JP2001088349A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an accurate PWM signal when a dot clock for setting the number of pulses of a reference signal to a predetermined number within a predetermined time is formed. SOLUTION: The cycle of a dot clock is slightly increased or decreased to form a signal wherein the number of pulses generated within a predetermined time is set to a predetermined number. That is, by successively selecting a delay signal which is finely changed in phase gradually without changing clock frequency itself within a predetermined time without finely adjusting clock frequency to set the number of pulses to the predetermined number, the number of pulses generated within the predetermined time is matched with the predetermined number. Further, since the start point and completion point of a PWH signal are selected from the delay signal finely changed in the phase of the dot clock gradually, pulse width is accurately set corresponding to image data. As a result, when a dot clock changed in phase gradually so as to set the number of pulses of a reference signal to a predetermined number within a predetermined time is formed within one integrated circuit without using an external part, an accurate PWM signal can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image forming apparatus, and more particularly, to an image forming apparatus capable of adjusting the number of pulses of a reference signal to a predetermined number within a predetermined time.

[0002]

2. Description of the Related Art In an image forming apparatus, a laser beam modulated according to image data is scanned in a main scanning direction and an image is formed on an image carrier rotating in a sub scanning direction. In this case, the laser beam is modulated with image data based on a reference signal called a dot clock.

Therefore, it is necessary to generate a dot clock such that the length of an image formed on the image carrier in the main scanning direction is always constant according to a predetermined number of dot clocks.

In recent years, in order to obtain a color image on recording paper, a plurality of units having charging, exposure and development means are provided near the image carrier, and the image carrier is provided on the image carrier within one rotation of the image carrier. 2. Description of the Related Art A color image forming apparatus that forms a color toner image and collectively transfers the color toner image onto recording paper has been developed. In addition, a plurality of image carriers are provided in the vicinity of the intermediate transfer member, and charging, exposure, development, and transfer means are provided around each image carrier, and a toner image formed on each image carrier is transferred to the intermediate transfer member. A color image forming apparatus has been developed in which color toner images carried on an intermediate transfer body are sequentially transferred and collectively transferred onto transfer paper.

[0005]

In the former image forming apparatus, the number of rotations of the polygon mirror for performing main scanning, the aberration of the optical system, etc., and the number of dot clocks on the image carrier depend on the aberration of the optical system. In some cases, the length of the image formed in the image varies.

In a color image forming apparatus for forming a color toner image on an image carrier or an intermediate transfer member using a plurality of exposure means as in the latter case, a polygon mirror, a lens and the like of each exposure means are used. The length of an image formed on the image carrier in the main scanning direction varies among the exposure units due to individual differences in the optical systems described above, which causes color misregistration.

In the above case, it is preferable that the timing (phase) and frequency of the rise of the dot clock can be finely adjusted. VCXO (voltage-controlled crystal oscillator), DDS (digital direct synthesizer), and the like are known as circuits that enable such phase and frequency adjustment.

Although the VCXO and DDS have no problem in terms of accuracy, they are expensive in terms of equipment, and are independant devices which are not suitable for integration into a single-chip system (integrated circuit). It is not suitable for generating the dot clock of the forming apparatus.

In the technique separately filed by the present applicant, by slightly increasing or decreasing the period of the dot clock, the pulse of the dot clock generated within a predetermined time within a predetermined exposure range by the writing means is obtained. There is a technique for generating a dot clock having a predetermined number. By using this technique, it is possible to keep the length of the image of the scanning line in the main scanning direction constant.

However, when this technique is used, the period of the dot clock increases or decreases stepwise during the period of one scanning line, so that the circuit shown in FIG. When the PWM signal is generated by the comparator 20, a phenomenon occurs in which an accurate pulse width cannot be obtained (see FIG. 13).

As a result, even if the image data has the same pixel density, a portion where the width of the PWM signal is different occurs. Therefore, there is a problem that accurate image density cannot be reproduced.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and a first object of the present invention is to provide a single integrated circuit without using external components in a single integrated circuit. It is an object of the present invention to provide an image forming apparatus capable of obtaining an accurate PWM signal when a dot clock is generated such that the number of dot clocks becomes a predetermined number.

A second object is to accurately generate a dot clock such that the number of pulses of a reference signal becomes a predetermined number within a predetermined time within one integrated circuit without using external parts. An object of the present invention is to provide an image forming apparatus capable of reproducing an image density.

[0014]

That is, the present invention as a means for solving the problem is as described below.

(1) An image carrier for carrying an electrostatic latent image or a toner image, and writing means for scanning the image carrier with scanning light deflected by a rotating polygon mirror. Developing means for visualizing an electrostatic latent image formed by scanning light on the image carrier to form a toner image; transferring means for transferring the toner image on the image carrier to a transfer material; A fixing unit for fixing the toner image transferred to the material, wherein the period of the dot clock is slightly increased or decreased so that the period within a predetermined exposure range by the writing unit is within a predetermined time. Dot clock adjusting means for generating a signal having a predetermined number of pulses of the dot clock generated in the dot clock adjusting means, and the dot clock adjusted by the dot clock adjusting means to a plurality of different phases by a multi-stage delay line. A delay dot clock group is generated by extending the delay dot clock, and a delay dot clock for starting and ending the pulse width according to the pixel density data is selected from the delay dot clock group. An image forming apparatus comprising: a pulse width modulation unit that generates a modulated scanning lighting signal.

In this image forming apparatus, by slightly increasing or decreasing the period of the dot clock, a signal is generated in which the number of pulses generated within a predetermined time is a predetermined number. In other words, instead of finely adjusting the clock frequency, instead of changing the clock frequency itself, by sequentially selecting within a predetermined time delay signals whose phases are gradually changed finely, the number of pulses within a predetermined time can be predetermined. I try to match the number.

Further, since the starting point and the ending point of the PWM signal are selected from among the delay signals obtained by gradually changing the phase of the dot clock, the pulse width is accurately determined according to the image data.

As a result, when a dot clock whose phase gradually changes so that the number of pulses of the reference signal becomes a predetermined number within a predetermined time in one integrated circuit without using external components, an accurate It is possible to obtain a suitable PWM signal.

