JPH03132715A - Light beam scanner - Google Patents

Abstract

PURPOSE:To apply a small-sized detector by detecting pulse light which is outputted from the entire area of an encoder grating as a light beam for scanning makes a main scan by a synchronizing signal generating means after the pulse light is reduced in sweep width by a width reducing means, and generating the synchronizing signal. CONSTITUTION:The encoder grating 88 is arranged on the prolongation of the optical path of light of 0th order deflected by 90 deg. through a polarization beam splitter 86. The encoder grating 88 has plural slit holes 90 in the main scanning direction of the light of 0th order and the light of 0th order is moved in the main scanning direction to project specific pulse light to the reverse surface side of the encoder grating 88. The main scanning with Ws of the light of 0th order is about 50 mm and the number of the slit holes 90 is determined corresponding to the width. Gap size WM at the end part of mirrors 92 and 94 provided on the reverse surface side of the encoder grating 88 is about 29 mm. A photoelectric detector 96 is provided at the end part of the mirrors 92 and 94.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a light beam scanning device that performs two-dimensional plane scanning by performing main scanning and sub-scanning of a light beam using a scanning optical system.

[Prior art]

Generally, a light beam emitted from a laser is irradiated onto the image,
In a light beam scanning device such as a light beam reader that reads the transmitted or reflected light, or a light beam recording device that irradiates a recording material with a light beam and records an image, the light beam from the laser is transferred to a rotating polygon mirror. ), a galvanometer mirror, etc., performs main scanning and sub-scanning to perform two-dimensional plane scanning.

That is, the light beam is reflected by the reflective surface of a polygon mirror that rotates at high speed to perform main scanning, and then this reflected light beam is reflected by a galvanometer that is tilted at a constant pitch at a predetermined timing. By doing so, sub-scanning is performed.

By the way, in the above-mentioned light beam scanning device, in order to keep the main scanning recording position constant, a light beam for forming a synchronization signal is required in addition to the scanning light beam.

A synchronization signal is obtained by passing this light beam through an encoder grating to create pulsed light, which is detected by a photoelectric detector.

By setting the time when this synchronization signal is input or when a predetermined time has elapsed since this manual input as the main scanning recording time, it is possible to synchronize each main scanning line.

The light beam for forming the synchronization signal is generally produced by disposing an acrylic rond on the back side of the encoder grating, and causing the pulsed light that has passed through the encoder lattice to be fired inward from the circumferential surface of the acrylic rond. The incoming pulsed light is guided to one end of the acrylic iron in the axial direction, and a photoelectric detector is disposed at this one end to detect the pulsed light.

[Problem to be solved by the invention]

However, with the above configuration, the photoelectric converter can detect only about 1 to 5% of the amount of light incident on the acrylic iron, which is wasteful. In addition, along with the main scanning of the pulsed light, it is sequentially output from the entire area of the encoder grating.
Depending on the scanning position, there is also a two-fold difference in the amount of input pulsed light between the minimum and maximum values (shading), which hinders improvement of the S/N ratio.

To solve this problem, it is possible to use a long photoelectric converter that covers the entire area of the encoder grating, but in order to correspond to the scanning time of the light beam, a rise time of 15 nsec is required. A photoelectric detector that takes time and has a long length is large and expensive, and is not practical.

The present invention takes the above-mentioned facts into account, and provides a light beam scanning device that is small and can sufficiently handle the scanning time of a light beam, can apply a small photoelectric detector, and can reliably obtain a synchronization signal. is the purpose.

[Means to solve the problem]

The invention according to claim (1) is a light beam scanning device that scans a two-dimensional planar image by performing main scanning and sub-scanning of a scanning light beam by a scanning optical system, wherein the scanning light beam output means for outputting a synchronizing signal generating optical beam for obtaining a synchronizing signal; and an encoder grating disposed on the optical path of the synchronizing signal generating optical beam and outputting pulsed light by sweeping the synchronizing signal generating optical beam. a width reducing means provided on the output side of the synchronizing signal generating light beam in the encoder grating to reduce the sweep width of the pulsed light in the main scanning direction; and a width reducing means for detecting the pulsed light reduced by the width reducing means. a synchronization signal creation means for creating a synchronization signal;
have.

In the invention as set forth in claim (2), the width reducing means is arranged such that the width reducing means moves from the encoder grating toward the synchronizing signal generating means,
It is characterized by having a pair of mirror surfaces arranged opposite each other so that the distance between them gradually narrows.

