JP2000206759A - Image forming apparatus and control method of image forming apparatus - Google Patents

Abstract

(57) [Problem] To reduce a color shift that periodically occurs due to eccentricity of a photosensitive drum or the like. A controller 1000 finely adjusts the frequency of a video clock 15 output from a voltage controlled oscillator 705 by adjusting a video clock fine adjustment signal 17 according to the eccentricity and phase of a photosensitive drum. .

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 having a plurality of image forming means including a scanning means for forming an image in accordance with a plurality of video clocks and a photosensitive member, and a method of controlling the image forming apparatus. is there.

[0002]

2. Description of the Related Art A conventional image forming apparatus such as an electrophotographic color printer has a plurality of image forming sections for outputting a color image at a high speed, and is formed on a photosensitive drum of the image forming section. Various methods have been proposed for sequentially transferring toner images of different colors onto a recording material held on a conveyance belt.

In such a conventional image forming apparatus having a plurality of image forming units, unevenness in rotation and movement of the photosensitive drums and conveying belts of the plurality of image forming units and unevenness in each image forming unit are caused by mechanical accuracy and the like. The deviation of the moving distance of the photosensitive drum from the outer peripheral surface of the transfer belt at the transfer position of each of the image forming units is generated separately, and the toner image of each color formed on the photosensitive drum of each image forming unit is recorded on the recording material. When the images are transferred to the printer, the toner images of the respective colors do not coincide with each other, resulting in a color shift (position shift).

In particular, in an image forming apparatus having a plurality of image forming units having a laser scanner and a photosensitive drum, there is an error in the distance between the laser scanner and the photosensitive drum in the image forming unit. If they are different, a difference occurs in the scanning width of the laser on the photosensitive drum of each image forming unit,
Color shift (position shift) occurs.

In order to reduce this color shift (position shift),
As shown in FIG. 11, which will be described later, a video clock generator for an image signal is provided for each color, the frequency of the video clock can be varied independently for each color, and the laser scanning width can be corrected by adjusting the frequency of the video clock. How to do it has been proposed.

FIG. 11 is a diagram illustrating the configuration of a video clock generator in a conventional image forming apparatus. In addition,
The video clock generator uses a PLL (Phase Lock).
edLoop) circuit.

In the figure, 101 is a crystal oscillator, 102
Is a 1 / N divider, 103 is a phase comparator, 104 is a low-pass filter, 105 is a voltage controlled oscillator, 106 is 1 / M
It is a frequency divider. Reference numeral 14 denotes an output signal, which is a crystal oscillator 1
Output from 01. Reference numeral 15 denotes a video clock, which is an output of the video clock generator, and is a video clock whose frequency has been changed.

Hereinafter, a method of changing the video clock frequency will be described. A phase comparator 1 compares a signal obtained by dividing the output signal 14 of the crystal oscillator 101 by N with a 1 / N divider 102 and a signal obtained by dividing a video clock 15 by M with a 1 / M divider 106.
03, and the output of the phase comparator 103 is input to the voltage controlled oscillator 105 through the low-pass filter 104.

For example, the output signal 14 of the crystal oscillator 101
If the phase of the signal obtained by dividing N by N is advanced from the phase of the signal obtained by dividing the video clock 15 by M, the voltage-controlled oscillator 1
The input voltage at 05 rises and advances the phase of the video clock. Assuming that the frequency of the crystal oscillator 101 is fin and the frequency of the video clock 15 is fout,

[0010]

Fout = fin * M / N (1) By adjusting the value of M / N according to the detected main scanning width, the frequency of the video clock output from the video clock generator is variable.

[0011]

However, the conventional image forming apparatus has the following disadvantages.

Regarding the color shift (position shift) caused by the difference in the scanning width of the laser on the photosensitive drum between the image forming units, only the color shift (position shift) caused by a steady distance error between the laser scanner and the photosensitive drum. In some cases, the eccentricity of the photosensitive drum causes a change in the distance between the exposure surface of the photosensitive drum and the laser scanner in the rotation cycle of the photosensitive drum. There has been a problem that the color shift as the cause cannot be reduced.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a video clock generated by a plurality of generating means in accordance with the eccentricity and phase of each photoconductor. Provided are an image forming apparatus and a method of controlling an image forming apparatus capable of reducing a color shift that periodically occurs due to eccentricity of a photosensitive drum or the like and adjusting the frequency so as to output a high-quality image. It is to be.

[0014]

According to a first aspect of the present invention, there is provided a scanning unit (first to fourth laser scanners 2a shown in FIG. 5).
To 2d) and a photoconductor (photosensitive drums 1a to 1d shown in FIG. 1)
Image forming means (image forming units for each color)
And a plurality of generating means (first to fourth video clock generators 602a to 602d shown in FIG. 5) for generating a video clock to be supplied to each of the scanning units, and are formed by each of the image forming means. An image forming apparatus capable of adjusting a frequency of a video clock generated by each of the generating units according to a shift amount of an image width in a main scanning direction, wherein the plurality of the plurality of photoconductors are adjusted according to an eccentric amount and a phase of each of the photoconductors. And the adjusting means (controller 1000 shown in FIG. 6) for adjusting the frequency of the video clock generated by the generating means.

According to a second aspect of the present invention, there is provided a detecting means (controller 1000 shown in FIG. 6) for detecting the amount of eccentricity and the phase of each photoconductor.

According to a third aspect of the present invention, in the image processing apparatus, the detecting means may be configured to detect the position of the plurality of patterns formed on the photoreceptor at different positions in the sub-scanning direction based on a fluctuation state of a width in the main scanning direction. It detects the amount of eccentricity and phase of the photoconductor.

