JP4336531B2 - Color image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a color image forming apparatus.
[0002]
[Prior art]
Conventionally, as a color image forming apparatus using an electrophotographic process, a YMCK four-color developing device is rotated to form a toner image on a photosensitive surface sequentially, and the formed toner image is transferred to a transfer material holder, A technique is known in which images are transferred one after another on a carrier such as an intermediate transfer member.
[Patent Document 1]
Japanese Patent Laid-Open No. 9-6123
[Problems to be solved by the invention]
In such a color image forming apparatus, every time the carrier is rotated, the developing device is rotated so as to switch to the next color, whereby images for four colors are sequentially formed, so that one full color image is obtained. Requires four rotations of the carrier.
[0004]
Conventionally, in this color image forming apparatus, when density / gradation control (hereinafter simply referred to as density control) is performed, a density control pattern is formed for each color. Since the developing device was switched every time the carrier was rotated once, a time corresponding to four rotations of the carrier was required.
[0005]
An object of the present invention is to solve the above-described problems.
[0006]
[Means for Solving the Problems]
The color image forming apparatus of the present invention is an image forming unit including a plurality of developing devices corresponding to respective colors and one photosensitive drum, and sequentially switches the developing devices to form a toner image formed on the one photosensitive drum. A color image forming apparatus comprising: an image forming unit capable of sequentially forming a toner image on a rotating carrier; and a control unit that causes the image forming unit to form an image. Detecting means including a light emitting element and a light receiving element for detecting the density of the toner image pattern formed on
Cleaning means for cleaning a toner image formed on the rotary carrier at the time of contact with the rotary carrier, and the control means within one rotation period of the rotary carrier. After the first color toner image pattern is formed on the rotary carrier, the developing device to be used is switched to form the second color toner image pattern, and then the rotary carrier is rotated to rotate the first color image. A third color toner image pattern is formed in a region between the color toner image pattern and the second color toner image pattern, and a fourth color toner image pattern is formed behind the second color toner image pattern. The image forming unit is controlled to form, and the cleaning unit collectively cleans the first to fourth color toner image patterns .
[0008]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a full-color image forming apparatus according to this embodiment. This will be described below with reference to the drawings. A photosensitive drum 1 as an electrostatic latent image carrier constituted by applying an organic photoreceptor (OPC) or a photoconductor made of A-Si, CdS, Se, etc. to the outer peripheral surface of an aluminum cylinder is not shown. Driven by the driving means in the direction of the arrow shown in the figure, the roller charger 2 uniformly charges to a predetermined potential. Next, the exposure device 3 scans the photosensitive drum 1 with light in accordance with a yellow image pattern, and a latent image is formed on the photosensitive drum 1. When the photosensitive drum 1 further advances in the direction of the arrow, the support 5 rotates so that the developing device 4a containing yellow toner among the developing devices 4a, b, c, d supported by the support 5 faces the photosensitive drum 1. And is visualized by the selected developing device 4a. The developed toner image is transferred onto the intermediate transfer member 6. In the intermediate transfer body 6, a transfer belt 61 made of rubber such as EPDM, NBR, urethane, silicone rubber or the like is stretched over three rollers, a driving roller 62, a driven roller 63, and a tension roller 64, and the driving roller 62 is The transfer belt 61 is driven in the direction of the arrow in the figure by being rotated in the direction of the arrow in the figure by a motor described later. A primary transfer roller 65 is provided with a conductive sponge layer on the shaft, and is in contact with the photosensitive drum 1 via the transfer belt 61. A bias is applied to the primary transfer roller 65 from a high voltage power supply (not shown), and the toner image on the photosensitive drum 1 is transferred onto the transfer belt 61.
[0009]
By performing the above steps for magenta, cyan, and black, a toner image of a plurality of colors is formed on the transfer belt 61. A position detection member (not shown) is provided at the end of the transfer belt 61, and a position reference signal is formed by reading the position detection member with an optical sensor or the like to align the toner image on the transfer belt 61.
[0010]
Next, FIG. 2 shows an image forming sequence specifically related to the position reference signal, image exposure, developing process, and rotation of the support 5 during normal image formation.
