JPS63102548A - Laser recording device - Google Patents

Abstract

PURPOSE:To accurately record a high gradation continuous image at a high speed by correcting the non-linearity of a light emitting level command signal pair scanning beam strength characteristic due to the fact that the incident light strength pair light transmittance characteristic of an optical element is non-linear, with a correcting table provided separately from a semiconductor laser light output stabilizing circuit. CONSTITUTION:A light output stabilizing circuit (APC) circuit 8 is constituted of a light detecting device 53 and a current voltage converting amplifier 54 including the channel from the light detecting device 53 to an adding point 2, and a light output Pf of a semiconductor laser 1 is in proportion to a light emitting level command signal Vref. A correcting table 40 corrects linearily the light emitting level command signal pair light output characteristic of a gradation correcting table 12, a reverse log converting table 13 and a semiconductor laser 1. The table is composed of a V-P characteristic correcting table 14, and arranged at the front step of a light stabilizing circuit. An image signal S1 inputted through a multiplexer 11 is inputted through the gradation correcting table 12, the reverse log converting table 13 and the V-F characteristic correcting table 14 to the adding point 2, and corrected so that the relation of a voltage value Vin and a scanning beam strength Ps corresponding to a light emitting level command signal S1'' can be linear.

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, as shown in Figure 2, the optical output characteristics of this semiconductor laser with respect to the drive current vary drastically between the LED region (natural light emitting region) and the laser oscillation region, so it is not suitable for continuous tone image recording. The problem is that it is difficult. In other words, if intensity modulation is performed using only the laser oscillation region where the optical output characteristics of the driving current lamp described above are linear,
The dynamic range of optical output is only about 2 digits at most. 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 and JP-A-56-1
As shown in No. 52372, etc., the optical output of the semiconductor laser is kept constant, and the semiconductor laser is continuously switched to zero.
Attempts have also been made to record a continuous tone image by turning off the scanning beam to make the scanning beam pulsed light, and controlling the number or width of the pulses for each pixel to change 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 1M
In the case of Hz, if the density scale, that is, the resolution of the scanning light m is to be maintained at 10 bits (approximately 3 digits), the pulse frequency must be set extremely high, at least 1 GH2. The semiconductor laser itself is 0N at this frequency.
- It is possible to turn it OFF, but the pulse count circuit for pulse number control or pulse width control cannot operate in response to such a high frequency, and in the end, the pixel clock frequency cannot be set higher than the above value. must be significantly lowered. Therefore, the recording speed of the device must be significantly reduced.

Furthermore, in the above method, the heating opening of the semiconductor laser chip changes depending on the number or width of pulses output during the recording period of each pixel, and therefore the driving current lamp light output characteristics of the semiconductor laser change. 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 also been proposed in which a high-gradation image is recorded 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 changes depending on the number or width of pulses as described above, and as a result, the amount of exposure per pulse changes.

Considering the above, for example, the concentration scale 1Qbit
In other words, to record a high gradation image of about 1024 gradations,
It is desirable to perform optical intensity modulation across the LED region and laser oscillation region shown in FIG. 2 described above to ensure a dynamic range of optical output of about three orders of magnitude. However, over the above two regions, the light output characteristics of the semiconductor laser driving current lamp are naturally not linear, so in order to easily and accurately record high-gradation images, images are generated at equal density intervals for a given amount of change in the image signal. In order to be able to control the concentration, it is necessary to compensate for the above characteristics in some way to linearly change the relationship between the 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 feeds back 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. A light emission level command signal V ref that commands the light emission intensity of the semiconductor laser 1 is input to the voltage-current conversion amplifier 3 through the addition point 2, and the amplifier 3 supplies the semiconductor laser 1 with a drive current proportional to this command signal V ref. supply A light beam 4 emitted forward from the semiconductor laser 1 is used to scan a 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 bin 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 input to the above-mentioned addition point. 2 is input. From this addition point 2, the light emission level command signal v r
A deviation signal Ve indicating the deviation between er and the feedback signal Vpd is output, and the deviation signal Ve is outputted from the voltage-current conversion amplifier 3.
is converted into an electric current 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 equal to the light emission level command signal V re
It is proportional to f. In other words, the light beam 4 used for image recording
The intensity (light output of the semiconductor laser 1) Pf is proportional to the light emission level command signal V ref. 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 drive current lamp light 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 differentiator efficiency, which is the gain of a single semiconductor laser, varies greatly between the LED region and the laser oscillation region, as shown in FIG. 5 when expressed logarithmically. In order to obtain this, 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 Figure 4 is
The figure shows an example of the light output characteristics of the semiconductor laser light emission level command signal lamp that changes according to the loop gain, and in order to obtain characteristics close to the ideal characteristics shown by the solid line as shown in the figure, a high gain of about 60 dB is required. It becomes necessary.

