JP2001267669A - Device and method for driving laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably start and oscillate a high output laser which is about 100 mW or more. SOLUTION: In changing a laser diode from a non-oscillated state to an oscillated state, the laser diode is operated so that laser currents Id can be gradually increased under ACC control (reference to points of time t1-t2). Finally, the laser diode is operated so that the laser currents Id can reach a target light quantum value under the APC control (reference to points of time t3-t4). Thus, it is possible to gradually increase the laser currents without allowing the laser currents to rapidly flow at the time of starting laser oscillation, and to safely start the laser.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser driving apparatus and method for stably oscillating a high-power laser such as a solid-state laser.

[0002]

2. Description of the Related Art Recently, high output lasers have been realized, and high output lasers having an output of about 100 mW or more, for example, have been put to practical use.

[0003] Such a high-power laser is, for example, a CTP (computer to computer) that directly writes an image on a printing plate.
plate) device.

In a CTP device, a drum around which a photosensitive material serving as a printing plate is wound is rotated, and a laser unit movable in the axial direction of the drum is arranged.

By irradiating the photosensitive material on the rotating drum with laser light output from the laser unit, an image is recorded in the main scanning direction of the photosensitive material. By being transported in the sub-scanning direction, which is the axial direction, a two-dimensional image can be recorded on the photosensitive material.

[0006]

By the way, conventionally,
When a laser is oscillated, oscillation control by a so-called automatic light amount control circuit (APC (automatic power control) circuit) is employed.

However, when the above-described high-power laser of about 100 mW or more is controlled to be turned on by a so-called APC circuit, the laser unit including the high-power laser is caused by a sudden flow of the laser current. It has been found that the amount of emitted light of the high-power laser may become unstable due to heat generation or the like.

The present invention has been made in view of such problems, and has as its object to provide a laser driving device and a method thereof that enable a laser to oscillate extremely stably.

It is another object of the present invention to provide a laser driving device and a method thereof that can shorten the time required for the target light amount to be stabilized.

[0010]

SUMMARY OF THE INVENTION The present invention provides a current control circuit for controlling a current flowing through a laser to a target current value, and a light amount control circuit for controlling an output light amount of the laser to a target light value. And a laser control circuit for controlling the current control circuit and the light quantity control circuit, and when the laser control circuit is to change the laser from a non-oscillation state to an oscillation state, the laser control circuit first The invention is characterized in that the control circuit is operated so that the target current value is gradually increased, and is finally operated by the light amount control circuit so as to reach the target light amount value (the invention according to claim 1).

According to the present invention, when the laser is to be changed from the non-oscillation state to the oscillation state, first, the current control circuit is operated so that the target current value gradually increases, and finally, Since the light amount control circuit is operated to reach the target light amount value, at the start of oscillation, the laser current does not suddenly flow and gradually increases,
The laser can be started up stably.

The control may be switched from the current control to the light amount control when the current value reaches a predetermined target current value (the invention according to claim 2), and the light amount value becomes the target light amount value. At this time, the control may be switched from the current control to the light amount control (the invention according to claim 3). Further, when the current control circuit is operated for a predetermined time, it is possible to switch from the current control to the light quantity control (the invention according to claim 4).

Further, the current control circuit controls the target current value so as to increase in a stepwise manner, thereby facilitating the control by a digital circuit, for example.

Furthermore, the present invention can be applied to any laser as a laser, and is particularly suitable for a high-power solid-state laser (the invention according to claim 6).

Further, when the method of the present invention is to change the laser from the non-oscillation state to the oscillation state, first,
A current control circuit is operated to gradually increase a current value flowing to the laser, and finally, a light amount control circuit is operated so that the light amount value of the laser becomes a target light amount value. (The invention according to claim 7).

According to the present invention, it is possible to cause the laser to oscillate extremely stably, and to shorten the time required for the laser to stabilize at the target light intensity value.

[0017]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a plate making system 30 to which the present invention is applied. The plate making system 30 shown in FIG. 1 is a so-called CTP (computer to platform) for directly making a printing plate on which an image for forming a printed matter is recorded from digital image data without using a film.
e) The device.

The plate making system 30 includes a plate feeding device 34 for supplying a photosensitive material 32 before exposure, and a light beam scanning device for scanning the photosensitive material 32 with a light beam L corresponding to image information to record an image. And a developing device 38 for developing the photosensitive material 32 on which an image is recorded.

