JP2000318211A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce displacement of the record starting position by generating a record starting signal for determining the sub scanning direction of a photosensitive surface, receiving a scanning light beam so as to generate a main scanning synchronous signal, detecting the time lag therebetween, and polarizing all of a plurality of light beams simultaneously in the sub scanning direction according to the detected signal. SOLUTION: When a record starting signal is inputted from a record starting signal detecting means 20 as well as a main scanning synchronous signal is inputted from a light receiving element 18 so that the record starting signal is detected by the record starting signal detecting means 20, a time lag detecting means 21 calculates the time lag with respect to the main scanning synchronous signal and inputs the same into a sub scanning polarization signal generating means 22. Moreover, a vertical resist signal from a vertical resist (record starting position) detecting means 19 is inputted to the sub scanning polarization signal generating means 22. Then, according to the time lag signal from the time lag detecting means 21, a sub scanning polarization signal for having the time lag between the record starting signal and the main scanning synchronous signal to be zero is generated so as to correct the vertical resist amount to be zero and output the same to a sub scanning polarization means 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a laser printer, a digital copying machine, a facsimile, etc., which records an image with a plurality of light beams.

[0002]

2. Description of the Related Art Conventionally, an image forming apparatus for recording an image on a photoreceptor using a plurality of light beams includes a laser printer, a digital copying machine, a facsimile, etc., for forming a monochromatic image.
There are a laser printer, a digital copying machine, a facsimile, and the like for forming a color image. Japanese Patent Application Laid-Open No. 8-142412 discloses that a multi-beam scanning optical system scans a plurality of light beams from a plurality of light sources in a main scanning direction by a scanning unit and irradiates a photoconductor moving in a sub-scanning direction. In an image forming apparatus that exposes the photosensitive member at a time with a plurality of light beams in the sub-scanning direction and records an image, the inter-page and color intervals generated when the main scanning synchronization signal and the recording start signal are asynchronous are generated. A recording start signal generating means for generating a recording start signal for determining a recording start position in the sub-scanning direction on the photoconductor in order to reduce the deviation of the vertical resist (the deviation of the recording start position in the sub-scanning direction); Main scanning synchronizing signal generating means arranged within a scanning range of the scanning means for receiving a scanning light beam from the scanning means and generating a main scanning synchronizing signal; Detecting means for detecting a time difference between a signal and a recording start signal from the recording start signal generating means, and light source selecting means for selecting a light source used for image recording of the first first line according to the signal from the detecting means Are described.

[0003]

In an image forming apparatus such as a laser printer, a digital copying machine, and a facsimile which forms a single-color image, a photosensitive member driving means for generating a recording start signal by a recording start signal generating means. And the scanning means such as a rotary polygon mirror of a multi-beam scanning optical system that determines the timing of generating the main scanning synchronization signal are not synchronized. Therefore, the time relationship between the recording start signal and the main scanning synchronization signal is always (1
(Every time image recording is performed).

[0006] For example, between the timing as in case 1 shown in FIG. 6 and the timing as in case 2 shown in FIG. 6, the recording start position in the sub-scanning direction of the image actually recorded (written) on the photosensitive member. (Vertical resist) has a displacement d as shown in FIG. In FIG. 6, LD1,
LD2 indicates a semiconductor laser which is a light source of the multi-beam scanning optical system, and a hatched circle in FIG.
1 shows a light beam from LD2. Further, t1 and t2 indicate a time difference between the recording start signal and the main scanning synchronization signal.

The maximum value of the deviation d corresponds to one scanning of the light beam, and when there are two light beams, the recording pitch p
Is twice as large as This shift d increases with an increase in the number of light beams from a plurality of light sources of the multi-beam scanning optical system. In particular, in an image forming apparatus such as a laser printer, a digital copying machine, and a facsimile that form a color image using a multi-beam scanning optical system, each time an image of each color is written on the photoconductor, the deviation d fluctuates. When a color image is formed by superimposing images of each color, image deterioration such as color shift occurs.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus capable of reducing the displacement of a vertical resist between pages when forming a monochromatic image and the color displacement between colors when forming a color image.