Further, the characteristics shown in FIG. 4 are the light emission level command signal V r
This is a case where ef is a very low frequency signal close to direct current, but another problem occurs when the command signal Vref is a high frequency signal.

This point will be explained below. FIG. 6 shows the case temperature dependence of the drive current lamp light output characteristics of the semiconductor laser shown in FIG. As shown in the figure, the optical output of the semiconductor laser decreases as the case temperature increases if the drive vJ current is constant. Generally, when a semiconductor laser is applied to a laser recording device, etc., control is performed to maintain the case temperature constant, but transient temperature changes in the laser diode chip that occur when a driving current is applied to the semiconductor laser It is impossible to suppress even this. In other words, when a driving current is applied to the semiconductor laser in a stepwise manner as shown in (1) of Fig. 7, the temperature of the laser diode chip changes as shown in Fig. 7 (2). As a result, the optical output of the semiconductor laser changes as shown in FIG. 7(3) 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 FIG. 3, it has been found that the above-mentioned loop gain is required to be about 10 dB in order to correct the nonlinearity of the laser-driven current lamp light output characteristic due to this droop characteristic, and therefore, the light emission level command signal V When a signal ranging from low frequency to high frequency (for example, 1 MH2) is used as ref, in order to maintain high responsiveness and obtain light output characteristics (linearity) of the light emission level command signal lamp close to the solid line in Fig. 4, In the laser oscillation region, a total of 70d including the above 60dB
A loop gain of about B is required. At present, it is almost impossible to realize such a high-speed, high-gain APC circuit.

Furthermore, when using a semiconductor laser by modulating its intensity from the LED region to the laser oscillation region, in addition to the problem that the driving current lamp light output characteristics become nonlinear, there is also the problem that the focusing ability of the scanning beam is impaired. arise. In other words, the spontaneous light emitted from a semiconductor laser contains various angular components compared to laser oscillation light, and for example, in the case of a longitudinal multi-mode semiconductor laser, the spectral components of laser oscillation light are within a range of about 2 nm. On the other hand, since it has a spectral component extending over about 40 nm, the laser oscillation light cannot be focused to a small spot diameter when focused by a focusing lens. For this reason, when using light in a low power region where naturally emitted light is dominant (of course 100% in the LED region) as well as light in a high power region where laser oscillation light is dominant, the scanning spatial This will result in loss of resolution.

In order to improve the convergence of this scanning beam, for example, a polarizing filter as shown in Japanese Patent Application No. 61-075077 by the present applicant, an interference filter as shown in Japanese Patent Application No. 61-150227, and 61-19
It is conceivable to use an aperture limiting plate as shown in No. 6352 Mei IIIB.

In other words, among the light emitted from the semiconductor laser, the laser oscillation light is linearly polarized in a direction parallel to the bonding surface of the laser diode chip, whereas the spontaneously emitted light is randomly polarized, so the laser oscillation light is When the emitted light beam is passed through a polarizing filter that transmits only the light polarized in the direction parallel to the junction surface of the laser diode chip, almost all of the laser oscillation light is transmitted, whereas only about 1/2 of the naturally emitted light is transmitted. Only about 2 points are transmitted. Therefore, near the threshold of semiconductor laser, that is, laser excavation and LED
If the light beam emitted from the semiconductor laser is passed through the polarizing filter in a region including both of the above properties, the ratio of laser oscillation light in the scanning beam will be further increased, so that the convergence of the scanning beam will be improved.

Furthermore, if the light beam emitted from the semiconductor laser is passed through an interference filter that only transmits light with a wavelength near the wavelength range of the laser oscillation light, the scanning beam can be converted into the laser oscillation light without cutting off the laser oscillation light. It may consist of similar very narrow spectral components. In this case, even if lenses such as a focusing lens disposed in the beam scanning system are not particularly precisely corrected for chromatic aberration, the focusing performance in scanning and the like will be improved.

Furthermore, by placing an aperture limiting plate with a small aperture that allows only a portion of the light beam to pass between the semiconductor laser and the collimator lens, or between the collimator lens and the focusing lens, the focusing ability of the scanning beam can be improved. I know I will.

