JPS5915219A - Light beam scanner - Google Patents

Abstract

PURPOSE:To converge plural light beams on a surface to be scanned to the points where the spacings between the convergent points of said beams are close to each other and to make a scanner difficult to receive the influence of the errors in positioning the surface to be scanned, feed errors, oscillation, etc. by providing troidal lenses for correcting the inclination of the mirror surface on a rotary polyhedral mirror to each of luminous fluxes. CONSTITUTION:The light emitted from light sources 1a-1c are converged to a horizontal line shape shown by points 4a-4c on the mirror surface of a rotary polyhedral mirror 4 by a cylindrical rod lens 3. Troidal lenses 5a-5c are disposed in such a way that the optical axes are in parallel with each other and run through the points 4a-4c. The convergence of the light from the light sources 1a-1c apart from each other by (d) on the surface to be scanned is accomplished by moving upward or downward the lenses 5a, 5c by the distance epsilon given by epsilon=(f/F)Xd where the focal length of an theta lens 6 is designated as F, and focal length of the lenses 5 as (f). The spacing between the scanning lines is made equal to the inter-dot spacing of a laser printer or the like or made proximate to each other to the extent of not so much larger than said spacing.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a light beam scanning device, and more particularly to a light beam scanning device using a plurality of light beams.

The optical beam 1 and scanning device are usually arranged between an optical system that converts the light emitted from the light source into a parallel beam, an optical system that focuses the parallel beam onto the surface to be scanned, and an intermediate between these two optical systems. It consists of a rotating polygon mirror, etc., and the optical beano can be swung by rotating the rotating shaft strip mirror. This type of device usually uses a single light beam, so it only sweeps one scanning line during - sweep operations, but if it uses multiple light beams, it can scan multiple lines at the same time. It is possible to sweep a line, the number of sweeping operations required to scan the same area is smaller than in the case of a single beam, and the number of rotations of the rotating polygon mirror can be reduced.
Effects such as reduced mechanical vibration and improved durability of moving parts can be obtained. However, each scan line must be swept across the scanned surface without resulting in any gaps. For this reason, a proposal has been made regarding a scanning method in which scanning is performed using a plurality of light beams, in which a second scanning line is inserted between the first scanning lines.

On the other hand, the optical system of the optical vino and scanning device is an optical system that enlarges and projects the light source onto the surface to be scanned, and has a magnification of about 100 times. Since the spacing between is about 100 μm, when using multiple beams, the spacing between multiple light sources is 17100 μm (100 μm).
That is, it is about 1 μm, and it is technically extremely difficult to arrange the light sources so close to each other in this way. One method of arranging multiple light sources close to each other is to use a semiconductor laser array, but even in this case, the spacing between the light emitting parts is limited to 100 μm due to structural and heat generation constraints.
is considered to be the limit. Even if a light source such as a semiconductor laser array is used, if the optical system of a normal light beam scanning device is used, the interval between multiple scanning lines that are swept simultaneously is about 10,000 m, which is the pixel interval. 100μ〃
It is also too thick compared to Z, and is easily affected by positioning errors, feeding errors, vibrations, etc. of the surface to be scanned.

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical system in which the spacing between scanning lines formed by a plurality of light beams can be made close to the dot spacing of a laser printer or the like to the extent that it is equal to or not much larger than the dot spacing. .

The present invention will be explained in detail below with reference to Examples. FIG. 1 is a perspective view of an embodiment of the present invention, and FIG. 2 is a straightly developed view of the optical system of the embodiment. In Fig. 1, 1 is a semiconductor laser array, which has three light emitting parts], a, lb, and IC, 2 is a collimator lens, 3 is a cylindrical lens, and 4 is a rotating polygon mirror that rotates around the arrow X. 5a + 5b, 5ci each toroidal lens, 6
For example, in the fθ lens, 7 is a scanning locus of a light spot formed on the surface to be scanned. In this embodiment, there are three light emitting parts of the light source, and scanning is performed with three beams, so the scanning locus 7 is drawn with three lines. In the single-beam light beam scanning device, the toroidal lenses 5a to 5C are one toroidal lens, and the present invention is characterized in that this toroidal lens is provided independently for each light beam. Therefore, in the order of explanation, first, FIG. 1 shows a light beam device with a single beam.

This will be explained using Figure 2. This is the toroidal lens 5a considering only the light source 1b in Figures 1 and 2.

It is the same as the one with 5C removed. Therefore, consider a case where the cylindrical lens 3, the toroidal lens 5b, etc. are not provided. The light emitted from the light source 1b becomes a parallel beam of light by the collimator lens 2, is reflected by the rotating polygon mirror 4, and is reflected by fθ
The light is focused onto the surface to be scanned by the lens 6. Rotation axis X of rotating polygon mirror 4; light source 1b; collimator lens 2.
1 is exactly perpendicular to the optical axis passing through the fθ lens 6, and each face of the rotating polygon mirror is exactly parallel to ll1lIIX. Scanning can be performed accurately even without the toroidal lens 5b or the like. However, due to manufacturing and assembly errors and gaps in the mechanism, each surface of the rotating polygon mirror is not exactly perpendicular to the plane containing the optical axis in Figure 1, and if the planes have different inclinations, the rotation On each surface of the polygon mirror, the scanning locus of the focal point on the surface to be scanned is vertically displaced (~, and accurate scanning at equal intervals is not performed. Therefore, in Fig. 1, the horizontal plane containing the optical axis (parallel to scanning line 7) A 7-linotrical lens 3 that has no refractive power in the inner plane and has a convergence effect in the vertical plane, and a toroidal lens that has a shape that is a curved cylindrical lens and has no refractive power in the horizontal plane but has a convergence effect in the vertical plane. The lens 51) corrects the inclination of the mirror surface of the rotating polygon mirror (inclination angle correction). toroidal lens 5b
The focal point in the vertical plane is the optical axis of the fθ lens 6 and the rotating polygon mirror 4.
It is set at a position close to the intersection with the mirror surface. Although this point of intersection moves somewhat due to the rotation of the rotating polygon mirror 4, it is convenient to consider it as a fixed point, and the focus of the toroidal lens 5b is set at an average position within the movement range of this point of intersection. The condensing line formed by the cylindrical lens 3 includes the focal position of the toroidal lens 5b.

Therefore, even if the reflected light swings up and down due to changes in the inclination of the surface of the rotating polygon mirror, the swing is centered around the focal point of the cylindrical lens 3, so the light that has passed through the toroidal lens 5 is the light from the fθ lens 6. The light flux becomes parallel to the axis, and fθ
Only the height of the point of incidence on the lens 6 changes. fθ
Since the lens 6 converges light parallel to the optical axis onto the surface to be scanned, even if the height of the point of incidence on the fθ lens 6 changes, the position of the focal point on the surface to be scanned does not change. This is the effect of tilt angle correction. After noon, we finished the explanation of the single beam light beam scanning device at 2.
The case of multiple luminous fluxes will be explained. In the illustrated embodiment, there are three light sources: la, :], b, and lc, and the light emitted from 1b has been described above. la.

The light beams 7 emitted from the IC are formed by the Lindorcal lens 3 on the mirror surface of the rotating polygon mirror 4, respectively, at points 4a in FIG.

It is converged into a horizontal line indicated by 4C. These 4a...
The distance between the three horizontal lines represented by 4b and 4c is the distance between the light sources 1a, ], b, lc and the cylindrical lens 3.
and the focal length of the collimator lens 2.

In the example, the focal length of the cylindrical lens 3 is 50 m.
m, the focal length of the collimator lens is 57 nm, and the light source 1
Since the distance between a, lb, and la is 0.4 mm, the distance between the condensing points (horizontal line) on the rotating polygon mirror 4'' is 4 mm.
Therefore, it is sufficient that the height of the rotating polygon mirror 4 is 4 m, or 10 to 12 mm, taking into account twice the length of m.

Assuming that the toroidal lenses 5a, 5b, and 5c have the same shape and are arranged so that their optical axes are parallel to each other and pass through the points 4a, 4b, and 4c, the toroidal lenses 5a, 5b, and 5c emerge from the light source 1a and rotate. The light beam converged horizontally on the polygon mirror 4 a is turned into a parallel light beam parallel to the optical axis of the fθ lens 6 by the toroidal lens 5 a. Similarly, the light emitted from the light source 1C also becomes a light beam parallel to the optical axis of the fθ lens 6 by the toroidal lens 5C. Since the fθ lens 6 converges the light beam parallel to the optical axis to one point on the scanned surface, all the lights emitted from the three light sources 1a, lb, and IC are ultimately converged to one point on the scanned surface. It will be done.

However, the purpose of the present invention is not to converge the light emitted from a plurality of light sources to one point, but to converge them to points close to each other. The distance between the two focal points on the scanned surface is d,
If the focal length of the fθ lens 6 is F, then the fθ lens 6
The light that converges at a point d away from the optical axis is a parallel beam of light that enters the fθ lens at an angle ψ−d/F with respect to the optical axis.

Therefore, in order to converge the lights emitted from the light sources 1a, lb, and lc on the surface to be scanned at a distance d from each other, the toroidal lens 5a
, 5b, 5c, the distance ε given by ψ-ε/f is l.Loidal lens 5a, 5c
It is only necessary to move it up or down from the above-mentioned position. In the example, the focal length F of the fθ lens 6 is 500 mm, )I:
l Focal length f of Idal lenses 5a to 5C =' 55
m, m and d = l OO/1 m, then ε= (
f / F ) X d = 0. Ol 1 m,
m. To actually adjust the positions of the toroidal lenses 5a and 5c, a well-known fine adjustment mechanism using fine adjustment screws may be used.

According to the present invention, since the same number of toroidal lenses are used as the number of light beams used, the height of the -. toroidal lenses becomes smaller, so let us consider the utilization rate of the light emitted from the light source. The light source is a semiconductor laser array, and the distance between each light emitting part is 0.4 m, yn, and the spread of light emitted from the semiconductor laser is approximately 50° in the horizontal direction (scanning direction) and 30°9 in the vertical direction as shown in Figure 1. , the collimator lens 2 has a focal length of 5
0 mm, NA=l, the beam cross section of the light emitted from the collimator lens has a horizontal width of 4.2 rn m and a vertical thickness of 2.6 rnm. Toroidal lens has a focal length of 55
mm, so the thickness of the luminous flux at the point where it enters the toroidal lens is 2.6 x 55/50 in the vertical direction.
= 2.9 mm, and each toroidal lens has a height of 3 m, which is sufficient if the height is 3 m. On the other hand, the distance between the centers of each toroidal lens is the focal point on the rotating polygon mirror 4 in FIG. 2 4a,
The distance between 4b and 4c is 4. The value of mm plus ε is 1,
Since ε has a value of around 0.01 mm as described above, the three toroidal lenses can be easily accommodated without interfering with each other.

FIG. 3 shows an example of the configuration of a semiconductor laser array. a,
a, ', etc. are semiconductor lasers, b is a p-type rad layer, C is an active layer (laser emitting part), d is an n-type rad layer, and e is an n-type rad layer.
shape substrate, k” etc. are optical waveguide grooves, g is each laser a,
This is a groove that electrically insulates a', etc.

The device of the present invention has the above-described configuration, and a toroidal lens, which is a part of the optical system for correcting the inclination of the mirror surface of the rotating polygon mirror, is provided for each light beam, and the scanned surface is adjusted by adjusting the position of the toroidal lens. Since the interval between the convergence points of the plurality of light beams is adjusted above, the scanning line interval adjustment using the tilt angle compensation and the plurality of correction binos are performed by the same optical system, and the scanning line interval can be adjusted. Since the adjustment meter for the position of the toroidal lens of the adjustment stopper is relatively large (about 1/10 of the amount of adjustment of the scanning line interval in the embodiment), the adjustment is easy.

[Brief explanation of the drawing]

Fig. 2 is a perspective view of an apparatus according to an embodiment of the present invention, Fig. 2 is a side view of the optical path developed in a straight line, and Fig. 3 is a side view of a semiconductor laser array. la, lb, lc... light source, 2... collimator lens, 3... cylindrical lens, 4... rotating polygon mirror of scanning device, 5a, 5b, 5C... toroidal lens, 7... Scan line on the scanned surface. Agent Patent Attorney Kosuke Agata

Claims (2)

[Claims] (1) A light source that generates multiple light beams arranged perpendicular to the scanning direction, a scanning device that swings these multiple light beams to perform scanning, and a light beam that is placed before and after the scanning device. The refractive power is different in the direction parallel to the scanning direction and the direction perpendicular to it, and the light beams entering the scanning device are respectively converged into lines parallel to the scanning direction, and the light beams exiting from the scanning device are returned to parallel light beams. 1. A light beam scanning device comprising an optical element, wherein the optical element for returning a light beam emitted from the scanning device to a parallel light beam is provided in each group. (2) The optical element for each light beam that returns the light beam emitted from the scanning device into a parallel light beam is provided so that its position can be adjusted in a direction perpendicular to the scanning direction. optical beam scanning device.