JPH04260026A - Power correcting method for plural light beams and light beam scanner - Google Patents

Abstract

PURPOSE:To make power of each of light beams, emitted by an acoustooptic element, constant regardless of the number of the emitted light beams even when a signal inputted to the acoustooptic element is varied in amplitude. CONSTITUTION:The AOM (acoustooptic element) 18 emits the laser beams, one by one, and local level control circuits 64A-64H control the power of the light beams to a reference value respectively; and then one laser beam is emitted and its power is measured. Further, eight laser beams are emitted and the power is measured. A deviation in power per laser beam is calculated from those two measured values and total level control circuits 70AB-70GH correct the amplitude so that the deviation becomes zero regardless of the number of the emitted beams.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for correcting the power of a plurality of light beams and a light beam scanning device using the method for correcting the power of a plurality of light beams.

0002

[Prior Art] Conventionally, multi-frequency acousto-optic elements (
A light beam scanning device has been proposed that can read or record stably and at high speed by forming multiple laser beams using an optical modulation device equipped with an AOM (Japanese Patent Publication No. 63-5741, No. 54-5455, Japanese Patent Publication No. 57-41618, Japanese Patent Publication No. 53-985
6, Utility Model Application Publication No. 55-29414, etc.).

[0003] A light beam scanning device such as a laser beam recording device that records an image using such a multi-frequency acousto-optic device includes a plurality of oscillators each outputting a signal of a different frequency, and a plurality of oscillators connected to each of the output terminals of the oscillators. It also includes a plurality of amplitude controllers that control the amplitude of the signals output from the oscillator, and a mixing means that mixes each of the signals output from the plurality of amplitude controllers and inputs the mixture to the acousto-optic element. When the plurality of signals are input with a laser beam incident on the acousto-optic element, the laser beam is diffracted by the acousto-optic effect, and the same number of laser beams as the number of signals are emitted from the acousto-optic element as diffracted light. It is ejected. In addition,
The diffraction angle of each emitted laser beam depends on the frequency of the signal, and the power of each laser beam approximately depends on the amplitude of the signal. In the laser beam recording device, the plurality of laser beams are simultaneously irradiated onto the photosensitive surface of the photosensitive material via a scanning optical system and a recording optical system.

By the way, when a predetermined number of signals with a constant amplitude and different frequencies are mixed and input to an acousto-optic element and a predetermined number of laser beams are emitted, one laser beam is emitted as shown in FIG. 10(A). It is known that the diffraction efficiency per laser beam, that is, the power per laser beam, decreases as the number of laser beams to be emitted increases. For this reason, density unevenness occurs in the recorded image in the above-mentioned laser beam recording apparatus and the like. To solve this problem, the applicant has already proposed a technique in which the power per laser beam is constant regardless of the number of emitted laser beams (Japanese Patent Application No. 1-272332, 2-274755).

[0005]

However, the relationship between the number of laser beams to be emitted and the power per laser beam also changes depending on the amplitude of each of the plurality of signals input to the acousto-optic element. As an example, as shown in Fig. 10(B), when the amplitude of the signal input to the acousto-optic element is increased in order to increase the power of the emitted laser beam, the number of emitted laser beams is increased. In this case, the rate of decrease in power per laser beam becomes larger. Therefore, when applying the technology of the simultaneous multi-beam optical modulator to a laser beam recording device,
For example, if the amplitude of the signal input to the acousto-optic element is changed in order to change the writing power of the laser beam to a predetermined value according to the recording magnification as the image recording magnification changes, density unevenness will occur in the image. .

[0006] In order to solve this problem, it is conceivable to perform correction using a circuit configured as shown in FIG. That is, the signal number counting circuit 200 obtains data representing the number of laser beams emitted from the acousto-optic element. This data is digital data for correcting the power according to the number of laser beams to be emitted, and the DAC2
02, the signal is converted into an analog signal and output to the relay circuit 204. Note that the DAC 202 has a constant reference voltage VR.
EF is input. The relay circuit 204 is provided with a plurality of relays 206A, 206B, etc. corresponding to each recording magnification, and the analog signal is transmitted to each relay 206A, 206B, etc.
It is guided to the input side of 06B, . Relay 206A, 2
Variable resistors 208A, 2 are connected to the output sides of 06B, .
08B,... are connected. variable resistor 208A,
The resistance value of each of 208B,... is determined by the number of laser beams to be emitted and the laser beam 1 as shown in FIG.
In relation to the true power, the value is set to correct the tilt that differs for each recording magnification.

On the other hand, the signal representing the recording magnification is sent to the decoder 21.
0, and the decoder 210 turns on the excitation coil of the relay 206 corresponding to the recording magnification represented by the input signal. Therefore, the converted analog signal passes through a relay 206 and a variable resistor 208 corresponding to the recording magnification, and is output as a correction signal corresponding to the recording magnification. By correcting the amplitude of the signal input to the acousto-optic element using this correction signal, the power per laser beam becomes a predetermined value according to the recording magnification, and the number of laser beams emitted from the acousto-optic element changes. It remains constant regardless of.

However, if the power of the laser beam incident on the acousto-optic element changes due to changes in the laser beam generator over time, etc., the amplitude of the signal input to the acousto-optic element must be adjusted to obtain a constant writing power. Adjustment is necessary, but this changes the relationship between the number of emitted laser beams and the power per laser beam, so if the correction amount for each recording magnification is constant, the laser beam 1
The actual power varies depending on the number of laser beams emitted. When changing the correction amount for each recording magnification in the circuit configuration, the large number of variable resistors 208A,
Since the resistance values of 208B, .

