JPS6410805B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an image recording and display device using a light source arranged in an array, such as a semiconductor array laser.

2. Description of the Related Art Image recording and display devices using a single light source have been well known. FIG. 1 is a diagram showing one embodiment of the present invention, in which, for example, an emitted/divergent beam from a semiconductor laser 1 is collimated by a collimator lens 2 and made incident on one surface of a rotating polygon mirror 3. The reflected/deflected light from the rotating polygonal mirror is imaged and scanned onto a scanning surface 5 by an imaging lens 4 such as a θ lens. By modulating the semiconductor laser, a desired image can be obtained on the surface to be scanned. By using such a device with an array light source,
Various benefits arise. Here, an array-like light source means, for example, as shown in Fig. 2,
It refers to a structure in which modulated semiconductor lasers 1a, 1b, and 1c are lined up in a row. The use of such an array light source has the following advantages compared to the case of using only one light source.

(1) High speed because multiple scanning lines can be recorded and displayed simultaneously.

(2) Therefore, the speed of rotating polygon mirrors, galvans, etc. may be slow.

(3) Also, the power of the semiconductor laser may be low, which is advantageous against deterioration.

For the above reasons, it is very effective to use an array light source.

However, if an array light source is used with a conventional optical system, the following drawbacks will occur.

FIG. 3 illustrates this, and the explanation will be given assuming that the semiconductor laser 1 is made up of three arrays 1a, 1b, and 1c.

The emitted beam from each semiconductor laser 1a, 1b, 1c oscillates with maximum intensity distribution in the normal direction perpendicular to its end face. When collimated with collimator lens 2, semiconductor laser 1 on the optical axis
Only the beam b runs parallel to the optical axis, and the semiconductor lasers 1a and 1c located outside the optical axis are collimated at a finite angle with the optical axis. The angle θ shown in this figure is the focal length of the collimator lens,
If the pitch of the light source array is θ=
nl/(rad). (where n is the number of arrays) When semiconductor lasers are arrayed, it is said that the limit is about 0.1 mm due to heat dissipation, manufacturing technology, etc., and it is difficult to make the size smaller than this. If the focal length of the collimating lens is = 10 mm and the number of arrays is n = 8, then θ = 8 x 0.1/10 = 0.08 (rad) (= 4.6°). Here, if the distance between the focal position 6 of the collimator lens and the rotating polygon mirror is d, then the spread △ on the reflecting surface of the rotating polygon mirror is d = 100 mm, then △ = d・θ = 100 x 0.08 = 8 mm. Can't be ignored. The phenomenon based on this cause is
For example, as shown in FIG. 4A, an array of light sources 1a, 1
b, 1c, and 1d are arranged parallel to the main scanning direction, or almost parallel to the main scanning direction, as shown in FIG. Become something. For this reason, each beam 7a, 7b, 7c is collimated by the collimator lens 2.
The reflected light amount distribution with respect to the rotation angle θ of the rotating polygon mirror 3 is as shown in FIG. 6, and the rotation angle portion 2θ ₀ that is effectively used for scanning is extremely narrow compared to the case where there is only one light source. In order to solve this problem, the diameter of the rotating polygon mirror must be increased, which makes the rotating polygon mirror vulnerable to high-speed rotation, and requires a motor with a large driving force. Moreover, the cost also increases and the size increases.

Further, as shown in FIG. 4B, array-shaped light sources 1a, 1
If b, 1c, and 1d are arranged perpendicular to the main scanning direction, the diameter of the rotating polygon mirror may be the same as in the case of one, but the spread of the beam on the reflecting surface is distributed in the direction of the rotation axis. Therefore, a thick rotating polygon mirror is required, and a motor with a large driving force is also required, which is disadvantageous for increasing speed, resulting in increased cost and larger size of the device.

The present invention aims to improve the above-mentioned drawbacks, and provides a scanning optical system that requires a small deflector, has a low manufacturing cost, and has a compact configuration even when an array light source is used. It is something.

In the scanning optical system according to the present invention, the above object is achieved by spatially concentrating a plurality of beams that are simultaneously deflected by the deflection surface of the deflector as close as possible to the deflection surface of the deflector. That is.