The plate feeding device 34 holds a plurality of photosensitive materials 32 and pushes the photosensitive materials 32 to the image recording device 36 in the direction of the arrow.
Supply one by one. The image recording device 36 conveys the photosensitive material 32 supplied from the plate feeding device 34 in the sub-scanning direction (the direction of the arrow Y) by the exposure stage 40, and modulates the light in accordance with image information from the image recording unit 42. An image is two-dimensionally recorded by scanning the beam L in the main scanning direction (the direction of the arrow X). The developing device 38 performs a developing process of image information recorded on the photosensitive material 32 supplied from the image recording device 36.

FIG. 2 shows a more detailed configuration including a control circuit of the image recording device 36 shown in FIG.

The image recording device 36 is driven by a laser driver 44 under the control of a CPU 110 as a laser control circuit, and emits a light beam L, which is a laser beam (laser light) for recording an image on the photosensitive material 32. And a synchronization unit that is driven by a laser driver 48 under the control of the CPU 110 and outputs a synchronization laser beam S for generating a synchronization clock for the main scanning of the photosensitive material 32 with the light beam L. And a light source 50.

In the optical path of the light beam L output from the laser unit 46, a mechanical shutter 52, a variable transmittance ND filter 54, an acousto-optic modulator (AOM) 5
6. A resonant scanner (light deflecting means) 58, a scanning lens 59, and reflection mirrors 60 and 62 are sequentially arranged.

The mechanical shutter 52 includes a driver 11
The light beam L can be moved in and out of the optical path of the light beam L by the displacement means 64 via the second member 2, and controls the supply or cutoff of the light beam L to the photosensitive material 32. Variable transmittance ND filter 54
The position of the light beam L with respect to the optical path is variable by the displacement means 66 via the driver 112, and the light amount of the light beam L is controlled according to the position.

The AOM 56 controls on / off of the light beam L in accordance with the image information to be recorded, and also controls the intensity of the light beam L when turned on. In this case, after the image information is read from the image memory 68 and converted into an on / off modulation signal by the image signal control circuit 70, the AOM
It is supplied to the driver 72. The AOM driver 72 combines, for example, signals having a plurality of different frequencies, each of which is ON / OFF-controlled in accordance with image information, to generate a drive signal A
Supply to OM56.

Therefore, the light beam L is turned on / off in the AOM 56 according to the image information, is divided into a plurality of beams corresponding to the frequency, and is supplied to the resonant scanner 58.

The resonant scanner 58 oscillates the mirror at a high speed in response to a drive signal supplied from the scanner driver 74, deflects the light beam L from the AOM 56 in the main scanning direction (the direction of the arrow X), and supplies it to the scanning lens 59. The light beam L transmitted through the scanning lens 59 is reflected by the reflection mirrors 60 and 62 after the scanning speed of the light beam L in the main scanning direction (the direction of the arrow X) is adjusted, and is reflected by the photosensitive material 3.
It is led to 2.

The CPU 110, which also functions as a laser control circuit, is provided between the reflection mirror 62 and the photosensitive material 32.
A reflecting mirror 78 that can move forward and backward in and out of the optical path of the light beam L by a displacement means 76 driven through a driver 75
When the reflection mirror 78 is in the optical path of the light beam L, the light beam L reflected thereby is guided to the light amount monitoring photosensor 80.

In this case, the light amount monitoring photo sensor 80
The light amount of the light beam L detected by the A / D converter 8
The digital signal is converted into a digital signal by 2 and supplied to the CPU 110. The CPU 110 drives the displacement unit 66 through the driver 112 according to the digital signal,
The intensity of the light beam L is coarsely adjusted and controlled through the transmittance variable ND filter 54, and the intensity of the light beam L is finely adjusted and controlled by controlling the AOM 56 through the AOM driver 72.

On the other hand, in the optical path of the synchronization laser beam S output from the synchronization light source 50, the resonance scanner 5
8, scanning lens 59, reflection mirrors 60 and 84, reference grid plate 86, condenser rod 88, photosensors 90a and 90b
Are arranged in order.

The synchronizing light source 50 transmits the synchronizing laser beam S from a different angle from the light beam L to the resonant scanner 58.
It is arranged to be incident on. In this case, in the configuration of FIG. 2, the synchronization laser beam S reflected and deflected by the resonant scanner 58 is guided from the scanning lens 59 to the reflection mirror 84 via the reflection mirror 60, and then to the reference grating plate 86. .

The reference grating plate 86 receives the synchronization laser beam S
The main scanning direction (the direction of the arrow X), which is the deflection direction, is elongated, and a number of slits 92 having a predetermined number corresponding to the resolution are formed along the longitudinal direction.

