JPS58153908A - Lens for scanning - Google Patents

Abstract

PURPOSE:To accurately assemble lenses into a scanning lens system, by changing the external shape of each of the lenses of a flat shape and by converting one surface of each of the lenses into a plane surface. CONSTITUTION:The constituent lenses L1-L3 of a scanning lens system are made flat in directions perpendicular to the direction of the optical axes and the direction of scanning, and one surface r2, r3, r5 of each of the lenses is converted into a plane surface. As a result, the lenses can be attached accurately to holding members 10, 11.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a scanning lens used in a scanning optical system such as a laser beam printer.

BACKGROUND OF THE INVENTION FIG. 1 shows a conventional example of a scanning optical system for a laser beam printer. In this figure, a laser beam generated by a semiconductor laser generator (1) is reflected by a rotating polygon mirror (2), passes through a scanning lens (3), and reaches a photosensitive drum (4). Then, by rotating the rotating polygon mirror (2), the deflection angle is changed and scanning is performed on the photosensitive drum (4) in the direction of arrow a, and this is repeated. Here, the scanning lens (3) is a lens that has distortion according to the rotational characteristics of the rotating polygon mirror (2), and is a lens that makes the scanning speed of the laser beam on the photosensitive drum (4) constant. It is. In such a scanning lens, when the deflector is a rotating polygon mirror, the bar image height y is
- If the f/θ lens is set to θ and the deflector is a sine oscillation mirror, it is an arcsine lens with the ideal image height y set to /-arcsin seconds. These 126 aberrations Dis are calculated by dividing the actual image height by y#.

As shown in FIG. 1, a conventional scanning lens is composed of a circular lens when viewed from the optical axis direction, and has a truncated conical or cylindrical shape as a whole. [However, as other elements of scanning optical systems, such as the use of semiconductor lasers, become more compact, the space occupied by scanning lenses of this shape increases, and it becomes more and more compact. It was wanted.

In a scanning lens composed of a circular lens, the light beam actually passes only through a rectangular portion parallel to the scanning direction of the light beam, which is indicated by hatching in FIG. 2A.
The other parts are unnecessary parts for the lens. Therefore, as shown in Figure 3, it is conceivable to flatten the scanning lens (3') in a direction perpendicular to the optical axis direction and the scanning direction. That is, the scanning lens is shaped along the beam passage area (hatched portion) as shown by the solid line in FIG. 2A. However, if this flattening is simply carried out, the following problems will arise.

In other words, conventional scanning lenses were positioned and fixed by making circumferential line contact with the inner surface of the lens barrel, as shown in Figure 2B, but this can be simply flattened and fixed in the conventional manner. When attempting to do this, as shown in Figure 2C, the arc-shaped abutment P must be machined to an accurate position and shape with respect to the center of the lens when viewed from the optical axis direction, and such processing is extremely difficult. The number of processes increases sharply. Further, even if the machining can be performed with a certain degree of precision, the contact surface is small, so each lens of the assembled scanning lens will be decentered, making it impossible to obtain sufficient performance. The second diagram shows the case where the lens barrel is milled, but in this case, it is supported at several points, making it impossible to obtain sufficient performance as in the above case.

Objective/Summary The present invention has been made in view of the above, and an object of the present invention is to provide a flat scanning lens that is easy to manufacture and can be assembled with high precision.

The above object is achieved by making one surface of each lens constituting the scanning lens a flat surface, and using this flat surface as a contact surface for positioning and holding.

Embodiment FIG. 4 shows a flat single lens (L) with one surface flat, and the other surface of the lens (L) is supported by point or line contact.

FIG. 5 shows a further improved flat unit of the present invention (FIG. 5B). Incidentally, FIG. 5C shows a plano-concave lens processed in the same manner. Flattening both ends can control eccentricity of the lens around the optical axis, and when manufacturing such a lens (L''), it is only necessary to process one side of the rectangular parallelepiped into a lens surface. Manufacturing becomes very easy.

Chamfering both ends of the curved lens surface in the scanning direction has the advantage that the lens can be held on two planes, making it possible to more accurately and reliably position the lens.

Incidentally, such a lens can also be manufactured by plastic molding.

FIG. 6 shows an example of an assembly of a scanning lens in which three flat single lenses each having one of the lens surfaces described above are combined.

