JPH0687240A - Image forming device - Google Patents

Abstract

PURPOSE:To eliminate an occurrence of color irregularities and a color shift in a transfer process by forming a multi-color image by overlapping substantially band-form images of two or more colors having different image forming angles. CONSTITUTION:A first color image is formed at an angle of 26.6 deg. and a second color image is formed at an angle of -26.6 deg. For arranging first color pixels as shown by a pixel arrangement A and second color pixels as shown by a pixel arrangement B, triangular pulse signals are used so as to be delayed for every scanning line. Based on the first and second color pixel arrangements, band-form first color images are formed on a photosensitive body and, thereafter, second color images are superimposed thereon. Even with an occurrence of a large or small resist shift, there is no color irregularities or tone change because an area of an overlapped part is not changed at all. This is clearly shown by a state A having no resist shift in a multiple color image and a state B having a resist shift.

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 such as a copying machine or a printer of an electrophotographic system or an electrostatic recording system,
In particular, the visible color developed image (color toner image) formed on the image carrier is transferred and carried on the intermediate transfer member, and subsequently the respective color developed images are sequentially transferred and carried on the intermediate transfer member in a superimposed manner. After that, the present invention relates to a color image forming apparatus using an intermediate transfer method in which the intermediate transfer member is collectively transferred to a transfer material.

[0002]

2. Description of the Related Art Conventionally, a visible developed image (toner image) formed on an image carrier is primarily transferred onto an endlessly traveling intermediate transfer member, and the primary transfer toner image on the intermediate transfer member is transferred to a sheet. In an image forming apparatus such as a copying machine or a printer that uses an intermediate transfer method of secondary transfer to a sheet-shaped transfer material, as means for preventing color misregistration, color unevenness, etc. in the transfer process, for example, Japanese Patent Laid-Open No. 57-673 is used. As described in Japanese Patent Laid-Open Publication No. 2003-242242, meandering of an endless belt-shaped intermediate transfer member is prevented.

Further, it is necessary to maintain accurate registration control necessary for a color image forming apparatus for obtaining a full-color image or a multi-color image by superposing a plurality of toner images of respective colors by using relatively inexpensive parts. Successful examples include, for example, US Pat. Nos. 4,652,115 and 4,788,5.
No. 72, and these U.S. Patents use a method of synchronizing a belt-shaped photosensitive member and a belt-shaped intermediate transfer member.

[0004]

However, in the intermediate transfer system, a multicolor image is formed by sequentially transferring the toner images of the respective colors onto the intermediate transfer body in an overlapping manner and then collectively transferring the toner images from the intermediate transfer body onto a transfer material. The image forming apparatus has the following problems. (1) Since there are two transfer steps, color unevenness and color misregistration are likely to occur in the transfer step, as compared with an image forming apparatus that requires only one transfer step. (2) Constant speed control of the intermediate transfer member, accuracy of resist control,
Color unevenness and color misregistration occur depending on the degree of meandering. (3) Color unevenness and color misregistration occur due to vibration of mechanical elements of the engine that constitutes the printer.

Such drawbacks become more serious as the influences of the accuracy of the constant velocity motion of the intermediate transfer member, the degree of deviation of the resist control, the meandering of the intermediate transfer member (intermediate transfer belt) and the mechanical vibration become worse. Therefore, in order to reduce the deterioration of the image quality depending on the above-mentioned drawbacks, it is necessary to improve the control accuracy and perform complicated control. Further, the rigidity of the device must be increased in order to suppress mechanical vibration as much as possible. Therefore, there is a drawback that the cost of the device is increased.

Therefore, an object of the present invention is to eliminate the occurrence of color unevenness and color misregistration in the transfer process in an image forming apparatus in which visible images of respective colors are sequentially transferred onto an intermediate transfer member and then transferred onto a transfer material at once. An object is to provide an intermediate transfer type image forming apparatus.

