrow by a driving roller 30.
[0040]
The states of the scanning lines formed at this time are shown in comparison with FIGS. 2 (a), (b), (c) and (d).
[0041]
FIG. 2A shows an ideal state, in which the polygon motor P.R. V. And a speed diagram ITB. Of the intermediate transfer belt 8 driven at a constant speed. At the same time as writing V, writing is performed at a fixed exposure timing Tbd0 when writing the scanning line transferred onto the intermediate transfer belt 8, a fixed line length L0 corresponding to a fixed exposure time T0, and a fixed sub-scanning interval X0. It shows how it is. The moving direction of the intermediate transfer belt ITB and the scanning line Scan direction are indicated by arrows in the figure.
[0042]
FIG. 2B shows a case where the transfer belt thickness varies over the entire circumference with respect to these ideal states. The transfer belt speed is not constant but changes based on the belt thickness. At this time, a plurality of scanning lines written on the transfer belt at predetermined exposure intervals are transferred onto the intermediate transfer belt 8 at intervals of X1, X2,. This shows a case of a single color, but as a result of passing through a plurality of image forming process units, the scanning line intervals are scattered and color shift occurs.
[0043]
The case where the present invention is applied to such a state will be described with reference to FIGS. First, as shown in (c), the rotation speed, that is, the rotation speed of the polygon motor 35 is changed in a direction to cancel the speed change based on the transfer belt thickness. That is, the speed of the polygon motor 35 is increased as the thickness of the intermediate transfer belt 8 is increased and the belt speed is increased, and the rotation speed is increased accordingly, and as the thickness of the intermediate transfer belt 8 is decreased and the belt speed is reduced, the rotation speed is increased accordingly. , The scanning line pitch on the intermediate transfer belt 8 can be made substantially equal to X0.
[0044]
However, changing the number of revolutions of the polygon motor 35 changes not only in the sub-scanning direction but also in the main scanning direction. As shown in (c), when the BD time Tbd0 is kept constant by increasing or decreasing the number of rotations, a problem occurs in which the writing start position of the scanning line differs for each scanning line. In addition, when the polygon rotation speed changes (acceleration / deceleration) while the scanning line exposure time is constant, the scanning line length also changes as L1, L2,... Ln.
[0045]
Thus, as shown in (d), by giving the following changes to the exposure time in the main scanning direction, it is possible to realize scanning lines having equal intervals and equal lengths in the main and sub scanning directions.
[0046]
A BD timing Tbd (f) obtained by modulating information based on the transfer belt thickness distribution with respect to the BD basic time Tbd0 is given. That is, when the belt thickness is increased and the belt moving speed is increased, the BD time is shortened. When the belt thickness is decreased and the belt moving speed is decreased, the BD time is increased. In addition, it is possible to prevent the variation of the writing portion of the scanning line.
[0047]
Further, information based on the thickness distribution of the transfer belt is modulated with respect to an exposure timing T0 for forming a scanning line to be T (f). In other words, when the belt thickness increases and the belt moving speed increases, the original exposure timing is shorter than the original exposure timing. When the belt thickness decreases and the belt moving speed decreases, the original exposure timing decreases. By making the length longer, it is possible to prevent the fluctuation of the scanning line length L0.
[0048]
Further, when performing thickness unevenness correction for the thickness distribution over the entire circumference of the belt body, a so-called home position is added to the belt body, and the thickness correction that is repeated for each rotation of the belt body is performed using a so-called home position signal. By doing so, thickness unevenness correction suitable for the belt cycle can be performed.
[0049]
The belt body thickness information is obtained by writing marks on the belt body at equal intervals in the sub-scanning direction as described in, for example, Japanese Patent Laid-Open No. It may be obtained by a method of obtaining the thickness distribution of the entire belt using the minutes.
[0050]
Even if there is no belt body thickness information, the surface speed of the belt body may be measured using a separately prepared laser Doppler velocimeter, for example, and polygon motor speed control and exposure time control suitable for the speed may be performed.
[0051]
Further, even if there is no belt body thickness information, the drive radius up to the surface of the belt body may be measured using, for example, a displacement meter separately prepared, and polygon motor speed control and exposure time control suitable for the displacement may be performed. .
[0052]
The belt member described above is formed in each color in a color image forming apparatus using an intermediate transfer belt in a so-called electrophotographic system, a color image forming apparatus using a transfer belt system, and a color image forming apparatus using a photosensitive belt system. Since it is possible to execute the toner image at a constant process speed, it is possible to eliminate the positional deviation between the respective colors, and it is also possible to eliminate the positional deviation between a plurality of toner images. Images can be obtained.
[0053]
【The invention's effect】
As described above, according to the present invention, the fluctuation of the belt body moving speed due to the difference in the thickness of the belt body is measured by using a belt thickness profile separately measured with reference to a reference mark provided on the belt or a real-time profile. By changing the number of rotations of the rotating polygon mirror and changing the exposure timing to cancel the amount of displacement due to the fluctuation of the belt speed, based on the measured speed of the belt speed It is possible to improve the accuracy of the image transfer position within the image and the accuracy of the reproducibility of the image transfer position between a plurality of images.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating an embodiment of the present invention. FIG. 2 is a diagram illustrating an embodiment of the present invention. FIG. 3 is a configuration of an image forming apparatus in a conventional example. FIG. 4 illustrates a conventional ideal image formation. FIG. 5 illustrates a conventional image forming problem. FIG. 6 illustrates a conventional image forming problem (belt thickness). FIG. 7 is a diagram for explaining a problem in conventional image formation (color shift in an image).
DESCRIPTION OF SYMBOLS 1 Cassette 2 Paper feed roller 3, 4, 5, 6 Conveyance roller 7 Registration roller 8 Intermediate transfer belt 9 Secondary transfer part 10 Electrophotographic process unit (image forming part)
12 Image reading device 13 Photoconductor (photosensitive drum)
14 Charger 15 Exposure device 16 Developing device 17 Transfer device 18 Cleaning device 19 Fixing device (fixing roller pair)
Reference Signs List 20 reversing unit 30 drive roller 31 laser light emitting device 32 BD detection device 35 polygon motor unit (polygon motor)

