JPS643389B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention enables images with halftones such as photographs to be
The present invention relates to a recording device using a semiconductor laser that can reproduce a density range above the level.

Methods for intensity modulating laser light to record halftone images include a method using an ultrasonic optical modulator, a method of varying the discharge current of a gas laser, and a method of varying the current of a semiconductor laser. The first method requires an expensive ultrasonic optical modulator and also requires a fine movement mechanism for the modulator to match the Bragg angle, which has the drawback of making the entire method expensive and complicated.

The second method of modulating the discharge current of a gas laser has the disadvantage that the modulation frequency can only be as low as several hundred hertz, and that changing the discharge current shortens the life of the laser tube. The third method of changing the current of a semiconductor laser is that the optical output-current characteristic of a semiconductor laser is such that the optical output changes greatly by changing the current slightly. The drawback was that it was very difficult to perform modulation.

Recently, a device has been proposed that utilizes the high-speed response of a semiconductor laser to convert an input signal into a pulse number and pulse width, optically modulate the signal, and record a halftone image. For example, there is a patent application (B) ``Laser Recording Apparatus'' filed on December 25, 1972 by the applicant of the present application.

However, even in the above device, the following problems occur in the following cases. For example, let gamma γ = 1, which indicates the gradation characteristics of the recording material, the image density reproduction range D = 2.0, the number of reproduction gradation steps η = 20, and therefore the step density difference is △D = 0.1.The image size is A4 size ( 210 mm x 297 mm), the number of resolution points is 16 pixels/mm, and the recording time is 60 sec, a high-frequency signal is required to reproduce the gradation as explained below.

FIG. 1 shows the characteristics of a recording material with gamma γ=1, with the horizontal axis representing the logarithmic exposure amount and the vertical axis representing the optical density.

Now, if the minimum exposure amount is E _O , then the next stage's exposure amount is E _I =E _O ·10D/ηr, and the maximum exposure amount is E _M =E _O ·10D/r. Taking the ratio of the maximum and minimum difference in exposure amount, δE _I = E _I −E _O = E _O (10D/ηr−1), δE _M = E _M −E _O = E _O (10D/r−1) ) Therefore, the ratio of δE _I and δE _M is δE _M /δE _I = 10D/r-1/10D/ηr-1=10 ² -1/
10 ^0.1 −1=382.

Also, the highest image frequency is 266KHz. Therefore, the sampling time is usually selected at a higher frequency than the highest image frequency, so if we set it to 300KHz, then multiplying this by 382 above, the high frequency pulse for pulse number modulation is
It becomes 115MHz.

Similarly, in the case of pulse width modulation, the maximum pulse frequency is 115 (MHz) or higher.

Furthermore, if the number of gradation steps mentioned above is n = 30, δE _M /δE _I = 592, and the necessary high frequency pulse is
It becomes 178MHz.

When handling high frequency signals such as those described above, the following problems arise. (1)Generally available logic
Cheap components such as IC TTL cannot be used because they cannot respond at such high speed. (2) It is necessary to use expensive parts such as ECL.
(3) The high frequency makes the circuit complicated and requires special technology.

An object of the present invention is to provide a laser recording device that can record images with rich intermediate tones.

SUMMARY OF THE INVENTION An object of the present invention is to provide a laser recording device using a semiconductor laser that can produce several tens of modulation levels by utilizing the high frequency modulation characteristics of the semiconductor laser.

SUMMARY OF THE INVENTION An object of the present invention is to provide a laser recording apparatus that solves the problems in pulse number or pulse width modulation.

The laser recording device of the present invention not only samples an input signal using a sampling pulse, but also supplies a drive current with a pulse number or pulse width controlled according to the value of the sampled input signal to a semiconductor laser constituting a writing light source device. In a laser recording apparatus configured to perform recording by scanning a recording medium with a light beam emitted from the light source device and scanning the light beam on a recording medium, the light source device may have a light beam intensity on the recording medium. A plurality of different configurations are arranged and used so that when a driving current controlled based on the same sampling pulse is applied, they each illuminate approximately the same point on the recording medium. A light source selection device configured such that the driving current can be applied in parallel to each semiconductor laser of the light source device, and selecting one or more semiconductor lasers to which the driving current is applied depending on the value of the input signal. It is characterized in that a means is provided.

The present invention will be explained below with reference to Examples.

