JPH09106129A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an excellent color image without image deviation by avoiding the decrease of a writing position accuracy in a subscanning direction even when a main scanning synchronizing signal is fluctuated resulting from the irregular rotation of a polygon motor and the machining accuracy of a polygon mirror in an image forming device provided with plural photoreceptors and optical writing parts and forming and transferring a color image by every color. SOLUTION: This image forming device provided with plural photoreceptors and optical writing pats and forming and transferring the color image by every color is provided with a DETP timing difference measuring part 305 outputting an image writing start timing signal for every optical writing means and an MPU 301 adjusting the image writing start timing signal, based on the output timing of each main scanning synchronizing signal after adjusting a phase by a motor phase control circuit 303.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a digital color printer or a digital color copying machine provided with an image forming station including a laser writing system and a photoconductor unit arranged in parallel for each color. More specifically, the present invention relates to an image forming apparatus that adjusts the image writing start timing based on the output timing of the main scanning synchronization signal of each image forming station.

[0002]

2. Description of the Related Art Conventionally, an image forming station composed of a laser writing system and a photoconductor unit, etc.
By arranging in parallel for each single color of C, a toner image of one color is formed by laser writing and an electrophotographic process, and this is transferred to a recording paper, and then another color is formed and transferred by overlapping. There is known a color printer that forms a color image on a recording sheet, that is, a so-called color printer using a plurality of photoconductors.

By the way, this type of color printer requires high-precision position control because it requires high precision of color superposition in comparison with an ordinary single-color laser printer.

Generally, the cycle of the main scanning synchronization signal of the laser printer is not constant but fluctuates within a certain range due to factors such as uneven rotation of the polygon motor and variations in processing accuracy of the polygon mirror. FIG. 11 shows the main scanning synchronization signal (DETPK) of the reference color and the main scanning synchronization signal (DET) of another color.
5 is a timing chart for explaining a change in DETPY with respect to DETPK when PY) is adjusted to have the same phase.

Here, assuming that the variation of DETPY with respect to DETPK is ± 9, the value of T9 is about 1/30 of the DETP cycle in the inventor's experimental data.
However, this value is considered to change due to uneven rotation of the polygon motor, processing accuracy of the polygon mirror, and the like.

On the other hand, the writing timing (FSYNC) of image data is usually MPU for performing sequence control.
The output of the image is started based on the main scanning synchronizing signal after the output of FSYNC.

[0007]

However, in the conventional color printer having a plurality of photoconductors and the optical writing section as described above, the main scanning synchronizing signal of the image forming station in the subsequent stage with respect to the reference color is used. For position,
If the image data write timing (FSYNC) is output without considering the fluctuation of the main scanning synchronization signal due to the uneven rotation of the polygon motor or the processing accuracy of the polygon mirror, the ± 1 line image may shift. There was a point.

The present invention has been made in view of the above, and in an image forming apparatus having a plurality of photoconductors and an optical writing unit for forming / transferring a color image for each color, uneven rotation of a polygon motor is caused. Even when the main scanning synchronization signal fluctuates due to the processing accuracy of the polygon mirror or the polygon mirror, a good color image with no image misregistration can be obtained by avoiding a decrease in the writing position accuracy in the sub scanning direction. The purpose is to get.

[0009]

In order to achieve the above object, in an image forming apparatus according to a first aspect of the present invention, a plurality of photoconductors arranged in parallel for each single color and a plurality of photoconductors corresponding to the photoconductors are provided. Optical writing means for writing and scanning laser light modulated by each color signal on the photoconductor, and motor control means for controlling the rotation speed of the scanning motor of the optical writing means by PLL control. Timing measurement means for measuring the output timing difference of the main scanning synchronization signal between the optical writing means based on a reference frequency for PLL control, and a reference frequency signal for PLL control based on the timing difference output by the timing measurement means. And an image writing timing output means for outputting an image writing timing signal for each of the optical writing means. It is obtained by a main control means for adjusting the image writing timing signal on the basis of the main scanning synchronization signal output timing after the phase adjustment by the motor phase control means.

In the image forming apparatus according to the second aspect, the image writing timing output means is provided for each color signal, the counting means for counting the main scanning synchronization signal corresponding to the color signal, and the counting means. Means for comparing the count value of the means with the set value of the main control means, and if the two values are equal, data comparison means for feeding back a compare match signal to the main control means,
The main control means determines the image writing timing based on the output signal of the data comparison means.