According to the polarizing filter, interference filter, or aperture limiting plate as described above, it is possible to narrow down the scanning beam to a smaller spot and record an image with high sharpness.

However, the polarizing filter, interference filter, and aperture limiting plate described above have a problem in that the light transmittance changes nonlinearly with respect to the intensity of incident light.

This will be explained with reference to FIG. 10, taking the case of a polarizing filter as an example. In FIG. 10, a curve Po indicates the intensity of the light beam emitted from the semiconductor laser. When this light beam is passed through the polarizing filter, the intensity of the output beam changes as shown by curve P in the figure.

That is, in the LED region, only naturally emitted light is emitted, and as described above, about 1/2 of it passes through the shoulder filter (that is, the light transmittance is about 50%). On the other hand, in the laser oscillation region as well, naturally emitted light is approximately 1
/2 is transmitted through the polarizing filter, but almost all of the laser oscillation light, which occupies a much larger proportion than the naturally emitted light in the emitted light in this region, is transmitted through the polarizing filter. Therefore, the polarization filter transmittance of the light beam emitted in this laser oscillation region is significantly higher than the above-mentioned 50%.

Moreover, this light transmittance increases as the intensity of the light beam increases and the ratio of laser oscillation light to it increases.

The above-mentioned problem also occurs when the above-mentioned interference filter is used.

On the other hand, as is well known, the divergence angle of a radiation beam emitted from a semiconductor laser varies as its optical output changes.

Therefore, when the above-mentioned aperture limiting plate is provided, the ratio of the amount of light blocked by the aperture limiting plate, in other words, the light transmittance changes depending on the optical output of the semiconductor laser, that is, the intensity of the light incident on the aperture limiting plate. do. Figure 11 shows the intensity of the light beam that has passed through the aperture limiting plate and the prism type polarizing beam splitter used as a polarizing filter when the light beam emitted from the semiconductor laser is passed through these elements. An example of the relationship between the voltage value and the value obtained by converting the output current of the pin photodiode with a built-in semiconductor laser into a voltage value is shown. Since the output current is proportional to the optical output of the semiconductor laser, that is, the intensity of the light beam before it enters the element, the intensity of the light beam and the light transmittance of the element become non-linear.

Further, the radiation beam emitted from the semiconductor laser is normally passed through a collimator lens to form a parallel beam, but in this case, depending on the lens diameter, if the radiation beam divergence angle becomes large, the beam may deviate from the collimator lens. The amount of light that leaves this lens (that is, the amount of light that enters the lens) changes as the semiconductor laser light output changes and the radiation beam divergence angle changes, so in this case as well, the light transmittance in the collimator lens is , changes depending on the intensity of light incident on the lens. Figure 12 shows an example of the relationship between the optical output detected by the pinned photodiode built in the semiconductor laser and the optical intensity emitted from the collimator lens, and as shown in the figure, the relationship between the two is nonlinear. There is.

As mentioned above, if the incident light intensity and incident light transmittance characteristics of an optical element such as a polarizing filter are nonlinear, even if the above-mentioned AP
Even if the ideal characteristics shown by the solid line in FIG. 4 are obtained using the C circuit or the like, the relationship between the intensity of the light beam actually scanning the photosensitive material and the light emission level command signal is not linear;
It becomes impossible to easily and accurately record a high gradation image.

Therefore, the present invention does not require the use of a high-gain APC circuit as described above, and also includes the above-mentioned polarizing filter in the beam scanning system.
Even if an optical element such as an interference filter or an aperture limiting plate is arranged, the emission level command signal of the semiconductor laser versus the scanning beam intensity characteristic can be made linear from the LED region to the laser oscillation region, so that the light intensity The object of the present invention is to provide a laser recording device that can record high-gradation images at high speed through modulation.

(Means for Solving the Problems) The laser recording device of the present invention includes a semiconductor laser and an optical element such as the polarizing filter that has a nonlinear relationship between the intensity of the incident light and the light transmittance, a beam scanning system that scans the light beam on the photosensitive material; a beam scanning system that generates a light emission level command signal corresponding to the image signal; and controls the driving current of the semiconductor laser based on the signal to control the light intensity of the laser beam. In a laser recording apparatus equipped with a modulating laser operation control circuit, the APC circuit of the laser operation control circuit detects the intensity of the light beam after passing through the optical element, and generates a feedback signal corresponding to this light intensity. The laser operation control circuit is configured to feed back the light emission level command signal, and the laser operation control circuit is configured to control the nonlinearity of the driving current lamp light output characteristics of the semiconductor laser and the nonlinearity of the incident light intensity and emitted light transmittance characteristics of the optical element. The present invention is characterized in that a correction table is provided which corrects the light emission level command signal so as to compensate, and makes the relationship between the intensity of the scanning beam based on the corrected signal and the light emission level command signal before correction linear. It is something.

