JP2003162111A - Color image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a color image forming apparatus capable of being made small in size and low in cost by reducing the number of sensors. <P>SOLUTION: This color image forming apparatus, where a multiple image is formed by respectively scanning and exposing a plurality of photoreceptors with a light beam modulated in accordance with an inputted image signal by a plurality of scanner optical systems, is provided with a means for forming a positional deviation detecting pattern, a positional deviation detecting sensor for reading the positional deviation detecting pattern, a means for forming a density detecting pattern and a means for detecting the density detecting pattern by the positional deviation detecting sensor. The density is detected by averaging output from the positional deviation detecting sensor at the time of reading the density detecting pattern. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image forming apparatus, such as a color printer or a color copying machine, which corrects a positional deviation.

[0002]

2. Description of the Related Art A plurality of image forming areas for irradiating a photosensitive drum with a laser beam to develop an electrostatic latent image on a photosensitive body by an electrophotographic process are provided. An apparatus is known in which a color image is transferred onto a recording paper while a paper is conveyed to an image forming area of an intermediate transfer body by a transfer belt to obtain a color image.

When an image forming apparatus of this type is used, when an electrostatic latent image is formed on each photoconductor drum and transferred to a sheet on a transfer belt, the transfer image position of each color deviates from the ideal position on the sheet. In the case, the tint changes, and as the degree further progresses, an image with color shift is formed. These phenomena significantly degrade the image quality. Alternatively, a device that directly transfers the image from the photoconductor to the paper or a device that performs multiple development on the photoconductor and transfers the image to the paper or an intermediate transfer member is known. Deviation occurs. For this reason, conventionally, the positional deviation pattern formed on each of the photosensitive drums on the intermediate transfer member, the transfer belt, or the photosensitive member is C
An optical element which is read by a CD sensor or a photo sensor, detects the amount of positional deviation on the photosensitive drum corresponding to each color, electrically corrects the image signal to be recorded, or is provided in the optical path of the laser beam. Is performed to correct the image and correct the positional deviation.

Further, in the above-described image forming apparatus, if the image density changes due to various conditions such as the environment in which it is used and the number of prints, the proper color tone cannot be obtained. Therefore, conventionally, in order to determine the image condition at the time of image formation, a toner image pattern (hereinafter, referred to as a dark detection pattern) for detecting each color density is formed on a photosensitive drum or an intermediate transfer member on a trial basis. The density is automatically detected, the detection result is fed back to the image forming conditions such as the exposure amount and the developing bias, and the density is controlled to form an original color image, and a stable image is obtained. One of the tasks of this concentration control is
There is a control for optimizing the developing bias to obtain a desired density according to the environment. Usually, there is a fixed relationship between the developing bias and the density. This relationship is susceptible to environmental changes such as the number of printed sheets, temperature and humidity, and changes every moment. for that reason,
With a proper number of prints, several dark test patterns are created while changing the developing bias, and the density of the dark test pattern is measured to estimate the developing bias that can obtain the desired density.

In the density control, there is a method of changing the process conditions such as the laser exposure amount and the photosensitive drum potential in addition to the above-mentioned method. Like the density control, the density detection pattern is changed while changing the process conditions. Print and observe the change in density to estimate the optimum process conditions. Normally, one of these density control methods is selected or several kinds of them are combined to execute the density control.

[0006]

However, in the conventional technique, it is necessary to perform the density detection and the positional deviation detection by separate sensors, which hinders downsizing and cost reduction of the apparatus.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a color image forming apparatus capable of reducing the number of sensors to reduce the size and cost of the apparatus. It is in.

[0008]

In order to achieve the above-mentioned object, according to the present invention, a plurality of scanner optical systems scan and expose a plurality of photoconductors by a light beam modulated according to an input image signal. In a color image forming apparatus capable of forming a multiple image by means of a position deviation detection pattern, a position deviation detection sensor for reading the position deviation detection pattern, a density detection pattern forming means, and a density detection by the position deviation detection sensor. A means for detecting a pattern is provided, and the density is detected by averaging the outputs of the positional deviation detection sensors when the density detection pattern is read.

