JP2685359B2 - Light beam scanning device and light beam scanning method - 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 provided with an acousto-optical element for diffracting an incident light beam in a direction corresponding to the frequency of an input signal and emitting the power with a power corresponding to the amplitude of the signal. The present invention relates to a scanning device and a light beam scanning method for recording an image using the acousto-optic device.

[0002]

2. Description of the Related Art Conventionally, there has been proposed an optical beam scanning apparatus capable of reading or recording stably and at high speed by forming a plurality of laser beams by using an optical modulator having a multi-frequency acousto-optic device (AOM). (JP-B-63-5741, JP-A-54-5455, JP-A-57-41618, JP-B-53-98)
No. 56, etc.).

In a light beam scanning device such as a laser beam recording device for recording an image using such a multi-frequency acousto-optic device, a plurality of oscillators for respectively outputting signals of different frequencies are connected to each of the output ends of the oscillators. And a plurality of amplitude controllers for controlling the amplitude of the signal output from the oscillator, and a mixing means for mixing each of the signals output from the plurality of amplitude controllers and inputting them to the acousto-optic element. I have it. When the plurality of signals are input in a state where the laser beam is incident on the acousto-optic element, the laser beam is diffracted by an acousto-optic effect, and the same number of laser beams as the number of the signals from the acousto-optic element are diffracted. Be injected. The diffraction angle of each emitted laser beam depends on the frequency of the signal, and the power of each laser beam depends on the amplitude of the signal. In a laser beam recording apparatus, the plurality of laser beams are simultaneously irradiated on a photosensitive surface of a photosensitive material via a scanning optical system and a recording optical system.

The scanning optical system is composed of a rotary polygon mirror (polygon mirror) and a galvano mirror. The plurality of laser beams incident on the scanning optical system are simultaneously deflected in the main scanning direction by being reflected by the reflecting surface of the polygon mirror rotating at a high speed, and further rotated at a predetermined speed. By being reflected by the galvanometer mirror, the light is deflected in the sub-scanning direction and an image is formed on a two-dimensional plane.

Further, the recording optical system includes a plurality of lenses having different magnifications, and one of the plurality of lenses is arranged on the optical path of the laser beam. The plurality of laser beams that have passed through the scanning optical system pass through the lens arranged on the optical path in the recording optical system and then are irradiated onto the photosensitive surface, so that an image of a predetermined size is formed on the photosensitive surface. By changing the lens through which the laser beam passes in the recording optical system, the size of the image formed on the photosensitive surface, that is, the image recording density is changed. Further, in order to keep the exposure amount per unit area of the photosensitive surface constant, when recording an image with a high recording density on the photosensitive surface for recording an image, that is, by arranging a lens with a high reduction ratio in the optical path, Is recorded, the amplitude of the signal input to the acousto-optic device is reduced. As a result, the power of the laser beam emitted from the acousto-optic element is suppressed, and overexposure of the photosensitive material is prevented.

[0006]

However, as is well known, the acousto-optic element is slightly scattered from the incident laser beam even if no signal is input,
The so-called flare is emitted. This flare is caused by uneven density of a medium such as glass (crystal striae) through which a laser beam passes, an antireflection film formed on the surface of glass, so-called uneven multi-layer film thickness, or adhesion on the surface of glass. It is generated by dust and the like. A part of this flare is irradiated onto the photosensitive surface via the scanning optical system and the recording optical system. As a result, the non-image portion of the photosensitive surface and the portion of the image that is not irradiated with the laser beam are slightly exposed by flare, and the image quality is degraded.

In particular, when an image is recorded on the photosensitive surface with a high recording density, the amplitude of the signal input to the acousto-optical element is reduced as described above to suppress the power of the laser beam emitted from the acousto-optical element. Therefore, the ratio of the power of the laser beam emitted when a signal is input to the acousto-optic element and the power of the flare when a signal is not input to the acousto-optic element, that is, the so-called extinction ratio decreases. Therefore, the difference between the exposure amount of the portion of the image that is irradiated with the laser beam and the exposure amount of the flare of the non-image portion of the photosensitive surface and the portion of the image that is not irradiated with the laser beam is small, and the image quality is reduced. Markedly reduced. As described above, in a light beam scanning device such as a laser beam recording device, especially when performing processing while suppressing the power of the light beam, the processing quality deteriorates as the extinction ratio decreases.

