JPH0215231A - Scanning optical system - Google Patents

Abstract

PURPOSE:To eliminate the need to arrange a scanning lens and to reduce the influence of the accuracy error of a reflecting surface by arranging a concave reflecting mirror which has an elliptic surface increasing gradually in the distance between two specific focuses from a scan center part to a scan peripheral part. CONSTITUTION:Infinite anamorphic optical systems 12, 14, 15, and 17 have such refracting power that a light source 1 and a scan image formation plate P2 where scanning deflected light by a scan deflecting plane P1 forms its image are almost conjugate to each other as to a main scanning direction between the light source 1 and the scan deflecting plate P1 where illumination light from the light source 1 is scanned and deflected. Further, the optical systems 12, 14, 15, and 17 have such refracting power that the light source 1 and scan deflecting plane P1 are nearly conjugate about a subscanning direction. Then, the concave reflecting mirror is arranged which has the elliptic surface increasing gradually in the distance between two specific focuses from the scan center part to the scan peripheral part in the main scanning direction.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a scanning optical system in an optical scanning device that polarizes a light beam to scan a scanning image plane.

(Conventional Technique t#) One of the technical issues of the scanning optical system in an optical scanning device is how to correct the deviation of the optical beam spot 1- on the scanning imaging plane. Various optical scanning optical systems using reflective curved mirrors with . Hereinafter, conventional examples of various types of optical scanning optical systems will be briefly described.

(1) A mirror surface of a rotating polygon mirror disclosed in Japanese Patent Publication No. 59-5882.Secondly, a cylindrical optical system that forms a line image perpendicular to the rotation axis, and a light beam deflected by the mirror surface is directed to the mirror surface perpendicular to the rotation axis. It has a cylindrical lens that focuses the light beam only in the direction, and a concave reflecting mirror that focuses the light beam polarized by the mirror surface only in the direction parallel to the rotation axis and converges it on the scanning imaging plane.

(2) Japanese Unexamined Patent Publication No. 61-86723 (Japanese Unexamined Patent Publication No. 61-84619) A cylindrical lens that is provided between the scanning lens and the scanning imaging surface and converges the light beam onto the scanning imaging surface only in the sub-scanning direction. A mirror is provided, and the scanning lens and cylindrical mirror cause the light beam that is incident on the deflector as a line image and is deflected to be focused on the scanning imaging plane as a point image.

(3) Japanese Unexamined Patent Publication No. 62-275216 The optical system between the deflector and the scanning imaging plane is composed of one spherical lens and a toric surface-shaped reflecting mirror in order from the deflector side. This reflecting mirror has a 1-rick shape in which the cross section in the scanning direction has a relatively large radius of curvature, and the cross section in the direction perpendicular thereto has a relatively small radius of curvature.

(4) Japanese Unexamined Patent Publication No. 62-253116 A curved mirror for light scanning that is interposed to receive scanning light and condense and image it on an imaging surface, the reflecting surface being approximately parabolic within the plane in the light scanning direction. The mirror has a concave curved surface shape, and an inclined surface shape in which the incident angle of the scanning light gradually increases from the center toward both sides in a plane perpendicular to the optical scanning direction.

(Problem to be Solved by the Invention) According to the optical system described in the publication (1) above, optically fθ
characteristics cannot be obtained, and changes in the beam waist on the scanning plane whose radius is the deflection plane cannot be corrected.

According to the optical system described in the publication (2), since there is no power on the main scanning side of the reflective curved surface, it is necessary to separately provide an fO lens.

According to the optical system described in the publication (3), the beam after passing through the scanning imaging lens is converged to one point on the imaging plane, and the beam is scanned in a straight line on the scanning imaging plane. A scanning imaging lens is required for this purpose. Furthermore, when a half mirror is placed on the optical path of the toric surface-shaped reflecting mirror, there is a problem in that the light energy is significantly reduced.

According to the optical system described in the publication (4), there is a problem that there is no correction function for beam deviation in the sub-scanning direction.

The present invention has been made to solve the problems of the prior art, and aims to reduce the cost by eliminating the scanning imaging lens, while scanning the beam in a straight line on the scanning plane, and A scanning optical system that can correct the deviation of the light beam in the sub-scanning direction, correct the change in the beam waist with the deflection surface as the radius, and maintain flatness on the main scanning plane. The purpose is to provide.