(2) A plurality of image carriers for each recording color for carrying an electrostatic latent image or a toner image,
A plurality of writing means for scanning the image carrier with scanning light deflected by a rotary polygon mirror, and developing an electrostatic latent image formed by the scanning light on the image carrier into a toner image An image forming apparatus comprising: a transfer unit configured to transfer a toner image on the image carrier to a transfer material; and a fixing unit configured to fix the toner image transferred to the transfer material. By slightly increasing or decreasing the period, a dot that matches the exposure range on the image carrier scanned by the reference writing unit with the exposure range on the image carrier scanned by another writing unit. A delay dot clock group is generated by delaying the dot clock adjusted by the clock adjustment unit and the dot clock adjustment unit to a plurality of different phases by a multi-stage delay line; Select delayed dot clock for start of the pulse width corresponding to the pixel density data from the group and end, and the pulse width modulating means for generating a pulse-width modulated scanning light-up signal by the delay dot clock,
An image forming apparatus comprising:

In this image forming apparatus, by slightly increasing or decreasing the period of the dot clock, the dot clock of another writing unit is generated so as to match the reference writing unit. That is, instead of finely adjusting the clock frequency and adjusting the clock frequency itself, without changing the clock frequency itself, the delay signals whose phases are gradually changed finely are sequentially selected within a predetermined time, so that the dot clock of the other writing means is selected. To the dot clock of the reference writing means.

Further, since the starting point and the ending point of the PWM signal are selected from the delay signals obtained by gradually changing the phase of the dot clock, the pulse width is accurately determined according to the image data.

As a result, when a dot clock whose phase gradually changes so that the number of pulses of the reference signal becomes a predetermined number within a predetermined time within one integrated circuit without using external components, an accurate It is possible to obtain a suitable PWM signal. Therefore, color shift in color image formation can be prevented.

The cycle corresponding to the difference between the exposure range on the image carrier scanned by the reference writing means and the exposure range on the image carrier scanned by the other writing means,
It is preferable that the amount by which the dot clock adjusting means increases or decreases the period of the dot clock supplied to another writing means is variable.

Further, the period of the dot clock is set to a value corresponding to the difference between the exposure range on the image carrier scanned by the reference writing means and the exposure range to be truly obtained. Is desirably increased or decreased.

(3) According to a fifth aspect of the present invention, there is provided an image carrier for carrying an electrostatic latent image or a toner image, and writing means for scanning the image carrier with scanning light deflected by a rotary polygon mirror. Developing means for visualizing an electrostatic latent image formed by scanning light on the image carrier to form a toner image; transferring means for transferring the toner image on the image carrier to a transfer material; A fixing unit for fixing the toner image transferred to the material, wherein the period of the dot clock is slightly increased or decreased so that the period within a predetermined exposure range by the writing unit is within a predetermined time. Dot clock adjusting means for generating a signal having a predetermined number of dot clock pulses generated in the writing means, and writing means for canceling the effect of increasing or decreasing the period of the dot clock supplied to the writing means. But A light amount adjusting means for adjusting the light quantity of the scanning light to an image forming apparatus comprising the.

In this image forming apparatus, by slightly increasing or decreasing the period of the dot clock, a signal is generated in which the number of pulses generated within a predetermined time is a predetermined number. In other words, instead of finely adjusting the clock frequency, instead of changing the clock frequency itself, by sequentially selecting within a predetermined time delay signals whose phases are gradually changed finely, the number of pulses within a predetermined time can be predetermined. I try to match the number.

Further, the light amount of the scanning light is changed so as to cancel out the effect of the dot clock whose period is changed by selecting the phase. As a result, when a dot clock whose phase gradually changes so that the number of pulses of the reference signal becomes a predetermined number within a predetermined time in one integrated circuit without using external components, an accurate image density can be obtained. Can be reproduced.

(4) The invention according to claim 6, wherein a plurality of image carriers for each recording color for carrying an electrostatic latent image or a toner image;
A plurality of writing means for scanning the image carrier with scanning light deflected by a rotary polygon mirror, and developing an electrostatic latent image formed by the scanning light on the image carrier into a toner image An image forming apparatus comprising: a transfer unit configured to transfer a toner image on the image carrier to a transfer material; and a fixing unit configured to fix the toner image transferred to the transfer material. By slightly increasing or decreasing the period, a dot that matches the exposure range on the image carrier scanned by the reference writing unit with the exposure range on the image carrier scanned by another writing unit. Clock adjusting means, and light amount adjusting means for adjusting the light amount of the scanning light emitted by the writing means so as to cancel out the effect of increasing or decreasing the period of the dot clock supplied to the writing means;
An image forming apparatus comprising:

In this image forming apparatus, by slightly increasing or decreasing the period of the dot clock, the dot clock of another writing unit is generated so as to match the reference writing unit. That is, instead of finely adjusting the clock frequency and adjusting the clock frequency itself, without changing the clock frequency itself, the delay signals whose phases are gradually changed finely are sequentially selected within a predetermined time, so that the dot clock of the other writing means is selected. To the dot clock of the reference writing means.

Further, the light amount of the scanning light is changed so as to cancel the influence of the dot clock whose period is changed by selecting the phase. As a result, when a dot clock whose phase gradually changes so that the number of pulses of the reference signal becomes a predetermined number within a predetermined time within one integrated circuit without using external components, an accurate color image can be obtained. It is possible to reproduce a high image density.

The cycle corresponding to the difference between the exposure range on the image carrier scanned by the reference writing means and the exposure range on the image carrier scanned by the other writing means,
It is preferable that the amount by which the dot clock adjusting means increases or decreases the period of the dot clock supplied to another writing means is variable.

Further, the period of the dot clock is set to a value corresponding to the difference between the exposure range on the image carrier scanned by the reference writing means and the exposure range to be truly obtained. Is desirably increased or decreased.

[0033]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an image forming apparatus according to the present invention will be described below in detail with reference to the drawings.

<Overall Configuration of Image Forming Apparatus> FIG. 2 is a configuration diagram showing an overall electrical configuration of an embodiment of the present invention. In FIG. 2, reference numeral 1 denotes an image carrier on which an image is formed; 200, a CPU serving as control means for generating a dot clock to be described later; 210, reflected light from a predetermined image formed on the image carrier 1. A reflection type sensor for reading the image signal and detecting a deviation; a Y exposure unit 250 for reading an image signal in accordance with a dot clock and outputting a laser beam having a power corresponding to the signal value of the image signal to the image carrier 1 Reference numeral 270 denotes an M exposure unit that reads out an image signal in accordance with a dot clock and outputs a laser beam having a power corresponding to the signal value of the image signal to the image carrier 1.
Reference numeral 90 denotes a C exposure unit that reads an image signal according to a dot clock and outputs a laser beam having a power corresponding to the signal value of the image signal to the image carrier 1. 310 reads an image signal according to the dot clock; A K exposure unit that outputs a laser beam having a power corresponding to a signal value of an image signal to the image carrier 1.