According to a fourth aspect of the present invention, there is provided a scanning unit (FIG. 5).
And a plurality of image forming units (image forming units for each color) each including a first to fourth laser scanners 2a to 2d shown in FIG. 1 and a photoconductor (photosensitive drums 1a to 1d shown in FIG. 1), and supply to each of the scanning units. A plurality of generating means (first to fourth video clock generators 602a shown in FIG. 5)
602d), wherein the frequency of the video clock generated by each of the generating units can be adjusted according to the amount of deviation of the image width in the main scanning direction formed by each of the image forming units. And adjusting means (controller 1000 shown in FIG. 6) for adjusting the frequency of the video clock generated by the plurality of generating means in accordance with the periodic variation of the distance between each of the photoconductors and each of the scanning units. Things.

According to a fifth aspect of the present invention, there is provided a detecting means (a controller 1000 shown in FIG. 6) for detecting a periodic variation in a distance between each of the photosensitive members and each of the scanning units.

According to a sixth aspect of the present invention, in the image processing apparatus, the detecting means includes a plurality of patterns formed on the photosensitive member having different positions in the sub-scanning direction, based on a fluctuation state of a width in the main scanning direction. This is to detect a change in the distance between each photoconductor and each of the scanning units.

According to a seventh aspect of the present invention, the generation means includes a high-precision clock supply unit (a crystal oscillator 6 shown in FIG. 5).
5) is shown in FIG. 5 (a first video clock generator 602a to 602d is provided with a PLL circuit configuration shown in FIG. 6). The adjusting means adjusts the frequency of the video clock by adjusting the voltage input to the voltage controlled oscillator of the PLL circuit (the video clock fine adjustment signal 17a as shown in FIG. 8).
To 17d are adjusted).

According to an eighth aspect of the present invention, in the image forming apparatus, the adjusting means includes a non-image forming timing in the sub-scanning direction (P shown in FIG. 8).
During the period when the LL control signal 16 rises), the P
At the image forming timing in the sub-scanning direction (period 21 during which the PLL control signal 16 falls in FIG. 8), the PLL circuit stops the PLL control and performs the image forming in the sub-scanning direction. At the image forming timing in the main scanning direction during the timing, the voltage is fixed, and at the non-image forming timing in the main scanning direction (a period during which the image signal 20 shown in FIG. 9 is not output), the voltage is made variable and the voltage is changed. It is to adjust.

According to a ninth aspect of the present invention, there is provided an image carrier (photosensitive drums 1a to 1d shown in FIG. 1) and a scanning unit (first to first shown in FIG. 1) for scanning a light beam on the image carrier. A plurality of image forming means (image forming units for each color) having fourth laser scanners 2a to 2d) and PLLs
A plurality of clock generating means (first to fourth video clock generators 60 shown in FIG. 5) having a circuit (shown in FIG. 6) and supplying a clock to each scanning unit of the plurality of image forming means.
2a to 602d), a first mode in which the PLL circuit is operated to generate the clock, and a second mode in which the operation of the PLL circuit is stopped to generate the clock at a constant frequency. Control means (controller 1000 shown in FIG. 6) for switching the operation modes of the plurality of clock generation means.

According to a tenth aspect of the present invention, a plurality of scanning units (first to fourth laser scanners 2a to 2d shown in FIG. 5) and photoconductors (photosensitive drums 1a to 1d shown in FIG. 1) are provided. An image forming unit (an image forming unit for each color) and a plurality of generating units (first to fourth video clock generators 602a shown in FIG. 5) for generating a video clock to be supplied to each scanning unit
602d), the control of the image forming apparatus capable of adjusting the frequency of the video clock generated by each of the generating means according to the shift amount of the image width in the main scanning direction formed by each of the image forming means. A detecting step (step (3) of a flowchart shown in FIG. 10) for detecting an eccentricity amount and a phase of each of the photoconductors, and generating the plurality of generating means according to a detection result of the detecting step. Adjustment process for adjusting the frequency of each of the video clocks (FIG. 1)
0 (step (5)) of the flowchart shown in FIG.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram illustrating a schematic configuration of an image forming apparatus according to an embodiment of the present invention. In the present embodiment, a color printer including image forming units for four colors, that is, yellow Y, magenta M, cyan C, and black K will be described as an example.

In the figure, reference numerals 1a to 1d denote photosensitive drums, the photosensitive drum 1a is black K, the photosensitive drum 1b is cyan C, the photosensitive drum 1c is magenta M, and the photosensitive drum 1d.
Is formed with an electrostatic latent image for yellow Y. Reference numerals 2a to 2d denote first to fourth laser scanners for exposing in accordance with image signals to form electrostatic latent images on the photosensitive drums 1a to 1d.

The black image forming section includes a photosensitive drum 1a, a first laser scanner 2a, and the like. The cyan image forming unit includes a photosensitive drum 1b, a second laser scanner 2b, and the like. The magenta image forming section includes a photosensitive drum 1c, a third laser scanner 2c, and the like.
The yellow image forming unit includes a photosensitive drum 1d, a fourth laser scanner 2d, and the like.

Reference numeral 3 denotes an endless transport belt, which also serves as a transfer belt for transporting paper (not shown) to the image forming units of each color sequentially. Reference numeral 4 denotes a driving roller, which is connected to a driving unit including a motor and gears (not shown) and drives the transport belt 3. Reference numeral 5 denotes a driven roller which rotates in accordance with the movement of the conveyor belt 3 and applies a constant tension to the conveyor belt 3. 6
Reference numerals a and 6b denote a pair of optical sensors, which are provided on both sides of the conveyor belt 3 and are used to detect positional deviations formed on the conveyor belt 3 (positional deviation detecting patterns 7a to 10a, shown in FIG. 7b to 10b).

