JPH0556712B2 - - Google Patents

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a laser recording device that records a continuous tone image by scanning a photosensitive material with a laser beam modulated based on an image signal. The present invention relates to a laser recording device capable of recording high-gradation images by modulating the light intensity of a laser beam in an analog manner.

(Prior Art) Conventionally, optical scanning recording apparatuses have been widely put into practical use, which record an image on a photosensitive material by deflecting a light beam using an optical deflector and scanning the photosensitive material.
A semiconductor laser has conventionally been used as one of the means for generating a light beam in such an optical scanning recording device. This semiconductor laser has many advantages, such as being smaller, cheaper, and consumes less power than gas lasers, and can be directly modulated by changing the drive current.

However, on the other hand, this semiconductor laser
As shown in FIG. 2, the optical output characteristics with respect to the drive current vary drastically between the LED region (natural light emitting region) and the laser oscillation region, so there is a problem that it is difficult to apply it to continuous tone image recording. That is, if intensity modulation is performed using only the laser oscillation region where the drive current vs. optical output characteristic is linear, the dynamic range of the optical output can only be about two orders of magnitude. As is well known, it is impossible to obtain a high quality continuous tone image with this level of dynamic range.

For example, JP-A-56-115077, JP-A No. 56-115077,
As shown in No. 152372, etc., the optical output of the semiconductor laser is kept constant, the semiconductor laser is turned ON and OFF continuously, the scanning beam is pulsed light, and the number or width of this pulse is changed for each pixel. Attempts have also been made to record continuous tone images by controlling and varying the amount of scanning light.

However, when performing pulse number modulation or pulse width modulation as described above, for example, when the pixel clock frequency is 1 MHz, if you try to secure a resolution of 10 bits (approximately 3 digits) for the density scale, that is, the amount of scanning light, the pulse frequency will be It must be set extremely high, at least 1GHz. Although the semiconductor laser itself can be turned on and off at this level of frequency, pulse count circuits for pulse number control or pulse width control cannot operate at such high frequencies, and in the end, requires the pixel clock frequency to be significantly lower than the above values. Therefore, the recording speed of the device has to be significantly reduced.

Furthermore, in the above method, the amount of heat generated by the semiconductor laser chip changes depending on the number or width of pulses output during the recording period of each pixel, and as a result, the driving current versus light output characteristics of the semiconductor laser changes. However, the amount of exposure per pulse may vary. If this happens, the gradation of the recorded image will shift, making it impossible to obtain a high-quality continuous tone image.

On the other hand, as shown in, for example, Japanese Patent Application Laid-Open No. 71374/1983, a method has been proposed for recording a high-gradation image by combining the above-mentioned pulse number modulation or pulse width modulation with the above-mentioned light intensity modulation. However, in this case as well, the problem arises that the amount of heat generated by the semiconductor laser chip varies depending on the number or width of pulses as described above, and as a result, the amount of exposure per pulse varies.

Considering the above, for example, the concentration scale
In order to record a high gradation image of approximately 10 bits, or 1024 gradations, light intensity modulation is performed across the LED area and laser oscillation area shown in Figure 2 above to increase the dynamic range of the optical output by 3. It is desirable to be able to secure about 10,000 digits. However, in the above two regions, the driving current vs. optical output characteristic of the semiconductor laser is naturally not linear, so in order to easily and accurately record high-gradation images, it is necessary to change the image signal at equal density intervals in response to a constant amount of change in the image signal. In order to make it possible to control the image density, it is necessary to compensate for the above-mentioned characteristics in some way to linearly change the relationship between the light emission level command signal of the semiconductor laser and the optical output.