<Mechanical Overall Configuration of Image Forming Apparatus> FIG. 3 is a mechanical configuration diagram of a color image forming apparatus to which the image forming apparatus according to an embodiment of the present invention can be applied. The overall configuration of the color image forming apparatus will be described with reference to FIG.

It should be noted that the image forming apparatus of this embodiment is
This is a multicolor image forming apparatus. Here, Y (yellow),
A color image forming apparatus using four color toners of M (magenta), C (cyan) and K (black) will be described as an example.

First, an endless belt-shaped image carrier (photoconductor) 1 wound around an upper roller 3, a lower roller 5, and a horizontal roller 7
Is vertically stretched by the upper roller 3 and the lower roller 5, and is driven in the direction of arrow I in the figure.

Further, the image carrier 1 is pressed in the direction of the closed space formed by the image carrier 1 on the surface where the image carrier 1 moves upward from below, and the image carrier 1 is guided in the direction of the closed space. A pressing roller 9 is provided as guide means for performing the operation.

Above the surface on which the image carrier 1 moves upward, a cleaning means 11 is provided which is in sliding contact with the image carrier 1 and removes the developer on the image carrier 1. Below the cleaning unit 11, a collection box 21 as a collection unit for collecting the developer removed by the cleaning unit 11 is provided along the image carrier 1.

Next, the latent image forming means for forming a latent image on the image carrier 1 will be described. Since the image forming apparatus of the present embodiment is a four-color image forming apparatus, it has four latent image forming means for each color.

That is, a Y optical writing section 25 for forming a Y (yellow) latent image on the image carrier 1 using a laser beam and an M (magenta) M) optical writing section 27 for forming a latent image for
A C optical writing unit 31 for forming a C (cyan) latent image on the image carrier 1 using laser light; and a K (black) latent image on the image carrier 1 using laser light Is a K optical writing unit.

Next, the developing device will be described. Image carrier 1
Four developing devices for developing the electrostatic latent images of the respective colors formed thereon are provided. That is, a Y developing unit 42 for developing the latent image formed by the Y optical writing unit 25 and an M developing unit 43 for developing the latent image formed by the M optical writing unit 27
A C developing unit 45 for developing the latent image formed by the C optical writing unit 29; and a K developing unit 47 for developing the latent image formed by the K optical writing unit 31.

Further, the developing units 42, 43, 45, 47 of the respective colors
In response to the above, a band electrode of a charging unit for applying a charge to the image carrier 1 is provided. That is, the band electrode 61 for Y
A band electrode 63 for M, a band electrode 65 for C, and a band electrode 67 for K. Further, the charging means of each color of the present embodiment has grids 71, 73, 75, 77 for controlling the charging potential on the image carrier 1.

Reference numeral 81 denotes a paper feed unit, which is a transfer paper P as a transfer material.
Is provided in the cassette 83. The transfer paper P in the cassette 83 is carried out by the carry roller 85, nipped and carried by the carry roller pair 87 and the registration roller 88, and fed to the transfer means 91.

The transfer means 91 is provided with a transfer roller 92 maintained at a potential having a polarity different from that of the image carrier 1, and the transfer roller 92 cooperates with the horizontal roller 7 so as to sandwich the image carrier 1. Is provided.

A reference numeral 100 denotes a heat roller pair 101 sandwiched between
A fixing unit that applies heat and pressure to the transfer sheet P to fuse the toner to the transfer sheet P is provided. Reference numeral 110 denotes a pair of transfer rollers that pinch and transfer the transfer sheet P, which has been thermally fixed, to a discharge tray 111.

Reference numeral 120 denotes a paper feed path through which transfer paper P of another size conveyed from a paper feed unit provided outside the apparatus passes. Next, the overall operation of the image forming apparatus having the above configuration will be described. When the image carrier 1 is driven in the direction of arrow I, the charging means for Y including the band electrode 61 and the grid 71
The surface of the image carrier 1 has a predetermined charging potential.

Next, an electrostatic latent image is formed on the image carrier 1 by the Y optical writing section 25. Then, the Y developing device 42
The toner in the developer carried on the developing sleeve 55 moves onto the image carrier 1 due to the Coulomb force, and a toner image is formed on the image carrier 1.

The same operation is performed for the remaining colors, that is,
M, C, and K are performed, and Y, M, C, and
A K toner image is formed. On the other hand, the transfer paper P is fed from the paper feeding unit 81 to the transfer unit 91 by the transport roller 85 and the transport roller pair 87.

The fed transfer paper P is transferred to registration rollers 8.
8, after the timing is adjusted with respect to the toner image on the image carrier 1, the toner image is synchronously fed to the transfer unit 91, charged by the transfer roller 92 of the transfer unit 91, and the developer image on the image carrier 1 is The image is transferred to the transfer paper P.

Next, the transfer paper P is heated in the fixing unit 100,
The toner is pressed, the toner is fused to the transfer paper P, and is discharged onto the discharge tray 111 by the pair of transport rollers 110. Also,
Excess toner on the image carrier 1 after the transfer is removed by the blade 17 of the cleaning unit 11 and stored in the collection box 21.

<Optical Configuration of Image Forming Apparatus> The configuration of the optical writing unit is as shown in FIG. That is, based on the signal generated by the circuit unit 480, the LD4
70 emits light. The laser beam from the LD 470 passes through a collimator lens 491 and a cylindrical lens 492, and is scanned by a polygon mirror 493.
The light passes through the fθ lens 494 and the cylindrical lens 495 and is written on the image carrier 1. A part of the laser beam scanned by the polygon mirror is guided to the index sensor 412, and the timing is detected.

<Detailed Configuration of Image Forming Apparatus> Hereinafter, an embodiment of the image forming apparatus of the present invention will be described in detail. FIG. 1 shows the Y exposure unit 250 and the M exposure unit 2 described above.
The circuit configuration of each of the electrical exposure units 70, C exposure unit 290, and K exposure unit 310
It is a block diagram shown with 200 etc. Although only one exposure unit is shown in FIG. 1, it is assumed that equivalent units actually exist in each of Y, M, C, and K.

In FIG. 1, the dot clock generating section 410 and the PWM processing section 420 can be roughly classified. Hereinafter, the configurations of the dot clock generation unit 410 and the PWM processing unit 420 will be described in order.