[Effect]

In the invention described in claim (1), by guiding the synchronization signal generation light beam outputted from the output means to the encoder grating, the pulsed light is outputted from the encoder grating by sweeping the synchronization signal generation light beam. . This pulsed light is output from the entire area of the encoder grating along with the main scanning of the scanning light beam, but after the sweep width of the pulsed light is reduced by the width reduction means, it is detected by the synchronization signal generation means, and the synchronization signal is generated. create.

Thereby, the detection width of the pulsed light by the synchronization signal generating means can be small, and a small-sized detector can be applied.

Furthermore, since pulsed light that is reflected directly or once or twice can be detected, the efficiency of using pulsed light can be greatly increased.

In the invention described in claim (2), a pair of mirror surfaces is used as the width reducing means. By gradually narrowing the distance between these mirror surfaces as they move away from the encoder grating, the pulsed light output from both ends of the encoder grating in the width direction (main scanning direction) is reflected by this mirror surface, thereby increasing the sweep width. It can be reduced.

〔Example〕

FIG. 2 shows a laser beam recording device 10 according to this embodiment.
It is shown.

The laser 12 outputs a laser beam in response to an on/off signal from a laser power source 14.
This laser beam is input through a lens 16 to an acousto-optic device (hereinafter referred to as AOM) 18 that constitutes a part of a simultaneous multi-beam optical modulator.

AOM 18 is controlled by AOM driver 20. The AOM driver 20 is connected to an optical modulation circuit 22 which together with the AOMI 8 constitutes a simultaneous multi-beam optical modulation device. This optical modulation circuit 22 has the role of controlling the AOM driver 20 to change the intensity of optical modulation by the AOM 18, and its configuration will be described later.

In this embodiment, the laser beam output from the AOM 18 is divided into eight laser beams and input to the polygon mirror 28 via the lens 24 and mirror 26.

Further, as shown in FIG. 1, in addition to the eight laser beams mentioned above, a radar beam which is not used for scanning is outputted from the AOM 18. This is zero-order light that is not diffracted by the AOM 18 and passes through the AOM 18 in a straight line. The zero-order light that has passed through the AOM 18 is manually inputted to a 1/2λ plate 80 arranged on the extension of the optical path.

This 1/2λ plate 80 is configured to change the polarization plane of the 0th-order light by 90° and output it. The zero-order light output from the 1/2λ plate 80 is input to a polarizing beam splitter 84 via a mirror 82. The polarizing beam splitter 84 is disposed on the optical path of the scanning laser beam output from the AOM 18, and as a result, the 0th order light is combined with this scanning laser beam (1st to 8th order lights). It is designed to reach a polygon mirror 28.

The polygon mirror 28 is configured to be rotated at high speed by a polygon driver 30, and is configured to perform main scanning by reflecting the input laser beam on a reflective surface. The laser beam reflected by the reflective surface of the polygon mirror 28 enters the scanning lens 29, and after exiting from the scanning lens 29, enters the mirror 32 and the relay lens 33 via the polarizing beam splitter 86. The laser beam reaching the relay lens 33 is a scanning laser beam that linearly passed through the polarizing beam splitter 86, and the zero-order laser beam is deflected at right angles by the polarizing beam splitter 86. That is, since the polarization plane of the zero-order light has been changed by the 1/2λ plate 80, it is separated from the scanning laser beam by the polarization beam splitter 86.

The laser beam reflected by the polarizing beam splitter 86 is input to the galvanometer 36 via the mirror 34.

The galvanometer 36 has a reflecting surface that is movable in the sub-scanning direction by a galvanometer driver 37, and moves in the sub-scanning direction every time one main scanning of the laser beam is completed to change the direction of reflection of the laser beam. . The laser beam reflected by the galvanometer 36 is reflected by a mirror 38,
It is designed to reach a stage 42 via a lens 40.

A recording material 44 is placed on the stage 42, and the laser beam is irradiated onto the recording material 44, so that an image can be recorded on the recording material 44.

The recording material 44 is wound in layers on reels 46 and 48 at both ends in the longitudinal direction, and when recording of one image is completed, the recording material 44 is wound from one reel 46 to the other reel 48.
This is the configuration that will be moved to.

As shown in FIG. 3, the AOM1 is connected to the optical modulation circuit 22.
A signal line 50 that propagates image data signals corresponding to the number of laser beams divided by 8 is manually operated. The signal lines 50 are each connected to a modulator 64.

Although not shown, the signal lines 50 are branched, one being sent to a delay circuit, and the other recognizing the number of on-state image data signals. Here, by changing the light intensity of the image data signal that is delayed and output by the delay circuit in accordance with the number of recognized image data signal ONs, output fluctuations due to so-called competition for light are prevented.