(Function) If the 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 emission level command signal before correction and the semiconductor laser light output will be as shown in Figure 4. It is possible to obtain optical output characteristics close to the ideal characteristics shown by the solid line. Furthermore, even if the incident light intensity and emitted light transmittance characteristics of optical elements such as the polarizing filter, interference filter, aperture limiting plate, and collimator lens mentioned above are nonlinear, this can be compensated for by the above APC circuit and correction table, and the light emission level Image density can be controlled at equal density intervals in response to a fixed amount of change in the command signal.

(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. Image signal generator 10 generates an image signal S1 carrying a continuous tone image. The 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 switches signals for one main scanning line based on a line clock S2, which will be described later, and outputs an image signal S1 for each pixel based on a pixel clock S3. In this example, the pixel clock frequency is set to 1M) (Z, in other words, the one pixel recording time is set to 1 μsec (second).

The above-mentioned image signal S1 passes through the multiplexer 11 and is sent to the RA
After being subjected to a correction described later in a correction table 40 consisting of M, it is converted into, for example, a 16-bit light emission level command signal S5. This light emission level command signal 85 is input to the D/A converter 16, where it is converted into a light emission level command signal Vref consisting of an analog voltage signal. This light emission level command signal Vref is transmitted to a signal changeover switch 15 which will be described later.
The signal is inputted to the addition point 2 of the APC circuit 8 via. APC
The summing point 2, voltage-current conversion amplifier 3, and semiconductor laser 1 of the circuit 8 are the same as those in the circuit shown in FIG. 3 described above. A light beam 4 having an intensity corresponding to the light emission level command signal Vref (that is, corresponding to the image signal S1) is emitted from the semiconductor laser 1. This light beam 4 is passed through a collimator lens 17 to become a parallel beam, and is passed through the aforementioned aperture limiting plate 50 and polarizing filter 51 to become a light beam 4'. This light beam 4' passes through a half mirror 52, and then enters an optical deflector 18, such as a polygon mirror, where it is reflected and deflected. The light beam 4' thus deflected passes through a focusing lens 19, which is usually an fθ lens, and is focused on a minute spot on the photosensitive material 20, and scans 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, since the light beam 4 (that is, the light beam 4') is intensity-modulated based on the image signal S1, the continuous tone image carried by the image signal S1 is displayed as a photographic latent image on the photosensitive material 20. recorded. Note that when the light beam 4' scans the photosensitive material 20 as described above, the photodetector 21 detects that the beam 4' passes through the starting point of main scanning, and the photodetector 21 outputs the starting point. The detection signal S6 is input to the clock generator 36. The clock generator 36 receives this start point detection signal S.
The above-mentioned line clock S2 and pixel clock S are outputted in synchronization with the input timing of 6.

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

Note that the polarizing filter 51 allows only light polarized in a direction parallel to the bonding surface of the laser diode chip of the semiconductor laser 1 to pass therethrough. By passing the light beam 4 through the polarizing filter 51 and the aperture limiting plate 50, the light beam (scanning beam) 4' that has passed through these becomes focused on an extremely small spot as described above. The light-sensitive material 20 is scanned by the scanning beam 4' thus focused.
By scanning, it becomes possible to record images with high sharpness.

The light beam 4'' reflected by a half mirror 52 that branches a part of the light beam 4' is received by a photodetector 53 such as a photodiode.The output current of this photodetector 53 is This indicates the intensity of the light beam 4'', but since the intensity of the light beam 4'' and the intensity of the scanning beam 4'' correspond to each other, the output current is the same as that of the scanning beam 4''.
The output current is the current -
It is converted into a voltage signal by the voltage conversion amplifier 54 and inputted to the above-mentioned addition point 2 as the feedback signal Vpd. That is, in this example, the APC circuit 8 includes a photodetector 53, a current-voltage conversion amplifier 54, and a path from the photodetector 53 to the addition point 2. In this APC circuit 8, unlike the APC circuit shown in FIG. Therefore, not only the non-linearity of the driving current lamp light output characteristic of the semiconductor laser 1 but also the non-linearity of the incident light intensity and emitted light transmittance characteristics of the aperture limiting plate 5° and the polarizing filter 51 are also affected by the APC circuit. 8 will be corrected to some extent.

