JP2000284194A - Multi-beam optical scanning device - Google Patents

Abstract

(57) Abstract: A high-speed and high-quality image is obtained by optimally setting an angle and a position at which a slit member of a scanning start timing detecting unit is arranged. SOLUTION: When there is a light amount difference between respective synchronization detection lights corresponding to a plurality of light sources 11a and 11b, the light source 11a
And the output timing of the synchronization detection signal corresponding to the light source 11b is shifted by δt2, and as a result, the writing positions of both are shifted by an amount corresponding to δt2. In order to correct the shift amount δY, the slit 18a is arranged at a predetermined angle with respect to a plane orthogonal to the plane scanned by the synchronization detection light.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a multi-beam optical scanning device used for a laser beam printer, a digital copying machine or the like.

[0002]

2. Description of the Related Art FIG. 16 is a plan view of a conventional multi-beam optical scanning device. Light beams A and B emitted from the semiconductor laser light sources 1a and 1b having a plurality of light-emitting points are converted into substantially parallel light or convergent light by a collimator lens 2, respectively, and the light beams are shaped by an aperture stop 3 to form a cylindrical lens 4.
As a result, the light converges only in the sub-scanning direction, and an image is formed in the vicinity of the deflecting reflection surface 5a of the polygon mirror 5, which is an optical deflector, in the form of a focal line elongated in the main scanning direction. The light beams reflected and deflected by the polygon mirror 5 rotating at a constant angular velocity in the direction of arrow R are condensed in a spot shape on the surface to be scanned 7 made of a photosensitive drum or the like by the fθ lens 6, and are directed in the direction of arrow D. At a constant speed. At this time, the slit 8a for synchronization detection, the lens 8b, the sensor 8
The write start position detecting means c detects a part of the scanning light to detect the write start position.

In such a multi-beam optical scanning device, as shown in FIG. 17A, a plurality of light sources 1a, 1b
Are arranged vertically in the sub-scanning direction, the distance between the lines in the sub-scanning direction on the surface to be scanned 7 is significantly larger than the recording density. For this purpose, usually, as shown in FIG. 17 (b), a plurality of light sources 1a and 1b are arranged obliquely, and by adjusting the inclination angle α, the distance between the respective lines in the sub-scanning direction on the surface 7 to be scanned. Is precisely adjusted according to the recording density.

[0004]

However, in the above-described conventional multi-beam optical scanning device, the plurality of light sources 1a and 1b are arranged obliquely, so that the light beams emitted from these light sources 1a and 1b are reduced. As shown in FIG. 18, on the reflection surface 5 a of the polygon mirror 5, the light beams reaching the positions separated in the main scanning direction and the angles of the light beams reflected from the polygon mirror 5 are different from each other. As in the case of the light beams A and B, the spot light forms an image at positions separated from each other in the main scanning direction.

For this reason, the timing is shifted by a predetermined time δT so that the position where one light source 1a as a reference forms an image on the surface 7 to be scanned is adjusted to the position where the light beam from the other light source 1b is formed. Image data. The reflection surface 5 of the polygon mirror 5 when it is shifted by the predetermined time δT
a is rotated by the angle β, the light beam B reflected at this time is reflected in the direction of the light beam B ′ in the same direction as the light beam A,
The imaging positions of the spot lights coincide.

The writing start point of each beam on the scanned surface 7 is determined as follows. That is, the timing at which the scanning light beam arrives at the sensor 8c of the writing position detecting means 8 provided upstream in the scanning direction of the surface to be scanned 7 is used as synchronization detection, and this synchronization detection is performed independently for each beam. The writing is started after a predetermined delay time from the result. Here, in order to more accurately detect the timing when the scanning light beam reaches the sensor 8c, the slit 8a is disposed at the focal point of the scanning light beam on the front surface of the sensor 8c. The synchronous detection is performed by detecting the rise of the amount of light when passing through.

If the slits 8a are arranged obliquely with respect to the surface formed by scanning the light beams from the plurality of light sources 1a and 1b, the image forming position of each light beam is shifted in the main scanning direction. Therefore, as shown in FIG. 19, the slit 8a is normally arranged perpendicular to a surface formed by scanning with the scanning light beam. However, even if the slit 8a is arranged perpendicular to the scanning surface of the scanning light beam, the difference in the light amount of each light beam, the difference in the spot shape of each light beam, the rising characteristic of each light source light beam, the inside of each light beam, Due to factors such as a difference in light intensity distribution, a shift occurs in the timing of synchronous detection of each light beam, and as a result, a shift occurs in an imaging position of a plurality of light beams, resulting in a decrease in printing accuracy and image quality. Exists.