On the back surface of the reference grating plate 86 through which the synchronizing laser beam S is transmitted, a substantially cylindrical focusing rod 88 is provided. The condensing rod 88 is formed of a light transmitting body, and after the incident synchronizing laser beam S is repeatedly reflected inside, the photosensors 90 disposed at both ends are formed.
a, 90b.

A synchronous clock generation circuit 94 for generating a synchronous clock SYNC from the synchronous laser beam S is connected to the photo sensors 90a and 90b. Synchronous clock SYN generated by this synchronous clock generation circuit 94
C is supplied to the image signal control circuit 70 as a recording timing signal for the image information in the main scanning direction (arrow X direction).

The exposure stage 40 on which the photosensitive material 32 is positioned and held is conveyed in the sub-scanning direction (the direction of the arrow Y) by a ball screw 100 driven to rotate by a sub-scanning motor 98. The sub-scanning motor 98 is driven by the sub-scanning motor driver 104 according to a motor driving reference clock supplied from the sub-scanning motor driving clock generation circuit 102. Note that the motor drive reference clock is generated in the sub-scanning motor drive clock generation circuit 102 based on the scan clock SCAN which is a main scan start timing signal supplied from the scanner driver 74.

FIG. 3 shows a detailed configuration of the laser unit 46 and a basic configuration of the laser driver 44.

The laser unit 46 has an SHG (second harness) comprising a laser diode 120 and a resonator 122.
Monic generation) The configuration of the solid-state laser is adopted. In this embodiment, the wavelength of the light beam L output from the laser unit 46 is 532 [μm] and the output is 250
[MW].

In this case, a half mirror 124 having a smaller reflection ratio than the transmission ratio is inserted on the output side of the resonator 122, and a certain amount of the light beam L output from the resonator 122 is supplied to the photodiode. And the like. The light amount of the light beam L is detected by the photodetector 126 as the output current Id. This output current Id is supplied to the CPU 110 via the laser driver 44.

The laser diode 120 is connected to the CPU 110
Current control circuit (automatic current control circuit) 128 for controlling the current flowing through the laser diode 120 to a target current value Itn described below under the control of
And a light amount control circuit (automatic power control circuit) 1 for controlling the light amount (output light amount) of the light beam L of the laser diode 120 to a target light amount value Pt described later.
Driven by 30.

The laser diode 120 and the resonator 122 constituting the laser unit 46 are provided with temperature control elements 132 and 134 such as a Peltier element and temperature detection elements 136 and 138 such as a thermistor, respectively. With the automatic temperature control performed by the CPU 110, the laser diode 120 and the resonator 122 are maintained at a predetermined temperature.

In practice, to keep the output light quantity constant,
The laser diode 120 and the resonator 122 need to be maintained at a predetermined temperature Ts on the basis of the laser oscillation characteristics 111 shown in FIG. The predetermined temperature Ts exists between + 15 ° C and + 50 ° C.

In order to accurately record a pixel having a size of about 10 μm on the photosensitive material 32, it is necessary to control and maintain the temperature within a range of ± 0.005 ° C. with respect to the predetermined temperature Ts. In order to maintain the light emission amount at the target light amount value Pt which is a constant light amount and to prevent the laser oscillation operation from becoming unstable, the predetermined temperature T
It is said that there must be no temperature change of ± 0.5 ° C. or more with respect to s.

Therefore, in order to change the laser diode 120 from the non-oscillation state to the stable oscillation state, first, in the non-oscillation state of the laser diode 120, the temperature inside the laser unit 46, in other words, the temperature detecting element 1
Laser diode 120 detected by 36, 138
And the detected temperatures Ta and Tb of the resonator 122 are equal to a predetermined temperature Ts.
The temperature is controlled so that the current I.
Supply so that d gradually increases. That is, the laser current Id is supplied while being gradually increased so as not to exceed ± 0.5 ° C. with respect to the predetermined temperature Ts.

As described above, if the laser current Id is controlled so that the element temperatures of the laser diode 120 and the resonator 122 do not deviate from the predetermined range of the predetermined temperature Ts, the laser diode 120 becomes unstable from the non-oscillation state. Without leading to a state, it is possible to smoothly lead to a stable state of oscillating at a target light amount value Pt that is a constant light amount.

FIG. 5 is a basic circuit diagram of the laser driver 44 for stably driving the laser diode 120 based on such findings. In this basic circuit diagram, in order to facilitate understanding of the present invention,
Electronic elements such as transistors and operational amplifiers are assumed to be ideal, and resistors for bias and the like are omitted.

