JP2002341622A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device that reduces, by a simple structure, image slippage caused by out of synchronization of a plurality of beams. SOLUTION: A counter 10 and a masking time measuring device 12 measure a time interval (masking time) from an output of a TR0 signal from a mark detection means 64 during first image formation to an output of the first SOS signal from a beam position detector 66. Then, during the subsequent image formation, an SOS signal to be outputted during the masking period is nullified by a masking means 14. Based upon the masking period, a writing permission signal generator 16 outputs a writing permission signal to an image data output device in synchronization with the SOS signal. A beam is determined according to the time calculated from a remainder of a TR0 signal cycle and an SOS signal cycle, which are stored in an offset quantitative memory 20. Image data is sent from an image data output device 18 to an N beam exposure device 22.

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, and more particularly, to an image forming apparatus such as a copying machine or a laser printer for forming a plurality of color images by repeating a process of forming an image by scanning a plurality of laser beams. Related to the device.

[0002]

2. Description of the Related Art As a method of forming a color image by using a so-called electrophotographic process (charging, exposure, development, transfer, fixing), an image forming apparatus having a structure as shown in FIG. 10 is known.

In this type of image forming apparatus, the surface of a photosensitive drum 40, which is a medium to be scanned, which moves in the direction of the arrow in FIG.
The photosensitive drum 40 is scanned and exposed with the laser light modulated in accordance with the image signal, and the image portion of the photosensitive drum 40 is discharged to form a latent image. Then, the latent image is developed by the developing device 46 to form a toner image. The toner image is transferred by the first transfer device 48 onto an intermediate transfer belt 50 as an image carrier. Then, a visible image is formed by rotating the developing device 46 and repeating the above-described processing with toners of different colors, whereby a color image is formed on the intermediate transfer belt 50.

[0006] The paper transport in the paper tray 54 is started by the paper transport start controller 36 so that the color image formed on the intermediate transfer belt 50 overlaps a predetermined position on the paper 52 as an image transfer body. The color image formed on the intermediate transfer belt 50 is transferred onto the sheet 52 conveyed by the sheet conveying roll 58 by the second transfer device 56,
The toner on the sheet 52 is fused and fixed by the fixing device 60.

[0005] In this type of image forming apparatus, the intermediate transfer belt 50 makes four revolutions to transfer a full-color image to the intermediate transfer belt 50.
Since the intermediate transfer belt 50 is formed on the intermediate transfer belt 50, a belt position detection mark 62 that moves in the sub-scanning direction is provided. Is output.

A beam position detecting device 66 (see FIG. 11) is provided in the exposure device 44 as a timing detecting device in the main scanning direction. FIG. 11 shows a schematic configuration of the exposure apparatus 44. The beam from the laser 68 is deflected at a constant angular velocity by a rotary polygon mirror 70 rotating in the direction of the arrow. The beam deflected at a constant angular velocity is converted into a constant velocity motion on the photosensitive drum 46 by the Fθ lens 72 and is collected as a beam spot. The beam position detector 66 detects the passage of the beam deflected by the rotary polygon mirror 70, and sends out a beam position reference signal (hereinafter, referred to as an SOS signal).

[0007] By the way, in addition to the color, the image forming apparatus,
Although high image quality and high speed are required, a method using a light source unit that emits a large number of beams has been proposed as a method for increasing the resolution and speed of an exposure apparatus. For example, FIG. 12 shows a state in which an object to be scanned is scanned using eight beams. In FIG. 12, since eight beams scan eight adjacent scanning lines at a time, high speed and high resolution can be realized without increasing the number of rotations of the rotating polygon mirror.

In an exposure apparatus using a plurality of beams, FIG.
1 outputs an SOS signal in response to the deflection by the rotary polygon mirror 70. Therefore, when a plurality of scanning lines are collectively scanned by a plurality of beams, a plurality of scanning lines (FIG. 1) are used.
In the case of 2, the SOS signal is output once every time 8) is written.

Generally, the period of the TR0 signal (the time during which the intermediate transfer belt 50 makes one rotation) does not coincide with the period of the SOS signal. Therefore, actually, the first SOS signal output after the output of TR0 is synchronized. Used (signal surrounded by dotted line in FIG. 13). In the case where eight beams are used and the TR0 signal is output immediately after the output of the SOS signal as described above, the SOS signal used for synchronization is output after being sent for about eight scans. .