The first delay chain unit 413 delays the input signal (the reference clock from the reference clock generation unit 411) to obtain a plurality of delay signals (first delay signal group: FIG. 1) having slightly different phases. This is a delay element group.

Here, the first delay chain section 413
It is preferable that the delay elements are cascade-connected in a chain shape so that the number of stages can be generated for two cycles of the reference clock for delay signals having slightly different phases.

The reference clock generator 411 may be built in each exposure unit, or a single reference clock generator 411 may distribute a reference clock to each exposure unit.

The index sensor 412 detects a reference position in scanning with a laser beam.
The synchronization detection unit 414 is a detection unit that receives the detection signal from the index sensor 412 and detects the number of stages (synchronization points) of the delay signal synchronized with the index signal in the first delay signal group (FIG. 1). The synchronization point information (FIG. 1) is output.

Here, in the first delay signal group (FIG. 1), the synchronization detecting section 414 firstly synchronizes the first synchronization point information SP1 with the index signal and secondly synchronizes with the index signal. Second synchronization point information SP
2 is preferably output.

The synchronization switching unit 415 includes a synchronization detection unit 41
4 and the synchronization point information from FIG.
A synchronization signal is obtained based on the frequency shift information (FIG. 1) from FIG. 1 and a select signal (FIG. 1) indicating which phase delay signal should be selected from the first delay signal group (FIG. 1).
Is output. The frequency deviation information will be described later.

The selector 416 receives the select signal (FIG. 1) from the synchronization switching unit 415 and selects a delay signal of a corresponding phase from the first delay signal group (FIG. 1).
It is output as a dot clock (FIG. 1).

As described above, by slightly increasing or decreasing the period of the dot clock, a signal is generated in which the number of pulses generated within a predetermined time is a predetermined number. In other words, instead of finely adjusting the clock frequency, instead of changing the clock frequency itself, by sequentially selecting within a predetermined time delay signals whose phases are gradually changed finely, the number of pulses within a predetermined time can be predetermined. I try to match the number.

The frequency divider 421 is a frequency divider that divides the dot clock by two. The frequency-divided dot clock is supplied to the second delay chain 422. The second delay chain unit 422 is configured to obtain a PWM signal to be obtained for a delayed signal (second delayed signal group: FIG. 1) having a slightly different phase.
It is preferable that the delay elements are cascade-connected in a chain shape so that the number of stages can generate a delay signal in a state finer than the signal.

The synchronization detecting section 423 is a detecting means for detecting the number of stages (synchronization points) of the delay signals synchronized with a predetermined time width in the second delay signal group (FIG. 1). 1) is output.

Note that, in this case, the synchronization detection unit 423 has a function of state detection for extracting two delayed signals having the same phase by using the detection signal from the index sensor 412 as a trigger, and a function of detecting the two delayed signals from these two delayed signals. The number of delay stages corresponding to one cycle of the dot clock is calculated and multiplied by a correction coefficient to obtain PW
And a function of calculating and correcting the number of delay stages to be converted into the number of delay stages for one cycle of the dot clock used for the M operation.

The PWM operation unit 424 includes a synchronization detection unit 423
A PWM operation is performed based on the synchronization point information (FIG. 1) from the image data and the second delay signal group (FIG. 1).
) To output a select signal (FIG. 1) indicating which phase of the two delay signals should be selected.

The selector 425 receives the select signal (FIG. 1) from the PWM operation unit 424, and, from the second delay signal group (FIG. 1), generates two delayed signals (FIG. 1) having phases corresponding to each other to generate a PWM signal. Select Fig. 1).

The PWM unit 426 is constituted by an exclusive-OR (ExOR) circuit which becomes an exclusive OR, and the like.
The two input delay signals (FIG. 1) are used as a start timing and an end timing, and a laser diode (L
D) Generate a PWM signal to drive 470. L
From D470, a laser beam pulse-width-modulated according to the value of the image signal is emitted toward the image carrier 1.

<Principle of Shift Detection> Here, the manner of shift detection will be briefly described with reference to FIG. Exposure units 250, 270, 290, 310 form an image of a predetermined pattern (here, a “F” -shaped pattern) on the end side of the image carrier in the main scanning direction. A pattern indicated by a solid line is formed on the image carrier, but it is assumed that a pattern indicated by a broken line was originally to be formed.

Here, a shift of dx occurs in the main scanning direction due to the aberration of the exposure unit and each optical system. In this case, while the image carrier is moved in the sub-scanning direction, the reading is performed by the reflection type sensor 210 disposed at the position where the pattern can be read, so that the distance Y from the horizontal line to the oblique line of the “F” -shaped pattern is obtained. 'Includes a shift of dy.

Assuming that the angle between the horizontal line and the oblique line is θ, d
x = dy / tan θ. Further, dy can be obtained from the moving speed of the image carrier in the sub-scanning direction and the difference between the reading times of the horizontal and oblique lines.

Therefore, by forming and reading such a predetermined pattern for each of the colors Y, M, C, and K, the CPU 200 allows the CPU 200 to determine the shift state (frequency shift information) related to the expansion and contraction of the image in the main scanning direction. Can be detected.

Further, at the same position in the sub-scanning direction,
By forming “F” -shaped patterns of the same shape on the start end side in the main scanning direction and on the end side in the main scanning direction, and by measuring the interval between the patterns, it is also possible to obtain the same state of misalignment of the image in the main scanning direction ( Frequency deviation information) can be detected.

In this manner, the CPU 200 performs the above-described detection processing to obtain the frequency shift information (FIGS. 1 and 2).
To the exposure unit. In the same manner, C
The PU 200 obtains image tip deviation information regarding the start position of the image in the main scanning direction by executing the detection of the “F” -shaped pattern at the start end side in the main scanning direction, and supplies this image tip deviation information to the exposure unit. It is also possible.

<Operation of Image Forming Apparatus> Next, the operation of the image forming apparatus of this embodiment will be described. Here, an example in which the present invention is applied to an image forming apparatus for forming images of four colors of Y, M, C, and K will be described.

The image forming apparatus using the image forming apparatus of the present embodiment includes a Y exposure unit 250, an M exposure unit 270, a C exposure unit 290, and a K exposure unit 310. An apparatus for forming an image of four colors during one rotation of the body, and an exposure unit and a photosensitive drum for each of Y, M, C, and K are provided.
An apparatus that forms an image by a pass corresponds to the apparatus.