FIG. 3 is a block diagram of an embodiment of the present invention, in which 1 is a first semiconductor laser, 1' is a second semiconductor laser, 2 and 2' are beam shaping lenses, 1
00 is a half mirror, 3 is a light deflector, 4 is a converging lens, and 5 is a recording paper.

The recording paper 5 is desirably one that is sensitive to the wavelength (red or infrared) of semiconductor laser light, such as silver halide photography or electrophotography, which produces halftones.

The current pulse modulated semiconductor laser beams 6 and 6' are collimated by beam shaping lenses 2 and 2', and the optical axes of both beams are made coaxial by a half mirror 100 having a transmittance of 90% and a reflectance of 10%, and the beams are deflected. The beam is deflected by the camera 3, focused into a predetermined spot size image by the converging lens 4, and main-scans the recording paper 5 to draw a scanning line 7. The sub-scanning is performed by feeding the recording paper 5 in the direction of the arrow 8. In this embodiment, a galvanometer was used as the deflector 3.

Next, a recording method using a semiconductor laser, which is a feature of the present invention, will be described.

In FIG. 3, an input image signal 9 is amplified by a waveform shaping amplifier 10 to a predetermined level. Here, the image signal 9 is, for example, a facsimile reception signal. On the other hand, a high frequency pulse 19 from a high frequency oscillator 15 is frequency-divided by a frequency divider 12, and a sampling pulse 20 is output from the frequency divider 12. The frequency of the sampling pulse 20 is preferably slightly higher than the highest image frequency of the image signal 9. The AD converter 11 samples the signal from the amplifier 10 at that time at the falling edge of the sampling pulse 2, converts it into one of the digital values consisting of n=20 gradation steps, and the falling edge of the next sampling pulse hold that value until this
The AD converted signal is sent to the digital value comparison circuit 22
is input. The signal corresponding to the concentration read from the facsimile transmitter is sent to the digital value comparison circuit 22.
will be entered into. This digital signal is converted by a digital value comparing circuit 22 into a digital value of a pulse having the relationship shown in FIG. The operation of the digital value comparison circuit 22 is shown in FIG. 2, for example, when reproducing a concentration of 0.1.
It outputs 12 pulses, 32 pulses when it is 0.5, 50 pulses when it is 0.7, 10 pulses when it is 1.0, and 100 pulses when it is 2.0.

FIG. 2 shows the case where γ of the recording material is 1, and since the curve in the figure naturally changes if γ is different, it is sufficient to change the contrast value depending on the recording material used. The digital value comparison circuit 22 is composed of a read-only memory, receives each bit of the AD conversion value of the input signal, becomes an address signal, and inputs a value corresponding to the number of comparison pulses at that address as data. The number of pulses corresponding to the address signal is output for every sampling pulse. In this example, the signal from the facsimile transmitter is expressed as a signal corresponding to the concentration, and the signal is logarithmically transformed. However, in the case of a signal that has not been logarithmically transformed, this logarithmically transform is also calculated by the digital value comparison circuit. It can be included.

Also, the signal from the AD converter 11 is sent to the comparator circuit 30.
Concentration D entered into and read by facsimile transmitter
It is determined whether is greater than or equal to 1.0 or less. and,
When the reading density D of the facsimile transmitter is smaller than 1.0, the gate 1 is set by the output of the comparator circuit 30.
6 is closed, and when the aforementioned concentration D is 1.0 or more, the gate 16 is opened by the output of the comparator circuit 30.

On the other hand, a high frequency pulse 19 from a high frequency oscillator 15
has a frequency approximately 100 times higher than that of the sampling pulse 20. The high frequency pulse 19 is inputted to the clock input of the counter 14 through the AND gate 17, causing the counter 14 to step.

This counter 14 is cleared by the sampling pulse 20 of the frequency divider 12. The outputs of the counter 14 and the digital value comparison circuit 22 are compared by the coincidence circuit 13, and when they become the same value, the coincidence circuit 13 uses the coincidence signal 21 to open the AND gate 17.
is gated to block the high frequency pulse 19 and close the AND gates 16 and 16'.

