JP3091920B2 - Light beam scanning device - Google Patents

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 a technique for recording an image by scanning a light beam such as a laser beam, and more particularly, to an output device for plate making and an original plate for making a printed circuit board. The present invention relates to a light beam scanning apparatus that is effective when a wide scanning width and a small focused beam diameter are required, as in the case of a film printer.

[0002]

2. Description of the Related Art As a light beam scanning device of this kind, the systems currently used are mainly classified into the following three types.
Each has advantages and disadvantages. FIG. 22 shows an outline of the most widely used so-called drum scanner system. In this method, main scanning is performed by winding a photosensitive material 51 around a rotating drum 52 and rotating by a motor 53, and sub-scanning is performed by moving the light source unit 54 in a direction substantially perpendicular to the main scanning by a sub-scanning mechanism 55. Is performed, and an image is recorded.

[0003] This method can obtain sufficiently good performance in terms of recording size and image quality. However, since the main scanning is realized by rotating a large drum on which a photosensitive material is mounted, the inertia of the drum is reduced. The rotation speed is limited by the magnitude of the moment, which is a factor that limits the recording speed. For this reason, as shown in FIG. 23, which schematically shows the inside of the light source unit 54, a plurality of optical fibers 56 are arranged, and a light beam emitted from the end face 57 is focused on the photosensitive material 51 by a lens 58. In many cases, a so-called multi-beam recording method of performing a plurality of main scans in one rotation using a plurality of light beams is used together. However, in terms of recording speed, two types of light beams described later are used. It is difficult to surpass the scanning method, and no dramatic improvement can be expected in the future.

Next, a plane scanning method will be described with reference to FIG. In this method, a light beam emitted from a light source 61 is rotated in a main scanning direction by a rotating polygon mirror 63 rotated by a motor 62, and is focused by a lens 64, so that the light beam is main-scanned on the photosensitive material 65. Then, the sub-scan is performed by moving the photosensitive material 65 in a direction substantially perpendicular to the main scan, and an image is recorded.

In this method, a main scanning is performed by rotating a light beam itself by using a so-called rotating polygon mirror or rotating pyramid mirror. Therefore, the moment of inertia of the rotating body itself can be reduced, so that it is relatively easy to improve the rotating speed. Further, since the main scanning is performed by the number of times of the number of mirror surfaces in one rotation, a high recording speed is obtained. Is relatively easy to obtain.

However, when a wide scanning width is required as described above, it is difficult to obtain a small focused beam diameter due to restrictions on the design and manufacturing of the lens. It becomes difficult to maintain the shape. In addition, it is required that unevenness of the scanning line interval, which is one of the major problems of this method, is reduced in proportion to the beam diameter, and it is difficult to suppress the unevenness to a necessary degree.

For the reasons described above, in the plane scanning method, a sufficient level of recording speed can be easily obtained, but it is difficult to realize both a sufficient recording size and image quality.
More specifically, in the planar scanning method, the focal length of the lens is usually about the same as or larger than the scanning width due to restrictions on the lens design, and the size of the scanning optical system is relatively large. .

As another type of rotating the light beam itself, a fixed drum (hereinafter referred to as a cylinder) is used, and the photosensitive material mounted on the cylindrical surface is scanned by rotating the light beam inside the cylinder. And an image recording method (see JP-A-63-158580). FIG. 25 shows an outline of this method.

A light beam from a light source 71 is reflected by a light reflecting element 73 rotated by a motor 72, and is focused on a photosensitive material 76 mounted on the inner surface of a cylinder 75 by a focusing action of a lens 74 in an optical path. The focused light beam is main-scanned, and the sub-scanning mechanism 77 performs sub-scanning to record an image. Incidentally, in FIGS. 22 to 25, optical components, light modulating means, motors for sub-scanning, and the like, which are not directly related to the outline of each system, are omitted for simplification.

As a method of mounting the photosensitive material on the cylindrical surface, the photosensitive material may be held on the inner surface of the cylinder, or the photosensitive material may be held on the outer surface of a cylinder made of a transparent member. In the following description, the former case will be described,
This method is called a cylindrical inner surface scanning method. Further, the light reflecting element 73 used in this method is referred to as a rotating reflecting element in the following description.

In this method, a light beam incident almost parallel along the rotation axis is reflected in a substantially right angle direction by a rotating reflection element that rotates about the center axis of the cylinder as a rotation axis, and is mounted on the inner surface of the cylinder. The photosensitive material is scanned and exposed. The direction of reflection does not necessarily have to be a right angle, and by reflecting the light in a direction different from the right angle, the distance between the reflection point and the point where the photosensitive material is exposed is increased, and the light beam on the cylindrical surface is not reflected. , The effect of increasing the axial size of the cylinder,
What is necessary is just a range which does not hinder practical use.

A feature of this method is that a relatively large scanning width can be obtained with a condenser lens having a short focal length as compared with the above-described flat scanning method. The fact that a lens with a short focal length can be used means that it is easy to obtain a small focused beam diameter required for high-quality recording. In addition, the short focal length of the lens leads to alleviation of the problem of uneven scanning line intervals, which is a major problem in the case of the planar scanning method.

The effective diameter of the condensing lens may be as large as the diameter of the incident beam, and must be large in order to cope with a wide incident angle, such as a lens used in a plane scanning system. There is no. In addition, by increasing the accuracy of aligning the rotation axis of the rotary reflection element with the center axis of the cylinder as necessary, it is easy to keep the beam diameter and beam shape on the cylinder surface constant over almost the entire circumference. It is.

That is, it can be said that the cylindrical inner surface scanning method can easily improve the image quality as compared with the plane scanning method.
To obtain a scanning width of about 70 to 80% of the entire circumference of the cylinder is considered due to restrictions on the mechanical arrangement of the photosensitive material entrance, the rotating reflection element holding mechanism, and the sub-scanning mechanism. Is also possible, and the focal length of the condenser lens is slightly longer than the radius of the cylinder, and is three times the focal length of the lens.
A double scan width is easily obtained.

