JPH0547153B2 - - 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.

Further, the light intensity distribution of the laser light beam emitted from the laser light source is not uniform, and has a Gaussian distribution G expressed by the following equation (), as shown in FIG. 10, for example.

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 / e ² radius) 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 divided by 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 a rotating recording cylinder and a cylindrical surface 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-mentioned 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 inconveniences 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 laser light beam from a single laser light source is divided into a plurality of laser light beams, and the plurality of divided laser light beams are projected in series onto an image recording surface to form a series recording beam spot array. In a laser exposure method for an image scanning recording apparatus that performs exposure recording on a recording medium by relatively scanning the serial recording beam spot array in a direction crossing the serial direction, the serial recording beam spot array is arranged in two groups. These two groups of beam spot rows are formed by two groups of recording beam rows in which laser beams are aligned in series at the same pitch and have an optical path difference of more than the coherence distance between them. , the two groups of beam spot rows are arranged in a direction perpendicular to the scanning direction, and each beam spot of one group of beam spot rows is located between each beam spot of the other group of beam spot rows. A laser of an image scanning and recording device characterized in that the above-mentioned serial recording beam spot array is constructed by arranging the recording beam spots of one group and partially overlapping the beam spots of the other group with each other. This is an exposure method.

(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, the above two groups of beam spot arrays are formed by two groups of recording beam arrays having an optical path difference greater than the mutual coherence distance, so that the beam spots of one group and the beam spots of the other group are mutually aligned. There will be no interference even if they overlap.

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 photosensitive film with a low γ value, such as a halftone film, is used, scanning line cracks are less likely to occur according to the present invention.
In other words, by partially overlapping adjacent recording beams with an optical path difference greater than the mutual coherence distance, occurrence of scanning line cracks in the band-shaped scanning lines can be prevented, and
By arranging the beam spot rows in a direction perpendicular to the main scanning direction, it is sufficient to output the image signals of each recording beam simultaneously, 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 apparatus according to an embodiment of the present invention, and FIG. 9 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

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

The basic configuration of this laser exposure apparatus 1 is a laser light source 2, a beam splitter 3, a beam shifter 4, multiple beam splitters 5, 6, multichannel optical modulators 7, 8, a right angle prism 9, and a beam Synthesizer 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 to _{M 3} are mirrors.

The beam splitter 3 splits the laser beam B ₁ from the laser light source 2 into a straight beam B 2 directed toward a straight optical path E and a _{direction-changing beam B 3 directed} toward a detour optical path F. In addition, a plurality of beam splitters 5,
Reference numerals 6 each divide the single beams B ₃ and B ₄ into multiple parallel beams and emit them as parallel beam arrays B ₅ and B ₆ .
For example, JP-A-52-122135 and JP-A-60-
As recorded in Publication No. 19101, a single incident beam is split into multiple parallel beams by using multiple internal reflections of a glass plate with parallel planes, and one plane has a completely reflective surface. The other surface is coated with a coating that changes the transmittance in stages so that the light intensity of each beam of the parallel beam arrays B ₅ and B ₆ emitted from the plane is almost uniform. has been done.

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. Incidentally, the multi-channel acousto-optic modulators 7 and 8 are disclosed in, for example, Japanese Patent Application Laid-Open No. 10742-1983.
As described in Japanese Patent 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 is
B ₇ and B8 are incident from two orthogonal directions, respectively, and the recording beam array B ₁₀ is emitted with the directions aligned as shown in FIG. At this time, the beam arrays are combined so that the beams belonging to the recording beam arrays B ₇ and B ₈ are alternately aligned (that is, the beams belonging to the recording beam arrays B ₇ and B ₈ are successively adjacent to each other).

The recording beam example 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 recording beam arrays B _{7 and} B 7 , which have optical path differences that are greater than the coherence distance, as described later.
Formed by B ₈ .

Also, the beam spot rows B _a and B _b of each group above are as follows:
In the sub-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
They 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.

The beam shifter 4 is composed of _{a transparent} parallel plane plate as shown in FIG. The emitted light beam _B4 is shifted in parallel by a required pitch (here, D/2).

P=t・(1−cosθ ₁ /√ ² − ² ₁ )・sinθ ₁ (However, t and n are the thickness and refractive index of the plane-parallel plate 4, respectively) The actual dimensions of P and D above are determined by the reduction optics. The parts before and after the system 11 differ depending on the reduction ratio, but in this specification, the same reference numerals are given and explained for ease of understanding.