In the scanning optical system according to the present invention, when a semiconductor laser array is used as the array light source, the optically conjugate position of the pupil plane on the deflector side of the collimator lens that collimates the light beam from the semiconductor laser is , is arranged very close to the deflecting reflection surface of a deflector such as a rotating polygon mirror or a galvano mirror.
In the embodiments according to the present invention described later, the optical axis of the collimator lens is included between the collimator lens and the deflector for collimating each light beam from the array light source section, and the deflection of the deflector is included between the collimator lens and the deflector. An afocal optical system is arranged in a plane parallel to the scanning plane, and the afocal optical system creates an optically conjugate relationship between the exit side pupil plane of the collimator lens and the deflection reflection surface of the deflector. ing. By adopting such a configuration, no matter how many light source arrays increase,
It is possible to use a deflector whose size is comparable to that of a single light source.

FIG. 7A is a plan view showing an embodiment of the scanning optical system according to the present invention, and FIG. 7B is a front view of the light emitting surface 13 of the semiconductor laser 11, which is a light source section, viewed from the collimator lens 12. . As shown in FIG. 7B, each light emitting part 13a, 13b, 13c of the semiconductor laser
is slightly shifted in the vertical direction when viewed from the optical axis direction of the collimator lens 12. Each luminous flux 1a, 1b, emitted from each light emitting part of the semiconductor laser
1c is collimated by the collimator lens 12, passes through the exit side pupil 14 of the collimator lens, and then is divided into two positive lens elements 15a, 15.
The light enters the afocal optical system 15 consisting of b.
The afocal optical system 15 emits an incident parallel beam as a parallel beam, but in the afocal optical system 15, the exit side pupil surface 14 of the collimator lens 12 and the surface 16a of the polygon mirror 16 that deflects and reflects the light beam are optically connected. They have a conjugate relationship. Therefore, an image of the pupil plane 14 is formed near the deflection reflection surface 16a. The beam that has been deflected and scanned by the polygon mirror 16 is directed to the photosensitive drum 1, which is the surface to be scanned, by the imaging lens system 17.
The drum surface is scanned by a plurality of beam spots as the polygon mirror rotates. Incidentally, since the light emitting section is slightly shifted vertically as shown in FIG. 7B, each spot of the light beam formed on the drum in FIG. 7A is slightly displaced in the direction perpendicular to the plane of the paper. ing.

FIG. 8 is a diagram showing the principle of the afocal optical system 15. The afocal optical system 15 consists of two groups of lenses: a positive lens 15a with a focal length a and a positive lens 15b with a focal length b. The exit pupil 14 of the collimator lens 12 is connected to the positive lens 15.
The deflection reflection surface 16a of the deflector 16 is located at the rear focal plane of the positive lens 15b. Further, the distance between both lenses 15a and 15b is the sum of the focal lengths of both lenses (a+b).
By arranging it in this manner, the conjugate plane of the exit pupil plane 14 of the collimator lens 12 can be formed on the reflecting surface of the deflector 16. This effect is superior to the case where the reflecting surface 16a of the scanner is directly placed on the exit surface 14 of the collimator lens in the following points.

(i) Compared to the focal length c of the collimator lens 12, the rear group lens 1 of the afocal lens system 15
By setting the focal length b of 5b to b>c,
It takes up a lot of space with the deflector and is easy to place.

(ii) As shown in FIG. 8, by changing the focal length a of the front group lens 115a and the focal length b of the rear group lens 15b of the afocal lens system 15, the angular magnification γ can be changed to γ=θb/θa= a/b However, θa is given by the angle of incidence on the front group lens, and θb is given by the angle of exit from the rear group lens, and the angular magnification can be changed arbitrarily.

For example, when γ→small, the distance S between the imaging spots on the imaging plane is given by S=l/c・γ・o=l/c・a/bo, so S→small. Become. This increases the degree of freedom in design.