The present invention has been made in consideration of the above fact, and even when the amplitude of the signal input to the acousto-optic element is changed, the power per single light beam emitted from the acousto-optic element can be increased. It is an object of the present invention to obtain a method for correcting the power of multiple light beams that can be made constant regardless of the number of light beams to be emitted.

[0010] Furthermore, the present invention provides that even when the amplitude of the signal input to the acousto-optic element is changed, the power per single light beam emitted from the acousto-optic element remains constant regardless of the number of emitted light beams. The object is to obtain a light beam scanning device capable of

[0011]

[Means for Solving the Problem] In the invention according to claim 1, at least one of a predetermined number of signals having a predetermined amplitude and different frequencies is inputted, and the power corresponding to the amplitude of the input signal is inputted. In correcting the power of a plurality of light beams of a light beam scanning system equipped with an acousto-optic element that emits an incident light beam in a direction corresponding to the frequency of the input signal, the predetermined number of signals are input individually. A single beam of multiple light beams is emitted when multiple signals are mixed and input after controlling the amplitude of each of the signals so that the power of the single light beam emitted becomes a predetermined value. The amplitude of the signal is corrected so that the power per beam is equal to the power of the single optical beam.

In the invention according to claim 2, a predetermined number of oscillation circuits each outputting signals of different frequencies; and a first control signal input with the amplitude of each of the signals output from the predetermined number of oscillation circuits. a predetermined number of first amplitude control circuits each independently controlled according to the input second control signal, and a predetermined number of first amplitude control circuits that control the amplitudes of the plurality of signals output from the predetermined number of oscillation circuits independently according to the input second control signal. a second amplitude control circuit to control, and at least one signal whose amplitude is controlled by the first amplitude control circuit and the second amplitude control circuit, and a power corresponding to the amplitude of the input signal. and an acousto-optic element that emits an incident light beam in a direction corresponding to the frequency of the input signal, and an acousto-optic element that emits each of the light beams that are emitted when the predetermined number of signals are respectively input to the acousto-optic element one by one. a first input means for inputting a first control signal that sets the power to a predetermined value to the first amplitude control circuit; and powers of the plurality of light beams emitted when the plurality of signals are input to the acousto-optic element. power per single optical beam of 1 to the acousto-optic element.
and second input means for inputting a second control signal to the second amplitude control circuit to make the power equal to the power of the light beam emitted when the two signals are input.

In the invention as claimed in claim 3, there are provided a predetermined number of oscillation circuits each outputting a signal of a different frequency, and a predetermined number of oscillation circuits that are connected to each of the oscillation circuits so that the amplitude of the signal output from the oscillation circuit is adjusted to the input amplitude control signal. an amplitude control circuit that controls according to the
At least one of the predetermined number of signals outputted from the amplitude control circuit is input, and the light beam is incident with a power corresponding to the amplitude of the input signal and in a direction corresponding to the frequency of the input signal. a first control signal that outputs a first control signal that sets the power of each light beam to a predetermined value when each of the predetermined number of signals is input to the acousto-optic element one by one; output means, and the power per single light beam of the power of the plurality of light beams emitted when a plurality of signals are input to the acousto-optic element, and the light emitted when one signal is input to the acousto-optic element. a second output means for outputting a second control signal equal to the power of the beam; a first control signal output from the first output means and a second control signal output from the second output means; and input means for inputting the sum with the control signal to the amplitude control circuit as the amplitude control signal.

[0014]

[Operation] In the invention according to claim 1, first, when a predetermined number of signals are individually input to an acousto-optic element, the amplitude of each of the signals is adjusted so that the power of a single light beam emitted each becomes a predetermined value. Control. As a result, even if the power of the light beam incident on the acousto-optic element fluctuates, for example, the amplitude of the signal input to the acousto-optic element is changed to correct for this fluctuation. Next, when multiple signals are mixed and input, the power per single light beam of the multiple light beams emitted is 1
The amplitude of the signal is corrected so that it becomes equal to the power of a single light beam emitted when these signals are input, that is, the predetermined value. Therefore, even if the amplitude of the signal input to the acousto-optic element is changed, the power per single light beam emitted from the acousto-optic element can be kept constant regardless of the number of emitted light beams. .

Regarding the above-mentioned correction, the power of the light beam emitted when one signal is input to the acousto-optic element, and the power of the light beam emitted when multiple signals are input to the acousto-optic element. It is possible to calculate the deviation between the power per single optical beam and correct the amplitude of the signal so that this deviation becomes zero. This deviation is, for example, the power of a light beam emitted when one signal is input to an acousto-optic element, and the power of multiple light beams emitted when multiple signals are input to an acousto-optic element. It can be determined by measurement. Furthermore, the relationship between the amplitude value of the signal and the correction amount that makes the deviation 0 when the signal having this amplitude value is input to the acousto-optic element is determined in advance, and the predetermined number of signals are input to the acousto-optic element. The correction amount can also be determined and corrected based on the amplitude value of the signal after controlling the power of the single light beam emitted when each input becomes a predetermined value.