[0011]
Here, a position detection member is provided at one end of the transfer belt 61, and the position reference signal is detected once in one rotation cycle of the transfer belt 61. When the position reference signal for the first color (Top1 in the figure) is detected, the first color yellow image exposure (Yexp) is performed. When the exposure position of the photosensitive drum 1 reaches the development position, a development process (Ydev) by the first color yellow developing device 4a is performed. When the image exposure portion formed on the photosensitive drum 1 passes the development position, the support 5 rotates and the second color magenta developer 4b faces the development position (Mr). Thereafter, a similar image forming sequence is performed for the second and subsequent colors, and image formation for each color is performed. As described above, a series of image forming steps for forming a one-color image is performed every rotation cycle of the transfer belt 61.
[0012]
When the four color toner images are transferred onto the transfer belt 61, the transfer material P synchronized with the movement of the transfer belt 61 is conveyed, and a secondary transfer roller 66 having the same configuration as the primary transfer roller 65 is formed. Abutting against the transfer belt 61 via the transfer material P, a bias is applied from a high voltage power source (not shown), and the four-color toner images on the transfer belt 61 are collectively transferred onto the transfer material P. The transfer material P on which the four-color toner image is transferred is melted and fixed by a conventionally known heating and pressure fixing device 8 to obtain a color image.
[0013]
Further, the transfer residual toner on the photosensitive drum 1 is cleaned by a known cleaning device 7 of blade means. Further, the transfer residual toner on the transfer belt 61 is also cleaned by a cleaning device 67 such as a fur brush or a web that can be contacted and separated.
[0014]
A density sensor 9 includes a light emitting element 91 such as an LED, a light receiving element 92 such as a phototransistor and a photodiode, a holder 93 and the like as shown in FIG. Using this density sensor 9, the density of the density measurement image pattern formed on the transfer belt 61 is measured, and density / gradation control is performed. The density control controls process conditions such as the developing bias, the charging potential of the photosensitive drum, and the exposure amount, and the gradation control controls the control of the image signal.
[0015]
On the other hand, at the time of density / gradation control, toner images for density / gradation control of two colors are formed during one rotation period of the transfer belt 61.
[0016]
FIG. 4 shows a control system in the present embodiment.
[0017]
In FIG. 4, an image processing unit 201 generates image information to be formed by the image forming apparatus.
[0018]
Reference numeral 202 denotes an engine control unit that controls main parts of the color image forming apparatus.
[0019]
Reference numeral 203 denotes a high-pressure generating unit that generates and supplies high pressure necessary for various process elements such as charging, development, and transfer described above.
[0020]
Reference numeral 204 denotes a motor for changing the color of the developing device in contact with the photosensitive drum 1 by rotating the support 4 described above. Reference numeral 205 denotes a position sensor for detecting the rotational position of the support 5, and the control unit 202 drives and controls the motor 204 based on the detection output of the position sensor 205 to photosensitive the developing device of a desired color. Abut against the drum 1.
[0021]
Reference numeral 206 denotes a motor for rotating the transfer belt 106 by rotating the roller 62. Reference numeral 207 denotes a position sensor for detecting the rotational position of the transfer belt 6 by reading a flag on the transfer belt 6, and the control 202 is performed by the exposure apparatus 3 based on the detection output of the position sensor. Control image exposure timing and the like.
[0022]
The engine control unit 202 controls the photosensitive drum 1, a conveyance roller for conveying the transfer material, a motor for driving various devices, a solenoid, and the like (not shown).
