JPS63184460A - Method and apparatus for controlling laser luminous quantity - Google Patents

Abstract

PURPOSE:To excluse the change in slope efficiency automatically by setting the modulation current in the range of prescribed luminous emitting quantity and changing the luminous quantity of the set current and applying scanning in applying the scanning one main scanning section with exposure. CONSTITUTION:When the slope efficiency of a laser diode 32 is decreased due to secular change or temperature change or the like and the characteristic is changed, the required current with a laser power of 3mW is 90mA, and with a power of 1.2mW the current is 70mA. Since two sample-and-hold operations are applied without fail at the start of one scanning with respect to the change, the current I2 is 35mA at one section of the SMPL1 when a 1st sampling pulse 52 is at a high level, then the resulting current I1+I2 is 90mA (55mA+35mA). In the period of SMPL2 when a 2nd sampling gate 54 is at a high level, since I1=35mA, the resulting current I1+I2 is 70mA.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for controlling a laser light source used to record an image by exposing a photographic material, that is, an image recording carrier such as a film. Necessary resonance in which the amount of light emitted by the laser diode is changed approximately sinusoidally in correspondence to one main scanning section of the image recording carrier in order to keep the exposure amount at any point in one main scanning section of the record carrier constant. In the method and apparatus for controlling the amount of laser light for a type deflector, a plurality of light amount value setting means are provided, and when exposing one main scanning section of the image recording carrier, first, the plurality of light amount value setting means The modulation current related to the slope efficiency of the diode (average increase in optical output per unit drive current light in the laser oscillation region, ΔP/Δ■) is set, and then the modulation current is set for one main scanning period based on the modulation current. , the amount of laser light is configured to adjust and control changes in the amount of light emitted by the laser diode in a substantially sinusoidal manner, and as a result, it is possible to automatically eliminate changes in the slope efficiency of the laser diode over time and changes in temperature. The present invention relates to a control method and device.

Generally, a resonant deflector is used as a high-speed image writing device, but the scanning speed within the main scanning section is approximately sinusoidal and not constant, as shown in FIG. 1a. Therefore, in order to keep the exposure amount of the film constant per unit time and eliminate uneven exposure of the film, as shown by the broken line in Figure 1, the light emission output of the exposure laser diode is changed to that of the resonant deflector. It is changed according to the scanning speed. In other words, by reducing the light emission output at both ends of the main scanning section where the scanning speed is slow, and increasing the light emission output at the center where the scanning speed is fast, the overall exposure amount per unit time to the film is uniform. It is configured so that

The output of this emitted light, that is, the laser power, has a maximum value of 3 m at the center, for example, as shown in Figure 1.
W is adjusted to a minimum value of 1.2 mW at the end. Note that the hatched portion in FIG. 1 indicates the portion where current is supplied to the laser diode and the laser diode emits light.

Here, an example of the characteristics of the supply current and laser power of a laser diode is shown in FIG. 1C.

In the characteristic example shown in FIG. 1C, the horizontal axis represents the supplied current, and the vertical axis represents the laser power.

Now, when considering the characteristics shown by the solid line in FIG. 1C, it is found that the laser power changes by an amount of 3 mW and 1.2 mW with respect to the supply current I'r (laser power modulation current). In this case, the laser power can be controlled between 3 mW and 1.2 mW by setting the current IA related to the maximum laser power output point of 3 mW (the current related to point A in the figure) and the modulation current IT. One thing is easy to understand.

By the way, the above control is valid when the slope efficiency value is constant, but for example, as shown by the broken line in FIG. 1C,
If the slope efficiency decreases due to temperature changes or aging, the current I related to the maximum output setting point of the laser power of 3 mW.

(current related to point B in the figure) and modulation current It, the minimum output value of the laser power is 2 mW,
In this case, the amount of exposure per unit time to the film is no longer constant, and there is a possibility that uneven exposure may occur on the film.

The present invention has been made to overcome the above-mentioned disadvantages, and in order to make the exposure amount constant at any point in one main scanning section of the film exposed through a resonant deflector, it is possible to A value setting means is provided, and when exposing one main scanning section of the image recording carrier, first, the modulation current related to the slope efficiency of the laser diode is set by the plurality of light amount value setting means, and then the modulation current related to the slope efficiency of the laser diode is set. By adjusting and controlling the change in the amount of light emitted by the diode in a substantially sinusoidal manner during one main scanning period based on the modulation current, it is possible to automatically eliminate secular change and temperature change in the slope efficiency of the laser diode. An object of the present invention is to provide a method and device for controlling the amount of laser light.