In the invention as set forth in claim 2, the first input means is configured to set the power of each light beam to a predetermined value when a predetermined number of signals are respectively input to the acousto-optic element one by one. A control signal is input to the first amplitude control circuit. As a result, for example, when the power of the light beam incident on the acousto-optic element fluctuates, the first control signal for correcting this fluctuation is input to the first amplitude control circuit, and the first
The amplitude control circuit changes the amplitude of the signal according to the first control signal, and the power of the light beam emitted when one signal is input to the acousto-optic element is maintained at a predetermined value. Further, the second input means calculates the power per single light beam of the power of the plurality of light beams emitted when a plurality of signals are input to the acousto-optic element, when one signal is input to the acousto-optic element. A second control signal that is made equal to the power of the emitted light beam is input to the second amplitude control circuit. As a result, the second amplitude control circuit generates a signal so that the power per single light beam emitted from the acousto-optic element is a constant predetermined value regardless of the number of light beams emitted from the acousto-optic element. The amplitude of is controlled. Therefore, even when the amplitude of the signal input to the acousto-optic element is changed, the power per single light beam emitted from the acousto-optic element can be kept constant regardless of the number of emitted light beams. Further, in the invention of claim 2, there is no need to use a large number of variable resistors, etc., and there is no need to adjust the resistance value, so the above correction can be easily performed.

In the invention of claim 2, the first amplitude control circuit and the second amplitude control circuit may be placed between the oscillation circuit and the acousto-optic element; The amplitude of the amplitude-controlled signal may be further controlled by the first amplitude control circuit.

In the third aspect of the invention, the amplitude control circuit controls the amplitude of the signal output from the oscillation circuit in accordance with the input amplitude control signal. On the other hand, the first output means outputs a first control signal that sets the power of each light beam emitted to a predetermined value when a predetermined number of signals are respectively input to the acousto-optic element one by one. For example, when the power of the light beam incident on the acousto-optic element fluctuates, a first control signal corrected for this fluctuation is output. Further, the second output means converts the power per single light beam of the power of the plurality of light beams emitted when a plurality of signals are input to the acousto-optic element into the power when one signal is input to the acousto-optic element. A second control signal is output that makes the power equal to the power of the emitted light beam. The input means inputs the sum of the first control signal and the second control signal to the amplitude control circuit as an amplitude control signal. Therefore, the amplitude control signal input to the amplitude control circuit maintains the power of the light beam emitted when one signal is input to the acousto-optic element at a predetermined value, and transmits multiple signals to the acousto-optic element. This signal makes the power per single light beam of the plurality of light beams emitted when inputted to the acousto-optic element equal to the power of the light beam emitted when one signal is inputted to the acousto-optic element. Therefore, even when the amplitude of the signal input to the acousto-optic element is changed, the power per single light beam emitted from the acousto-optic element can be kept constant regardless of the number of emitted light beams. Also, in the invention of claim 3, there is no need to use a large number of variable resistors, etc., and there is no need to adjust the resistance value, so the above correction can be easily performed.

[0019] In the above invention, when an image or the like is recorded using a light beam emitted from an acousto-optic element and the power of the light beam is changed according to the recording magnification, etc., one This can be achieved by changing the predetermined value, which is a reference value when controlling the power of a single light beam emitted by inputting a signal, in accordance with the recording magnification.

[0020]

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 3 shows a laser beam recording device 10 according to the invention. This laser beam recording device 10
includes a He-Ne laser 12 connected to a power source 14. Instead of this He-Ne laser, other gas lasers, solid lasers, semiconductor lasers, etc. may be used. H
On the laser beam emission side of the e-Ne laser 12, a lens 16, an AOM (acousto-optic device) 18, and a lens 24 are arranged in this order. The AOM 18 includes an acousto-optic medium 21 that produces an acousto-optic effect. A transducer 17 that outputs ultrasonic waves according to an input high-frequency signal and a sound absorber 19 that absorbs the ultrasonic waves that have passed through the acousto-optic medium 21 are attached to opposing surfaces of the acousto-optic medium 21. The transducer 17 drives the AOM 18.
The AOM driver 20 is connected to the OM driver 20, and the AOM driver 20 is connected to the control circuit 22. In this embodiment, AOM1
A maximum of eight laser beams are diffracted from the laser beam incident on the laser beam 8 and are emitted as recording laser beams.

On the laser beam exit side of the lens 24, a mirror 26, a dichroic mirror 25, a polygon mirror (rotating polygon mirror) 28, a lens 29, and a dichroic mirror 32 are arranged in this order. dichroic mirror 2
A lens 27 and a semiconductor laser 13 are arranged near the lens 5 . The semiconductor laser 13 is the semiconductor laser driver 1
5. The laser beam emitted from the semiconductor laser 13 is incident on the dichroic mirror 25 as a reference laser beam via the lens 27, and is reflected toward the polygon mirror 28 side. The polygon mirror 28 is connected to a polygon mirror driver 30 and is rotated at high speed by the polygon mirror driver 30. The recording laser beam and the reference laser beam are provided by a polygon mirror 28.
The recording laser beam is reflected by the dichroic mirror 32, and the reference laser beam is transmitted through the dichroic mirror 32. Further, a linear encoder 33 and a photoelectric converter 31 are arranged in this order at a position where the reference laser beam transmitted through the dichroic mirror 32 can be received. Thereby, the reference laser beam transmitted through the dichroic mirror 32 is scanned onto the linear encoder 33.

The linear encoder 33 is composed of a flat plate in which a large number of transparent parts and opaque parts are arranged alternately in stripes at a constant pitch in the main scanning direction. When scanning is performed with the reference laser beam, the reference laser beam passes through the transparent portion, so that the photoelectric converter 31 outputs a pulse signal. The pulse signal from this photoelectric converter 31 is transmitted to a galvanometer mirror driver 36 that controls the angle of the galvanometer mirror.
It is input to A. On the reflection side of the dichroic mirror 32, there are a mirror 34, a galvanometer mirror 36, and a mirror 3.
8 are arranged in order. The recording laser beam reflected by the mirror 38 is irradiated onto the stage 42 through the lens 40. A laser beam is provided between the mirror 38 and the lens 40 to block the laser beam when not recording (for example, when changing recording from one frame to another, when changing recording from one fish to another, etc.). A shutter 61 that can be closed is disposed. This shutter 61
A photoelectric converter 60 is attached to the surface on the laser beam incident side. A recording material 44 such as a microfilm is placed on the stage 42 . This recording material 44 is wound in layers around a reel 46 and a reel 48, respectively.