Reference numeral 1000 denotes a controller.
1, a RAM 1002, a ROM 1003, etc.
Overall control of the color printer.

Hereinafter, the operation of the image forming apparatus according to the present embodiment will be described.

When data to be printed is sent from a computer (PC) or the like (not shown) to the color printer, and image processing according to the printer engine is completed and the printer is ready for printing, paper is supplied from a paper cassette (not shown) and transported. The sheet arrives at the belt 3, and the sheet is sequentially conveyed to the image forming units of each color by the conveyor belt 3.

The image signals of the respective colors are transmitted to the respective laser scanners 2a to 2d in synchronism with the sheet conveyance by the conveyor belt 3.
d, and the first to fourth laser scanners 2a to 2d irradiate a laser beam to form an electrostatic latent image on each of the photosensitive drums 1a to 1d.
The electrostatic latent image formed thereon is developed with toner, and the toner images on the photosensitive drums 1 a to 1 d are transferred onto a sheet conveyed by the conveyor belt 3 by a transfer unit (not shown).

In the color printer shown in this embodiment,
Images are sequentially formed in the order of Y, M, C, and K. Thereafter, the sheet on which the toner image has been transferred is separated from the conveyor belt 3, and
The toner image is fixed on the paper by heat in a fixing device (not shown) and is discharged to the outside.

Hereinafter, referring to FIG. 2 and FIG.
An error in the scanning width that occurs when the distance between the laser scanners 2a to 2d and the photosensitive drums 1a to 1d differs in each image forming unit will be described.

FIG. 2 shows an example of a scanning width error on the photosensitive drums 1a to 1d when the distances between the first to fourth scanner units 2a to 2d and the photosensitive drums 1a to 1d shown in FIG. 1 are different. FIG.

In the figure, α is the angle of incidence, which is the angle of incidence of the scanning laser emitted from the scanner unit 2 (2a to 2d) shown in FIG. 1 on the photosensitive drum 1 (1a to 1d). ΔL is a distance error between the laser scanner 2 and the photosensitive drum 1. δs is an error of the scanning width caused by α and ΔL, and is “δs = ΔL * tanα”. For example,
When ΔL = 0.3 mm and α = 30 degrees, δs = 173 μ
m.

FIG. 3 is a diagram for explaining a difference in scanning width generated in an image transferred to a sheet conveyed by the conveying belt 3 shown in FIG.

In the figure, reference numeral 11 denotes a sheet, which is conveyed by the conveying belt 3 shown in FIG. 1, and each image forming section transfers a toner image of each color. 12a is an image, a certain color,
For example, it is a black image transferred to the sheet 11 in the black image forming unit. An image 13a is a color different from a certain color, for example, a magenta image transferred to the sheet 11 by the magenta image forming unit.

For example, under the same conditions as described above, that is, the distance between the photosensitive drum 1a of the black image forming unit and the laser scanner 2a and the photosensitive drum 1 of the magenta image forming unit
When the difference between c and the distance between the laser scanner 2c is ΔL, the error in the scanning width between the image 12a and the image 13a is 2 *
δs = 346 μm.

As described above, when the distance between the laser scanner and the photosensitive drum in each image forming unit is different, even if an attempt is made to form an image having the same width, an image having a different width is formed on a sheet.

In order to reduce this color shift (position shift),
On the conveyor belt 3 shown in FIG. 1, a misregistration detection pattern as shown in FIG. 4 to be described later is formed, read by a pair of sensors 6a and 6b provided on both sides of the conveyor belt 3, and the position of each color is read. The shift amount is detected.

FIG. 4 is a view for explaining the misregistration detection pattern transferred to the conveyor belt 3 and the like shown in FIG.

In the figure, reference numerals 7a and 7b denote misregistration detection patterns, which are linear patterns transferred to the conveyance belt 3 by the black image forming unit and extending in the laser scanning direction and the conveyance direction. 8a and 8b are misregistration detection patterns.
This is a linear pattern that is transferred to the transport belt 3 by the cyan image forming unit and extends in the laser scanning direction and the transport direction.

Reference numerals 9a and 9b denote misregistration detection patterns.
This is a linear pattern that is transferred to the transport belt 3 by the magenta image forming unit and extends in the laser scanning direction and the transport direction.
Reference numerals 10a and 10b denote misregistration detection patterns, which are linear patterns transferred to the conveyance belt 3 by the yellow image forming unit and extending in the laser scanning direction and the conveyance direction.

The position shift detecting patterns 7a to 10a
a is a pattern on the front side of the conveyor belt 3 shown in FIG. 1, and is read by the optical sensor 6a shown in FIG. The misregistration detection patterns 7b to 10b are patterns on the back side of the transport belt 3 shown in FIG. 1, and are read by the optical sensor 6b shown in FIG.

The controller 1000 shown in FIG. 1 determines the amount of displacement in the transport direction from the linear pattern extending in the laser scanning direction by using the displacement detection patterns read by the optical sensors 6a and 6b shown in FIG. The amount of displacement in the laser scanning direction is detected from the linear pattern extending in the direction. The scanning width of each color is determined by the linear patterns 7a and 7b, 8a and 8b, 9a and 9b, 10a and 1
It is calculated from the distance between 0b.