Claims (10)

An image is formed on the main body using one or more exposure devices and one or more parallel electrophotographic process units and a belt body, and after transferring a toner image onto a transfer material, the desired image is formed using a fixing device. An image forming apparatus that performs a process of fixing a toner image to a transfer material by applying heat and pressure of the transfer material to the transfer material,
A belt body and one drive roller for driving the belt;
At least one driven roller including means for stretching the belt body,
A criterion defining the start of the thickness profile of the stretched belt body,
An image forming apparatus, wherein a scanning speed and an exposure timing of an exposure device are changed so as to cancel an image shift caused by a speed variation caused by a thickness profile of the belt. The image forming apparatus according to claim 1, wherein the exposure device is a rotary polygon mirror. 2. The image forming apparatus according to claim 1, wherein the number of rotations of the exposure device is changed so as to cancel a position shift in the sub-scanning direction due to a thickness variation of the belt member. 3. In response to changing the rotation speed of the exposure device so as to cancel the displacement in the sub-scanning direction due to the thickness variation of the belt member, the main scanning synchronization reference signal of the exposure device is used to cancel the displacement in the main scanning direction. The image forming apparatus according to claim 3, wherein: In response to changing the rotation speed of the exposure device to cancel the positional deviation in the sub-scanning direction due to the thickness variation of the belt body, the main scanning direction exposure timing of the exposure device was modulated to correct the main scanning magnification. The image forming apparatus according to claim 3, wherein: The image forming apparatus according to claim 1, wherein the belt member is an intermediate transfer belt. 2. The image forming apparatus according to claim 1, wherein the belt is a transfer / conveyance belt. 2. The image forming apparatus according to claim 1, wherein the belt body is a photosensitive belt. 2. The image forming apparatus according to claim 1, wherein the thickness profile of the belt is measured using a displacement measuring device installed in the image forming apparatus, and fed back as information for controlling the rotation speed of the exposure device. 2. The image forming apparatus according to claim 1, wherein a speed profile of the belt is measured by using a speed measuring device installed in the image forming device, and fed back as information for controlling the rotation speed of the exposure device.

Images