That is, any image forming apparatus having a plurality of exposure units and in which color misregistration may occur even when the same reference clock is used, various image forming apparatuses other than the above-described type. It is possible to apply to.

<Operation Example> First, referring to the time chart of FIG. 6, the pulse of the reference clock is shifted every certain time by referring to the shift information for one specific color.
The operation of adjusting the number of pulses to a predetermined number and adjusting the time for generating the predetermined number of pulses to the predetermined time will be described up to the point where the dot clock is generated.

The shift information indicating the shift ER detected by the above-described formation and reading of the predetermined pattern, the clock cycle information of the clock cycle TC obtained from the frequency of the reference clock, and the number of pixels PH to be formed in the main scanning direction are shown. The information on the number of pixels per line is provided from the CPU 200 to the correction amount calculating means in the synchronization switching unit 415. Also, the first synchronization point information SP1 from the synchronization detection unit 414 and the second
From the synchronization point information SP2, the number of synchronization stages (the number of stages at which a delay of one cycle of the reference clock can be obtained) NS is obtained.

Here, the correction amount calculating means in the synchronization switching unit 415 obtains a correction count value (count load data) CC corresponding to the correction amount based on the following equation. CC = PH × (NS / TC) / ER This correction count value CC is for the switching count means in the synchronous switching unit 415 to count down and switch between the select signal and the lower-order select signal.
Therefore, the larger the correction amount, the smaller the correction count value CC.

Further, the synchronization detecting section 414 refers to the rise of the index signal from the index sensor 412, and uses the number of stages of the first delay chain section 413 which can obtain a delay signal synchronized with the rise of the index signal as synchronization point information. Ask.

Here, it is assumed that 20 has been obtained as the first synchronization point information SP1 and 50 has been obtained as the second synchronization point information SP2. In this case, the above-mentioned number NS of synchronization stages is 30.

Here, an index signal is generated at the timing when the index sensor detects the laser beam by scanning the laser beam of the exposure unit (FIG. 6).
(A)). Thereafter, H_V indicating the effective area in the horizontal direction
ALID becomes active.

Then, the switching counting means in the synchronization switching section 415 continues to repeatedly count down the correction count value CC in accordance with the reference clock. Then, every time the count value becomes 0 due to the countdown, the count data is given as an interrupt to the select signal calculation means 443 in the synchronization switching unit 415 (FIG. 6D to FIG. 6D).
(F)).

Further, the CPU 200 provides the shift direction information to the select signal calculating means in the synchronous switching unit 415, and performs "-correction" for performing a correction for reducing a shift extended in the main scanning direction, The information of “+ correction” for performing the correction for extending the contraction in the case of the contraction is given.
Here, the case of “−correction” is taken as an example.

It is assumed that the shift information ER and the shift direction information have been obtained by forming the above-described predetermined pattern and measuring the same. Here, ER = 6 ns, shift direction information =
It is assumed that “-correction” indicates that the image is corrected so as to be contracted because the image is stretched.

First, the synchronization detecting section 414 obtains the first synchronization point information SP1 and the second synchronization point information SP2 with reference to the rise of the index signal from the index sensor (not shown).

The first synchronization point information SP1 indicates the number of stages of the delay elements of the first delay chain unit 413 synchronized with the rise of the index signal, and the second synchronization point information SP2 is obtained from the first synchronization point information SP1. The number of stages of the delay element of the first delay chain unit 413 delayed by one cycle of the reference clock is shown.

Here, it is assumed that SP1 = 20 and SP2 = 50. FIG. 7 shows this state. Here, DL20 at the 20th stage (FIG. 7C) and this DL2
The 50th stage DL50 (FIG. 7 (m)) which is delayed by one clock cycle from 0 indicates the rising edge of the index signal (FIG. 7 (m)).
(A) shows a state of synchronization.

Next, the first synchronization point information SP1
And the second synchronization point information SP2 to determine the number NS of synchronization stages. Here, the synchronization stage number NS indicates how many stages of the delay element correspond to the delay time of one cycle of the reference clock. In the present embodiment, the number of synchronization stages NS =
NS = 30 from SP2-SP1.

The delay time DT of the delay element per stage is obtained from the NS and the period of the reference clock. For example, when the reference clock cycle TC is 30 ns, NS = 30, so that DT = 1 ns from DT = TC / NS. The delay time of the delay element per stage varies due to the temperature state of the integrated circuit, the fluctuation of the power supply voltage supplied to the integrated circuit, and the like. In some cases, the delay time is 1.5 ns or 0.5 ns. It is possible that However, the reference clock period TC
Since does not change, by calculating the number of synchronization stages NS,
The delay time of the delay element per stage at the time of measurement can be accurately obtained.

Then, in order to obtain an appropriate image signal, a correction count value CC indicating how many stages of the delay element are to be finally shifted is shifted by the shift information ER, the shift direction information and the delay time D.
Obtain from T. Here, ER = 6 ns, shift direction information = “− correction”, and DT = 1 ns, the correction count value CC
= −6.

In order to obtain an appropriate image signal from the above-mentioned correction count value CC, the number of stages of the delay element must be finally six.
You only have to step forward. That is, first, the signal from the 50th stage delay element is employed in synchronization with the rising edge of the index signal, and thereafter, in synchronization with the select signal, the 49th stage, 48th stage, 47th stage, 46
The signals in the 45th and 45th stages are sequentially replaced and adopted.
Finally, the signal from the 44th stage may be adopted.

When the correction amount is larger than the number of synchronization stages, the select signal may be circulated. In the above example, SP1 = 20, SP2 = 50, and the number of synchronization stages is 30.
In the case of “−correction” in the case of
.., 21, 20, when the select signal 20
, And 50 of the select signal have the same phase. That is, 50, 49,
.., 21, 20 (= 50), 49, 48. Also, in the “+ correction”, the select signal may be similarly circulated.

Also, 50, 47, 43,..., 22, 19
If "-correction" is performed three steps at a time, SP1 will exceed 20, but after 19, 50- (20-1)
9) -3 = 46. That is, by circulating in a state where the amount exceeding the synchronization point and one correction amount are added, circulation can be performed without any problem.

In the selector 416 receiving such a select signal, the first delay chain 413
From the delay signal group (FIG. 1), the 50th stage, the 49th stage,
The selection is made as in the 48th, 47th,... And output as a dot clock (FIG. 6 (g)).

