JP2003021939A - Image control method and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image control method for stabilizing an image by highly accurately detecting an image pattern and detecting the image density in a wide density area with high sensitivity. SOLUTION: In the image control method provided with an image forming means for forming an image on a photoreceptor drum (image carrier) 1, a detection part (optical detecting means) 50 for detecting the density and the toner of the image on the photoreceptor drum 1, a density adjusting means for adjusting the image density, a toner adjusting means for adjusting the toner characteristics of the image, and a speed changing means for adjusting the driving speed of the photoreceptor drum 1, at least one or more image patterns is formed on the photoreceptor drum 1 so as to judge the image characteristics, the formed image pattern is read by the detection part 50, an image forming condition is controlled based on the read image information and the driving speed of the photoreceptor drum 1 when detecting the image pattern is made differ from that when forming a normal image.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image control method for forming an image in a copying machine, a laser beam printer or the like, and an image forming apparatus using the method.

[0002]

2. Description of the Related Art Conventionally, the following method is known as a method (image control method) for adjusting the image processing characteristics of an image forming apparatus such as a copying machine or a printer.

First, the image forming apparatus is started, and after the warm-up operation is completed, a specific pattern is formed on an image carrier such as a photosensitive drum. Then, the formed pattern is read, and γ is read based on the read density value.
The quality of the image formed is stabilized by changing the operation of the circuit that determines the image forming conditions such as the correction circuit.

Further, even when the gradation characteristic is changed due to a change in environmental conditions, a specific pattern is formed again on the image carrier and read, and a circuit for determining the image forming condition such as a γ correction circuit is read again. By feeding back, the image quality can be stabilized according to the variation amount of the environmental condition.

[0005]

However, in the above-mentioned conventional example, there is a problem that the accuracy of the detected value of the image pattern by the sensor and the sensitivity in the high density portion are low.

The present invention has been made in view of the above problems, and an object thereof is to perform image pattern detection with high accuracy and to perform image stabilization by performing highly sensitive image density detection in a wide density region. An object of the present invention is to provide an image control method and an image forming apparatus that can be achieved.

[0007]

To achieve the above object, the present invention provides an image forming means for forming an image on an image carrier and an optical device for detecting the density and gradation of the image on the image carrier. A detecting means, a density adjusting means for adjusting the image density,
On the image carrier, at least one or more image patterns for determining the image property are provided, having a gradation adjusting unit for adjusting the gradation property of the image and a shifting unit for adjusting the driving speed of the image carrier. In the image control method of forming an image pattern on the image carrier, reading the formed image pattern by the optical detecting means, and controlling the image forming conditions based on the read image information, the driving speed of the image carrier at the time of detecting the image pattern is usually It is characterized by being different from the driving speed at the time of image formation.

The present invention also provides an image carrier, an image forming means for forming an image on the image carrier, a transfer means for transferring the image on the image carrier to a recording material, and the recording material for the recording material. An image forming apparatus is configured to include a fixing unit that fixes the transferred image on the recording material, and image density adjustment and image gradation adjustment are performed by the image control method.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings.

<First Embodiment> Here, a digital monochrome copying machine will be described as a typical example.

FIG. 1 is a block diagram showing a schematic structure of a digital monochrome copying machine. In FIG. 1, reference numeral 200 denotes a control unit for controlling the entire copying machine, which includes a CPU 28 such as a microprocessor and a control program for the CPU 28. A ROM 210 for storing various data, a RAM 212 used as a work area for the CPU 28, and the like. The ROM 210 stores a test pattern, which will be described later, in the test pattern area 211. Further, the image signal is corrected by the γ-LUT 25 described later and output to the printer unit 100.

In the printer section 100, 50 is a detection section for detecting the surface of a photosensitive drum (image carrier) 1 having a photosensitive layer on the surface thereof. The detection section 50 is a regular reflection type sensor having an LED 52 and a photo sensor 51. Is. The signal from the photo sensor 51 is converted by the density conversion circuit 41 of the control unit 200 and then input to the CPU 28, and control based on the signal from the photo sensor 51 is performed.

The control unit 2 also controls the bias potential applied to the developing device 4, the drive signal of the laser beam 3, the potential applied to the primary charger 2, and the like.
Controlled by 00.