The present invention has been made in view of the above facts, and an object thereof is to obtain a light beam scanning device capable of improving processing quality.

Another object of the present invention is to provide a light beam scanning method capable of improving the quality of an image recorded on a photosensitive material.

[0010]

According to a first aspect of the present invention, an acousto-optic device which diffracts an incident light beam in a direction according to the frequency of an input signal and emits the beam with a power according to the amplitude of the signal. An element, an input means for inputting a signal whose amplitude is equal to or larger than a predetermined value to the acousto-optic element, and an attenuating means arranged on the light beam emission side of the acousto-optic element for attenuating the power of light emitted from the acousto-optic element, have.

According to a second aspect of the present invention, an acousto-optical element for diffracting an incident light beam in a direction according to the frequency of an input signal and emitting the power with a power according to the amplitude of the signal, and the signal are described above. Input means for inputting into the acousto-optic element,
Attenuator movable between a first position for attenuating the power of the light emitted from the acousto-optic element and a second position retracted from the first position, and the attenuating unit according to scanning conditions. Moving means for moving the means, and control means for controlling the input means so that the amplitude of the signal becomes equal to or more than a predetermined value according to the scanning condition when the damping means is located at the first position, have.

According to a third aspect of the present invention, the light emitted from the acousto-optical element which diffracts the incident light beam in the direction corresponding to the frequency of the input signal and emits the light with a power corresponding to the amplitude of the signal. When an image is recorded by scanning with a beam so that the exposure amount per unit area of the photosensitive material becomes a predetermined value, the amplitude of the signal input to the acousto-optical element is increased and then emitted from the acousto-optical element. The light power is attenuated or the scanning speed is increased so that the exposure amount reaches the predetermined value.

[0013]

According to the first aspect of the present invention, since a signal having an amplitude of a predetermined value or more is input to the acousto-optical element, the power of the light beam emitted when the signal is input to the acousto-optical element becomes larger than that of the conventional one. . On the other hand, the power of scattered light emitted when no signal is input to the acousto-optic element, so-called flare power, depends on the power of the light beam incident on the acousto-optic element, and does not change even if the amplitude of the signal is increased. Therefore, the ratio of the power of the light beam emitted from the acousto-optic element and the power of the flare emitted from the acousto-optic element, that is, the so-called extinction ratio is improved. The power of the light beam emitted from the acousto-optic device is attenuated by the attenuator and adjusted to a power suitable for processing. Further, the power of flare emitted from the acousto-optic element is also attenuated by the attenuator, so that the power ratio between the light beam and the flare is maintained. Thereby, for example, in a light beam processing apparatus for recording an image on a photosensitive material, it is possible to suppress the exposure amount due to flare in the non-image portion of the photosensitive surface and the portion of the image which is not irradiated with the laser beam, and the image quality is improved. As described above, according to the first aspect of the invention, the extinction ratio can be improved, and the processing quality of the light beam scanning device can be improved.

According to a second aspect of the invention, the attenuating means is movable between a first position for attenuating the power of the light emitted from the acousto-optic element and a second position retracted from the first position. Then, the attenuating means is moved according to the scanning condition, and the amplitude of the signal is controlled to be a predetermined value or more according to the scanning condition when the attenuating means is located at the first position. Thus, for example, when processing is performed while suppressing the power of the light beam, which has been a problem in the related art, by moving the attenuator to the first position and controlling the amplitude of the signal to be a predetermined value or more, The extinction ratio can be improved, and the processing quality of the light beam scanning device can be improved. Further, when high processing quality is required, for example, in a light beam processing apparatus for recording an image on a photosensitive material, a fine mode for recording an image clearly is provided, and when this is selected, the control is performed as described above. May be. As described above, in the invention according to the second aspect, it is possible to selectively improve the processing quality as needed.