[0007]

The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention transfers and carries a visible color developed image formed on an image carrier on an intermediate transfer member, and transfers all of the plurality of color developed images by superimposing on the intermediate transfer member. After that, in an intermediate transfer type image forming apparatus that transfers the image to a transfer material all at once, a processing unit that gives a different image forming angle for each color component, and an image of each color is almost strip-shaped on the image carrier for each scanning line. And an image forming apparatus for forming a multicolor image by superimposing substantially band-shaped images of respective colors having different image forming angles of two or more colors.

[0008]

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Although the embodiments described below are applied to an electrophotographic color laser beam printer, the present invention is applicable to other electrophotographic printers, color image forming apparatuses such as copying machines, or electrophotographic systems. It is also applicable to other image forming apparatuses.

First, the overall construction of an electrophotographic color laser beam printer to which the present invention is applied will be described with reference to FIG. The color laser beam printer includes, for example, an OPC (organic semiconductor) photosensitive drum 5 as an image carrier, and a pre-exposure lamp 7, a primary charger 8, and a color signal corresponding to each color signal are provided around the photosensitive drum 5. A laser scanner 1 for irradiating the photosensitive drum 5 with a laser beam, an image exposure unit composed of first and second mirrors 2 and 3, and magenta, cyan, yellow and black developers (toners). Developing units M, C, Y, and BK for accommodating respectively
And a drum cleaner 6 for removing the toner remaining on the photosensitive drum 5.

Although not shown, each developing unit of the developing unit 4 includes a developing cylinder and a non-magnetic blade in this embodiment, and the developer is composed of toner and carrier, and is mixed at a constant ratio. The toner and carrier are triboelectrically charged so that the toner is negatively charged and the carrier is positively charged.
The developer is brushed on the surface of the developing cylinder by the magnetic field of the fixed magnet, and is formed into a developer layer having a uniform thickness by the blade.

A developing bias is simultaneously applied to the developing cylinder. Therefore, the negative component of the developing bias is larger than the positive component. Then, the toner is attracted to the bright portion of the photosensitive drum 5 by the surface potential of the photosensitive drum 5 and the negative component of the developing bias, and develops the electrostatic latent image formed on the photosensitive drum 5 into a visible image. In this case, when the image exposure unit irradiates a color-separated light image at a predetermined timing, for example, a color image that has passed through a green filter, an electrostatic latent image mainly composed of a magenta component in the color image is formed on the photoconductor. It is formed on the drum 5. In synchronization with the feeding of the latent image, the developing unit 4 arranges the developing device M containing the magenta developer at a developing position facing the photoconductor drum 5, so that the magenta toner electrostatically flies. As a result, the toner adheres to the electrostatic latent image on the photosensitive drum 5 and the developing operation is performed, so that only a magenta toner image is formed on the photosensitive drum 5.

The magenta toner image formed on the photosensitive drum 5 is an intermediate transfer member which runs endlessly in a state where it is in contact with or slightly separated from the photosensitive drum 5 in the primary transfer portion. In the example, the image is transferred onto the intermediate transfer belt 18. The intermediate transfer belt 18 is stretched between the fixed roller 15 and the tension roller 12 so as to run between a pair of opposing secondary transfer rollers 13A and 13B, and the primary transfer portion has a photosensitive drum. A primary transfer electrode 9 is arranged on the back side of the intermediate belt 18 so as to face the intermediate transfer belt 5. The motor 16 is driven by the motor control drive circuit 17 and the fixed roller 15 coupled to the motor output shaft rotates, so that the intermediate transfer belt 18 travels in the direction of the arrow in the figure. The pair of secondary transfer rollers 13A and 13B are arranged on the toner image holding surface (front surface) side of the intermediate transfer belt 18, while the pair of secondary transfer rollers 13A and 13B is a bias roller configured to be able to come into contact with and separate from the belt 18. Therefore, it is urged during the transfer operation and positioned so as to be in contact with or slightly separated from the belt 18. The primary transfer electrode 9 and the secondary transfer roller 13A on the surface side of the intermediate transfer belt are provided.
A change such as using a corona charger in place of the above is optional.