For the correction of the laser scanning width, as shown in FIGS. 5 and 6 described later, a video clock generator for an image signal is provided for each color, and the frequency of the video clock can be varied independently for each color. Adjustment is performed.

FIG. 5 is a view for explaining the flow of image signals sent to the first to fourth scanner units 2a to 2d shown in FIG.

In the figure, reference numeral 601 denotes a crystal oscillator, which is a high-precision source clock supply source, and outputs an output signal to first to fourth video clock generators 602a to 602d. The first to fourth video clock generators 602a to 602d have a configuration as shown in FIG. 6 described below, and generate video clocks to generate first to fourth image data control units 603a to 603.
Output to d.

First to fourth image data control units 603a to 603a
03d denotes first to fourth video clock generators 602a to 602a.
The image signal is output to the first to fourth laser scanners 2a to 2d according to the frequency of the video clock from 02d. The first to fourth laser scanners 2a to 2d control the lighting of the laser according to the image signal.

As described above, the image signals are output from the first to fourth laser scanners 2 according to the video clock frequencies output from the first to fourth video clock generators 602a to 602d.
a to 2d to control the lighting of the laser.

FIG. 6 is a block diagram illustrating the configuration of the first to fourth video clock generators 602a to 602d shown in FIG. Also, first to fourth video clock generators 6
02a to 602d are PLL (Phase Locke).
d Loop) circuit. Note that the same components as those in FIG. 5 are denoted by the same reference numerals.

In the figure, reference numeral 702 denotes a 1 / N frequency divider;
3 is a phase comparator, 704 is a low-pass filter, 705 is a voltage controlled oscillator, and 706 is a 1 / M frequency divider.

An output signal 14 is output from the crystal oscillator 601. The video clock 15 is an output of the first to fourth video clock generators 602a to 602d, and has a variable frequency. The PLL control stop signal 16 is output from the controller 1000 shown in FIG. 5, and will be described later in detail. The video clock frequency fine adjustment signal 17 is output from the controller 1000 shown in FIG. 5, and will be described later in detail.

Hereinafter, the first to fourth video clock generators 6
A method of changing the video clock frequency in 02a to 602d will be described.

The output signal 14 of the crystal oscillator 601 is 1 / N
A signal obtained by dividing the frequency of N by the frequency divider 702 and a signal obtained by dividing the video clock 15 by M by the 1 / M frequency divider 706 are input to the phase comparator 703, and the output of the phase comparator 703 is passed through the low-pass filter 704. Input to the control oscillator 705.

The first to fourth video clock generators 602a to 602d configured as described above use, for example, the phase of a signal obtained by dividing the output of the crystal oscillator 601 by N by the 1 / N divider 702 to the video clock 15. If the phase of the signal divided by M has been advanced by the 1 / M frequency divider 706, the input voltage of the voltage controlled oscillator 705 increases, and the phase of the video clock 15 advances.

Here, assuming that the frequency of the output signal 14 output from the crystal oscillator 601 is fin and the frequency of the video clock 15 is fout,

[0059]

Fout = fin * M / N (2)

The video clock frequency is variable by adjusting the value of M / N according to the main scanning width detected by the optical sensors 6a and 6b shown in FIG.

For example, “Main scanning width of reference color = 300,0
00 μm (300 mm) ”,“ adjustment color main scanning width = 30 ”
0, 300 μm ”,“ M / N of adjustment color = 1 ”(ex. M
= 10,000, N = 10,000), “M / N of adjusted color = 0.999 (= −0.1%) (ex.
9,990, N = 10,000) "
The main scanning width of the adjustment color image forming unit can be made to coincide with the main scanning width of the reference color image forming unit.

The photosensitive drums 1a to 1a shown in FIG.
1d is eccentric, and when the distance between the exposure surfaces of the photosensitive drums 1a to 1d and the first to fourth laser scanners 2a to 2d fluctuates due to the eccentricity of the photosensitive drums 1a to 1d, each image forming unit , An error in the main scanning width is generated.

For example, “Electricity eccentricity of photosensitive drum = 100 μ”
m ”,“ 2 * δs = 11 ”as described above.
A scanning width error of “5 μm” occurs in the rotation cycle of the photosensitive drum.

Hereinafter, the effect of the eccentricity of the photosensitive drums 1a to 1d shown in FIG. 1 on an image will be described with reference to FIG.

FIG. 7 is a view for explaining an example of a transfer result obtained by transferring an image formed on an eccentric photosensitive drum to a sheet.

In the figure, a two-color line 1 extending in the transport direction
Although 2b and 13b are formed on the sheet 11, a main scanning width error occurs due to the eccentricity of the photosensitive drum, and a color shift (position shift) occurs. Here, the lines 12b and 13b have a length of about two turns of the photosensitive drum.

The position shift detecting patterns 7a to 10a and 7b to 10b shown in FIG.
In order to understand the tendency for one rotation of 1d, it is formed a plurality of times and transferred to the conveyor belt 3 shown in FIG. 1, and the optical sensors 6a and 6b shown in FIG.
7b to 10b are detected, and the controller 10 shown in FIG.
00 detects the amount of eccentricity and the phase of each of the photosensitive drums 1a to 1d provided for each color image forming unit based on the detection result.

The first to fourth video clock generators 602a to 602 correspond to the respective eccentric amounts and phases of the photosensitive drums 1a to 1d detected by the controller 1000.
Based on the adjusted video clock frequency as described in d, the video clock frequency is finely adjusted during image formation as shown in FIGS.

FIG. 8 is a timing chart for explaining the state of each signal when outputting one page of paper in the image forming apparatus of this embodiment.

