JPH05249689A - Light beam scanner - Google Patents

Abstract

PURPOSE:To make a scanning angle large and to execute multiple beam scanning in a scanning system of the inside surface of a cylinder. CONSTITUTION:The optical path of light beams from a light beam generator 2 is changed by a reflection mirror 3, and the light beams are made incident on a reflection unit 5 in a direction perpendicular to the center axis of the cylinder 1 via a condenser lens 4. The reflection unit 5 is composed of two plane reflection surfaces 5-1 and 5-2, at right angles each other, and theses crossing mountain ridges are arranged so as to be perpendicular to the center axis of the cylinder 1. The reflection unit 5 is rotated through the use of the center axis of the cylinder 1 as a rotary shaft, by a motor 6. Thus, the inside surface of the cylinder 1 is parallelly scanned with plural light beams.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light beam scanning device in the field of technology for recording an image by scanning a light beam such as a laser, and more particularly to an output device for printing plate making and an original plate making for a printed circuit board. The present invention relates to a light beam scanning device of an effective system when a wide scanning width and a small focused beam diameter are required as in the output device of No.

[0002]

2. Description of the Related Art As a light beam scanning device of this kind, called a cylindrical inner surface scanning system, a fixed drum (herein referred to as a cylinder) is used, and a photosensitive material mounted on the cylindrical surface is
There is a system in which an image is recorded by scanning a light beam in the circumferential direction while rotating the light beam inside the cylinder (see Japanese Patent Laid-Open No. 63-158580).

FIG. 9 shows a conventional example of this system. Cylinder 101
While the photosensitive material 107 is mounted on the cylindrical surface of, the light beam from the light source 102 is incident along the central axis of the cylinder 101,
The light is reflected in a right angle direction by a light reflecting element 104 such as a reflecting mirror or a right angle prism which is rotated by a motor 103 with its central axis as a rotation axis in 101, and a light beam is focused by a condenser lens 105 in the optical path. The focused light beam is mainly scanned on the photosensitive material 107 mounted on the cylindrical surface of the cylinder 101.

A sub-scanning mechanism 106 driven by a motor (not shown) moves the motor 103, the light reflecting element 104 and the condenser lens 105 in the axial direction to perform sub-scanning, thereby recording an image. (Exposed). The advantage of this method is that the light beam incident almost along the center axis of the cylinder is reflected by the light reflecting element that rotates about the center axis of the cylinder, so that the center of rotation of the light beam coincides with the center of the cylinder. Therefore, the linearity is good over almost the entire circumference, and the focal point coincides with the cylindrical surface for scanning.

[0005]

However, in the above-mentioned conventional cylindrical inner surface scanning method, when there is a demand for increasing the recording speed, there are the following problems. In other words, this system has one light reflecting surface due to its structure in which the light reflecting surface is on the rotation axis, and as in the case of using a well known so-called polygon mirror, this method is performed a plurality of times for one rotation. Cannot scan.

There is also a method in which a plurality of light beams (hereinafter also referred to as multiple beams) are used to effectively perform a plurality of scans in one rotation. When this method is applied, the light beams are scanned on the scanning surface. Not parallel. In order to correct this, an optical element as a light beam rotating means (image rotating optical element), represented by a trapezoidal prism, is added, and this optical element is rotated at half the rotation speed of the light reflecting element. The necessity of rotation is described in Japanese Patent Application No. 3-199166 filed by the present applicant.

Further, as shown in FIG. 10, if a reflecting mirror 110 having a plane including the rotation axis as a reflection surface is provided and a plurality of light beams are made to enter from the light source 102 substantially at right angles to the rotation axis, a cylindrical surface can be obtained. Although a plurality of light beams are scanned in parallel above, it can be seen that the scanning angle cannot be increased because the incident light beam and the reflected light beam are in the same plane. In order to increase the scanning angle, it is necessary to increase the size of the reflecting mirror in the scanning direction, but it is impossible in principle to obtain a scanning angle exceeding 180 degrees.

In view of the above situation, the present invention realizes a cylindrical inner surface scanning method which has a large scanning angle and is capable of multi-beam scanning, and thereby a light beam which enables high-speed recording. It is an object to provide a scanning device.