The present invention is also a color image forming apparatus capable of forming a multiple image by scanning exposure of a plurality of photoconductors by a plurality of scanner optical systems by a light beam modulated according to an input image signal. In the above, the means for forming the positional deviation detection pattern, the positional deviation detection sensor for reading the positional deviation detection pattern, the means for forming the density detection pattern, and the means for detecting the density detection pattern by the positional deviation detection sensor are provided to detect the density. It is characterized in that density detection is performed by averaging the outputs of the misregistration detection sensors in a length that is an integral multiple of the length of the minimum unit of pattern repetition.

Further, the present invention is a color image forming apparatus capable of forming a multiple image by scanning exposure of a plurality of photoconductors by a plurality of scanner optical systems by a light beam modulated according to an input image signal. In the above, the means for forming the positional deviation detection pattern, the positional deviation detection sensor for reading the positional deviation detection pattern, the means for forming the density detection pattern, and the means for detecting the density detection pattern by the positional deviation detection sensor are provided to detect the density. It is characterized in that the density is detected by the output of a low-pass filter having a time constant longer than the time taken by the displacement detection sensor to scan the length of the minimum unit of pattern repetition in the direction perpendicular to the beam scanning direction.

[0011]

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

<First Embodiment> In the present embodiment, a photodiode (hereinafter abbreviated as PD) is used as a registration detection sensor.
A method of performing density detection by averaging outputs of integral multiples of the length of the minimum unit of the dark detection pattern in the sub-scanning direction will be described.

FIG. 1 is a perspective view of an essential part of a color image forming apparatus according to the first embodiment of the present invention. The color image forming apparatus according to the present embodiment is provided with image forming means for four colors, that is, yellow Y, magenta M, cyan C, and black K. In FIG. 1, reference numeral 1 forms an electrostatic latent image. Photosensitive drums (k, c, m, and y are for K, C, M, and Y), and 2 is a photosensitive drum 1 that is exposed in accordance with an image signal.
A laser scanner 3 for forming an electrostatic latent image thereon, 3 is an endless conveyor belt which also serves as a transfer belt for sequentially conveying paper to each color image forming city, and 4 is connected to a driving means (not shown) including a motor and a gear. The driving roller 5 that drives the conveyor belt 3 is a driven roller that rotates in accordance with the movement of the conveyor belt 3 to apply a constant tension to the conveyor belt 3, and 6 is the misregistration detection pattern formed on the conveyor belt 3. A pair of optical sensors provided on both sides of the conveyor belt 3 for detection.

The operation of the color image forming apparatus according to this embodiment will be described below.

Data to be printed is sent from the host computer such as a personal computer to the printer, and when image formation according to the printer engine system is completed and printing is ready, paper is supplied from the paper cassette and is conveyed to the conveyor belt 3. When the paper arrives, the paper is sequentially conveyed by the conveyor belt 3 to the image forming city of each color. The image signals of the respective colors are sent to the laser scanners 2 in synchronism with the sheet conveyance by the conveyor belt 3, and an electrostatic latent image is formed on the photosensitive drum 1.
The toner is developed by a developing device (not shown), and the toner image is transferred onto the paper by a transfer unit (not shown). In FIG. 1, Y,
Images are sequentially formed in the order of M, C, and K.

Thereafter, the paper is separated from the conveyor belt 3, the toner image is fixed on the paper by heat by a fixing device (not shown), and the paper on which the toner image is fixed is discharged to the outside.

Since there are a plurality of image forming sections, if there is a positional deviation in the main scanning direction or the sub scanning direction for each image forming section, it appears as a color deviation in the image.

In order to reduce this displacement, it is necessary to measure the displacement amount. FIG. 2 shows a pattern for detecting the positional deviation. This pattern is formed on the conveyor belt 3 by the image forming unit, and is read by a pair of positional deviation detection sensors 6 (6a, 6b) provided on both sides of the transportation belt 3, and the output of the positional deviation detection sensor is not shown in the CPU or the like. To obtain the amount of positional deviation.