[0007]

According to a first aspect of the present invention, a plurality of light beams from a plurality of light sources are scanned in a main scanning direction by a scanning unit and moved in a sub-scanning direction. In an image forming apparatus that irradiates a photosensitive surface to be exposed with a plurality of light beams at a time in the sub-scanning direction in the sub-scanning direction to record an image, a recording start position is determined on the photosensitive surface in the sub-scanning direction. Recording start signal generating means for generating a signal, main scanning synchronizing signal generating means arranged within a scanning range of the scanning means for receiving a scanning light beam from the scanning means and generating a main scanning synchronizing signal; Detecting means for detecting a time difference between a main scanning synchronizing signal from the scanning synchronizing signal generating means and a recording start signal from the recording start signal generating means; and a plurality of light sources from the plurality of light sources according to the signal from the detecting means. Those having the subscanning deflecting means for deflecting all light beams simultaneously in the sub-scanning direction.

According to a second aspect of the present invention, in the image forming apparatus of the first aspect, the sub-scanning deflecting means is a galvanomirror disposed between the plurality of light sources and the scanning means.

According to a third aspect of the present invention, in the image forming apparatus of the first aspect, the sub-scanning deflecting means is an electro-optic effect element disposed between the plurality of light sources and the scanning means. is there.

[0010]

FIG. 2 schematically shows a first embodiment of the present invention. The first embodiment is an embodiment of the invention according to claims 1 and 2, and is an example of a color image forming apparatus for forming a color image on a transfer material. This first embodiment is:
The image forming apparatus includes an image forming station 1 for forming a color image, and a transfer charger 3 as a transfer unit for transferring the color image formed by the image forming station 1 to a transfer sheet 2 as a transfer material. The image forming station 1 includes a photoconductor 4, a charging charger 5 as a charging unit, a multi-beam scanning optical system 6, a developing device 7, a cleaning device 8, and the like.

The photosensitive member 4 uses, for example, a photosensitive drum, but may use a photosensitive belt or the like. As the developing device 7, for example, a rotary developing device having a plurality of developing devices is used.
The plurality of developing units are, for example, a Y developing unit 7 for developing an electrostatic latent image on the photosensitive drum 4 into a yellow (hereinafter referred to as Y) image.
Y, an M developing unit 7M for developing the electrostatic latent image on the photosensitive drum 4 into a magenta (hereinafter referred to as M) image, and C for developing the electrostatic latent image on the photosensitive drum 4 into a cyan (hereinafter referred to as C) image
The developing unit 7C includes a K developing unit 7K for developing the electrostatic latent image on the photosensitive drum 4 into a black (hereinafter, referred to as K) image.

The rotary developing device 7 includes developing devices 7Y, 7M,
A developing device that performs development among 7C and 7K is rotationally driven by a developing device driving unit (not shown) so as to move to a developing position. The photoreceptor drum 4 is driven to rotate clockwise by a photoreceptor driving unit (not shown), and after being uniformly charged by the charger 5, a plurality of light beams modulated by, for example, a Y image signal by the multi-beam scanning optical system 6. The beam is scanned in the main scanning direction and exposed, thereby forming an electrostatic latent image and recording a Y image (hereinafter referred to as “writing”). The electrostatic latent image on the photosensitive drum 4 is transferred to a Y developing unit 7Y.
To develop a Y image.

Next, the photosensitive drum 4 passes through the transfer charger 3 and the cleaning device 8 as it is, is uniformly charged again by the charging charger 5, and is modulated by the multi-beam scanning optical system 6 with M image signals. The light beam is scanned in the main scanning direction and exposed to form an electrostatic latent image superimposed on the Y image, and the M image is written. The electrostatic latent image on the photosensitive drum 4 is developed by an M developing unit 7M to become an M image.

Next, the photosensitive drum 4 passes through the transfer charger 3 and the cleaning device 8 as it is, is uniformly charged again by the charging charger 5, and is modulated by the multi-beam scanning optical system 6 with a C image signal. By scanning in the main scanning direction with the light beam and exposing, an electrostatic latent image is formed over the Y image and the M image, and the C image is written. The electrostatic latent image on the photosensitive drum 4 is developed by a C developing device 7C to become a C image.

Further, the photosensitive drum 4 passes through the transfer charger 3 and the cleaning device 8 as it is and is uniformly charged again by the charging charger 5, and is modulated by the multi-beam scanning optical system 6 with the K image signal. Scanning in the main scanning direction by a light beam and exposing Y
Image, M image, and C image are overlaid to form an electrostatic latent image
The image is written. The electrostatic latent image on the photosensitive drum 4 is developed by the K developing unit 7K to become a K image, and a full-color image including a Y image, an M image, a C image, and a K image is formed.