The magenta toner image formed on the photoconductor drum 5 is described above by applying a predetermined positive voltage to the primary transfer electrode 9 which is an opposite electrode of the photoconductor drum 5 as shown in the figure. Intermediate transfer belt 18
It is electrostatically transferred upward. At the time of this primary transfer, a paper feed roller (not shown) for sending out the transfer material 19 from the paper feed cassette 30 is not operated. Further, at this time, the secondary transfer rollers 13A and 13B are open (that is, the bias roller 13A on the belt surface side is separated),
Therefore, the magenta toner image transferred onto the intermediate transfer belt 18 is not transferred even if the transfer material 19 is fed, and is held on the intermediate transfer belt 18 without contacting the secondary transfer rollers 13A and 13B. The belt 18 is conveyed to the primary transfer portion again as the belt 18 moves.

After the magenta toner image is transferred onto the intermediate transfer belt 18 in this manner, the residual toner on the photosensitive drum 5 is completely cleaned by the drum cleaner 6. Further, before the latent image of the next color is formed, the pre-exposure lamp 7 is operated to irradiate the surface of the photoconductor drum 5 with light to erase the residual charges on the surface of the drum.

The above-mentioned pre-exposure, primary charging, laser exposure,
A series of image forming processes of development, primary transfer, and drum cleaning are similarly repeated when forming and transferring a cyan toner image, a yellow toner image, and a black toner image.
Thus, the four color toner images of the magenta toner image, the cyan toner image, the yellow toner image and the black toner image are transferred onto the intermediate transfer belt 18 in an overlapping state.

The four color toner images are transferred to the intermediate transfer belt 18
When the image is multi-transferred onto the secondary transfer roller 13A, the paper feed roller is driven to transfer the transfer material 19 through the pair of registration rollers 10 and 11 in synchronization with the positions of the four color toner images on the intermediate transfer belt 18. , 13B are provided to the secondary transfer portion. When the transfer material 19 approaches the secondary transfer portion, the secondary transfer rollers 13A on the belt surface side of the secondary transfer rollers 13A and 13B are urged and the intermediate transfer belt 18 is urged.
The intermediate transfer belt 18 and the transfer material 19 are sandwiched between the secondary transfer rollers 13A and 13B. At this time, a predetermined positive voltage is applied to the secondary transfer roller 13A on the front surface side as shown in the figure. As a result, the bonding force between the transfer material 19 and the toner is more than that between the intermediate transfer belt 18 and the toner. Becomes stronger, the toner on the transfer belt 18 adheres to the transfer material 19, and the four color toner images are retransferred to the transfer material 19.

When the secondary transfer is performed, a transfer material separating means (not shown) is operated, the transfer material 19 on which the toner image is transferred is separated from the intermediate transfer belt 18 by the separating means, and a pair of fixing means is provided by a conveying means (not shown). The image is sent to a fixing unit composed of rollers 14, 14. In this embodiment, each fixing roller 14 has a built-in heater lamp, and when the transfer material 19 passes between the fixing rollers due to heat and pressure, the toner images of four colors are fixed together to form a permanent image. Convert to. When the secondary transfer is completed, a belt cleaner (not shown) which has been separated so far is brought into contact with the intermediate transfer belt 18, and the toner remaining on the transfer belt 18 without being transferred is cleaned. Further, the front side roller 13A, which functions as a bias roller of the secondary transfer roller, has its surface soiled by a scraper (not shown), so that the back side of the transfer material is soiled and the function of the roller 13A as an electrode is deteriorated. Is being prevented.

By the way, in order to apply an image density signal to such a color laser beam printer and reproduce a halftone image corresponding to this image density signal, the applicant has determined that the laser emission time is dependent on the image density signal. A method of modulating has already been proposed. FIG. 3 is a block diagram showing an example of a pulse width modulation circuit that realizes such a method.