Conventionally, as a circuit that linearizes the relationship between the light emission level command signal of the semiconductor laser and the optical output, it detects the light intensity of the laser beam and sends a feedback signal corresponding to the detected light intensity to the semiconductor laser light emission level command. An optical output stabilization circuit (hereinafter referred to as an APC circuit) that provides feedback to a signal is known. FIG. 3 shows an example of this APC circuit, and the APC circuit will be explained below with reference to FIG. 3. The light emission level command signal Vref that commands the light emission intensity of the semiconductor laser 1 is added at the addition point 2.
The voltage-to-current conversion amplifier 3 supplies the semiconductor laser 1 with a drive current proportional to the command signal Vref. Semiconductor laser 1
The light beam 4 emitted forward is used to scan the photosensitive material through a scanning optical system (not shown).
On the other hand, the intensity of the light beam 5 emitted to the rear side of the semiconductor laser 1 is detected by, for example, a pin photodiode 6 for monitoring the amount of light installed inside the case of the semiconductor laser. The intensity of the light beam 5 thus detected is proportional to the intensity of the light beam 4 actually used for image recording. The intensity of the light beam 5, that is, the output current of the photodiode 6 indicating the intensity of the light beam 4, is converted into a feedback signal (voltage signal) Vpd by a current-voltage conversion amplifier 7, and the feedback signal Vpd is as described above. It is input to addition point 2. This addition point 2 outputs a deviation signal Ve indicating the deviation between the light emission level command signal Vref and the feedback signal Vpd.
The current is converted into a current by the current conversion amplifier 3 and drives the semiconductor laser 1.

In the above APC circuit, if ideal linear compensation is performed, the intensity of the light beam 5 will be proportional to the light emission level command signal Vref. In other words, the intensity Pf of the light beam 4 used for image recording (light output of the semiconductor laser 1) is proportional to the light emission level command signal Vref. The solid line in FIG. 4 shows this ideal relationship.

(Problems to be Solved by the Invention) It is relatively easy to drive and control a semiconductor laser so that the light intensity Pf is always at a constant level using the APC circuit as described above. When driving a semiconductor laser by changing the light emission level command signal Vref in an analog manner at high speed in order to record a continuous tone image, it is difficult to obtain the characteristics shown by the solid line in FIG. 4. In particular, it is very difficult to record a high-gradation image with a density scale of about 10 bits when the pixel clock frequency is set to about 1 MHz as described above.

The reason for this will be explained below. The driving current vs. optical output characteristic of the semiconductor laser 1 inserted into the system of FIG. 3 is extremely nonlinear, as shown in FIG. In other words, the differential quantum efficiency, which is the gain of a single semiconductor laser, changes greatly between the LED region and the laser oscillation region, as shown in Figure 5 when expressed logarithmically. Therefore, it is necessary to make the loop gain of the system shown in FIG. 3 extremely large. The curve shown by the broken line in FIG. 4 shows an example of the light output level command signal versus light output characteristic of the semiconductor laser that changes according to the loop gain, and as shown in the figure, the curve shows the characteristic close to the ideal characteristic shown by the solid line. To achieve this, a high gain of around 60dB is required.

Furthermore, the characteristics shown in Fig. 4 are for the case where the light emission level command signal Vref is a very low frequency signal close to direct current, but when the command signal Vref is a high frequency signal, there are still other characteristics. A problem arises.
This point will be explained below. Figure 6 shows the second
It shows the case temperature dependence of the drive current vs. optical output characteristics of the semiconductor laser shown in the figure. As shown in the figure, the optical output of the semiconductor laser decreases as the case temperature increases if the drive current is constant. Generally, when applying a semiconductor laser to a laser recording device, etc.,
Control is performed to maintain the case temperature constant, but it is completely impossible to control the transient temperature change of the laser diode chip that occurs when a driving current is applied to the semiconductor laser. In other words, when a driving current is applied to the semiconductor laser in steps as shown in 1 of FIG. 7, the temperature of the laser diode chip becomes a steady state as shown in FIG. 7 2 due to the case temperature constant control. As a result, the optical output of the semiconductor laser changes as shown in FIG. 7 in accordance with the characteristics shown in FIG. 6. This is known as the droop characteristic of semiconductor lasers. In the APC circuit shown in Figure 3,
It has been found that the aforementioned loop gain of about 10 dB is required to correct the nonlinearity of the laser drive current vs. optical output characteristic due to this droop characteristic.
Therefore, when a signal ranging from low frequency to high frequency (for example, 1 MHz) is used as the light emission level command signal Vref, the light emission level command signal vs. light output characteristic is close to the solid line in Fig. 4 while maintaining high responsiveness. In order to obtain (linearity), a total loop gain of about 70 dB is required in the laser oscillation region, including the above-mentioned 60 dB. At present, it is almost impossible to realize such a high-speed, high-gain APC circuit.