As the rotary reflection element, a right-angle prism or a pentaprism may be used instead of a mirror. The lens may be provided in the optical path between the rotary reflecting element and the photosensitive material, and may be rotated integrally with the rotary reflecting element. In this case, there is a disadvantage that the inertia is increased although the lens rotates, but the focal length of the lens can be made shorter than the radius of the cylinder, and a small focused beam diameter can be easily obtained. Conversely, there is an advantage that the beam diameter incident on the lens can be reduced in obtaining a constant focused beam diameter.

In summary, the cylinder inner surface scanning method rotates, but has a smaller moment of inertia than the drum scanner method, so that the rotation speed is easily increased and the recording speed is easily increased. Also, compared to the planar scanning method,
It can be said that it is easy to make the recording size compatible with the image quality, and it is easy to reduce the size of the apparatus in order to obtain the same recording size.

[0017]

However, although the cylindrical inner surface scanning method has the advantages described above, it has a disadvantage that it is not easy to increase the recording speed as compared with the plane scanning method. The reason is as follows.

First, it is difficult to use multiple beams. Second, it is difficult to perform light beam scanning a plurality of times in one rotation using a rotating polygon mirror or a rotating pyramid mirror. The reason that it is difficult to use multiple beams is that when multiple beams are reflected by a rotating reflection element and scanned on the inner surface of the cylinder, the multiple beams intersect at two points on the inner surface of the cylinder, and image recording is performed. This is because the dot rows arranged in parallel necessary for the above are not formed.

The manner in which they intersect will be described with reference to FIGS. In these figures and the following description, a beam is indicated by a geometric optical ray for simplification, and the ray is also called a beam. For example, the light beam indicating the beam A is also referred to as the beam A
Call. Although the actual beam has a finite spread, it is focused on a point near the inner surface of the cylinder within the range of the spread due to aberration and diffraction.

FIG. 26 shows three mutually parallel beams A,
The case where B and C are incident on the reflection surface of the rotary reflection element 2 and irradiate the inner surface of the cylinder 1 is shown. The actual spacing of beams A, B, and C is very small for the purpose of multiple beam recording, but is shown spaced for clarity. The beam B is a beam that coincides with the rotation axis of the rotary reflection element 2.

When the rotary reflecting element 2 is rotated by 180 degrees to reach the position shown in FIG. 27, it can be seen that the beams A and C are turned upside down. As a result, beam A and beam C are changed as shown in FIG.
It can be seen that they intersect on the inner surface of the cylinder at a position between FIG. 27 and FIG. Further, as shown in FIG. 28, the beam A and the beam C are made to coincide with the beam B on the reflection surface of the rotary reflection element 2,
It can be understood from geometrical optics that even if the light is incident at a slight angle, the beam A and the beam C are also turned upside down when the rotary reflection element 2 rotates 180 degrees as shown in FIG.

In this case, the angle between the beams is extremely small for the purpose of multiple beam scanning.
The figures are shown at large angles for clarity.
FIGS. 30 and 31 are perspective views and developed views showing how beams A, B, and C intersect over a half circumference on the inner surface of the cylinder, respectively. Even when recording is performed not on the entire circumference of the cylinder but on a part of the cylinder, the beams A and C are
Even if they do not intersect, it is clear from the description so far that a curvature is generated, and it is found that this is unsuitable for multiple beam scanning for image recording.

It is possible to make the beams A, B, and C incident on the rotary reflecting element with the incident positions and incident angles matched, but in this case, the beams overlap even on the inner surface of the cylinder. It is not possible to increase the recording speed by the purpose of multi-beam recording, that is, by simultaneously scanning a plurality of beams. Also, in the case of the light beam scanning of the plane scanning method, the scanning can be performed a plurality of times in one rotation by using a well-known rotating polygon mirror. Out of 360 °
In order to take advantage of a relatively small structure and a large scanning width by scanning over as wide an angle as possible, a rotating polygon mirror or a rotating pyramid mirror is used. It is difficult to perform multiple scans.

In order to use a rotating polygon mirror or a rotating pyramid mirror for scanning the inner surface of a cylinder, the center of rotation is located at a position distant from the center axis of the cylinder or the light beam. It can be seen from geometrical optics that the reflection point is displaced in a plane perpendicular to the central axis, in the latter case, in the direction of the central axis of the cylinder. For that reason, it is difficult to use a rotating polygon mirror or a rotating pyramid mirror.

Therefore, in order to increase the recording speed with a single beam, extremely high-speed rotation of the rotary reflecting element is required. For the reasons described above, in the case of the cylindrical inner surface scanning method,
It is difficult to increase the recording speed as in the case of the planar scanning method. As means for solving this problem, Japanese Unexamined Patent Publication No.
As disclosed in JP-A-9-119960 and JP-A-57-151933, a plurality of light sources or a driving current source including the plurality of light sources are mounted on a rotating body provided inside a cylinder. There is also a method of realizing multiple beam scanning by rotating the central axis of the cylinder as a rotation axis. But,
In this method, it is necessary to mount a plurality of light sources, an electronic circuit for modulating the light sources, a generator for supplying power for the electronic circuits, a power supply stabilizing circuit, and the like on the rotating body. Including the mechanism for stably holding them on the rotating body, the moment of inertia becomes large, and there is a limit in obtaining a high rotation speed.

In view of such circumstances, an object of the present invention is to realize a light beam scanning apparatus which enables multiple beam scanning in a cylindrical inner surface scanning method, thereby enabling high-speed recording.

[0027]

SUMMARY OF THE INVENTION To this end, the present invention provides a method for rotating a plurality of light beams rotating on a rotation axis and incident substantially parallel to the rotation axis in a direction substantially perpendicular to the rotation axis. Rotating optical means for guiding, a plurality of light beams incident on the rotating optical means, a light beam rotating means for rotating at the same rotation speed as the rotating optical means, with a straight line substantially coincident with the rotating axis as a rotating axis, A light beam scanning device characterized by having:

More specifically, the rotating optical means is constituted by a rotating reflecting element for reflecting a light beam incident on the rotating shaft at a predetermined angle. Alternatively, the rotation optical means includes a member that rotates on a rotation axis, and an optical fiber bundle held on the member, and one end face of the fiber bundle is substantially in the vicinity of the rotation axis with respect to the rotation axis. The other end surface is arranged at a right angle to the radial direction of rotation.