An object of the present invention is to solve the above-mentioned problems,
It is an object of the present invention to provide a high-speed and high-quality multi-beam optical scanning device by optimally setting an angle and a position at which a slit member of a detection unit for detecting a scanning start timing is arranged.

[0009]

A multi-beam optical scanning device according to the present invention for achieving the above object comprises a light source for emitting a plurality of light beams, a deflector, and a light beam deflected and scanned by the deflector. In a multi-beam optical scanning apparatus comprising: an imaging optical system for condensing light on a scanning surface; and detection means for detecting a scanning start timing for each of the plurality of scanned light beams, a light beam incident side of the detection means The scanning start timing is obtained by arranging a slit member at a predetermined angle with respect to a plane orthogonal to a plane scanned by the light beam incident on the detecting means, and detecting a rising of the light amount of the light beam crossing the slit member. Is detected.

A multi-beam optical scanning device according to the present invention is a light source for emitting a plurality of light beams, a deflector, and an imaging optical system for condensing a light beam deflected and scanned by the deflector onto a surface to be scanned. And a detecting means for detecting a scanning start timing for each of the plurality of scanned light beams, wherein a light beam incident on the detecting means is provided on a light beam incident side of the detecting means. The scanning start timing is detected by arranging a slit member at a position shifted from the light spot by a predetermined distance and detecting the rising of the light amount of the light beam crossing the slit member.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail with reference to the embodiments shown in FIGS. FIG. 1 is a plan view of a multi-beam optical scanning device according to a first embodiment, and a collimator lens as a first optical system is provided on an optical path in front of a semiconductor laser light source 11 including two semiconductor light sources 11a and 11b. 12. Cylindrical lens 1 as second optical system
3, an aperture stop 14, and a polygon mirror 15, which is an optical deflector rotating at a constant angular velocity in the direction of arrow R, are sequentially arranged. In the reflection direction of the polygon mirror 15, an fθ lens 16, which is a third optical system, and a scanned surface 17 such as a photosensitive drum are arranged.

In order to determine the writing start point of each beam on the scanned surface 17, slits 18a,
A writing position detection unit 18 including a lens 18b and a sensor 18c is provided at a position upstream of the surface 17 to be scanned in the scanning direction. Here, the slit 18a is provided so that the scanning light beam is
In order to more accurately detect the timing at which the scanning light beam 8c is reached, the scanning light beam is arranged at the focal point of the scanning light beam in front of the sensor 18c.

With such a configuration, the light beam emitted from the semiconductor laser light source 11 is converted into substantially parallel light or convergent light by the collimator lens 12, converged only in the sub-scanning direction by the cylindrical lens 13, and passes through the aperture stop 14. The light beam width is limited, and an image is formed on the deflecting / reflecting surface 15a of the polygon mirror 15 in a focal line shape extending in the main scanning direction. The light beam reflected and deflected by the polygon mirror 15 is condensed by the fθ lens 16 on the surface 17 to be scanned of the photosensitive drum in the form of a spot, and the arrow D
Scanning at a constant speed in the direction.

At this time, the timing at which the scanning light beam arrives at the sensor 18c of the writing position detecting means 18 is regarded as synchronous detection, and this synchronous detection is performed independently for each beam, and writing starts after a predetermined delay time from the synchronous detection. And That is, as shown in FIG.
A synchronization detection signal is output when the output of the sensor 18c at the time of passing through 8a becomes equal to or higher than a certain slice level S, and an image signal is sent after a certain time t1 from this point. By performing this operation for each light beam, the writing position of each light beam can be matched.

In the case of the conventional example, the slit 18a is arranged perpendicular to the surface on which the light beam scans, but the light amount of each light beam, the spot shape on the slit 18a, and the light amount of the light source corresponding to each light beam And the rise characteristics and the light intensity distribution inside the light beam are not completely the same,
There is a relative difference due to these factors, which causes an error in the writing position of each light beam. For example,
When the spot diameter is reduced or the printing area is widened for the purpose of improving the printing quality, the deflection reflecting surface 15a of the polygon mirror 15 has no margin. It is necessary to use it after removing it.

