JPH0547152B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a laser exposure method applied to an image scanning recording device such as a laser plotter for manufacturing printed wiring boards, a color scanner for plate making, or a laser printer, and further relates to More specifically, the present invention relates to a laser exposure method in which an image recording surface is scanned with a plurality of laser light beams.

(Prior art) This type of device aligns multiple laser beams in series at the same pitch, projects the multiple laser beams aligned in series onto an image recording surface as a recording beam array, and records the laser beams in series. A strip-shaped scanning line is exposed and recorded on a recording medium by forming a recording beam spot array and relatively scanning the serial recording beam spot array in a direction intersecting the direction of the spot array.

By the way, when laser light beams emitted from a single laser light source are superimposed on each other, interference occurs,
The recording beam is disturbed. For this reason, conventionally the recording beams have not been overlapped with each other.

In addition, the light intensity distribution of the laser light beam emitted from the laser light source is not uniform, and for example, as shown in FIG.
have.

Iy＝I ₀ exp [−2(y/ω) ² ]……() Where, Iy is the power density y is the distance from the beam center ω is the beam radius (the power density is 1/with respect to the power density I ₀ at the center) In ^other words, the light intensity is extremely low at the periphery of the beam.

In addition, the beam spot diameter D (=2ω) is a beam corresponding to a light intensity distribution of 1/e ² (approximately 13.5%) with respect to the light intensity at the center of the laser light beam in the case of a laser light beam with a Gaussian distribution. Defined by diameter.

It can be said that the beams overlap if the beam spot diameters D overlap, and it can also be said that the beams overlap if interference occurs.

Therefore, if a plurality of such recording beams are connected to each other to perform exposure recording of strip-shaped scanning lines, the density of the portions corresponding to the valleys of the light intensity distribution between the beams will not be high enough, resulting in recording that should be of uniform density. A phenomenon in which the pattern appears to be broken down by the scanning lines (hereinafter referred to as "scanning line cracks") occurs.

Therefore, as a solution to this inconvenience, for example, Japanese Patent Application Laid-open Nos. 118302-1982 and 1983-
No. 69701 or Japanese Unexamined Patent Publication No. 60-203071 proposes the following technology.

That is, by arranging the serial beam spot rows at a constant angle with respect to the scanning direction, and by making adjacent scanning lines partially overlap each other after recording, the above-mentioned scanning line cracks can be avoided. It was designed to resolve this issue.

(Problem to be Solved by the Invention) However, in the conventional example described above, the serial beam spot rows are arranged at a constant angle with respect to the scanning direction, so the image signal output timing of each recording beam must be the same. If you do so, the image will be distorted depending on the tilt angle. Therefore, a delay circuit is required to control the image signal output timing of each recording beam in accordance with its inclination angle, but this is necessary depending on the number of recording beams, and the circuit becomes complicated.

On the other hand, for example, when the image recording surface is formed by the cylindrical surface of a rotating recording cylinder with the main scanning direction as the circumferential direction, the direction of the recording beam array B ₁₃ is Since it obliquely intersects the axial direction of the recording cylinder 25, the shape of the projection (beam spot) _B14 of each recording beam that irradiates the cylindrical recording surface is deformed. This will give another distortion to the light intensity distribution.

The present invention has been made in view of the above circumstances, and an object thereof is to eliminate the delay circuit for controlling the image signal output timing as in the conventional example and to eliminate the inconvenience on the cylindrical recording surface.

(Means for Solving the Problems) In order to achieve the above object, the present invention improves the conventional laser exposure method as follows.

That is, a plurality of laser beams are projected in series onto an image recording surface to form a series of recording beam spots, and this series of recording beam spots is relatively scanned in a direction intersecting the direction of the spot series. In a laser exposure method for an image scanning recording apparatus that performs exposure recording on a recording medium by exposure recording, the above-mentioned serial recording beam spot row is constituted by two groups of beam spot rows, and each beam spot row of these two groups is formed by using a different laser beam. A laser beam from a light source is formed by two groups of recording beam arrays arranged in series at the same pitch, and the beam spot arrays of the two groups are aligned in a direction perpendicular to the scanning direction, and the beam of one group is The beam spots in the spot row are aligned so that each beam spot in the beam spot row in the other group is located in the middle, and the beam spots in one group and the beam spots in the other group are partially overlapped with each other. According to the present invention, there is provided a laser exposure method for an image scanning and recording apparatus, characterized in that the recording beam spot array is arranged in series.