(Means for Solving the Problems) The present invention provides an image forming system between a light source and a scanning deflection surface that scans and deflects the irradiated light from the light source, in the main scanning direction, the scanning deflected light by the light source and the scanning deflection surface forms an image. A finite anamorphic optical system is interposed, which has a refractive power that is almost conjugate with the scanning imaging plane, and has a refractive power that is almost conjugate with the light source and the scanning deflection surface in the sub-scanning direction. On the scanning optical path from the scanning deflection plane, there is an ellipsoidal surface having a conjugate relationship in the sub-scanning direction such that the scanning deflection plane and the scanning imaging plane are located at the first and second focal points, respectively. Regarding the scanning direction, the distance between the first and second focal points gradually increases from the scanning center to the scanning periphery so that the second focal points on the scanning imaging plane are arranged in a straight line. It is characterized by disposing a concave reflecting mirror having a surface.

(Function) The ellipsoidal surface of the concave reflecting mirror is designed such that the distance between the first and second focal points gradually increases from the scanning center to the scanning periphery in the main scanning direction, so that the beam spot is spread over the entire scanning area. Scan in a straight line.

The above-mentioned concave reflecting mirror is a concave curved surface with different powers in the main scanning direction and the sub-scanning direction, and a combination of ellipsoidal surfaces in the sub-scanning direction, so that the deflection surface and the scanning surface correspond to the respective focal points. Because of the conjugate relationship, beam deviation in the sub-scanning direction can be corrected. In addition, a finite anamorphic optical system having a refractive power that is almost conjugate with the light source and the scanning imaging surface in the main scanning direction is interposed between the light source and the scanning deflection surface, and the concave reflecting mirror is connected to the deflection surface. Since it has an elliptical surface that is conjugate with the scanning surface, there is no need to separately provide a scanning imaging lens. Also,
By configuring the concave reflecting mirror as described above, the deviation of the beam waist around the deflection surface can be corrected, and flatness on the main scanning plane can be maintained.

(Embodiments) Hereinafter, embodiments of the scanning optical system according to the present invention will be described with reference to the drawings.

In Figures 1 and 2, the irradiation light emitted from a light source 1 such as a semiconductor laser is expanded into a parallel beam by a colli-two lens 2, passes through a cylindrical lens 3, and is reflected by a cylindrical mirror 4. Scanning deflection surface P of rotating polygon mirror 5
, guided by. As is well known, the rotating polygon mirror 5 has an outer peripheral surface mirror-finished into a plurality of planes to form the scanning deflection surface P, and also rotates around the rotation axis to keep the irradiation light from the light source 1 constant. scan deflection within the range of . This scanning direction is called the main scanning direction, and the direction perpendicular to this direction is called the sub-scanning direction. On the scanning optical path, a concave reflecting mirror 6 which is long in the main scanning direction is arranged at a predetermined inclination with respect to the scanning optical axis, so as to bend the optical scanning plane. Concave reflector 6
A photoreceptor drum 7 is disposed on the reflected optical path 2, and the surface of the photoreceptor drum 7 serves as a scanning imaging plane P2.

The cylindrical lens 3 has power only in the main scanning direction, and in the main scanning direction, the light source] and the scanning deflection surface P
It has a refractive power such that it has a substantially conjugate relationship with the scanning imaging plane P on which the scanning deflected light due to □ forms an image. On the other hand, the cylindrical mirror 4 has power only in the sub-scanning direction. The power in the sub-scanning direction is the power of the light source 1 and the scanning deflection surface P in the sub-scanning direction.

The light beam from the light source 1 side is converged in the sub-scanning direction to form a line image on and near the scanning deflection surface P. Note that the rotating polygon mirror 5 may be replaced with a galvanometer mirror or other mirror having the same function. In short, the optical system composed of the lens 2, cylinder I linear lens 3, and cylindrical mirror 4 is a finite anamorphic optical system, that is, it has convergence, not to the collimator 1, and has main scanning The optical system has a refractive power such that the light source and the scanning imaging plane have a nearly conjugate relationship in terms of direction, and a refractive power that has a nearly conjugate relationship between the light source and the scanning deflection plane in the sub-scanning direction. .