As shown in FIG. 1, it is placed at the position described above and receives the recording laser beam emitted as diffracted light from the AOM 18 and outputs a voltage corresponding to the power of the laser beam. The photoelectric converter 60 is connected to the input side of the amplifier 88 of the control circuit 22 . An ADC (analog-to-digital converter) 82 and a register 90 are connected to the output side of the amplifier 88 in this order. ADC8
2 converts the signal output from the photoelectric converter 60 and amplified by the amplifier 88 into digital data representing the power of the received laser beam. A register 90 temporarily holds the digital data. Register 90 is connected to data bus line 92. A CPU (central processing unit) 80 is also connected to the data bus line 92, and data and commands can be input and output between them. The CPU 80 performs processing based on data representing the power of the laser beam held in the register 90.

The data bus line 92 has a register 84A.
, 84B, 84C, 84D, 84E, 84F, 84G,
84H is connected, and each register is connected to a DAC (digital-to-analog converter) 86A, 86B, 86C, 8
Connected to 6D, 86E, 86F, 86G, and 86H. Registers 84A, 84B, 84C, 84D, 84E
, 84F, 84G, and 84H are supplied with digital data for adjusting the level of each of the eight laser beams emitted from the AOM 18. This digital data is for each DA.
It is converted to an analog signal by C86 and sent to AOM driver 20.
The signal is output as a level control signal to each of local level control circuits 64A to 64H, which will be described later.

A character generation circuit 9 is connected to the data bus line 92.
4 are connected. Image data transferred from a host computer or the like is supplied to the character generation circuit 94 by the CPU 80, and the character generation circuit 94 temporarily stores this data. A delay circuit 58 and a signal number counting circuit 54 are connected to the character generation circuit 94. The character generation circuit 94 extracts image data (8 bits) for every 8 pixels in the order of image recording by the laser beam from the once stored image data, and outputs it to the delay circuit 58 and the signal number counting circuit 54. After delaying the input image data for a predetermined time in the delay circuit 56, a switch circuit 66A (described later) of the AOM driver 20
-66H. On the other hand, the signal number counting circuit 54
converts the input 8-bit image data into 4-bit data representing the number of on (1) bits in the 8 bits, and
Output to DAC (digital-to-analog converter) 56.

Further, a register 50 and a first DAC (digital-to-analog converter) 52 are sequentially connected to the data bus line 92. 8-bit correction data is supplied to the register 50 from the CPU 80. This correction data is a correction amount to make the power per laser beam emitted from the AOM 18 constant regardless of the number of laser beams emitted, even when the amplitude of the signal input to the AOM 18 is changed. represents. The register 50 temporarily holds this correction data, and the first DA
Output to C52. The first DAC 52 converts the input digital correction data into an analog signal having a voltage level corresponding to the correction amount. The output terminal of the first DAC 52 is connected to the reference voltage input terminal of the second DAC 56, and the first DAC 52 converts the analog signal of the voltage level corresponding to the correction amount into the reference voltage VREF to the second DAC 56
Supply to 6.

As shown in FIG. 4, the voltage level of the signal output from the second DAC 56 is determined by the signal number counting circuit 54.
The higher the value of the data input from , that is, the more the number of image data turns on, the higher the value becomes, and the degree of increase changes depending on the voltage level of the reference voltage VREF. That is, when the voltage level of the reference voltage VREF is high, the degree to which the output voltage level of the second DAC 56 increases (the slope becomes large) with respect to the increase in the number of turned-on image data. Also, the reference voltage V
When the voltage level of REF is small, the degree to which the output voltage level of the second DAC 56 increases with respect to the increase in the number of turned-on image data becomes small (the slope becomes small). The magnitude of this slope continuously changes depending on the voltage level of reference voltage VREF. Therefore, by changing the voltage level of the reference voltage VREF, that is, the value of the correction data supplied to the register 50, the slope can be changed. Note that the voltage level of the signal output from the second DAC 56 when the number of on-states of image data is 1 is set so as not to change even if the reference voltage VREF is changed.

The output signal from the second DAC 56 is sent to the amplifier 9.
After being amplified in step 6, the signal is supplied as an amplitude correction signal to each of total level control circuits 70AB to 70GH, which will be described later, of the AOM driver 20.

As shown in FIG. 2, the AOM driver 20 includes oscillation circuits 62A, 62B, and 6 having frequencies f1 to f8, respectively.
2C, 62D, 62E, 62F, 62G, 62H, local level control circuit 64A, 64B, 64C, 64D,
64E, 64F, 64G, 64H, switch circuit 66A
, 66B, 66C, 66D, 66E, 66F, 66G,
Equipped with 66H. Local level control circuit 64A~
Each of the circuits 64H is connected to the output terminals of the oscillation circuits 62A to 62H, and the switch circuits 66A to 66H are connected to the output terminals of the local level control circuits 64A to 64H, respectively. A double balanced mixer or a pin diode attenuator can be used as the local level control circuit. Local level control circuits 64A to 64
Each of the level control terminals of H has the above-mentioned DACs 86A to 8.
Level control signals from each of the 6Hs are input. Also,
One bit of the image data input as an 8-bit parallel signal from the delay circuit 58 is input to each of the control terminals of the switch circuits 66A to 66H.