That is, the image forming apparatus according to the first and second aspects adjusts the image writing start timing based on the output timing of the main scanning synchronizing signal corresponding to each color signal, so that the rotation unevenness of the optical scanning motor and the polygon pattern can be reduced. The influence of the fluctuation of the main scanning synchronization signal due to the processing accuracy of the mirror and the like is absorbed to avoid the deterioration of the position accuracy in the sub scanning direction.

Further, in the image forming apparatus according to the third aspect of the present invention, the image writing timing output means includes counting means for counting a main scanning synchronization signal serving as a reference, a count value of the counting means, and the main control means. And a data comparison means for feeding back a compare match signal to the main control means when the two values are equal to each other, the main control means and the main scanning synchronization signal serving as the reference. The image writing start timing is determined based on the timing difference from other main scanning synchronization signals.

That is, since the image writing timing is determined by a single counting means, the circuit configuration is simple, and main scanning is caused by uneven rotation of the optical scanning motor and processing accuracy of the polygon mirror. The influence of the fluctuation of the synchronization signal is absorbed to avoid the deterioration of the position accuracy in the sub scanning direction.

Further, in the image forming apparatus according to the fourth aspect, the main scanning synchronization signal as the reference is the main scanning synchronization signal of the optical writing means corresponding to the photoconductor on which the recording sheet is first transferred. It is what

That is, by referring to the main scanning synchronizing signal of the image forming station through which the recording paper first passes,
Positional accuracy of laser writing in the sub-scanning direction is secured with the simplest configuration without complicating the circuit configuration.

[0016]

〔Example〕

(Structure of Embodiment) FIG. 1 is an explanatory diagram showing the main structure of a color laser printer (hereinafter referred to as a color printer) as an image forming apparatus suitable for applying the present invention. In the figure, this color printer has K (black), Y
An image forming station is provided for each of (yellow), M (magenta), and C (cyan). That is, the image forming station 101K for black, the image forming station 101Y for yellow, the image forming station 101M for magenta,
The cyan image forming stations 101C are arranged in this order.

Therefore, each of the image forming stations 10
The functional elements constituting 1K, 101Y, 101M, and 101C are common to each color, and are configured as follows.
Shape laser light output from laser diode, fθ
An optical writing unit 102 as an optical writing unit that corrects and scans to perform optical writing, a photoconductor drum 103 on which an electrostatic latent image is formed, and toner of a color corresponding to each color are accommodated and color development is performed. A developing unit 104 for performing, a transfer roller 105 for transferring the toner image formed on the photosensitive drum 103 to a recording sheet, and a cleaning unit 106 for removing / collecting the residual toner after the transfer on the photosensitive drum 103.
And a charger 107 for charging the photosensitive drum 103.

Further, a registration roller 110 for conveying the recording paper fed by a paper feeding unit (not shown) at a timing for carrying the recording paper, each image forming station 101K,
Below the 101Y, 101M, and 101C, a conveyance belt 111 for conveying the recording paper and a fixing unit 112 for fixing the unfixed toner transferred on the recording paper by heat and pressure are provided in parallel.

FIG. 2 shows the optical writing unit 10 shown in FIG.
It is explanatory drawing which shows the structure of 2. In the figure, 201 is a laser diode (LD) that modulates and outputs laser light according to image data, 202 is a condenser lens that condenses laser light, and 203 is laser light that is incident through the condenser lens 202. A polygon mirror for angular scanning, 204 is an fθ lens for performing optical correction for scanning the laser beam scanned by the polygon mirror 203 on the surface of the photosensitive drum 103 at an equal pitch, and 205 is a writing reference in the main scanning direction (main scanning). A light receiving element that detects a laser beam that becomes a synchronizing signal: detector pulse (hereinafter, referred to as DETP), and 206 is a mirror that guides the writing reference laser beam to the light receiving element 205.

FIG. 3 is a block diagram showing the main configuration of the control system of the color printer. In the figure, reference numeral 301 is an MPU (microprocessor) as a main control means for integrally controlling the entire color printer, and 302 is an operation panel for selecting various keys for color print output.