(Function) According to the laser exposure method of the present invention, the following functions occur.

The two groups of beam spot arrays with the same pitch that constitute the serial recording beam spot array are arranged in a direction perpendicular to the scanning direction, and each beam spot of the beam spot array of one group is connected to the beam spot of the other group. The beam spots of one group overlap each other with the beam spots of the other group.

At this time, since the above two groups of beam spot arrays are formed by two groups of recording beam arrays from different laser light sources, even if the beam spots of one group and the beam spots of the other group overlap each other, There will be no interference.

This makes it possible to make the light intensity distribution uniform while avoiding deterioration in image quality due to mutual interference between beam spots, and to prevent scanning line cracks even when there are variations in the sensitivity threshold of the recording material. . Furthermore, even when a soft-tone photosensitive film with a low γ value such as a half-tone film is used, scanning line cracks are less likely to occur according to the present invention.
In other words, adjacent recording beams are generated from separate laser light sources and partially overlapped with each other to prevent scanning line cracks from occurring in the belt-shaped scanning line, and
By arranging heavy spot rows in a direction perpendicular to the main scanning direction, it is sufficient to output the image signals of each recording beam at the same time, and there is no need to control the output timing.

(Example) Hereinafter, an example apparatus according to the present method invention will be described based on the drawings.

FIG. 1 is a perspective view showing an outline of an embodiment of an apparatus according to the present invention, and FIG. 8 is a perspective view of a laser plotter exemplified as an image scanning recording apparatus to which the present invention can be applied.

This laser plotter includes a console section 21, a data processing section 23 that performs arithmetic processing on data input via a storage medium such as a magnetic tape, and a data conversion generator that converts the data processed by the data processing section 23 into a required recording signal. 22 and a recording section 24 that scans and records an image on a photosensitive film on a recording cylinder 25 based on a recording signal, and is capable of recording a high-precision master pattern on a printed wiring board or the like at high speed by exposure. This is what I did.

During exposure recording, the recording cylinder 25 is rotated, and the laser exposure device shown in FIG. It is composed of

The embodiment apparatus according to the present invention is configured as a laser exposure apparatus 1 as shown in FIG.

The basic configuration of this laser exposure apparatus 1 is two laser light sources 2 and 3, multiple beam splitters 5 and 6, multichannel optical modulators 7 and 8, and a beam combiner 1.
0 and a beam reduction optical system 11, and is configured to form a serial recording beam spot array _B12 as shown in FIG. 3 in the axial direction of the recording cylinder 25. Note that M ₁ and M ₂ are mirrors.

Multiple beam splitters 5 and 6 each have a single beam
B ₄ and B ₃ are divided into a plurality of parallel beams and emitted as parallel beam arrays B ₅ and B _6. These multiple beam splitters 5 and 6 are, for example,
As described in Japanese Patent Application Laid-open No. 122135 and Japanese Patent Application Laid-Open No. 1983-19101, a single incident beam is split into multiple parallel beams using multiple internal reflections of a glass plate with parallel planes. One plane is coated with a coating that forms a completely reflective surface, and the other plane has a parallel beam array B ₅ , which is emitted from that plane.
A coating is applied that changes the transmittance in stages so that the light intensity of each _B6 beam is almost uniform.

The multi-channel optical modulators 7 and 8 are acousto-optic modulators, electro-optic modulators, etc., and parallel beam arrays are used.
The individual beams B ₅ and B ₆ are each independently modulated to emit recording beam arrays B ₇ and B ₈ for image recording. By the way, the multi-channel acousto-optic modulators 7 and 8 are disclosed in, for example, Japanese Patent Application Laid-Open No. 58-10742.
As described in Japanese Patent Application Laid-open No. 58-14135, a plurality of ultrasonic excitation members are attached on a single acousto-optic medium, and a plurality of ultrasonic excitation members are attached to a single acousto-optic medium parallel to a portion of the acousto-optic medium corresponding to the excitation member. Beam arrays B ₅ and B ₆ are incident, each incident laser beam is independently modulated by a control signal emitted based on a pattern signal, and parallel recording beam arrays B ₇ and B ₈ are emitted. has been done.

