JPH067230B2 - Scanning optics - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning optical device for correcting tilt of a rotary polygon mirror called a polygon mirror.

[Prior Art] Conventionally, for example, in an image recording apparatus, a rotary polygon mirror is often used to realize high-speed optical scanning. However, tilting of each reflecting surface causes scanning line unevenness in the sub-scanning direction. It was Therefore, a cylindrical lens is used to linearize the light beam between the cross sections perpendicular to the deflecting surface to form a reflecting surface, and an image is formed on the reflecting surface to provide a tilt correction effect.

That is, FIG. 3 shows a conventional tilt correction optical system, in which the incident laser light L is incident on the reflecting surface 3 of the rotary polygon mirror 2 through the cylindrical lens 1. In this case, the cylindrical lens 1 has no refracting power in the cross-sectional direction parallel to the deflecting surface shown in (a), but has refracting power in the direction perpendicular to the deflecting surface in (b), and the reflection of the rotary polygon mirror 2 An image is formed on the surface 3. Since the reflecting surface 3 of the rotary polygon mirror 2 is conjugate with the scanning surface P via the imaging lens 6 composed of the concave lens 4 and the toric lens 5, the image is scanned even if the reflecting surfaces 3 are tilted. The scanning line at does not move in the sub-scanning direction.

However, in reality, as the rotating polygon mirror rotates, the image formed by the cylindrical lens on the surface of the rotating polygon mirror does not always form on the surface of the rotating polygon mirror, so that the rotating polygon mirror as a whole falls. There is a drawback in that the effect of perfect tilt correction cannot be achieved.

That is, as shown in FIG. 4, when the rotary polygon mirror 2 rotates from the solid line to the broken line, the position where the incident light L intersects the reflecting surface 3 changes. This means that the image forming point of the cylindrical lens 1 does not always coincide with the reflecting surface of the rotary polygon mirror 2 in FIG. 3 (b).

The movement amount at this time will be described with reference to FIG. 5. If the imaging point is always on the reflecting surface 3 of the rotating polygon mirror 2 even if the rotating polygon mirror 2 rotates, as shown in (a). Even if the reflecting surface 3 is tilted, the relationship between the conjugate points OO ′ is held constant. However, as shown in (b), when the point O is not imaged on the reflecting surface 3, if there is no tilt, the point O ′ on the scanning surface P is obtained.
If there is a tilt, an image is formed on O ″ and a shift occurs. Here, the points O and O _o are in a mirror image relationship with the reflecting surface 3. Therefore, in reality, each reflecting surface If there is a random inclination in 3, the effect of this effect is that pitch unevenness occurs in the sub-scanning direction of the scanning line.

[Object of the Invention] An object of the present invention is to solve the above-mentioned drawbacks of the conventional example, and to provide a scanning optical device in which the image formation by the cylindrical lens is always present on the reflecting surface of the rotating polygon mirror. Especially.

[Summary of the Invention] The gist of the present invention for achieving the above-mentioned object is to introduce a light beam into a rotary polygon mirror through a cylindrical lens having a refractive power in a sectional direction perpendicular to a deflecting surface, An optical system for deflecting and scanning a light beam by rotation, comprising a mechanism for linearly reciprocating the cylindrical lens along its optical axis within the movement of the reflecting surface of the rotating polygonal mirror, and a sectional direction perpendicular to the deflecting surface. Thus, the scanning optical device is characterized in that the light flux is always focused on the reflecting surface.

Embodiments of the Invention The present invention will be described in detail based on the embodiment shown in FIG. The same reference numerals as those in FIGS. 3 to 5 denote the same members.

In the embodiment, the cylindrical lens 1 is movable in the optical axis direction by a very small amount. A pulley 11 is attached to the shaft of a drive motor 10 that rotates the rotary polygon mirror 2, and the rotation of the pulley 11 rotates a cam 13 via a belt 12. And cam 1
3 is a guide 15 for the support base 14 of the cylindrical lens 1.
It is designed to be linearly reciprocated along the optical axis. The cam 13 is adapted to rotate once with respect to one reflecting surface 3 of the rotary polygon mirror 2.

The magnitude of the linear reciprocating motion of the cylindrical lens 1 is theoretically determined, and as shown by the dotted line in FIG. 2, the cylindrical lens 1 moves downward when the reflecting surface 3 approaches, and the distance when the reflecting surface 3 moves away. Reflecting surface 3 as if going up
The distance between the cylindrical lens 1 and the cylindrical lens 1 is always constant. Therefore, the cylindrical lens 1
Allows the laser beam L to be constantly and accurately imaged on the reflecting surface 3 of the rotary polygon mirror 2, and even if the reflecting surface 3 is tilted, pitch unevenness in the sub-scanning direction on the scanning surface P can be eliminated.

In the embodiment, the cylindrical lens is moved via the cam, but it may be moved using other means, for example, the piezoelectric effect or magnetic force.

[Effects of the Invention] As described above, the scanning optical device according to the present invention makes it possible to realize a complete tilt correction scanning optical system by constantly forming an image of a light beam on a reflecting surface of a rotating rotary polygonal mirror surface by a cylindrical lens. I am trying.

[Brief description of drawings]

1 and 2 show an embodiment of a scanning optical device according to the present invention, FIG. 1 is a block diagram thereof, FIG. 2 is an operation explanatory diagram, and FIG. 3 is a block diagram of a conventional example, FIG. 4 and FIG. 5 are explanatory views of changes in the intersections of incident light with the rotation of the rotary polygon mirror. Reference numeral 1 is a cylindrical lens, 2 is a rotary polygon mirror, 3 is a reflecting surface, 4 is a concave lens, 5 is a toric lens, 6 is an imaging lens, 10 is a drive motor, 11 is a pulley, 12 is a belt, 13 is a cam, and 14 Is a lens support, and 15 is a guide.

Claims (4)

[Claims] 1. An optical system in which a light beam is incident on a rotary polygonal mirror through a cylindrical lens having a refractive power in a cross-sectional direction perpendicular to a deflecting surface, and the light beam is deflected and scanned by the rotation of the rotary polygonal mirror. A mechanism for linearly reciprocating the cylindrical lens along the optical axis direction within the movement of the reflecting surface of the rotating polygonal mirror is provided, so that the light beam is always imaged on the reflecting surface in a cross-sectional direction perpendicular to the deflecting surface. A scanning optical device characterized by the above. 2. The scanning optical device according to claim 1, wherein the cylindrical lens reciprocates once with respect to one reflecting surface of the rotary polygon mirror. 3. The scanning optical apparatus according to claim 1, wherein the cylindrical lens is linearly moved by the rotational movement of a cam coupled to the rotary driving motor of the rotary polygon mirror via a belt. 4. The scanning optical device according to claim 3, wherein the cam rotates once with respect to one reflection surface of the rotary polygon mirror.