JPS61184046A - Laser light scanner - Google Patents

Abstract

PURPOSE:To attain correction with low cost and lens deterioration over a long period by providing a lens having a focusing effect of light only in a direction at right angles to the scanning direction between a condenser lens and a scanned face. CONSTITUTION:A condenser lens 3 and a cylindrical lens 8 having a curvature in the direction Y only are arranged so that the reflection plane of a rotary polygon mirror 2 and the scanned face 4 are in optically conjugated relation in the direction Y. Further, the cylindrical lens 8 having a curvature at which the incident optical system to the rotary polygon mirror 2 is directed in the scanning direction only and a spherical cylindrical lens 8 being a cofocus with respect to the scanning direction with the cylindrical lens 6 are arranged. Since the reflection plane of the rotary polygon mirror 2 is arranged at a distance nearly equal to the focus of the spherical convex lens 7, even when the manufacturing accuracy of the rotary polygon mirror 2 is not good, the correction of facial deflection with high accuracy is attained and low cost is also attained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a laser beam scanning device for displaying, recording, and reading information such as two characters in an image using a laser.
The present invention relates to a laser beam scanning device applied to a laser printer, a laser facsimile, or a laser display.

2. Description of the Related Art A conventional laser beam scanning device for laser display or recording is schematically shown in FIG. The light beam from laser light source 1 is
It is reflected by the mirror surface of the rotating polygon mirror 2 rotating in the direction of the arrow, passes through the condensing lens 3 (f, θ lens), and is reflected on the scanned surface 4.
One scanning line is formed by scanning the top in the X direction. By moving the scanned surface 4 in the Y direction at a constant pitch and at a constant speed, the entire surface of the scanned surface 4 can be scanned.

However, if each mirror surface is not parallel to the rotation axis of the rotating polygon mirror 2, that is, if the surface of the rotating polygon mirror 2 is tilted,
Alternatively, if there is a wobble in the rotation axis of the rotating polygon mirror 2, pitch unevenness of scanning lines occurs in a direction perpendicular to the scanning direction (Y direction). For example, if the distance between the rotating polygon mirror 2 and the scanned surface 4 is e
If the permissible pitch unevenness of the scanning line on the surface to be scanned is 0.01mm, then the surface tilting precision of the rotating polygon mirror is required to be 8×10 2 or more. However, this accuracy is close to the limit of machining accuracy, and even if it could be achieved, it would be extremely expensive.

Conventionally, methods for solving the above drawbacks have been based on the ratio of the scanning direction of the cross section of the laser beam incident on the rotating polygon mirror to the direction perpendicular to the scanning direction, and the ratio of the laser beam reflected by the rotating polygon mirror 2 to the scanned surface. 2. A device in which the ratio of the focal length of the optical system in the scanning direction and the direction perpendicular to the scanning direction is equal (Japanese Patent Laid-Open No. 137752/1983), or a cross section of the laser beam incident on the rotating polygon mirror in the scanning direction. A cylindrical lens that is flat and parallel and has a curvature only in the direction perpendicular to the scanning surface, placed between the f/θ lens and the scanning surface, eliminates pitch unevenness in the scanning line due to the surface tilt of the rotating polygon mirror. There is a device (Japanese Unexamined Patent Application Publication No. 153456/1983) that reduces the amount of water. However, the effect of correcting the surface inclination of the rotating polygon mirror of these methods is not sufficient because the effect is only by utilizing the short focal length of the cylindrical lens.

Another conventional method is to measure the amount of surface tilt of a rotating polygon mirror for each surface, and use that data to create a deflection element such as an electro-optic element, an acousto-optic element, or an element in which a mirror is attached to a bimorph element. Device for correcting pitch unevenness on a scanned surface by changing the input signal to (Japanese Patent Application Laid-open No. 49-98256, Japanese Patent Application Laid-open No. 53-9548)
There is.

Problems to be Solved by the Invention These problems require time and effort to measure the amount of dynamic surface tilt of each reflective surface of a rotating polygon mirror and write the measured data to a semiconductor memory, etc. There is a drawback that deterioration such as play in the rotating shaft of a multi-plane rotation over many years cannot be corrected.

The present invention has been made in order to eliminate the above-mentioned drawbacks, and an object of the present invention is to provide a laser beam scanning device that is inexpensive and can perform correction with little deterioration over a long period of time.

Means for Solving the Problems The laser beam scanning device of the present invention includes a laser light source, a means for modulating the laser light from the laser light source, and a rotating polygon mirror for deflecting and scanning the laser light modulated by the modulating means. It consists of a condensing lens for condensing the laser beam scanned by the rotating polygon mirror onto the scanned surface, and between the modulating means and the rotating polygon mirror, the laser beam modulated by the modulating means has a curvature only in the scanning direction. The distance between this lens and the reflecting surface of the rotating polygon mirror is approximately the focal length of this lens. and a lens having a curvature only in a direction perpendicular to the scanning direction is disposed between the condenser lens and the surface to be scanned.

As a result, the present invention can realize a laser beam scanning device that is inexpensive and exhibits little deterioration in correction accuracy even when used for a long period of time.

Example An embodiment of the present invention will be described below.