In this case, from the first delay signal group (FIG. 1), the 50th, 49th, 48th, 47th,.
As a result, a delay signal synchronized with the index signal is obtained at first, and a delay signal having a gradually reduced delay (advanced phase) is obtained. As a result, “−correction” is realized, and correction is performed to reduce the displacement extending in the main scanning direction.

In the case of “+ correction”, the first synchronization point information SP1 is used as an initial value, and the 20th, 21st, 22nd, and 22nd stages are selected from the first delay signal group (FIG. 1). 23
By selecting the stages,..., A delay signal synchronized with the index signal is obtained at first, and a delay signal with a gradually reduced delay (phase delay) is obtained. As a result, "+ correction"
Is realized, and a correction is performed so as to extend the displacement shrunk in the main scanning direction.

That is, the pulse of the reference clock is shifted every certain time with reference to the shift information so that the number of pulses becomes a predetermined number, and the time for generating this predetermined number of pulses becomes the predetermined time. Such adjustments can be made.

Since the above correction is performed based on the shift information ER (frequency shift information), the length in the main scanning direction is accurately adjusted. FIG. 8 schematically shows the state of the expansion / contraction correction in the main scanning direction (that is, main scanning magnification correction). Here, a reference clock, a delay signal (1 to 9 delays) obtained by delaying the reference clock, and a dot clock are shown.

In the case shown in FIG. 8, by selecting one delay, two delays, three delays, and five delays during four periods of the reference clock, a 3.5 dot clock is generated in four periods. That is, 3.5 / 4 = 87.5%, and control is performed such that the frequency is reduced in a pseudo manner. Note that similar results can be obtained by executing other selection methods.

In the case of FIG. 8, since the eight delays have the same phase as the reference clock, by selecting eight delays, seven delays, six delays, and four delays during four cycles of the reference clock, The period becomes 4.5 dot clocks (not shown). That is, 4.5 / 4 = 112.5%, and control is performed such that the frequency is increased in a pseudo manner. Note that similar results can be obtained by executing other selection methods.

By the way, the dot clocks generated as described above have the same length in the main scanning direction, but the period of the dot clocks increases or decreases stepwise during one scanning line period as described above. Therefore, when a PWM signal is created with a triangular wave and an image signal using a circuit as shown in FIG.
A phenomenon occurs in which an accurate pulse width cannot be obtained (see FIG. 13). As a result, even if the image data has the same pixel density, a portion where the width of the PWM signal is different occurs.

Therefore, the PWM processing section 420 obtains an accurate PWM signal corresponding to the image data.
First, the frequency divider 421 divides the frequency of the dot clock by two to generate a signal having a period twice as long as the period. This is because the PWM unit 426, which will be described later, uses the ExOR logic of the two delayed signals to generate a PWM signal, so that the cycle needs to be doubled.

Then, the second delay chain unit creates a second delay signal group from the dot clock divided by two. Note that the synchronization point information of the synchronization detection unit 423 means the number of synchronization stages (the number of stages of the delay signal that matches the time interval of the pulse width of 100% in the PWM signal).

The PWM calculation section 424 performs a PWM calculation based on the synchronization point information (FIG. 1) from the synchronization detection section 423 and the image data, and performs a PWM calculation in the second delay signal group (FIG. 1). Then, in order to determine the start point and the end point of the rising (or falling) of the PWM signal, a select signal (FIG. 1) indicating which phase of the two delayed signals should be selected is output.

The selector 425 receives the select signal (FIG. 1) from the PWM operation unit 424, and selects a phase corresponding to a PWM signal from among a plurality of delay signals of the second delay signal group (FIG. 1). Select two delayed signals (FIG. 1).

Then, exclusive OR (ExOR)
The PWM unit 426 composed of a circuit or the like
The PWM signal is generated using the two delay signals (FIG. 1) selected in 5 as start timing and end timing.

FIG. 9 schematically shows how the PWM signal is generated by the exclusive OR in the PWM section 426. Here, the reference clock, a delay signal (1 delay to 9 delay) obtained by delaying the reference clock, and PWM
Signals.

In the case shown in FIG. 9, a dot clock is selected as a start point of a PWM signal, and a delay signal rising with a pulse width to be obtained as an end point is selected. A desired PWM signal is obtained by an exclusive OR of these two selected delay signals. In FIG. 9, 4 of 12.5%, 25%, 50%, and 100%
It shows how to generate different types of PWM signals.

Here, the fact that the width of the PWM signal does not change even if the period of the dot clock changes will be described with reference to FIG. FIG. 10 is the same as FIG. 8 described above with respect to how the dot clock is generated from the reference clock. That is, by selecting one delay, two delays, three delays, and five delays during four periods of the reference clock, a 3.5 dot clock is obtained in four periods.

Here, assuming that the number of synchronization stages of the reference clock as the original oscillation is 100, 1
The number of stages for generating the 00% PWM signal is reduced to 98 stages, which is slightly smaller than 100 stages, so that the PWM calculation section 424
Set in. The reason why the number of stages of the 100% PWM signal is made smaller than the number of synchronization stages is that it is assumed that the cycle of the dot clock is shorter than the cycle of the reference clock when the exposure range is narrowed. . Also,
To generate a 50% PWM signal, 98 × (5
(0/100) = 49 stages, and the selector 425 outputs the second
The 0 stage and the 49 stage are selected from the delay signal group, and the PWM unit 4
26 outputs a 50% PWM signal.

As described above, since the number of synchronization stages having a fixed period is used for the PWM operation, even if the period of the dot clock is different, the PWM is not changed.
The pulse width of the signal is not affected, and the density of the image is not adversely affected. When the dot clock cycle is different, the position of the PWM signal is only slightly shifted.

As described above, in the image forming apparatus of the present embodiment, by slightly increasing or decreasing the period, it is possible to generate a dot clock with a predetermined number of pulses generated within a predetermined time. Since the starting point and the ending point of the PWM signal corresponding to the image data are selected from the delay signals obtained by gradually changing the phase of the dot clock, the pulse width is accurately determined according to the image data.

As a result, even when a dot clock whose phase gradually changes so that the number of pulses of the reference signal becomes a predetermined number within a predetermined time in one integrated circuit without using external parts, An accurate PWM signal can be obtained for each dot.

In the image forming apparatus of the present embodiment, the main scanning length may be independently adjusted to be constant for each of the colors Y, M, C, and K, or any of the colors may be adjusted. Other colors may be adjusted with reference to. In addition, after adjusting so that the length of the main scan is constant for one of the reference colors,
Other colors may be matched to the reference color.