[0009]

Therefore, the present invention is a reflection unit which rotates about a predetermined rotation axis and reflects a light beam, and is included in a plane perpendicular to the rotation axis for incidence. The reflected light beam of the light beam is included in a plane that is plane-symmetric with respect to the plane including the incident light beam with respect to a predetermined plane perpendicular to the rotation axis, whereby the reflected light beam is incident. A light beam scanning device comprising: a reflection unit configured to prevent overlapping with a light beam; and rotating means for rotating the reflection unit about the rotation axis. The configuration is set so as to coincide with the center of rotation of the light beam.

Here, the reflecting unit and the rotating means thereof have two reflecting surfaces that are substantially perpendicular to each other and a straight line that intersects with a ridge line intersecting the two reflecting surfaces at a substantially right angle as a rotation axis. And means for rotating the. More specifically, the two reflecting surfaces may be double mirrors which are substantially perpendicular to each other and each form an angle of about 45 degrees with the rotation axis, or isosceles surfaces of a right-angle prism.

Further, the reflecting unit has a reflecting mirror having a reflecting surface which substantially coincides with a plane including the rotation axis, and a generatrix and an optical axis with a straight line substantially perpendicular to the rotation axis and the plane as an optical axis. An anamorphic optical system, the plane of which is substantially perpendicular to the rotation axis, can be used. A plurality of the reflection units may be provided around the rotation axis.

Further, in addition to a plurality of light beams, a light beam having a non-circular light beam cross-section may be incident on the reflecting unit. Further, at the time of image recording, the photosensitive material may be fixed on the cylindrical surface, or the photosensitive material may be slid on the cylindrical surface.

[0013]

In the above structure, since the reflected light beam is scanned in a plane different from that of the incident light beam, the reflected light beam is prevented from overlapping the incident light beam, and the reflected light beam is scanned on both sides in the direction of the incident light beam. Can be performed, and a large scanning angle can be taken.

Since a plurality of light beams incident on the reflection unit are scanned in parallel on the scanning surface after being reflected, the recording speed can be improved by so-called multiple beam scanning. Further, even when the beam divergence differs depending on the direction, such as an elliptical shape, instead of a circular cross-sectional shape of the light beam, scanning is performed while keeping the direction constant, so that recording on the photosensitive material is performed. The dot shape tends to be constant over the entire scanning width. This is an effective effect even in the single-beam cylindrical inner surface scanning method.

Further, by appropriately selecting the effective size of the reflection unit with respect to the cross section of the light beam, it is possible to obtain a scanning angle exceeding 180 degrees. Furthermore, even if the rotation axis of the reflection unit is tilted during rotation, the reflection direction of the light beam is less affected by it, and the light is reflected in a fixed direction, so image quality is improved in image recording by light beam scanning. It is extremely advantageous in terms of improvement.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing an embodiment of the present invention. Reference numeral 1 denotes a cylinder for mounting the photosensitive material, and in this case, the photosensitive material (not shown) is held on the inner surface of the cylinder. The photosensitive material may be held on the outer circumference of a transparent cylinder, or may have a structure in which an aperture of an appropriate size is provided on the cylinder so that the photosensitive material can be irradiated with a light beam.

Reference numeral 2 denotes a light beam generator (light source) for generating a plurality of light beams, and in this figure, it is shown as a light beam train emitted from a plurality of optical fibers whose tips are aligned. However, the means for obtaining the light beam train is not limited to this. The light beam has its optical path changed by an appropriate means such as a reflecting mirror 3, and enters a reflecting unit 5 through a condenser lens 4 in a direction perpendicular to the central axis of the cylinder 1. The condensing means such as the lens 4 is provided in the incident optical path in order to condense the light beam on the cylindrical surface of the cylinder 1 by the condensing function. In FIG. 1, for simplification, the optical system between the light source 2 and the reflecting mirror 3 is not shown, but an appropriate optical system depending on the performance required for image recording is not shown. It is provided.