In the figure, 801 is a page start signal, 8
02 is a line start signal, and 803 is an image signal. Reference numeral 16 denotes a PLL control signal (PLL control stop signal).
Reference numeral 17 denotes a video clock fine adjustment signal (video clock frequency fine adjustment signal). Pulse 18 indicates the start of a page. A period 23 indicates that an image is being formed. Period 21
Indicates stop of PLL control. A period 22 indicates that the video clock is being finely adjusted.

FIG. 9 is a timing chart for explaining the state of signals when outputting one main scanning line during image formation in the image forming apparatus of the present embodiment, and is an enlarged view of the timing chart shown in FIG. It is.

In the figure, similarly to FIG. 8, the pulse 19 of the line start signal 802 rising during the period 23 during the image formation indicates the line start, and the signal 20 of the image signal 803
Indicates an image signal for one line in the main scanning. The video clock fine adjustment signal 17 is a fine adjustment voltage whose voltage fluctuates within the period 22.

The operation will be described below with reference to FIGS. In the non-image forming period before the page and between the pages, the first to fourth video clock generators 602a to 602a
In 2d, PLL control is performed, and as described above, video clock frequency adjustment for correcting a steady difference in scanning width in each image forming unit due to a distance error between the laser scanner and the photosensitive drum is performed.

When the pulse 18 of the page start signal 801 indicating the start of the page is input to the controller 1000 shown in FIG. 6, the controller 1000 shown in FIG. The video clock frequency adjustment for lowering the control signal 16 and correcting the steady scanning width difference during the non-image forming period is fixed.

Further, like the fine adjustment voltage shown in the period 22 in FIGS. 8 and 9, the video clock fine adjustment is a voltage finely adjusted according to the eccentricity and phase of each of the photosensitive drums 1a to 1d. The signal is input to the voltage controlled oscillator 705 shown in FIG. Further, as shown in FIG. 9, the fine adjustment voltage is fixed during the image formation of one main scanning line, and the voltage is minutely changed as necessary in a non-image area between the lines. That is, the above equation (2) becomes

[0076]

Fout = fin * M / N ± α (3) α indicates the fine adjustment described above.

As described above, each of the first to fourth video clock generators 602a to 602d has a PLL circuit capable of independently adjusting the frequency for each image forming unit, and the voltage input to the voltage controlled oscillator 705 of the PLL circuit. Each of the first to fourth video clock generators 602 is supplied with the (video clock fine adjustment signal 17) according to the amount of eccentricity and the phase of each of the photosensitive drums 1a to 1d.
The frequency of each video clock can be finely adjusted by independently performing fine adjustment for each of a to 602d.

Thus, the laser scanning width of the first to fourth laser scanners 2a to 2d becomes constant irrespective of the eccentricity of the photosensitive drums 1a to 1d, and the color shift (position shift) caused by the eccentricity of the photosensitive drums 1a to 1d is achieved. ) Is reduced.

Although the sign is not described separately for each image forming unit in the PLL control signal 16 and the video clock frequency fine adjustment signal 17, the controller 1000 controls the first to fourth video clock generators 602a to 602a to 602a. Needless to say, each PLL control signal and each video clock frequency fine adjustment signal sent to 602d are different signals.

In this embodiment, the feedback control using the PLL circuit is performed.
Using (for example, VCXO (voltage control X'tal)), the video clock may be finely adjusted by directly fixing or varying the input voltage without applying feedback. Further, the eccentricity and phase of the photosensitive drums 1a to 1d are not detected by forming a pattern for detecting positional deviation, but are detected by detecting the home positions of the photosensitive drums 1a to 1d. Alternatively, another configuration such as storing in a memory may be used.

The eccentricity of the photosensitive drum includes, in addition to the displacement between the central axis of the photosensitive drum and the rotation axis, the displacement of the central axis with respect to the peripheral surface of the photosensitive drum (eccentricity in a narrow sense). Further, there is a case where the deviation of the center axis from the peripheral surface of the photosensitive drum is asymmetrical on the left and right sides of the photosensitive drum. In this case, the image does not look like the image formed on the sheet 11 shown in FIG. The shape (amplitude and position) of the image is different.

The eccentricity of the photosensitive drum indicates the amplitude and phase of the image shift as shown in FIG. 7 and indicates the position on the image in the paper transport direction. For example, line 1 shown in FIG.
Assuming that the amplitudes of 2b and 13b are the same, the eccentric amounts of the photosensitive drums on which the lines 12b and 13b are formed, for example, the photosensitive drum 1a of the black image forming unit and the photosensitive drum 1c of the magenta image forming unit are the same. The phases (positions on the paper) of the drum 1a and the photosensitive drum 1c are different.

Here, when adjusting the color misregistration caused by the image distortion such as the lines 12b and 13b shown in FIG. 7, the video clock fine adjustment signal 17 changes as shown in the timing chart of FIG. Let it.

FIG. 12 shows lines 12b and 13b shown in FIG.
5 is a timing chart illustrating an example of a video clock fine adjustment signal 17 when adjusting distortion of the video clock.

FIG. 12A shows a video clock fine adjustment signal 17 for adjusting the distortion of the line 12b.
2 (b) shows the video clock fine adjustment signal 17 for adjusting the distortion of the line 13b.

The video clock fine adjustment signal 17 in FIGS. 12A and 12B fluctuates at the same amplitude because the eccentricity of the photosensitive drums 1a and 1c is the same. This amplitude depends on the amount of eccentricity. Further, the initial voltage of each of the photosensitive drums 1a and 1c at the start of image formation changes according to the phase of each of the photosensitive drums 1a and 1c.