According to the third aspect of the present invention, in recording an image so that the exposure amount per unit area of the photosensitive material becomes a predetermined value, the amplitude of the signal input to the acousto-optic element is increased and then the acousto-optic element. The power of light emitted from the element is attenuated or the scanning speed is increased so that the exposure amount becomes the predetermined value. By increasing the amplitude of the signal input to the acousto-optic element, the power of the light beam emitted from the acousto-optic element increases. On the other hand, the flare power emitted from the acousto-optic element does not change even if the amplitude of the signal is increased. Therefore, the ratio between the power of the light beam output from the acousto-optic device and the power of flare, that is, the so-called extinction ratio is improved. Further, since the light emitted from the acousto-optic device, that is, the power of the light beam and flare is attenuated or the scanning speed is increased, the exposure amount per unit area of the photosensitive material is adjusted and the light beam is The ratio between the power of the flare and the power of the flare is maintained. Therefore, the quality of the image recorded on the photosensitive material can be improved.

An ND filter or the like can be used as the attenuating means for attenuating the power of the light.

[0017]

Embodiments of the present invention will be described below in detail with reference to the drawings. The present invention is not limited to the numerical values described in this embodiment.

FIG. 2 shows a laser beam scanning device 10 according to this embodiment. Laser beam scanning device 10
Is equipped with a base platen 11, and a He-Ne laser 1 connected to a power source (not shown) on the upper surface of the base platen 11.
2 are provided. In addition, this He-Ne laser 12
Instead of this, another gas laser, a semiconductor laser, or the like may be used. An AOM entrance lens 14 and a reflection mirror 16 are sequentially arranged on the laser beam emission side of the He-Ne laser 12. The laser beam emitted from the He-Ne laser 12 is reflected by the reflection mirror 1 via the AOM incidence lens 14.
6 and is reflected in a direction parallel to the upper surface of the base surface plate 11 and substantially orthogonal to the optical axis direction.

An AOM (acousto-optic light modulator) 18, an AOM emitting lens 20, a reflecting mirror 22 and a relay lens 24 are arranged in this order on the laser beam emitting side of the reflecting mirror 16. As shown in FIG. 1, the AOM 18 includes an acousto-optic medium 21 that produces an acousto-optic effect. A transducer 17 that outputs ultrasonic waves according to the input high-frequency signal and a sound absorber 19 that absorbs the ultrasonic waves that have propagated through the acousto-optic medium 21 are attached to the opposing surfaces of the acousto-optic medium 21. The transducer 17 is connected to an AOM driver 84 that drives the AOM. This AOM
The driver 84 will be described later. In this embodiment,
Eight laser beams are emitted as diffracted light from the laser beam incident on the AOM 18. The laser beam emitted from the AOM 18 is emitted to the reflection mirror 22 via the AOM emission lens 20, is reflected in a direction substantially parallel to the upper surface of the base surface plate 11 and substantially orthogonal to the optical axis direction, and is emitted to the relay lens 24. To be done.

A shutter (not shown) is provided between the AOM exit lens 20 and the reflection mirror 22. This shutter is, for example, from the end of recording of one frame to the start of recording of another frame, or from the end of recording on one fish to the start of recording on another fish, etc. Is moved so as to block the laser beam during non-recording. A photoelectric converter 80 (see FIG. 1) is attached to the surface of the shutter on the laser beam incident side. The photoelectric converter 80 is connected to the signal generating circuit 82, and outputs a voltage having a magnitude corresponding to the power of the laser beam received when the image is not recorded to the signal generating circuit 82. The signal generating circuit 82 will be described later.

As shown in FIG. 2, on the laser beam emitting side of the relay lens 24, a reflecting mirror 26, a first cylindrical lens 28, and a combining prism 30 are sequentially arranged. The laser beam emitted from the relay lens 24 is reflected by the reflection mirror 26 at a substantially right angle in a direction substantially orthogonal to the upper surface of the base surface plate 11, and is applied to the multiplexing prism 30 via the first cylindrical lens 28. On the other hand, a semiconductor laser 56 is arranged on the upper surface of the base platen 11, and the laser beam for synchronized light emitted from the semiconductor laser 56 is applied to the combining prism 30 via a collimator lens 58. The multiplexing prism 30 reflects the recording laser beam emitted from the first cylindrical lens 30 in a direction substantially parallel to the upper surface of the base surface plate 11 and substantially orthogonal to the optical axis direction, and is synchronized with the recording laser beam. Combine with the laser beam for light.