Therefore, the present invention aims to achieve high gain as described above.
Even without using an APC circuit, it is possible to make the emission level command signal vs. light output characteristic of a semiconductor laser linear from its LED area to the laser oscillation area, and thus high-gradation images can be recorded at high speed by light intensity modulation. The object of the present invention is to provide a laser recording device that can perform the following steps.

(Means for solving the problem) A laser recording device of the present invention includes a semiconductor laser,
A beam scanning system that scans a light beam emitted from the semiconductor laser onto a photosensitive material, and a beam scanning system that generates a light emission level command signal corresponding to an image signal and controls the drive current of the semiconductor laser based on the signal to generate a laser beam. In a laser recording device equipped with a laser operation control circuit that modulates the optical intensity of the beam, the laser operation control circuit is configured to compensate for the nonlinearity of the drive current vs. optical output characteristic of the APC circuit and the semiconductor laser. A correction table that corrects the light emission level command signal to linearize the relationship between the light output of the semiconductor laser based on the corrected signal and the light emission level command signal before correction,
The present invention is characterized by being provided with table creation means for inputting a test signal whose level changes into the laser operation control circuit and creating the correction table based on the relationship between the light beam intensity and the test signal at that time. be.

(Function) If the light emission level command signal of the semiconductor laser is corrected using the above correction table, even if the gain of the APC circuit is low, the light emission level command signal before correction and the semiconductor laser light output will be It is possible to obtain optical output characteristics close to the ideal characteristics shown by the solid line in the figure.

Furthermore, if the correction table creation means described above is provided, it is possible to create a new correction table at any time, so even if the performance of a semiconductor laser changes over time, for example, such changes can be compensated for and the correction table can be constantly updated. The correction table can be kept appropriate.

(Example) Hereinafter, the present invention will be described in detail based on an example shown in the drawings.

FIG. 1 shows a laser recording apparatus according to a first embodiment of the present invention. The image signal generator 10 is
An image signal S1 carrying a continuous tone image is generated.
This image signal S1 is, for example, a digital signal representing a continuous tone image with a 10-bit density scale. The image signal generator 10 is connected to a line clock S2, which will be described later.
Switches the signal for one main scanning line based on
It also outputs an image signal S1 for each pixel based on the pixel clock S3. In this example, the pixel clock frequency is 1MHz, in other words, the recording time for one pixel is
Set to 1μsec (seconds).

The above-mentioned image signal S1 passes through the multiplexer 11, undergoes a correction described later in a correction table 40 consisting of a RAM, and is converted into, for example, a 16-bit light emission level command signal S5. This light emission level command signal S5 is input to the D/A converter 16, where a light emission level command signal consisting of an analog voltage signal is sent to the D/A converter 16.
Converted to Vref. This light emission level command signal
Vref is input to the addition point 2 of the APC circuit 8 via a signal changeover switch 15, which will be described later. The summing point 2, voltage-current conversion amplifier 3, semiconductor laser 1, photodiode 6, and current-voltage conversion amplifier 7 of the APC circuit 8 are the same as those in the circuit shown in FIG. The semiconductor laser 1 then emits a light beam 4 with an intensity corresponding to the light emission level command signal Vref (that is, corresponding to the image signal S1). This light beam 4 is passed through a collimator lens 17 to become a parallel beam, and then enters an optical deflector 18, such as a polygon mirror, where it is reflected and deflected. The light beam 4 thus deflected is directed through a focusing lens 1, which is usually an fθ lens.
9 to focus on a minute spot on the photosensitive material 20, and scan the photosensitive material 20 in the X direction (main scan). The photosensitive material 20 is transported by a transport means (not shown) in the Y direction substantially perpendicular to the main scanning direction X, thereby causing the light beam 4 to perform sub-scanning. In this way, the photosensitive material 20 is two-dimensionally scanned by the light beam 4 and exposed. As mentioned above, the light beam 4 is intensity-modulated based on the image signal S1, so that on this photosensitive material 20,
The continuous tone image carried by the image signal S1 is recorded as a photographic latent image. Note that when the light beam 4 scans the photosensitive material 20 as described above, the photodetector 21 detects that the beam 4 has passed the main scanning starting point, and the photodetector 21 outputs the starting point. The detection signal S6 is input to the clock generator 36. The clock generator 36 outputs the aforementioned line clock S2 and pixel clock S in synchronization with the input timing of the start point detection signal S6.