In this figure, the video clock fine adjustment signals 17 input to the respective video clock generators 602a and 602c are shown side by side to compare the respective video clock fine adjustment signals 17. The timing at which the adjustment signal 17 starts to fluctuate
It goes without saying that the timing is shifted by the timing according to the distance between the image forming units.

Hereinafter, the control procedure of the image forming apparatus of the present embodiment will be described with reference to the flowchart of FIG.

FIG. 10 is a flowchart for explaining an example of a first data processing procedure in the image forming apparatus according to the present invention. The RO of the controller 1000 shown in FIG.
CP based on the control program stored in M1003
The process corresponds to the process of detecting the image width in the main scanning direction and the eccentric amounts and phases of the photosensitive drums 1a to 1d and the image forming process performed by U1001. In addition, (1) to (5) indicate each step.

First, on the conveyor belt 3 shown in FIG.
A pattern for detecting a displacement as shown in (1) is formed (1). Next, the optical sensor 6a, 6b detects a pattern for detecting a displacement (2). Then, based on the detection result in step (2), the image width of each image forming unit in the main scanning direction, and the eccentricity and phase of each of the photosensitive drums 1a to 1d are detected (3).

Next, image formation is started (4), and the first to fourth video clock generators 60 are set in accordance with the eccentric amounts and phases of the photosensitive drums 1a to 1d detected in step (3).
By adjusting the video clock fine adjustment signal input to the voltage controlled oscillator 705 every 2a to 602d, an image is formed while finely adjusting the video clock (5), and the process ends.

By performing such control on the first to fourth video clock generators 602a to 602d,
A color shift caused by a stationary distance error between the photosensitive drums 1a to 1d and the laser scanners 2a to 2d and an eccentricity of each of the photosensitive drums 1a to 1d (such as a shift between the center axis of the photosensitive drum and the rotation axis). Color shift can be reduced, and a high-quality image can be output.

As described above, the image forming apparatus according to the present embodiment includes a plurality of image forming units having a laser scanner and a photosensitive drum, a plurality of video clock generators 602a to 602d corresponding to each of the laser scanners 2a to 2d, and The clock frequency of the video clock generator can be adjusted according to the amount of shift between the image forming units in the image width of the laser scanner in the laser scanning direction formed by each image forming unit. , Video clock generators 602a to 602d according to the amount of eccentricity and the phase of each of the photosensitive drums 1a to 1d.
Has a controller 1000 for fine-tuning the clock frequency of.

The video clock generator includes a crystal oscillator for supplying a common high-precision clock to a plurality of image forming units, a PLL circuit capable of independently adjusting a clock frequency for each image forming unit, and the like. Controller 1000 is PL
The clock frequency is finely adjusted by finely adjusting the voltage input to the voltage controlled oscillator of the L circuit.

Further, the controller 1000 causes the PLL control circuit to perform the PLL control at the timing corresponding to the non-image forming area in the transport direction between the sheets before and between the sheets, and stops the PLL control in the PLL control circuit in the image forming area in the transport direction. And in the image forming area in the transport direction,
The frequency of the video clock is adjusted by fixing the voltage input to the voltage controlled oscillator in the image forming area in the laser scanning direction and making it variable in the non-image area.

Therefore, not only the color shift (position shift) due to the steady distance error between the laser scanners 2a to 2d and the photosensitive drums 1a to 1d, but also the photosensitive drums 1a to 1d
Of the photosensitive drums 1a to 1d and the laser scanners 2a to 2d,
It is possible to reduce the color misregistration occurring in the rotation cycle of a to 1d, and to improve the image quality output on the paper only by providing a simple configuration that is not easily affected by environmental changes and aging.

In the present embodiment, the controller 1000 shown in FIG. 6 is controlled by the PLL control signal 1 shown in FIG.
When the PLL circuit shown in FIG.
While the LL control is executed and the PLL control signal 16 is falling, the PLL circuit stops the PLL control and the video clock fine adjustment signal 17 is varied to finely adjust the video clock frequency.
A first mode in which the PLL circuit is operated to generate a video clock, and a second mode in which the operation of the PLL circuit is stopped to generate a video clock of a constant frequency (for example, the video clock fine adjustment signal 17 is fixed, etc. To generate a video clock of a constant frequency).
The controller 1000 may switch the operation mode of the fourth video clock generators 602a to 602d by the PLL control signal 16.

In the above embodiment, a color printer is described as an example, but various image forming apparatuses,
For example, electrophotographic equipment, color laser copying machines, monochrome copying machines, laser beam printers, color laser printers,
A facsimile machine, a color or monochrome multifunction copier having a copy function and / or a print function and / or a facsimile function, etc., may be configured to execute the processing, functions, and the like described in the above embodiments.

As described above, the storage medium storing the program codes of the software for realizing the functions of the above-described embodiments is supplied to the system or the apparatus, and the computer (or CPU or MP) of the system or the apparatus is supplied.
It goes without saying that the object of the present invention is also achieved when U) reads out and executes the program code stored in the storage medium.

In this case, the program code itself read from the storage medium realizes the novel function of the present invention, and the storage medium storing the program code constitutes the present invention.

As a storage medium for supplying the program code, for example, a floppy (registered trademark) disk, hard disk, optical disk, magneto-optical disk, C
D-ROM, CD-R, magnetic tape, nonvolatile memory card, ROM, EEPROM, etc. can be used.