First, from the digital data output device 31, for example, 8 bits (0
A digital image signal of up to 255 gradations is generated. The digital image signal is obtained, for example, by reading an original image with an image pickup device such as a CCD, amplifying the obtained analog image signal, and performing analog-digital conversion. Next, this digital image signal is supplied to a digital-analog converter (D / A converter) 32, converted into an analog image signal, and then supplied to one input of a comparator 36.

On the other hand, the reference clock signal 24 generated from the oscillator 33 is supplied to the timing signal generation circuit 34, and from the timing signal generation circuit 34, the digital data output device 31 and the digital data output device 31 are used as the transfer pixel clock of the digital image signal. -Analog converter 32
Is supplied to. At the same time, the reference clock signal 24 is frequency-divided (counted down to a half cycle in this example) in the timing signal generation circuit 34 to generate the screen clock 25, which is supplied to the pattern signal generator 35. The pattern signal generator 35 generates a pattern signal 26 (for example, a triangular wave signal) having the screen clock 25 as a synchronizing signal, and supplies the pattern signal 26 to the other input of the comparator 36. The comparator 36 compares the pattern signal with the analog image signal. For example, the binary image data 27 of "0" when the analog image signal is larger, and "1" when the analog image signal is smaller. To occur. That is, the pattern signal is pulse width modulated by the analog image signal. This pulse width modulated binary image signal is supplied to a laser drive circuit (not shown) and used as an ON / OFF control signal for light emission of, for example, a semiconductor laser of the laser scanner 1 of FIG.

As described above, according to the image processing method proposed by the present applicant, after converting a digital image signal into an analog image signal once, the image signal is compared with a pattern signal of a predetermined cycle, for example, a triangular wave signal to obtain a substantially continuous signal. The pulse width modulation is performed so that a high-quality image output with good gradation can be obtained.

Further, in the pulse width modulation circuit shown in FIG. 3, a shift register 37 is provided between the timing signal generation circuit 34 and the pattern signal generator 35 as shown in the figure, and the pattern signal 26 is provided for each scanning line. By delaying the phase of, the halftone dot image with a certain screen angle can be output. FIG. 4 shows an example of delay generation of the pattern signal for each scanning line by this delay circuit. FIG. 5 shows a pattern of a halftone dot output image of each color based on this pattern signal. 4 and 5, (A) shows the pattern of the first color, and (B) shows the pattern of the second color. In this case, the recording density is 80 dots / inch (dpi) in the main scanning direction and 400 dpi in the sub scanning direction, and the delay amount of the triangular wave signal is 2/5 pixels for the first color and 3 for the second color.
/ 5 pixels, and the respective image forming angles are 26.6 ° and −2.
It was set to 6.6 °.

Incidentally, FIG. 14 shows the exposure distribution on the photosensitive drum when halftone dots are output by the conventional image forming apparatus, and FIG. 15 shows the output image when it is printed out by the laser beam printer. As is clear from FIG. 15, many diagonal streaks are generated in the conventional output image.

As described above, by providing different screen angles for each color, a color laser printer incorporating a printing technique can obtain an output image with no color unevenness or tint change even if registration deviation occurs. it can.

Here, even if the resist shift occurs, color unevenness,
The reason why the color change does not occur will be described. When the patterns of the first color and the second color shown in FIGS. 5A and 5B are multiplexed, normally, if there is no deviation, as shown in FIG. And pixels that do not overlap with each other appear periodically. On the other hand, if the image of the second color in FIG. 5B is shifted to the right by one pixel from the position where it should be originally multiplexed,
The multiplexing pattern is as shown in FIG. Figure 6
Comparing (A) and (B), it can be seen that the positions where the superposed pixels and the non-superposed pixels appear are shifted, but the appearing patterns are exactly the same. It can also be seen that the number of pixels that should have overlapped due to the shift but did not overlap is the same as the number of pixels that did not overlap but did overlap. It can be said that this is the principle of directly producing an image with no color unevenness or tint change.