Hereinafter, these configurations and image formation (image formation)
The process will be described in detail with reference to the drawings.

FIG. 2 is a sectional view showing the internal structure of the copying machine according to this embodiment.

First, the image forming process will be described.

The document D is illuminated by the light source 12, and the optical system 13 focuses the image on the CCD 21 to form an image. The light source 12, the optical system 13 and the CCD 21 are on the same unit, and this unit moves in the direction of the arrow for scanning the document D. While moving, the sequential image data is A
It is digitized by the / D conversion circuit 22.

The digitized image signal is sent to the control unit 200.
Then, the semiconductor laser 32 is driven by image processing. The laser beam 3 emitted from the semiconductor laser 32 is applied by the polygon mirror 33 to the photosensitive drum 1 which has been uniformly charged by the primary charger 2 in advance to form a latent image in which an electrostatic pattern is formed by the image pattern. To do.

Toner is attached to the latent image by the developing device 4 according to the pattern of the latent image to make it visible. Then, the recording material P
Are conveyed in synchronism with the image front end of the visible toner image, and the transfer charger 6 transfers the toner image from the photosensitive drum 1 to the recording material P side. The recording material P on which the toner is transferred is heat-fixed by the fixing device 10, and the toner image is fixed on the recording material P.

Further, an LED 52 is provided on the downstream side of the developing device 4.
A detection unit 50 including a photo sensor 51 is arranged.

Next, referring to the block diagram of FIG. 3, the CCD
The flow of the image signal from 21 to the laser beam 3 will be described.

The light amount signal obtained by the CCD 21 is
It is digitized by the A / D conversion circuit 22. By the shading circuit 23, each sensor cell group of the CCD 21 arranged in a line is removed one by one in order to eliminate sensitivity variations.
The gain is optimized corresponding to one CCD sensor cell.

After that, the signal is converted from the luminance scale to the density scale by the LOG conversion circuit 24. The density signal is gradation-converted by the γ-LUT 25 rewritable by the CPU 28, converted by the pulse width conversion circuit 26 into the emission time of the laser light 3 according to the density signal, and the signal is passed to the laser driver 31 to pass the signal to the semiconductor laser 32. To drive.

A pattern generator 29 is mounted on this image forming apparatus, the gradation pattern shown in FIG. 4 is registered, and a signal can be directly passed to the pulse width conversion circuit 26.

Next, the role of the γ-LUT 25 will be described.

FIG. 5 is a 4-limit chart showing the characteristics of reproducing the density of the original image.

The quadrant I shows the characteristics of the image reading apparatus for converting the document density into the density signal, and the quadrant II shows the characteristics of the γ-LUT 25 for converting the density signal into the laser output signal. The third quadrant shows the characteristics of the printer that converts the laser output signal into the output density. IV
The quadrant shows the relationship between the document density and the recording density, and this characteristic represents the overall gradation characteristic in the copying machine according to the present embodiment.

In this embodiment, the number of gradations is 8 bits.
Since it is processed with the digital signal of, there are 256 gradations.

In this image forming apparatus, in order to make the gradation characteristics of the fourth quadrant linear as shown in FIG. 5, the bending of the recording characteristics of the printer section of the third quadrant is used for the γ − of the second quadrant.
It is corrected by the LUT 25. γ-LUT25 is the
It can be easily created by simply changing the input / output relationship of the characteristics of the III quadrant.

In the present embodiment, first, the gradation pattern as shown in FIG. 4 is output. When outputting this pattern, the γ-LUT 25 must be output without operating.

With respect to the output gradation pattern, the reflection output is detected by the detection unit 50 at the same timing. When this gradation pattern is detected, the drive speed of the photosensitive drum 1 is set lower than that during normal image formation. The detected reflection output is converted into density information by the density conversion circuit 41.

In the present embodiment, a high-resolution specular reflection type sensor with a spot diameter of 1.5 mm is used to detect the gradation pattern formed on the photosensitive drum 1, and the reflected light from the base portion is used. From the dot resolution and toner thickness,
To suppress the phenomenon that the detection accuracy is lowered because it is easily affected by the surface accuracy of the base, the distance change due to vibration, etc., by suppressing the photosensitive drum drive speed during detection and increasing the time resolution in a stable state. I was able to. Further, it was possible to maintain the sensitivity to the extreme decrease in the amount of reflected light in the high density area.