Reference numeral 303 denotes a motor phase control circuit as a motor phase control means, which is used for each image forming station 10.
Motor drivers 304K, 3 as motor control means for driving and controlling the drive motors MK, MY, MM, MC provided for each of 1K, 101Y, 101M, 101C.
The reference clock PCLK to the PLL control circuit in 04Y, 304M, 304C is generated based on the setting of the MPU 301.

Further, 305 is a DETP timing difference measuring unit as a timing measuring means for measuring the timing difference of the DETP signal and notifying the MPU 301, and 306 is the FS.
An FSYNC output timing measuring unit as an image writing timing output means for measuring the YNC output timing by counting the DETP signal and notifying it to the MPU 301,
Reference numeral 307 denotes an I / O port that outputs each FSYNC based on an instruction from the MPU 301, 308K, 308Y, 308
M and 308C are the FSYNC signal and D corresponding to each color.
An image data processing unit that processes image data based on a synchronization signal of the ETP signal.

Further, 309K, 309Y, 309M, 3
09C is the image data processing unit 308K, 308Y, 30
The LD driver corresponds to each of 8M and 308C and converts into a drive current of laser diodes LDK, LDY, LDM, and LDC.

(Operation of Embodiment) Next, the basic operation of the color printer configured as described above will be described. A generally known electrophotographic process is used as an image forming process around the photosensitive drum 103. Therefore, each image forming process is executed based on this process.

More specifically, first, the photosensitive drum 103
The surface thereof is uniformly charged by the charging charger 107, and the optical writing unit 102 irradiates laser light according to the image data to form an electrostatic latent image.

Then, toner is attached to the photosensitive drum 103 by the developing unit 104, and the electrostatic latent image is visualized as a toner image. Thereafter, the recording paper is sent by the registration roller 110 at a timing matched with the position of the toner image, and the toner image is transferred onto the surface of the transfer roller 105.
Is transcribed by the action of Further, the toner remaining on the surface of the photosensitive drum 103 after the transfer is removed and collected by the cleaning unit 106 to prepare for the next image formation.

When the processing for the first color is completed, the image formation for the next color is executed based on the same process as described above. In this way, images are sequentially formed for each color, and the toner images are transferred and superposed on the recording paper. Then, the recording sheet after the transfer is fixed by the fixing unit 112 and is discharged as a final color print image.

Next, the writing timing of each image forming station in the above operation will be described with reference to FIG. First, when the MPU 301 receives a start signal from a controller (not shown) or the operation panel 302, it feeds recording paper from a paper feeding unit (not shown). The recording paper is temporarily stopped at the nip portion of the registration roller 110, and after the predetermined transport timing T1, the registration roller 110 is restarted to restart the photosensitive drum 1.
It is transported to 03.

Subsequently, the MPU 301 turns on the black image writing synchronization signal FSYNC (K) after the registration roller 110 has been restarted and T2, and after a predetermined time T3, writes the yellow image. FSYNC (Y) which is a synchronizing signal is turned on. Hereinafter, the MPU 301 will perform the FSYNC (M), T5 after T4.
After that, the FSYNC (C) is turned on in order. On the other hand, on the recording paper, K, Y, M,
The toner images are superposed in the order of C, and then the fixing unit 1
The fixing process is performed by 12.

Next, the positional deviation adjustment in the sub-scanning direction will be described by taking black and yellow image formation as an example.

FIG. 5 is an explanatory diagram showing an example of positional deviation in the sub-scanning direction. Here, the reference color is K (black),
It is assumed that the recording position of Y (yellow) is displaced from the recording position of K by an interval of D. Here, the deviation amount D is smaller than the diameter of one recording dot.

Further, FIG. 6 shows that before and after the sub-scanning position adjustment,
7 is a timing chart showing ON / OFF output timings of K (black) and Y (yellow) DETP and PCLK, respectively.

As a method of checking the amount of deviation of the image data, for example, the motor phase control circuit 303 is adjusted so that PCLK has the same phase as the reference color, and the time difference of DETP with respect to the reference color is measured by the DETP timing measuring unit 305. . Now, the time difference between DETPK and DETPY is T6.