A reflecting mirror 32 and a polygon mirror 34 are sequentially arranged on the laser beam emitting side of the combining prism 30. The reflection mirror 32 reflects the laser beam emitted from the combining prism 30 in a direction inclined by about 45 ° from the optical axis direction so that the laser beam is incident on the polygon mirror 34.
A polygon mirror driver (not shown) that rotates the polygon mirror 34 at high speed is attached to the polygon mirror 34. The laser beam emitted from the reflection mirror 32 is deflected by the polygon mirror 34 in the main scanning direction, The scanning lens 36 arranged on the reflection side of the mirror 34 is irradiated.

On the laser beam emission side of the scanning lens 36, a synchronous light demultiplexing prism 38 and a second cylindrical lens 4 are provided.
2. The long mirror 44 is arranged in order, and the linear encoder 40 and the photoelectric converter 60 are arranged on the reflection side of the synchronous light demultiplexing prism 40. The laser beam emitted from the scanning lens 36 reflects the laser beam for synchronous light at the synchronous light branching prism 38, and the reflected laser beam for synchronous light is applied to the linear encoder 40. The linear encoder 40 is composed of a flat plate in which a plurality of transparent portions and opaque portions are alternately arranged in the main scanning direction at a constant pitch in a striped pattern. The synchronizing laser beam deflected in the main scanning direction by the polygon mirror 34 scans the linear encoder 40 in the main scanning direction via the synchronizing light demultiplexing prism 38. At this time, the synchronization laser beam transmitted through the transparent portion is detected by the photoelectric converter 60, and the photoelectric converter 60 outputs a pulse signal according to the scanning. The pulse signal from the photoelectric converter 60 is input to a galvanometer mirror driver (not shown) that controls the angle of the galvanometer mirror 48. On the other hand, the recording laser beam that has passed through the synchronous light demultiplexing prism 38 is applied to the elongated mirror 44 via the second cylindrical lens 42. The laser beam emitted from the second cylindrical lens 42 is reflected by the elongated mirror 44 in a direction substantially parallel to the upper surface of the base surface plate 11 and substantially orthogonal to the optical axis direction.

A relay lens 46 and a galvanometer mirror 48 are sequentially arranged on the laser beam reflecting side of the elongated mirror 44. The laser beam emitted from the relay lens 46 is deflected in the sub-scanning direction by the galvano mirror 48 and is reflected in the direction orthogonal to the upper surface of the base surface plate 11. Turret 5 on the reflective side of the galvano mirror 48
2. A photosensitive material 54 such as a microfilm is arranged in order. As the photosensitive material 54, a silver salt film, for example, a COM film NR or HR-II (both manufactured by Fuji Photo Film Co., Ltd., trade name) can be used. The turret 52 has five recording lenses 50A, 50B, 50
C, 50D and 50E are attached. Recording lens 5
0A is a reduction ratio of 1/48, and other recording lens 50
For B, 50C, 50D, and 50E, 1/4 in order
The reduction ratios are 2, 1/32, 1/27, and 1/24. In addition, the recording lens 50A with the highest reduction ratio has N
The D filter 51 is attached. ND filter 51
Constitutes an attenuating means for attenuating the power of the passing light to about 1/10.

A turret driver 53 (see FIG. 1) is attached to the turret 52. The turret 52 is rotated by a turret driver 53, and any one of the five recording lenses 50 is a galvano mirror 48.
And the photosensitive material 54. As shown in FIG. 1, the turret driver 53 is connected to a host computer 88 described later. A keyboard 90 for designating the reduction ratio and the like is connected to the host computer 88. The host computer 88 has a keyboard 90.
The operation of the turret driver 53 is controlled so that the recording lens of the reduction magnification designated through is inserted between the galvano mirror 48 and the photosensitive material 54. As shown in FIG. 1, the laser beam reflected by the galvanometer mirror 48 is applied to the photosensitive material 54 via any of the recording lenses, and the photosensitive material 54 is exposed. The photosensitive material 54 is wound in layers on a reel (not shown).