The photosensitive material 20 is then passed through a developer 22 where it undergoes a development process. As a result, the photosensitive material 20
Above, the continuous tone image is recorded as a visible image.

Here, the correction of the image signal S1 in the above-mentioned correction table 40 will be explained. The correction table 40 includes a gradation correction table 12, an inverse log conversion table 13, and a correction table (hereinafter referred to as a V-P characteristic correction table) 1 for linearly correcting the emission level command signal versus light output characteristic of the semiconductor laser 1.
Consists of 4. The gradation correction table 12 is a known one for correcting the gradation characteristics of the photosensitive material 20 and its development processing system. This gradation correction table 1
2 may have fixed correction characteristics, but in this embodiment, the gradation characteristics of the photosensitive material 20 change from lot to lot, or the developing device 22
In consideration of the fact that the characteristics of the developer contained therein change over time, the correction characteristics are configured to be able to be modified as appropriate in accordance with the actual gradation characteristics. That is, the test pattern generation circuit 26 outputs a test pattern signal S4 carrying several levels (for example, 16 levels) of image density on the photosensitive material 20.
is input to multiplexer 11. At this time, the multiplexer 11 is switched from the image recording state in which the image signal S1 is input to the correction table 40 as described above, and the test pattern signal S
4 is input into the correction table 40. The semiconductor laser 1 receives this test pattern signal S.
4 and the light beam 4 is therefore intensity modulated. As a result, the density changes stepwise on the photosensitive material 20, for example, 16
Step wedges (test patterns) are recorded as photographic latent images. This photosensitive material 20 is sent to a developing machine 22, and the step wedge is developed. After development, the photosensitive material 20 is placed in a densitometer 23, and the optical density of each of the step wedges is measured. The optical density thus measured is input to the density value input means 24 in association with each step wedge, and the density value input means 24 outputs a density signal S7 indicating the optical density of each step wedge. This concentration signal S7 is input to the table creation means 37, and the table creation means 3
7 creates a gradation correction table based on this density signal S7 and the test pattern signal S4 so that a predetermined image density can be obtained with the value of the predetermined image signal S1. As described above, this gradation correction table associates approximately 16 levels of image signal values with respective predetermined image density values. Data S8 indicating this tone correction table is input to the data interpolation means 38, where interpolation processing is performed to obtain a tone correction table that can correspond to the image signal S1 of 1024 steps (=10 bits). The aforementioned gradation correction table 12 is formed based on the data S9 indicating this gradation correction table.

When recording an image based on the image signal S1, the image signal S1 input to the gradation correction table 12 via the multiplexer 11 is converted into a signal S1' by the gradation correction table 12, and then the inverse log
The light emission level command signal S is determined by the conversion table 13.
1″.

The VP characteristic correction table 14 will now be explained. As mentioned earlier, even if the feedback signal Vpd is fed back to the addition point 2 in the APC circuit 8, the relationship between the light emission level command signal and the intensity of the light beam 4 is not ideal (the relationship indicated by the solid line in Fig. 4). )
It is difficult to do so. The above-mentioned VP characteristic correction table 14 is provided to obtain the above-mentioned ideal relationship. In other words, the light emission level command signal
Assuming that the ideal relationship between Vref and the optical output of the semiconductor laser 1 is a straight line indicated by a in FIG. 8, and the actual relationship is a curved line indicated by b in FIG. Light emission level command signal S1''
The voltage value when is directly D/A converted is Vin
Assuming that the voltage value Vin is V, it is formed to convert this voltage value Vin into a value V. That is, if the value of the light emission level command signal Vref is Vin, only a light intensity of P' can be obtained, but if the above conversion is performed, a light intensity of Po can be obtained for the voltage value Vin. In other words, the light emission level command signal S1''
The relationship between the voltage value Vin corresponding to , and the optical output intensity Pf is linear.