In FIG. 2, reference numerals 7, 8, 9, and 10 denote linear patterns extending in the K, C, M, and Y laser scanning directions and the carrying direction, respectively. a and b are patterns on the front side and the back side of the conveyor belt 3, respectively. The pattern of a is the displacement detection sensor 6a, and the pattern of b is the displacement detection sensor 6a.
read in b. The positional deviation in the sub-scanning direction is detected from the interval between the two linear patterns extending in the main scanning direction. The positional deviation in the main scanning direction is detected from the "U" pattern. In FIG. 2, if the "ku" character shifts to the right, the time from when the PD detects the upper diagonal line to when the PD detects the lower diagonal line becomes shorter, and the "ku" character shifts to the left. Then, since it takes longer for the PD to detect the upper diagonal line and the PD to detect the lower diagonal line, the positional shift in the main scanning direction can be detected.

FIG. 3 is a diagram for explaining the displacement detection sensor.

In FIG. 3, reference numeral 6 is a main body of the displacement detection sensor, 301 is a light emitting portion such as an LED, 302 is a light receiving portion such as a photodiode, and 3 is a conveyor belt. Light emitting unit 301
The light emitted from the sheet passes through optical components such as a lens (not shown) and is applied to the conveyor belt 3. The light is focused near the conveyor belt 3, is reflected by the conveyor belt 3, and enters the light receiving unit 302.

When the amount of light emitted from the light emitting unit 301 is constant, the amount of light received by the light receiving unit 302 differs depending on whether or not toner is placed on the conveyor belt 3. For example, when the reflectance at the wavelength of the light emitting unit 301 is compared with the state where the toner is not placed on the conveyor belt 3 and when the reflectance is high when the toner is not placed, the light receiving unit 302 is found.
The patterns 7 to 10 on the conveyor belt 3 can be read by reducing the output of the. The distance between the patterns can be obtained from the output of the light receiving unit 302, the pattern, and the moving speed of the surface of the conveyor belt 3.

Next, a method of using the above-described positional deviation detection sensor for density detection will be described.

FIG. 4 is a schematic representation of the dense test pattern for explaining the dense test pattern. The pattern shown on the right side of the figure is the minimum unit of the deep detection pattern, and the diagram shown on the left side is the deep detection pattern composed of 16 patterns of the minimum unit. One square is a minimum pixel unit (hereinafter referred to as a dot). The dark detection pattern is formed on the conveyor belt 3 by the image forming unit, and a pair of position deviation detection sensors 6 (6a, 6b) provided on both sides of the conveyor belt 3 are provided.
Read with.

Here, the method of detecting the density will be described step by step.

The above-mentioned deep inspection pattern is formed on both sides of the conveyor belt 3 by the image forming section. The formed deep inspection pattern moves to a position where it can be read by the misregistration detection sensor 6 as the conveyor belt 3 moves. After a certain period of time has passed after the formation of the dense test pattern, the A / D
Start conversion. The sampling period for A / D conversion is 1
The density can be accurately detected by setting the / 2 dot to a time shorter than the time required for the misregistration detection sensor to scan.

The output of the displacement detection sensor 6 is shown in FIG. In FIG. 5, the vertical axis represents the output of the displacement detection sensor and the horizontal axis represents time.

Since the conveyor belt 3 on which the dense detection pattern is formed is moving, the positional deviation detection sensor 6 scans the dense detection pattern. The reflectance of the portion shown in black in the dark inspection pattern is small, and therefore the output of the position shift detection sensor 6 is small. In addition, the misalignment detection sensor 6
When there is no resolution in dot units, the increase in output is small even in a portion where an image is not formed on dots as shown in the figure. When the pattern shown in FIG. 4 is scanned, the minimum unit of the deep detection pattern is 6 units.
Of these, the density can be obtained by averaging the outputs for the time corresponding to the minimum unit of four (16 dots).