The density value read and corrected stores the relationship between the laser output level and the density in the memory by associating the laser output level with the position where the gradation pattern is created. At this stage, the printer characteristic shown in the third quadrant of FIG. 5 can be obtained, and by changing the input / output relation of the printer characteristic, the γ-LUT 25 of this printer can be determined and set.

When the γ-LUT 25 is calculated, only the number of gradation patterns of the patch pattern is available. Therefore, the laser output level is insufficient for all levels from 0 to 255 of the density signal. The data being processed must be generated by performing interpolation.

Upon completion of the above control, during the copying operation, the setting of the γ-LUT 25 calculated by the above method causes
Good linear gradation can be obtained with respect to the density output signal.

<Embodiment 2> In the present embodiment, an image forming apparatus for forming a full-color gradation image will be described.

FIG. 6 is a block diagram showing the flow of image signals in the image forming apparatus according to this embodiment, and FIG. 7 is a sectional view of the image forming apparatus according to this embodiment.

In FIG. 7, reference numeral 100 denotes an image forming apparatus main body, which illuminates a document D placed on a document table glass 11 with a light source 12 and detects a light amount signal with a CCD 21. A /
After being digitally converted by the D converter 22, the image data is sent to the control unit 200.

The image signal is converted into a driving signal for the semiconductor laser 32 and output to the laser driver 31. The laser driver 31 is a circuit for driving the semiconductor laser 32, and switches the semiconductor laser 32 ON / OFF according to the input video signal. Laser light 3
The photosensitive drum 1 is swung left and right by the polygon mirror 33.
Scan over.

The scanning of the laser beam 3 causes the photosensitive drum 1 on which the latent image is formed to rotate in the direction of arrow R1. By this rotation, each color is developed by the rotary developing device 4 (in FIG. 7, a yellow developing state is shown).

On the other hand, the recording material P is the lower paper feed cassette 8
The material stored in a is supplied to the transfer drum 5 via the paper feed roller 8b, the conveyance roller 8c, the registration roller 8d, etc. and wound around the transfer drum 5, and each time the transfer drum 5 rotates once. Are transferred onto the recording material P in the order of Y (yellow), M (magenta), C (cyan), and Bk (black), and by rotating four times in total, four colors are transferred and color recording is completed. When the color transfer is completed in this way, the recording material P is separated from the transfer drum 5 and fixed by the fixing roller pair 10, and the color image print is completed.

A detector 50 is installed downstream of the developing device 4.

Now, the flow of the image signal will be described with reference to FIG.

The reading device uses the R
RGB information is obtained through three color separation filters of (red), G (green), and B (blue). The signal is converted into a digital signal by the A / D conversion circuit 22, and the signal of each cell of the CCD 21 is passed through a shading circuit 23.

The LOG conversion circuit 24 converts the RGB luminance signal into CMY density information. Bk generation circuit 24
A black signal is generated by a and data of four colors of MCYBk is created. After the gradation control is performed by the γ-LUT 25, the laser is driven by the pulse width conversion circuit 26 and the LD driver 31.

The color toners used in the copying machine according to the present embodiment are yellow, magenta, cyan, and
Black four-color toner is formed by dispersing color materials of each color of yellow, magenta, and cyan using a styrene-based copolymer resin as a binder, and black is formed by mixing the previous three colors.

As shown in FIG. 4, a gradation pattern for each color is generated by the pattern generator 29 to form a pattern on the photosensitive drum 1. The output gradation pattern is detected in reflection by the detection unit 50 at the same timing. When this gradation pattern is detected, the drive speed of the photosensitive drum 1 is set lower than that during normal image formation. The detected reflection output is converted into density information by the density conversion circuit 41. Then, the relationship between the laser output level and the obtained density is stored in the memory. The γ-LUT 25 for each color is obtained and set from the relationship between the laser output level and the density.

Upon completion of the above control, during the copying operation, the image density signal obtained by the original reading section 201 is converted through the γ-LUT 25 calculated by the above-mentioned method, so that the laser output signal is linear. It is possible to obtain excellent gradation.