With this configuration, the density in the photosensitive material 20 can be controlled at equal intervals by changing the image signal S1 by a predetermined amount. Further, the characteristic curve b in FIG. 8 shows the semiconductor laser 1 as described above.
This is the case when the LED area and the laser oscillation area are driven. In this way, a light output dynamic range of about 3 digits is secured, so as mentioned above, a high gradation image of about 1024 steps can be achieved. , it becomes possible to record easily and with high precision.

As described above, the nonlinearity of the light emission level command signal versus laser light output characteristic caused by the nonlinear drive current versus light output characteristic of the semiconductor laser 1 can be linearized by the V-P characteristic correction table 14. If corrected, the loop gain of the system returning from the summing point 2 of the APC circuit 8, the voltage-current conversion amplifier 3, the semiconductor laser 1, the photodiode 6, and the current-voltage conversion amplifier 7 to the summing point 2 will have the above-mentioned nonlinearity. It becomes unnecessary to include the gain necessary for correction. That is, this loop gain is used to correct deviations from the drive current vs. optical output characteristics of the semiconductor laser 1 due to transient temperature changes that occur during the operation of the semiconductor laser 1 or errors in the case temperature constant control of the semiconductor laser 1. Furthermore, it is only necessary to secure as much as necessary to correct the drift of the amplifier, etc. Specifically, for example, when the pixel clock frequency is 1MHz and the semiconductor laser 1 is operating with an optical output of 3mW, the above loop gain is
It is sufficient if approximately 30 dB is secured. This level of loop gain can be easily achieved with the current state of the art.

Next, the creation of the VP characteristic correction table 14 will be explained. The apparatus shown in FIG. 1 is provided with table creation means 70, and the table creation means 70
The test signal S10 emitted by the signal changeover switch 1
5 to the addition point 2, and the feedback signal Vpd of the APC circuit 8 is input to the table creation means 70. The correction table creation signal changeover switch 15 is switched from the state during image recording in which the light emission level command signal Vref is sent to the addition point 2 as described above, to the state in which the test signal S10 is sent to the addition point 2. At this time, the switch 71 provided on the feedback path of the feedback signal Vpd is opened in conjunction with the switching of the signal changeover switch 15 or by manual operation.

The level of the test signal S10 increases stepwise as time passes. In other words, the PROM 72 stores arithmetic sequence of numbers on the logarithmic axis, and these sequence of numbers are clocked.
Accessed sequentially by CLK. Thereby
The digital value read from PROM72 is
A converter 73 converts it into analog, and amplifier 74
When amplified by
A test signal S10 is obtained in which the number of CLKs, that is, the voltage value V increases stepwise as time passes. This test signal S10 is input to the addition point 2 via the signal changeover switch 15 as a substitute for the light emission level command signal Vref. Furthermore, the above
The PROM 72 stores a number sequence of, for example, 14 bits, which is sufficiently higher than the 10 bits of the aforementioned concentration scale (that is, the emission level resolution of the semiconductor laser 1).

When the test signal S10 as described above is input to the addition point 2, the semiconductor laser 1 emits the light beam 4, and a feedback signal Vpd corresponding to the optical output is input to the comparator 77. A reference signal Vg generated from the CPU 78 and converted into an analog signal by the D/A converter 76 is input to the comparator 77, and the feedback signal Vpd and the reference signal Vg are compared. At this time, the CPU 78
First, a reference signal Vg(1) corresponding to the lowest emission level of the semiconductor laser 1 is output, and when the reference signal Vg(1) and the feedback signal Vpd match, the comparator 77 outputs a match signal S11. This coincidence signal S
11 is input to latch 75. Latch 75 is
It receives the output from the PROM 72, and latches the output of the PROM 72 at the time when the coincidence signal S11 is input. This latched signal S12
If we explain with Figure 8, the value of the reference signal Vg is
The value of ΔV when the voltage is Vin is shown (hereinafter, the voltage value ΔV corresponding to the reference signal Vg(n) will be referred to as ΔV(n)).
The CPU 78 receives the signal S12 indicating the voltage value ΔV(1), and based on the signal S12 and the reference signal Vg(1), calculates the value V(1) such that V(1)=Vg(1)+ΔV(1). demand. Then, the CPU 78 forms in the RAM 79 a table for converting the reference signal Vg(1) into a signal of voltage value V(1).