Note that the delay circuit is set in consideration of the time required to recognize the number of on-states of the image data signal.

An oscillator 66 is connected to each of these modulators 64, and modulates each signal to a predetermined frequency for division by the AOM 18. The modulator 64 is
Each is connected to a mixer 68 via an amplifier 67. The mixer 68 mixes the image data signals output from the respective modulators 64 and outputs the mixed signal to the AOM driver 20.

As shown in FIG. 1, an encoder grating 88 is disposed on the optical path extension of the zero-order light that is polarized at right angles by the polarizing beam splitter 86.

The encoder grating 88 has a plurality of slit holes 90 along the main scanning direction of the 0th order light, and when the 0th order light is moved in the main scanning direction, a predetermined pulsed light is emitted to the back side of the encoder grating 88. It has become so. Note that the main scanning width W of the zero-order light is approximately 50 mm, and the slit hole 90
The number of is also provided corresponding to this width.

On the back side of the encoder grating 88, a pair of mirrors 92.
94 are arranged facing each other. These mirrors 92.94
One end of each abuts an encoder grating 88 . Furthermore, the distance between the mirrors 92 and 940 is inclined so that it gradually becomes narrower toward the other end. Therefore, the distance W,4 at the other end of these mirrors 92, 94 is approximately 29 mm.

A photodetector 96 is attached to the other end of the mirrors 92,94. This photoelectric detector 96 has a photodetecting surface entirely between the mirrors 92 and 94 in its width direction.
The rise time is 15 nsec, and the photoelectric detector has performance that can sufficiently correspond to the scanning time of the laser beam. That is, the spacing between the mirrors 92 and 94 was gradually narrowed to 29 mm, making the photoelectric detector 96 applicable.

The photoelectric detector 96 converts the detected light into a current value, and when this current value exceeds a predetermined threshold, it is applied as a synchronization signal to control the output timing of the scanning laser beam. It has become.

The operation of this embodiment will be explained below.

First, the image data signal is input to the delay circuit 52, delayed for a predetermined time, and then output. On the other hand, the number of on-states of the branched image data signal is recognized, and the light intensity of the image data signal output from the delay circuit 52 is controlled according to this number, thereby reducing the light intensity due to so-called competition for light. Fluctuations are prevented.

After the image data signals are modulated by respective modulators 64, they are mixed in a mixer 68 and sent to the AOM driver 20.
Output to. From this AOM driver 20 to AOM18
In synchronization with the output to the laser power source 14, the laser 1
2 is turned on to output a laser beam.

The laser beam output from the laser 12 passes through the lens 16
The laser beam reaches the AOM 18 via the AOM 18, and is divided into a plurality of (eight in this embodiment) laser beams in the sub-scanning direction. The divided laser beam reaches the polygon mirror 28 via the polarized beam splinter 84, the lens 24, and the mirror 26, and as the polygon mirror 28 rotates, the direction of reflection is changed and the laser beam is main-scanned.

The laser beam reflected by the reflective surface of the polygon mirror 28 is incident on the galvanometer 36 via mirrors 32 and 34. In the galvanometer 36, its reflecting surface is tilted in the sub-scanning direction for each main scanning of the laser beam. In this embodiment, since eight main scans are performed simultaneously, the tilt angle of the galvanometer 36 in the sub-scanning direction is every nine pitches.

The laser beam reflected by the galvanometer 36 is irradiated onto the recording material 44 on the stage 42 via the mirror 38, lens 40, and deflection beam splitter 86, and an image is recorded.

Here, in the laser beam recording apparatus 10 of this embodiment, AOM 18 is used as a synchronization signal that determines the main scanning recording timing.
The zero-order light output from the

That is, the 0th order light output from the AOM 18 is first
The plane of polarization is changed by 90° by the 1/2λ plate 80 , and then reflected by the mirror 82 to reach the polarizing beam splitter 84 . In the polarizing beam splitter 84, A
The scanning laser beam diffracted by the OM 18 and the zero-order light are combined, and as a result, the zero-order light passes through the same optical path as the scanning laser beam and is output from the lens 40.

The zero-order light output from the lens 40 is deflected in a right angle direction by a polarizing beam splitter 86 and separated from the scanning laser beam. This is because the polarization plane of the zero-order light is changed by 90 degrees from the polarization plane of the scanning laser beam, and even laser beams having the same wavelength can be easily separated.