On the other hand, as shown in FIG.
A host computer 88 is connected to 2. The host computer 88 outputs a signal indicating the amplitude value of the signal input to the acoustooptic device 18 to the signal generation circuit 82. The signal generating circuit 82 sets the amplitude value instructed by the host computer 88, and adjusts the set amplitude value based on the signal input from the photoelectric converter 80 during non-recording. The signal generation circuit 82 is connected to the AOM driver 84 and outputs an analog signal corresponding to the set amplitude value to the AOM driver 84.
Output to the OM driver 84.

A control circuit 86 is connected to the AOM driver 84, and the host computer 8 is connected to the control circuit 86.
8 are connected. The host computer 88 outputs the image data to be recorded on the photosensitive material 54 to the control circuit 86. This image data is given as an 8-bit parallel signal. The control circuit 22 temporarily stores the image data, and outputs an analog signal according to the number of input 8-bit image data to the AOM driver 84. The 8-bit image data is also output to the AOM driver 84.

The AOM driver 84, as shown in FIG.
Oscillation circuits 62A, 62B, 62C, 62D, 62E, 62F, 6 for generating signals having frequencies f1 to f8, respectively.
2G, 62H, local level control circuits 64A, 64
B, 64C, 64D, 64E, 64F, 64G, 64
H, switch circuits 66A, 66B, 66C, 66D, 6
6E, 66F, 66G, 66H are provided. Each of the local level control circuits 64A to 64H has an oscillation circuit 62A.
The switch circuit 66 is connected to the output terminals of the local level control circuits 64A to 64H.
A to 66H are connected to each other. Further, each of the level control terminals of the local level control circuits 64A to 64H is connected to the signal generating circuit 82, and the analog signal corresponding to the magnitude of the amplitude is input. The local level control circuit controls the amplitude of the signal output from each oscillating circuit so that it has a magnitude corresponding to the input analog signal. A double balanced mixer or a pin diode attenuator can be used as the local level control circuit. In addition, the switch circuit 6
Each of the control terminals 6A to 66H is connected to the control circuit 86, and any one bit of the 8-bit image data output from the control circuit 86 is input. Each switch circuit passes a signal when the input 1-bit data is on, and cuts off the signal when it is off.

Each output terminal of the switch circuits 66A and 66B has a combiner 6 for mixing two signals at a ratio of 1: 1.
8AB are connected to the input terminals. Similarly, each output terminal of the switch circuits 66C and 66D is connected to a combiner 68CD.
The output terminals of the switch circuits 66E and 66F are connected to the input terminals of the combiner 68EF, and the output terminals of the switch circuits 66G and 66H are connected to the combiner 68G.
It is connected to the input terminal of H.

The output terminal of the combiner 68AB is connected to the amplifier circuit 72AB via the total level control circuit 70AB. Similarly, the output terminal of the combiner 68CD is connected to the amplifier 72C via the total level control circuit 70CD.
D, the output terminal of the combiner 68EF is connected to the amplifier circuit 72EF via the total level control circuit 70EF, and the output terminal of the combiner 68GH is connected to the amplifier circuit 72GH via the total level control circuit 70GH. The total level control circuit is composed of a double balanced mixer and a pin diode attenuator like the local level control circuit. Each level control terminal of the total level control circuit is connected to the control circuit 86, and an analog signal corresponding to the number of ON of the above-mentioned image data is input. The total level control circuit adjusts the level of the signal according to the number of image data turned on. The output terminals of the amplifier circuits 72AB and 72CD are connected to the input terminal of the combiner 74, and the output terminals of the amplifier circuits 72EF and 72GH are connected to the input terminal of the combiner 76. The output terminals of the combiners 74 and 76 are connected to the combiner 78,
The output end of the combiner 78 is connected to the transducer 17.

Next, the operation of this embodiment will be described with reference to the flowchart of FIG. The flowchart of FIG. 4 shows that when the laser beam scanning device 10 is powered on,
It is executed by the host computer 88.

In step 100, it is determined whether or not to start recording an image. When recording an image, the operator gives an instruction to start the operation after instructing the reduction ratio of the recording lens 50 via the keyboard 90. If the determination in step 100 is affirmative, in step 102 the recording lens 50 of the designated reduction magnification is set to the galvano mirror 48 and the photosensitive material 5.
The operation of the turret driver 53 is controlled so that the turret driver 53 can be inserted between the turret driver 4 and the driver 4. When the reduction magnification of 1/48 is designated, the recording lens 50 having the reduction magnification of 1/48
The ND filter 51 is inserted together with A.