The coincidence signal S11 is also input to the CPU 78,
When the CPU 78 receives this match signal S11, it switches the reference signal Vg(1) to Vg(2), that is, the one corresponding to the second light emission level from the bottom of the semiconductor laser 1, and resets the comparator 77 at the same time. In this case as well, the CPU 78 calculates the value V(2) of V(2)=Vg(2)+ΔV(2), and converts the reference signal Vg(2) to the voltage value V(2).
A table for converting the signal into the signal is created in the RAM 79.

The above operations are performed sequentially up to the reference signal Vg (1024), that is, the reference signal corresponding to the maximum emission level of the semiconductor laser 1, and as a result, the RAM 79
, a table is created that converts each of the 1024 signal values Vin(n) to V(n). This table is further interpolated to become a 16-bit table, which is sent to the RAM that constitutes the correction table 40 via the data line 80, and the V-P characteristic correction table 14.
is set as . As described above, this correction table 14 is formed to convert the voltage value Vin in FIG.
The relationship between the light emission level command signal S1'' before passing through 4 and the optical output Pf of the semiconductor laser 1 is linear.

After creating the correction table 14 as described above, the signal changeover switch 15 is switched to the state at the time of image recording, and the switch 71 is closed.

As explained above, in addition to finding the relationship between the voltage values Vin and V corresponding to all image densities one by one, as in the case of creating the gradation correction table 12 explained earlier, the relationship between the voltage values Vin and V It is also possible to obtain the relationship for only some major cases and interpolate the data to create the V-P characteristic correction table 14. Also, the gradation correction table 12,
The inverse log conversion table 13 and the above-mentioned V-P characteristic correction table 14 may be formed as one correction table including all of their respective conversion characteristics, or may be formed in separate forms.

Further, in the above embodiment, the test signal S10 whose level increases stepwise as time passes is used, but on the contrary, the level decreases stepwise or continuously as time passes. A test signal can also be used.

Next, a second embodiment of the present invention will be described with reference to FIG. Note that in FIG. 10, elements equivalent to those in FIG. 1 are given the same numbers, and explanations thereof will be omitted. (Same below). Although FIG. 10 only shows the laser operation control circuit and table creation means 70', the parts not shown in the apparatus, such as the light beam scanning system, are formed in the same way as in the apparatus shown in FIG. be done. The table creation means 70' of the apparatus of the second embodiment differs from the table creation means 70 of the first embodiment in that a switch 71 is omitted. In other words, in this second embodiment device, the APC circuit 8 operates in the same manner as usual even when creating the correction table 14. Therefore, in this device, when the coincidence signal S11 is input, the latch 75 latches the signal S1.
2 corresponds to the voltage value V in FIG.
Therefore, the CPU 78 directly calculates the value of V(n) without performing the above-mentioned calculation of V(n) = Vg(n) + ΔV(n), and calculates the voltage value.
Create a table to convert Vg(n) to V(n).

Next, a third embodiment of the present invention will be described with reference to FIG. In the device of this third embodiment, the light emission level command signal S1'' output from the inverse log conversion table 13 is directly transmitted to the D/A converter 1.
6 is input. On the other hand, the image signal S1'' is branched and input to the V-P characteristic correction table 44. This V-P characteristic correction table 44 is slightly different from the V-P characteristic correction table 14 of the apparatus shown in FIG. Difference ΔV between voltage value V and Vin in Fig. 8
It is formed to seek. This voltage difference ΔV
The digital signal S5' indicating this is passed through the D/A converter 45, converted into an analog signal, and added to the voltage value Vin (corresponding to the light emission level command signal S1'') at the addition point 2. In this way, As a result, the addition point 2 is obtained as in the device shown in FIG.
This is the same as inputting a signal of the voltage value V as the light emission level command signal Vref, and the same effect as described above can be obtained.