The zero-order light separated by the polarizing beam splitter 86 passes through the encoder grating 88, and pulsed light is output on the back surface thereof. The pulsed light, either directly or reflected by mirrors 92.94, reaches a photodetector 96 where it is detected and applied as a synchronization signal.

The photoelectric detector 96 converts the manually input light amount into a current value, and outputs it when this current value exceeds a predetermined threshold value, thereby controlling the main scanning recording timing by the scanning laser beam. can.

Here, the photoelectric converter 96 of this embodiment is a photoelectric detector whose rise time is 15 nsec, and this rise time can correspond to the scanning time of the laser beam. By the way, the width Ws of the zero-order light in the main scanning direction
is approximately 5 Qmm, and even if the photoelectric detector 96 is placed directly on the back side of the encoder grating 88, detection over the entire width cannot be ensured. Therefore, the encoder grid 9
Since the mirrors 92 and 94 are arranged so that the distance between the mirrors 92 and 94 gradually narrows toward the back side of the mirror 6, it is possible to correspond to the detectable width of the photoelectric detector 96, and a synchronization signal can be reliably obtained.

In this way, in this embodiment, the 0 output from the AOM18
Since the polarization direction of the secondary light is changed and used for generating a synchronization signal, there is no need to separately provide a laser with a different wavelength, and the number of parts can be reduced. In addition, 1/2λ plate 80
Since the polarization plane of the 0th-order light was changed by 90 degrees with respect to the scanning laser beam, the polarization beam splitter 84.8
By using 6, it is easy to connect the scanning laser beam and 0
It is possible to combine and separate the following light.

Furthermore, since the pair of mirrors 92 and 94 are arranged so that the distance between them gradually narrows toward the back side of the encoder grating 88, the photoelectric detector has a rise time that can sufficiently correspond to the scanning time of the scanning laser beam. 96 can be applied. Therefore, fluctuations in the amount of light due to main scanning can be reduced, and the S/N ratio of the detection signal can also be improved.

In addition, the pulsed light obtained by passing through the encoder grating 88 is reflected directly or by mirrors 92 and 94 to the photoelectric detector 9.
6, the efficiency of using pulsed light can be greatly increased. In other words, when the conventional acrylic rond is injected from the circumferential surface and the pulsed light is detected at the axial end of the acrylic rond, the utilization efficiency of the pulsed light is 1.
Compared to the 5%, the utilization efficiency of this pulsed light can be 80 to 100% in this embodiment.

In this example, the 1/2 λ plate 80 was used to change the polarization plane of the 0th-order light by 90°, but 1/4 λ plates were provided on the incident side and the reflective side of the mirror to convert the polarized light once into circularly polarized light. After that, the plane of polarization may be changed by 90°.

In addition, the light that has passed through the encoder grating 88 is guided to the photoelectric converter 96 either directly or by being reflected by a mirror 92.94, but as shown in FIG. A box body 98 may be arranged.

In this case, the side surface 98A of the box body is connected to the mirror 92.94.
It needs to be tilted as well.

〔Effect of the invention〕

As explained above, the light beam scanning device according to the present invention has the advantage that it is small and can sufficiently correspond to the scanning time of the light beam, can apply a small photoelectric detector, and can reliably obtain a synchronization signal. It has a good effect.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of the scanning optical system according to this embodiment, and FIG.
3 is a block diagram of a light modulation circuit, and FIG. 4 is an enlarged view showing a modified example of a photoelectric converter for detecting a synchronizing signal and its surroundings. DESCRIPTION OF SYMBOLS 10... Laser beam recording device, 12... Laser, 28... Polygon mirror 36... Galvanometer, 88... Encoder grating, 90... Slit hole, 92.94... Mirror (width) reduction means), 96... photoelectric detector (synchronization signal generation means).

Claims (2)

[Claims] (1) A light beam scanning device that scans a two-dimensional planar image by performing main scanning and sub-scanning of a scanning light beam by a scanning optical system, the light beam being synchronized to obtain a synchronization signal for the scanning light beam. output means for outputting a light beam for signal generation;
an encoder grating disposed on the optical path of the synchronization signal creation light beam and outputting pulsed light by sweeping the synchronization signal creation light beam; A light beam scanning device comprising: width reduction means for reducing the sweep width of light in the main scanning direction; and synchronization signal generation means for generating a synchronization signal by detecting the pulsed light reduced by the width reduction means. (2) Claim (1) characterized in that the width reducing means is provided with a pair of mirror surfaces disposed oppositely so that the interval dimension gradually narrows from the encoder grating toward the synchronizing signal generating means. ).