In step 104, the data representing the correspondence between the reduction ratio and the amplitude value stored in the memory (not shown) is read. In the present laser beam scanning device 10, the photosensitive material 5
The power of the laser beam to irradiate 4 is the recording density of the image,
That is, it is changed according to the reduction magnification of the recording lens 50 used. For example, the writing power of the laser beam when recording an image at a reduction ratio of 1/24 is set to 40 μW,
The exposure amount of the photosensitive material 54 is adjusted by setting the writing power of the laser beam when recording an image at a reduction ratio of 1/48 to 10 μW. The memory stores the amplitude value of the signal input to the acousto-optic element 18 in order to obtain the laser beam of the above power in association with the reduction ratio of the recording lens, and in this step, corresponds to the specified reduction ratio. Read the amplitude value.

At the next step 106, it is determined whether or not the reduction ratio corresponding to the designated reduction ratio is large. For example, in this embodiment, the determination in step 106 is affirmative when the reduction ratio of 1/48 is designated. If the determination in step 106 is affirmative, the amplitude value read from the memory is multiplied by 10 in step 108 and the process proceeds to step 110. When the determination in step 106 is negative, the process proceeds to step 110 without executing step 108. In step 110, a signal indicating the amplitude value is output to the signal generating circuit 82.

In the next step 112, the photosensitive material 54 is positioned at the exposure position. In step 114, the amplitude of the signal input to the acousto-optic element 18 is adjusted. That is, the He-Ne laser emits a laser beam with the shutter closed and outputs a signal for turning on only one of the eight switch circuits 66 of the AOM driver 84. Further, the signal generation circuit 82 applies a voltage corresponding to the input amplitude value to the control end of the local level control circuit 64. As a result, one laser beam is emitted from the acousto-optic device 18 as diffracted light and is incident on the photoelectric converter 80 attached to the shutter. In the signal generating circuit 82, the power of the laser beam obtained by the photoelectric converter 80 is compared with a preset reference value, and if they are equal, the voltage value is applied without being changed. When the power of the laser beam and the reference value are different, a voltage having a value obtained by adding a deviation to the value of the voltage is applied. As a result, the amplitude of the signal input to the acousto-optic element 18 is changed so that the power of the laser beam becomes equal to the reference value. Such amplitude adjustment is performed on all eight laser beams emitted from the acousto-optic element 18 as diffracted light.

In step 116, an image of one area is recorded on the photosensitive material 54. That is, the control circuit 8 moves the shutter in the opening direction, and the image data corresponding to the case where the image to be recorded is raster-scanned with a width of 8 pixels in units of 8 bits.
Output to 6. The control circuit 86 inputs the image data to the control terminals of the switch circuits 66A to 66H, and inputs a signal according to the number of ON of the image data to each of the control terminals of the total level control circuits 70AB to 70GH.

The signals output from the oscillation circuits 62A to 62H of the AOM driver 84 are input to the switch circuits 66A to 66H after their amplitudes are adjusted by the local level control circuits 64A to 64H. When recording an image at a reduction ratio of 1/48, the local level control circuit sets the signal amplitude to 10 times the amplitude corresponding to the normal write power (10 μW) according to the signal input from the signal generation circuit 82. Adjust to the amplitude. Each switch circuit is turned on / off according to the image data input to the control terminal, and passes or blocks the input signal. The signals passed through the switch circuit are mixed by the combiners 68AB to 68GH, and then the total level control circuit 70
Input to AB to 70GH. The total level control circuit controls the signal amplitude according to the signal input to the control end. As a result, the power of each laser beam emitted from the acousto-optic element 18 becomes constant regardless of the number of signal ONs, and uneven image density due to the number of image data ONs is prevented. Total level control circuits 70AB to 7
The signals output from 0GH are amplified by the amplifier circuits 72AB to 72AB.
Combiner 74, 76 and combiner 7 via 2GH
Finally mixed at 8 and fed to transducer 17 of AOM 18.