In the image forming apparatus shown in FIG. 10 in which a plurality of images are superimposed, this synchronization delay causes a problem in that the read registration (the writing position in the sub-scanning direction) is shifted for each color and appears as a color registration shift.

As a method of correcting the writing position deviation due to the synchronization, there has been proposed a technique described in Japanese Utility Model Laid-Open No. 63-170819 and Japanese Patent Application Laid-Open No. 8-142412. For example, in the technique described in Japanese Patent Application Laid-Open No. 8-142412, a case is considered in which an SOS signal output in a time T cycle is output after t from generation of a recording start signal (TR0 signal), and the relationship between t and T / 2 is considered. Selects the beam for transmitting the first modulation signal from the two beams. When t> T / 2, the image data of the first line is sent to one beam, and when t <T / 2, the image data of the first line is sent to the other beam. In this way, it is possible to prevent the time lag between TR0 and SOS from increasing when there are a plurality of beams.

[0012]

However, in the technique described in Japanese Utility Model Laid-Open No. 63-170819 and Japanese Patent Application Laid-Open No. 8-142412, the color registration deviation due to the synchronization deviation of a plurality of beams is reduced. But dozens of them,
When the number is very large, there is a problem that a selection circuit for transmitting the first image data becomes complicated.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problem, and has as its object to provide an image forming apparatus capable of reducing an image shift due to a shift in synchronization of a plurality of beams with a simple configuration.

[0014]

According to a first aspect of the present invention, there is provided an image forming apparatus comprising: a plurality of beams which are modulated in accordance with image data; An image forming apparatus that forms an image on a body, and forms one image by superimposing a plurality of images formed on the object to be scanned on an image carrier that carries the image, the image forming apparatus comprising: Detecting the start position of the scan, sequentially forming images of each of a plurality of predetermined colors on the scanned object by scanning the scanned object with a plurality of beams modulated according to image data, An image forming apparatus for forming one image by sequentially superimposing images formed on the object to be scanned on an image carrier for carrying an image, wherein a position of the scanning by the plurality of beams is detected, and a beam position is detected. Beam position to output detection signal Output means, image carrier position detecting means for detecting that the reference position on the image carrier has reached a predetermined position, and outputting an image carrier position detection signal, and a first image on the image carrier. Measuring means for measuring the time from the image carrier position detection signal to the output of the beam position detection signal when forming the image, and forming an image after the first image on the image carrier. Invalidating means for invalidating the beam position detection signal detected during a period from when it is detected that the reference position has reached the predetermined position to when the time measured by the measuring means has elapsed, and Sending means for sending the image data to the beam determined according to the time calculated based on the surplus of the cycle of the body position detection signal and the cycle of the beam position detection signal based on the beam position detection signal When, It is characterized in that it comprises.

According to the first aspect of the present invention, the beam position detecting means detects the position of scanning by a plurality of beams when forming an image on the object to be scanned, outputs a beam position detection signal, and outputs the beam position detection signal. The carrier position detecting means detects that the reference position on the image carrier has reached a predetermined position, and outputs an image carrier position detection signal.

Although the beam position detection signal and the image carrier position detection signal are not synchronized with each other, their respective periods are constant, and the period deviation of each signal changes in a constant relationship. If image formation is performed at the timing when the first beam position detection signal is output after the image carrier position detection signal is output, the time from when the first carrier position detection signal is output until the first beam position detection signal is output is output. Is changed every time an image is sequentially formed. Therefore, depending on the output timing of the beam position detection signal with respect to the image carrier position detection signal, the image position formed based on the beam position detection signal is always formed at a different position on the image carrier, and a plurality of beams are formed. An image shift due to a synchronization shift occurs.

The measuring means measures the time from when the image carrier position detection signal is output when the first image is formed to when the beam position detection signal is output. When forming an image subsequent to the first image, the beam position detection signal detected by the beam position detection unit during a period from when the image carrier position detection signal is output to when the time measured by the measurement unit has elapsed is used. Invalidated. In this way, the time from when the image bearing member position detection signal is output when the first image measured by the measurement means is formed to when the beam position detection signal is output is measured, and then the image formation is performed. In this case, by invalidating the beam position detection signal output within the time after the image carrier position detection signal is output, the image position formed in synchronization with the beam position detection signal can be adjusted. Above, it is possible to prevent the output timing from being always formed at a different position.