The beam combiner 10 is a conventional beam splitter arranged in opposite directions for beam combining, and the recording beam array modulated by the modulators 7 and 8.
B ₇ and B ₈ are incident from two orthogonal directions,
The recording beam array is aligned in the same direction as shown in Figure 2.
Configured to inject B ₁₀ . On this occasion,
The beam arrays are combined so that the beams belonging to the recording beam arrays B ₇ and B ₈ are aligned alternately (that is, the beams belonging to the recording beam arrays B ₇ and B ₈ are sequentially adjacent to each other).

The recording beam array B _{10 combined by the beam combiner 10} is reduced by a beam reduction optical system,
Photosensitive film 26 attached to recording cylinder 25
A surface is irradiated to form a serial recording beam spot example B ₁₂ as shown in FIG.

That is, this serial recording beam spot row B ₁₂
have the same pitch Q as shown in Figure 3.
Two groups of beam spots arranged in series B _a ,
B consists of _b . These two groups of beam spot arrays B _a and B _b are formed by two groups of recording beam arrays B ₇ and B ₈ from mutually different laser light sources, as described above.

In addition, the beam spot rows B _a and B _b of each group above are as follows:
In the forward scanning direction (direction of arrow B in Figure 1) perpendicular to the main scanning direction (direction of arrow A in Figure 1), each beam spot a in beam spot row B _a of one group is connected to beam spot row B of the other group. Each beam spot _b
are arranged in a state that is located in the middle of . In this state, the pitch P between the beam spots of the recording beam spot array _B12 is such that each beam spot a,
The beam spot a of one group and the beam spot b of the other group partially overlap without mutual interference. In addition,
Specifically, a laser light source 2, a plurality of beam splitters 5,
By adjusting the optical axis of the optical system comprising the multi-channel optical modulator 7, the recording beam spot array _B12 is arranged in series.

Therefore, according to the above configuration, mutual interference between beam spots a and b constituting the recording beam spot array B ₁₂ is eliminated, and adjacent beam spots a and b
can be superimposed on each other. When a strip-shaped scanning line is recorded using the serial beam spot rows _B12 superimposed at intervals of 1/2 of the beam diameter as described above, the light quantity distribution becomes flat as shown by the solid line C in FIG. As a result, beam spots a, b
It is possible to prevent scanning line blur while avoiding deterioration in image quality due to mutual interference. Furthermore, even when a soft-tone photosensitive film with a low γ value, such as a half-tone film, is used, scanning line cracks are less likely to occur.

FIG. 5C shows an example of the light quantity distribution when the relationship between the pitch P between adjacent beam spots and the beam diameter D is set to P=0.6D. Even in this case,
By selectively using a high-contrast photosensitive film, scanning line cracks will not occur.

As shown in FIG. 6a, the beam combiner 10 receives the recording beam arrays B ₇ and B ₈ from two directions whose angles are not perpendicular to each other, and passes them through the beam reduction optical system 11 to the recording surface. It may also be used to form a serial recording beam spot array _B12 .

In addition, although Figures 2 and 6a use a cube-type beam splitter as a beam combining means, a plane-type beam splitter using a half mirror or a pellicle-type beam splitter can also be used. I can do it.

In addition, as the above-mentioned beam combining means, in particular,
When a polarizing type beam splitter is used, the energy loss of the laser beam can be minimized. A polarizing beam splitter is a dielectric polarizing film coated on an inclined surface. When a P-polarized laser beam is incident on this inclined surface, approximately 98% of it is transmitted, and an S-polarized laser beam is incident. Approximately 98% of the light is reflected. Therefore, in the apparatus shown in FIG. 1, a polarizing beam splitter is used as the beam combiner 10, and the positions of the laser light sources 2 and 3 in the rotational direction are adjusted, or a half-wave plate or the like is used. recording beam array B ₇ is set to P deflection, and recording beam array B ₈ is set to S polarization.
By entering the beam combiner 10 in a polarized state, the energy loss of the laser light sources 2 and 3 can be reduced to a very small amount.

Furthermore, without using the beam combiner 10, the sixth
As shown in Figure b, an optical system having a mirror _M7 may be used as beam combining means to form a serial recording beam spot array _B12 .

FIG. 7 is a diagram corresponding to FIG. 1 showing another embodiment of the present invention. This alternative embodiment device includes, in place of the laser light sources 2 and 3 and the multiple beam splitters 5 and 6 in FIG.
Array semiconductor laser 1 having a plurality of emission ends
This device differs from the previous embodiment in that the mirrors M 2 and 13 are used and that the mirror M ₀ is provided to be finely adjustable in the direction of arrow E. Further, as is well known, since the semiconductor laser element itself has a modulation function, the multi-channel optical modulators 7 and 8 shown in FIG. 1 can be omitted in this alternative embodiment. Note that 14 is a collimator lens.

