JP2000255096A - Imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance compatibility of scanner unit by previously adjusting the fixing position of a BD unit such that a scanning light for obtaining an image writing reference signal impinges on the center of effective detection part of the BD unit. SOLUTION: A part of scanning light deflected by a rotary polygon mirror 3 is separated by a BD mirror 6 disposed on the outside of an optical box 10 and introduced into a BD unit 11 thence transmitted, as an image writing reference signal, to a semiconductor laser 1. In order to eliminate the possibility that the BD unit 11 can not receive the light due to unit tolerance of the optical box 10 or assembling error of reflectors 5a-5c when a scanner unit is replaced, the BD unit 11 is moved up and down using the emboss 31a of a body side plate 31 as a slide guide and the fixing position of the BD unit 11 is adjusted such that the scanning light impinges on the center of the light receiving plane of the BD unit 11 before the BD unit 11 is secured by means of screws 32.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light deflection scanning device (laser scanner) for deflecting and scanning a light beam such as a laser beam by a rotating polygon mirror rotating at a high speed and forming a latent image by forming an image on a photosensitive member. The present invention relates to an image forming apparatus such as a laser beam printer or a laser facsimile to be mounted.

[0002]

2. Description of the Related Art A light deflection scanning device used in an image forming apparatus such as a laser beam printer or a laser facsimile is
A light beam such as a laser beam (laser light) is reflected by a rotating polygon mirror that rotates at a high speed, and the reflected light beam is deflected and scanned, and the obtained scanning light is formed on a photosensitive member on a rotating drum to form an electrostatic latent image. I do. Next, the electrostatic latent image on the photoreceptor is visualized into a toner image by a developing device, transferred to a recording medium such as recording paper, sent to a fixing device, and printed by heating and fixing the toner on the recording medium ( Print) is performed.

FIG. 6 shows an image forming apparatus according to a conventional example. An image forming apparatus main body A has an image reading section B serving as image reading means for reading image information on the image surface of a book document at an upper portion thereof. , And a seat deck D is attached to a lower portion thereof.

The image reading section B includes a scanning light source 20.
1, a platen glass 202, a document pressure plate 203 that can be opened and closed with respect to the apparatus main body A, a mirror 204, a lens 205, a light receiving element (photoelectric conversion element) 206, an image processing unit, and the like. Then, the platen glass 202
When a book document or sheet-shaped document such as a book, cardboard, or curled paper is placed on the top with the document surface facing down, the back is pressed by the document pressure plate 203, the document is set in a stationary state, and the reading start key is pressed. The scanning system light source 201 is a platen glass 202
Is scanned in the direction of arrow a to read the image information on the document surface. Image information of the document read by the scanning light source 201 is processed by an image processing unit, converted into an electric signal, and transmitted to a laser scanner (optical deflection scanning device) 111.

Here, the image forming apparatus main body A functions as a copying machine when the processing signal of the image processing section is input to the laser scanner 111, and functions as a printer when the output signal of the personal computer is input. If a transmission signal from a facsimile device of another device is input or a processing signal of the image processing unit is transmitted to a facsimile device of another device, the device functions as a facsimile device.

Reference numeral 209 denotes a heat exhaust fan for discharging the heated air in the main body to the outside of the main body.

On the other hand, a sheet cassette 208 is mounted below the image forming section C.
Are two lower cassettes 208a and upper cassettes 208b, which are configured as one feeding unit. In this apparatus, three feeding units U1, U2 and U3 are provided and 6
Each cassette is to be mounted. One upper feed unit U1 is detachably attached to the apparatus main body A, and two lower feed units U2 and U3 are detachably attached to the sheet deck D.

The sheets (recording paper) accommodated in each of the cassettes 208a and 208b are fed out by a pickup roller 103 serving as a feed rotary member as described later, and cooperate with a feed roller 104 and a retard roller 105. After being separated and fed one by one by the
The sheet is guided by the registration rollers 106 and fed to the image forming section C by the registration rollers 106 in synchronization with the image forming operation.

The image forming section C includes an electrophotographic photosensitive drum (rotating drum) 112, a reflecting mirror 113, and a developing device 11.
4 and a transfer charger 115.
Then, a laser scanner 111 is provided on the surface of the electrophotographic photosensitive drum 112, which is uniformly charged by the transfer charger 115.
A laser beam corresponding to image information emitted from the image forming apparatus is scanned by an image writing optical system to form a latent image, and a toner image is formed on the latent image by a developing unit 114, and the electrophotographic photosensitive drum is formed by a registration roller 106. The toner image is transferred onto the first surface of the sheet by the transfer charger 115 on the sheet conveyed in synchronization with the rotation of the 112.

