JPH10239617A - Optical scanner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make the focal length of a collimator lens relatively large by converting a beam into a lightly converged light beam by the collimator lens, and arranging a shaping lens and converting it into a parallel light beam only in a horizontal scanning direction. SOLUTION: A semiconductor laser 11 is used as a light source and a laser beam emitted as divergent light is shaped by the collimator lens 21 into the converged light beam which has a small angle of convergence. The projection surface of the collimator lens 21 is formed into an aspherical surface which is rotationally symmetrical about the optical axis so as to reduce the spherical aberration. The light beam projected from the collimator lens 21 is made incident on the shaping lens 22 which has a plane on the incidence side and a concave cylindrical surface on the projection side. The shaping lens 22 has negative refractive power only in the horizontal scanning direction and the incident converged light beam is converted into the parallel light beam which has a relatively small diameter in the horizontal scanning direction. The beam is the converged light beam converted by the collimator lens 21 as it is in a vertical scanning direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning device used for a laser beam printer or the like, and more particularly to a structure of an optical scanning device using an optical system in which a light beam is incident twice on a reflecting surface of a rotary polygon mirror. .

[0002]

2. Description of the Related Art Rotary polygon mirrors have been widely used as deflectors for deflecting and scanning light beams in image recording devices such as laser beam printers and optical scanning devices used for various image reading and measuring devices.

In these devices, a light beam is repeatedly scanned on a surface to be scanned by a light scanning device on a straight line or a curved line, and a medium to be scanned positioned on the surface to be scanned is substantially perpendicular to the scanning direction. Two-dimensional scanning is performed by relative movement. Note that the former scanning direction by the optical scanning device is defined as a “main scanning direction”, and the latter relative movement direction of a medium to be scanned is defined as a “sub-scanning direction”.

In recent years, a higher-speed optical scanning device has been required in the above-mentioned devices in order to improve resolution and processing speed. In an optical scanning apparatus using a rotating polygon mirror for deflecting a light beam, in order to increase the scanning speed (scanning frequency), (1) increase the number of revolutions of the rotating polygon mirror (2) increase the number of faces of the rotating polygon mirror There are two ways to do this.

[0005] In order to increase the rotation speed of the rotary polygon mirror, a bearing capable of high-speed rotation is required. However, the most frequently used ball bearing at present has a maximum of about 20,000 rotations per minute. 3000 per minute with air bearing
Although it can be used at a rotation speed of 0 rotation or more, usable devices are limited because the bearing is expensive. In particular, it cannot be used for inexpensive laser beam printers for general consumers.

On the other hand, when the number of faces of the rotary polygon mirror is increased,
The rotation angle per reflection surface becomes small. Further, if it is attempted to secure the size of each reflecting surface to a certain value or more, the diameter of the rotary polygon mirror becomes large.

In an optical scanning device, a light beam is imaged on a surface to be scanned, and when a laser beam is scanned, in order to form an image on a small spot, a rotating polygon mirror is used in accordance with the spread angle of the light beam. The reflection surface needs to have a certain size in the main scanning direction. However, when the number of surfaces of the rotating polygon mirror is increased, the scanning angle of the light beam becomes smaller because the rotation angle on one reflecting surface is small. If the scanning angle of the light beam is small, the focal length of the scanning optical system becomes longer in order to obtain a predetermined scanning width, and the optical path length from the rotary polygon mirror to the surface to be scanned also becomes longer. For this reason, the diameter of the light beam on the reflecting surface of the rotating polygon mirror in the main scanning direction also increases, and the reflecting surface becomes larger than when the number of surfaces is small, and the size of the rotating polygon mirror further increases. .

That is, as the number of rotating polygon mirrors increases, the required size of the reflecting surface becomes inconsistent with that when the number of rotating polygon mirrors is small. Once the size of the tangent cylinder is determined, the upper limit of the number of faces is determined. For example, in an optical scanning device used for a laser beam printer, the required scanning width is 350 mm, the wavelength is 780 nm, and the radius of the inscribed cylinder of the rotating polygon mirror is 25 m.
m, the spot diameter in the main scanning direction on the surface to be scanned is 50 μm
In the case where the number is set to be less than or equal to seven, the upper limit is approximately seven.

Therefore, when the diameter of the rotary polygon mirror is increased to increase the number of surfaces, the weight and the second moment of inertia of the rotary polygon mirror increase, and the air resistance (windage) accompanying rotation increases. The number of revolutions is limited low.

As described above, the number of faces and the number of revolutions of the rotating polygon mirror have upper limits, and each has contradictory characteristics. Therefore, various scanning devices have been devised in order to obtain a scanning speed exceeding that.

For example, in the technique described in Japanese Patent Application Laid-Open No. 51-100742, a semiconductor laser array is used as a light source,
By simultaneously scanning the surface to be scanned with a plurality of laser beams, the scanning speed is improved. According to this method, the scanning speed can be increased by the number of lasers integrated in the element without increasing the rotation speed of the rotary polygon mirror.

On the other hand, in Japanese Patent Application Laid-Open No. 51-32340, a light beam emitted from a light source is made to enter a rotary polygon mirror with a very small diameter in the main scanning direction, and a deflected light beam is transmitted to a transmission optical system. A method is disclosed in which the light is again incident on the rotating polygon mirror via the. After the second incidence on the rotating polygon mirror, the light beam forms an image as a spot on the surface to be scanned by the scanning optical system. That is, the light beam is made to enter the rotating polygon mirror twice.

In the latter method, the diameter of the light beam in the main scanning direction when the light beam first enters the rotary polygon mirror is extremely small as compared with the case where the light beam first enters the rotating polygon mirror, and the second rotation is performed. The transmission optical system is configured so that the light beam incident on the polygon mirror follows the center point of the rotating reflecting surface in the main scanning direction.

With this configuration, when the light beam first enters the rotary polygon mirror, the diameter of the light beam can be extremely reduced, so that scanning can be performed to the full division angle of the rotary polygon mirror. When the light beam deflected by the first reflecting surface is incident on the rotary polygon mirror for the second time via the transmission optical system, the diameter of the light beam is set to a value required to obtain a predetermined spot on the surface to be scanned. Although it is enlarged to a necessary size, the size of the light beam can be set independently of the rotation angle of the rotating polygon mirror because it follows the rotation of the reflecting surface. Therefore, the size of the reflection surface of the rotary polygon mirror in the main scanning direction can be reduced, and a rotary polygon mirror having a small diameter and a large number of surfaces can be used.