However, if the image is formed as it is, the images of the respective colors are shifted and overlap in a certain relationship on the image carrier.

Therefore, this image shift (shift of each image with respect to the first image formed) is calculated based on the surplus of the period of the image carrier position detection signal and the period of the beam position detection signal. Can be expressed in time
In the sending means, based on the beam position detection signal performed as described above, the time is determined according to a time calculated based on the surplus of the period of the image carrier position detection signal and the period of the beam position detection signal. Image data is sent to the beam.
That is, according to the time calculated from the surplus of the cycle of the image carrier position detection signal and the cycle of the beam position detection signal,
A beam for transmitting image data is selected from among the plurality of beams, and the displacement of each image can be corrected using the arrangement offset of the plurality of beams.

The time ΔT calculated on the basis of the surplus of the cycle of the image carrier position detection signal and the cycle of the beam position detection signal is represented by Ttr for the cycle of the image carrier position detection signal, Ttr for the beam position detection signal, Assuming that the period is Tss, ΔT = (T
trMOD Tss) × Tss, where N is the number of beams of a plurality of beams, the scanning line ΔL scanned during ΔT is ΔL = ΔT × (N / Ts
s), and the transmitting means transmits the image data to the beam determined according to ΔL. Here, Ttr MOD Tss indicates the remainder of Ttr / Tss.

As described above, the time from when the image carrier position detection signal at the time of the first image formation is output to when the first beam position detection signal is output is measured, and the time is measured at the time of the subsequent image formation. The beam position detection signal output at the specified time is invalidated, and the image data is transmitted to the beam determined according to the time calculated from the surplus of the period of the image bearing member position detection signal and the period of the beam position detection signal. by doing,
It is possible to correct a shift when a plurality of images are superimposed, and to reduce an image shift due to a synchronization shift of a plurality of beams with a simple configuration.

However, the relationship between the period difference between the beam position detection signal and the image bearing member position detection signal varies due to the expansion and contraction of a belt or the like used for the image bearing member due to the ambient temperature where the image forming apparatus is installed. Occurs. Therefore, as in the invention according to claim 2, by further comprising updating means for updating the time calculated from the surplus, a beam corresponding to the time calculated from the updated surplus is selected by the transmitting means. Then, the image shift due to the synchronization shift of the plurality of beams can be reduced with high accuracy.

Further, the above-described arrangement can reduce the displacement of the image on the image bearing member. However, the image is transferred to the image transfer member for transferring the image on the image bearing member such as paper. In such a case, an absolute displacement of the image transfer body occurs, and a plurality of images are printed on one image transfer body, and the image transfer body is cut and used based on an end of the image transfer body. In this case, the image position on each cut image transfer body is not constant, and in some cases, the image may be cut off.
Therefore, as in the third aspect of the present invention, by adjusting the timing of transferring the image to the image transfer body based on the time measured by the measurement unit, the absolute shift of the image transfer body is prevented. be able to.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In this embodiment, the present invention is applied to a color image forming apparatus for forming an image in the order of color Y → color M → color C → color K shown in FIG.

The schematic configuration of the image forming apparatus according to the embodiment of the present invention is the same as the configuration described with reference to FIG. [First Embodiment] FIG. 1 shows a control system of an image forming apparatus according to a first embodiment.

As shown in FIG. 1, the control system of the image forming apparatus according to the present embodiment includes a counter 10, and a belt movement reference signal (TR 0 signal) detected by the mark detector 64 in the counter 10. , Beam position detecting device 6
6, a beam position reference signal (SOS signal) and a predetermined clock (CLK) signal are input.
Note that the mark detecting means 64 corresponds to the image carrier position detecting means of the present invention, and the beam position detecting device 66 corresponds to the beam position detecting means of the present invention.

The counter 10 performs SOS based on the TR0 signal.
The number of clocks of the CLK signal until the signal is input is counted and output to the mask time measuring device 12.