Reference numeral 117 denotes a conveying belt for conveying a sheet on which toner is formed, 118 denotes a fixing device, and 119 denotes a discharge roller. The sheet on which the toner image has been formed is conveyed to a fixing device 118 by a conveying belt 117, and is heated and pressed to fix the toner image on the sheet surface.
Discharged and loaded.

When an image is recorded on both sides of a sheet, the sheet discharged from the fixing device 118 is sandwiched by discharge rollers 119, and when the rear end of the sheet passes the branch point 207, the discharge rollers 119 are turned off. After being reversed and once placed on the sheet double-sided tray 121, the transport rollers 107,
The sheet conveyed by the roller 108 and reaches the registration roller 106, is formed such that an image is formed on the second surface in the same manner as described above, and then discharged and stacked on the sorter 120.

FIG. 7 shows the inside of a laser scanner 111, which is an optical deflection scanning device. Laser light generated from a semiconductor laser of a light source unit 501 is collimated by a collimator lens, passes through a diaphragm, and is converted into a line by a cylindrical lens 502. Is condensed into a beam of light, and
03 enters the reflection surface. The reflected light is applied to the rotating polygon mirror 5
The scanning light is deflected by the rotation of the scanning lens 03 and becomes scanning light in a predetermined direction (main scanning direction), and forms an image on the above-described electrophotographic photosensitive drum 112 via the imaging lens system 504 and the like. The light flux formed on the photoreceptor forms an electrostatic latent image in accordance with the main scanning by the rotation of the rotating polygon mirror 503 and the sub-scanning by the rotation of the electrophotographic photosensitive drum 112.

A part of the scanning light obtained by the deflection scanning of the rotary polygon mirror 503 is BD at one end in the main scanning direction.
The light is separated by a mirror 505 below the scanning surface, is introduced to a BD sensor 507 via a BD lens 506, and is converted into a reference signal for creating a latent image. The formation of the latent image is B
After the reference signal is generated by the D sensor 507, the semiconductor laser of the light source unit 501 is turned off, and after a certain time has elapsed, light emission is performed again. The time at this time is input to the CPU of the image forming apparatus from the operation unit using a numeric keypad or the like.

A light source unit 501 including a semiconductor laser, a cylindrical lens 502, a rotating polygon mirror 503, an imaging lens system 504, and the like are mounted on a side wall or a bottom wall of the optical box 510. The scanning light is applied to one end of the optical box 510.
There is provided a window for taking out from 10.

The imaging lens system 504 includes a spherical lens 504
a and a toric lens 504b, and a rotating polygon mirror 5
03 has a so-called fθ function for converting scanning light scanned at a constant angular speed into scanning light scanning at a constant speed on the electrophotographic photosensitive drum 112.

A motor 5 for rotatingly driving the polygon mirror 503
03a is a driving IC mounted on the motor board 503b.
And a magnetic circuit including a stator excited by a driving current supplied from the driving IC, a rotor opposed thereto, and the like.

In the optical deflection scanning apparatus having the above-described configuration, assuming that the printing speed P (mm / s) of the image forming apparatus, the printer resolution T (dpi), and the number M of the reflecting surfaces of the rotating polygon mirror 503 are M, the rotating polygon mirror is used. 503 rotation speed N (rpm)
Is determined by the following equation: N = P / 25.4 × T / M × 60

[0018]

However, according to the above prior art, if the process speed of the image forming apparatus is increased in order to speed up printing, the rotating polygon mirror must be rotated at a higher speed. Noise due to the wind noise of the rotating polygon mirror increases.

Furthermore, since the effect of centrifugal force during rotation is multiplied by a multiplier, deformation of the reflecting surface of the rotating polygon mirror leads to problems such as distortion of the output image.

As is apparent from the above equation, it is effective to increase the number of surfaces of the rotary polygon mirror in order to suppress the increase in the number of rotations of the rotary polygon mirror as much as possible. Increasing the number of faces of the rotating polygon mirror makes the polygon closer to a circle, which also contributes to a reduction in wind noise.