[0015]

As described above, in the optical system in which the light beam is incident twice on the rotating polygon mirror, the light beam is first incident on the rotating polygon mirror and the light beam is incident on the second time. In particular, when the light beam is parallel to the main scanning direction, the imaging point does not shift from the surface to be scanned due to the influence of the fluctuation of the position of the reflection point in the optical axis direction. On the other hand, in the sub-scanning direction, the first reflection surface and the second reflection surface of the rotary polygon mirror may be configured in an optically conjugate relationship so as to eliminate the influence of the tilt error of the reflection surface of the rotary polygon mirror. desirable.

In order to obtain a light beam having such characteristics, a light beam from a light source must be parallel to the main scanning direction and be a focused light beam in the sub-scanning direction at the first reflection surface incident on the rotary polygon mirror. The beam needs to be shaped. The simplest way to obtain such a light beam is to use one anamorphic collimator lens. But,
In such a configuration, the focal length of the collimator lens is reduced, and accordingly, the radius of the lens surface of the collimator lens is also reduced, making it difficult to process the lens surface or a mold for molding the lens surface. In addition, when the size of the lens surface is reduced, accuracy required for the lens surface becomes strict due to aberrations, making it difficult to manufacture, and at the same time, there is a concern that the imaging performance on the surface to be scanned may be deteriorated.

Since the distance between the light source and the first reflecting surface of the rotary polygon mirror is short, the distance from the first reflecting mirror of the transmission optical system to the first reflecting surface of the rotary polygon mirror is shorter. I will. However, when a part of the beam shaping optical system and the transmission optical system are arranged in the rotation axis direction of the rotary polygon mirror, that is, in the sub-scanning direction, the member of the light source unit and the circuit board for driving the semiconductor laser are transmitted. In order to prevent interference with the optical elements of the optical system and the light beam, it is necessary to impose great restrictions on the shape and position, which is not preferable in terms of function.

To avoid this problem, a convex cylindrical lens having a characteristic that is rotationally symmetric about the optical axis, is once converted into a parallel light beam by a collimator lens, and has a refractive power only in the sub-scanning direction at a distance. And a method of converting into a focused light beam in the sub-scanning direction is also conceivable.

However, in this case, the light beam that has exited the collimator lens becomes a parallel light beam having a small diameter, and the diameter becomes considerably small especially in the sub-scanning direction. For this reason, as a Gaussian beam characteristic, there is a problem that even if the light beam is a parallel light beam immediately after exiting the collimator lens, the diameter of the light beam increases as the distance from the lens increases. Furthermore, there is still a problem that the focal length of the collimator lens is short among the problems already described.

In view of the above problems, in the first invention of the present application,
2. Description of the Related Art In an optical scanning device that deflects and scans a light beam by irradiating a light beam twice to a rotating polygon mirror, the lens surface has a large radius of curvature and the lens surface has a large size. It is an object of the present invention to obtain a collimator lens that can easily process a mold and at the same time achieve good imaging performance. It is another object of the present invention to reduce the accuracy required for the lens surface in terms of aberration, thereby facilitating the manufacture, and at the same time, improving the imaging performance on the surface to be scanned.

It is another object of the present invention to easily obtain a desired imaging spot size by not using a configuration in which a thin parallel light beam state continues for a long time.

Next, according to a second aspect of the present invention, in an optical scanning device that deflects and scans a light beam by irradiating the light beam twice to a rotary polygon mirror, an obstacle in a space around the light source unit is eliminated. It is another object of the present invention to secure a sufficient circuit board space for driving the light source.

[0023]

In order to solve the above-mentioned problems, an optical scanning device according to a first aspect of the present invention comprises a light source and a beam shaping device for converting a light beam from the light source into a shaped light beam having predetermined characteristics. An optical system, a shaped light beam deflected by a first reflecting surface, a rotating polygon mirror having at least a first reflecting surface and a second reflecting surface, and light deflected by the first reflecting surface of the rotating polygon mirror. A transmission optical system for making the beam incident on the second reflection surface of the rotary polygon mirror, and a scanning optical system for forming an image of the scanning light beam deflected by the second reflection surface of the rotary polygon mirror on a predetermined surface to be scanned. A beam shaping optical system configured to scan a surface to be scanned with a scanning light beam, wherein the beam shaping optical system emits a divergent light beam from a light source into a focused light beam in a main scanning surface, and a collimator lens. Focused light beam in the main scanning plane Characterized by comprising the shaping lens for converting a parallel light beam.

Next, in the optical scanning device of the second invention of the present application,
A light source, a beam shaping optical system that converts a light beam from the light source into a shaped light beam having predetermined characteristics,
And a rotating polygon mirror having at least a first reflecting surface and a second reflecting surface, and a light beam deflected by the first reflecting surface of the rotating polygon mirror being reflected by a second reflecting surface of the rotating polygon mirror. A transmission optical system to be incident on the surface, a reflection mirror in the optical path of the transmission optical system for bending the optical axis of the transmission optical system, and a scanning light beam deflected by the second reflection surface of the rotary polygon mirror. A scanning optical system for forming an image on the surface to be scanned, wherein the distance from the first reflecting surface to the light source is from the first reflecting surface to the reflecting mirror. Is larger than the distance to the one closest to the first reflection surface.

[0025]

1 and 2 are perspective views showing an overview of an optical scanning device according to an embodiment of the present invention, and FIG.
FIG. 9 is a perspective view showing a state where the correction lens 62 and the third folding mirror 93 are further removed. FIGS. 3 and 4 are plan views of the optical scanning device according to the embodiment of the present invention in a main scanning section. 3 and 4, the light beam after the first reflecting surface 31 of the rotary polygon mirror 30 is divided into four positions: a beam detection position, a scanning start position, an optical axis position of the scanning optical system, and a scanning end position.
The light beam positions at various locations are shown. FIG. 3 shows a scanning optical system and a light beam detecting optical system and a light beam passing therethrough, and FIG. 4 shows a transmission optical system, a beam shaping optical system and a light beam passing therethrough. FIG. 5 is a sectional view of a sub-scanning plane including a beam shaping optical system according to an embodiment of the optical scanning device according to the present invention. FIG. 6 is a scanning optical system according to the embodiment of the optical scanning device according to the present invention. FIG. 3 is a cross-sectional view in the sub-scanning plane, including FIG.

A semiconductor laser 11 is used as a light source. A laser beam emitted as divergent light is shaped by a collimator lens 21 into a focused light beam having a gentle focusing angle. The exit surface of the collimator lens 21 is formed in an aspherical shape rotationally symmetric with respect to the optical axis in order to reduce spherical aberration.