As mentioned above, when the read density D of the facsimile transmitter is 1.0 or more, the output of the comparator circuit 30 opens the gate 16, so the high frequency oscillator is activated while the coincidence signal 21' is output from the coincidence circuit 13. The high frequency pulse 19 from 15 is the gate 1
6 and 16', and is applied to the first semiconductor laser 1 and the second semiconductor laser 1' through the first semiconductor laser drive circuit 18 and the second semiconductor laser drive circuit 18', respectively.

When the coincidence signal 21 is output, the gates 16 and 16', which have been open until now, are closed.

Also, the reading density of the facsimile transmitter is D=
If it is smaller than 1.0, the gate 16 is closed and the first semiconductor laser 1 is not driven. However, since the gate 16' is open, the high frequency pulse 19 is applied to the second semiconductor laser 1' via the second semiconductor laser drive circuit 18' until the coincidence circuit 13 issues the coincidence signal 21. When the coincidence signal 21 is output, the gate 16' which has been open until now is closed and the AD converter 11 and counter 1 are turned on again.
The sampling pulse 20 is input to the input signal 4, and the AD converter 11 converts the input signal into a digital value and inputs it to the digital value comparison circuit 22.
2 displays the converted digital value. On the other hand, counter 14 is cleared. If the input signal is not zero at this time, the coincidence circuit 13 outputs a mismatch signal 21' and opens the AND gates 16, 16' and 17. Thereafter, as described above, high frequency pulses are applied to both semiconductor lasers 1 or the second semiconductor laser depending on whether the read density is 1.0 or more or less than 1.0.

Next, the read density and various signals mentioned above,
The relationship with the exposure amount applied to the recording paper will be explained using FIG. 4. In FIG. 4, the horizontal axis is the time axis, and the vertical axis shows the state or magnitude of the signal. In the figure, a shows the high frequency pulse 19, b shows the sampling pulse 20, c shows the state of the gate 16,
d is the light output after the first semiconductor laser 1 emits light and is transmitted through the half mirror 100; e is the state of the gate 16';
f indicates the optical output after the second semiconductor laser 1' emits light and is reflected by the half mirror 100. As shown on the left side of the figure, when the read signal is 1.0 or more, the gates 16 and 16' are simultaneously activated. Open,
The same number of pulses through each is applied to the first semiconductor laser 1 and the second semiconductor laser 1'. As a result, the light emitted from the first semiconductor laser 1 whose light intensity is reduced to 90% by the half mirror 100 with a transmittance of 90%, and the light emitted from the second semiconductor laser 1'
The light emitted from the mirror 100 whose light intensity is reduced to 10% by the half mirror 100 having a reflectance of 10% is combined. When the light emitted by both lasers is equal, the light output is equal to the light output of one semiconductor laser. The light thus synthesized is irradiated onto the recording paper by the number of pulses mentioned above, and the recording paper is recorded with a halftone density corresponding to the number of pulses.

Also, as shown on the right side of the figure, the read signal is
If it is less than 1.0, only gate 16'opens;
Only the second semiconductor laser 1' emits light, and the half mirror 100 irradiates the recording paper with a light amount of 10%. In this case, the exposure amount will be weak.

As explained above, according to this embodiment, even under the above-mentioned recording conditions, the result is 100×300KHz, which is 30MHz.
By using high-frequency pulses, it is possible to reproduce 20 levels of gradation. Therefore, the frequency (1/
3.8) enables multi-tone reproduction. Furthermore, when using pulses of the same frequency, it is possible to reproduce finer gradations than in the past.

Although an embodiment in which two semiconductor lasers are used has been described, three or more semiconductor lasers may be used. For example, in Fig. 3, half mirror 1
00 and optical deflector 3 with a transmittance of 90% and a reflectance of 10.
% half mirror is inserted, the light output from the third semiconductor laser is made to be 1/10 of the intensity of the first and second semiconductor lasers, and is made incident on the half mirror, and the reflected light is transmitted to the first and second semiconductor lasers. The light beams from the semiconductor lasers 1 and 1' may be coaxial. In this case, if the comparator circuit 30 compares the read densities in two stages and outputs the result, the circuit can be constructed in the same manner as in the above-mentioned embodiment. In this case, if the number of gradation stages η=30, in the conventional method, δE _M /δE _I =592, but in the present invention, the number of pulses is only 100 by using three semiconductor lasers.

Therefore, it is sufficient to handle a frequency of 1/5.9 in terms of the number of pulses.