FIG. 1 is a drawing that best represents the features of the present invention. In FIG. 1, the thick shaded portions show the image formation state. In FIG. 1A, the first color, FIG. B)
Shows the patterns of the second color and represent the output state of the half-tone image. In the present invention, FIG.
As shown in FIG. 5, pixels of each color are formed in a strip shape, and the image forming angle is made different for each color.

Next, the means of this embodiment for forming the above image will be described. The basic structure of the image forming apparatus according to the present embodiment has already been described with reference to FIG.

In this embodiment, FIG. 13 similar to the conventional one is used.
Using a laser beam having a light amount distribution as shown in, each pixel was arranged so that the exposure distribution of each pixel was linearly connected as shown in FIG. The arrangement state of each pixel in this case is shown in FIG. The recording density in the main scanning direction is 1
The recording density is 60 dpi, the recording density in the sub-scanning direction is 400 dpi, and the image forming angle is 26.6 ° for the first color and −2 for the second color.
It was set to 6.6 °. 13A shows the light amount distribution of the main scanning laser beam, and FIG. 13B shows the light amount distribution of the sub-scanning laser beam. Further, FIG. 8A shows the pixel arrangement of the first color, and FIG. 8B shows the second pixel arrangement.
The pixel arrangement of colors is shown.

In order to arrange each pixel as described above, a triangular wave signal as shown in FIG. 9 is used in this embodiment, and this triangular wave signal is delayed for each scanning line. The delay amount of this triangular wave signal is 4/5 pixels for the first color and 1/5 for the second color.
Pixels. Since the delay of the triangular wave signal is performed by the same means as described above with reference to FIG. 3, the description thereof will be omitted.

In FIG. 10, pixels of the first color and the second color are arranged as shown in FIGS. 8A and 8B, and a band-shaped first color image is formed on the photosensitive drum based on these arrangements. FIG. 2A shows a multiplexing state when the second band-shaped image is formed on the first color image in an overlapping manner, and FIG. (B) shows a state when the registration shift occurs. This FIG.
As is clear from (A) and (B), according to the present embodiment, even if a larger or smaller registration shift occurs in multiplexing of each color image, the area of the overlapping portion does not change at all, so that the color It can be seen that a multicolored output image with no unevenness or change in tint can be obtained.

FIG. 11 is an explanatory view similar to FIG. 1 showing the output state of the highlight image in the present embodiment. FIG. 11A shows the image forming pattern of the first color and FIG. ) Indicates the image forming pattern of the second color. Since it is a highlight image, the diagonal lines are thinner than in the half tone image of FIG.

Incidentally, in order to obtain a more linear image with respect to the latent image having the linear exposure distribution as shown in FIG. 7, in the present embodiment, the developing unit 4 shown in FIG. The well-known two-component magnetic brush developing method was used for each developing device.

In the above embodiment, the pulse width modulation circuit having the structure as shown in FIG. 3 is used to pulse-width-modulate the pattern signal with the analog image signal, and the pulse-width-modulated binary image signal is used to emit the laser beam. However, the present invention is not limited to this, and can be applied to a laser beam printer using a threshold matrix, for example.

FIG. 12 shows the threshold matrix used in the second embodiment in which the present invention is applied to such a laser beam printer. This threshold matrix is 6 × 6
Based on the matrix of 1 pixel is 400 dpi x 4
This corresponds to 00 dpi. In FIG. 12, (A) corresponds to the threshold matrix for the first color, (B) corresponds to the threshold matrix for the second color, and (C) corresponds to the threshold matrix for the third color.