The light beam emitted from the collimator lens 21 enters a shaping lens 22 having a flat cylindrical surface on the incident side and a concave cylindrical surface on the emitting side. The shaping lens 22 has a negative refractive power only in the main scanning direction, and the incident focused light beam is converted into a parallel light beam having a relatively small diameter in the main scanning direction. On the other hand, in the sub scanning direction, the focused light beam converted by the collimator lens 21 remains. The collimator lens 21 and the shaping lens 22 described above constitute a beam shaping optical system.

That is, as shown in FIG.
The light beam incident on the first reflecting surface 31 is a parallel light beam having a smaller diameter in the main scanning direction than that of a normal optical scanning device, and is incident on the first reflecting surface 31 in the sub-scanning direction. It is a focused light beam that forms an image. In addition, the rotating polygon mirror 3
0 will be described later.

As described above, in the first aspect of the present invention, the light beam emitted from the semiconductor laser 11 is converted into a loose focused light beam by the collimator lens 21 at a position where the diameter of the light beam is widened to some extent.
A shaping lens 22, which is a concave cylindrical lens, is disposed at a distance from 1 to convert the beam into a parallel light beam only in the main scanning direction. For this reason, the focal length of the collimator lens 21 can be made relatively large, whereby the radius of curvature of the lens surface of the collimator lens 21 can be made large, and processing of the lens surface or a mold for molding the lens surface becomes easy. In addition, by increasing the size of the lens surface, it is expected that the accuracy required for the lens surface in terms of aberrations is eased to facilitate manufacture, and that the imaging performance on the surface to be scanned is also improved.

In the second invention of the present application, FIG.
As shown in FIG. 5, since the optical path from the semiconductor laser 11 as the light source to the first reflection surface 31 of the rotary polygon mirror 30 can be lengthened, the first reflection surface 31 when viewed in the main scanning plane can be obtained. The distance from the first reflection surface 31 to the light source unit is longer than the distance from the transmission optical system to the first reflection mirror 51 described later. Therefore, as shown in FIG. 5, there is no spatial restriction in the vertical direction of the light source unit, and in particular, the size of the drive circuit board of the semiconductor laser 11 can be arbitrarily set. for that reason,
An electronic circuit for performing advanced control of the semiconductor laser 11, in particular, gradation control, can be integrated in the immediate vicinity of the semiconductor laser 11.

The light beam that has exited the shaping lens 22 is incident on the first reflecting surface 31 of the rotating polygon mirror 30. The optical axis of the beam shaping optical system through which the light beam incident on the first reflecting surface 31 passes and the optical axis of the transmission optical system through which the reflected light beam passes, as shown in FIG. overlapping.
On the other hand, as shown in FIG. 5, in the sub-scanning plane, the light has an angle γ1 with the perpendicular of the first reflection surface 31, that is, it is incident at an incident angle γ1 in the sub-scanning plane. Therefore, the light beam reflected and deflected by the first reflection surface 31 and the incident light beam form an angle of 2 · γ1 in the sub-scanning surface, and do not interfere with each other. In this embodiment, γ1 is set to 6 °.

The light beam reflected and deflected by the first reflecting surface 31 is transmitted to a first lens group 41 of a transmission lens constituting a transmission optical system.
Incident on. The transmission lens first group 41 is arranged in order from the entrance side.
A first transmission lens comprising a plane and a convex cylindrical surface,
A second transmission lens composed of a convex cylindrical surface and a flat surface,
It is composed of three third transmission lenses each having a concave cylindrical surface and a flat surface, and each lens has a refractive power only in the main scanning direction.

The light beam that has exited the transmission lens first group 41 is
In the main scanning direction, the light beam becomes a converged light beam, and once forms an image on the rear focal point of the first group of transmission lenses 41. The light beam once formed as an image becomes a divergent light beam, is reflected by the reflecting mirror 51, and travels to the second group of transmission lenses 42. Transmission lens second group 4
Reference numeral 2 denotes a single fourth transmission lens having a convex cylindrical surface on the entrance side and a flat exit side. Transmission lens 2
The group 42 has a refractive power only in the sub-scanning direction.

The light beam exiting the second group of transmission lenses 42 is
The light enters the third group of transmission lenses 43. Transmission lens third group 4
Reference numeral 3 denotes a single fifth transmission lens having a flat cylindrical surface on the incident side and a convex cylindrical surface on the exit side. The third group of transmission lenses 43 has a refractive power only in the main scanning direction.

The light beam that has exited the third lens group 43 is
The light beams are substantially parallel in the main scanning direction. The direction of the optical axis of this parallel light beam is changed by the reflecting mirror 52,
The light enters the second reflecting surface 32 of the rotating polygon mirror 30. As the light beam incident on the second reflection surface 32 is deflected by the first reflection surface 31, the center of the light beam moves so as to follow the center of the second reflection surface 32. These transmission lenses
The transmission optical system is constituted by three groups of lenses from the group 41 to the third group 43.

Although the diameter of the parallel light beam incident on the second reflecting surface 32 in the main scanning direction is several times larger than the diameter of the parallel light beam incident on the first reflecting surface 31, the second reflecting surface Since the light beam moves following the rotational movement of the surface 32, the size of the reflecting surface does not protrude.

The optical axis of the transmission optical system through which the light beam incident on the second reflecting surface 32 passes and the optical axis of the scanning optical system through which the deflected light beam passes are as shown in FIG. They overlap in the main scanning plane. On the other hand, as shown in FIG. 6, in the plane including the rotation axis of the rotary polygon mirror 30, that is, in the sub-scanning plane, the mirror is arranged in an oblique direction different from the direction perpendicular to the second reflection surface 32. In this embodiment, the angle of the light beam incident on the second reflecting surface 32 in the sub-scanning surface with respect to the perpendicular to the reflecting surface, that is, the incident angle γ2 is 6 °.

As the reflecting mirrors 51 and 52 placed in the transmission optical system, mirrors obtained by depositing a reflecting film on the surface of float glass are used. Float glass produced continuously has different flatness in the direction in which the manufacturing process proceeds and in the direction perpendicular thereto. In the embodiment of the present invention, an inexpensive reflecting mirror can be used by matching the direction of good flatness with the main scanning direction. In addition, the fact that a predetermined thickness is necessary to maintain the flatness of the glass is the same for both polished glass and float glass.
5 mm thick glass is used to obtain sufficient flatness.