V-P correction table 4 of this FIG. 3 embodiment device
4 must be formed to determine the voltage difference ΔV as described above, it is impossible to use the table creation means 70' shown in FIG. 10 in this example, and the table creation means 70' shown in FIG. A table creation means 70 similar to means 70 is used. In this case, the table creation means 70 does not perform the above-mentioned calculation V(n)=Vg(n)+ΔV(n), but calculates the signal S1 with respect to the reference signal Vg(n).
Correction table 44 that outputs the value of ΔV(n) indicated by 2
formed to create.

Next, a fourth embodiment of the present invention will be described with reference to FIG. In the device shown in FIG. 12, the light emission level command signal S1'' is branched to V-
The structure is similar to that of the apparatus shown in FIG. 11 until inputting the signal S5' into the P characteristic correction table 44, performing the correction as described above, and converting the obtained signal S5' into an analog signal in the D/A converter 45. There is. However, the voltage signal ΔV output from the D/A converter 45 is not input to the addition point 2, but is passed through the voltage-current conversion amplifier 46 and converted into a current Δi. This current Δi is added to the drive current obtained by converting the deviation signal Ve at the addition point 47 at the subsequent stage of the voltage-current conversion amplifier 3 of the APC circuit 8. The device of the fourth embodiment differs from the device of the third embodiment only in that the voltage signal ΔV is not directly input to the APC circuit 8, but is converted to a current Δi and then input to the APC circuit 8. In this case as well, the same effects as in the first embodiment can be obtained.

Table creation means 70'' of this fourth embodiment device
differs from the table creation means 70 of FIG. 1 only in that the test signal S10 is input to the addition point 47, but in this case also, the CPU 78 receives the signal S12 indicating the voltage value ΔV of FIG. Therefore, the CPU 78 should be configured to create a correction table 44 that outputs the value of ΔV(n) for the reference signal Vg(n) based on the signal S12 and the reference signal Vg(n). Bye.

(Effects of the Invention) As explained in detail above, in the laser recording device of the present invention, the nonlinearity of the light emission level command signal versus laser light output characteristic caused by the nonlinearity of the drive current versus light output characteristic of the semiconductor laser is Since the correction is performed using a correction table provided separately from the semiconductor laser light output stabilization circuit, the loop gain of the closed loop formed by the above light output stabilization circuit can be set to a low value that is sufficiently achievable with the current technology level. Even when set to , the relationship between the light emission level command signal and the semiconductor laser light output is
It can be made linear across the LED area and the laser oscillation area. Therefore, according to the apparatus of the present invention, the image density can be controlled at equal density intervals by changing the image signal by a predetermined amount, and the optical output dynamic range of the semiconductor laser, that is, the exposure amount of the photosensitive material can be controlled over a wide range of about 3 orders of magnitude. As a result, it is possible to record extremely high-gradation continuous-tone images with a density resolution of about 10 bits at high speed and precision, for example.