The light beam rotating means comprises a single or a plurality of optical components, and the component rotates about a straight line substantially coincident with the rotation axis as a rotation axis. Input parallel to a specific plane containing
An emission beam is incident on the structure and exits the structure
If the outgoing light beam and the incident light beam are not
The virtual light beam that advances when the
Thus, the mirrors are arranged so as to have a mirror-symmetrical positional relationship, and undergo an odd number of reflections in the optical path from the time when the light beam enters the structure to the time when the light beam emerges.

More specifically, as the optical structure, a combination of a refracting surface for refracting a light beam and an odd number of reflecting surfaces for reflecting the light beam, three or more odd number of reflecting surfaces , An element that diffracts a light beam and a reflection surface that reflects the light beam, or a trapezoidal prism can be used.

[0031]

In the above arrangement, a plurality of beams incident on the rotating optical means are rotated at the same rotating speed as the rotating optical means by the action of the optical component as the light beam rotating means. By rotating with a rotation axis substantially coincident with the rotation axis of the means, a plurality of beams emitted from the rotating optical means are prevented from intersecting, and a substantially parallel beam train is formed on the cylindrical surface in scanning the inner surface of the cylinder. I do. Thereby, multiple beam scanning becomes possible, and high-speed recording becomes possible.

Here, by making the rotation phase relationship between the light beam rotating means and the rotating optical means (rotating reflection element) variable, the interval between a plurality of light beams in a direction perpendicular to the main scanning direction is obtained. May be variably set. Also,
By changing the angle of the rows of multiple light beam sources,
It is preferable that the interval between the light beams in a direction perpendicular to the main scanning direction is variable.

When an optical fiber bundle is used as the rotating optical means, the angle between the end faces of the individual optical fibers on the exit side of the optical fiber bundle is made variable, so that the interval between the light beams in the direction perpendicular to the main scanning direction is made variable. It is good to
Note that a plurality of light beams having different wavelengths may be used.

[0034]

Embodiments of the present invention will be described below with reference to the drawings. FIGS. 1 and 2 show an embodiment of the present invention. FIG. 1 shows a state where a single beam B is incident. This figure shows the finite spread of the beam. Reference numeral 1 denotes a cylinder for mounting a photosensitive material. In this case, a photosensitive material (not shown) is held on the inner surface of the cylinder.

Reference numeral 2 denotes a rotary reflecting element as rotary optical means, which is rotated by a motor 6 around a straight line substantially coincident with the center axis of the cylinder 1 as a rotation axis. In this example, a rectangular prism is used as the rotary reflection element 2. Reference numeral 3 denotes a trapezoidal prism, which is held by holding means (not shown).
In this example, in the same direction as the rotation direction of the rotary reflection element 2, 1 /
At a rotation speed of 2 by a rotation drive unit or a rotation transmission unit (not shown), the rotation is performed on a rotation axis substantially coincident with the rotation axis. This forms the optical component of the light beam rotating means.

Reference numerals 4 and 5 denote lenses. In the case of this figure, a beam B emitted from the point Pb with a spread is incident on the trapezoidal prism 3 by the lens 5 as a substantially parallel beam.
The beam emitted from this is focused by the lens 4 through the rotary reflecting element 2 near the inner surface of the cylinder 1. The beam B is a straight line that is parallel to the plane D of the trapezoidal prism 3 and parallel or included in a plane perpendicular to the planes E and F, and is an extension of the straight line when the beam goes straight without the trapezoidal prism. Is a beam incident on a position where the beam coincides with the output beam. By appropriately selecting the length of the trapezoidal prism 3 in the direction of the rotation axis, such a beam incident position can exist.

The extent of the spread of the beam B depends on each of the optical elements 2,
The effective incident range is set to 3, 4, and 5. FIG.
Shows a case where the beams A and C are located close to the beam B.
In this figure, the beams are shown by light rays. In actuality, similarly to the beam B shown in FIG. 1, the beams A and C also have a finite spread and are emitted from the respective points Pa and Pc, and are made substantially parallel by the lens 5. , Through the trapezoidal prism 3, through the lens 4 and the rotary reflecting element 2, to be focused near the inner surface of the cylinder 1.

Next, the operation of the trapezoidal prism 3 according to the present invention will be described with reference to FIG. The trapezoidal prism 3 is also called a Dove prism, and is a prism having the shape of a prism having a trapezoidal bottom whose opposite non-parallel sides form an equal angle with other sides. That is, the side surfaces E and F of the prism make the same angle θ with the side surface D. Also, side D,
E and F are perpendicular to the bottom surface. Side G is also usually perpendicular to the bottom, and parallel to side D because the bottom is trapezoidal,
In the present invention, since it is not used as a reflection surface or the like, it does not need to be at a specific angle. In that respect, the same applies to both bottom surfaces of the prism, but in order to obtain the processing accuracy of the surface that requires a predetermined angular accuracy, and to achieve the accuracy of holding the prism, the side surface and the bottom surface are at right angles. It is usually processed as a trapezoidal prism.

More specifically, the function and effect of the present invention can be obtained even if the surface G is eliminated, that is, the prism is formed in a prism shape having an isosceles triangular bottom surface. In order to consider the state of the beam exiting the trapezoidal prism 3, the beam A
Is incident on the trapezoidal prism 3 as shown. The angle of incidence of the beam A is not limited to a specific direction,
The beam B may be tilted in any direction, but the interval between the points Pa and Pb in FIG. 2 is very small for the purpose of the present invention, and therefore, the tilt angle is small.

The beam A enters the surface E at the point P, reflects at the point Q on the surface D, and emerges from the point R on the surface F. The beams A and B after exiting the trapezoidal prism 3 are referred to as a beam A0 and a beam B0, respectively, as shown in the figure. As described above, the beam B0 coincides with the extension of the beam B before the incidence. The plane H is a plane that includes the beams B and B0 and is parallel to the plane D. Assuming that the trapezoidal prism 3 does not exist, a virtual beam that the beam A travels is defined as a beam A2, and the beam A2 and the surface F
Is assumed to be R2.

Further, as shown in FIG. 3, the same trapezoidal prism 7 is arranged mirror-symmetrically with respect to the plane D,
Assume that they are united. Each surface of the hypothetical trapezoidal prism 7 is given a symbol as shown. Beam B1 is assumed as described above, and beam B passes through surface D and passes through surface F1.
Is a beam when the light is emitted.