On the other hand, transfer paper 2 is fed from a paper feeding device (not shown), and a full-color image on the photosensitive drum 4 is transferred by the transfer charger 3 on the transfer paper 2 and the full-color image is fixed by a fixing device (not shown). After being discharged. The photosensitive drum 4 is cleaned by the cleaning device 8 after the transfer of the full-color image.

FIG. 3 shows the configuration of the multi-beam scanning optical system 6. The multi-beam scanning optical system 6 includes a light source unit 9 having a plurality of light sources that generate a plurality of light beams that can be independently modulated, for example, two light beams, a cylindrical lens 10, and a galvanometer mirror 1 as a sub-scanning deflection unit.
1. Rotating polygon mirror 12 as scanning means, fθ lens 13
Imaging system composed of a long lens 14 and a folded lens 1
5, a mirror 16, a lens 17, a light receiving element 18 as a main scanning synchronization signal generating means, a vertical registration detecting means 19, and a recording start signal detecting means 20. The recording start signal detecting means 20 includes a disk 20a having a slit and connected to the photosensitive drum 4, and a photo interrupter 20b for detecting a slit on the disk 20a. The rotary polygon mirror 12 is driven to rotate by a motor (not shown).

Each light source of the light source unit 9 is independently modulated by an image signal by a modulation means (not shown) to emit a light beam modulated by the image signal.
Are deflected and scanned in the main scanning direction by a rotating polygon mirror 12 via a cylindrical lens 10 and a galvanometer mirror 11. A plurality of scanning light beams from the rotary polygon mirror 12 are irradiated on the photosensitive drum 4 via an imaging system including an fθ lens 13 and a long lens 14 and a folding lens 15.

After the photosensitive drum 4 is uniformly charged by the charging charger 5, the photosensitive drum 4 is scanned in parallel with the main scanning direction by a plurality of scanning light beams from the folding lens 15 and is exposed, so that a plurality of photosensitive drums 4 are arranged in the sub-scanning direction. Is exposed at one time by the scanning light beam, and is moved two-dimensionally in the sub-scanning direction by rotational driving by a photoconductor driving unit (not shown) at the exposure position to form an electrostatic latent image. Also,
The light receiving element 18 receives the scanning light beam from the rotary polygon mirror 12 via the fθ lens 13, the mirror 16, and the lens 17, and generates a main scanning synchronization signal.

The disk 20a having the slit rotates in conjunction with the photosensitive drum 4, and the photo interrupter 20b detects the slit on the disk 20a and generates a recording start signal. The vertical registration detecting unit 19 receives the scanning light beam from the rotary polygon mirror 12 through an imaging system including the fθ lens 13 and the long lens 14 and the folding lens 15 and receives a vertical registration (recording start position in the sub-scanning direction). ) Is detected, and a vertical registration signal indicating the vertical registration is output.

As shown in FIG. 1, the time difference detecting means 21
Is the photo interrupter 2 of the recording start signal detecting means 20.
0b, a main scanning synchronization signal is input from the light receiving element 18 as a main scanning synchronization signal generating means, and when the recording start signal detecting means 20 detects the recording start signal, the recording start signal and A time difference from the main scanning synchronizing signal from the main scanning synchronizing signal generating means 18 is calculated, and a time difference signal indicating the time difference is calculated by the sub-scanning deflection signal generating means 2.
Enter 2 Further, a vertical registration signal from the vertical registration detection unit 19 is input to the sub-scanning deflection signal generation unit 22.

The sub-scanning deflection signal generating means 22 generates a sub-scanning deflection signal based on the time difference signal from the time difference detecting means 21 so that the time difference between the recording start signal and the main scanning synchronization signal becomes zero. Signal for vertical resist detection 1
The vertical registration signal corresponding to the deviation of the recording start position in the sub-scanning direction is corrected by the vertical registration signal from the sub-scanner 9 to zero, and is output to the galvanomirror 11 as the sub-scanning deflection / deflection means.