The concave reflecting mirror 6 has different power in the main scanning direction and power in the sub-scanning direction. The curved surface on the main scanning side is almost a paraboloid, and this paraboloid is also a curved surface that can approximately obtain fO characteristics. On the other hand, the curved surface in the sub-scanning direction is an elliptical surface, and includes a scanning deflection surface P1 and a scanning imaging surface P2.
is a combination of ellipsoids having a military service relationship such that and are located at the first and second foci of the ellipse. 3, 4 and 5 show the curved surface of the concave reflecting mirror 6 in detail.

As shown in FIG. 3, the curved surface of the concave reflecting mirror 6 is tilted from the center to the periphery of the scanning range by the inclination angle formed by the scanning optical axis and the tangent of the ellipsoid to obtain an imaging effect in the sub-scanning direction. It is formed so that it gradually becomes smaller. In FIG. 3, reference numeral 9 is an ellipsoidal surface at the center, and 9'' is an ellipsoidal surface at the periphery. OX is an inclination angle between the tangent to the ellipsoidal surface 9 at the center and the scanning optical axis, Ox' represents the inclination angle between the tangent to the peripheral elliptical surface 9'' and the scanning optical axis. 1
Ox' is smaller than 9x, so that the light beam spot 1- can be linearly scanned on the scanning imaging plane P2.

In addition, as described above, the first and second focal points of the ellipsoidal surface constituting the curved surface in the sub-scanning direction of the concave reflecting mirror 6 coincide with the scanning deflection plane P and the scanning imaging plane P. However, as shown in FIGS. 4 and 5, the eccentric distance between the two focal points of the ellipsoidal surface gradually increases from the center to the periphery of the scanning range. In FIGS. 4 and 5, 9 is an ellipsoid at the center of the scanning range, 9' is an ellipsoid at the periphery, and 9' is an ellipsoid at the center.
The eccentric distance L'' of the elliptical surface 9' in the peripheral part is larger than the eccentric distance of the concave reflecting mirror 6.
The curved surface 8 in the main scanning direction is approximately a paraboloid. Further, the second focal point of the elliptical surface forming the curved surface 4i1 of the concave reflecting mirror 6 in the sub-scanning direction is arranged in a straight line on the surface ``2'' of the photoreceptor drum 7, and is The movement locus of the scanning deflected light on the scanning imaging plane P2 becomes a straight line. Here, if the concave reflecting mirror 6 does not have a curved surface 8 on a parabola in the main scanning direction, the scanning imaging plane will be the first
As shown by the chain line 10 in the figure, it draws an arc centered on the scanning deflection plane P□, and it comes off the surface of the photoreceptor drum 7. Note that ΔX shown in FIG.
shows the amount of positional deviation of the reflecting surface in the scanning axis direction.

FIG. 2 shows how the light beam changes in the sub-scanning direction due to the inclination of the scanning deflection surface P1 of the rotating polygon mirror 5 (so-called "plane deflection"). Since the two foci of the elliptical surface are in a conjugate relationship such that they are located on the scanning deflection plane and the scanning imaging plane, respectively, the scanning deflection plane P
It can be seen that the deviation of the scanning imaging point due to the surface wobbling of No. 1 is corrected.

Next, various modified embodiments of the present invention will be described.

FIG. 6 shows a finite anamorphic optical system interposed between the light source 1 and the scanning deflection plane P
2 and a cylindrical reflecting mirror 4 which is a second reflecting mirror. The reflecting surface of the reflecting mirror 12 is a spherical or aspherical surface that has power only in the main scanning direction, and is connected to the light source 1 and the scanning imaging surface P2.
It has the power to have an almost conjugate relationship. The configuration from the cylindrical reflecting mirror 4 to the imaging plane P2 is the same as that of the previous embodiment. This embodiment also provides the same effects as the previous embodiment.

The functions of the first reflecting mirror 12 and the second reflecting mirror 4 in the embodiment of FIG. 6 may be combined into one reflecting mirror. 7th
The figure shows such an embodiment, in which the reflecting surface of one concave reflecting mirror 14 interposed between the light source 1 and the scanning deflection plane P1 is replaced with the spherical surface of the reflecting mirror 12 in the embodiment of FIG. This is a finite toroidal reflecting surface that is a combination of an aspherical reflecting surface and a cylindrical reflecting surface of the reflecting mirror 4.