Under the above assumption, the beam B1 is parallel to the beam B0 and is mirror-symmetric with respect to the plane D with respect to the beam B0 from the theorem of geometrical optics and geometry. The distance between the two beams is indicated by d in the figure. The plane H1 is a plane that includes B1 and is parallel to the plane D. Under the same assumption, the beam A that passes through the surface D and exits from the surface F1 at the point S from the surface F1 is referred to as a beam A1.

From the geometric optics and the theorem of geometry, it can be seen that the beam A1 is similarly mirror-symmetric with respect to the plane A with respect to the beam A0. Further, since the plane E and the plane F1 are parallel, the beam A1 and the beam A before incidence are parallel and therefore parallel to the beam A2 from the theorem of geometry and geometrical optics. The relative positional relationship between the beams A1 and B1 and the relative positional relationship between the beams A2 and B0 will be described. The former is the case where the beam A and the beam B pass through a parallel plane plate composed of the surface E and the surface F1, and the latter is equivalent to the case where the beam goes straight. From geometric optics theorem, a plane-parallel plate will produce aberrations for non-parallel beams. The relative positional relationship of the beam A1 with respect to the beam B1 is different from the relative positional relationship of the beam A2 with respect to the beam B0 by an amount corresponding to the aberration caused by passing through the parallel plane plate. The inclination of B is extremely small, and the relative positional relationship is almost the same within the range of the aberration.

Therefore, the surface H1, beam B1, beam A1
Is translated by a distance d, and the surface H1 is changed to the surface H, and the beam B is
When beam 1 is superimposed on beam B0, beam A1 and beam A2
Nearly overlap. On the other hand, the beam A1 and the beam A0, which are mirror-symmetric with respect to the plane D, cause the plane H
It can be seen that is mirror-symmetric with respect to. From the above considerations, it can be seen that the beam A0 is almost mirror symmetric with respect to the plane H with respect to the beam A2.

This situation is shown in FIG. 4, which is a view of FIG. 3 as viewed from the side from which the beam is emitted. Therefore, the trapezoidal prism 3 is
By rotating the beam B0 around the straight line of the beam B0, the outgoing beam A0 can rotate around the rotation axis at a speed twice as high as the rotation speed of the trapezoidal prism 3. It can be seen from consideration. Therefore, the rotation speed of the trapezoidal prism 3 is set to 1 / the rotation speed of the rotary reflection element 2.
By setting the speed to 2 and making the rotation axes coincide, the beam incident on the rotary reflection element 2 rotates about the rotation axis of the rotary reflection element 2 at the same speed as the rotation reflection element 2.

Therefore, the relative positional relationship between the reflecting surface of the rotary reflecting element and the beam incident thereon is maintained substantially constant during rotation, and the beams intersect on the inner surface of the cylinder as described above. Such a phenomenon does not occur. The fact that the beams do not intersect means that if the rotating reflective element and the plurality of beams are rotating while the relative positional relationship is kept constant,
Conversely, even if it is considered that the cylinder rotates and the rotating reflection element and the beam stop, the relative movement between the beam and the cylinder can be said to be the same, in which case the cylindrical surface is irradiated with the beam This is self-evident, given the situation.

Although the embodiment of FIG. 2 has been described using three beams, it is obvious from the principle of the present invention that the present invention is not limited to three beams, but can be applied to other beams. It is. In addition, the plurality of light beams do not necessarily have to be on a straight line at the center of the beam B outside the trapezoidal prism 3, that is, on a plane including a straight line to be the rotation axis of the trapezoidal prism 3. If the rotation axis coincides with the rotation axis of the rotary reflecting element 2, the beam emitted from the surface F of the trapezoidal prism 3 rotates following the rotary reflecting element 2 and is at the same position on the reflecting surface. Incident at an angle of.

FIG. 5 shows another embodiment of the present invention. In this example, three trapezoidal prisms are provided in the optical path incident on the rotary reflecting element, and each is rotated in a staggered direction. First, second, and third trapezoidal prisms 3 from the entrance side
a, 3b, 3c, and the rotation speed is N per minute for simplicity.
Rotation, -N rotation, and N rotation. Note that the clockwise direction when viewed in the traveling direction of the beam is described as positive.

The beam emitted from the first trapezoidal prism 3a enters the second trapezoidal prism 3b while rotating at 2N revolutions per minute as described above. The beam exiting the second trapezoidal prism 3b is mirror symmetric with respect to a plane corresponding to the plane H described in FIG. 3 of this prism rotating at -N rotations per minute. Therefore, assuming that the rotation speed of the beam emitted from the second trapezoidal prism 3b is L rotations per minute, L = the rotation speed of the prism 3b + (prism 3
(rotation speed of b−rotation speed of incident beam), and L = −N + (− N−2N) = − 4N.

Similarly, if the rotation speed of the beam emitted from the third trapezoidal prism 3c is M rotations per minute, then M = N + (NL) = N + 5N = 6N. In this case, the rotation speed of the rotating reflection element is 6 N / min.
Set to rotation.

Thus, using a plurality of trapezoidal prisms,
By rotating adjacent prisms in directions opposite to each other, the object of the present invention can be achieved at a rotation speed of the trapezoidal prism sufficiently lower than the rotation speed of the rotary reflection element, and the conditions required for the motor and the rotation transmission means Can be alleviated. Note that rotating the trapezoidal prisms adjacent to each other in the same direction is not preferable because the rotation speed of the emitted beam decreases and the rotation speed of the trapezoidal prism needs to be increased.

The magnitude of the rotational speed of each trapezoidal prism does not need to be the same as in this example, and the rotational speed of the beam emitted from the last trapezoidal prism coincides with the rotational speed of the rotary reflection element. The rotation speed of the trapezoidal prism may be set. Next, a method for holding and rotating the trapezoidal prism will be described with reference to examples.

FIG. 6 shows that a motor 10 is constituted by using a cylindrical member as a rotor 11 and a stator 12 surrounding the rotor.
This is an example in which the trapezoidal prism 3 is held in the rotor 11,
According to this method, the motor 10 can be directly rotated without using a mechanical rotation transmission means such as a gear, and can cope with high-speed rotation. FIG. 7 shows an example in which a mechanical rotation transmitting means such as a gear is used to rotate the trapezoidal prism.
The bevel gear 14 is rotated by the motor 13, and the trapezoidal prism 3 is rotated via the bevel gear 15. When the required rotation speed is low, such mechanical rotation transmission means can sufficiently cope with the problem.