In that case, each of the light sources 11a, 1
The light beam emitted from 1b is shifted in the main scanning direction on the deflecting / reflecting surface 15a of the polygon mirror 15, so that
The amount of light flux displacement is not the same, resulting in a difference in light quantity. For example, in FIG. 1, the amount of the light beam A corresponding to the light source 11a is greater than the amount of the light beam B corresponding to the light source 11b, and the former synchronization detection light has a smaller amount of light.

As described above, when there is a light amount difference between the respective synchronization detection lights A and B corresponding to the light sources 11a and 11b, the output of the synchronization detection signal corresponding to the light source 11a as shown in FIG. A shift of δt2 occurs in the output timing of the synchronization detection signal corresponding to 11b, and as a result, the write-out positions of both shift by an amount corresponding to δt2. That is, assuming that the scanning speed of each light beam on the slit 18a in the main scanning direction is Vmm / sec, if a shift occurs in the output timing of the synchronization detection signal by δt2 seconds, δY (mm) = V · δt2 The writing position of the light beam corresponding to the light source 11b is delayed.

Therefore, in this embodiment, the deviation amount δY
Is corrected, the slit 18a is arranged at a predetermined angle with respect to a plane orthogonal to the plane scanned by the synchronization detection light. Specifically, when the sub-scanning resolution is 600 DPI, the distance between the two scanning lines on the slit 18a in the sub-scanning direction is 0.042333 mm, so that the slit 18a moves in the direction shown in FIG. θ = tan ⁻¹ (δY / 0.
04233) It is only necessary to incline by degrees.

FIG. 5 is a graph showing the output of the sensor 18c according to the second embodiment. In the first embodiment, when there is a difference between the amounts of light beams A and B, only a difference occurs in the amount of light. However, a difference also occurs in the spot shape in the main scanning direction on the slit 18a. Specifically, since the light beam width of the light beam A is smaller than the light beam width of the light beam B, the F number of the light beam A at the time of emission becomes darker than the light beam B, and the spot shape on the slit 18a is The spot diameter of the light beam A in the main scanning direction becomes larger than the spot diameter of the light beam B.

As described above, when the spot diameter in the main scanning direction increases, the time required to pass through the slit 18a increases, so that two spot light beams having a difference in the light amount and the spot diameter in the main scanning direction scan the slit 18a. When you do
The output of the sensor 18c is shifted by δt3 as shown in FIG. As a result, the light source 11 only has δY (mm) = V · δt3.
The writing position of the light beam B corresponding to b is shifted.

For this reason, also in this embodiment, the light source 1
In order to correct the writing position deviation δY caused by the difference between the spot shape and the light amount of the light beams A and B corresponding to the light beams 1a and 11b on the slit 18a, a slit is formed on a plane orthogonal to the plane scanned by the synchronization detection light. 18a are arranged at a predetermined angle.

FIG. 6 is an explanatory diagram of the timing of the light emission amount control according to the third embodiment. In an optical scanning device used for a laser beam printer, a digital copying machine, or the like, usually, in order to improve the printing quality, the light sources 11a, 11a
b is controlled. For example, a laser light source is usually provided with a photodiode inside the package in order to monitor its own light emission amount. By monitoring the output current from this photodiode, that is, the value of the monitor current, a predetermined light emission amount is obtained. It is possible to control the amount of emitted light by adjusting the laser drive current so that

Ideally, the control of the amount of emitted light is performed in real time within the image range. However, in an optical scanning device using multi-beam laser light, there are cases where a plurality of light sources 11a and 11b emit light simultaneously. Therefore, it is impossible to control the amount of emitted light in real time. Therefore,
Immediately before synchronization detection, each light source 11a, 1
1b is emitted independently in time, and the laser drive current is determined from the monitor current at that time.

FIG. 6A shows a positional relationship when the spot lights A and B corresponding to the light sources 11a and 11b do not reach the slit 18a. At this time, first, only the light source 11a emits light, and the drive current of the light source 11a is determined from the monitor current. FIG. 6 (b)
Indicates that only the spot light A corresponding to the light source 11a has the slit 1
The spot light B corresponding to the light source 11b after passing through the light source 8b represents a state in front of the slit 18a. At this time, since the spot light A has passed through the slit 18a, the synchronization detection has been completed for the light source 11a.
Therefore, the light source 11a is turned off immediately after the completion of the synchronization detection, and the light source 11b emits light immediately. Thereafter, when the light source 11b also enters the state shown in FIG. 6C after passing through the slit 18a, the synchronization detection for the light source 11b is completed.