Next, the image data is actually output at the timing shown in FIG. 5, and the deviation amount D is measured. The deviation amount D is-(minus) when Y is behind K in the direction of movement of the recording paper, and + when Y is behind.
(Plus)

Here, assuming that the diameter of one dot is X and the theoretical period of DETP is T7, DETPK and DE after adjustment are adjusted.
The timing difference T8 from TPY is T8 = T6 + (D / X) × T7.

Next, the output timing of the FSYNC when the positional deviation adjustment in the sub-scanning direction is performed in this embodiment will be described.

FIG. 7 is a block diagram showing the detailed arrangement of the FSYNC output timing measuring section 306. In the figure, 701K, 701Y, 701M, and 701C are DEs.
It is a counter as a counting means for counting TP. 702K, 702Y, 702M, and 702C compare the values of the counters 701K, 701Y, 701M, and 701C with the values set by the MPU 301, and notify the MPU 301 when the values are equal. It is a comparator as a means.

The operation of the above configuration will be described. FIG. 8 is a timing chart showing the output timing of DETP and FSYNC in FIG. MPU3
Reference numeral 01 denotes each of the comparators 702K, 702Y, 702 at the timing of starting (restarting) the registration roller 110.
Set the FSYNC output timing to M and 702C.

Further, the above set values are set to the registration roller 11
When the time from the start of driving (restart) of 0 to the output of FSYNC is T10 and the period of DETP is T7, it is calculated by the following formula. That is, it is obtained by the following: comparator set value = INT (T10 / T7) -1. Note that INT in the above formula represents an integer, and fractions are rounded down.

Comparators 702K, 702Y, 702M, 7
02C When A and B are equal, each comparator 7
02K, 702Y, 702M, and 702C turn on the compare match signal, and continue to turn on FSYNC for one DETP cycle.

Therefore, as described above, the color misregistration in the sub-scanning direction is eliminated by adjusting the phase of the main scanning synchronization signal, and the image writing timing is synchronized with each main scanning synchronization signal. It is possible to realize accurate position adjustment in the sub-scanning direction without being affected by the fluctuation of the main-scanning synchronization signal due to the uneven rotation of the disk, the processing accuracy of the polygon mirror 203, and the like.

Next, an embodiment different from the embodiments shown in FIGS. 7 and 8 will be described. FIG. 9 is a block diagram showing the detailed arrangement of another embodiment of the FSYNC output timing measuring unit 306. In the figure, 901K is DE
A counter as a counting means for counting TPK,
902K, 902Y, 902M and 902C are counters 9
It is a comparator as a data comparison means having a function of comparing the value of 01K and each value set from the MPU 301 and notifying the MPU 301 when the values are equal.

The operation of the above configuration will be described. FIG. 10 is a timing chart showing the output timing of DETP and FSYNC. The MPU 301, when the driving (restart) of the registration rollers 110 is started, each of the comparators 702K, 702Y, 702M, 702C.
Set the FSYNC output timing to.

This set value is the time from the start (restart) of the registration roller 110 to the output of FSYNC, which is T1.
0, DETP cycle is T7, and DE is more than DETPK
When the phase of TP * is delayed or has the same phase, the comparator setting value = INT (T10 / T7) -1.

When the phase of DETP * is ahead of DETPK, the comparator setting value = INT (T10 / T7) -2. In the above formula, INT represents an integer, and fractions are rounded down.

In addition, the respective comparators 702K and 702
When the values of A and B of Y, 702M and 702C become equal, the respective comparators 702K, 702Y, 702M and 702C
Sends a compare match signal to the MPU 301.

In the case of K color, the MPU 301 receiving this signal turns on FSYNC before the next DETPK is output and keeps on FSYNC for one DETP cycle.

For other colors, if the time difference between DETPK and DETP * after phase adjustment is T11,
After "T11 + T9", FSYNC is turned on, and FSYNC is kept on for one DETP cycle.

Therefore, as described above, the image writing timing is determined by the single counter 901K, so that the circuit configuration is simplified and the cost can be reduced.

[0050]

As described above, according to the image forming apparatus of the present invention (claims 1 and 2), the image writing start timing is adjusted based on the output timing of the main scanning synchronizing signal corresponding to each color signal. Therefore, by absorbing the influence of the fluctuation of the main scanning synchronization signal caused by the unevenness of rotation of the optical scanning motor and the processing accuracy of the polygon mirror, it is possible to avoid the deterioration of the writing position accuracy in the sub scanning direction. It is possible to obtain a good color image without deviation.