FIG. 1 shows a laser beam scanning device of this embodiment.

Components that are the same as those in the conventional example are given the same numerals and the description thereof will be omitted. 6 is a cylindrical lens with a focal length f1, and 7 is a spherical convex lens with a focal length f2, which are respectively provided between the modulator 6 and the rotating polygon mirror 2.

Further, 8 is a cylindrical lens having a focal length f4, and is provided between the f/θ lens 3 and the surface to be scanned 4.

Cylindrical lens 6, spherical convex lens 7, and rotating polygon mirror 20
The cross-sectional shapes of each laser beam incident on the reflective surface are shown in Figure 2 a and b.
, c. The reflecting surface of the rotating polygon mirror 2 is approximately at the beam waist position with respect to the direction perpendicular to the laser beam scanning direction. Lens 3 is a condensing lens, and in this embodiment, f.
Use a θ lens. The f/θ lens 3 directs the beam in the X direction f on the surface to be scanned in proportion to the deflection angle of the laser beam by the rotating polygon mirror 2.
- It has a function of focusing the laser beam to the position of θ (f is a constant). The surface to be scanned 4 may include photoreceptors such as Se, Cd, S, amorphous silicon, organic photoreceptors, and ZNO used in electrophotography, various photographic papers or films used in silver halide photography, and photocurable materials. It may also be made of resin having thermoplasticity or thermosetting properties.

3 and 4 are a sectional view in the Y direction and a sectional view in the X direction of a portion of the laser beam scanning device of the present invention shown in FIG. 1. FIG. The distance between the reflective surface of the rotating polygon mirror 2 and the f/θ lens 3 is set to 11. , the distance between the f-θ lens 3 and the cylindrical lens 8 is e2
shall be. As shown in Figures 2, 3 and 4, a, h
, θ11. θ soil.

When h, .

θ −tan’ ・・・・・・(1) Therefore, from equations 1 to 4, Obtain the conditions.

For example, when narrowing down the spot diameter (ω) of the laser beam to 60 μm, f + =400j1m, λ=488
If the shoulder is X10m, then a = 2.49 mm due to π・ω0. l, =7Q
jjljl, f.

=25Qff, 1l=Q, A” + f 2 =96y
If g, then 42=213.9 MII from equation 5. Yacht, cylindrical lens 3 from f/θ lens 2 to 213.9f
By placing it at the position f, a light spot of approximately 60 μm can be focused onto the scanned surface 4. Also, the focal length of the cylindrical lens 8 can be arbitrarily selected and the distance between the cylindrical lens 8 and the surface to be scanned 4 can be adjusted, or the diameters 2a and 2h of the cross section of the incident light to the spherical convex lens 7 shown in FIG. By changing the cylindrical lens 8 and adjusting the cylindrical lens 8, the shape of the laser beam spot on the surface to be scanned can be arbitrarily adjusted to some extent.

In FIG. 1, an f.theta. lens is shown as the scanning distortion correcting optical section, but a scanning distortion correcting optical system using a parabolic mirror may also be used.

Effects of the Invention As explained in detail above, in the present invention, in order to reduce the pitch unevenness of the scanning line on the surface to be scanned, which is caused by the vibration or surface tilt of the rotating polygon mirror during laser beam scanning, the rotating polygon mirror reflection surface and A condenser lens and a cylindrical lens having curvature only in the Y direction are arranged so that the surface to be scanned has an optically conjugate relationship in the Y direction, and the input optical system to the rotating polygon mirror is arranged only in the scanning direction. By arranging a cylindrical lens with curvature, a spherical cylindrical lens so that it is confocal with the cylindrical lens in the scanning direction, and further arranging the reflective surface of a rotating polygon mirror at a distance approximately equal to the focal length of the spherical convex lens, rotation can be achieved. Even if the manufacturing accuracy of multi-sided printing is poor, it is possible to perform surface tilt correction with high precision, and to realize cost reduction.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing a laser beam scanning device according to an embodiment of the present invention, and FIG. 2 is a perspective view of a conventional laser beam scanning device showing the cross-sectional shape of the same laser beam. 1...Laser light source, 2...Rotating polygon mirror, 3...Condensing lens, 4...Scanned surface, 6...- Modulator, 6°8...Cylindrical lens, 7...Spherical convex lens. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 (a)Cb) (Figure 3

Claims (1)

[Claims] A laser light source, a modulating means for modulating the laser light from the laser light source, a rotating polygon mirror for deflecting and scanning the laser light modulated by the modulating means, and a rotating polygon mirror for deflecting and scanning the laser light scanned by the rotating polygon mirror. A condensing lens for condensing light onto a scanning surface is provided, and a lens that spreads the laser light from the laser light source only in the scanning direction is provided between the laser light source and the rotating polygon mirror, and a lens that spreads the laser light from the laser light source only in the scanning direction; A lens is provided on the reflective surface of the rotating polygon mirror to create a beam waist only in the direction perpendicular to the scanning direction, and is arranged to produce parallel light in the scanning direction, and the condenser lens and the surface to be scanned A laser beam scanning device characterized in that a lens having a light focusing effect only in a direction perpendicular to a scanning direction is provided between the lenses.