<Third Embodiment> In this embodiment, a full-color image forming apparatus having an intermediate transfer member will be described.

FIG. 8 shows an image forming apparatus F according to this embodiment.
1 is a cross-sectional view of the main components of the image forming unit 1, in which reference numeral 1 denotes a photosensitive drum as an image carrier, and a primary charger 2 as a charging means around a cylindrical photosensitive member surface 1a. A cleaning device 11 having a cleaning roller 12 for cleaning the photosensitive drum 1 by collecting the residual toner on the surface 1a of the photoconductor, and an exposure unit for forming an electrostatic latent image by laser exposing the surface 1a of the photoconductor. Laser scanner unit 3, photoconductor surface 1a
Black developing device 8 as a developing means for developing the electrostatic latent image of
A color developing device 9 for developing yellow, magenta, and cyan colors, and an intermediate transfer drum 7 as an image carrier for transferring the developed toner image on the surface 1a of the photosensitive member are arranged.

Around the intermediate transfer drum 7, the intermediate transfer drum cleaning roller 13 for cleaning the intermediate transfer drum 7 in addition to the photosensitive drum 1, and the image density of the toner image transferred from the photosensitive drum 1 are measured. For transferring the toner image at the nip portion with the intermediate transfer drum 7 while conveying the density sensor 50 as the density detecting means, the transfer charger 6, the sheet material P which is the material to be transferred.
A conveyor belt device 14 is arranged.

As shown in the figure, the detected value of the density sensor 50 is A / D converted and the CPU 28 which is the density control means.
It is input to (also performs other controls).

Further, various controls such as the primary charging bias control of the primary charger 2, the developing bias control of the developing devices 8 and 9 and the charging voltage control of the transfer charger 6 are based on the control signal from the CPU (D / A Conversion) controlled.

In this image forming apparatus F1, the digital image signal is D / A converted and the semiconductor laser in the laser scanner unit 3 is caused to emit light through a laser driver (not shown). The laser light is applied to the photosensitive drum 1 uniformly charged to a certain potential by the primary charger 2.
An electrostatic latent image is formed on the photosensitive drum 1.

The electrostatic latent image drawn on the photosensitive drum 1 by the laser light is developed as a toner image by the developing devices 8 and 9 to be visualized. The toner image is once transferred onto the intermediate transfer drum 7, and the transfer charging device 6 transfers the sheet material P.
And a toner image is fixed on the sheet material P by a fixing device (not shown) arranged on the downstream side of the conveying path of the sheet material P, and the sheet material P on which the toner image is fixed is output from the paper discharge unit. Output as an image.

Further, the image forming apparatus is equipped with a density sensor 50 for measuring the image density on the intermediate transfer drum 7. The density sensor 50 measures the image density to control the density.

When performing image density control, as shown in FIG. 4, a gradation pattern for each color is generated by the pattern generator 29, a pattern is formed on the photosensitive drum 1 and transferred onto the intermediate transfer drum 7.

With respect to the output gradation pattern, the reflection output is detected by the density sensor 50 at the same timing. At the time of detecting this gradation pattern, the driving speed of the intermediate transfer member is set lower than that at the time of normal image formation. The detected reflection output is converted into density information by the density conversion circuit.

Then, the relationship between the laser output level and the obtained density is stored in the memory. The γ-LUT of each color is obtained and set from the relationship between the laser output level and the density.

When the above control is completed, during the copying operation, the image density signal obtained by the document reading section is converted through the γ-LUT calculated by the above-mentioned method.
Good linear gradation can be obtained with respect to the laser output signal.

[0061]

As is apparent from the above description, according to the present invention, an image forming means for forming an image on an image carrier,
Optical detection means for detecting the density and gradation of the image on the image carrier, density adjusting means for adjusting the image density, gradation adjusting means for adjusting the gradation characteristics of the image, and driving of the image carrier At least one image pattern for determining image characteristics is formed on the image carrier, and the formed image pattern is read by the optical detecting means and read by the speed detecting means. In the image control method of controlling the image forming condition based on the image information, the driving speed of the image carrier at the time of detecting the image pattern is different from the driving speed at the time of forming the normal image, so that the image pattern is detected with high accuracy. The effect that image stabilization can be achieved by performing highly sensitive image density detection in a wide density region is obtained.