In Fig. 6, the scanning lenses are plano-concave lens (Ll), plano-convex lens (L4), plano-convex lens aJ3) from the incident side.
These lenses are composed of holding members (10) (1
1) Spring holding members (12a) (12b) (
13a) (lab) (t4a) (14b) and are held and positioned by upper and lower lid members (not shown). That is, the plane side lens surfaces of the lenses (Ll) (Lx) (L3) are the contact surfaces (10-1) (1) of the holding members (10) (11).
l-1) (10-2) (11-2) (10-3)
(11-3), and the holding members (12a) (12b) (13a) (13b)
) (14a) (14b). The pressing member may be flat as shown, but it may also be formed into a concave shape so that it can press against the curved surface of the lens at at least two points. Furthermore, when the lens is molded from plastic, a through hole may be provided at the end of the lens and screwed onto the contact surface.

The scanning lens constructed in this manner is very easy to assemble, and sufficient accuracy can be obtained.

Since the scanning lens of the present invention has a flat surface in one direction, it is desirable to have a configuration of two or more lenses in order to obtain sufficient lens performance. However, if too many lenses are used, it is effective in correcting aberrations, but the intensity of the transmitted beam decreases.
Since there are disadvantages such as high cost, a five-lens configuration of two or three lenses is practical.

In addition, since the scanning lens of the present invention includes many flat surfaces, the free seat for aberration correction is reduced, and the scanning speed is uniform. 1. In order to control the aberrations that are the main causes of laser beam distortion, namely distortion and astigmatism, in a well-balanced manner, certain conditions must be satisfied.
In the case of a plano-convex/plano-convex three-element f/theta lens, a uniform condition is required.

−0,14≦d2/c≦−0,05・・・・・・・・・
(1) 0.028≦dye≦0.19...
(2) d2: Distance between the second and third surfaces of the lens f1: Focal length of the lens f: Focal length of the entire lens.

Here, if d2 is too small, both distortion and astigmatism will be under, and if d2 is too large, it will be over. The same can be said about Ha. Therefore, the condition (1
), it is possible to control the difference between both stations in a well-balanced manner.

That is, if the upper or lower limit of condition (1) is exceeded due to the combination of d2 and c, even if one of distortion or astigmatism can be controlled, the other becomes a large aberration.

The lower limit of condition (2) is similarly advantageous in correcting aberrations.

It's a special thing. Further, the upper limit is for regulating the effective width of the lens, and is advantageous in processing the lens.

In the case of an f/theta lens consisting of two plano-concave and plano-convex lenses from the object side, the following condition (3) must be satisfied.

−0,25≦d2/c≦−0,07・・・・・・・・・
(3) This condition (3) corresponds to the condition (1) for the three-sheet configuration. There is no particular need to limit dx7t in condition (2).

An example of the configuration of an f/θ lens to which the present invention is applied will be shown below. In each configuration example, the focal length of the entire lens is 100 al
l and Fm are 80, and a semiconductor laser with a wavelength of 780 M is used as the light source.

Configuration example 1 (Figure 137) Radius of curvature r Distance between surfaces d Refractive index n/1 = -5
5,168 Configuration example 2 (Fig. 8) Radius of curvature r Distance between surfaces d Refractive index nr1 = -4
0,816 d*=1.895 nA=1.48437f2==
00 (12=11.662 n0=l, Qr3=
o.

ds=4.373 nA=1.48437r4= −
32,824 d4= 2.332 n0=1.0 r5= 00 ds= 2.624 nA=1.48437rs=-
130,380 /1 = -84,268 Configuration example 3 (Fig. 9) Radius of curvature r Distance between surfaces d Refractive index nrl = -22,
716 dl=1.895 nA-1,48437r2=
o mouth d4-2.947 no-1,0 r3= Ql:1 d4"2.332 n0=1.0 75g 00 /1--46.899 Configuration example 4 (Fig. 10) Radius of curvature r Surface spacing d Refractive index nr1=
o.

dl-1,370nB=1.51118r2=46.
032 d2=6.240 n0=1.0 r3-80.838 da=1.634 nB-1,51118r4-
0O d4=2.693 n0=1. O rs Tsu 0 ds=3.499 nB=1.51118r'=-
39,051 /1--90.050 Configuration example 5 (Fig. 11) Radius of curvature r Distance d Refractive index nr 00 ds-1,312nB=1.51118r2-" 9
7.585 dz=11.690 n0=1.0 r3=o.

ds=1.749 nB-1, 51118ra=-1
70,616 d4=0.583 no-1,0 15m 00 f+ --190,899 Configuration example 6 (Fig. 12) Radius of curvature r Distance d Refractive index nrl=
oa dl-1,020nB=1.51118r2=1
44.379 da-14,140no-1,0 f3-= 00 da-2,073nB=1.51118r4=-299
6,661 d4=4.373 no=1.0 r5” 00°dli-4,082nC-1,76241r6=-
61,481 /1--282.440 Configuration example 7 (Figure iJ13) Radius of curvature r Distance between surfaces d Refractive index nr1=
0Oji−1,020nB=1.51118r! -149,
722 d goose=19.864 n0=1. Or3 wealth 00 ds-4,373nc=1.76241r4--61.
140 bar 292.894 Configuration example 8 (Fig. 14) Radius of curvature r Surface spacing d Refractive index nrl=
o.

dz-16,786n0=1.0 r@m 00 da=5.453 nB=1.51118r4-
-26.753 8-63,250 In configuration examples 1 to 8, the sign of the radius of curvature is the first surface.