Each output terminal of the switch circuits 66A and 66B is connected to a combiner 68 that mixes two signals at a ratio of 1:1.
They are respectively connected to the input terminals of AB. Similarly, each output terminal of the switch circuits 66C, 66D is connected to the input terminal of the combiner 68CD, each output terminal of the switch circuits 66E, 66F is connected to the input terminal of the combiner 68EF, and each output terminal of the switch circuits 66G, 66H is connected to the input terminal of the combiner 68EF. is combiner 68GH
is connected to the input end of the

The output end of combiner 68AB is connected to amplifier circuit 72AB via total level control circuit 70AB. Similarly, the output terminal of the combiner 68CD is connected to the amplifier circuit 72C via the total level control circuit 70CD.
The output end of combiner 68EF is connected to amplifier circuit 72EF via total level control circuit 70EF, and the output end of combiner GH is connected to amplifier circuit 72GH via total level control circuit 70GH. 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 72AB and 72CD are connected to the input terminal of the combiner 74.
Each output terminal of H is connected to an input terminal of combiner 76. The output ends of the combiners 74 and 76 are connected to a combiner 78, and the output end of the combiner 78 is connected to the input end of an amplifier circuit 79. The amplifier circuit 79 amplifies the input signal at a constant amplification factor. The output terminal of the amplifier circuit 79 is A
It is connected to the transducer 17 of the OM18. The total level control circuits 70AB to 70GH are composed of double balanced mixers and pin diode attenuators, and the amplitude correction signal output from the amplifier circuit 96 of the control circuit 22 described above is distributed and supplied to each level control terminal. .

Next, the operation of this embodiment will be explained. Signals output from each oscillation circuit 62A-62H are input to local level control circuits 64A-64H. Local level control circuits 64A to 64H receive level control signals representing levels set by level adjustment processing described later from DACs 86A to 86H, respectively. Local level control circuits 64A-64H adjust the amplitude based on the level control signal. Local level control circuits 64A to 64H
The level-adjusted signals are sent to switch circuits 66A to 66H.
supplied to On the other hand, image data supplied from a host computer etc. is temporarily stored in the character generation circuit 94.
The data is supplied as image data every 8 bits to the delay circuit 58 and the signal number counting circuit 54 in the order in which images are recorded by the laser beam. The 8-bit image data delayed for a certain period of time by the delay circuit 58 is distributed to each switch circuit 66A to 66H one bit at a time and input. Switch circuits 66A to 66
H allows the signal to pass when the input 1-bit image data is on (1), and blocks the signal when it is off (0). The signals passing through switch circuits 66A-66H are mixed by combiners 68AB-68GH and output to total level control circuits 70AB-70GH.

On the other hand, the signal number counting circuit 54 outputs to the second DAC 56 a digital signal corresponding to the number of ON signals inputted from the character generating circuit 94. The correction data converted into an analog signal via the register 50 and the first DAC 52 is inputted as a reference voltage VREF to the second DAC 56 together with a digital signal corresponding to the number of on-states of this signal. An amplitude correction signal is output to make the power per laser beam constant regardless of the number of laser beams to be emitted. Note that the amplitude correction process for setting the level of this amplitude correction signal to correct the amplitude of the signal will be described later. The amplitude correction signal is sent to the total level control circuits 70AB to 70AB.
It is input to each of the control terminals of 0GH. Total level control circuits 70AB to 70GH adjust the amplitude of the signal based on the input amplitude correction signal. The respective signals whose amplitudes have been adjusted by the total level control circuits 70AB to 70GH are sent to amplifier circuits 72AB to 72GH and combiners 74 and 76.
, are mixed via a combiner 78, amplified at a constant amplification factor by an amplifier circuit 79, and then supplied to the transducer 17 of the AOM 18.

The transducer 17 converts the input signals into ultrasonic signals according to the number, frequency, and amplitude of the input signals. This ultrasonic signal is transmitted through an acousto-optic medium 21
The sound propagates and is absorbed by the sound absorbing body 19. At this time, He-
When a laser beam is input from the Ne laser 12, the same number of laser beams as the number of signals input from this laser beam are emitted with a power corresponding to the amplitude of the signal and in a direction corresponding to the frequency of each signal. It is emitted as diffracted light. The laser beam emitted from the AOM 18 is scanned in the main scanning direction by the polygon mirror 28 and scanned in the sub-scanning direction by the galvanometer mirror 36.

FIG. 7 shows the mirror angle of the galvanometer mirror 36 as a function of elapsed time. In a non-recording period before the start of recording of the n-th exposure, image data of the n-th exposure is prepared, the recording material is conveyed for one exposure, and the recording material is positioned. At this time, the shutter is closed. Note that when recording is started, the shutter is opened and the data of the nth scan is transferred and the image recording of the nth scan is performed until the mirror angle of the galvanometer mirror 36 reaches the recording end angle. Furthermore, during the check period of this non-recording period, the above-mentioned level adjustment process and amplitude correction process are performed.

First, the level adjustment process will be explained with reference to the flowchart shown in FIG. The laser beam emitted from the AOM 18 is incident on a photoelectric converter 60 attached to a closed shutter. This level adjustment processing is performed while an amplitude correction signal of a constant voltage level is supplied to the total level control circuits 70AB to 70GH, and is processed as follows for each laser beam corresponding to each oscillation circuit 62A to 62H. .