In the case where a reflecting mirror is interposed not only in the transmission optical system but also in the beam shaping optical system, an inexpensive float glass can be obtained by making the direction of good flatness coincide with the main scanning direction in the same manner as described above. It can be used. Further, the reflecting mirror interposed in such a beam shaping optical system is not limited to an optical system in which a light beam is incident twice on a reflecting surface of a rotary polygon mirror as in the embodiment of the present invention, but also a general scanning optical system. In the system, it can be widely applied to an optical system for guiding a light beam from a light source to a rotating polygon mirror.

When the transmission optical system according to the embodiment of the present invention is viewed in the sub-scanning section, only the transmission lens second group 42 has optical refraction, and the first reflection surface 31 and the second reflection lens Reflective surface 32
Are arranged in an optically conjugate relationship. For this reason, even if each of the first reflecting surfaces 31 of the rotary polygon mirror 30 has a tilt error in the sub-scanning direction, the reflected light beam is incident on the second reflecting surface 32 at the same position in the sub-scanning direction. . That is, it has a tilt correction function.

Next, the light beam deflected by the second reflecting surface 32 enters the image forming lens 61 and the correction lens 62 and is formed into a converged light beam, and then forms an image on the surface 71 to be scanned.
The imaging lens 61 and the correction lens 62 constitute a scanning optical system, and the light beam scanned at a constant angular velocity is scanned at a constant linear velocity with the rotation of the rotating polygon mirror 30 rotating at a constant velocity. The surface 71 is scanned.

As shown in FIG. 6, the light beam that has exited the imaging lens 61 is passed through a first folding mirror 91 to a rotating polygon mirror 30.
Folded over. This folded light beam is further folded by the second folding mirror 92, and the correction lens 6
2 is incident. The light beam that has exited the correction lens 62 is finally turned back by the third turning mirror 93 and travels toward the surface to be scanned 70. These three folding mirrors are attached to an optical case 82 serving as a container of the optical scanning device.

As described above, when viewed in the sub-scanning plane including the optical axis of the scanning optical system, (A) the second reflecting mirror 52 of the transmission optical system is placed on the base member 81 or the optical case 82 described later. (B) from the second reflecting surface 32 of the rotating polygon mirror 30 of the scanning optical system to the first folding mirror 91 including the imaging lens 61
(C) a portion from the first folding mirror 91 to the second folding mirror 92, and (D) a second folding mirror 93.
From the third reflecting mirror 93 via the correction lens 62
The optical path is folded in four steps, namely, the part reaching.

In the embodiment of the present invention, by adopting such a structure, the length of the scanning optical system of the optical scanning device in the optical axis direction can be shortened regardless of the optical path length of the entire scanning optical system.

In the scanning optical system, since the light beam is rotationally deflected, the second reflecting surface 3 of the rotary polygon mirror 30 is rotated.
As the distance increases, the amplitude of the light beam to be scanned increases, and the required width of the folding mirror also increases. On the other hand, in the case of the above-described structure, the width of the folding mirror increases as the distance from the bottom of the optical case 82 increases. Side) and interference with the scanned light beam is avoided.

Further, since all the folding mirrors are arranged on the front side of the optical case, that is, on the side on which the lens group constituting the rotary polygon mirror and the scanning optical system is mounted, assembly, adjustment and inspection work can be performed. The simplicity reduces manufacturing costs and increases device reliability.

In particular, when the transmission optical system is located close to the bottom surface of the optical case 82 as in the embodiment of the present invention, the transmission optical system is folded back while avoiding the transmission lenses and reflecting mirrors constituting the transmission optical system. It becomes easy to provide a mirror support.

The spot obtained by forming a light beam on the surface 71 to be scanned moves linearly in a direction corresponding to the rotation of the rotary polygon mirror 30 to form a scanning line. In the embodiment of the present invention, as described above, a light beam is incident on the sub-scanning plane in a direction different from a direction perpendicular to the rotation axis of the rotary polygon mirror 30. Since the light is deflected at an angle different from the direction perpendicular to the rotation axis of the mirror 30, the surface formed by the swept deflection light beam is not a flat surface but a conical surface. Therefore, the imaging lens 61 and the correction lens 6
The trajectory of the light beam incident on 2 is also curved, but the scanning optical system is configured so that the scanning line obtained on the scanned surface 71 is a straight line.

An object to be scanned is set on the surface 71 to be scanned. Since the optical scanning device of the present invention scans the light beam only in one direction in the main scanning direction, it is necessary to move the object to be scanned in a sub-scanning direction orthogonal to the main scanning direction in order to realize two-dimensional scanning. . In the movement in the sub-scanning direction, a flat medium may be moved linearly, or a cylindrical medium having a rotation axis parallel to the scanning line direction may be rotated. For example, when the optical scanning device of the present invention is used in a laser beam printer, a photoconductor is placed on the secret scanning surface 71, and an electrostatic latent image is formed by scanning the light beam.

Here, the features of the arrangement of the optical paths of the transmission optical system according to the embodiment of the present invention will be described. As described above, in the embodiment of the present invention, the optical axis of the beam shaping optical system is located at the position of the rotary polygon mirror 30 at the time of scanning near the center of the scanning range of the optical scanning device in the main scanning plane. The positional relationship between the optical axis of the transmission optical system incident on the first reflecting surface 31 or the second reflecting surface 32 of the rotating polygon mirror 30 and the second reflecting surface 32 of the rotating polygon mirror 30 is determined by the respective optical systems. Are arranged so that their optical axes are substantially perpendicular to the respective reflecting surfaces.

In other words, the optical axis of each optical system that guides the light beam to the two reflection surfaces of the rotary polygon mirror is spatially “twisted” with respect to the rotation axis of the rotary polygon mirror. There is almost no intersection. Such a positional relationship between the optical axis of the optical system and the reflecting surface is hereinafter defined as a “front incidence” state.

In the embodiment of the present invention, the size of the second reflecting surface 32 of the rotary polygon mirror 30 is most effective with respect to the cross-sectional diameter of the light beam by adopting the “front incidence” arrangement as described above. Used for The light beam incident from the beam shaping optical system relatively moves with respect to the first reflecting surface 31 of the rotary polygon mirror 30, but the reflection point moves in a direction substantially perpendicular to the incident light beam. Therefore, the size of the reflecting surface for movement can be minimized.

As described above, since the size of each reflecting surface can be reduced, the size of the rotary polygon mirror 30 can be minimized. Therefore, the second moment of inertia, weight, and centrifugal force acting on the reflecting surface of the rotary polygon mirror can be reduced, and it is possible to rotate the mirror to a higher rotation speed.