[Brief description of drawings]

FIG. 1 is a control block diagram of an image forming apparatus according to a first embodiment of the present invention.

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

FIG. 3 is a block diagram showing a flow of image signals in the image forming apparatus according to the first embodiment of the present invention.

FIG. 4 is a diagram illustrating an operation of reading a gradation patch pattern.

FIG. 5 is a fourth limit chart showing gradation reproduction characteristics.

FIG. 6 is a block diagram showing the flow of image signals in the image forming apparatus according to the second embodiment of the present invention.

FIG. 7 is a vertical sectional view showing a schematic configuration of an image forming apparatus according to a second embodiment of the present invention.

FIG. 8 is a vertical sectional view showing a schematic configuration of an image forming apparatus according to a second embodiment of the present invention.

[Explanation of symbols]

1 Photosensitive drum (image carrier) 2 Primary charger (image forming means) 3 Laser light (image forming means) 4 Charger (image forming means) 5 Transfer drum (transfer means) 6 Transfer charger (transfer means) 7 Intermediate transfer drum (intermediate transfer body) 8 Developing device (black) 9 Developer (color) 10 Fixing device (fixing means) 11 Cleaning device 12 Cleaning roller 13 Intermediate transfer drum cleaning roller 14 Transfer / transport belt device 21 CCD 25 γ-LUT 28 CPU 29 pattern generator 32 Semiconductor laser 50 Detection unit (optical detection means) 51 photo sensor 52 LED 100 printer section 200 Control unit 201 Image reading unit

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Issei Suzuki             Kyano, 3-30-2 Shimomaruko, Ota-ku, Tokyo             Within the corporation F term (reference) 2H027 DA09 DA10 DE02 EA18 EB01                       EB04 EC03 EE03                 2H200 FA16 GA23 GA34 GA44 GA47                       GA50 GB15 GB25 GB41 HA00                       JA02 JB02 JB50 LA12 PB17

Claims (11)

[Claims] 1. An image forming unit for forming an image on an image carrier, an optical detecting unit for detecting the density and gradation of an image on the image carrier, and a density adjusting unit for adjusting the image density.
On the image carrier, at least one or more image patterns for determining the image property are provided, having a gradation adjusting unit for adjusting the gradation property of the image and a shifting unit for adjusting the driving speed of the image carrier. In the image control method of forming an image pattern on the image carrier, reading the formed image pattern by the optical detecting means, and controlling the image forming condition based on the read image information, the driving speed of the image carrier at the time of detecting the image pattern is usually An image control method, which is different from the driving speed at the time of image formation. 2. The image control method according to claim 1, wherein the drive speed of the image carrier at the time of detecting the image pattern is lower than that at the time of normal image formation. 3. The image density information about the image pattern on the image carrier is read by the optical detecting means,
3. The image control method according to claim 1, further comprising a density control step of correcting an image forming condition based on the read image density information. 4. The image control method according to claim 1, wherein the optical detection unit is a specular reflection type sensor. 5. The image control method according to claim 1, wherein the image signal formed by the image forming unit is an image signal converted according to the correction information. 6. An image carrier, an image forming means for forming an image on the image carrier, a transfer means for transferring the image on the image carrier to a recording material, and an image transferred to the recording material. An image forming apparatus comprising: a fixing unit configured to fix the image on the recording material, and performing image density adjustment and image gradation adjustment by the image control method according to claim 1. 7. The image bearing member is a drum-shaped photosensitive drum having a photosensitive layer on the surface thereof.
The image forming apparatus described. 8. The image carrier is a sheet-shaped photosensitive sheet having a photosensitive layer on its surface.
The image forming apparatus described. 9. The image carrier is a belt-shaped photosensitive belt having a photosensitive layer on the surface thereof.
The image forming apparatus described. 10. The image bearing member is a transfer member on which a toner image is transferred from a photosensitive member.
The image forming apparatus described. 11. The image forming apparatus according to claim 10, wherein the transfer body is an intermediate transfer body.