In step 100, the initial value of N is set to 1, and in step 102, the first value of the eight laser beams is set.
Image data that turns on only the switch circuit of the th AOM driver 20 is supplied to the switch circuits 66A to 66H via the character generation circuit 94 and the delay circuit 58. As a result, only the switch circuit 66A is turned on while signals are output from the oscillation circuits 62A to 62H. In the next step 104, a reference value L1 corresponding to the currently set recording magnification among the pre-stored reference values for each recording magnification.
Incorporate. In step 106, the photoelectric converter 60 receives the light, the ADC 82 converts it into a digital value, and the register 90 receives the light.
The power P1 of the first laser beam of the eight laser beams held at is taken in. In step 108, the deviation X between the set value L1 and the P1 value is calculated, and the deviation
Determine whether the values are equal to 1. If the determination in step 108 is affirmative, that is, if the deviation Further, if the determination in step 108 is negative, that is, if the deviation X is other than 0, the process moves to step 112, and the deviation Save the value.

In step 114, the data representing the voltage level of the level control signal stored in step 110 or step 112 is output to the register 84A corresponding to the local level control circuit 64A that controls the power of the first laser beam. . As a result, the value stored in the register 84A is transferred to the local level control circuit 64A.
It is converted into an analog voltage value by AC86A and inputted as a level control signal. Therefore, when the power of the laser beam received by the photoelectric converter 60 is greater than the reference value, the voltage level of the level control signal output to the local level control circuit 64A is lowered, and the amplitude of the signal is controlled to be smaller. When the power of the received laser beam is smaller than the reference value, the voltage level of the level control signal output to the local level control circuit 64A is increased to increase the amplitude of the signal. As a result, AOM
The power of the first laser beam emitted from the recording magnification is adjusted to a reference value L1 corresponding to the recording magnification.

In step 116, it is determined whether N≧8 or not, and the remaining number of laser beams to be level adjusted is determined.
If there is still a laser beam to be level-adjusted, N is incremented by 1 in step 118, and the process proceeds to step 102.
Return to and adjust the level of the next laser beam. As a result, the switch circuits 66B to 66H are sequentially turned on and the level adjustment is performed for the oscillation circuits 62B to 62H in the same manner as described above, and during this check period, the oscillation circuits 62A to 62H are level adjusted.
Level adjustment for all 62H is done individually. When the level adjustment of all laser beams is completed,
End this control routine. In this way, the amplitude of the signal is adjusted according to changes in recording magnification and fluctuations in the power of the laser beam incident from the He-Ne laser 12.
When one laser beam is emitted from the AOM 18, the power of the laser beam becomes a predetermined value depending on the recording magnification. Further, voltage values P1 to P8 are stored in each of the registers 84A to 84H so that the power of the laser beam when one laser beam is emitted from the AOM 18 during image recording maintains the predetermined value. Ru.

[0040] Following the level adjustment process described above, amplitude correction process is performed. This amplitude correction process will be explained with reference to the flowchart of FIG.

In step 120, the correction step width GA1
and set an initial value to the correction value GA2. Next step 1
22, the correction value GA2 is sent to the register 50 as correction data.
Set to . As a result, the second DAC 56 receives the correction value G.
A reference voltage VREF of a voltage level corresponding to A2 is input. In step 124, switch circuits 66A to 66
Image data such that any one of
Supply to 6H. Further, this image data is also supplied to the second DAC 56 via the signal number counting circuit 54, and the second DAC 56
C56 supplies an amplitude correction signal for emitting one laser beam to the total level control circuits 70AB to 70GH. As a result, only one of the eight laser beams is emitted from the AOM 18 and received by the photoelectric converter 60, and the power of the laser beam is transferred to the amplifier 88 and the ADC.
82 into digital data, and register 90
is maintained. In step 126, the power of the laser beam held in the register 90 is taken in and stored as LE1.

In step 128, the switch circuits 66A to
Image data such that all of 66H are turned on is sent to the switch circuits 66A to 66H via the character generation circuit 94 and the delay circuit 58.
Supply to 6H. Further, the second DAC 56 sends an amplitude correction signal to the total level control circuit 7 at a level corresponding to the reference voltage VREF when emitting eight laser beams.
Supply from 0AB to 70GH. As a result, eight laser beams are emitted from the AOM 18 and received by the photoelectric converter 60, and data representing the total power of the eight laser beams is converted to digital data via the amplifier 88 and ADC 82, and is registered in the register. It is held at 90. In step 130, the power of the laser beam held in the register 90 is taken in and stored as LE8. Next step 1
In step 32, a deviation ΔL between the power of LE1 multiplied by 8 and LE8 is calculated. This deviation ΔL is 8 of the deviation between the laser beam power when one laser beam is emitted from the AOM 18 and the power per laser beam when eight laser beams are emitted from the AOM 18. This is double the value.

In step 134, the correction step width GA1
Divide by 2. In step 136, it is determined whether GA1 has become smaller than 1 as a result of the calculation in step 134. If the determination at step 136 is negative, the process moves to step 138, where it is determined whether the value of ΔL is 0, greater than 0, or less than 0. Step 13
If it is determined in step 8 that the value of ΔL is larger than 0, in step 140 the correction step width GA is set to the correction value GA2.
The value obtained by adding 1 is set and the process returns to step 122. Further, if it is determined in step 138 that the value of ΔL is smaller than 0, a value obtained by subtracting the correction step width GA1 from the correction value GA2 is set in step 142, and step 12
Return to 2.