Here, the image signal @S1 in the above-mentioned correction table 4o
The correction will be explained below. The correction table 40 is obtained from a gradation correction table 12, an inverse log conversion table 13, and a correction table (hereinafter referred to as ■-P characteristic correction table) 14 for linearly correcting the light emission level command signal lamp light output characteristic of the semiconductor laser 1. Become.

The gradation correction table 12 is a known one for correcting the gradation characteristics of the photosensitive material 2o and its development processing system. Although this gradation correction table 12 may have fixed correction characteristics, in this embodiment, the gradation correction table 12 has fixed correction characteristics.
The gradation characteristics of the developing machine 2 may change from lot to lot, or
In consideration of the fact that the characteristics of the developing solution in 2 change with time, etc., 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 that carries image densities of several levels (for example, 16 levels) on the photosensitive material 20, and this signal S4 is input to the multiplexer 11. At this time, the multiplexer 11 is switched from the image recording state in which the image signal S1 is inputted to the correction table 40 as described above, and the test pattern signal S4 is inputted to the correction table 40.
The state is such that the input is made. The semiconductor laser 1 is driven as described above based on this test pattern signal S4,
The light beam 4' is therefore intensity modulated. As a result, the density changes stepwise on the photosensitive material 20, for example, 1
Six step wedges (test patterns) are recorded as photographic latent images. This photosensitive material 20 is sent to a developing station 22, and the step wedge is developed. After development, the photosensitive material 20 is set in a densitometer 23, and the optical density of each of the step wedges is measured. The optical density thus measured is inputted into the density value input means 24 in association with each step wedge, and the density value input means 24 receives an 811 signal S indicating the optical density of each step wedge.
7 is output. This density signal s7 is input to the table creation means 37, and the table creation means 37 obtains a predetermined image@density based on the density signal S7 and the test pattern signal S4 based on the value of the predetermined image signal S1. Create a tone correction table. 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 gradation correction table is input to the data interpolation means 38, where it is interpolated and processed in 1024 steps (=1
A gradation correction table that can correspond to the image signal s1 of Qbit) is obtained. Data S9 indicating this gradation correction table
The above-mentioned gradation correction table 12 is formed based on the above.

When recording an image based on the image signal S1, the image signal S1 input to the tone correction table 12 via the multiplexer 11 is converted into a signal 81 by the tone correction table 12.
', and then converted into a light emission level command signal 81'' by the inverse log conversion table 13.

Next, the VP characteristic correction table 14 will be explained. As mentioned earlier, even if the feedback signal Vpd is fed back to the summing 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). ) is difficult. In addition, since the incident light intensity and emitted light transmittance characteristics of the aperture limiting plate 50 and the polarizing filter 51 are nonlinear as described above, the relationship between the light emission level command signal and the light intensity of the scanning beam 4' is It is more difficult to make it linear. The VP characteristic correction table 14 is provided to make the relationship between the scanning beam intensity and the light emission level command signal linear. That is, the light emission level command signal Vref and the scanning beam 4'
Assuming that the ideal relationship between the light intensity Ps and the light intensity Ps is a straight line shown as a in FIG. 8, and the actual relationship is a curve as shown in b in FIG. The voltage value when 81″ is directly converted to D/A is ■
Assuming that it is in, the voltage value V1n is formed to be converted into a value V. In other words, if the value of the light emission level command signal Vrer is ■in, then P'
However, if the above conversion is performed, P for the voltage value Vin. The light intensity is 19.

That is, the relationship between the voltage value Vin corresponding to the light emission level command signal 81°' and the scanning beam intensity Ps 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 j. The characteristic curve in FIG. 8 is obtained when the semiconductor laser 1 is driven across its LED region and laser oscillation region as described above. Since this is ensured, a high gradation image of about 1024 levels can be recorded easily and with high precision as described above.

As described above, the light emission level command signal is generated due to the fact that the driving current lamp light output characteristic of the semiconductor laser 1 is nonlinear, and the incident light intensity and emitted light transmittance characteristics of the aperture limiting plate 50 and the polarizing filter 51 are nonlinear. If the nonlinearity of the scanning beam intensity characteristic is linearly corrected using the V-P characteristic correction table 14, the addition point 2 of the APC circuit 8, the voltage -
The loop gain of the system returning from the current conversion amplifier 3, semiconductor laser 1, photodetector 53, and current-voltage conversion amplifier 54 to the summing point 2 does not include the gain necessary to correct the nonlinearity described above. It will be done. In other words, this loop gain corrects deviations from the driving current lamp light output characteristics of the semiconductor laser 1 due to transient temperature changes that occur during the operation of the semiconductor laser 1, or errors or hunting in case temperature-stop control of the semiconductor laser 1. Therefore, in general, it is only necessary to secure as much as necessary to correct the drift of the amplifier, etc.