In addition, in this other embodiment device, the mirror M ₀
One recording beam array B ₇ which is orthogonally reversed at 1 and is incident on the beam combiner 10 remains aligned with the other recording beam array B ₈ by moving and adjusting the mirror M ₀ by the required pitch P in the E direction. They are mutually shifted by the required pitch P.

Note that the present invention is not limited to the above embodiments, and can be implemented with various modifications.

Further, although the above-mentioned embodiments relate to an apparatus in which a photosensitive film as a recording medium is mounted on a recording cylinder and recording is performed on the photosensitive film, the same applies to an apparatus using a photosensitive drum as a recording medium. It can be applied to

Further, in the above embodiment, the present invention is applied to a rotating cylinder type image recording apparatus that performs scanning exposure by rotating a recording cylinder. As described in the publication, the present invention can also be applied to a flying spot type image recording apparatus that uses a rotating polygon mirror, a galvano mirror, etc., and causes a laser beam to travel back and forth on a recording medium.

(Effects of the Invention) According to the present invention, since adjacent beam spots are partially overlapped with each other without causing interference, and the recording beam spot array is arranged in a direction perpendicular to the scanning direction, images due to mutual interference of the beam spots can be It is possible to prevent scanning line cracks while avoiding deterioration in quality. Furthermore, even when a soft-tone photosensitive film with a low γ value, such as a half-tone film, is used, scanning line cracks are less likely to occur. Moreover, it is only necessary to output the image signals of each recording beam at the same time.
It is possible to eliminate the delay circuit that controls the output timing of each recording beam as in the conventional example.

Further, even in the case of a cylindrical recording surface, it is possible to eliminate the disadvantage that the shape of the irradiated surface of each beam spot is deformed as in the conventional example.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an outline of an embodiment of the device according to the present invention, FIG. 2 is a side view of the main parts thereof, FIG. 3 is a layout diagram of beam spot rows, and FIGS. 4 and 5 are beam spot views. 6a and 6b are views corresponding to FIG. 2 showing another embodiment of the means for combining beams, and FIG. 7 is a diagram showing another embodiment of the beam combining means, and FIG. FIG. 1 is a view corresponding to the embodiment of the apparatus, FIG. 8 is a perspective view of a laser plotter, and FIG. 9 is a perspective view of a laser plotter.
This figure is a light intensity distribution diagram of a laser light beam, and FIG. 10 is a perspective view illustrating a projection mode of a beam spot when a recording beam array is irradiated onto a cylindrical recording surface. 2, 3... Laser light source, 5, 6... Multiple beam splitter, 7, 8... Multi-channel optical modulator, 1
0... Beam combiner, 11... Beam reduction optical system, 12, 13... Array semiconductor laser, A...
...Main scanning direction, B...Sub-scanning direction, _B7 , _B8 ...
Recording beam array, B ₁₂ ...Recording beam spot array,
B _a , B _b ...Beam spot rows of each group, a, b...
...beam spot.

Claims (1)

[Claims] 1. A plurality of laser beams are projected in series onto an image recording surface to form a series recording beam spot row, and the series recording beam spot row is made to intersect with the direction of the spot row. In a laser exposure method for an image scanning recording apparatus that performs exposure recording on a recording medium by relative scanning in a direction, the above-mentioned serial recording beam spot row is constituted by two groups of beam spot rows, and each beam spot row of these two groups is formed by two groups of recording beam arrays in which laser light beams from different laser light sources are aligned in series at the same pitch, and the beam spot arrays of the two groups are arranged in a direction perpendicular to the scanning direction, and The beam spots of one group are aligned so that each beam spot of the beam spot row of the other group is located midway between the beam spots of the beam spot row of the other group, and the beam spots of one group and the beam spots of the other group are mutually aligned. A laser exposure method for an image scanning and recording apparatus, characterized in that the serial recording beam spot array is constructed by partially overlapping the recording beam spots. 2. A laser exposure method for an image scanning and recording apparatus according to claim 1, wherein the pitch P between the beam spots of the recording beam spot array is set to 0.5 to 0.6 times the beam spot diameter D.