The mask time measuring device 12 includes a counter 10
The number of clocks counted by is input and
A COLOR signal indicating any of color Y, color M, color C, and color K is input, and TR0 signal is
The time (mask time) from the input of 0 to the input of the SOS signal is calculated from the number of clocks counted by the counter 10 and output to the mask means 14 as a mask time signal. Note that the counter 1
0 and the mask time measuring device 12 correspond to the measuring means of the present invention.

The TR0 signal and the SOS signal are further input to the masking means 14, and the SOS input from the input of the TR0 signal until the mask time elapses.
The signal is invalidated, and the other SOS signals are output as they are. The mask means 14 outputs a mask SOS signal (MSOS) signal to the write permission signal generator 16. Further, the mask means 14 corresponds to the invalidating means of the present invention.

The write request signal (PS_REQ) signal is input to the write permission signal generator 16. In response to the ON / OFF of the PS_REQ signal, the color Y signal is synchronized with the MSOS signal from the mask means 14. The page writing permission signal PS_Y is output to the image data output device 18, and the line writing permission signal LS_ for giving data writing permission at every predetermined timing from the SOS signal at each scan.
Y is output to the image data output device 18.

The image data output device 18 outputs a page write enable signal PS output from the write enable signal generator 16.
Only when both _Y and the line writing permission signal LS_Y are turned on, image data is output to the N-beam exposure device 22 to form an image. Further, an offset amount memory 20 is connected to the image data output device 18, and blank data (Y blank data, M blank data, C blank data, and K blank data) are stored in the offset amount memory 20.
Blank data) is input.

The offset amount memory 20 stores the above-mentioned blank data determined according to the time calculated from the surplus of the image carrier position detection signal cycle and the beam position detection signal cycle. The blank data defines a beam for transmitting image data of the N-beam exposure device.

Here, a method of calculating the blank data stored in the offset amount memory 20 will be described below.

Assuming that the period of the image carrier position detection signal is Ttr, the period of the beam position detection signal is Tss, and the number of beams of the light source of the N-beam exposure device 22 is N, the T for each color image forming unit is T.
With reference to the R0 signal, as shown in FIG. 2, every time a color image is formed, an SOS signal is generated at a timing shifted by a time ΔT obtained by the following equation (1).

ΔT = (Ttr MOD Tss) × Tss (1) Since N images are written in one scan, the line image ΔL written in time ΔT is expressed by the following equation (2).

[0036] Here, for example, if Ttr = 6s Tss = 0.7 ms N = 5, ΔL = (6 MOD 0.0007) × 5 = 2.1428571 lines.

The position at which the sub-running image forming position is adjusted in units of one line may be a value obtained by rounding off the decimal point of ΔL each time the image forming color is changed, in this case, the image may be formed by two lines at an earlier timing. Will be. However, since it is difficult to advance the image forming timing, the same effect can be obtained by inserting the blank data consisting of the above ΔL at the start of the color image formation formed at the earlier timing and delaying the actual image forming timing. be able to.

When forming an image of four colors as shown in FIG. 2, the Y blank data is represented by ΔL + ΔL + ΔL = 2 + 2 + 2 =
The blank data of 6 lines, M blank data, ΔL + ΔL = 2 + 2 = 4 lines, C blank data, ΔL = 2 lines, and K blank data of 0 line are stored in the offset amount memory 20 in advance.

The write permission signal generator 16, the image data output device 18, and the offset amount memory 20 correspond to the transmitting means of the present invention.

Next, the image data output device 18 will be described. FIG. 3 shows a schematic configuration of the image data output device 18.

As shown in FIG. 3, the image data output device 1
Reference numeral 8 denotes a processing unit (color Y processing unit 24Y, color M processing unit 24M, color C processing unit 24) for each color image.
C and a color K processing unit 24K), and the respective processing units have the same configuration. Therefore, the color Y processing unit 24Y will be described as a representative.

The color Y processing section 24Y comprises color Y control means 26 and page data memory Y28. The page data memory Y28 stores M-line data using one beam of scan data as line data. The Y control means 26 has a write permission signal PS_ output from the write permission signal generator 16 for each color.
Y, a line write permission signal LS_Y and a Y blank (data) are input.

The color Y control means 26 controls line data output to the selector 30 and blank data insertion based on the input signal.

