JP3507088B2 - Optical scanning device - Google Patents

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 in laser beam printers, digital copying machines, facsimiles, laser displays and the like.

[0002]

2. Description of the Related Art An optical scanning device used in a conventional laser beam printer or the like will be described with reference to FIG. A light beam emitted from a light source 11 such as a semiconductor laser and collimated by a collimator lens 12 is deflected and scanned by a rotary polygon mirror 13, and a scanning spot is formed on a photosensitive member surface 16 by an imaging lens 15. Rotating polygon mirror 1
When 3 rotates at a constant speed, the light beam is scanned at a constant angular velocity, but in order to scan the imaging spot on the photoconductor surface 15 at a constant speed, the imaging lens 15 is formed by the optical axis of the lens and the light beam. When the angle is θ, the focal length of the lens is f, and the image height is y, constant-speed scanning can be realized by giving a distortion characteristic of y = f · θ.

By the way, the rotating polygon mirror 13 usually has an error in parallelism of each surface and an error in mounting the rotating shaft and the polygon mirror, which occur during the manufacturing process of the polygon mirror, and the traveling direction of the reflected light beam is deflected. The variation occurs in the plane perpendicular to the plane, resulting in uneven scanning pitch. A highly accurate deflection device that does not cause this pitch unevenness becomes extremely expensive. Therefore, conventionally, various methods for correcting this, so-called misalignment correction optical systems have been devised. The methods will be described below.

(Conjugate tilt correction method) Japanese Patent Laid-Open No. 48-49
No. 315 and JP-A-56-36622, anamorphic scanning in which the deflecting surface (hereinafter referred to as the main scanning surface) and the surface perpendicular to the deflecting surface (hereinafter referred to as the sub-scanning surface) have different powers. An optical system is used to form an image of a light beam on the reflection surface of the rotary polygon mirror on the sub-scanning surface so that the reflection surface and the photoconductor surface are optically conjugate.

(Relaxation type tilt correction system) Japanese Patent Laid-Open No. 52-15
As disclosed in Japanese Patent No. 3456 and Japanese Patent Laid-Open No. 58-134618, a long cylindrical lens is arranged in the vicinity of the surface of the photosensitive member so as to alleviate a change in the deflection direction of the sub-scanning surface due to surface tilt.

(Polygon indexing correction method)
As indicated by reference numeral 100620, the rotary polygon mirror mounting position is set so that the relative surface tilt amount of each surface of the two-sided polygon mirror becomes substantially zero.

[0007]

However, all the above-mentioned conventional examples have the following problems. That is, in the conjugate type, it is necessary to use a toroidal lens that requires a special manufacturing method as compared with a spherical lens, and if a cylindrical lens is used, a large number of lenses are required, which is inevitably expensive. Also, it was trying to increase the size of the device. In the case of the relaxation type, there is a problem that it is expensive because a long cylindrical lens is required and the tilt correction magnification is low. In the polygon indexing method, the optical system itself does not require anything special,
The parallelism between the two reflecting surfaces must be highly accurate, and the manufacturing cost was high.

The present invention has been made to solve the above-mentioned problems, and provides an optical scanning device which simultaneously realizes miniaturization, cost reduction and high performance.

[0009]

The present invention comprises (1) two optical elements each having a reflecting surface, an entrance surface, and an exit surface, which are formed as independent surfaces. The entrance surface and the exit surface have a predetermined surface shape so as to perform a predetermined aberration correction, and the reflecting surfaces of the optical element are fixed so as to be in contact with each other, and are on the reflecting surface. An optical scanning device which deflects and scans a light beam by rotating the two optical elements about a rotation axis. (2) Two optical elements each having a reflecting surface, an entrance surface, and an exit surface formed integrally as independent surfaces are provided, and the entrance surface and the exit surface have a predetermined shape. It has a predetermined surface shape so as to correct aberrations, and is fixed so that the reflecting surface is in contact with the axis of a motor that rotationally drives the optical element. By rotating the two optical elements, An optical scanning device which deflects and scans a light beam.

[0010]

EXAMPLE A first example of the present invention will be described with reference to the perspective view of FIG.

The rotating mirror 3 is formed by adhering the reflecting surfaces R, R of the prisms 30, 30 made of a transparent member such as glass or resin such as PMMA (polymethylmethacrylate) or PC (polycarbonate) so as to be in close contact with each other. , Is fixed to the motor 4 via a mounting plate 40. The reflecting surfaces R, R of the prisms 30, 30 may be vapor-deposited surfaces of aluminum, gold or the like, or total reflection may be used. Also,
The prisms 30 and 30 have an entrance surface S1 and an exit surface S2, respectively. The light emitted from the light source 1 such as a semiconductor laser is made into a thin light beam by the collimator lens 2. The light beam is incident on the incident surface S1 of the rotating mirror 3 rotating about the rotation axis (point O) substantially on the reflecting surface R by the motor 4, is then reflected by the reflecting surface R1, and is emitted from the emitting surface S2. . The light beam is deflected by the rotation of the rotating mirror 3. The deflected light beam enters the imaging lens 5,
A spot is formed on the photoconductor 6.

As described above, the factors that cause the surface tilt error are the parallelism error between the reflecting surfaces and the parallelism error between the rotation axis direction of the motor 4 and the reflecting surfaces R, R. In the rotating mirror 3, since the reflecting surfaces R of the two prisms 30 are in direct contact with each other, the two reflecting surfaces R, R may be regarded as substantially the same plane, and the two parallel reflecting surfaces R, R are sufficiently parallel without requiring an expensive manufacturing method. Degree is achieved. The latter can be easily corrected by using the adjusting method disclosed in the above-mentioned conventional polygon indexing method.

The prisms 30 and 30 are fixed by adhesion,
Fusing, pressure contact with a spring member, etc. are possible. In the case of adhesion, in order to prevent a large amount of adhesive from flowing between the reflecting surfaces R and disturbing the parallelism, the adhesion is performed under pressure contact.
As the adhesive, epoxy resin, polyester resin or the like is desirable.

FIG. 2 shows a fixed state by pressure contact with a spring member. 2a) is a plan view and b) is a front view. The leaf spring member 31 includes spring portions 32, 32, 32, 32 provided near the apex of the prism so as not to block the optical path.
0 and 30 are urged in a direction in which they are pressed against each other, and are further urged so as to hold the prisms 30 and 30 in two directions with respect to the leaf spring member 31 so as not to move.

As described above, the present invention has the effect that the surface tilt can be corrected with a simple structure, but further, it is unexpected that the optical performance does not deteriorate due to the movement of the deflection point that deflects the light beam by the rotating mirror. It was also found to have an effect. This is because, as shown in FIG. 7, in the case of the rotating polygon mirror, the center of rotation is not on the reflecting surface, so when comparing the center portion and the end portion of the polygon mirror surface, the end portion produces a light beam on the outer peripheral side of the rotation circle. Will be reflected. This means that the entrance pupil position fluctuates asymmetrically due to changes in the angle of view, and field curvature aberration and distortion aberration appear due to it. In particular, when the image forming spot is made smaller so that high density recording is performed, for example, when the spot size is 50 μm or less, it has a great influence. On the other hand, if the rotating mirror of the present invention is used, the center of rotation can be set on the reflecting surface, and the fluctuation of the entrance pupil position is eliminated. Therefore, a scanning optical system with high recording density can be realized.

Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 3 is a perspective view showing the structure near the rotating mirror. In this embodiment, the rotating mirror 13 is made of glass, PMMA or P.
A plane parallel plate 130 made of a transparent member such as resin such as C,
The reflecting surface R is fixed to the surface 130 by bringing the reflecting surfaces R and R into close contact with each other. In this embodiment, the entrance surface and the exit surface are on the same plane S. The configuration of the other parts is the same as that of the first embodiment described above. In this embodiment as well, similar to the above-described first embodiment, the face tilt correction can be easily performed. Further, in this embodiment, since the plane parallel plate is used, the element itself is easy to manufacture.

A third embodiment of the present invention will be described with reference to FIGS. FIG. 4 is a perspective view showing the structure near the rotating mirror, and FIG. 5 is an optical path diagram of the scanning optical system. In this embodiment, the rotating mirror 2
No. 3 is a rotary lens mirror 230, 230 disclosed in Japanese Patent Application No. 4-166042 by the present applicant, and the reflecting surfaces R, R are closely attached to each other and fixed. Japanese Patent Application 4-166
Rotating lens mirror 230, as detailed in No. 042.
The entrance surface S1 and the exit surface S2 are shaped so as to perform predetermined aberration correction, and an extremely small-sized and low-cost scanning optical system can be configured. This is because in order to correct the field curvature aberration, astigmatism, and distortion that are required in the case of ordinary laser beam printers, etc., it is necessary to reduce the size of an optical system that uses an inexpensive axisymmetric shape. Therefore, if the scanning angle is sufficiently large, two or more imaging lenses are required. However, according to the above-mentioned rotary lens mirror 230, the degree of freedom for aberration removal is equivalent to that, and it is expensive. This is because the lens function and the function of the deflecting mirror are fulfilled by one component so that the number of optical components is not increased. However, when the optical scanning device is configured only by the description of Japanese Patent Application No. 4-166042, only one scanning can be performed for one rotation of the rotary lens mirror 230, which is not suitable for a high speed machine.
On the other hand, if the present invention is applied, a double scanning speed can be obtained, so it can be said that the combination of the present invention and Japanese Patent Application No. 4-166042 is very suitable.