Further, as shown in FIG. 6, each lens and reflector constituting the transmission optical system and the lens constituting the scanning optical system can be arranged separately in the sub-scanning plane. Do not interfere with each other in the main scanning plane, so that there is no restriction on the size of the lens, and good optical characteristics can be obtained.

Next, the positional relationship between the two reflecting mirrors of the transmission optical system and each lens will be considered. As described above, in the embodiment of the present invention, as shown in FIGS. 5 and 6, the optical axis of the portion after the second reflecting mirror 52 in the transmission optical system and the optical axis of the scanning optical system are sub-scanning. Since they are arranged at an angle in the plane, there is no restriction on the size of the lens in the main scanning plane.

Further, in the embodiment of the present invention, the first group of transmission lenses 41 is located between the first reflecting surface 31 and the first reflecting mirror 51 of the rotating polygon mirror, and the second reflecting mirror 52 is provided. And the second
The transmission lens second group 42 and the transmission lens third group 43 are located between the reflection surfaces 32 of the first and second transmission lenses. That is, since there is no lens on the optical axis of the transmission optical system after the second reflecting mirror 52, the lens of the transmission optical system and the lens of the scanning optical system do not overlap even when viewed on the main scanning plane. For this reason, there is no restriction on the size and mounting method of the lens of the scanning optical system, particularly the imaging lens 61, and it is possible to use an imaging lens having an optically optimum position and size.

Next, the positional relationship between the transmission optical system and the beam shaping optical system or the scanning optical system according to the embodiment of the present invention will be described.

As can be seen from FIG. 5 or FIG. 6, in the portion where the transmission optical system and the beam shaping optical system or the scanning optical system overlap in the main scanning plane, the optical axis with respect to the base member 81 supporting each lens and mirror. Looking up and down, a beam shaping optical system or a scanning optical system overlaps on the transmission optical system or on the side far from the bottom surface of the base member 81.

In the embodiment of the present invention, by adopting such a structure, a part of the base member 81 which is integrally formed from the base member 81 and which supports a lens or a reflecting mirror which constitutes the transmission optical system is supported. The projection height can be kept low, and these lenses and reflecting mirrors can be attached to the base member 81 with high accuracy.

On the other hand, since the mounting accuracy of the imaging lens 61 or the correction lens 62 constituting the scanning optical system does not need to be so high as compared with the transmission optical system, it is supported at a high position from the base member 81. It doesn't matter. On the other hand, the positional accuracy of the lens and the light source of the beam shaping optical system is very strict, but the required accuracy is too strict to be adjusted. For this reason, the position accuracy of the member that supports the lens and the like of the beam shaping optical system does not need to be very high, and a structure that can be easily adjusted is desired. From this viewpoint as well, it is preferable that the beam shaping optical system be located above the transmission optical system because the adjustment operation becomes easier.

Further, in the embodiment of the present invention, as shown in FIG. 8, each lens of the transmission optical system, two reflecting mirrors and a rotary polygon mirror are integrally mounted on a base member 81 manufactured in a high-precision machining direction. The mounting and other parts are mounted on an optical case 82 manufactured by a general manufacturing method.

For example, in order to manufacture the base member 81, it is preferable to use a method in which a metal cast by die-casting is machined only at a portion requiring precision, such as a mounting surface of a lens or a reflector. In addition, even when using a plastic injection molding method, desired precision can be obtained by using a recently developed special molding method with a small shrinkage after molding.

On the other hand, the optical case 82 can be manufactured by a general processing method, and can be manufactured at a low cost by, for example, injection-molding a polycarbonate resin containing glass fiber. Further, it can also be manufactured by pressing a sheet metal depending on the shape of the device.

As described above, in the embodiment of the present invention, the size of the base member 81 requiring accuracy is kept to the minimum necessary size, and the other optical case 82 is manufactured by a relatively inexpensive manufacturing method. The manufacturing cost of the entire apparatus can be reduced.

In this embodiment, the structure of the imaging lens 61 and the shaping lens 22 located above the transmission optical system in a plan view is more preferably attached to the base member 81 than to the optical case 82. Since it is simple and does not increase the size of the base member 81, it is attached to the base member 81.

Next, a detailed description will be given of the following operation of the transmission optical system of the embodiment of the optical scanning device according to the present invention with respect to the reflecting surface of the rotary polygon mirror 30. FIG. 7 is a diagram showing a main scanning section in which the transmission optical system of the optical scanning device of the present invention described with reference to FIG. However, the transmission lens second group 42 is omitted because it has no refractive power in the main scanning direction.

Looking at the transmission optical system in the main scanning direction,
The rear focal point P of the third group of transmission lenses 43 is positioned at the rear focal position P of the first group of transmission lenses 41,
These two lens groups constitute an afocal optical system. Therefore, the light beam that has passed through the third group of transmission lenses 43 becomes a parallel light beam again, the direction of the optical axis is changed by the reflecting mirror 52, and is incident on the second reflecting surface 32 of the rotating polygon mirror 30.

Now, let it be assumed that the parallel light beam incident on the first reflecting surface 31 has a diameter wi at the position of this reflecting surface. Since the transmission optical system forms an afocal optical system, the light is converted into a parallel light beam having a diameter wo at the position of the second reflection surface 32. Here, the focal length of the transmission lens first group 41 is f
1. If the focal length of the transmission lens third group 43 is f2,
The value of the ratio of the diameter of the light beam obtained by dividing wo by wi is equal to the value obtained by dividing f2 by f1.

Here, when the rotary polygon mirror 30 rotates by θ1, the light beam is deflected by 2 · θ1 on the first reflecting surface 31. The deflected light beam is transmitted to the first lens group 41,
The light passes through the third lens unit 43 and is deflected at an angle θ2. This light beam intersects the optical axis at point Q. The distance between the deflected light beam and the optical axis at the position where the light enters the second reflection surface 32 after crossing is δ, and this δ is equal to the amount of movement of the reflection surface when the rotary polygon mirror 3 rotates θ1. .

At this time, the deflected light beam is deflected to the side where the incident angle increases by an angle θ2 with respect to the second reflection surface 32, so that the scanning angle θs of the light beam reflected by the second reflection surface 32 Is expressed as θs = 2 · θ1 + θ2. That is, a method in which the light enters the rotating polygon mirror only once,
Alternatively, the deflection angle of the light beam is set to θ2 as compared with the method in which the light beam follows the second reflection surface 32 while moving in parallel.
Can only be increased.