Furthermore, since the laser recording apparatus of the present invention is equipped with means for creating the above-mentioned correction table, the correction table can be re-created at any time. Therefore, in the device of the present invention, even if, for example, the performance of the semiconductor laser changes over time, such changes can be compensated for and the correction table can always be kept at an appropriate level, allowing precise recording to be performed. can be maintained over a long period of time.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a laser recording device according to a first embodiment of the present invention, FIG. 2 is a graph showing drive current versus light output characteristics of a semiconductor laser, and FIG. 3 is an example of a semiconductor laser light output stabilizing circuit. Figure 4 is a graph showing the relationship between the light emission level command signal and the semiconductor laser optical output, Figure 5 is a graph showing the relationship between the semiconductor laser optical output and differential quantum efficiency, and Figure 6 is the graph showing the relationship between the semiconductor laser optical output and the differential quantum efficiency. A graph showing the temperature dependence of the drive current vs. optical output characteristic of a laser, FIG. 7 is a graph explaining the droop characteristic of a semiconductor laser, and FIG. 8 is a graph explaining the effect of the V-P characteristic correction table in the device of the present invention. , FIG. 9 is a graph showing the waveform of a test signal emitted by the table creation means of the apparatus according to the first embodiment, and FIG. 10 is a graph showing the semiconductor laser operation control circuit and table creation of the laser recording apparatus according to the second embodiment of the present invention. Block diagram showing the means, No. 11
The figure is a block diagram showing a semiconductor laser operation control circuit and table creation means of a laser recording apparatus according to a third embodiment of the present invention, and FIG. 12 is a block diagram showing a semiconductor laser operation control circuit of a laser recording apparatus according to a fourth embodiment of the present invention. FIG. 3 is a block diagram showing table creation means. 1... Semiconductor laser, 2,47... Addition point,
3,46...Voltage-current conversion amplifier, 4,5...
Light beam, 6...Photodiode, 7...Current-voltage conversion amplifier, 8...APC circuit, 10...
Image signal generator, 14, 44... V-P characteristic correction table, 16, 45, 73, 76... D/A converter, 17... Collimator lens, 18... Light deflector, 19... Focusing lens , 20...photosensitive material,
40...Correction table, 70, 70', 70''...
Table creation means, 71... switch, 72...
PROM, 75...Latch, 77...Comparator, 78...CPU, 79...RAM, S1...Image signal, S1''...Emission level command signal before correction,
Vref: Light emission level command signal, Vpd: Feedback signal, Ve: Deviation signal.

Claims (1)

[Scope of Claims] 1. A semiconductor laser that emits a light beam; a beam scanning system that scans the light beam on the photosensitive material; and a beam scanning system that generates a light emission level command signal corresponding to an image signal and controls the semiconductor laser based on the signal. and a laser operation control circuit that modulates the intensity of the light beam by controlling a drive current of the laser, the laser operation control circuit detects the intensity of the light beam and modulates the intensity of the light beam. an optical output stabilization circuit that feeds back a corresponding feedback signal to the emission level command signal; and a light output stabilization circuit that feeds back a corresponding feedback signal to the emission level command signal; It has a correction table that linearizes the relationship between the optical output of the semiconductor laser based on the subsequent signal and the emission level command signal before correction, and inputs a test signal whose level changes to the laser operation control circuit, and 1. A laser recording apparatus, further comprising table creation means for creating the correction table based on the relationship between the intensity of the light beam and the test signal. 2. The table creation means includes a switch that opens a feedback path for the feedback signal when creating the table, a test signal generator that generates a test signal whose level changes over time, and a test signal generator that corresponds to the light emission level command signal. a reference signal generator that outputs a reference signal with its level sequentially changed step by step, and a comparator that compares each reference signal having a different level with the feedback signal and outputs a matching signal when the levels of both signals match. , a signal holding means that is connected to the comparator and the test signal generation section and holds the level of the test signal at the time when the coincidence signal is input; and a held test signal outputted by the signal holding means and the reference signal. and a table creation section that creates a table of characteristics for converting this reference signal into a signal obtained by adding the retention test signal to the signal based on the above, and sets this as the correction table. A laser recording device according to claim 1. 3. The table creation means includes a test signal generating section that generates a test signal whose level changes over time, and a standard that outputs a reference signal corresponding to the light emission level command signal with the level sequentially changed in a stepwise manner. a signal generating section; a comparator that compares each reference signal having different levels with the feedback signal and outputs a match signal when the levels of these two signals match; connected to the comparator and the test signal generating section; signal holding means for holding the level of the test signal at the time when the coincidence signal was input; and based on the holding test signal outputted by the signal holding means and the reference signal, converting this reference signal into the holding test signal. 2. The laser recording apparatus according to claim 1, further comprising a table creation section that creates a table of characteristics to be converted and sets this as the correction table.