As shown in FIG. 5, the laser driver 44
Has a transistor 140 for APC control and a transistor 142 for ACC control. These transistors 140 and 142 are connected to an inverter 144, transistors 146 and 148,
The operation state is switched via a switching circuit 145 including resistors 147 and 149.

When the switching signal Sw is at a low level, the transistor 146 is turned on and the transistor 14
As a result, the transistor 140 for APC control is turned off, and the transistor 142 for ACC control is turned on. As a result, the laser driver 44 operates as a current control circuit 128 that performs ACC control.

On the other hand, when the switching signal Sw is at a high level, the transistor 146 is turned off and the transistor 148 is turned on. As a result, the ACC control transistor 142 is turned off and the APC control transistor 142 is turned off. Transistor 140 is activated. This allows
The laser driver 44 operates as a light amount control circuit 130 that performs APC control.

The collector terminals and the emitter terminals of the transistors 140 and 142 are commonly connected. The common collector terminal is connected to the cathode terminal of the laser diode 120 whose anode terminal is connected to the power supply Vcc, and the common emitter terminal. Is connected to a resistor 150 having a resistance value R [Ω] whose other terminal is grounded.

The light quantity of the laser diode 120, that is, the so-called laser power, is detected by the photodetector 126 via the half mirror 124 shown in FIG.

Here, in order to facilitate understanding of the present invention, for convenience, the laser diode 120 is set to the target light amount value Pt.
The current value (also referred to as a laser current) Id flowing through the laser diode 120 when the laser beam is output is changed to the light amount target current value Ip.
It is referred to as t (Id = Ipt) (see FIG. 8 described later). Also, the transmission efficiency between the laser current Id and the output current Ip of the photodetector 126 near the light amount target current value Ipt is 1 / T (= Ip / Id).

The output current Ip [A] of the photodetector 126, which is proportional to the light amount P of the laser diode 120, is obtained by converting the current-voltage converter 152 whose conversion coefficient is set to the reciprocal T of the transmission efficiency.
, And is supplied to the negative input terminal of a differential amplifier 156 that operates as a comparator, and the detected light amount Dp of a digital signal through an AD converter 154. Is taken in by the CPU 110. The laser light amount characteristic 165 shown in FIG. 8 is previously stored in a memory in the CPU 110 as a memory table, and by referring to this memory table, the CPU 110 determines the current light amount P from the detected light amount value Dp.
You can know the value of

The CPU 110 is connected to the positive input terminal of the differential amplifier 156 in which the detected light amount T · Ip is supplied to the negative input terminal.
The target light amount DPt of the digital signal output from the
The target light amount value Pt of the analog signal is supplied via the converter 158. The output signal of the differential amplifier 156 is supplied to the base terminal of the transistor 140 for APC control.

When the switching circuit 145 turns off the ACC control transistor 142 and activates the APC control transistor 140, the detected light amount T · Ip output from the current-voltage converter 152 is reduced. The differential amplifier 156, the transistor 140, the laser diode 120, the photodetector 126, and the current / voltage converter 1 are set so as to be equal to the target light amount value Pt output from the DA converter 158.
Feedback control is performed by a closed loop consisting of 52.

Here, the target light amount value Pt as a reference input
Is set to Pt = T × Ipt (Ipt is a light amount target current value), so that the light amount value of the laser diode 120 is set to the target light amount value Pt at Id = Ipt.

That is, when the transistor 140 is in the active state, the laser driver 44
Operates as 0.

On the other hand, the target current value DItn of the digital signal output from the CPU 110 is set as the target current value Itn of the analog signal via the DA converter 160 and supplied to the non-inverting input terminal of the operational amplifier 162.

The output terminal of the operational amplifier 162 is connected to the base terminal of the transistor 142 for ACC control, and the emitter terminal of the transistor 142 is connected to the inverting input terminal of the operational amplifier 162.
, Transistor 142 and resistor 150 operate as a buffer.

That is, when the APC control transistor 140 is turned off by the switching circuit 145 and the ACC control transistor 142 is activated, the target current value Itn, which is the output of the DA converter 160, is output.
And the output voltage Vo appearing at the emitter terminal of the transistor 142 has the same voltage value (Itn = Vo).