The galvanomirror 11 is driven and rotated by the sub-scanning deflection signal from the sub-scanning deflection signal generating means 22, and outputs a plurality of light beams from the cylindrical lens 10 with the time difference between the recording start signal and the main scanning synchronization signal. Becomes zero and the vertical registration amount corresponding to the shift of the recording start position in the sub-scanning direction becomes zero. Therefore, the time difference between the recording start signal and the main scanning synchronization signal (the time difference t1 or t2 shown in FIG. 6) is eliminated, and FIG.
A plurality of light beams move on the photosensitive drum 4 in the sub-scanning direction so that the vertical resist amount corresponding to the positional deviation d as shown in FIG. As a result, as shown in FIG. 5, the vertical registration fluctuation for each color image from the recording start signal becomes zero, and the color shift between the colors in the color image writing can be reduced. In FIG. 5, hatched circles indicate light beams from the light sources LD1 and LD2 in the light source unit 9.

FIG. 4 schematically shows a second embodiment of the present invention. The second embodiment is another embodiment of the first and second aspects of the present invention, and is another example of a color image forming apparatus for forming a color image on a transfer material. This second embodiment is:
Image forming stations 1Y, 1M, 1C, 1K for forming images of a plurality of colors, for example, Y, M, C, K images, respectively.
And an intermediate transfer belt 23 as an intermediate transfer member, and transfer chargers 24Y and 24M as transfer means for transferring images of respective colors formed by the image forming stations 1Y, 1M, 1C and 1K on the intermediate transfer belt 23 in a superimposed manner. , 24
C, 24K, and a transfer charger 26 as a transfer unit for transferring the superimposed image on the intermediate transfer belt 23 to transfer paper 25 as a transfer material. The intermediate transfer belt 23 is stretched around rollers 27 to 29 and is driven to rotate counterclockwise by a driving source (not shown).

Each image forming station 1Y, 1M, 1
C and 1K denote multi-beam scanning optical systems 6Y, 6M, 6C and 6K having the same configuration as the multi-beam scanning optical system 6 in the first embodiment, and photoconductors 4Y, 4M and 4K.
4C, 4K, charging chargers 5Y, 5 as charging means
M, 5C, 5K, Y developing device 7Y, M developing device 7M, C developing device 7C, K developing device 7K, cleaning devices 8Y, 8M,
8C, 8K, etc. Photoconductors 4Y, 4M, 4C, 4
For K, for example, a photosensitive drum is used.

Each image forming station 1Y, 1M, 1
In C and 1K, the photosensitive drums 4Y and 4
M, 4C, and 4K are driven to rotate clockwise by a photoconductor driving unit (not shown), and charge chargers 5Y, 5M, and 5K are driven.
After being uniformly charged by C and 5K, a Y image signal and a Y image signal are output by the multi-beam scanning optical systems 6Y, 6M, 6C and 6K.
An electrostatic latent image is formed by being scanned and exposed in the main scanning direction by a plurality of light beams respectively modulated by the image signal M, the image signal C, and the image signal K, thereby forming a Y image, an M image, and a C image.
The image and the K image are written. This photosensitive drum 4Y,
The electrostatic latent images on 4M, 4C, and 4K are respectively
The Y, M, C, and K images are developed by the Y and M developing units 7M, 7C, and 7K.

The Y, M, C, and K images on the photosensitive drums 4Y, 4M, 4C, and 4K are transferred to the transfer charger 24.
Y, 24M, 24C, 24K, the intermediate transfer belt 23
The image is transferred to be superimposed on the image to form a full-color image. On the other hand, transfer paper 25 is fed from a paper feeding device (not shown), and the transfer paper 25 is discharged after the full-color image on the intermediate transfer belt 23 is transferred by the transfer charger 26 and the full-color image is fixed by a fixing device (not shown). Is done. The photosensitive drums 4Y, 4M, 4C, and 4K are cleaned by the cleaning devices 8Y, 8M, 8C, and 8K after image transfer.

The multi-beam scanning optical system 6Y, 6M, 6
C and 6K denote a galvano mirror 11 as a sub-scanning deflecting unit, a light receiving element 18 as a main scanning synchronizing signal generating unit, a vertical registration detecting unit 19, a recording start signal detecting unit 20, a time difference in the first embodiment, respectively. Detecting means 2
1. Galvano mirror as sub-scanning deflection means similar to sub-scanning deflection signal generation means 22, light receiving element as main scanning synchronization signal generation means, vertical registration detection means, recording start signal detection means, time difference detection means, sub-scan deflection Signal generating means, which are provided in each of the image forming stations 1Y, 1M, 1
The operations at C and 1K are the same as those in the first embodiment.