The selector 30 selects and outputs the input line data and blank data for each beam of the N-beam exposure device 22, whereby an image is formed by the N-beam exposure device 22.

Next, the operation of the present embodiment will be described.

At the start of printing, first, a COLOR signal representing the color Y is supplied to the mask time measuring device 12 as a COLOR signal.
The signal is input, and the image formation of color Y is started. The mask time measuring device 12 outputs the mask time signal to the mask means 14 as 0, and then calculates the number of clocks of the CLK signal from the input of the TR0 signal counted by the counter 10 to the input of the SOS signal for the first time. The mask time is measured. Then, the mask time is output to the mask means 14 as a mask time signal.

In the masking means 14, after the TR0 signal is inputted, the inputted S signal is kept until the mask time (mask time signal) inputted from the mask time measuring device 12 elapses.
The OS signal is invalidated. Otherwise, the SOS signal is output as it is to the write permission generator 16 as the MSOS signal.

At the start of the image formation of the first color Y, the mask time becomes 0, and there is no SOS signal to be invalidated by the mask means 14. After the processing of color Y is started and the write request signal PS_REQ input to the write permission signal generator 16 is turned on, the page write permission signal PS_Y of color Y is turned on in synchronization with the MSOS signal from the mask unit 14. And output to the image data output device 18.

In the write permission signal generator 16, S
At a predetermined timing from the OS signal, a line write permission signal LS_Y for giving a data write permission for each scan is turned on and output.

On the other hand, from the offset amount memory 20, Y
The blank data is output to the image data output device 18.

The color Y control unit 26 in the color Y processing unit 24Y of the image data output device 18
_Y, LS_Y, and Y blank data are input, and insertion of line data and blank data to be output to the selector 30 is controlled. In the color Y control means 26,
Only when both PS_Y and LS_Y are turned on, image data corresponding to each beam is output from the image data output device 18 to the N-beam exposure device 22, whereby an image is formed.

Here, as for the image data 1 to image data N to the N-beam exposure device 22, if the smaller the number of the signal name is, the more the image is formed on the image forming start end side, the blank Y is as in the above-described example. In the first scan after the start of image formation, all of the image data 1 to 6 are turned off. Otherwise, in the S-th scan from the start of image formation, the image data N is line data (S × N). -A blank Y) is output.

When the image formation for the color Y is completed as described above, a COLOR signal representing the color M is subsequently input to the mask time measuring device 12 and processed in the same manner as for the color Y. The same processing is performed for K, and the image formation ends.

Normally, the SOS signal and the TR0 signal are not synchronized with each other, but their respective periods are constant.
The period of the S signal is determined by the rotation speed of the rotating polygon mirror and the number of reflecting surfaces, and the period of the TR0 signal is determined by the circumference and the moving speed of the belt. Therefore, the synchronization shift between the SOS signal and the TR0 signal changes in a fixed relationship.

Therefore, in the present embodiment, as described above, the change in the synchronization shift between the SOS signal and the TR0 signal whose shift is constant is stored in the offset amount memory 20 in advance, and based on this, the change in the N beams is performed. The image data of the first line is transmitted to one of the beams. This makes it possible to correct the change in the synchronization shift between the SOS signal and the TR0 signal.

However, even if the deviation of the synchronization is constant, the manner in which the color registration occurs depends on the timing of the TR0 signal. However, in the present embodiment, the above-described mask time is provided, and The SOS signal during the period is invalidated, whereby it is possible to prevent the color registration from occurring in a different manner.

FIG. 4 shows an image without a mask time. FIG. 4 shows an SOS synchronized with the TR0 signal.
4 shows four patterns (a to d) of how the color registration shifts when a signal has a relationship that the writing image gradually delays later.

FIG. 4 (a) shows that the SOS signal of the first color () is output immediately after the TR0 signal,
This shows a state in which the time until the OS signal becomes longer as the image is written later. In this case, the color register on the paper is shown in FIG.
From the lead edge (upper end) as shown on the right
The image is shifted in the order of,.

As shown in FIG. 4B, the SOS of the first color
When the TR0 signal is generated immediately after the signal is output, TR
The time from the 0 signal to the SOS signal used for synchronization is
,..., The order of appearance of the color registration deviation is different from that of FIG. Similarly, (c),
(D) also has a different shift. Therefore, even if the synchronization shift between the SOS signal and the TR0 signal is changed in a fixed relationship, the shift of the color registration depends on at which timing of the TR0 signal occurs in FIGS. 4A to 4D. It has various shapes.