In this example, the reflecting unit 5 is composed of two plane reflecting surfaces (double mirrors) 5-1 and 5-2 which are substantially perpendicular to each other, and the ridges where these reflecting surfaces 5-1 and 5-2 intersect. Intersect with the central axis of the cylinder 1 at right angles, and the reflecting surfaces 5-1 and 5
-2 are arranged so as to form an angle of approximately 45 degrees with respect to the central axis of the cylinder 1. And the reflection unit 5
Is rotated at a predetermined rotation speed by a motor 6 serving as a rotating unit with a straight line that coincides with the central axis of the cylinder 1 as a rotation axis.

Further, the reflecting mirror 3, the condenser lens 4, the reflecting unit 5 and the motor 6 are moved in parallel with the central axis of the cylinder 1 by the sub-scanning means (not shown),
Image recording is performed. The rotating unit of the reflecting unit 5 is not limited to the rotating unit such as the motor 6, but may be a vibration rotating unit that drives a so-called galvanometer mirror.

Further, in FIG. 1, in order to make the following description easy to understand, a plurality of light beams that have passed through the lens 4 as the light converging means are represented by light rays, and the respective light rays become parallel, so-called telecentric optics. Although the case where the system is configured is illustrated, it will be understood from the following description that the light beam is scanned in parallel even in an optical system other than the telecentric optical system. Further, for the purpose of multiple beam recording, the intervals of the respective light beams on the cylindrical surface are extremely small, but they are illustrated with intervals for the sake of clarity.

The light beam passes through a condensing means such as the lens 4 and is incident on one reflection surface 5-1 of the reflection unit 5. At this time, the manner of reflection of the light rays traveling toward the rotating shaft of the reflecting unit 5 will be described with reference to FIGS. 2 and 3. FIG. 2 is a view of the reflection unit 5 as seen from the direction of the rotation axis, and shows a state in which light rays are incident at a right angle to the ridgeline and a state in which the reflection unit 5 is rotated by an angle α from that position.

FIG. 3 is a diagram showing a state in which light rays are incident on the ridgeline of the reflection unit 5 at a right angle, as viewed from the direction of the ridgeline. Let L be the straight line of the rotation axis, O be the intersection of L and the ridge, and P and Q be the intersections of the incident ray M and the reflecting surface 5-1. However,
Q is an intersection when the reflection unit 5 rotates by the angle α.

Further, P ₁ is the incident point P before being rotated by the angle α.
Is the point moved by rotation. Further, the intersection of the extension line of the ray M and the rotation axis L is R. The line segment QR and the line segment that is plane-symmetric with respect to the reflecting surface 5-1 indicate the reflected ray of the ray M by the reflecting surface 5-1 and it is referred to as QR ₁ .

Where OR ₁ = OR and OR = RP
Since = RP ₁ , OR ₁ = RP ₁ . And OR
Since the angles formed by and OR ₁ with respect to the reflecting surface are 45 degrees, ∠R ₁ OR = 90 degrees. From the above consideration, when the direction of the rotation axis L is taken as the height direction, R ₁ is always at the same height as the point O and is located directly above (or just below) P ₁ .

The reflection unit 5 includes a point O and has a rotation axis L.
Since symmetric with respect to a plane perpendicular, light M after passing through the R _1, it is reflected at a point S on the reflecting surface 5-2 of Figure 2, contained in a plane perpendicular to the rotation axis L, progressive reflection light beam When it extends in the opposite direction, it intersects with the rotation axis L. That is, the reflected light ray is a light ray that rotates about a point on the rotation axis L.

Although FIG. 3 does not show the state in which the reflection unit 5 is rotated by the angle α, Q, which corresponds to FIG.
The positions of R ₁ and S are shown. A light ray N which is parallel to the light ray M and has a different height and also goes toward the rotation axis L can be considered in the same manner. Therefore, the rays M and N are scanned in parallel on the cylindrical surface. As described above, the incident light ray has been considered to be the light ray traveling toward the rotation axis L, but the reflection unit 5 also applies to a light ray having an inclination with respect to the light ray M or the light ray N or a light ray whose extension line does not intersect with the rotation axis L. Since it is an aberration-free optical system composed of plane mirrors, the distance relationship with the light ray M and the light ray N does not change, and therefore it rotates at a constant angular velocity about the rotation axis L and scans parallel on a cylindrical surface. What is done is self-evident.