As means for obtaining a plurality of beams, a multi-frequency high frequency may be applied to the acousto-optic modulator. Alternatively, one end faces of the plurality of optical fibers may be aligned and arranged, and a light beam such as a laser may be incident from the opposite end face. Further, the beam may be split by an optical means such as a beam splitter, or a plurality of independent light sources may be prepared.

The optical components of the beam rotating means include:
In addition to the trapezoidal prism, as shown in FIG.
Even if a mirror is arranged so as to have a to 21c, an effect equivalent to that of a trapezoidal prism can be obtained. In FIGS. 8 and 9, 10, 13, and 14, each of the components is an example in which the output beam rotates twice as much as the rotation angle of each optical component. The situation when rotated by 90 degrees is shown.

As the mirror, a plane mirror is suitable,
It is possible to realize the object of the present invention with a curved mirror, and it is also possible to combine the functions of the lenses 4 and 5 in FIG. In the three-piece mirror, the optical path of each beam inside the structure is different from that of the trapezoidal prism. However, in the effect described above, the effect of rotating the emitted beam is equivalent to that of the trapezoidal prism. is there.

If the mirror is a plane mirror, since the plane mirror is an aberration-free optical system, the degree of divergence of the light beam is large, which is advantageous in the case where the trapezoidal prism causes an aberration.
On the other hand, the trapezoidal prism can be said to be advantageous in terms of simplicity of the holding mechanism since only a single optical element is required. When the reflecting surfaces are used in this way, the number is not limited to three, and the object of the present invention can be realized by using an odd number of reflecting surfaces. FIG. 9 shows an example using five reflecting surfaces 22a to 22e.

As a means for realizing the reflecting surface, FIG.
A configuration using internal reflection or total reflection as in the ten reflection surfaces 23a to 23e is also possible. 11 and 12 as reference examples.
In the case where the number of reflection surfaces is two or four, the state in which each component is rotated by 90 degrees is shown to show that there is no function of rotating the light beam.

The optical components of the beam rotating means include:
A configuration as shown in FIG. 13 may be employed. FIG. 13 shows an embodiment in which the refraction by the prism and the reflection surface are combined. The prisms 24 and 25 have functions corresponding to the surfaces E and F in FIG. 1, and the reflection surface 26 is in FIG. It can be seen that it has a function corresponding to the surface D.

Similarly, as shown in FIG. 14, an optical structure of the present invention can be realized by a structure in which diffraction gratings 27a and 27b, which are elements for diffracting a light beam, and a reflection surface 28 are combined. Can also. The requirement that the optical components of the trapezoidal prism and other various embodiments described above have the function of rotating the incident light beam is that the optical beam must enter the optical component and exit. In the optical path of the optical disk.

With the configuration according to the present invention described above, it is possible to realize scanning of a plurality of beams in scanning the inner surface of a cylinder. As means for rotating the rotary reflecting element and the trapezoidal prism at a predetermined rotation speed ratio, a well-known PL is used.
In L control, a plurality of motors may be rotated. It is also possible to realize using a plurality of synchronous motors.

It is also possible to use a single motor and mechanical means such as gears, chains, belts, etc., to obtain a predetermined rotational speed. When a plurality of beams are focused on a cylindrical surface by the method described above to form a focused beam train, the beam train is fixed at a right angle to the main scanning direction, that is, the moving direction of the beam, or at a predetermined inclination. Must be maintained at an angle of

The interval between the main scanning lines is determined by the angle. Whether the angle is variable or fixed is determined according to the purpose of use of the present scanning apparatus, but in order to set the beam train to a predetermined angle, the phase of rotation between the rotary reflecting element and the trapezoidal prism is required. It is necessary that the relationship be kept at a predetermined value. This will be described with reference to FIGS. 30 and 31 for easy understanding.

FIGS. 30 and 31 show that the direction in which the beams A, B, and C are arranged on the inner surface of the cylinder changes depending on the direction in which the beams A, B, and C are reflected by the rotary reflection element. From FIGS. 30 and 31, setting the angle at which the beams A, B, and C line up on the cylindrical surface to a predetermined value means that the relative position relationship between the rotating reflection element and the beams A, B, and C incident thereon Is set to a given value,
For that purpose, it is understood that it is necessary to set the rotation phase relationship between the rotating reflection element and the trapezoidal prism to a predetermined value.

When the beam train is inclined with respect to the direction perpendicular to the main scanning direction line on the cylindrical surface, the recording signal is applied to each column at a shifted timing in accordance with the shift amount in the main scanning direction. Thus, an image is formed. An example of a method of setting the rotation phase relationship between the rotating reflection element and the trapezoidal prism to a predetermined value will be described below.

FIG. 15 shows an embodiment in which the rotary reflecting element 2 and the trapezoidal prism 3 are rotated synchronously by a single motor 6 by gears 31, 32, 33, 34. In this case, the phase relationship between the two rotations is made variable by means such as the clutch mechanism 35 if necessary. FIG. 16 shows a functional block diagram of the embodiment in the case where the rotations of both are controlled by different synchronous motors.

In this embodiment, the motors 41, 42
The phase is detected by the respective phase detection circuits 43 and 44 when a predetermined rotation speed is reached after activation, and if necessary, the phase difference is passed through a frequency dividing circuit 45, and the phase difference is detected by a phase difference detection circuit. Detected by 46, compared with the reference phase difference set by the reference phase difference setting circuit 47 and the phase difference comparison circuit 48,
The phase shift circuit 49 shifts the phase of the reference signal to be applied to one synchronous motor when the reference signal is applied to both synchronous motors 41 and 42 via the amplifiers 81 and 82 by the reference signal generator 80. Adjust the phases of 41 and 42. Also,
The display circuit 50 displays the phase difference, and the reference phase difference setting circuit 47 changes the setting of the reference phase difference to make the phase difference variable.