In this embodiment, as shown in FIG. 5, as described above, the mask time (the thick line portion in FIG. 5) representing the time from the TR0 signal to the SOS signal of the first color is provided, and the second color is provided. Thereafter, the SOS signal generated until the mask time elapses from the generation of the TR0 signal is ignored, and the SOS signal output first after the mask time elapses from the TR0 signal is used as a synchronization signal. As described above, when the SOS signal generated within the mask time is ignored, as shown in the right side of FIG.
Regardless of the timings (a) to (d) at which the R0 signal is generated, the manner in which the color registration shifts is always constant. Therefore, by determining the beam for transmitting the first line image data of each color in accordance with the constant color registration deviation relationship, the signal for transmitting the first line image data is always determined from the relationship between TR0 and the SOS signal. The color register can be kept constant without switching.

As shown in FIG. 6, even when the SOS signal synchronized with the TR0 signal gradually delays, the color registration can be kept constant similarly. FIGS. 6 and 7 show the case where the SOS signal gradually shifts ahead of the TR0 signal. In FIG. 6 where the mask time is not set, as in FIG. However, assuming that the time from the TR0 signal of the first color to the SOS signal is the mask time (the thick line in FIG. 7), as shown in FIG. Is output, the color registration is shifted in the same manner. [Second Embodiment] In the control system of the image forming apparatus according to the first embodiment, the blank data of each color stored in the offset amount memory 20 is a fixed value. For this purpose, the body position detection (TR0) signal period at the image end and the beam position detection (S
When at least one of the periods (OS) and the signal period has changed, the blank data stored in the offset amount memory 20 needs to be updated.

For example, the SOS signal shown in FIGS.
The relationship of the color registration deviation due to the period difference of the R0 signal changes when the intermediate transfer belt 50 expands and contracts under the influence of the ambient temperature where the image forming apparatus is installed.

Therefore, in the control system of the image forming apparatus according to the second embodiment, the cause of the period change of the image carrier position detection signal cycle or the beam position detection signal cycle is detected as the apparatus temperature fluctuation and updated. Has become.

The other configuration is the same as that of the first embodiment, and therefore, the same reference numerals are given and the description is omitted.

FIG. 8 shows a control system of the image forming apparatus according to the second embodiment. As shown in FIG. 8, the control system of the image forming apparatus according to the second embodiment differs from the control system of the first embodiment in that
A temperature detection sensor 32 for detecting a temperature in the image forming apparatus and outputting a temperature (TEMP) signal representing the detected temperature is provided, and a TEMP signal output from the temperature detection sensor 32 is subjected to a temperature correction calculation. Is input to the device 34.

The temperature correction calculator 34 has a memory (not shown). The memory stores a correction table in which the relationship between the temperature in the apparatus and the offset amount for each color is predetermined. Blank data corresponding to the obtained offset amount is calculated and output as offset data. The temperature correction computing unit 34 updates the blank data stored in the offset amount memory 20A at a predetermined timing such as when power is turned on or when printing is performed after the standby time exceeds 30 minutes. (W
RITE) signal to the offset amount memory 20A, and new offset data obtained by the temperature correction calculator 34 to the offset amount memory 34. The offset amount memory 20A is connected to the offset amount memory 20A. The stored blank data is rewritten with new offset data output from the temperature correction calculator 34.

The temperature sensor 32 and the temperature correction calculator 34 correspond to the updating means of the present invention.

Next, the operation of the second embodiment will be described.

The temperature detection sensor 32 detects the temperature inside the image forming apparatus and outputs it as a TEMP signal to the temperature correction calculator 34. In the temperature correction calculator 34, TEMP
An offset amount is calculated from the signal and a predetermined correction table, and blank data corresponding to the offset amount is calculated.

Then, at a predetermined timing,
The WRITE signal and the blank data calculated by the temperature correction calculator 34 are output to the offset amount memory 20A as offset data.

In the offset amount memory 20 A, the stored blank data is rewritten to the offset data input from the temperature correction calculator 34.