Specifically, for example, when the pixel frequency is IMH2 and the semiconductor laser 1 is operating with an optical output of 3 mW, it is sufficient that the loop gain is maintained at about 30 dB. This level of loop gain can be easily achieved with the current state of the art.

Next, the creation of the -P characteristic correction table 14 will be explained. The apparatus shown in FIG.
0 is input to the addition point 2 via the signal changeover switch 15, and the feedback signal Vpd of the APC circuit 8 is input to the table creation means 10. When creating the correction table, the 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. Further, at this time, the switch 71 provided in 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. That is, PROM7
2 stores equidistant number sequences on the logarithmic axis, and these number sequences are sequentially accessed by the clock CLK. As a result, the digital value read from the PROM 72 is converted into an analog value by the D/A converter 73 and amplified by the amplifier 74. As shown in FIG.
The number of LK, that is, the voltage 1ifI increases over time.
A test signal 310 is obtained in which v increases stepwise. This test signal 310 is passed through the signal changeover switch 15.
It is input to addition point 2 as an alternative to the light emission level command signal v rer. Note that the above PRO1v172 is, for example, 14 bits, which is sufficiently higher than 1Qbit of the aforementioned concentration scale (that is, the emission level resolution of the semiconductor laser 1).
The distribution of the number sequence is used.

When the test signal $10 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 light output is input to the comparator 77. This comparator 77 includes the CPU 7
A reference signal V(+) generated from C 8 and converted into an analog signal by a D/A converter 76 is input, and the feedback signal Vpd and the reference signal V9 are compared.
P U 7g first outputs the reference signal Vg (1) corresponding to the lowest emission level of the semiconductor laser 1, and the comparator 77 outputs this reference signal V (1 (1) and the feedback signal Vpd).
When they match, a match signal S11 is output. This minus number multiple 311 is input to the latch 75. Latch 75 is P
It receives the output from ROM72, and the above - several times 31
The output of I]RO to 172 at the time when 1 is input is latched. This latched signal 312 is expressed as ΔV when the value of the reference signal VC+ is Vin, as explained in FIG.
(Hereinafter, the voltage value ΔV corresponding to the reference signal Vg (n) will be referred to as ΔV(n)). The CPU 78 receives a signal 312 indicating the voltage value ΔV(1), and based on the signal g312 and the reference signal VJ<1), calculates the value v such that V(1)=V(+(1)+ΔV(1)) (1
). And CP Ll 78 is the reference signal Vg
A table for converting (1) into a signal of voltage value (1) is formed in the RAM 79.

The minus number multiple number 311 is also input to the CPU 78, and
When the p IJ 78 receives this coincidence signal 811, it converts the reference signal Vq<1) to VC+(2>, that is, the semiconductor laser 7
The light emission level is switched to that corresponding to the second light emission level from the bottom, and the comparator 77 is reset at the same time. In this case as well, the CPU 78 performs V(2>=V(1(2
)+ΔV(2) A table is created in the RAM 79 for converting the reference signal Vg(2> to a signal of voltage value ■(2)).

The above operations are performed sequentially up to the reference signal @VQ (7024), that is, the reference signal corresponding to the maximum emission level of the semiconductor laser 1, and as a result, each of the 1024 signal values Vin(n) is stored in the RAM 79. V(n
＞ A table is created to convert it to ＞. This table is
The data is sent to the RAM forming the correction table 40 via the data line 80 and set as the v-P characteristic correction table 14. As described above, this correction table 14 is formed to convert the voltage value ■1n in FIG. The relationship 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.
Also, switch 71 is closed.

Furthermore, as explained above, the voltage value V in+! corresponding to all image densities! : As in the case of creating the gradation correction table 12 described earlier, the relationship between the voltage value Vin and V is determined only in some major cases, and the data is The VP characteristic correction table 14 may be created by interpolation. Furthermore, 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 a single correction table including all of their respective conversion characteristics, or may be formed in separate forms. may be configured.

Further, in the above embodiment, the test signal S10 whose level increases stepwise as time passes is used, but on the contrary, a test signal whose level gradually or continuously decreases as time passes is used. You can also do that.