By the way, as described above, the first of the rotary polygon mirrors
When the center ray of the light beam deflected by the reflecting surface 31 intersects with the optical axis of the transmission optical system at one point only at the point Q, the optical path is folded in the middle of the transmission optical system. If the number of reflecting mirrors is even, the direction of rotation of the second reflecting surface 32 and the direction of movement of the light beam match.

A more general study shows that when the number of times the deflected light beam intersects the optical axis is an odd number, the number of turning-back reflecting mirrors should be even. Since the flatness of the folded reflecting mirrors of the transmission optical system affects the imaging performance on the surface to be scanned and the power efficiency of the optical system is reduced by the reflectance, the number of the reflecting mirrors is preferably as small as possible. However, without at least one reflecting mirror, the light beam cannot be returned to the same rotating polygon mirror, so the minimum value is 1.

Also, the second polygonal mirror is moved from the first reflecting surface to the second polygonal mirror.
In order to shorten the distance to the reflecting surface, it is better that the number of times that the deflected light beam intersects the optical axis is small. In practice, it is preferable that the deflected light beam does not intersect at all or intersects only once. desirable.

Considering these conditions, the following 4
A combination of the two is a realistic option. (1) The number of times that the deflected light beam intersects the optical axis is 0, and the number of the reflecting mirrors is one. (2) The number of times the deflected light beam intersects the optical axis is 0, and the number of the reflecting mirrors is three. (3) The number of times that the deflected light beam intersects the optical axis is one, and the number of the reflecting mirrors is two. (4) The number of times that the deflected light beam intersects the optical axis is one, and the number of the reflecting mirrors is four.

However, in the case of (1), the number of reflecting mirrors is one, and it is impossible to simultaneously realize the "frontal incidence" state on two different reflecting surfaces of the rotary polygon mirror as in the present invention. I can not adopt it.

In the case of (2), since the number of reflecting mirrors is large, there is an increased risk that the imaging performance is deteriorated due to the influence of the flatness of the reflecting mirror. In addition, the reflectance per reflector is 85
%, The efficiency of the optical power when passing through the reflecting mirror 3 is 61%. Furthermore, since the mounting angle accuracy of each reflecting surface affects the direction of the optical axis,
It is not preferable in ensuring the accuracy of the position through which the light beam passes. Similarly, in the case of (4), the number of additional reflecting mirrors increases, so that the problem of the above (2) becomes more severe.

Therefore, in the embodiment of the present invention, as shown in FIG. 4, the number of reflecting mirrors of the optical path of the transmission optical system corresponding to the above (3) is set to 2, and the inside of the transmission optical system is deflected. By making the intersection of the light beam that is moved and the optical axis of the transmission optical system into one, the incidence of the light beam on the rotary polygon mirror 30 is made frontal incidence, and the number of reflecting mirrors is minimized. As a result, the attenuation of the optical power can be reduced, and at the same time, the optical path length of the transmission optical system can be shortened.

Next, the number of reflecting surfaces of the rotary polygon mirror 30 will be described. In the embodiment of the present invention, the number of surfaces of the rotary polygon mirror 30 is set to 12 which is a multiple of four. Rotating polygon mirror 30
By making the number of surfaces a multiple of 4, it is possible to make the angle between two reflecting surfaces used simultaneously by the rotating polygon mirror 30 90 degrees. Of the tilt error and the position error of the reflecting surface with respect to the rotation axis of the rotary polygon mirror 30, for the component that changes gradually (approximately in a sine wave) in one rotation, the phases of the two reflecting surfaces are shifted by 90 degrees. Therefore, the first reflecting surface 3
Since there is no case where both the first and second reflection surfaces 32 have the worst values at the same time, the influence of the inclination error and the position error of the reflection surface can be reduced. This effect is widely applied not only to an optical system having a configuration of front incidence as in the embodiment of the present invention, but also to an optical scanning device in which a light beam is incident twice on the same rotary polygon mirror.

Further, as shown in FIG. 4, the angle between the light beam incident on the first reflection surface 31 and the light beam incident on the second reflection surface 32 via the transmission optical system in the main scanning plane. η can be set to 90 degrees. By arranging in this way, the first reflecting surface 31 to the second reflecting surface 3
2 can be appropriately secured on the optical axis, and a transmission optical system having an optimal configuration can be obtained.

Further, considering the mechanical design of the optical scanning device, it is easier to lay out each element if the optical axis of the beam shaping optical system and the optical axis of the scanning optical system are orthogonal to each other. So there are advantages too.

On the other hand, considering the processing method of the rotary polygon mirror, the index angle of the reflecting surface processing machine is often limited to an integer. That is, the angle of the adjacent reflecting surface is 360
Is a divisor of Therefore, in order to make the shape of the rotating polygon mirror into a regular polygon (regular polyhedron), 10, 12, 15
Polygon mirrors with the number of faces, such as 18 faces, can be machined, but 11 faces,
The 13th, 14th, 16th and 17th faces may not be machined. Considering this condition and the condition that is a multiple of 4 described above, as shown in the embodiment of the present invention, the rotating polygon mirror 3
The number of surfaces N of 0 is twelve, which is suitable for the design of the apparatus and the processing of the polygon mirror.

Of course, if the angles formed by the respective reflecting surfaces of the rotary polygon mirror are not made equal, the above-mentioned restrictions are not imposed. However, the sizes of the respective reflecting surfaces become unequal, and the optical system is adjusted in accordance with the smaller reflecting surface. Since it has to be designed, the size of the polygon mirror is wasted.

Next, a light beam detecting method according to an embodiment of the present invention will be described. Generally, when an optical scanning device is applied to an image recording device or an image input device, a means for generating a synchronization signal serving as a base point of each scan is required. In the embodiment of the optical scanning device of the present invention, the light beam is detected by the light beam detector 63 at a position before scanning the effective scanning area on the surface to be scanned.
And a synchronization signal is obtained by converting the arrival of the light beam into an electric signal. The light beam detector 63 does not necessarily have to be on the surface 71 to be scanned. However, for the optical scanning device, the required scanning range is from the position of the light beam detector 63 to the rear end of the effective scanning area.

More specifically, the light beam deflected by the rotary polygon mirror 30 is converted into a convergent light beam in the main scanning direction by the imaging lens 61, and then converted into a first turning mirror 9
First, after being folded by the second folding mirror 92 and separated from the original optical path toward the scanned surface 71 by the separating mirror 64 provided immediately before the correction lens as shown in FIG. After being converted into a light beam converged in the sub-scanning direction by the light beam detection lens 65 via the turning mirror 92, the light beam enters the light beam detector 63. In FIG. 9, the light beam detector 6
The light beam incident on 3 is indicated by the symbol Ls.