It is impossible to make the rise of the monitor current completely coincide with the rise of the amount of received light, and it is common that the rise of the monitor current is later than the rise of the amount of received light. In this case, since the laser drive current is fed back based on the monitor current, if the rise characteristic of the monitor current is poor, it is considered that the light emission amount is low, and as shown in FIG. appear.

If the time required for the spot light B of the light source 11b to pass through the slit 18a from the state shown in FIG. 6B is short, the synchronous detection is performed in a state where the light amount of the light source 11b is overshooting. I may go. In this case, the synchronization detection based on the output of the sensor 18c is performed in a state where there is a light amount difference between the light sources 11a and 11b, and a writing position shift δt4 occurs as shown in FIG.
As a result, the writing position of the light flux B corresponding to the light source 11b is delayed by δY (mm) = V · δt4.

In this embodiment, in order to correct the writing position shift caused by the shift δt4 caused by the rising characteristic of the light source itself, a slit 18a is formed on a plane orthogonal to the plane scanned by the synchronization detection light. Are arranged at a predetermined angle.

FIG. 9 shows a fourth embodiment in which light beams emitted from the multi-beam laser light sources 11a and 11b are converted by the collimator lens 12 into substantially parallel light or convergent light as shown in FIG. In addition, as shown in (b) and (c), a difference occurs in the internal light intensity distribution of each light beam in the main scanning direction. As described above, when a light beam having a difference in light intensity distribution inside the light beam forms an image in the form of a spot, as shown in FIG.
A difference occurs between the spot light B of b and the intensity distribution in the main scanning direction of the spot cross section.

When the spot lights A and B having different intensity distributions traverse the slit 18a, the output timings of the synchronization detection signal corresponding to the light source 11a and the synchronization detection signal corresponding to the light source 11b as shown in FIG. , A shift of δt5 occurs. As a result, δY (mm) = V · δ
The writing position of the light beam A corresponding to the light source 11b is shifted by t5.

In the present embodiment, in order to correct the writing position shift caused by δt5 caused by the difference in the internal light intensity distribution of the respective light beams in the main scanning direction, the plane perpendicular to the plane scanned by the synchronization detection light is corrected. To the surface
The slit 18a is arranged at a predetermined angle.

In the above-described first to fourth embodiments, factors that cause a shift in the write start position do not always exist independently, and in that case, the predetermined factors are considered in consideration of a plurality of combinations of the main factors. The angle may be determined. Further, if the predetermined angle is determined in consideration of all the factors, it becomes possible to correct the writing start position deviation more accurately.

FIG. 12 is a plan view of a main scanning section of the fifth embodiment, and FIG. 13 is a side view of a sub-scanning section of the synchronization detection light viewed from the surface to be scanned. A folding mirror 19 that reflects only the synchronization detection light is provided, and a slit 18a, a lens 18b, and a sensor 18c are arranged in the reflection direction of the folding mirror 19. As described above, the synchronization detection light is bent at a predetermined angle in the deflection main scanning plane, and further reflected at a predetermined angle in the sub-scanning direction, so that the optical housing is made as small as possible and the scanner unit is downsized. I have.

In the case of an arrangement in which the synchronization detection light is folded at a predetermined angle in the sub-scanning direction by the folding mirror 19, the surface scanned by the synchronization detection light is inclined with respect to the deflection main scanning surface scanned by the scanning light. The synchronization detection light scans the slit 18a obliquely as shown in FIG. As described above, when the synchronization detection light scans the slit 18a obliquely, the light flux A of the light source 11a by tan (θbd).
In the prior art, as shown in FIG. 14B, the slit 18a is tilted by θbd so as to be perpendicular to the scanning surface of the synchronization detection light.

However, by merely arranging the slit 18a so as to be perpendicular to the surface on which the synchronization detection light is scanned, the difference in light amount, the difference in spot shape, the rising characteristic of the light amount of the light source itself, the internal light of the light beam, etc. If there is a difference in the intensity distribution or the like, the writing position shifts. For example, when there is a difference in the light amount, the light source 1 has only δY (mm) = V · δt2.
The writing position of the light beam B corresponding to 1b is delayed.