[0023]
Next, it is most characteristic in the present embodiment, when forming the density and gradation control patterns, the transfer belt 61 a position reference signal, image exposure, development process, the image forming sequence for rotation of the support member 5 Figure As shown in FIG. Explaining along the drawing, when the position reference signal (Top1 in the figure) of the transfer belt 61 is detected, the first color yellow density / tone control image exposure (Yexp) is performed, and Yd development (Ydev). . Here, the density measurement image pattern is set to be shorter than the maximum length of a normal image, and after the yellow development is completed, the support 5 is rotated to switch to the second color magenta developer (Mr), and the density / tone control of the second color magenta. Image exposure (Mexp) and development (Mdev). The density measurement image pattern will be described in detail. One density measurement image pattern image is preferably about 5 mm × 5 mm to 15 mm × 15 mm, depending on the density sensor used. In terms of density control, a plurality of density measurement image patterns with different printing conditions such as charging potential, exposure amount, and developing bias are required, but it is sufficient if there are three to five different printing conditions. . In terms of gradation control, a plurality of density measurement image patterns with different image printing rates are required, but it is sufficient that there are 5 to 8 images with different image printing rates. Accordingly, the maximum combination of the image size and the number described above is 15 mm × 8 = 120 mm, and the length of A4 that is normally printed can be less than half the length of 297 mm.
[0024]
When the transfer belt 61 makes one revolution and the next position reference signal (Top2) is detected, the support 5 rotates and switches to the third color cyan developer (Cr). Next, image exposure (Cexp) for density / gradation control of the third color cyan is performed. To perform density / gradation control, toner images that do not overlap each other are necessary. The exposure is performed in accordance with the position where there is no density measurement image pattern of the first color yellow and the second color magenta indicated by diagonal lines in FIG. Since the transfer belt 61 moves even during the operation of switching the developing device, there is always a portion where printing cannot be performed between the first color yellow and the second color magenta. By making this portion the next cyan print area for the third color, a toner image can be formed without creating a useless gap across the transfer belt 61 moving direction, and more detection images can be printed. It was.
[0025]
After developing the third color cyan image exposure (Cdev), the support 5 rotates and switches to the fourth color black developer (Kr). As with the third color, the fourth color black density / gradation control image exposure is also performed by aligning with a position where there is no density measurement image pattern of the first color yellow and the second color magenta already formed on the transfer belt 61. Perform (Kexp) and develop (Kdev). After four-color toner images are formed and the respective densities are detected by the density sensor 9, the toner image is cleaned by the cleaner 68 as in normal image printing.
[0026]
Thus, in the second rotation (or later), the pattern is formed in a region other than the region where the pattern has already been formed.
[0027]
Further, the engine control unit 202 corrects high-voltage conditions such as charging, development, and transfer based on the detection output of the density detection sensor 9 so as to obtain the target image density.
[0028]
Further, after the above sequence, a halftone pattern for gradation control is formed in the same sequence, and the density is detected by the density detection sensor. Based on the density detection result of the gradation control pattern, the image data conversion table in the image processing unit 201 is adjusted so that the density characteristic of the output image with respect to the image data is linear.
[0029]
As described above, in the density control sequence, conventionally, four rotation cycles of the transfer belt 61 are required to obtain the detected images of four colors, but in this embodiment, only two rotations are necessary. The time required is reduced.
[0030]
In addition, when the gradation control sequence is executed after the density control sequence, the effect is doubled.
[0031]
(Second embodiment)
FIG. 6 shows a second embodiment of the present invention. The present embodiment relates to an image forming apparatus that sequentially transfers four-color toner images onto a transfer material carried on a transfer material carrier and obtains a color image.
[0032]
Components having the same configuration and function as those of the previous embodiment are denoted by the same reference numerals, and description thereof is omitted. Referring to the drawing, reference numeral 10 denotes a transfer drum as a transfer material carrier, which has a conductive sponge layer 102 on a conductive support 101 to which a transfer bias is applied, and further a dielectric layer 103 such as PVdF as a surface layer. Have The conveyed transfer material P is electrostatically attracted and fixed to the transfer drum 10 by an attracting roller 105 to which a predetermined bias is applied, while a leading end is supported by a gripper 104 provided on the transfer drum 10. The The first color toner image on the photosensitive drum 1 formed in the same process as in the first embodiment is transferred onto the transfer material P in synchronization with the movement of the transfer drum 10. Thereafter, the toner images for the second and subsequent colors are developed and transferred by the same process, and the four-color toner image is transferred. Then, the transfer material P is separated from the transfer drum 10 via a separation claw 106 that can move in the direction of the arrow in the figure. Then, the image is fixed by the fixing device 8. Reference numeral 107 denotes a cleaner such as a fur brush which can move toward and away from the transfer drum 10 by moving in the direction of the arrow in the figure, and cleans the transfer drum 10.