In this case, assuming that the resistance value R of the resistor 150 is 1 [Ω] for convenience, a target current value Itn flows through the resistor 150 as a constant current. The current value (also referred to as a laser current) Id is equal to Id. That is, the laser current Id
Becomes Id = Vo / R = Itn / 1 = Itn.

Therefore, when transistor 142 is active, laser driver 44 supplies laser current Id
Is the target current value DItn =
It operates as a current control circuit 128 in which ACC control equal to Itn is performed.

The plate making system 30 of this embodiment
Is basically configured as described above. Next, the operation thereof will be described.

First, the overall operation of image recording in the plate making system 30 will be described with reference to FIG.

When the power of the plate making system 30 is turned on, the scanner driver 74 in the image recording device 36 is turned on.
Supplies a driving signal to the resonant scanner 58, whereby the mirror of the resonant scanner 58 starts high-speed oscillation. At this time, the scanner driver 74 generates a scan clock SCAN for each mirror scan of the resonant scanner 58 and supplies it to the image signal control circuit 70.

Next, a drive signal is supplied from the laser driver 48 to the synchronization light source 50, and a synchronization laser beam S is output. The synchronization laser beam S output from the synchronization light source 50 is reflected and deflected by the resonant scanner 58, and then guided to the reference lattice plate 86 via the scanning lens 59 and the reflection mirrors 60 and 84.

The synchronizing laser beam S passes through a number of slits 92 formed in the reference grating plate 86 along the main scanning direction (the direction of arrow X), and is incident on the focusing rod 88 as a pulsed optical signal. . The pulsed synchronization laser beam S incident on the condensing rod 88 is repeatedly reflected in the condensing rod 88, and then the photosensors 90a, 90b at both ends.
It is led to. The photo sensors 90a and 90b convert the synchronization laser beam S into an electric signal, and supply the electric signal to the synchronization clock generation circuit 94. The synchronous clock generation circuit 94 forms a waveform of the electric signal and generates a synchronous clock SYN.
Generate C. The synchronous clock SYNC generated by the synchronous clock generation circuit 94 is
Supplied to

Therefore, the image signal control circuit 70 supplies the supplied scan clock SCAN and synchronous clock SY
According to the NC, the image information read from the image memory 68 is converted into an on / off modulation signal and supplied to the AOM driver 72. The AOM driver 72 supplies to the AOM 56, for example, a drive signal obtained by synthesizing signals having a plurality of different frequencies, each of which is on / off controlled according to image information.

On the other hand, the laser unit 46 driven by the laser driver 44 as described later outputs a light beam L for image recording. This light beam L is transmitted through the variable transmittance ND filter 54 adjusted by the displacement means 66 so as to obtain a predetermined amount of light beam L.
It is led to M56. The transmittance variable ND filter 54
The mechanical shutter 52 arranged at the preceding stage is retracted outside the optical path by the displacement means 64 at the time of image recording.

The light beam L incident on the AOM 56 is
On / off control is performed by M56 in accordance with the image information, and the light beam is divided into a plurality of light beams in accordance with the frequency and supplied to the resonant scanner 58. Next, the light beam L reflected and deflected by the resonant scanner 58 is
The light is guided to the photosensitive material 32 via the scanning lens 59 and the reflection mirrors 60 and 62.

The scanner driver 74 supplies the sub-scanning motor drive clock generation circuit 102 with a scan clock SCAN generated for each main scan. The sub-scanning motor drive clock generation circuit 102 supplies a motor drive reference clock to the sub-scanning motor driver 104 based on the supplied scan clock SCAN. The sub-scanning motor driver 104 generates a driving signal according to the motor driving reference clock to drive the sub-scanning motor 98, whereby the ball screw 100 rotates and the exposure stage 4
0 moves in the sub-scanning direction (direction of arrow Y) in synchronization with the scan clock SCAN.

Accordingly, the photosensitive material 32 conveyed in the sub-scanning direction (arrow Y direction) is irradiated with the light beam L modulated in accordance with the image information in the main scanning direction (arrow X direction). , An image is formed two-dimensionally. Then
The photosensitive material 32 on which the image has been formed is conveyed to a developing device 38, where it is subjected to a developing process and then subjected to printing.

Next, the operation of the laser driver 44 incorporated in the plate making system 30 that operates as described above will be described with reference to the flowchart shown in FIG. 6 and the waveform chart shown in FIG.