However, if the diameter of the circumscribed circle (outer dimension) of the rotating polygon mirror is increased when the number of faces is increased, the moment of inertia due to the increase in the moment of inertia accompanying the increase in the diameter of the rotating polygon mirror is increased. The deformation of the reflecting surface due to the centrifugal force increases, which adversely affects latent image formation.

Further, since the torque of the motor needs to be increased by increasing the diameter of the rotary polygon mirror, the power consumption also increases.

If the diameter of the circumscribed circle of the rotary polygon mirror is set to be the same as or slightly increased from that of the low-speed model, the width of the image on the image plane is the same as that of the low-speed model. However, if the space occupied by the image writing optical system in the main body of the image forming apparatus is increased in order to increase the optical path length, the size of the main body is increased, which impairs the merchantability.

Therefore, a device has been devised to extend the optical path length in a small space by inserting a plurality of reflection mirrors for folding the scanning light into the optical path of the scanning light from the imaging lens system to the photosensitive member. Is being developed.

In this case, the optical path length to the BD sensor for obtaining a reference signal for image writing must be increased. However, if the BD sensor or the like is built in the optical box of the scanner unit, the image forming apparatus will not operate. The entire scanner unit to be assembled becomes large. In order to avoid such an increase in the size of the scanner unit and to realize a compact and high-speed image forming apparatus, it is desirable to dispose a BD sensor or the like outside the optical box. However, when the BD sensor or the like is installed outside the optical box (scanner unit), the relative position with respect to the BD sensor changes due to a unit tolerance when the scanner unit is replaced, so that light serving as a reference signal cannot be received. A new problem arises.

In particular, if the configuration is such that light serving as a reference signal is reflected by a plurality of reflecting mirrors and then introduced into the BD sensor, the light is reflected by the reflecting mirror.
In some cases, the D sensor cannot receive light.

That is, in the conventional image forming apparatus, when the scanner unit is replaced, the reference signal for image writing may not be able to be received, and there is an unsolved problem that the compatibility of the scanner unit is poor.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned unresolved problems of the prior art, and is intended to increase the size of a rotary polygon mirror or an image forming apparatus while maintaining the compatibility of a scanner unit. It is an object of the present invention to provide an image forming apparatus provided with a compact image writing optical system capable of increasing the process speed without any problem.

[0029]

In order to achieve the above object, an image forming apparatus according to the present invention comprises: a rotary polygon mirror for deflecting and scanning a light beam to convert it into scanning light; and forming an image of the scanning light on a photosensitive member. A scanning optical system having an imaging unit for causing the scanning unit to detect a part of the scanning light as a reference signal for image writing; a housing supporting the scanning optical system and the detecting unit; And a mounting position adjusting means for adjusting the mounting position of the detecting means with respect to the housing so that the part of the scanning light is incident on the center of the detection effective portion.

It is preferable that the detecting means has a unit housing for unitizing the sensor, the slit and the condenser lens.

[0031]

When the optical box containing at least a part of the rotating polygon mirror and the image forming means is replaced as a scanner unit, a relative displacement with respect to the detecting means provided outside the optical box occurs, and a reference signal for image writing is generated. May not be detected. In order to avoid such a situation, at the time of the initial assembly of the image forming apparatus, the mounting position of the detection unit is adjusted in advance so that the scanning light serving as a reference signal for image writing enters the center of the detection effective portion of the detection unit. deep.

Even if the incident position of the scanning light slightly deviates from the center of the detecting means when the scanner unit is replaced, the reference signal can be detected within the range of the effective detection portion, so that the compatibility of the scanner unit is greatly improved. Can be improved.

In particular, in a compact image forming apparatus designed to secure a required optical path length by folding the scanning light by a plurality of reflecting mirrors, the optical path of the scanning light greatly changes due to a slight angle shift of the reflecting mirror. Therefore, adjusting the mounting position of the detecting means for detecting the reference signal as described above and effectively utilizing the area of the detection effective portion is not necessary for image forming while maintaining the compatibility of the scanner unit. This is extremely effective in responding to miniaturization and speeding up of the device.

[0034]

Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows a main part of an image forming apparatus according to an embodiment. An image reading optical system (not shown) having a light receiving element and a lens similar to the conventional example is supported on the upper part of the image forming apparatus. The read image information is converted into an electric signal and transmitted to the semiconductor laser 1 of the optical box 10 as a scanner unit.