It is preferable that the two reflecting surfaces 5-1 and 5-2 are flat surfaces, but one or both of the reflecting surfaces may be curved mirrors. In that case, it is also possible to combine the function of focusing the light beam. In that case, the influence of aberration occurs as compared with the case where the reflecting surface is a flat surface, but it is effective as long as there is no problem depending on the purpose.

The above description has been made by taking two reflecting surfaces which are perpendicular to each other as an example, but other means for obtaining the same effect will be described. There are various well-known image rotation optical systems. "Optics and Laser Technology"
(Optics and Laser Technology) August 1972, p.175-p.188, in a paper entitled "Image Rotator-Comparative Study".

The so-called image rotating optical system described in this paper rotates an optical system having a function of moving a light ray to a plane-symmetrical position with respect to a predetermined plane with a straight line included in the surface as a rotation axis. By doing so, it has the function of rotating the image. The two plane reflecting surfaces perpendicular to each other described in FIGS. 2 and 3 are also a kind of image rotating optical system,
It is the type that reflects the light beam.

In the present invention, among such image rotating optical systems, the one configured to reflect light is rotated about a straight line perpendicular to the plane, not a straight line included in the plane. It can be seen from the description of FIGS. 2 and 3 that the position of the rotation axis is determined so that the reflected and reflected light beam rotates about a point on the rotation axis.

Therefore, various types of reflecting units 5 having the same functions and effects as those described with reference to FIGS. 2 and 3 can be considered. FIG. 4 is an example using the right-angle prism 7. This is similar to the two reflecting mirrors, but it is disadvantageous than the two reflecting mirrors because aberration occurs due to refraction, but it is advantageous in that the rotating body can be downsized.

FIG. 5 shows examples of different uses of the right angle prism. The right-angle prism 8 here is equivalent to a reflection-type image rotation optical system in which a ladder prism, which is a typical image rotation optical system, is provided in the center, and a reflection mirror is provided in the center. It is more disadvantageous than that constructed by a mirror. FIG. 6 shows an example in which an anamorphic optical system (an optical system represented by a cylindrical lens and having different powers in mutually perpendicular directions) is used, and a cylindrical lens 9 and a reflecting mirror 10 are combined. ..

That is, the reflecting mirror 10 is arranged on the focal plane of the cylindrical lens 9, and a reflection line having a rotation axis is a straight line included in the reflecting surface and perpendicular to the generatrix of the cylindrical lens 9 (the center line in the direction in which there is no power). It is a unit. Since this also includes an element for refracting light in the optical system, it is more disadvantageous than the combination of two reflecting mirrors in terms of aberration, but as shown in FIG. 7, the cylindrical lens 9 is bent with the reflecting point as the center of curvature. If the anamorphic optical system is properly designed, the problem of aberration can be alleviated.

The optical system that can be used in the present invention is not limited to those described above, but a so-called image rotating optical system of a reflection type or a combination of an image rotating optical system and a reflecting mirror is used. It can be used from the above description. Also, in the explanation so far,
Although the case where the single reflection unit is described has been described, it is possible to provide a plurality of reflection units around the rotation axis. In that case, it is necessary to improve the accuracy of processing and assembling the reflection units so that the positions and directions of the reflected light beams of the plurality of reflection units match, but there is an advantage that scanning can be performed a plurality of times in one rotation. ..

FIG. 8 shows an example of a structure provided with a plurality of reflection units. Further, in the present invention, the photosensitive material exposed by the light beam is fixed to the inner surface of the cylinder, which is a preferred embodiment in that the photosensitive material is stably held. It is also possible to fix the optical system consisting of and move the cylinder in the axial direction to perform the sub-scan. If the photosensitive material has mechanical durability such as abrasion resistance, the sub-scanning may be carried out by sliding the cylindrical surface having the openings in the axial direction.

[0036]

As described above, according to the light beam scanning device of the present invention, a plurality of incident light beams are reflected by the action of the rotating reflection unit which is composed of two reflecting surfaces and the like. , Are scanned in parallel on the scanning plane. Even in the case of a single light beam, when the beam divergence differs depending on the direction such that the light beam cross-sectional shape is not circular but elliptical, scanning is performed while maintaining that direction constant. Have an effect.