<Detailed Configuration of Image Forming Apparatus> Hereinafter, a second embodiment of the image forming apparatus of the present invention will be described in detail. This embodiment shows a configuration in which the light amount is changed in real time so as to cancel out the density change due to the increase and decrease of the period of the dot clock.

In FIG. 11, a dot clock generating section 410 and a light intensity modulating section 430 can be roughly classified. The dot clock generator 410 is the same as that of the first embodiment, and a description thereof will be omitted.

The light intensity modulator 430 includes a phase adjustment amount detector 431, an image data corrector 432, and a D / A converter 43.
3, an amplifier 434, an LD driver 435, a laser diode (LD), and a photodiode (PD).

<Operation of Image Forming Apparatus> Here, the phase adjustment amount detecting section 431 selects the select signal (FIG. 1) output from the synchronization switching section 415 of the dot clock generating section 410.
1: a signal indicating which phase of the delay signal should be selected from the first delay signal group (FIG. 11));
With reference to the synchronization point information from 14, it is detected how much the phase has been adjusted. For example, if the N-th delay stage number is selected as the immediately preceding dot clock and the (N + 2) -th delay stage number is selected as the next dot clock, the phase adjustment amount is + 2 / M. Here, M is the number of delay stages corresponding to one cycle of the reference clock.

The image data correction unit 432 adds or multiplies the phase adjustment amount of the dot clock detected by the phase adjustment amount detection unit 431 to the image data, thereby detecting the density change in accordance with the period variation of the dot clock. The image data is corrected in the erasing direction.

The image data corrected according to the period variation of the dot clock as described above is converted into an analog signal by the D / A converter 433 together with the dot clock (FIG. 11). The analog signal is amplified by the amplifier 434, and an LD drive unit 435 generates an LD drive current for driving the laser diode LD. Note that the LD driving unit 435 controls the light emission amount of the laser diode LD to a predetermined value based on the detection output of the photodiode PD.

That is, in this image forming apparatus, the dot clock generation section 410 generates a signal in which the number of pulses generated within a predetermined time is made a predetermined number by slightly increasing or decreasing the period of the dot clock. In this case, the light intensity modulation unit 430 changes the light amount of the scanning light so as to cancel out the effect of the dot clock whose period has been changed.

As a result, when a dot clock whose phase gradually changes so that the number of pulses of the reference signal becomes a predetermined number within a predetermined time within one integrated circuit without using external components, an accurate It is possible to reproduce a high image density.

<Other Embodiments> In the above-described first embodiment and the second embodiment, a four-color image forming apparatus having four writing units has been described. However, a similar process can be performed for at least two colors to eliminate color misregistration. Further, the present invention can be used for an image forming apparatus having more writing units.

[0126]

As described above, according to the present invention, the following effects can be obtained. (1) According to the first aspect of the invention, a signal in which the number of pulses generated within a predetermined time is set to a predetermined number is generated by slightly increasing or decreasing the period of the dot clock. In other words, instead of finely adjusting the clock frequency, instead of changing the clock frequency itself, by sequentially selecting within a predetermined time delay signals whose phases are gradually changed finely, the number of pulses within a predetermined time can be predetermined. I try to match the number. Further, since the starting point and the ending point of the PWM signal are selected from the delay signals obtained by gradually changing the phase of the dot clock, the pulse width is accurately determined according to the image data. As a result, when a dot clock whose phase gradually changes so that the number of pulses of the reference signal becomes a predetermined number within a predetermined time in one integrated circuit without using external components, an accurate PWM signal is generated. Can be obtained.

(2) According to the second aspect of the invention, by slightly increasing or decreasing the period of the dot clock, the dot clock of another writing unit is generated so as to match the writing unit serving as a reference. I have to. That is, instead of fine-tuning and adjusting the clock frequency,
The clock frequency itself is not changed, and the delay signal whose phase is gradually changed finely is sequentially selected within a predetermined time so that the dot clock of the other writing unit is adjusted to the dot clock of the reference writing unit. I have. Furthermore, PW is selected from the delay signals obtained by gradually changing the phase of the dot clock.
Since the start point and end point of the M signal are selected, the pulse width is accurately determined according to the image data. As a result, when a dot clock whose phase gradually changes so that the number of pulses of the reference signal becomes a predetermined number within a predetermined time in one integrated circuit without using external components, an accurate PWM signal is generated. Can be obtained. Therefore, color shift in color image formation can be prevented.

(3) According to the fifth aspect of the present invention, a signal in which the number of pulses generated within a predetermined time is set to a predetermined number is generated by slightly increasing or decreasing the period of the dot clock. In other words, instead of finely adjusting the clock frequency, instead of changing the clock frequency itself, by sequentially selecting within a predetermined time delay signals whose phases are gradually changed finely, the number of pulses within a predetermined time can be predetermined. I try to match the number. Further, the light amount of the scanning light is changed so as to cancel out the effect of the dot clock in which the cycle is changed by selecting the phase. As a result, when a dot clock whose phase gradually changes so that the number of pulses of the reference signal becomes a predetermined number within a predetermined time in one integrated circuit without using external components, an accurate image density can be obtained. Can be reproduced.

(4) According to the sixth aspect of the invention, by slightly increasing or decreasing the period of the dot clock, the dot clock of another writing unit is generated so as to match the writing unit serving as a reference. I have to. That is, instead of fine-tuning and adjusting the clock frequency,
The clock frequency itself is not changed, and the delay signal whose phase is gradually changed finely is sequentially selected within a predetermined time so that the dot clock of the other writing unit is adjusted to the dot clock of the reference writing unit. I have. Further, the light amount of the scanning light is changed so as to cancel out the effect of the dot clock in which the cycle is changed by selecting the phase. As a result, when a dot clock whose phase gradually changes so that the number of pulses of the reference signal becomes a predetermined number within a predetermined time within one integrated circuit without using external components, an accurate color image can be obtained. It is possible to reproduce a high image density.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an electrical configuration of a main part of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a configuration diagram illustrating an electrical configuration of the image forming apparatus according to the embodiment of the present invention;

FIG. 3 is a configuration diagram illustrating a mechanical configuration of an image forming apparatus to which the image forming apparatus according to the embodiment of the present invention is applied;

FIG. 4 is a perspective view showing a mechanical configuration of a main part of the image forming apparatus according to the embodiment of the present invention.

FIG. 5 is an explanatory diagram showing a state of displacement detection.

