KR940006346B1 - Laser beam scanning apparatus - Google Patents

Abstract

The F theta error can be decreased by using a grin lenz having plane faces on both sides and different refractive index by positions. The laser beam scanner includes a light source for generating laser beam, a rotating polyhedral mirror (4) for reflecting with a certain angle laser beam transmitted through a colimator lenz, and a lenz module for scanning a laser beam for the polyhedron mirror on a drum (6). The lenz module is composed of a grin lenz of which refractive index satisfying delta Z = F.theta characteristics.

Description

Laser beam scanning device using green lens

1 is a perspective view showing a conventional scanning optical system.

2 is a plan view of a conventional F.θ lens system.

3 is a schematic diagram of a scanning optical system of the present invention.

4 is a schematic diagram showing a distribution of refractive index and a green lens having a characteristic of ΔZ = F.θ.

5 is a schematic diagram showing the refraction of the laser beam.

* Explanation of symbols for main parts of the drawings

1: light source 2: collimator lens

3: motor 4: rotating mirror

5: F.θ lens system 6: Drum

7 Detector 8 Green Lens (F.θ Lens)

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lens system of a laser beam scanning device, and in particular, it is easy to assemble using a green lens having both flat surfaces and different refractive indices according to each position of the lens and satisfying the characteristic of ΔZ = F.θ. The present invention relates to a laser beam scanning device capable of reducing mechanical and F.θ characteristic errors.

In the laser beam scanning apparatus generally used in the related art, as shown in FIG. 1, the laser beam L emitted from the light source 1 becomes a parallel beam in the collimator lens 2, and the beam passing therethrough is Rotation of the rotating mirror 4 passes through the F.θ lens system 5 and is scanned on the drum 6 with beams of L1 and L2. The F.θ lens system 5 serves to adjust the beam in the scanning optical system so that the laser beam can be scanned from the drum 6 in a suitable direction and at regular intervals (see FIG. 2).

When the incident laser beam is scanned on the drum 6 surface through the F.θ lens system 5 in accordance with the rotation of the rotating mirror mirror 4, when the lens 5 is a general optical system, the dice Δ on the drum 6 Although Z = F. tan θ (θ is the scan angle), the beam output position in the drum 6 must satisfy the relational expression of ΔZ = F. θ, and thus an F. θ lens system is required. This lens system is composed of three different lenses as shown in Fig. 2, each lens having two surfaces having different curvatures and a constant refractive index. Acting as variables of this F.θ lens system 5 are the thickness, curvature radius, refractive index, and distance between the lenses. Since each lens has a constant refractive index, several lenses with different curvatures are required to scan the laser beam according to the F.θ characteristic, and the F.θ lens system is composed of a combination of these lenses. In this regard, the F.θ lens system 5 is composed of three different lenses, each having a different refractive index of n1, n2, n3.

The mechanism of the scanning optical system of the prior art will be described with reference to FIG. 2. When the rotating polygon mirror 4 is rotated by an arbitrary angle θ, the laser beam L1 passes through the F.θ lens system 5 and the drum ( 6) Scanning is performed at the ΔZ position on the surface. Here, the F.θ lens system is an optical system in which the angular velocity of the rotating polygon mirror 4 and the linear velocity on the drum 6 satisfy the relationship ΔZ = F.θ. In Fig. 2, P is a reference plane of the lens system, which is called a main plane, and F is an effective focal length, where the main plane P and the optical axis meet (0 ') and an imaging plane (drum) on the imaging plane (drum). Distance between.

While the laser beam reflected by the rotating polygon mirror 4 passes through the F.θ lens system 5, the direction of the beam and the size of the beam are changed. The laser load is refracted when incident at oblique angles at interfaces having different refractive indices. In the F.θ lens system 5 shown in FIG. 2, the incident laser beam is refracted at the first face first because it is different from the refractive index of air and n1, even when passing through the first lens. Similarly, each time it passes through the second and third lenses, it is refracted to reach the ΔZ position on the drum 6 surface. Therefore, since the refractive index of each lens of the F.θ lens system 5 is constant, in order to make the beam incident at an arbitrary angle θ reach a specific position Z, the laser passing through varying the curvature of each lens The beam must be controlled. In addition, in order to control the direction and beam size of the laser beam, not only a lens having different curvatures is required but also a plurality of lenses, which may cause a large error when fixing the lenses to the scanning device. It takes a lot of time to follow. In addition, there is a problem that the loss of the laser beam to pass through each surface of the lens system.