Next, a second embodiment of the present invention will be described with reference to FIG. Note that in FIG. 13, elements that are equivalent to those in FIG. FIG. 13 also shows the laser operation i, II'M circuit and table creation means 70'.
Although only the portion shown in FIG. 1 is shown, the not-illustrated portions such as the light beam scanning system in this device are formed in the same manner as in the device shown in FIG. 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 the switch 71 is removed. In other words, in this second embodiment, the APC circuit 8 operates in the same manner as usual even when creating the correction table 14. Therefore, in this device, the signal S12 latched by the latch 75 at the time when the minus multiple sign S11 is input corresponds to the voltage value ■ in FIG.

Therefore, the CPU 78 uses the above-mentioned V(n>=Vg
(n)+ΔV(n), directly calculate the value of V(n), and calculate the voltage value V
Create a table to convert o(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 81 output from the inverse log conversion table 13
" is input as is to the D/A converter 16. On the other hand, the image signal 81" is branched and input to the V-P characteristic correction table 44. This V-P characteristic correction table 44
is slightly different from the −P characteristic correction table 14 of the device in FIG. 1; the difference ΔV between the voltage value V and Vin in FIG.
It is formed to seek. The digital signal S5' indicating this voltage difference ΔV is passed through the D/A converter 45, converted into an analog signal, and added to the voltage value ■in (corresponding to the light emission level command signal 81'') at the addition point 2. be done. By doing this, the light emission level command signal y r
This is the same as inputting a signal with a voltage value V as , and the same effect as described above can be obtained.

Since the V-P correction table 44 of this third embodiment device must be formed to obtain the voltage difference ΔV as described above, it is not necessary to use the table creation means 70' shown in FIG. 13 in this example. A table creation means 70 similar to the table creation means 70 shown in FIG.
is used. In this case, the table creation means 70 calculates the above-mentioned calculation V(n>=Vg (n) +ΔV (
n) is not performed, and the signal S
A correction table 44 that outputs the value of ΔV(n) indicated by 12
formed to create.

Next, a fourth embodiment of the present invention will be described with reference to FIG. In the device shown in FIG. 15, the light emission level command signal 81'' is branched to
The apparatus is constructed in the same manner as the apparatus shown in FIG. 14 up to the point where the signal 85' is input into the signal 85', the signal 85' is corrected as described above, and the obtained signal 85' is converted into an analog signal by the D/A converter 45. However, the voltage signal ΔV outputted 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 laminar flow 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 Δ■ 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 effect as in the first embodiment device can be obtained by 1!7.

The table creation means 70'' of this fourth embodiment device includes the first
Compared to the table creation means 70 shown in the figure, the test signal 310
The only difference is that the signal S12 indicating the voltage value ΔV in FIG. 8 is input to the CPU 78, so the signal S12 and the reference signal Vv(n) The CPU 78 may be configured to create a correction table 44 that outputs the value of ΔV (n) with respect to the reference signal Vg (n) based on the above.

In the embodiment described above, the aperture limiting plate 50 and the polarizing filter 51 are provided in order to improve the focusing property of the scanning beam 4', but only one of these may be used. Alternatively, the above-mentioned interference filter may be used in place of these optical elements, or two or all of these three optical elements may be used in an appropriate combination.

(Effects of the Invention) As explained in detail above, in the laser recording device of the present invention, the drive current lamp light output characteristics of the semiconductor laser are nonlinear, and the polarization filter etc. provided to improve the focusing property of the scanning beam is used. The nonlinearity of the light emission level command signal versus the scanning beam intensity characteristic caused by the nonlinearity of the incident light intensity and emitted light transmittance characteristic of the optical element is corrected by a semiconductor laser light output stabilization circuit, and a semiconductor laser light output stabilization circuit is provided separately from the circuit. Since the correction is performed using a correction table, high response can be achieved even if the loop gain of the closed loop formed by the optical output stabilization circuit in the laser drive circuit is set to a low value that is sufficiently achievable with the current technology level. The relationship between the light emission level command signal and the scanning beam intensity can be made linear over the LED region and the laser oscillation region while maintaining the same property. 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 aperture of the photosensitive material can be controlled over a wide range of 3 strokes and 1 stroke. For example, concentration resolution of 10
It becomes possible to record continuous-tone images with extremely high gradations of the order of bits at high speed and precision.