First, as soon as the power of the image recording device 36 is turned on in step S1, the temperature control of the laser unit 46 by the CPU 110 in step S2 is started. In the temperature control, the CPU 110 operates as a comparator, and based on its own program, the predetermined temperature Ts set in advance, the laser diode 120 detected by the temperature detecting elements 136 and 138, and the detected temperatures Ta and Tb of the resonator 122. And the detected temperatures Ta, T
The temperature control elements 132 and 134 are feedback-controlled so that b becomes the predetermined temperature Ts. After the temperature reaches the predetermined temperature Ts, temperature control (hereinafter, referred to as predetermined temperature control) for maintaining the detected temperatures Ta and Tb within a predetermined temperature range of the predetermined constant temperature Ts is continuously performed.

When the temperatures of the laser diode 120 and the resonator 122 reach the predetermined temperature Ts, in step S3, the CPU 110 changes the switching signal Sw shown in FIG.
As shown at time point t0, the level is set to the low level. In practice, the switching signal Sw has been at a low level since the power was turned on.

When the switching signal Sw is at the low level, as described above, the transistor 148 to which the low-level switching signal Sw is supplied to the base terminal is turned off, and the ACC control transistor 142 is turned on. It is said. On the other hand, the transistor 146 supplied with the high-level switching signal Sw inverted by the inverter 144 to the base terminal is turned on, and the APC control transistor 140 is turned off.

When the power of the image recording apparatus 36 is turned on by the low level of the switching signal Sw, the current control circuit 128
Is set to the operating state.

In this state, in step S 4, the non-inverting input terminal of the operational amplifier 162
Target current value Itn supplied through A converter 160
Is set to the target current value Itn = Ibias for flowing the bias current Ibias to the laser diode 120 in the laser light amount characteristic 165 shown in FIG. 8 (at time t in FIG. 7B).
0).

If the target current value Itn in this case is represented by a voltage value, Itn = Ibias × R (R: resistor 150
Resistance value). In the laser light amount characteristic 165, a region indicated by a characteristic 163 is a laser non-oscillation region,
The region indicated by 4 is a laser oscillation region. Bias current I
Bias is a current value corresponding to a laser non-oscillation region near the laser oscillation region.

In the ACC control, as described above, the non-inverting input terminal of the operational amplifier 162 is connected to the target current value Itn.
(Itn = Ibias · R), and the operational amplifier 162
And the operational action of the operational amplifier 16
The two inverting input terminals are set equal to the target current value Itn.
That is, the emitter voltage value Vo of the transistor 142 is set to Vo = Itn = Ibias · R.

At this time, Vo / R = Ibias R / R = I
The bias current flows, and the laser current Id flowing through the laser diode 120 is set to Id = Ibias.

Next, in steps S5 and S6, under the condition that the above-mentioned predetermined temperature range is maintained, the target current value Itn is gradually changed from the bias current value Ibias to the vicinity of the target light amount current value Ipt. ACC control is performed so as to increase gradually.

In this embodiment, the target light amount P
t = P (Ipt) is set to 250 [mW], and
From time t1 to time t2, at every minute time Δt (Δt = 1 second in this embodiment), ΔIt is set as ΔIt as a minute current value ΔIt.
ACC control is performed such that = Ipt / N = Ipt / 10 (N is the number of steps) in a stepwise manner.

That is, as shown in FIG. 6, the current target current value Itn is gradually increased stepwise by a minute current value ΔIt to the previous target current value Itn−1, and the target current value Itn becomes the target light amount. Time point t2 at which the current value becomes close to Ipt
Until t3, the ACC control is performed by the current control circuit 128 (steps S5 and S6).

Next, at time t3 when the current flowing through the laser diode 120 becomes close to the target light amount current value Ipt, in step S7, the switching signal Sw is changed from the low level to the high level. The control is switched from the ACC control to the APC control by the light amount control circuit 130.

As a result, the transistor 142, which was in the active state during the ACC control, is turned off, and conversely, the transistor 140, which was in the off state, is turned on.

Thereafter, the light quantity control is performed in a closed loop using the photodetector 126 as the feedback element described above. That is, from the CPU 110 to the DA converter 158
Pt = T × Ipt
, The light amount value of the laser diode 120 is set to the target light amount value Pt when the laser current Id is Id = Ipt (see FIG. 8). Also at this time point t3, the above-described temperature control in step S2 is continued. The setting of the target light amount value Pt may be performed when the power is turned on in step S1, or may be performed near the time point t2.

In practice, at time t3 immediately after switching from the ACC control to the APC control, the current value Ip detected by the photodetector 126 is slightly different. By appropriately setting the number of steps N, this difference can be easily set to a value within the temperature control range.