As a result, even if there is disturbance such as temperature, the lead registration deviation can be corrected with high accuracy.

In the second embodiment, the TEMP signal obtained from the temperature detection sensor 32 is used as the external signal. However, the present invention is not limited to this.
As in the technique described in JP-A-63-27127,
A position detection image (registration mark) of each color is formed at a predetermined position on the image carrier, and offset data is measured using a measurement signal obtained by directly measuring a deviation of the registration mark from an ideal position by a registration detection device. It may be generated so that the correction can be performed with high accuracy. [Third Embodiment] The sheet conveyance start control device 36 shown in FIG.
Starts the conveyance of the paper 52 at the timing when the image forming process ends (for example, after the lapse of the time Tps from the generation of the TR0 signal of the final image).
In the embodiment, the color registration misregistration can be corrected, but the absolute lead registration on the paper is misaligned, and a plurality of images are printed on one sheet of paper and cut and used based on the end of the paper for use. However, the position of the image on the cut paper may not be constant, and in some cases, the image may be cut off.

Therefore, the control system according to the image forming apparatus of the third embodiment is configured to control the sheet conveyance timing controlled by the sheet conveyance start control unit 36.

The same components as those in the second embodiment are denoted by the same reference numerals, and description thereof will be omitted.

FIG. 9 shows a control system of the image forming apparatus according to the third embodiment. As shown in FIG. 9, the second embodiment differs from the second embodiment in that the sheet transport timing Tps
Is provided, the timing correction calculator 38 is connected to the mask time measuring device 12, and the paper transport timing Tps calculated by the timing correction calculator 38 is used to start the paper transport. The data is output to the control device 36.

Further, the paper transport start control device 36
The OLOR signal and the TR0 signal are input.

Incidentally, the sheet conveyance start control device 36 and the timing correction calculator 38 correspond to the adjusting means of the present invention.

Next, the operation of the third embodiment configured as described above will be described.

The read registration shift amount of the image written on the paper becomes longer in proportion to the mask time. Therefore, the timing correction calculator 38 sets the sheet conveyance start timing at which the mask time is Tm and the read register on the sheet becomes ideal when the mask time is 0 (Tpsn (from the generation of the TR0 signal of the final image to the start of the sheet conveyance). ), The paper transport timing Tps is calculated so that the paper transport timing Tps = Tpsn−Tm (3), and the calculation result (Tps) is output to the paper transport start control device 36. .

In the sheet transport start control unit 36, the COLO
The R signal becomes color K, which is the final image forming color, and TR0
A predetermined time Tps from the signal, that is, a paper transport start timing Tps obtained from the timing correction arithmetic unit 38
When the time elapses, the sheet conveyance is started. As a result, it is possible to obtain a good image in which both the color registration and the lead registration on the paper are not shifted.

When not only the color registration but also the absolute position of the image with respect to the paper is adjusted, the timing at which the paper is started to be transported by the paper transport start controller 36 is synchronized with the SOS signal. Can also be adjusted.

In the first to third embodiments, the present invention is applied to an image forming apparatus in which images of a plurality of colors are superimposed on the intermediate transfer belt 50 as shown in FIG. For example, the sheet is held by a sheet holding drum 74 that electrostatically holds the sheet instead of the intermediate transfer belt 50 as shown in FIG.
An image forming apparatus that superimposes and fixes four color toner images on paper, an image forming apparatus that superimposes four color toner images on a photosensitive drum 40 as shown in FIG. The present invention can be applied to an image forming apparatus that generates an image in time series on a scanned object (the photosensitive drum 40 in the present embodiment), and the same effect as that of the present embodiment is obtained. be able to. Here, in the case of FIG.
The object to be scanned is the photosensitive drum 40 and the image carrier is the paper holding drum 74. In FIG. 15, the object to be scanned and the image carrier are also used by the photosensitive drum 40.

[0084]

As described above, according to the present invention, the time from when the image carrier position detection signal is output during the first image formation to when the first beam position detection signal is output is measured. During the subsequent image formation, the beam position detection signal output at the measured time is invalidated, and according to the time calculated from the surplus of the period of the image bearing member position detection signal and the period of the beam position detection signal. By sending image data to a predetermined beam, it is possible to correct a shift when superimposing a plurality of images, so that an image shift due to a synchronization shift of a plurality of beams can be reduced with a simple configuration. There is.