The transducer 17 converts the input signal into an ultrasonic signal corresponding to the frequency and amplitude of the input signal. This ultrasonic signal propagates through the acousto-optic medium 21 and is absorbed by the sound absorber 19. As a result, when the acousto-optic effect acts on the laser beam incident on the acousto-optic element 18 and passes through the acousto-optic medium 21, diffraction occurs,
A laser beam corresponding to the ultrasonic signal is emitted as diffracted light. The number of laser beams emitted as this diffracted light is the same as the number of signals that have passed through the switch circuit, and each laser beam is emitted with a power according to the amplitude of the passed signal and in a direction according to frequency. It Further, when the set reduction ratio is 1/48, a laser beam having a power 10 times the normal power is emitted as described above.
The laser beam emitted from the acousto-optic element 18 is deflected in the main scanning direction by the polygon mirror 28, is deflected in the sub scanning direction by the galvanometer mirror 36, and is then irradiated onto the photosensitive material 54 via the recording lens 50.

Here, when the designated reduction magnification is 1/48, the ND together with the recording lens 50A having the reduction magnification of 1/48 is provided on the optical path of the laser beam between the galvano mirror 48 and the photosensitive material 54. The filter 51 is inserted.
Therefore, the laser beam emitted from the acousto-optic device 18 with a power 10 times higher than usual is attenuated to a power of about 1/10 by the ND filter 51, and is irradiated onto the photosensitive material 54 with normal writing power (for example, 10 μW). To be done. Further, the power of flare emitted from the acousto-optic element 18 and applied to the photosensitive material 54 is also attenuated to about 1/10 by the ND filter 51. Therefore, when the reduction ratio is 1/48, the ratio between the power of the laser beam and the flare power applied to the photosensitive material 54 is improved by about 10 times.

For example, when a laser beam having a constant power is incident on the acousto-optic element 18, the photosensitive material is irradiated with a flare power of 1 μW and a reduction ratio of 1/48. When the writing power of the laser beam is 5 μW, the conventional extinction ratio is “5”. However, in this embodiment, the power of the flare applied to the photosensitive material 54 by the ND filter 51 is 0.1.
The laser beam emitted from the acousto-optic element 18 after being attenuated to μW is emitted at a power of 10 times and then attenuated to 5 μW by the ND filter 51 and applied to the photosensitive material 54, so that the photosensitive material 54 is irradiated. The power ratio between the laser beam and flare is “50”, and the photosensitive material 5
4 improves the quality of the image recorded.

When the recording of one image has been completed as described above, it is determined in step 118 whether the recording of the image is completed. If it is judged that the recording of the image is not completed, step 112 is executed. Returning to step 118, steps 112 to 118 are repeated until the determination at step 118 is affirmative. If the determination in step 118 is affirmative, the process returns to step 100.

As described above, in the present embodiment, the acousto-optical element 1 is used when an image is recorded on the photosensitive material 54 with a large reduction ratio.
Since the amplitude of the signal input to 8 is approximately 10 times and the ND filter 51 that attenuates the power of light to 1/10 is inserted in the optical path of the laser beam, the laser beam that irradiates the photosensitive material 54 And the flare ratio can be improved, and the quality of the image recorded on the photosensitive material 54 can be improved.

Although an example in which an acousto-optic element is used as the optical modulator has been described above, an optical waveguide type modulator may be used. Further, in this embodiment, ND is used as the damping means.
Although the filter 51 is used, for example, a recording lens may be multi-layer coated to act as an attenuator that attenuates the light emitted from the acousto-optic element 18.

Further, in this embodiment, the ND filter 51 is attached only to the recording lens 50A having the highest reduction ratio, but all the recording lenses 50 attached to the turret 52 are attached.
Alternatively, an ND filter or a glass plate having a light transmittance of 100% may be attached to prevent dust and the like from adhering to the recording lens 50. Further, ND filters having different light transmittances, that is, different attenuation factors are attached to all recording lenses 50, and the amplitude of the signal input to the acousto-optic element 18 is changed for each recording lens 50 according to the attenuation factor. Good.

Further, in the present embodiment, the power of the laser beam and the flare applied to the photosensitive material 54 is attenuated by the ND filter 51 to adjust the exposure amount per unit area of the photosensitive material 54. The exposure amount per unit area of the photosensitive material may be adjusted by controlling the operation of the galvanometer mirror 48 to increase the main scanning and sub-scanning speeds.