In this manner, the light amount of the light beam L, which is the laser light output from the laser unit 46 (see FIGS. 2 and 3), is a constant value (in this embodiment, 250 [m
W]), in step S8,
In accordance with the type of the photosensitive material 32 and the like, a recording light amount control is performed in which the light of the light beam L applied to the photosensitive material 32 is controlled to a predetermined light amount value.

In this case, the CPU 110 sends the driver 75
The reflection mirror 78 is arranged in the optical path of the light beam L through the displacement means 76 and the light beam L reflected by the reflection mirror 78 is guided to the light quantity monitoring photosensor 80.

The light amount of the light beam L detected by the light amount monitoring photosensor 80 is converted into a digital signal by the AD converter 82 and supplied to the CPU 110. C
The PU 110 compares the digital signal with a predetermined light amount value stored in advance in a memory corresponding to the type of the photosensitive material 32, and compares the coarse adjustment amount in the transmittance variable ND filter 54 with the A
The fine adjustment amount in the OM 56 is determined, and the transmittance variable N through the driver 112 and the displacement means 66 is determined according to the coarse adjustment amount.
The position of the D filter 54 is determined, and the control amount of the AOM 56 (the amplitude of the voltage signal supplied to the AOM 56) is adjusted according to the fine adjustment amount.

When the light amount of the light beam L detected by the light amount monitoring photosensor 80 coincides with the predetermined light amount value, the fine adjustment by the AOM 56 is terminated.

After the adjustment of the light amount corresponding to the kind of the photosensitive material 32 or the like is completed, in step S9, the image recording device 36 scans the scanning light beam L
The above-described image recording is performed.

After the recording of the image on the photosensitive material 32 is completed, in step S10, the CPU 110 again changes the switching signal Sw from the high level to the low level to set the laser unit 46 to the non-oscillation state, thereby controlling the light amount. Is switched from APC control to ACC control (time t4
reference).

Next, in steps S11 and S12, contrary to the control in steps S5 and S6, the target current value I
ACC control for gradually decreasing t from the target light amount current value Ipt to the bias current Ibias is performed.

That is, as shown in FIG. 6, the current target current value Itn is gradually and gradually reduced from the previous target current value Itn-1 by the minute current value ΔIt, and the target current value Itn is changed to the bias current. The ACC control by the current control circuit 128 is performed until the time point t5 when the value becomes Ibais.

Next, in step S13, the temperature control is terminated (time t6). At that time, the ACC control is terminated, and the power of the image recording device 36 is turned off.

As described above, according to the above-described embodiment, first, the laser diode 120 is gradually driven to the vicinity of the target light amount value Pt by the ACC control by the current control circuit 128, and finally, the APC control is performed. Like that. Therefore, compared to the conventional technique in which the laser diode 120 is started under the APC control immediately after the power is turned on, it is possible to suppress a transient current increase to the laser diode 120, and to oscillate the laser diode 120 from the non-oscillation state. It is possible to stably shift to the state. By controlling similarly, the laser diode 12
0 can be stably shifted from the oscillation state to the non-oscillation state.

In the above embodiment, when the laser current Id becomes a value near the predetermined target current value Itn = Ipt, the ACC control by the current control circuit 128 is changed to the APC control by the light quantity control circuit 130. The output current Ip of the photodetector 126 corresponding to the light amount P is detected during the ACC control by the current control circuit 128, and the output current Ip corresponding to the light amount P becomes the light amount target current value Ipt. Sometimes AC by the current control circuit 128
The C control may be switched to the APC control by the light amount control circuit 130.

Alternatively, a timer 168 as time measuring means
(See FIG. 5), the time measurement is started from the time t1 when the increase of the target current value Itn by the current control circuit 128 is started, and the light amount is determined from the ACC control by the current control circuit 128 at the time t3 when a predetermined time Δt × N has elapsed. The control circuit 130 may switch to APC control.

Furthermore, a sequence may be adopted in which the light amount control circuit 130 starts up gradually from the start up. In this case, when the laser diode 120 is kept at the predetermined temperature Ts, the current value Is that causes the laser diode 120 to enter a laser oscillation state with a very small amount of light Pt (see FIG. 8) slightly exceeding the bias current Ibias is set to D.
When the output current Ip of the photodetector 126 is obtained in addition to the positive input terminal of the differential amplifier 156 by the A-converter 158, the voltage value applied to the positive input terminal of the differential amplifier 156 is determined by the output current Ip. Control is performed so that the light amount target current value Ipt corresponding to the value Pt is gradually increased until the light amount target current value Ipt is reached. Alternatively, the laser current Id is equal to the bias current value Ibi.
ACC control by the current control circuit 128 is performed until the output of the differential amplifier 156 changes to APC control by the light amount control circuit 130 until the output current Ip becomes the target light amount value Pt. The control may be performed such that the value gradually increases gradually until the corresponding light amount target current value Ipt is reached.