In order to achieve the above object, the present invention provides a method for controlling the light intensity of a laser light source, in which, when scanning one main scanning section of an image recording carrier by exposing it to light by conducting/non-conducting the laser diode, first, A modulation current related to a predetermined light emission amount range of the laser diode is set by the first light amount setting means and a second light amount setting means, and then a predetermined light amount related to the set modulation current is applied to one of the image recording carriers. It is characterized in that scanning is performed by changing it in accordance with the main scanning section.

Furthermore, the present invention provides a control device for a laser light source of a resonant deflector that changes the amount of light emitted from a laser diode approximately sinusoidally in accordance with one main scanning section of an image recording carrier. A conversion means and a plurality of light amount value setting means are provided, and the plurality of light amount value setting means detect a voltage related to a predetermined light emission amount range of the laser diode, and the voltage-current conversion means is converted by the detected voltage. The present invention is characterized in that it is configured to control the output current value of.

Next, the method for controlling the amount of laser light according to the present invention will be described in detail below with reference to the accompanying drawings, citing preferred embodiments in relation to the apparatus for implementing the method.

FIG. 2 is a basic block diagram for implementing the present invention, in which reference numeral 10 is a terminal to which a gate signal, so-called scan signal, related to one main scanning section is connected,
The connection terminal 10 of the scan signal is connected to the reset input terminal R of the counter 14. On the other hand, a grid pulse is introduced from the grid pulse introduction terminal 12 into the clock input terminal of the counter 14, and at that time, the counter 14 counts up for each grid pulse, and its output signal is sent to the address input terminal of the memory 1716 as a look-up table. will be introduced in

The output digital signals of the memory 16 (in this embodiment, the OO to FF signals) are introduced into the digital input terminal of the multiplication type D/A converter 18. The analog input terminal M of the multiplication type D/A converter 18 is connected to the output terminal of the first operational amplifier 20, and the analog output terminal A of the D/A converter 18 is connected to the digital input terminal and the analog input terminal M. A product signal of the signals introduced into is output.

An analog output terminal A of the D/A converter 18 is connected to a first input terminal of a second operational amplifier 22.

The output terminal of the second operational amplifier 22 is connected to the first transistor 2
4, the first transistor 24 is connected to the base terminal of the first transistor 24.
The emitter of is connected to the second input terminal of the second operational amplifier 22 and to the power supply +V via a resistor 26.

Next, the first transistor 24 through which the first reference current I flows
The collector is connected to the collector of the second transistor 28 through which the second reference current I2 flows, the collector of the third transistor 30, and the anode of the laser diode 32. The cathode of laser diode 32 is grounded. and,
The emitter of the second transistor 28 is connected to the +■ power supply via a resistor 34. Further, the base of the second transistor 28 is connected to the output terminal of the third operational amplifier 36. The emitter of the third transistor 30 is then connected to the -V power supply through a resistor 38. A conduction/non-conduction signal for film exposure is introduced into the terminal 40 related to the base of the third transistor 30.

On the other hand, the optical output of the laser diode 32 is detected by a PIN photodiode 42. The anode of the PIN photodiode 42 is connected to a power supply via a resistor 44, and is also connected to the input terminal of a fourth operational amplifier 46 as a buffer. Said PI
The cathode of the N photodiode 42 is grounded. The output terminal of the fourth operational amplifier 46 is connected to an analog input terminal of a first sample and hold circuit 48 and also to an analog input terminal of a second sample and hold circuit 50. Here, the first sampling gate pulse 52 is applied to the gate terminal GI of the first sample and hold circuit 48.
will be introduced. Further, a second sampling gate pulse 5 is applied to the gate terminal G2 of the sample and hold circuit 50.
4 will be introduced. The hold output terminal of the first sample and hold circuit 48 is connected to one input terminal of the third operational amplifier 36, and the output terminal of the second sample and hold circuit 50 is connected to one input terminal of the first operational amplifier 20. Connected.

Then, the third operational amplifier 36 and the first operational amplifier 20
A first variable reference voltage source V2 having a reference light amount of 3 mW and a second variable reference voltage source V2 having a reference light amount of 1.2 mW are respectively connected to the other input terminal of the power source.

The apparatus for carrying out the method for controlling the amount of laser light according to this embodiment is basically constructed as described above, and its operation and effects will be explained next.