Further, by appropriately selecting the effective size of the reflection unit for the cross section of the light beam, it is possible to obtain a scanning angle exceeding 180 degrees. Further, even if the rotation axis of the reflection unit is tilted during rotation, the reflection direction of the light beam is hardly affected by it and is reflected in a fixed direction, which improves the image quality in image recording by light beam scanning. It is extremely advantageous in that respect.

Therefore, in the cylindrical inner surface scanning method, it is possible to realize recording by high-speed, high-quality and light beam scanning with a large recording size. Further, the present invention can obtain a scanning angle exceeding 180 degrees as its effect. However, even if it is used for a scanning angle smaller than that, the light beam is scanned in parallel and the light beam has a constant point. Has the effect of rotating around the rotation axis, and less blurring of the rotation axis in the direction perpendicular to the scanning direction of the light beam with respect to so-called shaft blurring. It is also effective as a container.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a light beam scanning device according to the present invention.

FIG. 2 is a diagram showing the action of the double mirror as seen from the direction of the rotation axis.

FIG. 3 is a view showing the action of the double mirror as seen from the direction of the ridgeline.

FIG. 4 is a diagram showing an example using a right-angle prism.

FIG. 5 is a diagram showing examples of different uses of the right-angle prism.

FIG. 6 is a diagram showing an example using an anamorphic optical system.

FIG. 7 is a diagram showing another example using an anamorphic optical system.

FIG. 8 is a diagram showing an example in which a plurality of reflection units are provided.

FIG. 9 is a perspective view showing an example of a conventional cylindrical inner surface scanning method.

FIG. 10 is a perspective view of a method of performing multiple beam scanning using a plane mirror.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cylinder 2 Optical beam generator 3 Reflector 4 Condenser lens (condenser) 5 Reflector unit 5-1 and 5-2 Reflector 6 Motor (rotator) 7 Right angle prism 8 Right angle prism 9 Cylindrical lens 10 Reflector

Claims (10)

[Claims] 1. A reflection unit which rotates about a predetermined rotation axis and reflects a light beam, the reflection light beam being a light beam included in a plane perpendicular to the rotation axis and incident on the reflection unit. Is a reflection unit characterized by being included in a plane that is plane-symmetric with respect to the plane in which the incident light beam is included, with respect to a predetermined plane perpendicular to the rotation axis, and rotating the reflection unit about the rotation axis. And a rotation means for rotating the rotation axis, and the rotation axis is set at a position that coincides with the center of rotation of the reflected light beam. 2. The reflecting unit and its rotating means are configured such that the two reflecting surfaces are substantially perpendicular to each other and the straight line intersecting the ridge line intersecting the two reflecting surfaces at a right angle is a rotation axis. The light beam scanning device according to claim 1, further comprising: a rotating unit. 3. The light beam scanning device according to claim 2, wherein the two reflecting surfaces are two mirrors which are substantially perpendicular to each other and each form an angle of about 45 degrees with the rotation axis. 4. The light beam scanning device according to claim 2, wherein the two reflecting surfaces are isosceles surfaces of a rectangular prism. 5. The reflecting unit has a reflecting mirror having a reflecting surface that substantially coincides with a plane including the rotation axis, and a bus line and an optical axis with a straight line substantially perpendicular to the rotation axis and the plane as an optical axis. The light beam scanning device according to claim 1, wherein the plane including the anamorphic optical system is substantially perpendicular to the rotation axis. 6. The light beam scanning device according to claim 1, wherein a plurality of the reflection units are provided around the rotation axis. 7. The light beam scanning device according to claim 1, wherein a plurality of light beams are incident on the reflection unit. 8. The light beam scanning device according to claim 1, wherein a light beam whose light beam cross-sectional shape is not circular is made incident on the reflection unit. 9. The image recording method according to claim 1, wherein a photosensitive material is fixed on the cylindrical surface to record an image.
And a light beam scanning device described in. 10. The light beam scanning device according to claim 1, wherein an image is recorded by sliding a photosensitive material on a cylindrical surface.