JPH07101257B2 - Optical scanning device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a post-object type optical scanning device using a polygon mirror.

2. Description of the Related Art An optical scanning device used in a laser printer or the like includes a post-object type optical scanning device in which a beam is made into a convergent light beam by a converging lens and then enters a light deflector, and after being deflected by a deflector. A pre-object type optical scanning device that passes through a focusing lens is known.

Among them, the pre-object type optical scanning device is currently widely used because it is easy to correct the field curvature and the fθ characteristic by a converging lens and it is easy to make the converging position a plane. However, since the converging lens must be configured as a wide-angle lens that covers the deflection angle, the configuration tends to be complicated and expensive. For this reason, the post-object type is selected when it is necessary to use a converging lens having a simple structure.

Problems to be Solved by the Invention In the post-object type optical scanning device, the converging lens has a simple structure, but the converging point is generally on a curved surface. Therefore, the curvature of field must be corrected.

Therefore, as described in Japanese Patent Laid-Open No. 61-156020, the curvature of field is reduced by making the reflecting surface of the polygon mirror a spherical surface or a cylindrical surface. As a result, the field curvature is corrected to the point where there is no practical problem, but the scanning non-linearity cannot be corrected, and the scanning non-linearity is corrected by electrical means. It is a thing. For example, in a laser printer or the like, correction is performed by means such as changing the clock of the signal continuously or stepwise.

Means for Solving the Problems A light source system that focuses light to enter a deflector, a polygon mirror whose reflection surface is a convex elliptic cylinder surface, and a cross section that is arranged between the polygon mirror and the scanning surface. Is a concave curved surface with respect to the incident beam and reflects a light beam from the polygon mirror to reach the scanning surface, and a cylindrical optical element arranged between the fixed mirror and the scanning surface. The focusing action on the beam in the main scanning direction is set so that the light source system is positive, the polygon mirror is negative, and the fixed mirror is positive.

Operation With the above-described configuration, an optical system that does not require correction by other means such as electrical correction by only setting a certain condition found by optical simulation in order to minimize an error in field curvature, particularly the fθ characteristic. Is what you can get.

Embodiment A first embodiment of the present invention will be described with reference to FIGS. 1 to 4. First, the light source system 3 is formed by the converging lens 2 that focuses the light emitted from the light source 1 of the light source 1. The converging lens 2 has a focal length of F and focuses on S ₁ .

Then, the light from the converging lens 2 passes through the cylindrical lens 11a and then is irradiated on the reflecting surface 5 of the polygon mirror 4 which rotates about O. The polygon mirror 4 is driven at a high speed by a driving body 6, and its reflecting surface 5 has the shape shown in FIG. That is, the reflecting surface 5 is an elliptic cylindrical surface having an inscribed circle radius R ₂ and having 2A and 2B as major and minor axes. However, A ≧ B or A ≦ B.

The light reflected by the reflecting surface 5 of the polygon mirror 4 is reflected by the reflecting surface 8 of the fixed mirror 7, and the light from the reflecting surface 8 reaches the scanning surface 9. The reflecting surface 8 of the fixed mirror 7 is centered on O ₂ , and the major and minor axes of the ellipse are 2P ₁ ,
It is an elliptic cylindrical surface with 2P ₂ . However, P ₁ ≧ P ₂ or P ₁ ≦ P
_{Is 2} . A plane mirror 10 and a cylindrical lens 11 as a cylindrical optical element are arranged between the fixed mirror 7 and the scanning surface 9.

As the fixed mirror 7, as shown in FIG.
It is also possible to use a fixed mirror 12 having O ₂ as a focal point, having a focal length of P ₃ and having a parabola in a plane cross section.

In such a configuration, the laser beam from the light source system 3 is converged by the converging lens 2 and applied to the polygon mirror 4, is reflected by the reflecting surface 5 of the polygon mirror 4, and is fixed, the plane mirror 10 and the cylindrical lens 11. The scanning surface 9 is reached through the scanning path and the scanning surface 9 is scanned.

Thus, according to the above-described configuration, the focusing action on the beam in the main scanning direction is such that the light source system 3 is positive, the polygon mirror 4 is negative, and the fixed mirror 7 is positive.

In order to correct the field curvature on the scanning surface 9 and the fθ characteristic, R ₂ , A, B, P ₁ , P ₂ , P ₃ , F, F is searched by optical simulation.
The value of S, P, J is changed variously and set appropriately. Here, S is the distance between the center O of the polygon mirror 4 and the focal point S ₁ of the fixed mirror 7, J is the distance between the O point and the apex of the fixed mirror 7, and P is the O point and the scanning plane 9. Is the distance.

Next, a second embodiment of the present invention will be described based on FIGS. 6 and 7. The same parts as those in the above-mentioned embodiment are designated by the same reference numerals and the description thereof will be omitted. In this embodiment, the fixed mirror 7 shown in FIG. 4 has a reflecting surface 8 having a toroidal curvature with a radius R ₃ in order to converge the beam in the sub-scanning direction. In this case, the fixed mirror 7 acts as a cylindrical optical element, and the cylindrical lens 11 is omitted. Also in this case, the optical simulation allows the values of R ₂ , A, B, P ₁ , P ₂ , P ₃ , F, S, P and J to be changed in consideration of R _{3 in} addition to the above values. Set it appropriately.