The reflective surface of the concave reflecting mirror 14 has a power such that the light source 1 and the scanning imaging plane are in a conjugate relationship in the main scanning direction, and the light source 1 and the scanning deflection plane P□ are in a conjugate relationship in the sub-scanning direction. It has powers that are almost conjugate. Scanning deflection surface P1
The following configuration may be the same as the previous embodiment.

The anamorphic optical system interposed between the light source and the scanning deflection surface is not limited to a reflective optical system, but may be a refractive optical system. For example, as shown in FIG. 8, an anamorphic convex lens 15 may be arranged between the light source 1 and the scanning deflection plane P□. The convex lens 15 has a convex toric surface on its light source side, and if the radius of the curved surface in the main scanning direction is Rx and the radius in the sub-scanning direction is Ry, then Rx
) Ry relationship. The surface of the convex lens 15 on the scanning deflection surface P1 side may be a flat surface or a spherical surface. The convex lens 15 is
In the main scanning direction, the light source 1 and the scanning imaging plane P2 have a refractive power that is in a nearly conjugate relationship, and in the i- sub-scanning direction, the light source 1 and the scanning deflection surface P□ have a refractive power that is in a nearly conjugate relationship. has. The other configurations are the same as those of the previous embodiment, and the same effects are achieved.

The finite anamorphic optical system may be configured with a lens 16 having power in both the main scanning direction and the sub-scanning direction and a cylindrical lens 17 having power only in the sub-scanning direction, as shown in FIG. . These lenses 1
The anamorphic optical system constituted by 6.17 also has the refractive index conditions in the main scanning direction and the sub-scanning direction set in the same manner as in the previous embodiments, and produces the same effects.

(Effects of the Invention) According to the present invention, on the scanning optical path, in the sub-scanning direction, the scanning deflection plane and the scanning imaging plane are arranged in the first and second positions, respectively.
It has an ellipsoidal surface having a conjugate relationship such that it is located at the focal point of the scanning image plane, and in the main scanning direction, the second focal point on the scanning imaging plane is arranged in a straight line from the scanning center to the scanning periphery. Since a concave reflecting mirror having an ellipse [nl] in which the distance between the first and second focal points gradually increases toward the center, there is no need to arrange an I-nonce for scanning, and it is possible to significantly reduce the cost I~. Moreover, since the concave reflecting mirror can be placed near the scanning imaging plane, it has the advantage of being less susceptible to accuracy errors of the reflecting surface. Furthermore, since everything except the finite imaging system on the main scanning side can be configured with reflective systems, it is possible to make the components of these reflective systems from inexpensive organic materials such as Plus Deck, and from this point of view, It is possible to significantly reduce the cost to 1.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an embodiment of the scanning optical system according to the present invention, FIG. 2 is a side view of the same, and FIG. The side view shown in Figure 4 is
- A perspective view showing the change in the main scanning direction of the concave reflective surface on the road side, FIG. 5 is a plan view of the same, and FIG. 6 is another embodiment of the scanning optical system according to the present invention. 7 is a perspective view showing still another embodiment of the scanning optical system according to the present invention; FIG. 8 is a perspective view showing still another embodiment of the scanning optical system according to the present invention; FIG. 9 FIG. 2 is a perspective view showing still another embodiment of the scanning optical system according to the present invention. 1... Light source 2.3.4... Anamorphic optical system 6... Concave reflecting mirror 9.9'... Elliptical surface 12.14.15.17... Anamorphic optical system Pl...Scanning deflection plane P2...Scanning imaging plane ゝq Cn

Claims (1)

[Claims] Between the light source and the scanning deflection surface that scans and deflects the irradiated light from the light source, there is a scanning imaging surface on which the scanning deflected light by the light source and the scanning deflection surface forms an image in the main scanning direction. A finite anamorphic optical system is interposed, which has a refractive power that is almost conjugate with the light source and the scanning deflection surface in the sub-scanning direction, and the scanning light from the scanning deflection surface is interposed. On the road, there is an elliptical surface having a conjugate relationship such that the scanning deflection plane and the scanning imaging plane are located at the first and second focal points, respectively, in the sub-scanning direction, and the scanning imaging plane in the main scanning direction. a concave reflecting mirror having an elliptical surface in which the distance between the first and second focal points gradually increases from the scanning center to the scanning periphery so that the second focal points on the image plane are arranged in a straight line; A scanning optical system characterized by: