JPS63292109A - Optical scanning device - Google Patents

Abstract

PURPOSE:To execute a good and stable optical scanning by constituting a rotary polygon mirror of even pieces of plane-like reflecting surfaces so that an incident light beam is reflected even times, and also, placing a light source and a collimator lens so that the light beam is made incident toward the rotary polygon mirror. CONSTITUTION:Each reflecting surface 1b, 1c which is arranged in the peripheral direction of a rotary polygon mirror 5 is constituted of even pieces of plane-like reflecting surfaces Ib, Ic so as to reflect an incident light beam even times. Also, in a plane where a light beam I from a light source 2 contains a revolving axis 6 of the rotary polygon mirror 5 and orthogonal to the surface to be scanned, the light source 2 and a collimator lens 3 are placed so that the light beam is made incident toward the rotary polygon mirror 5. In such a way, the displacement of a scanning line in the direction vertical to the scanning line can be eliminated essentially.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] "Industrial Application Field" The present invention relates to a scanning optical device having a light source such as a laser light source, a collimator lens, a rotating polygon mirror, and an fθ lens.

"Prior Art and its Problems" In general, by rotating a rotating polygonal mirror having a single planar reflective surface on each side, light beams such as laser beams are scanned, and the beams of light such as a laser beam are scanned. It is possible to display computer output, characters, etc., or measure the surface shape of a test object. Figure 5(a),
(b) and FIG. 6 are a plan view and a diagram, respectively, of a scanning optical device using a conventional rotating polygon mirror 10 having a single planar reflecting surface, and the light beams from the two laser light sources are The collimator lens δ converts the light beam into a parallel beam, and the light beam reflected by the rotating polygon mirror 10 passes through the fθ lens 4 to
It is designed to converge within the Y range. Rotating polygon mirror 1o
For example, a regular hexagonal prism is surrounded by a single planar reflective surface, and a laser light source 2, a collimator lens 3, and a rotating polygon mirror 1 are used.
0, fθ lenses 4 were at the same height.

However, these scanning systems had the following drawbacks.

(1) The scanning line may be affected by the inclination of the rotating shaft 11 to which the rotating polygon mirror 10 is fixed and the error in the arrangement angle of each reflecting surface composed of a single planar reflecting surface with respect to the rotating polygon mirror body (rotating member). is disturbed.

(2) As shown in FIGS. 5(a) and 5(b), the laser light source 2 and collimator lens 3 block the light beam reflected by the rotating polygon mirror 10 and scanning between the effective widths X and Y of the scanned surface A. It needs to be placed in a position that does not exist. Therefore, collimator lens 3
The angle of incidence ψ of the light beam from the rotating polygon mirror 10 on the reflecting surface
distribution becomes asymmetric, and the maximum angle of incidence becomes large. If the diameter of the light beam after the collimator lens δ is D, the width of the reflecting surface of the rotating polygon mirror 10 is required to be D1008ψ, but ψ
Since the reflection surface has a large width, the width of the reflecting surface becomes large. Furthermore, when the rotating polygon mirror 10 is rotated for scanning, the incident angle ψ is large, so the circumferential length E of the reflective surface used is also large.

Because of the above-mentioned drawback (1), it was necessary to make the rotational axis (rotational accuracy) extremely precise, and it was also necessary to make the reflecting surface of the rotating polygon mirror very precisely geometrically. Disadvantages (2)
), the rotating polygon mirror becomes large, and the arrangement of collimator lenses and the like increases the overall arrangement range, resulting in the drawbacks of being expensive and heavy.

Regarding the above-mentioned drawback (1) in terms of rotation accuracy, in order to maintain the rotating shaft in an accurate and constant rotational state, the rotating shaft is supported by, for example, an air bearing. By doing so, the problem of the rotating shaft falling during rotation is almost solved, and therefore, the above-mentioned disturbance of the scanning line due to the rotating shaft falling is eliminated. However, the air bearing does not eliminate any disturbance in the scanning line caused by an error in the angle at which the reflecting surface is disposed on the rotating member.

Moreover, complicated procedures are required to properly operate the air bearing, which inevitably results in an expensive device.

Another method, as proposed in U.S. Pat. This eliminates disturbances in the scanning line caused by inclination of the rotation axis and errors in the arrangement angle of the reflective surface. However, using the method disclosed in this US patent, it is generally very difficult to manufacture high-quality cylindrical lenses, and furthermore, when incorporating the cylindrical lens into an optical device, it is difficult to position it easily. .

For this reason, Japanese Patent Application Laid-Open No. 50-109757 discloses a method in which each of the reflecting sections is composed of an even number of planar reflecting surfaces so that the light rays incident on each of the reflecting sections are reflected an even number of times. A rotating polygon mirror has been proposed. By using this rotating polygon mirror, displacement of the scanning line in a direction perpendicular to the scanning line can be essentially eliminated. However, as mentioned above (2)
This drawback could not be avoided as long as each of the reflecting surfaces of the rotary mirror was composed of a single flat reflecting surface.

It is an object of the present invention to provide a scanning optical device that does not have the drawbacks of the above-mentioned conventional examples.

[Structure of the invention]

"Means for Solving the Problems" The present invention includes a light source that emits thin line light, a collimator lens that converts the light from the light source into parallel light, a rotating polygon mirror that receives and reflects the parallel light, and a rotating polygon mirror that receives and reflects the parallel light. In a scanning optical device having an fθ lens that transmits reflected light from a mirror and converges it on a surface to be scanned, each reflective surface arranged in the circumferential direction of the rotating polygon mirror has an even number of reflecting surfaces so that the incident light beam is reflected an even number of times. A light source and a collimator are arranged so that the light rays from the light source enter the rotating polygon mirror in a plane that includes the rotation axis of the rotating polygon mirror and is orthogonal to the surface to be scanned. This is a scanning optical device characterized in that a lens is arranged.

"Embodiments" Examples of the present invention will be described below with reference to the drawings. FIG. 1 is a side view, and FIG. 4 is a plan view of FIG. 1. A light beam from a light source 2 such as a laser that emits thin line light becomes an incident light beam through a collimator lens 3 that converts it into parallel light, and the reflection surface 1a, 1b of a rotating polygon mirror 5 rotated by a rotation axis 6.
Reflect an even number of times. This reflected light beam R passes through the fθ lens 4, is refracted by the mirror 7, and converges in the XY range of the scanned surface. When the rotating polygon mirror 5 rotates around the rotation axis 6, a scanning line is drawn on the scanned surface A.

FIG. 6 is a perspective view of the rotating polygon mirror 5. The rotating polygon mirror 5 is made of, for example, two congruent regular hexagonal truncated pyramids with corresponding sides on both top bases coincident and fixed to a rotating shaft 6 at the center of the regular hexagonal truncated pyramid, so that even number of incident rays of light are reflected. It is provided with reflective surfaces ta and 1k so as to reflect the same, and reflective surfaces la and jb are arranged in the central direction. In FIG. 1, the light source 2 is arranged so that the light beam from the light source 2 enters the rotating polygon mirror 5 in a plane that includes the rotation axis 6 of the rotating polygon mirror 5 and is perpendicular to the surface to be scanned.
, collimator lenses 3 are arranged.

In the following, in such an optical device, how the convergence position of the scanning light changes depending on the inclination of the rotating shaft 6 will be explained.

In Figures 1 and 2 (&) J□□□, the reflective surface IJ
1b, Incident Ray The incident ray R is shown as an orthogonal projection onto a plane perpendicular to both the reflecting surface 1a and the reflecting surface 1). In Fig. 2 (L), if the included angle of reflective surface 1& and reflective surface 1j) is 0, then reflective surface 1a and reflective surface 1
The angle formed by the respective orthogonal projections of the incident light beam and the reflected light beam onto a plane orthogonal to both of b, that is, α shown in this figure can be expressed as α==tao'-2θ. Therefore, the rotating polygon mirror 5 is
When rotating around , the incident light beam becomes thin line-like,
Moreover, assuming that the direction is kept constant, the reflected light ray R is linear and moves from the reflection point on the reflection surface 1a to the reflection surface 1f1- and the reflection surface 1b according to the rotation of the rotating polygon mirror 5.
In Fig. 2(b),
When the rotating shaft 6 is tilted at an angle r on the paper as shown by the dotted line, for example, from the normal position direction shown by the solid line, the reflecting surface 1a and the reflecting surface 1b are each tilted by the angle r, and as shown in the figure, the reflecting surface 1a
', and 1b'.

The angle of incidence of the incident ray I on the reflecting surface 1a when the rotation axis 6 is in the normal position direction is 1, and the reflection angle at which the ray is reflected by the reflecting surface 1b on its optical path is j1 reflecting section. Let R be the final reflected ray at . Next, the axis of rotation when the axis of rotation 6 is tilted at an angle r on the paper surface is 61, and the angle of incidence with respect to the reflection ffi I &' of the incident light beam is 11. When the light ray reaches the reflective surface t in its optical path
The angle of reflection reflected by b' is j11, and the final reflected light beam at the reflection section is R1. Said i, i'.

The following relationship exists between each angle of j and j'.

11=1+γ ■ j'=j−γ ■ By the way, even if the reflective surface 1bl is tilted by the angle r with respect to the reflective surface 1b as shown in the figure, 1'+j'=i from the above formula
+j, the reflected ray R and the reflected ray R1 become parallel. Therefore, both reflected light beams R and R' converge at the same position on the scanned surface after passing through the f0 lens 4. In other words, in optical scanning using the rotating polygon mirror 5, the scanning line formed always maintains a preset regular position direction regardless of the tilting of the rotating shaft 6, and therefore provides a stable and high-quality image. Optical scanning becomes possible.

As can be seen from FIG. 1, each of the nine reflecting parts of the rotating polygon mirror 55 is composed of an even number of planar reflecting surfaces ja, jb, so that the laser light source 2 and collimator lens 3 are reflected by the rotating polygon mirror 5. Therefore, the light beam scanning the scanned surface A cannot be blocked. Therefore, since the plane that includes the rotation axis 6 on which the incident light beam is located and is orthogonal to the scanned surface A passes through the center 0 of the scanned range XM, the orthogonal projection plan view As shown in FIG. 4, the angle ψ between the normal to the reflecting surface 1a or 1b of the rotating polygon mirror 6 and the incident ray I or the reflected ray is different from that in the conventional case where a rotating polygon mirror 10 with a single planar reflecting surface is used. The scanning system can be made smaller in comparison. Therefore, since the scanning light beam is distributed symmetrically to the rotation axis 6 and the center 0, the maximum incident angle ψ to the rotating polygon mirror 5 is
□8 becomes smaller.

〔Effect of the invention〕

Since the present invention has the above-described configuration, (1) even if the rotation axis of the rotating polygon mirror is tilted, it is possible to maintain the spatial stability of the reflected light beam without using any auxiliary means such as air bearings or cylindrical lenses. One of the directional components can always be kept constant, thus essentially eliminating displacements of the scan line in a direction perpendicular to the scan line.

(2) Since the light rays incident on the reflective surface of the rotating polygon mirror and the reflected rays can have a step difference, the angle between the normal to the reflective surface of the rotating polygon mirror and the incident ray can be made small. The mirror can be made into a shed, which makes the rotating polygon mirror cheaper. Also, since the rotating polygon mirror is made into a shed, the moment of inertia is reduced, and the motor that rotates the polygon mirror can take a long time to change from a stationary state to a steady rotation state. It is also possible to speed up the rise time.

There is an effect.

[Brief explanation of the drawing]

FIG. 1 is a side view of an embodiment of the present invention, and FIG. 2(a). (1)) is a side view of the rotating polygon mirror, FIG. 6 is a perspective view of the rotating polygon mirror, FIG. 4 is a plan view of FIG. 1, and FIG. 5(a). (b) is a plan view of the conventional example, and FIG. 6 is a plan view of the conventional example.
)) is a side view. ja, 1b...Reflecting surface 2...Light source 2...Collimator lens 4...Fθ lens 5...Rotating polygon mirror.

Claims (1)

[Claims] 1. A laser light source, etc., a collimator lens that converts the light from the light source into parallel light, a rotating polygon mirror that receives and reflects the parallel light, and the reflected light from the rotating polygon mirror is transmitted and focused on the scanned surface. In a scanning optical device having an fθ lens, each of the reflective surfaces arranged in the circumferential direction of the rotating polygon mirror is composed of an even number of planar reflective surfaces so as to reflect an incident light ray an even number of times, and the light source A scanning optical device characterized in that a light source and a collimator lens are arranged so that the light beam from the rotating polygon mirror is directed toward and incident on the rotating polygon mirror in a plane that includes the rotation axis of the rotating polygon mirror and is perpendicular to the surface to be scanned.