JPS6224768B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved laser recording device.

A drive signal modulated by the image signal is applied to an acousto-optic modulator to obtain primary light optically modulated by the drive signal from the acousto-optic modulator, which is guided to a recording medium. In a laser recording apparatus that records an image using a laser beam, a recorded image is composed of a large number of scanning lines. Conventionally, density unevenness appears between scanning lines.
It has become inevitable.

For example, as shown in FIG. 1, the density unevenness is caused by a portion 1 between two scanning lines along the main scanning direction XX and not irradiated with the primary light, and a portion 2 on the scanning line irradiated with the primary light. This occurs due to the difference in shading between the
As shown in the figure, the distance between adjacent scanning lines is too small, and therefore, in the sub-scanning direction YY perpendicular to the main scanning direction This occurs due to the difference in shading between the area 4 and the other areas.

Macroscopically, the above density unevenness appears as striped shading as shown in FIG. Such density unevenness is particularly noticeable in photographs and so-called solid images, and seriously impairs image quality.

The present invention was made by focusing on the above-mentioned drawbacks.
Make sure that the scanning lines in the recorded image are not noticeable, especially
It is an object of the present invention to provide a laser recording device that can obtain high-quality recorded images in which scanning lines do not appear on the images even when recording photographs, solid images, etc.

The present invention will be explained in detail according to the embodiments illustrated below.

In FIG. 5, reference numeral 5 indicates a laser light source. Hereinafter, in order along the optical path of the laser beam Lb, reference numeral 6 is a beam expander, reference numeral 7 is a focusing lens, reference numeral 8 is an acousto-optic modulator, and reference numeral 9 is a magnification. Each adjustment lens is shown. moreover,
Reference numeral 10 indicates a cylindrical lens, reference numeral 11 a rotating polygon mirror, reference numeral 12 a -θ lens, reference numeral 13 a cylindrical lens, and reference numeral 14 a photosensitive drum as a recording medium. Then, the magnification adjustment lens 9 and the cylindrical lens 1
A knife edge 15 for blocking the 0th-order light L _p is provided between the 0th-order light L p and the 0th-order light L p .

Reference numeral 16 denotes a driver incorporating a drive circuit 17 for driving the acousto-optic modulator 8.
Details of this drive circuit 17 are shown in FIG.

In FIG. 6, reference numeral 18 is an image signal generator, and reference numeral 19 is an image signal generator.
is a voltage-controlled variable frequency generator (hereinafter referred to as VCO) that outputs a current at a frequency, and 20 is a frequency
The external oscillators that output a current of _M (where > _M ) are shown, and the current of frequency _M output from the external oscillator 20 is superimposed on the current of frequency output from the VCO 19, and then
is input to a mixer shown by , and is modulated by the image signal from the image signal generator 18 in the mixer 21,
The signal is further amplified by an amplifier 22 and input to the acousto-optic modulator 8 as a drive signal.

By the way, when a high-frequency current is applied to the acousto-optic modulator 8, the high-frequency current is converted into an ultrasonic wave by the transducer 8a, and propagates within the acoustic wave medium 8b. On the other hand, if the laser beam Lb is simultaneously incident on the acousto-optic modulator 8 at an angle that satisfies the Bratub condition, the laser beam
Lb is diffracted according to the frequency of the ultrasonic wave propagating in the acoustic medium 8b. Here, the diffracted first-order light
If the angle between L ₁ and the O-order light L _p that is not diffracted is the deflection angle θ, the polarization angle θ is given by the following equation.

θ=λ/V _s ...(1) (However, λ is the wavelength of the laser beam, V _s is the sound speed of the ultrasound in the acoustic medium, and is the frequency of the ultrasound.) In other words, the deflection angle θ is the above ( 1) As can be seen from the equation, it is proportional to the frequency; therefore, if the frequency of the high-frequency current input to the acousto-optic modulator 8 is changed periodically, the deflection angle θ will also change periodically accordingly. I will do it. In other words, it is possible to freely vary the scanning line finely, and by utilizing the above phenomenon, the width of the scanning line can actually be increased. The present invention utilizes the above phenomenon,
By increasing the actual width of the scanning line, density unevenness occurring between the scanning lines is eliminated.

Now, in Fig. 7, a voltage V is applied to the VCO 19 to obtain a carrier current having a predetermined frequency (usually several tens of MHz to 200 MHz is used), which is optimal for image printing. Oscillator 2
A current 23 with a frequency of _M outputted from 0 is superimposed.