When the computer executes the readout program code, not only the functions of the above-described embodiment are realized, but also the OS (Operating System) running on the computer based on the instruction of the program code. ) And the like perform part or all of the actual processing, and the processing realizes the functions of the above-described embodiments.

Further, after the program code read from the storage medium is written into a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer, based on the instruction of the program code, The CPU provided in the function expansion board or function expansion unit performs part or all of the actual processing,
It goes without saying that a case where the function of the above-described embodiment is realized by the processing is also included.

Further, the present invention may be applied to a system composed of a plurality of devices or an apparatus composed of one device. Needless to say, the present invention can be applied to a case where the present invention is achieved by supplying a program to a system or an apparatus. In this case, by reading a storage medium storing a program represented by software for achieving the present invention into the system or the apparatus, the system or the apparatus can enjoy the effects of the present invention. .

Further, by downloading and reading out a program represented by software for achieving the present invention from a database on a network by a communication program, the system or apparatus can be
It is possible to enjoy the effects of the present invention.

[0106]

As described above, the first embodiment according to the present invention is described.
According to the invention, the image forming apparatus includes a plurality of image forming units each including a scanning unit and a photoconductor, and a plurality of generating units that generate a video clock to be supplied to each of the scanning units. An image forming apparatus capable of adjusting a frequency of a video clock generated by each of the generating units in accordance with an amount of deviation of an image width in a main scanning direction. Since there are adjusting means for adjusting the frequencies of the video clocks generated by the plurality of generating means, periodic color misregistration caused by eccentricity of the photosensitive drum can be reduced, and a high quality image can be output. it can.

According to the second aspect of the present invention, since the detecting means for detecting the eccentricity and the phase of each photoconductor is provided, it is not influenced by the eccentricity and the phase change due to the secular change of each photoconductor. Periodic color shift can be appropriately corrected according to the detected eccentricity and phase of the photoconductor, and a high-quality image can be output.

[0108] According to the third aspect, the detecting means is configured to determine the position of the plurality of patterns formed on the photoconductor at different positions in the sub-scanning direction based on the fluctuation state of the width in the main scanning direction of the plurality of patterns. Since the eccentricity and phase of the photosensitive drum are detected, the eccentricity and phase of the photosensitive drum can be accurately detected.

According to the fourth aspect, there are provided a plurality of image forming means having a scanning section and a photosensitive member, and a plurality of generating means for generating a video clock to be supplied to each of the scanning sections.
An image forming apparatus capable of adjusting a frequency of a video clock generated by each of the generating units according to a shift amount of an image width in a main scanning direction formed by each of the image forming units. Since it has adjusting means for adjusting the frequency of the video clock generated by the plurality of generating means in accordance with the periodic fluctuation of the distance to each scanning unit, it is generated by the periodic distance fluctuation between the photosensitive drum and the laser scanner. Color shift can be reduced, and a high-quality image can be output.

According to the fifth aspect of the present invention, since there is provided a detecting means for detecting a periodic variation in the distance between each of the photoconductors and each of the scanning sections, the detection means is not affected by aging of each of the photoconductors and the like. Periodic color misregistration can be appropriately corrected according to the detected fluctuation in the distance between the photosensitive drum and the laser scanner,
High quality images can be output.

[0111] According to the sixth aspect of the invention, the detecting means is configured to detect the position of each of the plurality of patterns formed on the photoconductor at different positions in the sub-scanning direction based on the fluctuation state of the width in the main scanning direction. Since the change in the distance between the body and each of the scanning units is detected, the periodic change in the distance between the photosensitive drum and the laser scanner can be accurately detected.

According to the seventh aspect, the generating means has a PLL circuit capable of independently adjusting the frequency of a clock supplied from a high-precision clock supply unit for each of the image forming means. Since the means adjusts the frequency of the video clock by adjusting the voltage input to the voltage controlled oscillator of the PLL circuit, the video clock can be finely adjusted with a simple configuration.

According to the eighth aspect, the adjusting means causes the PLL circuit to execute the PLL control at the non-image forming timing in the sub-scanning direction, and performs the PLL control at the image forming timing in the sub-scanning direction. Since the voltage is fixed at the image forming timing in the main scanning direction during the image forming timing in the sub-scanning direction, and the voltage is adjusted at the non-image forming timing in the main scanning direction, the voltage is adjusted. With this configuration, it is possible to output a high-quality image by adjusting the clock frequency without receiving a change in the installation environment or a change with time.

According to the ninth aspect, a plurality of image forming means each having an image carrier and a scanning section for scanning a light beam on the image carrier, and the plurality of image forming means each having a PLL circuit are provided. A plurality of clock generating means for supplying a clock to each scanning unit of the means; a first mode for operating the PLL circuit to generate the clock;
Control means for switching the operation modes of the plurality of clock generation means between a second mode in which the operation of the PLL circuit is stopped and the clock of a constant frequency is generated. Can be freely switched between PLL control and PLL control stop of the clock supplied to the clock.

Therefore, color shift periodically occurring due to the eccentricity of the photosensitive drum or the like can be reduced, and the effect of outputting a high-quality image can be obtained.

According to the tenth aspect, there are provided a plurality of image forming means having a scanning section and a photosensitive member, and a plurality of generating means for generating a video clock to be supplied to each of the scanning sections. A method of controlling an image forming apparatus capable of adjusting a frequency of a video clock generated by each of said generating means according to a shift amount of an image width in a main scanning direction formed by a forming means, wherein: A detecting step of detecting the amount and phase, and an adjusting step of adjusting the frequency of the video clock generated by the plurality of generating means in accordance with the detection result of the detecting step. Periodic color shift can be reduced, and a high-quality image can be output.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a schematic configuration of an image forming apparatus according to an exemplary embodiment of the present invention.