[0033]
The transfer drum 10 is provided with a position reference member as in the previous embodiment, and the image forming sequence is controlled in accordance with the position reference signal obtained thereby. Done every time. Position reference signal, image exposure, development process, the image forming printing sequence relating to rotation of the support 5 is the same as that shown in FIG.
[0034]
A density sensor 9 detects the density of the density / tone control toner image formed on the transfer drum 10, and has the same configuration as that of the first embodiment shown in FIG. In this embodiment, the density measurement image pattern is directly transferred to the transfer drum 10 because a separate transfer material is not required.
[0035]
Also in this embodiment, at the time of density / gradation control, control for two colors is performed during one rotation of the transfer drum 10 as in the sequence shown in FIG. After the control for four colors is completed, the toner image on the transfer drum 10 is cleaned by the cleaner 107.
[0036]
As described above, even in an apparatus that sequentially transfers a four-color toner image onto a transfer material carried on a transfer material carrier and forms a color image, this is a series of image forming steps for forming a one-color image. By performing density / gradation control for two colors within one rotation period of the transfer drum, the time required for density / gradation control could be shortened.
[0037]
(Third embodiment)
FIG. 7 shows a third embodiment of the present invention. In this embodiment, a four-color toner image is formed on an electrostatic latent image carrier by sequentially repeating exposure and development, and the four-color toner image on the electrostatic latent image carrier is collectively transferred to a transfer material. The present invention relates to an image forming apparatus for obtaining a color image.
[0038]
Components having the same configuration and function as those of the previous embodiment are denoted by the same reference numerals, and description thereof is omitted. Referring to the drawing, reference numeral 1 denotes a photosensitive drum, and the circumference of the photosensitive drum is equal to or longer than the length of the image size to be printed plus the length corresponding to the time required for switching the developing device. Reference numeral 2 denotes a charger for charging the photosensitive drum 1. However, since it is necessary to charge the photosensitive drum 1 carrying a toner image, a non-contact type charger such as a corona charger is preferable.
[0039]
The image forming process will be briefly described below. A photosensitive drum 1 as an electrostatic latent image carrier formed by applying an organic photoreceptor (OPC) or a photoconductor made of A-Si, CdS, Se, etc. to the outer peripheral surface of an aluminum cylinder is not shown. Driven by the driving means in the direction of the arrow shown in the figure, the corona charger 2 uniformly charges to a predetermined potential. Next, the exposure device 3 scans the photosensitive drum 1 with light in accordance with a yellow image pattern, and a latent image is formed on the photosensitive drum 1. When the photosensitive drum 1 further advances in the direction of the arrow, the support 5 rotates so that the developing device 4a containing yellow toner among the developing devices 4a, b, c, d supported by the support 5 faces the photosensitive drum 1. And is visualized by the selected developing device 4a. After the first color yellow development, the photosensitive drum 1 is uniformly charged again by the charger 2, and then the exposure of the second color magenta is performed by the exposure device 3. By the time the magenta exposure unit reaches the development position, the support 5 rotates, and the magenta developer 4b is switched to the development position to perform development. By performing cyan and black, a multi-color toner image is formed on the photosensitive drum 1. When the four-color toner image is formed on the photosensitive drum 1, the transfer material P synchronized with the movement of the photosensitive drum 1 is conveyed, and the transfer roller 11 contacts the photosensitive drum 1 through the transfer material P, so A bias is applied from the illustrated high voltage power source, and the four-color toner images on the photosensitive drum 1 are collectively transferred onto the transfer material P. The transfer material P onto which the four-color toner image has been transferred is melted and fixed by a conventionally known heat and pressure fixing device 8. On the other hand, the transfer residual toner on the photosensitive drum 1 is cleaned by the cleaner 7. As shown in the figure, the cleaning blade 71 of the cleaner 7 is configured to be able to contact and separate from the photosensitive drum 1 (the contact state is indicated by a dotted line and the separation state is indicated by a solid line). 1 apart.