Here, the purpose of averaging the outputs having a length which is an integral multiple of the minimum unit of the deep detection pattern is to prevent a difference due to the measurement position in the main scanning direction. For example, 3 /
When the outputs of the lengths of 4 minimum units are averaged, (a) the measured 3/4 minimum unit includes a point where dots are not formed, and (b) the measured 3/4 minimum unit. The output result is different from when the dot is not formed in. It is determined that the density of (b) is higher than that of (a). On the other hand, when the output obtained by scanning the position shift detection sensor 6 for a length that is an integral multiple of the minimum unit is averaged, an output corresponding to the density of the dark detection pattern is obtained. That is, even if the position of the dense test pattern is slightly displaced due to the positional deviation, the density of the dense test pattern can be accurately detected by averaging the outputs corresponding to the integral multiples of the minimum unit of the dense test pattern. .

The density is adjusted as follows.

A plurality of dark detection patterns formed by changing the image forming conditions are formed, and the density of each dark detection pattern is detected. The optimum image forming condition is selected from the detection result of the density, or the optimum image forming is estimated and the image is formed under the image forming condition.

With the configuration of the present embodiment, it is possible to detect the density using the position shift detection sensor 6, and the device can be made smaller and the cost can be reduced as compared with the case where the density detection sensor is provided. Moreover, since the density is measured by an integral multiple of the minimum unit of the dense test pattern, the density of the dense test pattern can be accurately detected.

<Embodiment 2> In this embodiment, a configuration will be described in which a PD is used as a positional deviation detection sensor and a low-pass filter is used to detect density.

The overall structure of the apparatus is similar to that of the first embodiment. The present embodiment is different in that a low-pass filter is provided between the displacement detection sensor and the AD converter.

FIG. 6 shows the structure of the positional deviation detection sensor according to this embodiment.

The output is A / D to the displacement detection sensor.
There are a path for directly inputting to the converter 305 and a path for inputting to the A / D converter 307 through the low-pass filter 306. When detecting the positional deviation, the output of the A / D converter 305 is used as in the first embodiment. On the other hand, for density detection, the output of the positional deviation detection sensor is averaged by the low-pass filter 306, the output of the low-pass filter 306 is input to the A / D converter 307, and the output is used. The time constant of the low-pass filter 306 is set such that the length of the dark detection pattern in the sub-scanning direction, which is the minimum unit, is larger than the time required for the misregistration detection sensor to scan, and the length of the dark detection pattern in the sub-scanning direction is set. It is set smaller than the time required for the shift detection sensor to scan.

By setting the time constant of the low-pass filter 306 to be longer than the time required for the position shift detection sensor of the minimum unit of the dark detection pattern to scan, the length of the minimum unit of the dark detection pattern in the sub-scanning direction is increased. An effect equivalent to averaging the output when the position shift detection sensor scans is obtained.

Further, by making the time constant of the low-pass filter 306 shorter than the time for which the position shift detection sensor scans the dense test pattern, the output of the low-pass filter 306 near the center of the dense test pattern becomes stable. Read the value near the center of the pattern.

Here, the method for detecting the density will be described step by step.

When it is determined that the image density needs to be adjusted, such as when the apparatus is activated, after a certain temperature change, after printing a certain number of sheets, density detection is started. After the image can be formed, the image data of the deep inspection pattern is sent to the laser scanner and an electrostatic latent image is formed on the photosensitive drum.
The toner is developed by the developing device. The developed toner is transferred to the conveyor belt at the transfer section. Then, the image formed on the conveyor belt moves to the position of the displacement detection sensor as the conveyor belt rotates.

The CPU measures the time from the formation of the dense detection pattern, and outputs the output of the positional deviation detection sensor through the low-pass filter 306 and the A / D converter 307 when the dense detection pattern reaches the detection range of the positional deviation detection sensor. To detect. FIG. 7 shows the output of the misregistration detection sensor when the dense test pattern is scanned in the sub-scanning direction.