Therefore, each image forming station 1
In Y, 1M, 1C, and 1K, as in the first embodiment, the galvanomirror as the sub-scanning deflecting means is rotated by being driven by the sub-scanning deflecting signal from the sub-scanning deflecting signal generating means. A plurality of light beams from the cylindrical lens are moved in the sub-scanning direction so that the time difference between the recording start signal and the main scanning synchronization signal becomes zero and the vertical registration amount corresponding to the deviation of the recording start position in the sub-scanning direction becomes zero. Deflect.

Therefore, the time difference (time difference t1 or t2 shown in FIG. 6) between the recording start signal and the main scanning synchronizing signal is eliminated, and the vertical resist amount corresponding to the displacement d shown in FIG. 7 is eliminated. A plurality of light beams move on the photosensitive drums 4Y, 4M, 4C, and 4K in the sub-scanning direction.
Thereby, the vertical registration fluctuation for each color image from the recording start signal becomes zero, and the color shift between the colors in the color image writing can be reduced.

The invention according to claims 1 and 2 can be applied to an image forming apparatus for forming a monochromatic image using a multi-beam scanning optical system in the same manner as in the above embodiment. That is, the galvanomirror 11 as the sub-scanning deflecting means in the first embodiment as the multi-beam scanning optical system,
A light receiving element 18 as a main scanning synchronization signal generating means, a vertical registration detecting means 19, a recording start signal detecting means 20, a time difference detecting means 21, a galvano mirror as a sub-scanning deflecting means similar to the sub-scanning deflection signal generating means 22, Using a multi-beam scanning optical system having a light receiving element as a scanning synchronization signal generating unit, a vertical registration detecting unit, a recording start signal detecting unit, a time difference detecting unit, and a sub-scanning deflection signal generating unit, the recording start signal and the main scanning synchronizing signal are used. A plurality of light beams can be moved in the sub-scanning direction on the photoconductor drum so that the time difference between the two is eliminated and the vertical registration amount corresponding to the shift of the recording start position in the sub-scanning direction is eliminated. Thus, the vertical registration fluctuation for each single-color image from the recording start signal becomes zero, and the vertical registration deviation between pages in writing a single-color image can be reduced.

FIG. 8 schematically shows a third embodiment of the present invention. The third embodiment is an embodiment of the invention according to claims 1 and 3, and is an example of a color image forming apparatus for forming a color image on a transfer material. In the third embodiment, an electro-optic effect element 30 is used instead of the galvanometer mirror 11 as the sub-scanning deflection unit in the first embodiment. The electro-optical effect element 30 is disposed between the light source unit 9 and the cylindrical lens 10.

As shown in FIG. 9, the electro-optic effect element 30
Is composed of PLZT, and its polarization axis C is arranged in the sub-scanning direction, and triangular electrodes 30a and 30b are formed on two opposing surfaces in the main scanning direction. Also,
In front of the electro-optic effect element 30, a half-wave plate 31 for changing the polarization of the incident light from the light source unit 9 in the main scanning direction is arranged.

When the sub-scanning deflection signal generating means 22 converts the sub-scanning deflection signal into a voltage and applies it between the electrodes 30a and 30b of the electro-optical effect element 30, as shown in FIG. A triangular refractive index reduction region 30c is formed inside the PLZT, and a plurality of light beams from the half-wave plate 31 are refracted upward (sub-scanning direction) and emitted to the cylindrical lens 10. For this reason, on the photosensitive drum 4, a plurality of light beams are deflected to the rotation direction side of the photosensitive drum 4 (the sub-scanning direction at the writing position).

Therefore, a plurality of light beams move on the photosensitive drum 4 in the sub-scanning direction so as to correct the vertical registration amount corresponding to the positional deviation d shown in FIG. As a result, FIG.
As shown in (1), the vertical registration fluctuation for each color image from the recording start signal becomes zero, and the color shift between the colors in the color image writing can be reduced.

The fourth embodiment of the present invention is another embodiment of the first and third aspects of the present invention, and is another example of a color image forming apparatus for forming a color image on a transfer material. This fourth
In the second embodiment, the electro-optic effect element 30 is used in place of the galvanomirror 11 as the sub-scanning deflecting means in the second embodiment as in the third embodiment. The half-wave plate 31 is disposed in the same manner as in the third embodiment, so that the vertical registration fluctuation for each color image from the recording start signal becomes zero, and the color shift between the colors in the color image writing is reduced. can do.