A fourth embodiment of the present invention will be described with reference to FIG. FIG. 6a) is a plan view showing the structure near the rotating mirror,
b) is a front view. This embodiment is similar to the above-mentioned third embodiment in that the rotary lens mirrors 230, 230 have reflecting surfaces R, R.
Is closely attached to and fixed to the rotary shaft 42 of the motor 4. The configuration of the other parts is the same as that of the first embodiment described above. The rotating shaft 42 of the motor 4 is rotatably supported by a bearing such as a ball bearing (not shown), but it is possible to easily finish the cylindricity of the peripheral surface of the rotating shaft with high accuracy by using a lathe or the like. It is possible. Therefore, the rotary lens mirror 23 is formed on the same surface as the peripheral surface supported by the bearing.
By bringing the reflecting surfaces R and R of 0 and 230 into close contact,
The center of the rotation axis and the reflecting surfaces R, R can all be made parallel to each other with high accuracy. As described above, the factors that cause the surface tilt error are the parallelism error between the reflecting surfaces and the parallelism error between the rotation axis direction of the motor 4 and the reflecting surfaces R, R. Thus, according to the present embodiment, , Without any adjustment at the time of installation,
Both can be corrected at the same time.

The rotary shaft 42 of the rotary lens mirrors 230, 230
As for the method of fixing to, the same as in the above-described first embodiment, adhesion, fusion, pressure contact with a spring member, or the like is possible. The embodiment of FIG. 6 shows a case of fixing by the spring member 231. At this time, the pressure contact area between the rotary shaft 42 and the rotary lens mirror 230 is very small, and the pressure contact pressure becomes high, so that the reflective surface R may be locally deformed. Therefore, by interposing an elastic member 232 such as rubber between the rotating lens mirrors 230, 230, the pressure contact force can be dispersed and the local deformation of the reflecting surface R can be eliminated.

[0020]

As described above, according to the present invention, it is possible to eliminate the need for a plane tilt correction optical system which requires an expensive lens or polygonal mirror. Further, it is possible to provide a small-sized and low-cost scanning optical system that does not require adjustment during assembly.

[Brief description of drawings]

FIG. 1 is a perspective view showing a first embodiment of the present invention.

2A is a plan view showing an example of a prism fixing method according to an embodiment of the present invention, and FIG. 2B is a front view.

FIG. 3 is a perspective view showing a second embodiment of the present invention.

FIG. 4 is a perspective view showing a third embodiment of the present invention.

FIG. 5 is an optical path diagram of a third embodiment of the present invention.

FIG. 6A is a plan view showing a fourth embodiment of the present invention,
b) is a front view.

FIG. 7 is a diagram showing movement of a reflection point of a conventional rotary polygon mirror.

FIG. 8 is a diagram showing a configuration of a conventional scanning optical system.

[Explanation of symbols]

1, 11 light source 2,12 Collimator lens 3,13 rotating mirror 4 motor 5, 15 Imaging lens 6, 16 photoconductor 30 prisms 31 leaf spring member 40 mounting plate 42 rotation axis 130 parallel plate 230 rotating lens mirror 231 spring member 232 Elastic member

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G02B 26/10

Claims (2)

(57) [Claims] 1. An optical element comprising two optical elements each integrally formed with a reflecting surface, an entrance surface and an exit surface, each of which is formed as an independent surface, wherein the entrance surface and the exit surface are provided.
Make a predetermined surface shape so as to perform predetermined aberration correction ,
In addition, the reflecting surfaces of the optical element are fixed so as to be in contact with each other, and the two optical elements are rotated about a rotation axis on the reflecting surface to deflect and scan the light beam. Optical scanning device. Wherein each of which is formed as an independent facing each other, a reflecting surface, the incident surface, and the exit surface is provided with two optical elements formed integrally with the exit surface and the entrance surface
Make a predetermined surface shape so as to perform predetermined aberration correction ,
Further, the optical scanning device is fixed so that the reflecting surface is in contact with an axis of a motor that rotationally drives the optical element, and deflects and scans a light beam by rotating the two optical elements. .