The means itself for detecting the phase difference of rotation of the rotating body and adjusting it to a variable or fixed predetermined value as described above is a well-known technique. It can be realized by well-known means such as a slit or a pinhole on a member that rotates integrally, or a Hall element.
The adjustment can be performed by a method such as PLL control or phase control of an alternating current applied to the synchronous motor as described in the description of FIG.

The direction in which Pa, Pb, and Pc, which are points at which three beams are emitted in FIG. 2, are arranged on a cylindrical surface by rotating the beam in the traveling direction as a rotation axis. The direction in which the beams are arranged can be changed. This makes it possible to make the interval in the direction perpendicular to the main scanning direction on the cylindrical surface variable. In this case, it is possible to change the scanning line interval of the main scanning by the light beam while keeping the rotation phase of the rotating reflection element and the light beam rotating means fixed.

Various means, such as mechanical or optical, can be considered as means for changing the direction in which Pa, Pb, and Pc are arranged. A suitable method may be selected according to means for obtaining a plurality of beams. As the rotating optical means, not only a means for reflecting light (a rotating reflection element) such as a prism or a mirror, but also an optical fiber bundle in which a plurality of optical fibers are bundled as shown in FIG. 17 may be used.

FIG. 17 is a view in which the rotary reflecting element 2 in FIG. 2 is replaced by an optical fiber bundle 90, and the same components as those in FIG. 2 are denoted by the same reference numerals. Although the optical fiber bundle 90 is shown by three optical fibers in FIG. 17, it is obvious that the optical fiber bundle 90 is not limited to three. In FIG. 17, individual optical fibers corresponding to the light beams A, B, and C are respectively denoted by 90a, 90b, and 90c.
And

Reference numeral 91 denotes a holding member for holding the optical fiber bundle, which is rotated by the motor 6. Reference numeral 92 denotes a condensing means such as a lens, which condenses a plurality of light beams emitted from the light beam rotating means such as the trapezoidal prism 3 on the incident end face of the optical fiber bundle 90. FIG. 18 shows an enlarged end face of the optical fiber bundle 90 on the incident side. In FIG. 18, the core of the optical fiber 90a that actually transmits light is represented by 90a-1, and the outer covering material is represented by 90a-2. The same applies to 90b and 90c. On the incident-side end face, each end face and each beam rotate coaxially at the same rotational speed, and the relative positional relationship is constant. From the function of the light beam rotating means described so far, by assembling the light beam rotating means and the optical fiber bundle with a high-precision axis, it is possible to maintain a constant positional relationship between the light beam and the end face of the optical fiber. It turns out that it is possible.

It is not always necessary that the light beam and the end face of the optical fiber have a one-to-one correspondence, but in order to effectively use the energy of the light beam, each beam is incident on one optical fiber. It is desirable.
The arrangement of the end faces on the incident side of the optical fiber bundle is not limited to being aligned on a straight line or on a circumference.
It is sufficient that B and C have an arrangement substantially matching the arrangement at the position focused by the optical system including the lens 5, the trapezoidal prism 3, and the lens 92.

The light beam that has exited the end face on the emission side of the optical fiber is condensed on a cylindrical surface by condensing means such as a lens 93. Again, the light beam is shown as a light beam as a geometric straight line, but in practice each light beam has a certain spread determined by the characteristics of the optical fiber and the wavelength of the light.
The lens 93 is fixed to a rotating holding member 91, like the optical fiber bundle 90. The function of the lens 93 is the same as that of the lens 4 in FIG. 2 in that the light beam is focused on a cylinder,
The position where the optical fiber bundle is the rotating optical means
Limited to 90 outgoing sides.

When an optical fiber bundle is used, the angle at which a plurality of light beams are arranged on the cylindrical surface is determined by the direction in which the end faces on the emission side of the optical fiber bundle are arranged and the light collecting means. Unlike the case of using the rotating reflection element, the direction in which the light beams are arranged on the cylindrical surface cannot be changed due to the phase relationship between the rotating optical means and the light beam rotating means. The arrangement of the end faces on the emission side of the optical fiber bundle may be any arrangement suitable for light beam recording when an image of the end faces is projected onto a cylindrical surface by the lens 93.

FIG. 19 shows an example of the arrangement. In the direction perpendicular to the main scanning, it is necessary that the intervals be substantially equal. In the main scanning direction, it is not necessary that the intervals be equal, but FIG.
If the intervals are equal as shown in (a), the timing difference of the image signal given to each beam can be made constant. When a large number of optical fibers are used, the arrangement as shown in the nineteenth (b) may be adopted so that the required field of view of the lens 93 is not increased.

It is obvious that the angle at which the light beams are arranged on the cylindrical surface can be adjusted by adjusting the angle at which the end faces on the emission side of the optical fiber bundle are arranged. When an optical fiber bundle is used, the diameter of the light beam on the cylindrical surface can be easily reduced by disposing the end face of the fiber, the lens, and the like near the cylindrical surface. In this case, there is a disadvantage that the moment of inertia of the rotating optical means becomes large and it is difficult to increase the number of rotations. However, since the light beam diameter on the cylindrical surface can be reduced, there is an advantage that high image quality is easily obtained.

In each of the above embodiments, each beam of the multiple beam scanning may be monochromatic, or may be applied to beams having different wavelengths. When different wavelengths are used, it is also possible to use one or more light beams for each wavelength at different wavelengths at the same time. It is also possible to record with a plurality of beams at one wavelength and then record with a plurality of beams at another wavelength.

The light beam scanning device of the present invention using different wavelengths is suitable for recording on a color photosensitive material such as a color film or color photographic paper with a light source such as a laser. When using different wavelengths, the means using refraction, such as a prism, is affected by the difference in the refractive index depending on the wavelength. Therefore, it is preferable to configure the light beam rotating means by combining reflection surfaces. If the difference in the refractive index does not matter depending on the purpose of use, a prism can also be used. The same can be said for an element that diffracts a light beam. However, since diffraction has a greater wavelength-dependent difference than refraction, it is somewhat unsuitable to use it at a different wavelength.

If the mounting accuracy and the processing accuracy of the optical component composed of a trapezoidal prism or the like are insufficient, the beam position shifts on the cylindrical surface. This situation will be described with reference to FIG. 20, taking as an example the case where the optical component is one trapezoidal prism. In this case, for the same position of the rotating optical means,
It can be seen from the description so far that the trapezoidal prism has two rotational positions.