A laser beam, which is a light beam generated from the semiconductor laser 1, is collimated by a collimator lens 1a, condensed into a linear light beam by a cylindrical lens 2 through a stop, and reflected by a reflecting surface of a rotary polygon mirror 3. Incident on. The reflected light is deflected and scanned by the rotation of the rotary polygon mirror 3 to become scanning light in a predetermined direction (main scanning direction).
An imaging lens system 4 which is an imaging means constituting a scanning optical system together with the rotary polygon mirror, and first to third reflection mirrors 5a to 5a to
An image is formed on the photosensitive member on the rotating drum 40 (see FIG. 2) via 5c. The light beam that forms an image on the photoreceptor forms an electrostatic latent image in accordance with the main scanning by the rotation of the rotary polygon mirror 3 and the sub-scanning by the rotation of the rotating drum 40.

The semiconductor laser 1, the cylindrical lens 2, the rotary polygon mirror 3, the imaging lens system 4 and the like are mounted on the side wall and the bottom wall of the optical box 10.

The imaging lens system 4 comprises a spherical lens 4a and a toric lens 4b, and converts the scanning light scanned at a constant angular speed by the rotary polygon mirror 3 into the scanning light scanned at a constant speed on the rotating drum 40. fθ function.

The upward opening of the optical box 10 is
After the rotating polygon mirror 3 and the imaging lens system 4 and the like are assembled therein, it is closed by the lid member 20.

Motor 3a for driving rotary polygon mirror 3 for rotation
Is constituted by a motor circuit, a magnetic circuit including a stator which is excited by a driving current supplied from a driving IC mounted on the motor substrate, and a rotor opposed thereto.

When the rotary polygon mirror 3 is rotated at a high speed, noise due to wind noise increases. Therefore, a closed cover 22 that covers the rotary polygon mirror 3 is provided. The cover 22 is integrally formed of a metal material such as aluminum die-cast, and has an opening through which laser light is emitted and emitted, and a dust-proof glass 23 for dust prevention is attached to the opening.

The electrostatic latent image formed on the photoreceptor on the rotating drum 40 is visualized as a toner image by a developing device (not shown), and is transferred to a sheet as a recording medium conveyed from a conveying roller by a transfer charger. Transcribed. The sheet on which the toner image has been transferred is sent to a fixing device by a transport belt,
Fixing of the toner image by pressing and heating is performed. The sheets printed in this way are discharged and stacked on a sorter by discharge rollers.

The first and second reflection mirrors 5a and 5b are incorporated in a housing 51 and are unitized to form a mirror unit 50. The mirror unit 50 is assembled between the optical box 10 and the third reflection mirror 5c after assembling the first and second reflection mirrors 5a and 5b therein. In other words, the first and second reflection mirrors 5a and 5b built in the mirror unit 50 provide an optical path for the scanning light before the scanning light emitted from the window of the optical box 10 reaches the third reflection mirror 5c. Is repeatedly inserted into the space above the rotary drum 40 together with the third reflection mirror 5c so as to obtain the required optical path length reaching the rotary drum 40.

By using the plurality of reflection mirrors 5a to 5c in this manner, the optical path of the scanning light can be extended in a space which is almost the same as that of the related art without increasing the size of the entire image forming apparatus. The width of the image on the imaging plane can be enlarged as needed.

A part of the scanning light obtained by the deflection scanning of the rotary polygon mirror 3 is divided into first and second reflection mirrors 5a and 5b.
After being reflected by the optical box 10, the optical box 10 is separated from the optical box 10 by the BD mirror 6 disposed on the stay 30.
BD lens 7 which is folded back to the side of
The signal is introduced into the BD sensor 8 as a sensor through (see FIG. 3), and is converted into a reference signal for image writing.

The BD lens 7 and the BD sensor 8 are unitized by a unit housing 11a together with a slit plate 9 having a slit 9a, as will be described later, to constitute a BD unit 11 serving as detecting means. BD unit 1
1 is fixed to the main body side plate 31 which forms a housing together with the stay 30 via the support plate 12 after adjusting the mounting position as described below.

The main body side plate 31 has a pair of embosses 31 a as a slide guide, and the support plate 12, which is a mounting position adjusting means for holding the BD unit 11, has a long hole 12 a into which each emboss 31 a of the main body side plate 31 is inserted. Having. The support plate 12 is moved up and down together with the BD unit 11 so that the BD
After adjusting the mounting position of the BD unit 11 so that scanning light serving as a reference signal for image writing is incident on the center of the detection effective portion of the unit 11, the support plate 12 is screwed to the main body side plate 31 with the screw 32. Thus, the BD unit 11 is attached.