Since there is a low-pass filter, there is no increase in output in the area where dots are not formed, and the detected value is smoothed and stable. Therefore, the output value near the center of the dense test pattern is read, and the density is detected from that value.
Also, read the output value several times near the center of the dense test pattern,
By averaging the values, it is possible to obtain a value less affected by disturbance. As in the first embodiment, the density is adjusted by changing the image forming conditions such as the developing bias based on the detected density.

With the configuration of this embodiment, it is possible to detect the density using the position shift detection sensor, the apparatus can be downsized as compared with the case having the density detection sensor, and the cost can be reduced. To be Further, since the output of the position shift detection sensor is smoothed by the low-pass filter 306 having an appropriate time constant, the density of the dark detection pattern can be accurately detected.

<Third Embodiment> In the present embodiment, a CCD (Charge Coupled Device) sensor is used as a position shift detection sensor, and the output of an integral multiple in the main scanning direction of the minimum unit of the dark detection pattern is averaged. A method of performing density detection by will be described.

The basic device configuration is the same as that of the first embodiment. In the present embodiment, a CCD sensor is used as the displacement detection sensor. This CCD sensor is a one-dimensional sensor array in which sensors are arranged in the main scanning direction.
The array interval is shorter than the length corresponding to one dot. The length of the array is longer than the minimum unit length of the dense detection pattern in the main scanning direction.

FIG. 8 shows the misregistration detection pattern. This pattern is formed on the conveyor belt by the image forming unit,
A pair of misregistration detection sensors (CCD) 6 provided on both sides of the conveyor belt read it, and the output of the CCD 6 is processed by a CPU (not shown) or the like to obtain the amount of misregistration.

In FIG. 8, reference numerals 11, 12, 13, and 14 denote linear patterns extending in the K, C, M, and Y laser scanning directions and the carrying direction, respectively. a and b are patterns on the front side and the back side of the conveyor belt 3, respectively. The pattern a is read by the position shift detection sensor (CCD) 6a, and the pattern b is read by the position shift detection sensor (CCD) 6b. The amount of positional deviation in the sub-scanning direction is detected from the linear pattern extending in the main scanning direction, and the amount of positional deviation in the main scanning direction is detected from the linear pattern extending in the sub-scanning direction.

The concentration detection is performed as follows.

The deep inspection pattern is the same as in the first embodiment. The dark inspection pattern is formed on both sides of the conveyor belt by the image forming unit. The formed deep inspection pattern moves along with the movement of the conveyor belt, and the positional deviation detection sensor (C
CCD when it is moved to a position where it can be read by (CD) 6
The reading is started by 6.

The density of the dark detection pattern can be detected by averaging the output of the image read by the CCD 6 and having an integral multiple of the minimum unit length of the dark detection pattern in the main scanning direction. By averaging the output having a length that is an integral multiple of the length of the darkness detection pattern in the main scanning direction, the density of the darkness detection pattern can be accurately detected regardless of the measurement position.

Further, the number of times of detecting the density does not have to be 1 degree, and the detection results at the different sub-scanning positions of the same darkness detection pattern are further averaged so that the detection is less likely to be affected by the disturbance. It can be carried out.

With the configuration of this embodiment, the density can be detected by using the CCD 6 which is the displacement detection sensor, the apparatus can be downsized as compared with the case having the density detection sensor, and the cost can be reduced. Be promoted. Further, since the density is detected by an integral multiple of the minimum unit length of the dark detection pattern in the main scanning direction, it is possible to accurately detect the density of the dark detection pattern.

[0053]

As is apparent from the above description, according to the present invention, a plurality of scanner optical systems scan and expose a plurality of photoconductors with a light beam modulated according to an input image signal. In a color image forming apparatus capable of forming multiple images by means of a position deviation detection pattern, a position deviation detection sensor for reading the position deviation detection pattern, a density detection pattern forming means, and a density detection by the position deviation detection sensor. A means for detecting the pattern is provided, and the density detection is performed by averaging the output of the position shift detection sensor when the density detection pattern is read, so that the number of sensors is reduced and the apparatus is downsized and the cost is reduced. The effect that it can be achieved is obtained.