With the center of the radius of curvature r1 as a reference, if the center of each radius of curvature is on the object side (left side in the figure) from the reference, it is considered positive, and if it is on the image side, it is negative.

Effects As mentioned above, in the present invention, each lens constituting the scanning lens has a flat shape in a direction perpendicular to the optical axis direction and the scanning direction, and one lens surface is formed into a flat surface. The scanning lens can be well positioned and maintained, and the scanning lens can be manufactured and assembled easily.

Furthermore, if both ends of each lens in the scanning direction are made flat, each side can be formed from a rectangular parallelepiped glass material, which is advantageous in lens processing, and can also control eccentricity around the optical axis of the lens. It is.

Furthermore, if flat portions are formed at both ends in the scanning direction of the curved lens surface of each lens, the holding can be carried out even more securely.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the scanning optical system of a conventional laser beam printer, Figs. 4 and 5 are diagrams explaining the flattening of the scanning lens of the present invention, and Fig. 6 is a diagram showing the scanning lens of the present invention. FIGS. 7 to 14 are diagrams illustrating assembly examples, and are diagrams showing lens configurations and aberrations of configuration examples 1 to 8 of the scanning lens of the present invention. 1... Laser beam generator applicant Minolta Camera Co., Ltd. No. 1F71 'IJI5@B Fig. 5 C Fig. 61 12a Fig. 7 A Fig. 7 8 1PJ3 Fig. A Fig. 8 8 Fig. q A 'ip, Figure l1B IJsto@A Figure 10B Imouto 1. L41 Collection L Figure 1f A Figure 11B %1z@A Figure 12B Procedural amendment 1. Display of the case 1982 Patent Application No. 37391 2, Name of the invention Scanning lens 3, Person making the correction Relationship to the case Applicant Address 2-80 Azuchi-cho, Higashi-ku, Osaka City Osaka Kokusai Building name (607) Minolta Camera Co., Ltd. 1982
June 11, 2016 (Delivery date: June 29, 1982) 5. Column for brief explanation of drawings in the specification subject to amendment and drawings 6. Contents of amendment (1) Brief explanation of drawings in the specification Column, page 15, line 15, insert the following text after "This is a diagram showing...". "In addition, in Figure 2, Figure 4, and Figure 5 A, the left side is a front view as seen from the optical axis direction, and the right side is a front view as seen from the optical axis direction. is a side view seen from a direction parallel to the front direction.'' (2) Correct the drawings W, 2, 4, and 5 as shown in the attached sheet. (. * @ N N * @ Ward Ward 1# 0 111 Taste

Claims (1)

[Claims] 1. In a scanning lens for scanning a beam from a light source at a constant speed on an image forming plane by a deflector, each lens constituting the scanning lens is arranged in the optical axis direction and in the scanning direction. A scanning lens characterized in that it has a flat shape in an orthogonal direction and one lens surface is formed as a flat surface, and that each lens is held by bringing the flat lens surface of each lens into contact with the contact surface of a lens holding member. . 2. The scanning lens according to claim 1, wherein both ends of each lens in the scanning direction are flat. (a) A flat portion is formed at both ends in the scanning direction of the curved lens surface of each lens, and each lens is held by the flat lens surface and the flat portion of the curved lens surface. The scanning lens according to item 1 or 2. 4. The scanning lens according to any one of claims 1 to 3, characterized in that the scanning lens is -5</.theta. Each lens constituting the δ scanning lens is a plano-concave lens, a plano-convex lens, and a plano-convex lens in order from the incident side, and the conditions are −0,14≦”//, '< −0,050,028≦
d 17t≦0,19 d! 5. The scanning lens according to claim 4, wherein: distance f1 between the second and third surfaces of the lens: focal length f of the lens: focal length of the entire lens. 6 Each lens constituting the quantitative lens is a plano-concave lens or a plano-convex lens from the entrance side, and the conditions -0,25≦d
The scanning lens according to claim 4, characterized in that R7t≦-0,07 d2: distance between the second lens surface and 's3 surface fl: focal length of the lens.