At step 122, the correction value GA2 whose value was changed at step 140 or step 142 is set again. As a result, an amplitude correction signal corresponding to the changed correction value is supplied to the total level control circuits 70AB to 70GH, and in steps 124 and below, the ΔL is calculated based on the changed correction value and the correction value GA2 is calculated again. . Note that the value of the correction step width GA1 is halved each time the processes from step 122 to step 144 are executed, and the change width of the correction value GA2 is gradually reduced. Therefore, the value of the correction value GA2 converges quickly, and the number of times the processes from step 122 to step 144 are executed can be reduced. If the value of ΔL is determined to be 0 in step 138, the process ends.

Further, if the determination at step 136 is affirmative, the process moves to step 144. Step 144
Then, it is determined whether the value of GA2 has become 0 or FFH. Note that H represents hexadecimal representation, and F
FH represents that all 8 bits are 1. If the determination in step 144 is affirmative, step 1
At step 46, it is displayed that correction is not possible, and the process is terminated. Further, if the determination in step 144 is negative, the correction step width G
Since A1 cannot be reduced to 1 or less, the process ends.

The correction value GA2 is determined by the above processing and is held in the register 50 as correction data. This correction value GA2 is converted into an analog signal by the first DAC 52, and is sent to the second DAC 56 as a reference voltage V while recording an image.
Supplied as REF. Further, the second DAC 56 is supplied with data corresponding to the number of ons of the image data from the signal number counting circuit 54, and the second DAC 56 is supplied with a reference voltage VR when emitting laser beams corresponding to the number of ons of the image data.
Outputs an amplitude correction signal according to EF. This amplitude correction signal is sent to the total level control circuit 70 via an amplifier 96.
It is supplied to each of AB, 70CD, 70EF, and 70GH. The total level control circuit corrects the amplitudes of the signals output from combiners 68AB to 68GH in accordance with this amplitude correction signal. As a result, the power of each laser beam output from the AOM 18 is constant regardless of the number of ON signals, as shown in FIG. 8, and is constant regardless of the image recording magnification. In addition, the He-Ne laser 12
It remains constant even if the power of the laser beam incident from the source changes. Therefore, uneven density of the image is prevented.

As described above, in this embodiment, first, a plurality of laser beams are emitted one by one from the AOM 18, and the local level control circuit 64 is set so that the power of each laser beam becomes the reference value.
Control with A to 64H, then emit one laser beam and measure the power, emit eight laser beams and measure the power, and based on these two measured values, the power per laser beam is The amplitude is corrected so that this deviation becomes 0 regardless of the number of emitted laser beams by calculating the power deviation of The power of each laser beam of a plurality of laser beams to be emitted can be accurately and automatically made constant regardless of the number of laser beams to be emitted.

Furthermore, since this embodiment does not use parts such as relays and variable resistors, it is easy to improve the degree of integration, and the laser beam scanning device can be miniaturized. Furthermore, since components such as variable resistors are not used, work such as adjusting the resistance value is not necessary.

Note that the AOM driver 20 may have a circuit configuration as shown in FIG. In the AOM driver 20 shown in FIG. 9, level control circuits 99A to 99H and adders 98A to 98H are provided in place of local level control circuits 64A to 64H and total level control circuits 70AB to 70GH. Level control signals output from each of DACs 86A-86H are input to adders 98A-98H. Further, the amplitude correction signals outputted from the second AC 56 are also inputted to the adders 98A to 98H via the amplifier 96, respectively. Adders 98A-98H input amplitude control signals of a level corresponding to the sum of the level control signal and amplitude correction signal inputted to each adder to the control terminals of level control circuits 99A-99H. Therefore, this amplitude control signal is
The power when emitting one laser beam from M18 is maintained at the reference value according to the recording magnification, and the AOM18
This is a signal that sets the power of one laser beam when a plurality of laser beams are emitted from the reference value to the reference value. Therefore, even if the amplitude of the signal input to the AOM 18 is changed, the power of each laser beam emitted from the AOM 18 can be kept constant regardless of the number of laser beams emitted.

In this embodiment, an example has been described in which the photoelectric converter 60 for detecting the power of the laser beam is installed on the shutter 61 provided on the recording scanning optical path of the laser beam. A mirror with low transmittance may be arranged and the sensor may be arranged on the back side of this mirror. Alternatively, a reflecting mirror may be provided on the shutter, and a photoelectric converter or the like may be provided at a position where the reflected light can be received to detect the power of the laser beam.

Furthermore, in this embodiment, an example has been described in which the total level control circuits 70AB to 70GH are connected after the combiners 68AB to 68GH that mix two signals. A total level control circuit may also be connected. Moreover, 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 also be used.

Furthermore, in this embodiment, an example has been described in which the laser beam power is corrected for each shot during non-recording. You may go at any time, or you may go at a combination of these times.

Furthermore, in this embodiment, an example of a light beam scanning device that uses a laser beam as a light beam has been described, but a scanning device that uses LED light as a light beam may also be used, or another light source may be used to scan light. It can also be a beam.

[0054]

According to the invention as claimed in claim 1, the amplitude of the signals is adjusted so that when a predetermined number of signals are individually input to the acousto-optic element, the power of each single light beam emitted becomes a predetermined value. After each control, the power per single light beam of the multiple light beams emitted when multiple signals are mixed and input is the power of the single light beam emitted when one signal is input. Since the amplitude of the signal is corrected so that it is equal to An excellent effect can be obtained in that the light beams can be made constant regardless of the number of light beams.