[Brief description of drawings]

FIG. 1 is a perspective view of a main part of a color image forming apparatus according to the present invention.

FIG. 2 is a diagram illustrating a misregistration detection pattern according to the first embodiment of the present invention.

FIG. 3 is a diagram illustrating a positional deviation detection sensor according to the first embodiment of the present invention.

FIG. 4 is a diagram illustrating a deep detection pattern according to the first embodiment of the present invention.

FIG. 5 is a diagram illustrating output of the positional deviation detection pattern according to the first embodiment of the present invention.

FIG. 6 is a diagram illustrating a positional deviation detection sensor according to a second embodiment of the present invention.

FIG. 7 is a diagram illustrating an output of the position shift detection sensor according to the second embodiment of the present invention.

FIG. 8 is a diagram illustrating a deep detection pattern according to the third embodiment of the present invention.

[Explanation of symbols]

1 photoconductor drum 2 laser scanner 3 Conveyor belt 6 Position shift detection sensor 7 to 14 Misalignment detection pattern

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G03G 21/14 B41J 3/00 M 5C074 H04N 1/04 G03G 21/00 372 1/29 H04N 1/04 D F-term (reference) 2C362 BA52 BA67 BA68 BA71 BB37 BB46 CA22 CA23 CA39 CB73 CB80 DA09 2G059 AA01 BB10 EE02 EE11 GG01 HH02 KK04 MM03 2H027 DA23 DA32 DE02 DE07 DE07 EE02 ED06 5EE02 ED06 5EE02 EF06 EE02 ED06 5EE02 ED06 5EE02 ED06 5EE02 ED06 5EE02 ED06 5EE02 ED06 5EE02 ED06 5EE02 ED06 5EE02 ED06 5EE02EE02 AA03 BA01 BA19 BA20 HA02 HB08 QA10 QA17 RA18 UA17 5C074 AA10 DD01 DD11 DD15 DD24 DD28 EE02 EE04 FF15

Claims (6)

[Claims] 1. A color image forming apparatus capable of forming a multiple image by scanning exposure of a plurality of photoconductors by a plurality of scanner optical systems by a light beam modulated according to an input image signal The means for forming the detection pattern, the position deviation detection sensor for reading the position deviation detection pattern, the means for forming the density detection pattern, and the means for detecting the density detection pattern with the position deviation detection sensor are provided, and the density detection pattern is read. A color image forming apparatus, wherein density detection is performed by averaging the outputs of the positional deviation detection sensors at this time. 2. A color image forming apparatus capable of forming a multiple image by scanning and exposing a plurality of photoconductors by a plurality of scanner optical systems by a light beam modulated according to an input image signal A means for forming a detection pattern, a positional deviation detection sensor for reading the positional deviation detection pattern, a means for forming a density detection pattern, and a means for detecting the density detection pattern with the positional deviation detection sensor are provided to repeat the density detection pattern. A color image forming apparatus, characterized in that density detection is performed by averaging the output of a position shift detection sensor in a length that is an integral multiple of the length of the minimum unit. 3. The color image forming apparatus according to claim 1, wherein the averaging direction is a direction perpendicular to the beam scanning direction. 4. The color image forming apparatus according to claim 1, wherein the averaging direction is a beam scanning direction. 5. The output of the displacement detection sensor is analog.
4. The color image forming apparatus according to claim 1, wherein the density is detected by averaging by calculation after digital conversion. 6. A color image forming apparatus capable of forming a multiple image by scanning exposure of a plurality of photoconductors by a plurality of scanner optical systems by a light beam modulated according to an input image signal A means for forming a detection pattern, a positional deviation detection sensor for reading the positional deviation detection pattern, a means for forming a density detection pattern, and a means for detecting the density detection pattern with the positional deviation detection sensor are provided to repeat the density detection pattern. A color image forming apparatus characterized in that density detection is performed by an output of a low-pass filter having a time constant longer than a time for which a position shift detection sensor scans a length in a direction perpendicular to a beam scanning direction of a minimum unit.