This superimposed current 24 changes periodically from frequency _u to frequency l around the frequency, and the frequency of the change is the frequency
Matches _M. The current 24 is then passed through the mixer 21
The signal is modulated by the image signal from the image signal generator 18, further amplified by the amplifier 22, and input to the acousto-optic modulator 8 as a drive signal for driving the acousto-optic modulator 8. Here, the amplitude of the current 23 having the frequency _M corresponds to the amount of change in the frequency of the current 24 (the difference between the frequencies _u and l), and this amount of frequency change further determines the magnitude of the deflection angle θ.
The magnitude of this deflection angle θ, that is, the amount of deflection of the primary light L ₁ in the sub-scanning direction YY is determined to be an appropriate constant amount depending on the scanning line density and the beam diameter.

In this way, if the output of the VCO 19 is FM-modulated by the output of the external oscillator 20, then modulated by the image signal, and further amplified and input to the acousto-optic modulator 8, the ultrasonic waves propagating in the acoustic medium 8b can be The frequency also changes accordingly, and as a result, the primary light L ₁ has a small deflection angle determined from frequency _u to frequency l around the deflection angle θ determined by the frequency, as shown by the imaginary line in Figure 6. You can swing it with _M. Therefore, if the direction of this deflection is adjusted to the sub-scanning direction XX, the scanning line will deflect as shown in FIG.
Density unevenness between scanning lines is eliminated.

Next, another embodiment of the present invention will be described with reference to FIG. The embodiment shown in FIG. 8 is similar to the sixth embodiment described above.
Since it has the same constituent parts as the embodiment shown in the figures, the same parts will be described with the same reference numerals.

This embodiment is an embodiment of the present invention for a multi-beam simultaneous modulation system, and as an example, a drive circuit 25 configured to simultaneously perform six scans is shown.

The current of frequency _M output from the external oscillator 20 is divided into six by the divider 26, and the corresponding VCO 19a, 19b, 19c, 19d, 19
e and 19f, respectively.
Furthermore, VCO19a, 19b, 19c, 1
The currents of frequencies a, b, c, e, f outputted from the respective mixers 21a, 21b, 21c, 21
d, 21e, 21f, and the mixer 21
a, 21b, 21c, 21d, 21e, 21f, image signals 28a, 28b, 28 for each scanning line
After being mixed with components c, 28d, 28e, and 28f, the signal is coupled to a coupler 27, further amplified by an amplifier 22, and outputted to the acousto-optic modulator 8 as a drive signal.

According to this embodiment, each of the six primary lights emitted from the acousto-optic modulator 8 is also deflected as shown in FIG. 4 based on the principle explained in the previous embodiment. be able to.

In this embodiment, the distributor 26 may be removed and six external oscillators 20 may be provided independently.

As described above, according to the present invention, density unevenness that occurs between scanning lines is eliminated, and a high quality so-called solid image can be obtained.

[Brief explanation of the drawing]

1 to 3 are diagrams of scanning lines causing density unevenness, FIG. 4 is a diagram of scanning lines by the laser recording apparatus of the present invention, and FIG. 5 is a diagram of a laser recording suitable for carrying out the present invention. A configuration diagram of the device, Fig. 6 is a diagram showing the drive circuit of the acousto-optic modulator according to the present invention together with the acousto-optic modulator, and Fig. 7 shows the current output from the external oscillator and the output from the voltage-controlled variable frequency oscillator. FIG. 8 is a diagram of a drive circuit according to another embodiment of the present invention. 8... Acousto-optic light modulator, L ₁ ... Primary light, X
-X...Main scanning direction, Y-Y...Sub scanning direction.

Claims (1)

[Claims] 1 Applying a drive signal modulated by an image signal to an acousto-optic modulator to obtain primary light optically modulated by the drive signal from the acousto-optic modulator, and guiding this to a recording medium. In a laser recording device that records an image using a laser beam, the laser beam is oscillated with a predetermined minute amplitude in the sub-scanning direction perpendicular to the main-scanning direction so as to blur the spot image in the sub-scanning direction and make density unevenness between scanning lines in the recorded image less noticeable. In order to obtain the primary light, the frequency of the drive signal input to the acousto-optic modulator is periodically changed within a certain range centered on the set frequency of the drive signal. laser recording device.