The length of the long hole 12a of the main body side plate 31 is set sufficiently long so that the mounting height can be adjusted by moving the BD unit 11 within a wider range than the deviation tolerance of the scanning light with respect to the BD unit 11. You.

FIGS. 3 and 4 illustrate the structure of the BD unit 11, and the BD lens 7 is indicated by a broken line in FIG. The slit plate 9 has a slit 9a for narrowing down the amount of light so that the BD sensor 8 does not saturate,
The BD lens 7 is arranged between the slit plate 9 and the BD sensor 8.

The longitudinal direction of the slit 9a is perpendicular to the main scanning direction of laser light (scanning light) and has a predetermined opening length.
The center of the effective portion of the lens 7, that is, the optical axis, and the slit 9a
The center of the effective portion, ie the center in the longitudinal direction, and BD
The longitudinal center of the light receiving portion, which is the effective detection portion of the sensor 8, is set to be on the same straight line.

Further, the slit 9a is provided with a wide portion 9b at the center in the longitudinal direction, which widens in the main scanning direction of the laser beam.

The length of the slit 9a in the longitudinal direction depends on the length of the optical box 1 incorporating the rotary polygon mirror 3 and the imaging lens system 4.
0, which is longer than the standard value of the height deviation of the irradiation position of the scanner unit.

The effective portion of the BD lens 7 is designed to include the entire length of the slit 9a. That is, the size of the BD lens 7 is determined by the size of the slit 9a.

During the initial assembly of the image forming apparatus, the BD unit 11 is slid along the embossment 31a of the main body side plate 31, and the height position (mounting position) is adjusted as described above, and then fixed by screws.

The BD mirror 7 is arranged at a certain angle with respect to the reflection mirrors 5a to 5c of the image writing system. This is for contributing to the miniaturization of the main body. To prevent the main body from increasing in the depth direction, the optical path is limited and folded back, so that the BD unit only uses the dead space beside the scanner unit. 11 is provided.

Next, the reflection mirrors 5a to 5a of the image writing system
How the angle shift 5c affects the phase shift of the latent image on the photoconductor surface will be described.

As shown in FIG. 5, for example, when the first reflecting mirror 5a causes an angle shift of 0.50 ° (30 minutes), the designed optical path F ₀ shifts to F ₁ and a two-dot chain line. The imaging position corresponding to the virtual photosensitive member surface S indicated by .DELTA.t = 3.
Move 26 mm. This is equivalent to an incident shift of the laser beam incident on the BD unit 11 in a direction perpendicular to the main scanning direction.

The cause of such a displacement is that the rotating polygon mirror 3 is tilted, that is, the scanner unit is
For example, the inclination when the reflecting mirrors 5a to 5c are attached to the stay 30 may be considered. When these are stacked, Δt becomes 5 mm or more at the worst tolerance.

Even if the deviation is adjusted so as to be canceled by adjusting the angle of the reflection mirror 5a in the optical path, the image formation position of the light imaged on the photoconductor and the image formation of the light imaged on the BD unit 11 can be achieved. The position cannot be corrected at the same time because the optical path before reaching the position is different.

If the height shifts by ± 5 mm, that is, 10 mm in the range, the laser beam comes off the effective portion of the BD lens 7 or slips off the slit 9a, and the reference signal is
There is a possibility that the detection will not be performed by the sensor 8.

Therefore, as described above, a step of assembling the BD unit 11 to the main body side plate 31 (at the time of initial assembly).
Then, the mounting position of the BD unit 11 is adjusted so that light is incident on the center of the detection effective portion including the optical axis position of the BD lens 7 and the like.

Even if a height deviation occurs in the scanning light when the scanner unit, that is, the optical box 10 is replaced, if the deviation is within the standard value, the reference signal for image writing is changed to the BD unit 1.
1 and enters the detection effective portion. Therefore, the trouble unlike the conventional example does not occur. The method of adjusting the mounting position of the BD unit 11 is as follows.

First, the laser chip of the semiconductor laser 1 is made to emit light, and the detection output of the scanning light reflected by the rotating polygon mirror 3 is measured by a measuring instrument such as an oscilloscope, using a BD unit 1
It is detected as one incident time.

The mounting position is set by moving the BD unit 11 up and down along the emboss 31a so that the detection time is about the center position of the longest area, and the BD unit 11 is fixed to the main body side plate 31 by screws 32.