As described above, according to the present invention, the laser diode 120 and the resonator 12 are capable of obtaining a very large output (high output) laser beam in a compact volume.
2 is particularly preferable when applied to a semiconductor laser pumped solid-state laser or the like.

The present invention is not limited to the above-described embodiment, but can adopt various configurations without departing from the gist of the present invention.

[0103]

As described above, according to the present invention, when the laser is oscillated, the current value is gradually increased by current control first, and finally the light amount is controlled so that the light amount becomes the target value. To do.

Therefore, an effect that the laser can be oscillated extremely stably is achieved. In addition, since the laser can be oscillated stably, the effect of shortening the time until the light quantity becomes stable can be achieved.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of a plate making system to which an embodiment of the present invention is applied.

FIG. 2 is a schematic configuration diagram of an image recording apparatus.

FIG. 3 is a schematic configuration diagram of a laser unit and a laser driver.

FIG. 4 is a diagram illustrating laser oscillation characteristics.

FIG. 5 is a circuit block diagram illustrating a detailed configuration example of a laser driver.

FIG. 6 is a flowchart provided to explain the operation of the laser driver and the like;

FIG. 7 is a waveform chart used for explaining operations such as ACC control;

FIG. 8 is a diagram showing laser light quantity characteristics.

[Explanation of symbols]

Reference Signs List 30 printing plate making system 32 photosensitive material 34 plate supply device 36 image recording device 38 developing device 40 exposure stage 44, 48 laser driver 46 laser unit 54 variable transmittance ND filter 56 acousto-optic modulation (AOM) 64, 66 ... displacement means 68 ... image memory 70 ... image signal control circuit 60, 62, 7
8, 84: Reflection mirror 80: Photosensor for monitoring light amount 110: CPU 120: Laser diode 122: Resonator 124: Half mirror 126: Photodetector 128: Current control circuit 130: Light control circuit 132, 134: Temperature control element 136, 138
... Temperature detecting element 140 ... APC control transistor 142 ... ACC
Control transistor 145 Switch circuit 156 Differential amplifier 168 Timer Ibias Bias current value Id Laser current Ipt Target light amount current value Itn Target current value Pt Target light amount L Light beam

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H04N 1/036 H01S 3/094 F term (Reference) 2H084 AA14 AA30 AE05 AE06 AE08 BB13 CC05 5C051 AA02 CA07 DB07 DB30 DE02 DE03 5F072 AB20 HH02 HH04 KK12 KK30 MM20 QQ02 TT15 TT22 TT29 YY20

Claims (7)

[Claims] A current control circuit that controls a current flowing through the laser to a target current value; a light amount control circuit that controls an output light amount of the laser to a target light amount value; A laser control circuit that controls a light amount control circuit. When the laser control circuit attempts to change the laser from a non-oscillation state to an oscillation state, first, the current control circuit sets the target current value to A laser driving device, wherein the laser driving device is operated so as to increase gradually, and finally operated so as to reach the target light amount value by the light amount control circuit. 2. The laser driving device according to claim 1, wherein the laser control circuit switches an operation from the current control circuit to the light amount control circuit when the current value reaches a predetermined target current value. Characteristic laser drive. 3. The laser driving device according to claim 1, wherein the laser control circuit detects the light amount value while operating the current control circuit, and the detected light amount value corresponds to the target light amount value. A laser driving device for switching the operation from the current control circuit to the light amount control circuit when the current control circuit is turned off. 4. The laser driving device according to claim 1, wherein the laser control circuit has a timer for measuring a predetermined time, and when the current control circuit is operated for a predetermined time, an output of the clock is output. A laser drive device that switches from the operation by the current control circuit to the operation by the light amount control circuit based on the current control circuit. 5. The laser driving device according to claim 1, wherein the current control circuit controls the target current value to increase stepwise. 6. The laser driving device according to claim 1, wherein said laser is a solid-state laser. 7. When the laser is to be changed from a non-oscillation state to an oscillation state, first, a current control circuit is operated to gradually increase a current value flowing through the laser, and finally, A laser driving method comprising operating a control circuit so that a light amount value of the laser becomes a target light amount value.