FIG. 2 is a diagram illustrating an example of a scan width error on a photosensitive drum when the distance between the first to fourth scanner units illustrated in FIG. 1 and the photosensitive drum is different.

FIG. 3 is a diagram illustrating a difference in a scanning width generated in an image transferred to a sheet conveyed by a conveyance belt illustrated in FIG. 1;

FIG. 4 is a view for explaining a misregistration detection pattern transferred to a conveyor belt or the like shown in FIG. 1;

FIG. 5 is a diagram illustrating a flow of an image signal transmitted to first to fourth scanner units illustrated in FIG. 1;

FIG. 6 is a block diagram illustrating a configuration of first to fourth video clock generators illustrated in FIG.

FIG. 7 is a diagram illustrating an example of a transfer result obtained by transferring an image formed on an eccentric photosensitive drum to a sheet.

FIG. 8 is a timing chart illustrating the state of each signal when outputting one page of paper in the image forming apparatus of the present embodiment.

FIG. 9 is a timing chart illustrating the state of signals when outputting one main scanning line during image formation in the image forming apparatus of the present embodiment.

FIG. 10 is a flowchart illustrating an example of a first data processing procedure in the image forming apparatus according to the present invention.

FIG. 11 is a block diagram illustrating a configuration of a video clock generator in a conventional image forming apparatus.

FIG. 12 is a timing chart illustrating an example of a video clock fine adjustment signal when adjusting the distortion of the line illustrated in FIG. 7;

[Explanation of symbols]

 1a to 1d Photosensitive drum 2a to 2d Laser scanner 3 Conveyor belt 6a, 6b Optical sensor 16 PLL control stop signal 17 Video clock fine adjustment signal 702 1 / N divider 703 Phase comparator 704 Low pass filter 705 Voltage control oscillator 706 1 / M divider

Claims (10)

[Claims] An image forming apparatus includes: a plurality of image forming units each including a scanning unit and a photoconductor; and a plurality of generating units configured to generate a video clock to be supplied to each of the scanning units. An image forming apparatus capable of adjusting a frequency of a video clock generated by each of the generating units in accordance with a shift amount of an image width in a main scanning direction, wherein the plurality of the plurality of photoconductors are adjusted in accordance with an eccentric amount and a phase of each of the photosensitive members An image forming apparatus comprising adjusting means for adjusting the frequency of the video clock generated by the generating means. 2. The image forming apparatus according to claim 1, further comprising a detection unit configured to detect an eccentric amount and a phase of each of the photoconductors. 3. The eccentricity and phase of the photoconductor according to a fluctuation state of a width in a main scanning direction of a plurality of patterns formed on the photoconductor at different positions in the sub-scanning direction. The image forming apparatus according to claim 2, wherein the image is detected. 4. A plurality of image forming units each including a scanning unit and a photoconductor, and a plurality of generating units that generate a video clock to be supplied to each of the scanning units, and are formed by each of the image forming units. An image forming apparatus capable of adjusting a frequency of a video clock generated by each of the generating units according to a shift amount of an image width in a main scanning direction, wherein a periodicity of a distance between each of the photoconductors and each of the scanning units is provided. An image forming apparatus comprising: an adjusting unit that adjusts the frequency of a video clock generated by the plurality of generating units according to a change. 5. The image forming apparatus according to claim 4, further comprising a detecting unit configured to detect a periodic change in a distance between each of the photoconductors and each of the scanning units. 6. The scanning unit according to claim 1, wherein the detecting unit is configured to detect the positions of the plurality of patterns formed on the photosensitive member at different positions in the sub-scanning direction based on a variation in width of the plurality of patterns in the main scanning direction. 6. The image forming apparatus according to claim 5, wherein a change in distance from the image forming apparatus is detected. 7. The generating means includes a PLL circuit capable of independently adjusting a frequency of a clock supplied from a high-precision clock supply unit for each of the image forming means. 5. The image forming apparatus according to claim 1, wherein the frequency of the video clock is adjusted by adjusting a voltage input to the voltage controlled oscillator. 8. The adjustment means causes the PLL circuit to execute PLL control at a non-image forming timing in the sub-scanning direction, and causes the PLL circuit to stop PLL control at an image forming timing in the sub-scanning direction. 8. The image forming apparatus according to claim 7, wherein the voltage is fixed at an image forming timing in the main scanning direction during the image forming timing, and the voltage is adjusted at a non-image forming timing in the main scanning direction to adjust the voltage. Image forming device. 9. A plurality of image forming units each having an image carrier and a scanning unit for scanning a light beam on the image carrier, and each scanning unit of the plurality of image forming units having a PLL circuit. A plurality of clock generating means for supplying a clock to the first circuit; a first mode for operating the PLL circuit to generate the clock; and a second mode for stopping the operation of the PLL circuit and generating the clock having a constant frequency. Control means for switching the operation modes of the plurality of clock generation means between the two modes. 10. An image forming apparatus comprising: a plurality of image forming units each including a scanning unit and a photoconductor; and a plurality of generating units configured to generate a video clock to be supplied to each of the scanning units. A method of controlling an image forming apparatus capable of adjusting a frequency of a video clock generated by each of the generating units according to a shift amount of an image width in a main scanning direction, the method including detecting an eccentric amount and a phase of each photoconductor. A control step of adjusting a frequency of a video clock generated by the plurality of generating units in accordance with a detection result of the detection step.