For this reason, in this embodiment, as shown in FIG. 14C, scanning of the light beam on the slit 18a when the synchronization detection mirror 19 reflects the synchronization detection light at a predetermined angle in the sub-scanning direction. Angle θbd and, for example, 600D
Angle θ = tan ^-1 for correcting deviation δY in case of PI
(δY / 0.04233) and by disposing the slit 18a at an angle by the amount, the deviation of the writing position is corrected more accurately.

At this time, the cause of the writing start position deviation does not always exist independently in the light sources 1a and 1b. In this case, the synchronization detection light is reflected by the folding mirror 19 at a predetermined angle in the sub-scanning direction. The angle θbd at which the light beam scans on the slit 18a,
The predetermined angle is determined in consideration of a plurality of combinations of the main factors. Furthermore, if the predetermined angle is determined in consideration of all the factors, the writing start position deviation can be more accurately corrected.

FIG. 15 shows a sixth embodiment, in which the first to fifth embodiments are described.
In the embodiment of the present invention, the slit 18a is arranged to be inclined in order to correct the writing position deviation. However, the writing position deviation can be corrected by shifting the position of the slit 18a while keeping the angle of the slit 18a vertical. FIG. 15A shows an arrow C.
The light beams A and B scanned in the directions reach the slit 18a. The light beam B reaches the end surface of the slit 18a δT after the light beam A reaches the end surface of the slit 18a.

In this state, the position of the slit 18a may be left as it is if there is no error factor causing the writing start position shift. However, in actuality, in each of the light beams A and B, the light amount, the spot shape on the slit 18a, Since the light quantity rising characteristics of the light sources corresponding to the respective light beams, the light intensity distribution inside the light beams, and the like are not completely the same, a shift occurs in the writing start position. For example, if there is a light amount difference, δY (mm) = V ·
The writing position of the light beam B corresponding to the light source 11b is delayed by δt2.

Therefore, in this embodiment, FIG.
As shown in (b), in order to correct the shift δY, the slit 18a is disposed behind the converging point by L = 2 · tan (δY / 2). By arranging in this way,
The synchronization detection light A reaches the end face of the slit 18a later than the specified time, while the synchronization detection light B reaches the end face of the slit 18a earlier than the specified time. As a result, the writing position of the light beam B corresponding to the light source 11b can be advanced to the same position as the light beam A.

At this time, the cause of the shift in the writing position does not always exist in each of the light sources 1a and 1b, and the predetermined shift amount L is determined in consideration of a plurality of combinations of the main factors. Further, if the predetermined angle is determined in consideration of all factors, the writing position deviation can be corrected more accurately.

As described in the fifth embodiment, when the synchronization detection light is reflected at a predetermined angle in the sub-scanning direction by the turning mirror 19, the light is generated by the scanning angle θbd of the light beam on the slit 18a. The shift amount L may be determined so as to correct the writing position shift. Further, it is more effective to determine the shift amount L in consideration of the influence of the difference in the light amount, the difference in the spot shape, the rising characteristic of the light amount of the light source itself, the difference in the internal light intensity distribution of the light beam, and the like.

In the above embodiment, the inclination angle / shift amount L of the slit 18a may be determined in advance.
When there are variations in error factors such as a difference in light amount, a difference in spot shape, a rising characteristic of the light amount of the light source itself, and a difference in internal light intensity distribution of the light beam, a configuration in which the tilt angle and the shift amount can be adjusted. Good.

[0043]

As described above, in the multi-beam optical scanning device according to the present invention, the slit member through which each synchronous detection light passes is set at a predetermined angle with respect to the plane orthogonal to the scanning plane of the light beam incident on the detection means. By tilting the arrangement, the scanning start timing is accurately detected from the rising of the light amount of the light beam crossing the slit member, and a high-speed and high-quality image is formed.

Further, in the multi-beam optical scanning device according to the present invention, the slit member through which each synchronous detection light passes is disposed at a position shifted by a predetermined distance from the converging point of the light beam incident on the detecting means. A scanning start timing is accurately detected from the rising of the light amount of the light beam crossing the member, and a high-speed and high-quality image is formed.