It is needless to say that the present invention is not limited to the illustrated threshold matrix pattern, and can be applied if the output image is a pattern in which a band-shaped image is formed. Further, although the above-mentioned embodiment describes the case of forming a two-color and three-color multiple image,
The present invention is not limited to this, and it is needless to say that the present invention can be applied and is effective in all cases where a multi-color image of two or more colors including full color is formed by the intermediate transfer method.
Further, in the above-described embodiment, the case where the present invention is applied to the electrophotographic color image forming apparatus is shown. However, the present invention is not limited to the embodiment, and various copying machines such as an electrophotographic method and an electrostatic recording method, a printer, etc. The present invention is equally applicable to the image forming apparatus. Further, it goes without saying that various modifications and changes can be made to the members, elements, etc. constituting the image forming apparatus, as necessary.

[0036]

As described above, in the image forming apparatus according to the present invention, the image of each color is formed in a substantially strip shape for each scanning line, and the image forming angle is made different for each color. Even if the precision of constant speed control and resist control is improved more than necessary, and even if complicated control is not performed and the rigidity of the device is not increased more than necessary, color unevenness and color shift will occur in the transfer process. do not do. Therefore, the disadvantage that the tint of the multicolor output image changes each time it is printed can be eliminated, and there is a remarkable effect that an always stable and high-quality image can be obtained. Furthermore, since it is not necessary to improve the control accuracy more than necessary and to perform complicated control,
Since there is no need to increase the rigidity of the device to suppress mechanical vibration as much as possible, there is also an effect that the drawback of increasing the cost of the device can be eliminated.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a half-tone image output state of a first embodiment of an image forming apparatus according to the present invention.

FIG. 2 is a schematic sectional view showing the overall configuration of a first embodiment of the image forming apparatus according to the present invention.

FIG. 3 is a block diagram showing an example of a pulse width modulation circuit that can be used to drive the laser scanner in the first embodiment of the image forming apparatus according to the present invention.

FIG. 4 is a waveform diagram showing a delay pattern of a triangular wave signal used in the pulse width modulation circuit of FIG.

5 is a schematic diagram showing a pattern of a halftone dot output image of each color by the triangular wave signal of FIG. 4;

FIG. 6 is an explanatory diagram showing a state when the two patterns in FIG. 5 are multiplexed.

FIG. 7 is an explanatory diagram showing an exposure distribution on the photosensitive drum of the first embodiment of the present invention.

FIG. 8 is an explanatory diagram showing an array state of pixels according to the first embodiment of the present invention.

FIG. 9 is a waveform diagram showing a delay pattern of a triangular wave signal used in the first embodiment of the present invention.

FIG. 10 is an explanatory diagram showing a multiplexed state of the strip pixels according to the first embodiment of the present invention.

FIG. 11 is a schematic diagram showing an output state of a highlight image according to the first embodiment of the present invention.

FIG. 12 is an explanatory diagram showing a threshold matrix according to the second embodiment of the present invention.

FIG. 13 is a characteristic diagram showing a light quantity distribution of a laser beam.

FIG. 14 is an explanatory diagram showing an exposure distribution on a photoconductor drum when halftone dots are output in a conventional image forming apparatus.

FIG. 15 is a plan view showing an enlarged halftone dot image printed out by the conventional image forming apparatus.

[Explanation of symbols]

 1 Laser Scanner 4 Developing Unit 5 Photosensitive Drum 9 Primary Transfer Electrode 12 Tension Rollers 13A, 13B Secondary Transfer Roller 15 Fixed Roller 18 Intermediate Transfer Belt 19 Transfer Material

Claims (1)

[Claims] 1. A visible color developed image formed on an image bearing member is transferred and carried on an intermediate transfer member, and after transferring all a plurality of color developed images on the intermediate transfer member in an overlapping manner, In an image forming apparatus of an intermediate transfer system which transfers images to a transfer material all at once, processing means for giving an image forming angle different for each color component, and an image of each color is formed in a substantially band shape on the image carrier for each scanning line. And a means for forming a multicolor image by superimposing substantially band-shaped images of respective colors having different image forming angles of two or more colors.