FIG. 3 is a waveform diagram related to the basic block diagram shown in FIG. 2. FIG. 3a shows a scan signal related to one main scanning section, and the counter 14 is activated by the high level of the scan signal. At this time, the counter 14 counts up every time a grid pulse (not shown) is introduced into the counter 14. When the output signal of the counter 14 is introduced into the address input terminal of the memory 16, the digital output of the memory 16 outputs the predetermined digital pattern values shown in FIG. 3f. The digital value shown in Fig. 3 f is the SM shown in Fig. 3 S.
The high level part of PLI becomes the FF value, and then the
It becomes OO at the high level portion of SMPL2 shown in , and then increases and decreases sinusoidally so that it becomes FF at approximately the center of the scan signal and becomes OO at both ends.

Therefore, the first variable reference voltage source 1 is now adjusted to a voltage related to the first reference light amount, for example, 3 mW, and the second variable reference voltage source
Assume that the variable reference voltage source (2) is adjusted to a voltage related to the second reference light amount of 1.2 mW. In this case, first, the first sampling gate pulse 52 shown in FIG.
In one section, the voltage introduced into the analog input voltage terminal M of the multiplication type D/A converter 18 is ignored, so the current supplied from the first transistor 24 to the laser diode 32 is as shown in FIG. 3d. Assume that the resistor 26 is adjusted so that the current peaks at 55 mA. Then, at the time of the SMPLI, as shown in FIG. 3C, the second
Current I2 supplied from transistor 28 to laser diode 32 gradually increases. And 1. +I 2
= 75 mA, that is, the voltage between the terminals of the PIN photodiode 42 and the laser power of the laser diode 32 are 3 mA.
When the voltage reaches mW, the first sample and hold circuit 48 is held (point S1 in the figure), and as a result, the second
The value of the second transistor current ■2 supplied from the transistor 28 to the laser diode 32 is SM as shown in the following figure 3.
The current is maintained at 20 mA until the PL1 signal becomes high level. Through the above operation, the voltage related to the first reference light amount of 3 mW is sampled and held by the sample and hold circuit 48.

Next, the operation in the period in which the second sampling gate 54 is in the high level state shown in FIG.
The sample and hold operation related to the second reference light amount W point of 1.2 m in the PL2 section will be explained. In this case, the second transistor current I2 is constant at 20 mA, so the third
As shown in FIG. d, the first transistor current 2 of the first transistor 24 is controlled. However, as described above, the first transistor current 1. is the output voltage of the first operational amplifier 20, which is the voltage applied to the analog input terminal M of the D/A converter 18, and the output voltage of the memory 16, which is applied to the digital input terminal of the D/A converter 18, that is, in this case. is determined by the product of the voltage related to the output signal OO in the SMPL2 section. Therefore, in this case, SMPL
The first transistor current shown in FIG. 3d in two sections is 1. gradually decreases, I + + I z =65 mA.

That is, when the voltage between the terminals of the PIN photodiode 42 reaches a voltage corresponding to the laser power of the laser diode 32 of 1.2 mW, the second sample and hold circuit 50 is held (point 82 in the figure). As a result, the first
The value of transistor current {circle around (2)} is held at 45 mA.

Through the above operation, the voltage related to the second reference light amount of 1.2 mW is sampled and held.

After the SMPL2 interval shown in FIG. 3e, the output value of the memory 16 is controlled by the output value of the counter 14,
As shown in Figure 3 f, 10.20.40...FOl
Since FF, FO...40.20.10.00 are output in a substantially sinusoidal manner, in this case, the current flowing through the first transistor 24 is also substantially sinusoidal as shown from point 32 onward in FIG. 3d. Change. As a result, the amount of light from the laser diode 32 is output in a substantially sinusoidal manner, with a maximum value of 3 mW and a minimum value of 1.2 mW, as shown by the broken line in the third diagram. This value is inversely proportional to the scanning speed of the resonant deflector, and as a result, the exposure time per unit time for the film (not shown) is made uniform.

In this case, when a conducting/non-conducting signal for film exposure is applied to the base terminal of the third transistor 30 as shown in FIG. As shown in Figure 3, a prescribed amount of light is irradiated.

Next, let us assume that the slope efficiency of the laser diode 32 decreases due to aging, temperature changes, etc., and changes from the characteristic shown by the solid line in FIG. 4 to the characteristic shown by the broken line in FIG. 4. In this case, as can be easily understood from Figure 4, the required current when the laser power is 3 mW is 90 mA, which is 1.2 m.
The required current at W is 70 mA.