Thus, the mounting height of the BD unit 11 is adjusted, and the height deviation of the image forming position of the laser beam on the BD sensor 8 is canceled at the time of initial (initial assembly).

In this embodiment, a multifunction copier is described, but a similar device may be mounted on a laser printer or the like.

Although three reflecting mirrors are used, the number of reflecting mirrors is not limited to three, and one or more reflecting mirrors may be used.

In the present embodiment, the height deviation of the image formation position of the laser beam on the BD sensor is adjusted by adjusting the height of the BD unit.
It is configured so that it can be canceled at the time of initial assembly,
Even if a plurality of reflecting mirrors are arranged in the optical path of the laser beam, if the image forming position shift to the BD unit when the scanner unit is replaced is within the range of a detection effective portion such as a BD sensor, a reference for image writing. A signal can be obtained reliably. That is, an image writing optical system having a long optical path length can be realized without increasing the size of the apparatus main body, and the compatibility of the scanner unit with the apparatus main body can be greatly improved.

Further, by minimizing the deviation of the image forming position on the BD sensor, the size of the BD lens can be reduced to the minimum size, so that cost reduction can be expected.

[0070]

Since the present invention is configured as described above, it has the following effects.

BD for obtaining reference signal for image writing
By adjusting the mounting position of the unit in advance so that the scanning light serving as the reference signal is incident on the center of the effective detection unit such as a BD sensor, the compatibility of the scanner unit including the rotary polygon mirror and the imaging lens system is adjusted. It is possible to cope with downsizing and speeding up of the image forming apparatus while maintaining the above. Further, since the imaging position shift on the BD sensor is reduced, the size of the BD lens can be reduced, which can contribute to cost reduction and the like.

[Brief description of the drawings]

FIG. 1 is a partial plan view showing a main part of an image forming apparatus according to an embodiment.

2 is a partial cross-sectional side view showing a portion of the apparatus of FIG. 1 in cross section.

FIG. 3 is an elevational view showing only a BD unit of the apparatus of FIG. 1;

FIG. 4 is a plan view showing the BD unit of FIG. 3;

FIG. 5 is a diagram illustrating a change in an optical path of scanning light due to an angle shift of a reflection mirror.

FIG. 6 is a schematic diagram illustrating an image forming apparatus according to a conventional example.

FIG. 7 is a schematic plan view showing the light deflection scanning device of FIG.

[Explanation of symbols]

 Reference Signs List 1 semiconductor laser 3 rotating polygon mirror 3a motor 4 imaging lens system 5a to 5c reflection mirror 6 BD mirror 7 BD lens 8 BD sensor 9 slit plate 9a slit 10 optical box 11 BD unit 11a unit housing 12 support plate 20 lid member 30 stay 31 body side plate 31a emboss 32 screw 40 rotating drum

Claims (8)

[Claims] A scanning optical system having a rotary polygon mirror for deflecting and scanning a light beam to convert it into scanning light, and an image forming means for forming an image of the scanning light on a photosensitive member; Detecting means for detecting as a reference signal; a housing supporting the scanning optical system and the detecting means; and the housing such that the part of the scanning light is made incident on a center of a detection effective portion of the detecting means. An image forming apparatus having an attachment position adjusting unit for adjusting an attachment position of the detection unit with respect to the image forming apparatus. 2. The apparatus according to claim 1, wherein said mounting position adjusting means is configured to be able to move said detecting means within a range wider than an incident deviation tolerance of a part of the scanning light with respect to the detecting means. Image forming apparatus. 3. A mounting position where the part of the scanning light is incident on the center of a detection effective portion of the detecting means by measuring an incident time during which a part of the scanning light is incident on the detecting means. The image forming apparatus according to claim 1, wherein: 4. An image forming apparatus according to claim 1, wherein said detecting means has a sensor for receiving a part of the scanning light and a slit. 5. An image forming apparatus according to claim 4, wherein said detecting means has a condensing lens for condensing a part of the scanning light. 6. The image forming apparatus according to claim 5, wherein the detection means has a unit housing that unitizes the sensor, the slit, and the condenser lens. 7. An optical box for accommodating at least a part of the rotary polygon mirror and the scanning optical system, wherein a detecting means is provided outside the optical box.
7. The image forming apparatus according to any one of claims 6 to 6. 8. The image forming apparatus according to claim 1, wherein the image forming means has a plurality of reflection mirrors for turning back the scanning light.