[Brief description of the drawings]

FIG. 1 is a plan view of a multi-beam optical scanning device according to a first embodiment.

FIG. 2 is a graph showing a synchronization detection signal and an image signal.

FIG. 3 is an explanatory diagram of a shift of a synchronization detection signal due to a light amount difference.

FIG. 4 is an explanatory diagram of how to incline a slit for correcting displacement.

FIG. 5 is a graph showing a deviation of a synchronization detection signal according to the second embodiment.

FIG. 6 is an explanatory diagram of light emission amount control in synchronization detection according to the third embodiment.

FIG. 7 is a graph showing an overshoot of light quantity.

FIG. 8 is a graph showing a deviation of a synchronization detection signal due to a rising characteristic of a light source.

FIG. 9 is an explanatory diagram of an internal light intensity distribution of a plurality of light beams according to the fourth embodiment.

FIG. 10 is a graph of a spot light intensity distribution when there is a difference in light intensity distribution.

FIG. 11 is a graph showing a shift of a synchronization detection signal when there is a difference in light intensity distribution.

FIG. 12 is a plan view of a multi-beam optical scanning optical device according to a fifth embodiment.

FIG. 13 is a side view.

FIG. 14 is an explanatory diagram of how to tilt a slit when there is a light amount difference.

FIG. 15 is an explanatory diagram of how to shift a slit for correcting a shift according to the sixth embodiment.

FIG. 16 is a plan view of a conventional multi-beam optical scanning device.

FIG. 17 is an explanatory diagram of an arrangement of a plurality of light sources.

FIG. 18 is a plan view of an image writing timing.

FIG. 19 is an explanatory diagram of an arrangement of slits.

[Explanation of symbols]

 Reference Signs List 11 semiconductor laser light source 13 cylindrical lens 14 aperture 15 polygon mirror 16 fθ lens 17 scanned surface 18 position detecting means 18a slit 18c sensor 19 folding mirror

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2C362 AA03 AA10 BA04 BA57 BA69 BA70 2H045 BA21 BA42 CA82 CA88 CA98 CB33 DA02 DA22

Claims (27)