Furthermore, in the laser recording apparatus of the present invention, optical elements such as a falling light filter, an interference filter, and an aperture limiting plate can be placed in the beam scanning system without any problems in controlling image density, so such optical elements can be This allows the scanning beam to be focused on a minute spot, making it possible to record highly sharp images.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing a laser recording device according to the first embodiment of the present invention, Fig. 2 is a graph showing the light output characteristics of a semiconductor laser in a 1FJl current lamp, and Fig. 3 is an example of a semiconductor laser light output stabilizing circuit. FIG. 4 is a graph showing the relationship between the light emission level command signal and the semiconductor laser light output, FIG. 5 is a graph showing the relationship between the semiconductor laser light output and the differential hanger efficiency, and FIG. A graph showing the humidity dependence of the drive current lamp light output characteristics of a semiconductor laser. FIG. 7 is a graph explaining the droop characteristics of the semiconductor laser. 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 the D1~ signal emitted by the table creation means of the apparatus of the above embodiment, FIG. 10 is a graph explaining the action of the polarizing filter according to the present invention, and FIG. 11 is a graph showing the polarizing filter and FIG. 12 is a graph showing an example of the incident light intensity versus output light intensity characteristic for a combination of aperture limiting plates; FIG. 12 is a graph showing an example of the incident light intensity versus output light intensity characteristic of a collimator lens; FIG. FIG. 14 is a block diagram showing a semiconductor laser operation control circuit and table creation means of a laser recording device according to a third embodiment of the present invention. FIG. , FIG. 15 is a block diagram showing a semiconductor laser operation control circuit and table creation means of a laser recording apparatus according to a fourth embodiment of the present invention. 1...Semiconductor laser 2.47...Additional point 3
．． 46... Voltage-current conversion amplifier 4.4', 4''... Light beam 7.54... Current-voltage conversion amplifier 8... APC circuit 10... Image signal generator 14.44.・・VP 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
50...Aperture limiting plate 51...Polarizing filter
52... Half mirror 53... Photodetector 70, 70', 70''... Table creation means 71.
・Switch 72...PRO~175・
... Latch 77 ... Comparator 78
...CPU 79...RAM$1
...Image signal 81''...Emission level command signal Vref before correction...
・Emission level command signal Vpd...Feedback signal Ve...Deviation signal Figure 8 "" Vref to LO Figure 9 Haruma Figure 10 Figure 11 Figure 12 Figure 71 Missing +-p' ☆-1 Force 151] (Voluntary amendment) Procedural amendment Commissioner of the Japan Patent Office Mr. Showa November 25, 1961, No. 1, Indication of the case, Patent Application No. 61-248878, 2, Name of the invention, Laser recording device 3, Person making the amendment, Relationship to the case, Patent applicant, Address, 210 Nakanuma, Minamiashigara City, Kanagawa Prefecture. name
Fuji Photo Film Co., Ltd. 4, Agent Address: 5-2-1 Roppongi, Minato-ku, Tokyo 160 6. Number of inventions increased by amendment None 7. Subject of amendment Drawing 8. Contents of amendment Inking of hand-drawn drawing will be corrected.

Claims (4)

[Claims] (1) A semiconductor laser that emits a light beam, a beam scanning system that includes an optical element with a nonlinear relationship between incident light intensity and light transmittance and scans the light beam onto a photosensitive material, and a light emission level command that corresponds to an image signal. A laser recording device comprising: a laser operation control circuit that generates a signal and modulates the intensity of the light beam by controlling a driving current of the semiconductor laser based on the signal, the laser operation control circuit controlling the optical element. a light output stabilization circuit that detects the intensity of the light beam that has passed through the light beam and feeds back a feedback signal corresponding to the detected light intensity to the light emission level command signal; and nonlinearity of the driving current lamp light output characteristics of the semiconductor laser. , and correcting the light emission level command signal so as to compensate for the nonlinearity of the incident light intensity lamp light transmittance characteristic of the optical element, and adjusting the intensity of the scanning beam based on the corrected signal and the light emission level command before correction. A laser recording device comprising: a correction table that linearizes a signal relationship. (2) The laser recording apparatus according to claim 1, wherein the correction table is arranged before the optical output stabilizing circuit. (3) The correction table is arranged on a path branching from the path of the light emission level command signal, and is configured to obtain a correction amount of the light emission level command signal, and the correction signal indicating the correction amount is the light emission level command signal. 2. The laser recording device according to claim 1, wherein the laser recording device is adapted to be added to a signal. (4) The correction table is arranged on a path branching from the path of the light emission level command signal, and is configured to calculate a correction amount of the light emission level command signal and output a current corresponding to this correction amount. 2. A laser recording apparatus according to claim 1, wherein said current is added to said semiconductor laser drive current.