Further, in the present embodiment, the present invention is applied only when an image is recorded on the photosensitive material 54 at a high reduction rate, but the present invention is also applied when an image is recorded at a low reduction rate. Good. Further, although the amplitude of the signal input to the acousto-optic element 18 is changed according to the designated reduction ratio in the present embodiment, the present invention is not limited to this.
For example, you may change according to the kind of photosensitive material. Further, as the image writing mode, the laser beam scanning device 10 is provided with a normal mode for recording an image with standard definition, a fine mode for recording an image more clearly by reducing the size of one pixel, and the like. The writing pitch (the size of one pixel), the writing power, the ratio of the power of the laser beam to the flare, and the like may be changed according to the selected mode.

Although the laser beam scanning device 10 for recording an image using a laser beam has been described in the present embodiment, a light beam scanning device for recording an image by using light from an LED as a light beam, or another light source. It can be applied to a light beam scanning device for recording an image by using. Also,
Although the laser beam scanning device 10 that records an image as the light beam scanning device has been described above, the present invention is not limited to this, and a light beam scanning device that performs processing such as reading using the light beam is described. It can be applied to improve the processing quality.

[0048]

According to the first aspect of the invention, since the acousto-optical element is supplied with a signal whose amplitude is equal to or larger than a predetermined value and the attenuating means for attenuating the power of the light emitted from the acousto-optical element is provided, The excellent effect that the processing quality of the beam processing apparatus can be improved is obtained.

According to the second aspect of the invention, the attenuator can be moved between a first position for attenuating the power of the light emitted from the acousto-optic element and a second position retracted from the first position. Then, the attenuating means is moved according to the scanning condition, and when the attenuating means is located at the first position, the amplitude of the signal is controlled to be equal to or more than a predetermined value according to the scanning condition. In addition to this, the excellent effect that the processing quality can be selectively improved as required can be obtained.

In the third aspect of the invention, the power of the light emitted from the acousto-optical element is attenuated after the amplitude of the signal input to the acousto-optical element is increased, or the scanning speed is increased to make the exposure amount predetermined. Since it has a value, it is possible to improve the quality of the image recorded on the photosensitive material.
An excellent effect is obtained.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram showing a control unit of a laser beam scanning device of this embodiment.

FIG. 2 is a schematic perspective view of a laser beam scanning device.

FIG. 3 is a schematic block diagram showing a configuration of an AOM driver.

FIG. 4 is a flowchart illustrating the operation of this embodiment.

[Explanation of symbols]

 10 Laser Beam Scanner 18 Acousto-Optical Element (AOM) 51 ND Filter 82 Signal Generation Circuit 84 AOM Driver 88 Host Computer

Claims (3)

(57) [Claims] 1. An acousto-optic device for diffracting an incident light beam in a direction according to a frequency of an input signal and emitting the power with a power according to the amplitude of the signal, and a signal having an amplitude of a predetermined value or more. A light beam scanning device comprising: input means for inputting to the acousto-optic element; and attenuating means arranged on the light beam emission side of the acousto-optic element for attenuating the power of light emitted from the acousto-optic element. 2. An acousto-optic device for diffracting an incident light beam in a direction according to the frequency of an input signal and emitting the power with a power according to the amplitude of the signal, and the signal is input to the acousto-optic device. The input means, the attenuating means capable of moving between the first position for attenuating the power of the light emitted from the acousto-optic element and the second position retracted from the first position, and the scanning condition In response to the moving means for moving the attenuating means and the attenuating means at the first position, the input means is controlled so that the amplitude of the signal becomes a predetermined value or more according to the scanning condition. A light beam scanning device having a control means. 3. A light beam emitted from an acousto-optic device that diffracts an incident light beam in a direction corresponding to the frequency of an input signal and emits with a power corresponding to the amplitude of the signal to scan the light beam. When recording an image so that the exposure amount per unit area of the material becomes a predetermined value, the power of the light emitted from the acousto-optical element is attenuated after increasing the amplitude of the signal input to the acousto-optical element. Alternatively, a light beam scanning method in which the scanning speed is increased so that the exposure amount becomes the predetermined value.