Accordingly, an object of the present invention is to provide a laser that can hardly cause an error when the lens is fixed to the scanning device so as to solve the problems encountered in the prior art as described above, and to prevent the beam from being lost when passing through the lens system. It is to provide a beam scanning device.

The object of the present invention is a light source that emits a laser beam emitted from a light source, a rotating polyhedron that reflects the laser beam from the light source through a collimator lens at a predetermined angle, and receives a beam from the rotating polyhedral drum A laser beam scanning device composed of a lens system for focusing on the laser beam scanning apparatus, wherein the lens system comprises a green lens having a planar surface and a green lens having a refractive index distribution satisfying a characteristic relationship of ΔZ = F.θ. Device, where ΔZ is the distance from the scanning center position on the drum to the scanned position, F is the effective focal length, and θ is the angle of rotation of the rotating polyhedron.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

3 shows an optical system of the laser beam scanning apparatus according to the present invention, which includes a light source 1, a collimator lens 2, and a rotating polyscopy 4 as described in connection with FIG. The laser beam (L) is received through the process, which is the same as described with reference to FIG. 1, and thus, a detailed description thereof will be omitted.

The lens system of the scanning optical system of the present invention is constituted by one green lens 8 whose surfaces are both flat. This lens has a non-uniform refractive index distribution, and has a refractive index as indicated by the characteristic curve C of FIG. Since the green lens 8 changes the refractive index according to the position inside the lens, the green lens 8 can control the direction and size of the laser beam passing through the lens.

5 shows the refractive characteristics of the laser beam. As shown in FIG. 5, when the laser beam passes through the interface having different refractive indices (n, n '), the refractive index (n, n') and the curvature of the interface are shown. Accordingly, the direction and size of the laser beam change. Here, when the refractive indices n and n 'are constant, the degree of change in the transmission direction and the magnitude of the beam passing through the interface is constant even if the value of Δd changes. Therefore, in order to change the degree of change of the transmission beam according to the size of Δd, the boundary surface must be treated as a curved surface or the refractive index n 'must be changed to correspond to the size of Δd. In view of the above, the present invention allows the lens system to be constructed using the green lens 8 in which the regulation rate n 'can be changed in correspondence with the magnitude of Δd. That is, in the present invention, as shown in FIG. 4, as the scanning angle θ becomes larger when viewed from the center of the lens, that is, as the length r from the center of the lens to the incident point becomes larger, the refractive index n becomes curved. The lens system is constructed by using a green lens composed of both flat plates capable of providing a refractive index characteristic curve satisfying the characteristic relationship of ΔZ = F.θ so as to decrease. ΔZ is the distance from the scanning center position 0 on the drum 6 to the irradiated position Z, F is the effective focal length, and θ is the rotation angle of the rotating polygon mirror 4.

As described above, according to the present invention, it is possible to use one planar lens system for controlling the laser beam by varying the refractive index instead of the F.θ lens system composed of several lenses having a complicated curvature. It is easy to align, reduces mechanical errors and can be assembled quickly. In addition, since the lens system of the present invention is composed of one piece, the laser beam loss is small and can be applied to small products.

Claims (1)

A light source that emits a laser beam, a rotating polygon mirror 4 that receives a laser beam from the light source through a collimator lens and reflects the beam at a predetermined angle, and receives a beam from the rotating mirror mirror 4 and receives a drum 6 A laser beam scanning device comprising a lens system for scanning a lens), wherein the lens system comprises a green lens 8 having a planar surface on both sides and a refractive index distribution satisfying a characteristic relationship of ΔZ = F.θ. Laser beam scanning device using a green lens.