As described above, even in an optical scanning device in which the optical path of the scanning optical system is complicatedly folded by using a plurality of folding mirrors, it is necessary to newly provide a reflecting mirror for guiding the light beam for detection to the detector. Because of this, the configuration of the scanning optical system becomes very simple.

With reference to the second reflecting surface 32 of the rotary polygon mirror 30, the light beam detector 63 is at the same distance as the surface 71 to be scanned on the optical axis of the scanning optical system. When viewed in the sub-scanning plane, the position of the light beam detector 63 is set to be optically conjugate to the second reflecting surface 32 of the rotary polygon mirror 30 as in the case of the scanned surface 71. Beam detection lens 65
Is provided.

During the deflection period of the light beam, the light beam does not reach the surface 71 to be scanned while the light beam crosses the separation mirror 64. In order for the light beam detector 63 to detect the arrival of the light beam, it is necessary to turn on the light source immediately before the light beam reaches the light beam detector 63. A shielding plate 66 is provided at a portion of the mounting portion of the separation mirror 64 located upstream of the scan so that the light beam during this lighting period does not enter the correction lens 62.

In the embodiment of the present invention, as shown in FIG. 8, the light beam detector 63 is located within the main scanning plane.
Is inclined with respect to the incoming light beam,
The reflected light Lg reflected on the surface of the package enclosing the element of the light beam detector 63 or the surface of the element itself
Is reflected by the second folding mirror 92 and the above-mentioned shielding plate 6
6, the light passes through the correction lens 62 and passes through the scanning surface 7.
1 is prevented.

Next, the structure of the optical scanning device according to the embodiment of the present invention for preventing generation of a ghost image will be described. In the embodiment of the present invention, a shielding plate 34 is provided between the reflecting surface 33 and the imaging lens 61 as shown in FIG. 10, and the light is reflected by the plane of incidence of the first transmission lens of the first group of transmission lenses. The applied light beam is prevented from entering the imaging lens 61. Needless to say, the shielding plate 34 is located at a position that does not block the original scanning light beam deflected by the second reflecting surface 32 of the rotary polygon mirror 30.

Note that, depending on the configuration of the optical system, the light beam that causes the ghost image may not be on the reflection surface 33 adjacent to the first reflection surface 31 but on the next reflection surface. Even in such a case, the same effect can be obtained by placing the shielding plate 34 between the reflective surface and the imaging lens 31, which is a problem.

Next, a method of adjusting the optical system of the above-described embodiment will be described with reference to FIGS. The shaped light beam emitted from the beam shaping optical system is incident on the first reflecting surface 31 of the rotary polygon mirror 30, and a knife edge (M) 83 having an edge parallel to the sub-scanning direction on an extension of its optical axis. , Knife edge (S) 84 having an edge parallel to the main scanning direction
Are provided integrally with the optical case 82. The tips of these knife edges coincide with the optical axis L1 of the beam shaping optical system. In this embodiment, a knife edge (S) 84 is provided by cutting out the lower part of the side wall of the optical case 82.

In the vicinity of the two knife edges, FIG.
As shown in FIG. 7, on the optical axis of the beam shaping optical system, a notch A is provided before the knife hedge (M) 83, and a notch B is provided between the knife edge (M) 83 and the knife edge (S) 84. Is provided, and a sensor for detecting the optical power before and after passing through the knife edge can enter.

The actual adjustment operation is performed by irradiating the two knife edges with the light beam that has passed through the beam shaping optical system with the rotary polygon mirror 30 removed. The light beam that has passed through the beam shaping optical system is a parallel light beam in the main scanning direction. On the other hand, the focused light beam forms an image on the first reflecting surface 31 of the rotary polygon mirror 30 in the sub-scanning direction. Therefore, at the position of the knife edge, the light beam spreads to some extent in the sub-scanning direction.

First, a sensor for detecting the optical power is inserted into the notch A, and the power of the optical beam is measured.
Next, a sensor is inserted into the notch B, and the optical power of the light beam passing through the knife edge (M) 83 is measured.
At this time, since the tip of the knife edge (M) 83 coincides with the optical axis of the beam shaping optical system, the optical power at the notch B is made to be exactly half the optical power measured at the notch A. If the semiconductor laser 11 or the collimator lens 21 is adjusted in the main scanning direction, the adjustment of the beam shaping optical system in the main scanning direction has been correctly performed.

Similarly, the optical power of the notch B is compared with the optical power behind the knife edge (S) 84, that is, the optical power outside the optical case 81, and the semiconductor laser 11 or the collimator is adjusted so that the optical power becomes exactly half. Lens 21
Is adjusted in the sub-scanning direction, the adjustment of the beam shaping optical system in the sub-scanning direction is completed. As described above, the light beam spreads in the sub-scanning direction at the position of the knife edge.
Although the detection accuracy is reduced, the accuracy is practically sufficient and there is no problem.

By using such an adjusting method, it is possible to perform an adjusting operation without mounting other optical elements by merely attaching the semiconductor laser 11 and the beam shaping optical system to the optical case 82. 30 reflective surfaces 31
Accurate adjustment can be performed without being affected by errors of optical elements located thereafter.

Further, since the optical characteristics can be confirmed at an intermediate step of the assembly process of the optical scanning device, quality assurance can be performed step by step, and the work for ensuring the quality of the product can be facilitated.

Further, the adjustment operation can be performed only by comparing the optical power passing through the knife edge, so that the scanned surface 71 can be adjusted.
This eliminates the need for a large-scale measurement device required for measuring the imaging performance.

In addition, since the two knife edges are formed integrally with the optical base 82, the position of the light beam can be adjusted more accurately than when a jig composed of separate members is used. It becomes possible.

Adjustment of the position of the light beam in the direction orthogonal to the optical axis of the beam shaping optical system is performed by moving the semiconductor laser 11 or by adjusting the collimator lens 2.
It can also be done by moving 1. In this embodiment, the semiconductor laser 11 is integrated with the circuit board on which the drive circuit is mounted, and is adjusted by moving the collimator lens 21 up and down and left and right in a direction orthogonal to the optical axis. Be demonstrated.

As described above, the light beam emitted from the adjusted beam shaping optical system is also reflected by the reflecting mirror 5 existing in the transmission optical form.
1. By passing through the reflecting mirror 52 and the three folding mirrors of the scanning optical system, the position of each mirror incident on the correction lens 62 in the sub-scanning direction is affected by the mounting angle accuracy in the sub-scanning direction. .