(iii) In the system with the arrangement shown in FIG. 7A, the front group lens 15a
By using a cylindrical lens group, tilting can be corrected. Here, the tilt correction is to optically correct pitch unevenness on the scanning surface caused by the inclination of each reflective surface of the rotating polygon mirror 16 or the like. That is, the optical axis direction component of the scanning beam, that is, the component in the direction perpendicular to the deflection scanning direction of the light flux is imaged on the deflection reflection surface 16a of the deflector 16, and the scanning beam is focused on the deflection reflection surface 16a.
It is formed in a linear shape on a. For this purpose,
The positive lens 15a is replaced by a cylindrical lens 1.
5a', and is arranged so that its generatrix direction coincides with the direction of the rotation axis of the deflector, that is, the direction perpendicular to the deflection scanning plane. This situation is shown in Figure 9A.
and FIG. 9B, A is a diagram showing the optical path within the deflection scanning plane, and B is a diagram showing the optical path within a cross section perpendicular to the deflection scanning plane.

In the deflection plane shown in Fig. 9A, Fig. 7A
The light beam is imaged in the same way as in the case shown in . On the other hand, in the cross section perpendicular to the deflection plane, as shown in FIG. 9B, the light beam from the collimator lens is not subjected to imaging action by the cylindrical positive lens 15a'.
The light is focused by the positive lens 15b and formed as a line image on the deflection surface 16a. When the afocal optical system has such a configuration, the imaging lens system 17 is an anamorphic optical system, and in a cross section perpendicular to the deflection scanning surface, it optically converts the line image on the deflection reflection surface 16a and the photosensitive drum 18. is kept conjugate. Therefore, the influence on the light beam due to the tilting of the deflection-reflecting surface can be eliminated in the cross-sectional direction perpendicular to the deflection-scanning surface. On the other hand, in the deflection scanning plane of the imaging lens system 17, as shown in FIG.
This is to form an image on the photosensitive drum 18 of the light beam deflected by the photosensitive drum 18.

FIG. 10 is a plan view showing another embodiment of the scanning optical system according to the present invention, in which the afocal optical system 19 is composed of two parabolic mirrors 19a and 19b. The function of the afocal system using this parabolic mirror is the same as the function of the afocal system described above, so a description thereof will be omitted here.
Furthermore, it goes without saying that the above-mentioned tilt correction can be performed by using a cylindrical parabolic mirror as the parabolic mirror 19a.

As described above, in the scanning optical system according to the present invention, the image of the exit pupil plane of the collimator lens that collimates the light flux from the array light source is transmitted very close to the deflection surface of the deflector via the afocal optical system. By forming the scanning optical system, the scanning optical system can be designed compactly even though an array light source is used, and an excellent effect can be obtained with a simple means.

[Brief explanation of drawings]

Figure 1 is a schematic diagram showing a conventional scanning optical system, Figure 2 is a schematic diagram showing a conventional scanning optical system.
The figure shows an example of an array-shaped semiconductor laser, and Figures 3, 4, A, B, 5, and 6 show examples of an array-shaped light source in a conventional scanning optical system. 7A is a plan view showing an embodiment of the scanning optical system according to the present invention, FIG. 7B is a front view of the light source section shown in FIG. 7A, and FIG. 8 is a diagram for explaining the inconvenience. Figures 9A and B are diagrams for explaining the afocal optical system applied to the scanning optical system according to the present invention.
10 shows another embodiment of the scanning optical system according to the present invention. FIG. 10 shows another embodiment of the scanning optical system according to the present invention. A plan view shown. DESCRIPTION OF SYMBOLS 11... Array light source, 12... Collimator lens, 14... Output side pupil of collimator lens, 15... Affocal optical system, 16... Polygon mirror, 16a... Deflection reflective surface.

Claims (1)

[Claims] 1. A plurality of light source units arranged in an array, a collimating optical system that collimates each light beam from the arrayed light source unit, and a collimating optical system that deflects the light beam from the collimating optical system in a predetermined direction. a deflector having a deflection surface; and an afocal optical system disposed between the collimating optical system and the deflector, which is arranged in a plane that includes the optical axis of the collimating optical system and is parallel to the deflection scanning plane of the deflector. What is claimed is: 1. A scanning optical system for an array light source, comprising: an optical system that makes an exit pupil plane of the collimating optical system and a deflection surface of the deflector in a conjugate relationship. 2. An optical system disposed between the collimating optical system and the deflector is arranged so that each beam from the collimating optical system is disposed between the collimating optical system and the deflector in a plane that includes the optical axis of the collimating optical system and is perpendicular to the deflection scanning plane of the deflector. 2. A scanning optical system for an array light source according to claim 1, which is an optical system for forming an image of a light beam on a deflection surface of said deflector.