FIG. 6 is a time chart illustrating an operation state of the image forming apparatus according to the embodiment of the present invention.

FIG. 7 is a time chart illustrating an operation state of the image forming apparatus according to the embodiment of the present invention.

FIG. 8 is a time chart for explaining an operation state of the image forming apparatus according to the embodiment of the present invention;

FIG. 9 is a time chart illustrating an operation state of the image forming apparatus according to the embodiment of the present invention.

FIG. 10 is a time chart illustrating an operation state of the image forming apparatus according to the embodiment of the present invention.

FIG. 11 is a block diagram illustrating a configuration of an image forming apparatus according to a second embodiment of the present invention.

FIG. 12 is a block diagram illustrating a configuration of a conventional image forming apparatus.

FIG. 13 is a time chart illustrating an operation state of a conventional image forming apparatus.

[Description of Signs] 200 CPU 210 Reflective sensor 250, 270, 290, 310 Exposure unit 410 Dot clock generator 411 Reference clock generator 412 Index sensor 413 First delay chain unit 414 Synchronization detector 415 Synchronization switch 416 Selector 420 PWM processing section 421 Frequency dividing section 422 Second delay chain section 423 Synchronization detecting section 424 PWM calculating section 425 Selector 426 PWM section

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) H04N 1/113 H04N 1/04 D 5C071 / 23 103 104A (72) Inventor Mitsuo Higashii Ishikawa, Hachioji-shi, Tokyo 2970, Town Konica Corporation F-term (Reference) 2C362 AA10 BA04 BA50 BA52 BA68 CA09 CA22 CA39 2H027 DA32 DA50 DE07 EB04 EB06 ED04 EE01 EF09 HB07 ZA07 2H030 AA01 AA02 AB02 AD17 BB13 BB16 BB23 BB24 ABB023 BA19 HA02 HA13 HB06 HB08 QA14 QA17 UA18 XA05 5C074 AA10 BB02 BB03 BB26 CC22 CC26 DD07 DD15 DD24 EE06 FF15 GG09 GG12

Claims (8)

[Claims] An image carrier for carrying an electrostatic latent image or a toner image; writing means for scanning the image carrier with scanning light deflected by a rotary polygon mirror; and a scanning light on the image carrier. Developing means for visualizing the electrostatic latent image formed in the step to form a toner image, transferring means for transferring the toner image on the image carrier to a transfer material, and fixing the toner image transferred to the transfer material An image forming apparatus comprising: Dot clock adjusting means for generating a predetermined number of signals; and a delay dot by delaying the dot clock adjusted by the dot clock adjusting means to a plurality of different phases by a multi-stage delay line A lock group is generated, a delay dot clock for starting and ending a pulse width according to pixel density data is selected from the delay dot clock group, and a scan lighting signal pulse width modulated by the delay dot clock. An image forming apparatus comprising: 2. A plurality of image carriers for each recording color carrying an electrostatic latent image or a toner image, and a plurality of writing means for scanning the image carrier with scanning light deflected by a rotary polygon mirror.
Developing means for visualizing an electrostatic latent image formed by scanning light on the image carrier to form a toner image; transfer means for transferring the toner image on the image carrier to a transfer material; Fixing means for fixing the toner image transferred to the image carrier, the image carrier being scanned by the reference writing means by slightly increasing or decreasing the period of the dot clock. Dot clock adjusting means for matching the upper exposure range with the exposure range on the image carrier scanned by another writing means, and a plurality of different dot clocks adjusted by the dot clock adjusting means by a multi-stage delay line. A delay dot clock group is generated by delaying to a phase, and a delay dot for starting and ending a pulse width corresponding to pixel density data is generated from the delay dot clock group. Select lock, an image forming apparatus characterized by comprising a pulse width modulating means for generating a pulse-width modulated scanning light-up signal by the delay dot clock. 3. The method according to claim 1, wherein the exposure range on the image carrier scanned by the reference writing unit and the exposure range on the image carrier scanned by another writing unit are different from each other at a period corresponding to a difference. 3. The image forming apparatus according to claim 2, wherein the amount by which the dot clock adjusting unit increases or decreases the period of the dot clock supplied to the writing unit is variable. 4. The dot clock adjusting means, wherein the cycle of the dot clock is a cycle corresponding to the difference between the exposure range on the image carrier scanned by the reference writing means and the exposure range to be truly obtained. The image forming apparatus according to claim 2, wherein the value increases or decreases. 5. An image carrier for carrying an electrostatic latent image or a toner image, writing means for scanning the image carrier with scanning light deflected by a rotary polygon mirror, and scanning light on the image carrier. Developing means for visualizing the electrostatic latent image formed in the step to form a toner image, transferring means for transferring the toner image on the image carrier to a transfer material, and fixing the toner image transferred to the transfer material An image forming apparatus comprising: Dot clock adjusting means for generating a predetermined number of signals; and adjusting the amount of scanning light emitted by the writing means so as to cancel out the effect of increasing or decreasing the period of the dot clock supplied to the writing means. An image forming apparatus comprising: the light amount adjusting means. 6. A plurality of image carriers for each recording color carrying an electrostatic latent image or toner image, and a plurality of writing means for scanning the image carrier with scanning light deflected by a rotating polygon mirror.
Developing means for visualizing an electrostatic latent image formed by scanning light on the image carrier to form a toner image; transfer means for transferring the toner image on the image carrier to a transfer material; Fixing means for fixing the toner image transferred to the image carrier, the image carrier being scanned by the reference writing means by slightly increasing or decreasing the period of the dot clock. Dot clock adjusting means for matching the above exposure range with the exposure range on the image carrier scanned by another writing means, and the effect of increasing or decreasing the period of the dot clock supplied to the writing means. An image forming apparatus, comprising: light amount adjusting means for adjusting the light amount of the scanning light emitted by the writing means so as to erase the light. 7. An image processing apparatus according to claim 1, wherein the exposure range on the image carrier scanned by the reference writing unit and the exposure range on the image carrier scanned by another writing unit are different from each other at a period corresponding to a difference. 7. The image forming apparatus according to claim 6, wherein the amount by which the dot clock adjusting unit increases or decreases the period of the dot clock supplied to the writing unit is variable. 8. The dot clock adjusting means, wherein a cycle of a dot clock is set to a cycle corresponding to a difference between an exposure range on an image carrier scanned by a reference writing means and an exposure range to be truly obtained. The image forming apparatus according to claim 6, wherein is increased or decreased.