[0040]
The photosensitive drum 1 is provided with a position reference member as in the previous embodiment, and the registration of each color is performed according to the position reference signal obtained thereby, and the image forming sequence is controlled. In this embodiment, a series of image forming steps for forming a one-color image is performed for each rotation cycle of the photosensitive drum 1. The image forming sequence relating to the position reference signal, image exposure, developing process, and rotation of the support 5 is the same as that shown in FIG.
[0041]
A density sensor 9 detects the density of the toner image for density / gradation control formed on the photosensitive drum 1 and has the same configuration as the conventional one shown in FIG. Also in this embodiment, at the time of density / gradation control, control for two colors is performed while the photosensitive drum 1 rotates once, as in the sequence shown in FIG. After the control for four colors is completed, the toner image on the photosensitive drum 1 is cleaned by the cleaner 7.
[0042]
As described above, even in an apparatus that sequentially exposes and develops a four-color toner image on a photosensitive drum and forms a color image, it is a series of image forming steps for forming a one-color image within one rotation period of the photosensitive drum. By controlling the density and gradation for two colors, the time required for density and gradation control could be shortened.
[0043]
In each of the embodiments described above, the case where the density / gradation control patterns for two colors are formed in a series of image forming steps for forming a one-color image has been described. It goes without saying that it is also good.
[0044]
【The invention's effect】
As described above, according to the present invention, a toner image can be formed without creating a useless gap, and more detection images can be printed.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a color image forming apparatus according to a first embodiment. FIG. 2 is a diagram illustrating an image forming sequence when a normal image is formed. FIG. 3 is a schematic diagram of a density sensor. FIG. 5 is a diagram illustrating an image forming sequence when forming a density control pattern. FIG. 6 is a cross-sectional view of a color image forming apparatus according to a second embodiment. Sectional view of the color image forming apparatus of the embodiment
DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Charging device 3 Exposure apparatus 4 Developing device 5 Developing device support body 6 Intermediate transfer body 7 Cleaner 8 Fixing device 9 Density sensor

Claims (6)

An image forming unit including a plurality of developing devices corresponding to each color and one photosensitive drum, wherein the toner image formed on the one photosensitive drum by sequentially switching the developing devices is a rotating carrier that carries the toner image A color image forming apparatus comprising: an image forming unit that can be sequentially formed ; and a control unit that causes the image forming unit to form an image.
Detecting means including a light emitting element and a light receiving element for detecting the density of the toner image pattern formed on the rotating carrier;
Cleaning means for cleaning the toner image formed on the rotating carrier when contacting and separating from the rotating carrier,
The control means switches the developing device to be used after forming the first color toner image pattern on the rotation carrier within one rotation period of the rotation carrier, and changes the second color toner image pattern. Forming the third color toner image pattern in a region between the first color toner image pattern and the second color toner image pattern. Controlling the image forming means to form a fourth color toner image pattern behind the color toner image pattern;
The color image forming apparatus , wherein the cleaning unit collectively cleans the first to fourth color toner image patterns . Detection means for detecting a position reference signal of the rotating carrier is provided, and the control means applies a third color toner image pattern to the image forming means in the region between them in response to detection of the position reference signal. 2. The color image forming apparatus according to claim 1, wherein a fourth color toner image pattern is formed after the second color toner image pattern. On the basis of the detection of the detecting means, a color image forming apparatus according to claim 1 or 2 characterized by having a process adjusting means for adjusting an electrophotographic process element. On the basis of the detection of the detecting means, a color image forming apparatus according to any one of claims 1 to 3, characterized in that it has a conversion condition adjusting means for adjusting the image data conversion condition. The rotating carrier is an intermediate transfer member;
It said image forming means toner image formed on the one photosensitive body, a color image forming apparatus according to any one of claims 1 to 4, characterized in that to transfer to the intermediate transfer member. The rotating carrier is a transfer material holder,
It said image forming means when forming a normal image, the toner image is formed on one of the photosensitive member, transferring the toner image on the photosensitive member of the one to the transfer material support to be held transfer material whereas, when forming a toner image pattern is a toner image formed on the one photosensitive body, to any one of claims 1 to 5, characterized in that transferred onto the transfer material holding member The color image forming apparatus described.

Images