On the other hand, the right angle prism 9 is provided on the detour optical path F, and is used to adjust the optical path difference L between the straight optical path E and the detour optical path F to a required coherence distance or more. Note that the optical path difference L is approximately equal to L ₁ and L ₂ in Figure 1a.
The optical path difference L can be adjusted by moving _the right angle prism 9 in the direction of arrow H. Incidentally, the coherence distance is expressed by the following equation (), and is generally said to be approximately 10 cm for a He-Ne laser and several cm for an Ar laser.

l=C/Δν...() where l is the coherence length, Δν is the laser linewidth, C is the speed of light, and of course, twice _L3 is approximately the optical path difference L,
If the coherence distance is longer than that, the prism 9 may be omitted and the position of the mirror _M1 may be changed to change the beam optical path from F to _B3 , as shown in FIG. 1b.

Therefore, according to the above configuration, interference is eliminated by providing an optical path difference L greater than the coherence distance between the beam spots a and b constituting the recording beam spot array B ₁₂ , and the adjacent beam spots a and b are It becomes possible to overlap each other. This makes it possible to avoid deterioration in image quality due to mutual interference between beam spots a and b, and to prevent scanning line cracks. Furthermore, as in halftone films, γ
Even when using a photosensitive film with a low value and a soft tone, scanning line cracks are less likely to occur. When a strip-shaped scanning line is recorded using the recording beam spot rows _B12 superimposed one-half of the beam diameter D as described above, the light quantity distribution becomes flat as shown by the solid line C in FIG.

FIG. 6C 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. 7a, 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 the beam reduction optical system 1
It may also be used to form a serial recording beam spot array _B12 on the recording surface via the recording beam spot array B12.

In addition, although Figures 2 and 7a 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.

Furthermore, without using the beam combiner 10, the seventh
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 .

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

For example, a plurality of mirrors may be used in place of the right-angle prism 9 to obtain an optical path difference L greater than the coherence distance.

In addition, the plural beam splitters 5 and 6 are shown in FIG.
Instead of placing it in the position shown in Figure 8a, b
It may be arranged between the beam splitter 3 and the laser light source 2 as shown in FIG.

Further, although the above-mentioned embodiments relate to an apparatus in which a photosensitive film is mounted as a recording medium on a recording cylinder and recording is performed on the photosensitive film, it may also be applied to an apparatus using other photosensitive materials as a recording medium. The same applies.

Further, in the above-mentioned embodiment, the present invention is applied to a rotating cylinder type image recording apparatus that performs scanning exposure by rotating a recording cylinder, but the present invention is applied to, for example, Japanese Patent Application Laid-Open No. 56-67277. As described in , 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]

1a and 1b are respectively perspective views showing an overview 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 FIG. 4 is an explanatory diagram of the action of the beam shifter, FIGS. 5 and 6 are diagrams showing the light amount distribution of strip-shaped scanning lines with different pitches between beams, and FIGS.
Figure b is a view corresponding to Figure 2 showing another embodiment of the means for combining beams, Figures 8a and 8b are perspective views showing an outline of another embodiment of the device, and Figure 9 is a perspective view of a laser plotter. 10 is a light intensity distribution diagram of a laser beam, and FIG. 11 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... Laser light source, 3... Beam splitter, 4...
...beam shifter, 5,6...multiple beam splitter,
7, 8...Multi-channel optical modulator, 9...Right angle prism, 10...Beam combiner, 11...Beam reduction optical system, A...Main scanning direction, B...Sub-scanning direction, _B7 , B ₈ ... Recording beam array, B ₁₂ ... Recording beam spot row, B _a , B _b ... Beam spot rows of each group, a, b... Beam spots.

Claims (1)

[Claims] 1 A laser beam from a single laser light source is divided into a plurality of laser beams, and the plurality of divided laser beams are projected in series on an image recording surface to form a serial recording beam. In a laser exposure method for an image scanning recording apparatus that forms a spot row and performs exposure recording on a recording medium by relatively scanning the serial recording beam spot row in a direction crossing the spot row direction, the above-mentioned serial recording is performed. The beam spot array is composed of two groups of beam spot arrays, and these two groups of beam spot arrays are composed of two groups of laser light beams arranged in series at the same pitch with an optical path difference greater than the coherence distance between them. The recording beam is formed by a recording beam array, and the beam spot arrays of the two groups 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 each beam spot of the beam spot array of the other group. The recording beam spots are arranged so that they are located in the middle of the recording beam spots, and the beam spots of one group and the beam spots of the other group are partially overlapped with each other to form the serial recording beam spot array. Laser exposure method for image scanning recording device. 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.