As described above, two or more semiconductor lasers are used,
Halftones can be recorded by turning the light ON and OFF to modulate the light. When applying current to a semiconductor laser using such a high-frequency pulse,
The amount of laser light is lower than when the current is applied continuously. For example, if the duty of the high-frequency pulse is 1:1, the amount of laser light will be halved. However, there is no practical problem if the duty ratio of the high frequency pulse, laser beam scanning speed, laser beam output, etc. are changed.

What has been described above is controlled by the number of pulses, but the flip-flop 40 is set by the sampling pulse 20 and reset by the waveform of the gate state of the gate 16 as shown in FIG.
is provided to control the ON time of the first semiconductor laser 1 by modulating the pulse width, and similarly, the coincidence circuit 1 is
3 to the drive circuit 1 of the second semiconductor laser 1'.
8' of the second semiconductor laser 1'.
The ON time can be controlled. In FIG. 5, blocks having the same function as those shown in FIG. 3 are omitted.

In the above embodiments, the laser beams output from a plurality of semiconductor lasers are all coaxial, and are effective when scanning a light beam one-dimensionally or two-dimensionally. However, in cases where it is only necessary to move the recording material or where it is not necessary to make the light beam into an extremely small spot, see Figure 6a.
It goes without saying that the light beams output from the two semiconductor lasers 1 and 1' do not have to be coaxial as shown in FIG. In the case shown in FIG. 6a, a density filter 50 is installed in the laser optical path from the second semiconductor laser 1' without using a half mirror.
By inserting , light sources with different outputs can be created. In this case, both semiconductor lasers 1 and 1' are driven using the circuit described above.
Further, instead of the above-mentioned circuit, only one of the two may be selected depending on the magnitude of the read signal. The device shown in FIG. 6b delays one of the optical outputs of the first and second semiconductor lasers 1 and 1' by a time T. In this case, the recording material is moved in time T by the distance over which the two light beams are irradiated.

As explained above, according to the present invention, by using a plurality of semiconductor lasers, it is possible to reproduce halftones at high speed. According to the present invention, the exposure amount is controlled by controlling a semiconductor laser using high-frequency pulses, and for example, optical light modulation such as an acousto-optic modulator or a neutral density filter and a single laser are used. This makes it possible to change the exposure amount at a higher frequency than when using the conventional method. Therefore, it has become possible to reproduce halftones at a high speed that could not be achieved when using a combination of a conventional laser and an optical modulator. Furthermore, according to the present invention, since an external optical modulator is not used, it is possible to manufacture a laser recording device that has a high light utilization rate, consumes little power, can be designed compactly, and is inexpensive. In particular, since the commercially available logic IC TTC as described above can be used, the device can be manufactured easily.

[Brief explanation of drawings]

Figure 1 shows the characteristic curve of a recording material with gamma γ=1.
FIG. 2 is a diagram for explaining the contents of the digital value comparison circuit, FIG. 3 is a block diagram of an embodiment of the present invention, and FIG. 4 is a diagram for explaining the optical output of pulse width modulation of the present invention. , FIG. 5 is a block diagram of another embodiment of the invention, and FIG. 6 is an optical path diagram of another embodiment of the invention. In the figure, 1 and 1' are semiconductor lasers, 9 is an input signal, 13 is a matching circuit, 14 is a counter, and 1
5 is a high frequency oscillator, 16, 16', 17 are AND gates, 18, 18' are semiconductor laser drive circuits,
19 is a high frequency pulse, 20 is a sampling pulse, 22 is a digital value comparison circuit, 30 is a comparison circuit, and 100 is a half mirror.

Claims (1)

[Claims] 1. An input signal is sampled using a sampling pulse, and a drive current is supplied to a semiconductor laser constituting a writing light source device, the number of pulses or pulse width of which is controlled according to the value of the sampled input signal. In a laser recording apparatus configured to perform recording by applying a light beam to a light beam, the light beam is emitted from the light source device, and the light beam is scanned onto a recording medium, the light source device has a light beam intensity on the recording medium. A plurality of devices having different configurations are arranged and used so that when a driving current controlled based on the same sampling pulse is applied, they each illuminate approximately the same point on the recording medium. A light source selection device configured such that the driving current can be applied in parallel to each semiconductor laser of the light source device, and selecting one or more semiconductor lasers to which the driving current is applied depending on the value of the input signal. A laser recording device characterized in that a means is provided.