FIG. 20 shows a case where the trapezoidal prism is tilted with respect to its rotation axis. With the above inclination, the direction of the beam emitted from the trapezoidal prism changes depending on the rotational position of the trapezoidal prism. Therefore, the directions of the emitted beams are not parallel to each other due to the two positions of the trapezoidal prism corresponding to the same position of the rotating optical element. Therefore, as shown in FIG. 1, in an arrangement in which beams incident parallel to the lens 4 are focused on a cylindrical surface, the beams are not focused on the same position on the cylindrical surface. This results in unevenness of the interval between the scanning lines on the scanning surface, and appears as periodic unevenness of the image with one rotation of the rotating optical unit as one cycle.

It can be seen that the same phenomenon occurs even if the processing accuracy of the trapezoidal prism is insufficient. The same occurs if the trapezoidal prism is not tilted with respect to the rotation axis, but the rotation axis itself is tilted with respect to the rotation axis of the rotating optical means. Figure
When an optical fiber bundle is used as shown in FIG. 17, it can be seen that the point where the beam is focused on the end surface of the optical fiber bundle shifts due to the rotational position of the trapezoidal prism or the like, and the result is that the beam does not enter the optical fiber efficiently. .

This problem can be solved by making the processing accuracy and mounting accuracy of the trapezoidal prism sufficiently high. Another means for solving this problem will be described. An example in which the optical structure includes one trapezoidal prism as shown in FIG. 20 will be described. In this case, it has already been described that the trapezoidal prism makes one rotation for every two rotations of the rotating optical means. However, one rotation of the two rotations of the rotating optical means turns off the light beam, and Light beam scanning is performed every other rotation without scanning. In this way, the trapezoidal prism
Since only a specific 180-degree rotation range of the 360-degree rotation is used, unevenness of the scanning line interval due to the shift of the focusing position as shown in FIG. 20 does not occur. Further, the problem described in the case of the arrangement of FIG. 17 does not occur. As described above, even if one of the two rotations is invalid, a scanning speed that is １ ／ the number of beams of the multiplex beam can be obtained at the same rotation speed as compared with the single-beam inner surface scanning method even if one rotation is invalidated. .

As shown in FIGS. 5 and 7, when a plurality of optical components are used, only a specific range of the rotational position of the optical components may be used as the effective scanning range. In this case, the scanning speed is further reduced, so that there is little practical effect. Another means for solving this problem will be described. In the above description, the trapezoidal prism is placed at the position where the beam is substantially parallelized between the lenses 4 and 5 in the example of FIG. It is obvious from the principle that the function of rotating the light beam can be obtained even at an arbitrary position between the rotating optical means and the light source, and it is within the scope of the present invention.

As shown in FIG. 21, if the trapezoidal prism is placed at a position substantially coincident with the points Pa, Pb, and Pc in FIG. 1, that is, at a position substantially conjugate with the scanning plane, the problem described with reference to FIG. The point is greatly relaxed. When it is difficult to arrange a trapezoidal prism there, for example, when the points Pa, Pb, and Pc represent an object in which the end faces of the optical fibers are arranged, the real image is formed by appropriate optical imaging means and the real image is formed. What is necessary is just to put a trapezoid prism in a position.

In this case, the dimensions of the trapezoidal prism may be extremely small, since it is near the position where the beam is focused. As a problem in this case, there is a possibility that the influence of aberration may appear because the beam is not collimated. If this hinders practical use, a combination of flat reflecting surfaces as shown in FIGS. 8 and 9 may be used.

In this case, another problem is that since the trapezoidal prism and the like are located at positions conjugate to the scanning plane, fluctuations in the beam direction have little effect on the position on the scanning plane. The fluctuation appears as unevenness in the interval between scanning lines on the scanning surface. Therefore, in order to reduce the fluctuation of the beam position after exiting the trapezoidal prism or the like, it is necessary to maintain high accuracy the factors that affect the coaxiality and positional fluctuation of the trapezoidal prism or the like.

The position at which the trapezoidal prism and the like are arranged may be determined in consideration of the above-described considerations and the difficulty in designing and manufacturing. Further, another effect of the present invention will be described. When performing image recording by scanning a light beam, the light beam moves at a high speed in the main scanning direction, while the exposure time for recording one pixel has a finite length. Therefore, the shape of the light beam focused on the recording surface is smaller in the main scanning direction and larger in a direction perpendicular to the main scanning direction, because the shape of the pixel to be recorded tends to be the same in the vertical and horizontal sizes. ,preferable. In the conventional cylindrical inner surface scanning method, as is clear from the description so far, it is understood that the single focused beam itself is also scanned on the cylindrical surface while rotating. This is obvious if the beam B and the beams A and C are considered to be the center and the periphery of a single beam in FIGS. 26 and 30, respectively. Therefore, in the conventional cylindrical inner surface scanning method, it is difficult to use focused beam shapes having different aspect ratios as described above.

According to the present invention, the focused beam is not scanned while rotating on the cylindrical surface, and a constant aspect ratio is maintained with respect to the direction of the main scanning line. In addition, the present invention has an effect of enabling multiple beam scanning over the entire circumference of a cylindrical surface in principle. However, even when a part of the cylindrical surface is scanned, it is possible to prevent a scan line from being curved. The effect is apparent from the description of FIGS.

[0090]

As described above, according to the light beam scanning device of the present invention, a predetermined rotation is given to a plurality of beams incident on the rotating optical means by the optical structure as the light beam rotating means. Therefore, the plurality of beams emitted from the rotating optical means do not intersect, and a substantially parallel beam train is formed on the cylindrical surface in the scanning of the inner surface of the cylinder, thereby enabling multiple beam scanning. Thus, high-speed recording becomes possible.

Further, it has the various effects described above,
Good light beam scanning can be realized in three items of image quality, recording speed, and scanning width. The light beam scanning device according to the present invention is, among devices for scanning a laser beam to record an image, particularly an output device for outputting halftone dots for printing plate making and a laser for producing an original plate of a printed circuit board. It is suitable for devices requiring a wide scanning width and a small focused beam diameter, such as an output device.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a light beam scanning device of a cylindrical inner surface scanning type showing an embodiment of the present invention.