In response to this change, in the circuit configuration shown in the embodiment of the present invention shown in FIG. 2, sample and hold operations are always performed once and twice at the start of one scan. At the time of the interval, I 2
= 35 mA, therefore, the combined current I + + I z flowing through the laser diode 32 becomes 90 mA, and in the SMPL2 section, I l = 35 mA, so the combined current ■.

+ 12 = 70 mA, and as a result, even if the slope efficiency of the laser diode 32 decreases, the light amount width remains the same,
That is, an output of 3 mW to 1.2 mW can be obtained.

The above is the first embodiment of the present invention. Next, another embodiment of the present invention is shown in FIG. 5, and its operation will be explained. In FIG. 5, the same components as those shown in the first embodiment shown in FIG. 2 are given the same reference numerals, and detailed explanation thereof will be omitted.

In FIG. 5, reference numeral 60 is a D/A converter, and the D/A converter 60 has a first output setting terminal 01 and a second output setting terminal 01.
The VIIEF value of the output is determined by the respective values introduced into the output setting terminal 02 and the digital input terminal.

For example, the voltage at the 01 terminal is 3V, and the voltage at the 02 terminal is 5V.
When , the digital value of the D terminal is 00. FF, 80.1
When it changes to 0.00, ■REF value is 3■, 5V, 4V
, 3.125 V, changes to 3v. Sunawachi, D/A
The number of current supply transistors of the laser diode 32 in the first embodiment shown in FIG.
It is possible to reduce the number of In another embodiment shown in FIG. 5, the first sample and hold circuit 4
8 to determine the light amount related to the first reference light amount of 3 mW, and
The second reference light amount is set to 1.2 by the sample hold circuit 50 of
This means that the amount of light in mW can be uniquely determined.

As described above, according to the present invention, when a plurality of light amount value setting means are provided and one main scanning section of an image recording carrier is exposed,
First, a modulation current related to the slope efficiency of the laser diode is set by the plurality of light amount value setting means, and then,
Since the change in the amount of light emitted by the laser diode can be adjusted and controlled in a substantially sinusoidal manner during one main scanning period based on the modulation current, it is possible to automatically eliminate secular changes and temperature changes in the light emitting efficiency of the laser diode. Thus, a method and apparatus for controlling the amount of laser light can be obtained.

Although the present invention has been described above with reference to preferred embodiments, the present invention is not limited to these embodiments.
For example, the polarity of the current supply transistor of the laser diode is reversed to make it a voltage follower or emitter follower, and a resistor for setting the supply current is inserted between the output terminal of the follower and the laser diode. Alternatively, the slope efficiency detection circuit may be configured to operate only when power is input, instead of sampling and holding every scan, and the current value may be set by reading the result with a microcomputer, etc., according to the present invention. Of course, various improvements and changes in design are possible without departing from the gist of the invention.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the light amount control of a resonant deflector, FIG. 2 is a block diagram of the first embodiment of the laser diode light amount control circuit according to the present invention, and FIG. 3 is the light amount shown in FIG. 2. FIG. 4 is an explanatory diagram of waveforms of the control circuit, FIG. 4 is an explanatory diagram of changes in light amount output of a laser diode, and FIG. 5 is a circuit block diagram of another embodiment of the present invention. 10... Connection terminal 12... Grid pulse introduction terminal 14... Counter 16... Memory 1
8... Multiplying D/A converter 20.22... Operational amplifier 32... Laser diode 42... PIN photodiode 46... Operational amplifier

Claims (3)

[Claims] (1) A method for controlling the light intensity of a laser light source, in which when one main scanning section of an image recording carrier is exposed and scanned by conduction/non-conduction of a laser diode, first, a first light intensity setting means and a second light intensity setting means are controlled. A modulation current related to a predetermined light emission amount range of the laser diode is set by the light amount setting means, and then a predetermined light amount related to the set modulation current is changed corresponding to one main scanning section of the image recording carrier. 1. A method for controlling the amount of laser light, characterized in that scanning is performed using a laser beam. (2) A method for controlling the amount of laser light, which comprises setting the modulation current for a predetermined range of light emission amount only at a predetermined time when the device is powered on. (3) In a control device for a laser light source of a resonant deflector that changes the amount of light emitted from a laser diode substantially sinusoidally in correspondence to one main scanning section of an image recording carrier, a voltage-current conversion means for driving the laser diode; , a plurality of light amount value setting means are arranged, the plurality of light amount value setting means detects a voltage related to a predetermined light emission amount range of the laser diode, and the output current of the voltage-current conversion means is adjusted based on the detected voltage. 1. A laser light amount control device, characterized in that it is configured to control a value.