The invention according to claims 1 and 3 can be applied to an image forming apparatus for forming a monochromatic image using a multi-beam scanning optical system in the same manner as in the above embodiment. That is, the electro-optical effect element 3 as the sub-scanning deflecting means in the third embodiment serves as a multi-beam scanning optical system.
0, 1/2 wavelength plate 31, light receiving element 18 as main scanning synchronization signal generating means, vertical registration detecting means 19, recording start signal detecting means 20, time difference detecting means 21, sub scanning deflection signal generating means 22 It has an electro-optic effect element as a scanning deflection unit, a half-wave plate, a light receiving element as a main scanning synchronization signal generation unit, a vertical registration detection unit, a recording start signal detection unit, a time difference detection unit, and a sub-scanning deflection signal generation unit. Using a multi-beam scanning optical system, a plurality of light beams are applied to the photosensitive drum so that the time difference between the recording start signal and the main scanning synchronization signal is eliminated, and the vertical registration amount corresponding to the deviation of the recording start position in the sub-scanning direction is eliminated. Can be moved in the sub-scanning direction. Thus, the vertical registration fluctuation for each single-color image from the recording start signal becomes zero, and the vertical registration deviation between pages in writing a single-color image can be reduced.

[0038]

As described above, according to the first aspect of the present invention, with the above-described structure, the displacement of the vertical resist between the respective pages when forming a monochromatic image and the color deviation between the respective colors when forming a color image are reduced. can do.

According to the second aspect of the present invention, it is possible to reduce the displacement of the vertical resist between the pages during the formation of a single color image and the color deviation between the colors during the formation of a color image.

According to the third aspect of the present invention, with the above configuration, it is possible to reduce the displacement of the vertical resist between the respective pages during the formation of a single-color image and the color deviation between the respective colors during the formation of a color image.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a circuit unit according to a first embodiment of the present invention.

FIG. 2 is a sectional view schematically showing the first embodiment.

FIG. 3 is a perspective view showing a configuration of a multi-beam scanning optical system according to the first embodiment.

FIG. 4 is a sectional view schematically showing a second embodiment of the present invention.

FIG. 5 is a diagram showing a state in which a vertical registration fluctuation for each color image from a recording start signal becomes zero in the first embodiment.

FIG. 6 is a timing chart showing how the temporal relationship between a recording start signal and a main scanning synchronization signal changes each time in a conventional image forming apparatus.

FIG. 7 is a diagram illustrating a deviation of a recording start position of an image in a sub-scanning direction in a conventional image forming apparatus.

FIG. 8 is a perspective view showing a configuration of a multi-beam scanning optical system according to a third embodiment of the present invention.

FIG. 9 shows an electro-optic effect element and a half of the third embodiment.
It is a perspective view which shows a wave plate.

FIG. 10 is a view for explaining an electro-optical effect element according to the third embodiment.

[Explanation of symbols]

 Reference Signs List 4 photoreceptor drum 9 light source unit 11 galvanometer mirror 12 rotating polygon mirror 18 light receiving element 19 vertical registration detecting means 20 recording start signal detecting means 21 time difference detecting means 22 sub-scanning deflection signal generating means 30 electro-optical effect element 31 1/2 wavelength plate

Claims (3)

[Claims] A plurality of light beams from a plurality of light sources are scanned in a main scanning direction by a scanning means, and irradiated on a photosensitive surface moving in a sub-scanning direction, whereby a plurality of light beams are irradiated on the photosensitive surface in the sub-scanning direction. In an image forming apparatus that records an image by exposing all at once with a beam, a recording start signal generating unit that generates a recording start signal that determines a recording start position in the sub-scanning direction on the photosensitive surface, A main scanning synchronizing signal generating unit disposed to receive a scanning light beam from the scanning unit and generate a main scanning synchronizing signal; and a main scanning synchronizing signal from the main scanning synchronizing signal generating unit and the recording start signal generating unit. Detecting means for detecting a time difference from the recording start signal, and sub-scanning deflecting means for simultaneously deflecting all of the plurality of light beams from the plurality of light sources in the sub-scanning direction in accordance with the signal from the detecting means. Image forming apparatus, characterized in that was e. 2. An image forming apparatus according to claim 1, wherein said sub-scanning deflecting means is a galvanomirror arranged between said plurality of light sources and said scanning means. 3. An image forming apparatus according to claim 1, wherein said sub-scanning deflecting means is an electro-optic effect element arranged between said plurality of light sources and said scanning means. .