[Brief description of the drawings]

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

FIG. 2 is a diagram for explaining blank data stored in an offset amount memory.

FIG. 3 is a block diagram illustrating a configuration of an image data output device.

FIG. 4 is a diagram illustrating an image in which a mask time is not provided when an SOS signal synchronized with a TR0 signal gradually delays for an image to be written later.

FIG. 5 is a diagram illustrating an image in a case where a mask time is provided in which an SOS signal synchronized with the TR0 signal gradually delays for an image to be written later.

FIG. 6 is a diagram illustrating an image in a case where a mask time is not provided when an SOS signal synchronized with a TR0 signal becomes progressively earlier as an image is written later.

FIG. 7 is a diagram illustrating an image in a case where a mask time is provided in which an SOS signal synchronized with a TR0 signal becomes earlier as an image is written later.

FIG. 8 is a block diagram illustrating a control system of an image forming apparatus according to a second embodiment of the present invention.

FIG. 9 is a block diagram illustrating a control system of an image forming apparatus according to a third embodiment of the present invention.

FIG. 10 is a diagram illustrating a schematic configuration of an image forming apparatus that generates images on a scanned object in a time-series manner.

FIG. 11 is a view showing a schematic configuration of an exposure apparatus.

FIG. 12 is a diagram illustrating a state in which a scanning target is scanned collectively on a scanning target using a plurality of (eight) beams.

FIG. 13 is a diagram showing an SOS signal used for synchronization in a TR0 signal cycle and an SOS signal cycle.

FIG. 14 is a diagram illustrating an image forming apparatus that holds a sheet by a sheet holding drum that electrostatically holds the sheet instead of the intermediate transfer belt, and fixes the toner image by superimposing four color toner images on the sheet.

FIG. 15 is a diagram illustrating an image forming apparatus that superimposes four color toner images on a photosensitive drum, transfers the toner images to a sheet, and then fixes the toner images on a sheet.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Counter 12 Mask time measuring device 14 Masking means 16 Write permission signal generator 18 Image data output device 20 Offset amount memory 22 N beam exposure device 32 Temperature sensor 34 Temperature correction computing device 36 Paper transport start control device 38 Timing correction computing device 64 Mark detecting means 66 Beam position detecting device

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H04N 1/04 B41J 3/00 M 5C074 1/113 H04N 1/04 104A 1/23 103 DF term (reference) ) 2C362 BA52 BA68 BA70 BB32 BB38 BB39 BB47 BB50 CA18 CA22 CA39 2H027 DA22 DA23 DA38 EB04 ED04 ED06 2H030 AA01 AD17 BB02 BB16 BB24 BB42 BB56 2H076 AB06 AB12 AB67 AB68 EA01 5C07 A0203A07 BA07 DD08

Claims (3)

[Claims] 1. A plurality of beams modulated in accordance with image data are scanned over an object to be scanned, thereby sequentially forming images of a plurality of predetermined colors on the object to be scanned, and carrying the image. An image forming apparatus for forming one image by sequentially superimposing images formed on the object to be scanned on an image carrier, detecting a position of the scanning by the plurality of beams, and outputting a beam position detection signal. A beam position detecting means for detecting that a reference position on the image carrier has reached a predetermined position, and an image carrier position detecting means for outputting an image carrier position detection signal; Measuring means for measuring the time from the image carrier position detection signal when the first image is formed to the output of the beam position detection signal; and when forming the image after the first image, the image The reference position on the carrier Nullification means for nullifying the beam position detection signal detected during a period from when the arrival at the home position is detected until the time measured by the measurement means elapses, and the image carrier position detection signal Sending means for sending the image data to a beam determined according to a time calculated based on a surplus of the cycle of the beam position detection signal and the cycle of the beam position detection signal based on the beam position detection signal. An image forming apparatus comprising: 2. The image forming apparatus according to claim 1, further comprising an updating unit that updates a time calculated from the surplus. 3. The image forming apparatus according to claim 1, further comprising an adjusting unit that adjusts a timing at which an image on the image carrier is transferred to an image transfer member that transfers the image based on the time measured by the measuring unit. Or the image forming apparatus according to claim 2.