[Claims] A light source that emits a plurality of light beams; a deflector;
A multi-beam light comprising: an imaging optical system for condensing a light beam deflected and scanned by the deflector on a surface to be scanned; and a detecting means for detecting a scanning start timing for each of the plurality of scanned light beams. In the scanning device, a slit member is disposed on the light beam incident side of the detecting means at a predetermined angle with respect to a plane orthogonal to a plane on which the light beam incident on the detecting means scans, and a light amount of the light beam traversing the slit member is provided. A multi-beam optical scanning device, wherein the scanning start timing is detected by detecting a rising edge. 2. The multi-beam optical scanning device according to claim 1, wherein the predetermined angle of the slit member is determined based on a difference between light amounts of the plurality of light beams. 3. The multi-beam optical scanning device according to claim 1, wherein the predetermined angle of the slit member is determined based on a difference between spot shapes of the plurality of light beams on the slit member. 4. The multi-beam optical scanning device according to claim 1, wherein the predetermined angle of the slit member is determined based on a rising characteristic of light amounts of the plurality of light sources themselves. 5. The predetermined angle of the slit member is determined based on a difference between internal light intensity distributions of the plurality of light beams.
2. The multi-beam optical scanning device according to claim 1. 6. The predetermined angle of the slit member includes a difference between the light amounts of the plurality of light beams, a difference between spot shapes of the plurality of light beams on the slit member, and a light amount of the plurality of light sources themselves. The multi-beam optical scanning device according to claim 1, wherein the multi-beam optical scanning device is determined based on a combination of two or more factors of a rising characteristic and a difference between internal light intensity distributions of the plurality of light beams. 7. The multi-beam optical scanning apparatus according to claim 1, further comprising a reflection unit that reflects the plurality of light beams at a predetermined angle in at least a sub-scanning direction and guides the plurality of light beams to the detection unit. 8. The multi-beam optical scanning device according to claim 7, wherein the predetermined angle of the slit member is determined based on a reflection angle of the reflection unit and a difference between light amounts of the plurality of light beams. 9. The multi-beam according to claim 7, wherein the predetermined angle of the slit member is determined based on a reflection angle of the reflection means and a difference between spot shapes of the plurality of light beams on the slit member. Optical scanning device. 10. The multi-beam optical scanning device according to claim 7, wherein the predetermined angle of the slit member is determined based on a reflection angle of the reflection means and a rising characteristic of light amounts of the plurality of light sources themselves. 11. The multi-beam optical scanning device according to claim 7, wherein the predetermined angle of the slit member is determined based on a reflection angle of the reflection unit and a difference between internal light intensity distributions of the plurality of light beams. 12. The predetermined angle of the slit member includes a difference between the light amounts of the plurality of light beams, a difference between spot shapes of the plurality of light beams on the slit member, and a light amount of the plurality of light sources themselves. The multi-beam optical scanning device according to claim 7, wherein the multi-beam optical scanning device is determined based on a combination of two or more factors of a rising characteristic, a difference between internal light intensity distributions of the plurality of light beams, and a reflection angle of the reflection unit. . 13. The multi-beam optical scanning device according to claim 1, wherein a predetermined angle of the slit member can be adjusted. 14. A light source for emitting a plurality of light beams, a deflector, an image forming optical system for condensing a light beam deflected and scanned by the deflector on a surface to be scanned, and a light source for each of the plurality of scanned light beams. And a detecting means for detecting a scanning start timing, wherein a slit member is provided on a light beam incident side of the detecting means at a position shifted by a predetermined distance from a focal point of a light beam incident on the detecting means. A multi-beam optical scanning apparatus, wherein the scanning start timing is detected by detecting rising of a light amount of a light beam crossing the slit member. 15. The multi-beam optical scanning device according to claim 14, wherein the predetermined distance at which the slit member is shifted is determined based on a difference between the light amounts of the plurality of light beams. 16. The multi-beam optical scanning device according to claim 14, wherein the predetermined distance for displacing the slit member is determined based on a difference in a spot shape of each of the plurality of light beams on the slit member. 17. The multi-beam optical scanning device according to claim 14, wherein the predetermined distance at which the slit member is shifted is determined based on a rising characteristic of light amounts of the plurality of light sources themselves. 18. The multi-beam optical scanning device according to claim 14, wherein the predetermined distance for displacing the slit member is determined based on a difference between internal light intensity distributions of the plurality of light beams. 19. The predetermined distance for shifting the slit member includes a difference between the light amounts of the plurality of light beams, a difference between spot shapes of the plurality of light beams on the slit member, and a light amount of the plurality of light sources themselves. And the rising characteristics of
The multi-beam optical scanning device according to claim 14, wherein the determination is performed based on a combination of two or more factors among the differences in the internal light intensity distributions of the plurality of light beams. 20. The multi-beam optical scanning device according to claim 14, further comprising a reflection unit that reflects the plurality of light beams at a predetermined angle in at least a sub-scanning direction and guides the plurality of light beams to the detection unit. 21. The multi-beam optical scanning device according to claim 20, wherein the predetermined distance for shifting the slit member is determined based on a reflection angle of the reflection means and a difference between the light amounts of the plurality of light beams. 22. The multi-beam according to claim 20, wherein the predetermined distance for shifting the slit member is determined based on a reflection angle of the reflection means and a difference between spot shapes of the plurality of light beams on the slit member. Optical scanning device. 23. The multi-beam optical scanning device according to claim 20, wherein the predetermined distance at which the slit member is shifted is determined based on a reflection angle of the reflection unit and a rising characteristic of light amounts of the plurality of light sources. 24. The multi-beam optical scanning device according to claim 20, wherein the predetermined distance for shifting the slit member is determined based on a reflection angle of the reflection means and a difference between internal light intensity distributions of the plurality of light beams. 25. A predetermined distance by which the slit member is displaced is a difference between light amounts of the plurality of light beams, a difference between spot shapes of the plurality of light beams on the slit member, and a light amount of the plurality of light sources themselves. And the rising characteristics of
21. The multi-beam optical scanning device according to claim 20, wherein the determination is performed based on a combination of two or more factors among the differences in the internal light intensity distributions of the plurality of light beams and a reflection angle of the reflection unit. 26. The multi-beam optical scanning device according to claim 14, wherein a predetermined distance for shifting the slit member is adjustable. 27. An image forming apparatus equipped with the multi-beam optical scanning device according to at least one of claims 1 to 26.