FIG. 2 is a schematic diagram showing the same embodiment as in the case of a plurality of beams.

FIG. 3 is a diagram showing the operation of a trapezoidal prism.

FIG. 4 is a view of FIG. 3 as viewed from a light beam emission side.

FIG. 5 is a diagram showing an example in which three trapezoidal prisms are used.

FIG. 6 is a diagram showing a means for rotating a trapezoidal prism.

FIG. 7 shows another means for rotating the trapezoidal prism.

FIG. 8 is a diagram showing an example using a reflection surface.

FIG. 9 is a diagram showing another example using a reflection surface.

FIG. 10 is a diagram showing another example using a reflection surface.

FIG. 11 is a diagram illustrating that a light beam does not rotate when the number of reflection surfaces is an even number (two) as a reference example.

FIG. 12 is a diagram illustrating that a light beam does not rotate when the number of reflection surfaces is an even number (four) as a reference example.

FIG. 13 is a diagram illustrating an example in which a prism and a reflecting surface are used.

FIG. 14 is a diagram illustrating an example in which a diffraction grating and a reflecting surface are used.

FIG. 15 is a diagram showing an example in which a single motor rotates a rotary reflecting element and a trapezoidal prism in synchronization.

FIG. 16 is a functional block diagram of an example in which the motors are rotated by different motors.

FIG. 17 is a diagram illustrating an example in which an optical fiber bundle is used as a rotating optical unit.

FIG. 18 is an enlarged view of the end face on the incident side of the optical fiber bundle.

FIG. 19 is a diagram illustrating an example of an array of end faces on the emission side of the optical fiber bundle.

FIG. 20 is a diagram showing a case where the trapezoidal prism is inclined with respect to the rotation axis.

FIG. 21 is a diagram illustrating an example of an arrangement of a trapezoidal prism.

FIG. 22 is a schematic diagram of a conventional drum scanner type light beam scanning device.

23 is a diagram schematically showing the inside of the light source unit of FIG. 22.

FIG. 24 is a schematic diagram of a conventional planar scanning light beam scanning device.

FIG. 25 is a schematic view of a conventional light beam scanning device using a cylindrical inner surface scanning method.

FIG. 26 is a diagram in the case of a parallel beam showing a conventional problem.

FIG. 27 is a diagram in which the rotating reflection element is rotated by 180 degrees from FIG. 26

FIG. 28 is a diagram of a case of an inclined beam showing a conventional problem.

FIG. 29 is a diagram in which the rotating reflection element is rotated by 180 degrees from FIG. 28

FIG. 30 is a perspective view showing a state in which beams intersect in the related art.

FIG. 31 is an expanded view of FIG. 30.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cylinder 2 Rotating reflective element (right angle prism) 3 Trapezoidal prism 3a-3c Trapezoidal prism 4,5 Lens 6 Motor 10 Motor 13 Motor 21a-21c Reflection surface 22a-22e Reflection surface 23a-23e Reflection surface 24,25 prism 26 Reflection surface 27a, 27b: Diffraction grating 28 Reflecting surface 35 Clutch mechanism 47 Reference phase difference setting circuit 90 Optical fiber bundle 91 Holding member

Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G02B 26/10

Claims (13)

(57) [Claims] 1. A rotating on a rotary shaft, a rotary optical means for guiding a schematic perpendicular direction a plurality of light beams to the axis of rotation substantially parallel to incident on the rotating shaft, a plurality of incident on the rotary optical means A light beam rotating device for rotating the light beam at the same rotation speed as that of the rotating optical device, using a straight line substantially coincident with the rotation axis as a rotation axis. 2. The light beam scanning device according to claim 1, wherein said rotation optical means comprises a rotation reflection element for reflecting the light beam incident on said rotation axis at a predetermined angle. 3. The rotating optical means comprises a member rotating on a rotating shaft and an optical fiber bundle held on the member, and one end face of the fiber bundle is located near the rotating shaft. 2. The light beam scanning device according to claim 1, wherein the light beam scanning device is disposed substantially at right angles to the first direction, and the other end surface is disposed substantially at right angles to the radial direction of rotation. (4) The light beam rotating means may be a single or multiple
An optical component, which is substantially aligned with the axis of rotation.
It rotates with the coincident straight line as a rotation axis,
Incident light beam approximately parallel to a specific plane containing the axis of rotation
Beam enters the structure and exits from the structure
And the incident light beam is assumed to be free of the component.
Virtual light beam traveling in
3. A mirror-symmetric positional relationship.
The light beam scanning device according to claim 3. 5. The light beam rotating means comprises a single or a plurality of optical components, and the component rotates about a straight line substantially coincident with the rotation axis as a rotation axis. When the light beam is incident parallel to the axis, the light beam emitted from the structure is substantially parallel to the light beam incident on the structure, and the light beam is incident on the structure. 5. The light beam scanning device according to claim 4 , wherein the light beam is reflected an odd number of times in an optical path from the light beam to the light beam. 6. The light beam scanning device according to claim 5, wherein said optical structure is a combination of a refraction surface for refracting a light beam and an odd number of reflection surfaces for reflecting the light beam. 7. The light beam scanning device according to claim 5 , wherein said optical component comprises an odd number of reflecting surfaces of three or more. 8. The light beam scanning device according to claim 5, wherein said optical structure is a combination of an element for diffracting a light beam and a reflection surface for reflecting the light beam. 9. The light beam scanning device according to claim 5 , wherein said optical component is a trapezoidal prism. 10. The variable phase relationship between the rotation of the light beam rotating means and the rotation of the rotating optical means makes it possible to variably set the interval between a plurality of light beams in a direction perpendicular to the main scanning direction. The light beam scanning device according to claim 1 or 2, wherein 11. The light beam scanning device according to claim 1, wherein an interval between the light beams in a direction perpendicular to the main scanning direction is variable by changing an angle of a row of the plurality of light beam light sources. 12. The light beam scanning apparatus according to claim 3, wherein the angle between the end faces of the individual fibers on the exit side of the optical fiber bundle is made variable, so that the interval between the light beams in a direction perpendicular to the main scanning direction is made variable. . 13. The light beam scanning device according to claim 1, wherein a plurality of light beams having different wavelengths are used.