According to the image forming apparatus of the present invention (Claim 3), the image writing timing is determined by the single counting means, so that the circuit configuration is simple and the rotation unevenness of the optical scanning motor is uneven. A good color image with no image misregistration is obtained by absorbing the effect of fluctuations in the main scanning synchronization signal due to the processing accuracy of the polygon mirror and the like, and avoiding a decrease in writing position accuracy in the sub scanning direction. be able to.

Further, according to the image forming apparatus of the present invention (Claim 4), since the main scanning synchronizing signal of the image forming station through which the recording sheet first passes is used as a reference, the circuit configuration is not complicated. With the simplest configuration, it is possible to avoid a decrease in position accuracy in the sub-scanning direction.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a main configuration of a color printer as an image forming apparatus suitable for applying the present invention.

FIG. 2 is an explanatory diagram showing a configuration of an optical writing unit in FIG.

3 is a block diagram showing a main configuration of a control system of the color printer in FIG.

FIG. 4 is a timing chart showing the write timing of each image forming station.

FIG. 5 is an explanatory diagram showing an example of positional deviation in the sub-scanning direction.

FIG. 6 shows K (black) and Y before and after the sub-scanning position adjustment.
6 is a timing chart showing on / off timings of (yellow) respective DETP and PCLK.

7 is a block diagram showing a detailed configuration of an FSYNC output timing measuring unit in FIG.

8 is a timing chart showing the output timing of DETP and FSYNC in FIG.

9 is a block diagram showing a detailed configuration of another embodiment of the FSYNC output timing measuring unit in FIG.

10 is a timing chart showing the output timing of DETP and FSYNC in FIG.

FIG. 11 is a timing chart for explaining a change in DETPY with respect to DETPK when the main scanning synchronization signal (DETPK) of the reference color and the main scanning synchronization signal (DETPY) of another color are adjusted to have the same phase.

[Explanation of symbols]

102 optical writing unit 103 photoconductor drum 203 polygon mirror 205 light receiving element 301 MPU 302 motor phase control circuit 304K, 304Y, 304M, 304C motor driver 305 DETP timing difference measuring unit 306 FSYNC output timing measuring unit 701K, 701Y, 701M, 701C Counter 702K, 702Y, 702M, 702C Comparator 901K Counter 902K, 902Y, 902M, 902C Comparator

Claims (4)

[Claims] 1. A plurality of photoconductors arranged in parallel for each single color, and an optical writing unit provided corresponding to the photoconductors, for writing and scanning a laser beam modulated by each color signal on the photoconductor. Measuring the output timing difference of the main scanning synchronization signal between the motor control means for controlling the rotation speed of the scanning motor of the optical writing means by PLL control and the optical writing means based on the reference frequency for PLL control. And a motor phase control means for adjusting the phase of the reference frequency signal in the PLL control based on the timing difference output by the timing measurement means.
An image writing timing output means for outputting an image writing timing signal for each of the optical writing means, and a main for adjusting the image writing timing signal based on each main scanning synchronization signal output timing after phase adjustment by the motor phase control means An image forming apparatus comprising: a control unit. 2. An image writing timing output means is provided for each color signal, and count means for counting a main scanning synchronization signal corresponding to the color signal, a count value of the count means and a set value of the main control means. And compare
And a data comparison means for feeding back a compare match signal to the main control means when the two values are equal, and the main control means determines the image writing start timing based on the output signal of the data comparison means. The image forming apparatus according to claim 1, wherein: 3. The image writing start timing output means compares the count means for counting the reference main scanning synchronization signal with the count value of the count means and the set value of the main control means, and the two values are If they are equal,
Data comparison means for feeding back a compare match signal to the main control means, and the main control means determines the image writing timing based on a timing difference between the reference main scanning synchronization signal and another main scanning synchronization signal. The image forming apparatus according to claim 1, wherein the image forming apparatus determines. 4. The image according to claim 3, wherein the reference main-scan synchronizing signal is a main-scan synchronizing signal of an optical writing unit corresponding to a photoconductor on which a recording sheet is first transferred. Forming equipment.