Next, as an example 1, when the constants of the respective parts are set as follows, the rotation angle α of the polygon mirror 4, the deflection length l of the scanning line,
Table 1 shows the relationship between the field curvature in the main scanning direction, the field curvature in the sub scanning direction, and the fθ characteristic.

Rotation angle of polygon mirror α = ± 24 ° Deflection length on scanning line l = ± 105.3mm R ₂ ＝ 13mm, A ＝ 116.83mm B ＝ 136.5mm, F ＝ 140mm S ＝ 36.58mm, J ＝ P ＝ 71mm P ₁ = P ₂ -291mm Here, the data of the field curvature in the sub-scanning direction is the one when the fixed mirror 7 having the toroidal concave surface shown in FIG. 7 is used.

However, Sθ = 5.7 mm and R ₃ = 74.72 mm.

For reference, Table 2 shows an example of a conventional post-object type optical scanning device that does not use a fixed mirror and has an equivalent scanning amplitude.

Polygon mirror rotation angle = ± 16 ° Deflection length l = ± 104.8 mm R ₂ = 12 mm, A = 136.7 mm B = 136.7 mm, F = 92 mm S = 38.156 mm, P = 200.5 mm Next, as an example 2, a case where the polygon mirror 4 is an ellipse and the fixed mirror 7 is a parabolic cylindrical surface shown in FIG.
Shown in the table.

Rotation angle of polygon mirror α = ± 26 ° Deflection length on scanning line l = ± 135.44mm R ₂ ＝ 11mm, A ＝ 119.6mm B ＝ 100.0mm, F ＝ 200mm S ＝ 60.5mm, J ＝ 79.5mm P ＝ 80.4 mm, P ₃ ＝ 160.0mm Next, as Example 3, Table 4 shows a case where the polygon mirror 4 is an ellipse and the fixed mirror 7 is also an ellipse.

Rotation angle of polygon mirror α = ± 24 ° Deflection length on scanning line l = ± 157.80mm R ₂ ＝ 11mm, A ＝ 169.11mm B ＝ 200.0mm, F ＝ 200mm S ＝ 59.49mm, J ＝ P ＝ 100.0mm P ₁ = 400.0mm, P ₂ = 383.7mm Sθ = 3.95mm, R ₃ = 116.26mm EFFECTS OF THE INVENTION As described above, the present invention provides a light source system that focuses light to enter a deflector, a polygon mirror whose reflection surface is a convex elliptic cylinder surface, and an arrangement between the polygon mirror and the scanning surface. A fixed mirror having a quadric surface whose cross section is concave with respect to the incident beam and which reflects the light beam from the polygon mirror to reach the scanning surface, and is disposed between the fixed mirror and the scanning surface. It is composed of a cylindrical optical element, and the focusing action on the beam in the main scanning direction is set so that the optical system is positive, the polygon mirror is negative, and the fixed mirror is positive, so that correction by other means such as electrical correction is performed. It is possible to obtain an optical system in which the field curvature, in particular, the error in fθ is improved to the extent that there is no practical problem, and the fixed mirror for obtaining such a function is on the optical path relatively close to the scanning surface. Be installed in Since it is, it can be easily manufactured without requiring a precision of about a polygon mirror, also,
When viewed as the entire optical system, the number of times of folding is increased, so that the optical system can be formed compactly and is easy to use in equipment such as a printer.

[Brief description of drawings]

FIG. 1 is a plan view showing a first embodiment of the present invention, FIG. 2 is a side view thereof, FIG. 3 is a plan view of a polygon mirror, FIG. 4 is a side view of a fixed mirror, and FIG. FIG. 6 is a side view showing a modified example of the mirror, FIG. 6 is a side view showing the second embodiment of the present invention, and FIG. 7 is a side view of the fixed mirror. 3 ... Light source system, 4 ... Polygon mirror, 7 ... Fixed mirror, 11 ... Cylindrical lens (cylindrical optical element)

Claims (2)

[Claims] 1. A light source system for converging light to enter a deflector,
A polygon mirror whose reflection surface is a convex elliptic cylinder surface, and a quadratic curved surface which is disposed between the polygon mirror and the scanning surface and whose cross section is concave with respect to the incident beam, reflect the light beam from the polygon mirror. A fixed mirror for reaching the scanning surface and a cylindrical optical element arranged between the fixed mirror and the scanning surface. The focusing action on the beam in the main scanning direction is positive in the light source system and negative in the polygon mirror. The optical scanning device is characterized in that the fixed mirror is set to be positive. 2. The optical scanning device according to claim 1, wherein the reflecting surface of the fixed mirror is provided with a concave curvature in the sub-scanning direction so as to have a function of a cylindrical optical element.