In the invention as set forth in claim 2, the first input means sets the power of each light beam emitted to a predetermined value when each of the predetermined number of signals is input to the acousto-optic element one by one. input the control signal to the first amplitude control circuit, and
The power per single light beam of the power of multiple light beams emitted when the input means inputs a plurality of signals to the acousto-optic element is the light emitted when one signal is input to the acousto-optic element. Since the second control signal that is made equal to the power of the beam is input to the second amplitude control circuit, even if the amplitude of the signal input to the acousto-optic element is changed, the single light beam emitted from the acousto-optic element can be maintained. An excellent effect can be obtained in that the power per beam can be made constant regardless of the number of emitted light beams.

In the invention as set forth in claim 3, the first output means sets the power of each light beam emitted when a predetermined number of signals are respectively input to the acousto-optic element to a predetermined value. The second output means outputs the power per single light beam of the power of the plurality of light beams emitted when the plurality of signals are input to the acousto-optic element, and outputs one signal to the acousto-optic element. The amplitude control circuit outputs a second control signal that makes the power equal to the power of the light beam emitted when inputting the input means, and the input means uses the sum of the first control signal and the second control signal as an amplitude control signal. Therefore, even if the amplitude of the signal input to the acousto-optic element is changed, the power per single light beam emitted from the acousto-optic element remains constant regardless of the number of emitted light beams. The excellent effect of being able to do this can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a schematic block diagram showing a schematic configuration near a control circuit of a laser beam recording apparatus according to an embodiment.

FIG. 2 is a schematic block diagram showing a schematic configuration of an AOM driver.

FIG. 3 is a schematic configuration diagram of a laser beam recording device.

FIG. 4 is a diagram showing a change in the relationship between the number of ON signals and the level of an output signal when the reference voltage VREF of a DAC (digital-to-analog converter) is changed.

FIG. 5 is a flowchart illustrating level adjustment processing as an effect of the present embodiment.

FIG. 6 is a flowchart illustrating amplitude correction processing.

FIG. 7 is a time chart illustrating a non-recording period.

FIG. 8 is a diagram showing the relationship between the number of signal ONs and the power of the laser beam emitted from the AOM when the recording magnification is changed.

FIG. 9 is a schematic block diagram showing the schematic configuration of another example of the AOM driver.

FIG. 10 (A) is a chart showing the change in diffraction efficiency per beam when the number of beams emitted from the acousto-optic element is changed, and (B) is a graph showing the change in diffraction efficiency per beam when the beam power is changed. It is a chart showing changes in true diffraction efficiency.

FIG. 11 is a schematic configuration diagram of a circuit that prevents density unevenness in an image due to a change in the writing power of a laser beam using a conventional technique.

[Explanation of symbols]

10 Laser beam recording device 12 He-Ne laser 18 AOM (acousto-optic device) 52 First DAC (digital-analog converter)
56 2nd DAC (digital-analog converter)
60 Photoelectric converter 62 Oscillation circuit 64 Local level control circuit 68 Combiner 70 Total level control circuit 74 Combiner 76 Combiner 80 CPU

Claims (3)

[Claims] Claim 1: At least one of a predetermined number of signals having a predetermined amplitude and different frequencies is input, and is incident with a power corresponding to the amplitude of the input signal and in a direction corresponding to the frequency of the input signal. In correcting the power of a plurality of light beams of a light beam scanning system equipped with an acousto-optic element that emits a light beam, the power of a single light beam emitted when the predetermined number of signals are individually input is After controlling the amplitudes of the signals to each have a predetermined value, the power per single light beam of the plurality of light beams emitted when a plurality of signals are mixed and input is the power of the single light beam. A power correction method for a plurality of light beams, which corrects the amplitude of the signal so that it is equal to the amplitude of the signal. 2. A predetermined number of oscillation circuits each outputting a signal of a different frequency, and the amplitude of each of the signals output from the predetermined number of oscillation circuits is independently adjusted according to an input first control signal. a predetermined number of first amplitude control circuits to control;
a second amplitude control circuit that controls the amplitudes of a plurality of signals output from the predetermined number of oscillation circuits in the same manner according to an input second control signal; At least one signal whose amplitude is controlled by the second amplitude control circuit is input, and an incident light beam is emitted with a power corresponding to the amplitude of the input signal and in a direction corresponding to the frequency of the input signal. an acousto-optic element to control the acousto-optic element, and a first control signal that controls the power of each light beam to a predetermined value when the predetermined number of signals are respectively input to the acousto-optic element to a predetermined value. a first input means for inputting to the circuit; and inputting one signal to the acousto-optic element, the power per single light beam of the power of the plurality of light beams emitted when the plurality of signals are input to the acousto-optic element; a second input means for inputting a second control signal to the second amplitude control circuit to make the power equal to the power of the light beam emitted when the light beam is emitted. 3. A predetermined number of oscillation circuits each outputting signals of different frequencies, and an amplitude control device connected to each of the oscillation circuits and controlling the amplitude of the signal output from the oscillation circuit according to an input amplitude control signal. At least one of the predetermined number of signals outputted from the circuit and the amplitude control circuit is input, and the input signal is inputted with a power corresponding to the amplitude of the input signal and in a direction corresponding to the frequency of the input signal. an acousto-optic element that emits a light beam, and outputs a first control signal that sets the power of each light beam to a predetermined value when the predetermined number of signals are respectively input to the acousto-optic element one by one. a first output means; and outputting power per single light beam of the power of the plurality of light beams emitted when a plurality of signals are input to the acousto-optic element when one signal is input to the acousto-optic element; a second output means for outputting a second control signal equal to the power of the light beam to be output, and a first control signal output from the first output means and a second control signal output from the second output means; A light beam scanning device comprising: input means for inputting the sum of the second control signal and the amplitude control signal to the amplitude control circuit.