In the embodiment of the present invention, the first reflecting mirror 51 or the second reflecting mirror 52 of the transmission optical system, the first reflecting mirror 91, the second reflecting mirror 92, and the second reflecting mirror 92 in the scanning optical system. By rotating any one of the five reflection mirrors of the third folding mirror 93 in the sub-scanning plane, the position of the light beam incident on the correction lens 62 is adjusted.

For example, by adjusting the first reflecting mirror 51 by rotating it in the sub-scanning plane, the adjustment of the other four reflecting mirrors becomes unnecessary. In particular, since the first reflecting mirror 51 is closest to the light source among the five reflecting mirrors, an error in the optical path can be reduced as compared with the case where the reflecting mirror located downstream of the first reflecting mirror is adjusted.

As described above, by adjusting the angle in the sub-scanning direction of one of the five reflection mirrors based on the position of the light beam in the sub-scanning direction with respect to the correction lens 62,
There is no need to adjust the other four reflection mirrors. Further, it is possible to make the light beam incident on the correction lens 62 at an accurate position in the sub-scanning direction only by adjusting one reflection mirror, and it is possible to form the light beam on the surface to be scanned well. Image performance can be obtained.

Further, the position of the light beam incident on the correction lens 62 in the sub-scanning direction is adjusted so as to fall within a predetermined range.
The position in the sub-scanning direction of the scanning line formed as a spot or a locus of the spot to be imaged on the upper side is also substantially at a regular position.

In the embodiment of the present invention, the adjustment of the five reflection mirrors after the first reflection surface 31 of the rotary polygon mirror is not performed at all, and the first correction lens 62 is displaced in the sub-scanning direction. Thus, the relative position in the sub-scanning direction with respect to the light beam incident on the correction lens 61 is within a predetermined range. Then, such adjustment can be performed independently at the left and right sides of the correction lens 62, that is, at the start end and the end end of scanning, so that optimum imaging performance can be obtained independently for the start side and the end side. .

[0107]

As described above, in the optical scanning device according to the first aspect of the present invention, a light beam emitted from a semiconductor laser is converted into a loose focused light beam by a collimator lens at a position where the diameter of the light beam is widened to some extent. Furthermore, by disposing a shaping lens which is a concave cylindrical lens at a distance from the collimator lens and converting it into a parallel light beam only in the main scanning direction, the focal length of the collimator lens can be made relatively large.

Therefore, the radius of curvature of the lens surface of the collimator lens can be increased, and processing of the lens surface or a mold for molding the lens surface becomes easy. In addition, by increasing the size of the lens surface, the accuracy required for the lens surface in terms of aberration is eased, the manufacturing is facilitated, and at the same time, the image forming performance on the surface to be scanned is improved.

Further, in the optical scanning device according to the second aspect of the present invention, the distance from the first reflecting surface of the rotary polygon mirror to the light source is
By configuring the beam shaping optical system so as to be longer than the distance from the first reflecting surface to the reflecting mirror closest to the first reflecting surface among the reflecting mirrors of the transmission optical system, the vertical direction of the light source unit can be increased. In particular, the size of the drive circuit board of the semiconductor laser can be set arbitrarily, and the electronic circuit for performing advanced control of the semiconductor laser can be placed very close to the semiconductor laser. This has the effect of enabling modulation.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an overall view of an optical scanning device according to an embodiment of the present invention.

FIG. 2 is a perspective view showing an overall view of the optical scanning device according to the embodiment of the present invention, excluding a long lens and a third folding mirror.

FIG. 3 is a plan view in a main scanning plane including a scanning optical system of the optical scanning device according to the embodiment of the present invention.

FIG. 4 is a plan view in the main scanning plane including the transmission optical system of the optical scanning device according to the embodiment of the present invention.

FIG. 5 is a sectional view in the sub-scanning plane including the beam shaping optical system of the optical scanning device according to the embodiment of the present invention.

FIG. 6 is a sectional view in the sub-scanning plane including the scanning optical system of the optical scanning device according to the embodiment of the present invention.

FIG. 7 is a developed view of the transmission optical system of the optical scanning device in the main scanning plane according to the embodiment of the present invention.

FIG. 8 is a perspective view showing a relationship between an optical base and an optical case of the optical scanning device according to the embodiment of the present invention.

FIG. 9 is a perspective view of an optical system for guiding a light beam to a light beam detector of the optical scanning device according to the embodiment of the present invention.

FIG. 10 is a plan view showing the periphery of a rotary polygon mirror and a shielding plate of the optical scanning device according to the embodiment of the present invention.

[Explanation of symbols]

 11 semiconductor laser 21 collimator lens 22 shaping lens 30 rotating polygon mirror 41, 42, 43 transmission lens 51, 52 reflecting mirror 61 An imaging lens 62 A correction lens 63 A light beam detector 71 A surface to be scanned 81 An optical base 82 An optical case 91 92 93 ... Folding mirror

Claims (2)

[Claims] 1. A light source, a beam shaping optical system for converting a light beam from the light source into a shaped light beam having predetermined characteristics, and a light source for deflecting the shaped light beam by a first reflecting surface; A rotating polygon mirror having a reflecting surface and a second reflecting surface;
A transmission optical system for causing the light beam deflected by the first reflecting surface of the rotating polygon mirror to enter the second reflecting surface of the rotating polygon mirror; and a transmission optical system for deflecting the light beam by the second reflecting surface of the rotating polygon mirror. A scanning optical system that forms an image of the scanned light beam on a predetermined surface to be scanned, and an optical scanning device that scans the surface to be scanned with the scanning light beam. A collimator lens for converting the divergent light beam into a focused light beam in the main scanning plane, and a shaping lens for converting the focused light beam emitted from the collimator lens to a parallel light beam in the main scanning plane. Optical scanning device. 2. A light source, a beam shaping optical system for converting a light beam from the light source into a shaped light beam having predetermined characteristics, and a light source for deflecting the shaped light beam by a first reflecting surface; A rotating polygon mirror having a reflecting surface and a second reflecting surface;
A transmission optical system that causes the light beam deflected by the first reflection surface of the rotary polygon mirror to enter the second reflection surface of the rotary polygon mirror; and the transmission optical system in an optical path of the transmission optical system. A reflecting mirror for bending an optical axis of the system, and a scanning optical system for forming an image of a scanning light beam deflected by the second reflecting surface of the rotary polygon mirror on a predetermined surface to be scanned, In an optical scanning device that scans the surface to be scanned with a beam, a distance from the first reflection surface to the light source is closest to the first reflection surface in the reflection mirror from the first reflection surface. An optical scanning device characterized by being larger than a distance to an object.