JPS5893038A - Laser scan recording method - Google Patents

Abstract

PURPOSE:To improve the quality of both characters and images, by varying the beam diameter between the main scanning direction and the secondary scanning direction in accordance with the images output form. CONSTITUTION:An AOM (acoustooptical modulator) 10 is provided between modulating optical systems 3 that modulate laser light. The AOM10 contains a transducer 10y which transmits the ultrasonic wave in the direction (y) and a transducer 10x which transmits the ultrasonic wave in the direction (x). These two transducers are attached orthogonally to each other. The inputs to these transducers are switched with changeover switches S1 and S2 and by a picture signal 11y of portrait type and an image signal 11x of landscape type in the form of the image output form. The direction (y) is larger than the direction (x) in terms of the beam diameter with the output form of portrait type, and vice versa with the output form of landscape type.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an acousto-optic modulator (
The present invention relates to a laser scanning recording method using an AOM (hereinafter referred to as an AOM). Specific devices to which the present invention can be applied include laser printers, laser plotters, and their application devices.

When a character is composed of a set of dots in units of pixels, there is an empirical fact that character quality is improved if the shape of each dot is an ellipse whose major axis coincides with the direction of the character.

On the other hand, in laser scanning recording devices, images such as characters are formed by scanning a laser beam spot onto a recording medium such as a photoreceptor, but in conventional laser scanning recording devices, it is independent of the direction of the printed characters. In this case, the laser beam spot shape remains unchanged. Therefore, depending on the character direction,
The problem is that the character quality deteriorates.

The above relationship will be further explained. There are two types of output formats for laser scanning recording devices: portrait type and landscape type. The portrait type refers to a form in which the vertical direction of the image recording medium 1 matches the direction of the characters, as shown in Figure 1, and the landscape type refers to
As shown in FIG. 2, this refers to a form in which the vertical direction of the image recording medium 1 and the direction of the characters are perpendicular to each other. In each figure, the arrow direction indicates the main scanning direction of the beam.

In the case of a portrait type, as shown in Figure 3, if the shape of the beam spot S is an ellipse that is long in the vertical direction, the direction of its long axis (orthogonal to the scanning direction indicated by the wooden arrow) is the letter rAJ. Experience has shown that character quality improves if the direction matches the direction of , and portrait type is more commonly used as an image output format, so this is generally fixedly set.

Incidentally, as the image output format, there is a landscape type as described above, and there is also a mixed format of a portrait type and a landscape type. The above mixed forms are often seen in graphs, charts, etc.

Therefore, as shown in Figure 6, the shape of the beam spore S remains an ellipse that is elongated in the vertical direction, and the direction of its long axis remains perpendicular to the scanning direction indicated by the wooden arrow, as shown in Figure 4. If landscape type printing is performed as described above, the quality of the characters will be inferior to that of the characters formed in the portrait type as described above, based on empirical facts. ′: In the conventional technology, a beam spot is set in a shape that is suitable for the often-frequent portrait type output format and improves character quality, but since this beam spot shape is fixed, Character quality becomes poor when landscape type output format is used.

The present invention has been made in view of the above-mentioned circumstances, and it is an object of the present invention to provide a laser scanning recording device that is suitable for both portrait type and landscape type output formats and can improve character and image quality. With the goal.

The present invention will be explained in detail below.

The laser scanning recording method according to the present invention has a beam diameter in the main scanning direction and a beam diameter in the sub-scanning direction depending on the image output form.
It is characterized by changing and recording.

FIG. 5 shows a schematic configuration of a laser scanning recording device suitable for carrying out the floor invention.

In the figure, since most of the configuration of the device is well known, the names of each member are listed as follows: 2 is a laser light source, 3 is a modulation source system, 4 is an AOM, and 5 is a
Reference numeral 6 indicates a rotating polygon mirror, reference numeral 6 indicates an fθ lens, reference numeral 7 indicates a synchronization detection element, and reference numeral 8 indicates a photosensitive drum.

Incidentally, the beam shape of AOM modulated light is generally an ellipse having a minor axis in the direction of ultrasound propagation. To explain this with a diagram, in FIG. 6, reference numeral 4a is a transducer.

Then, the direction of travel of the ultrasonic wave becomes the X direction. Therefore, the modulated light I4. If the beam is irradiated onto a screen 0-0 perpendicular to the optical axis and its shape is examined, it becomes an ellipse with a minor axis in the X direction, as shown in FIG.

By the way, the technical document JOPTI indicates that the beam ellipticity ratio (major axis/minor axis) of this modulated light Lb1 can also be changed by changing the following factors (1) to (6).
CALENGINEERINGJ 16b5 ('77
), pages 452-454.

11), Wavelength of laser incident on AOM: λ.

(Laser beam diameter incident on 21AOM: W.

(3) Refractive index of AoM at laser wavelength 20 (4)
Speed of sound in AOM medium: V (5) Carrier frequency of AOM: fo (6) Length of transducer: L For example, zinc molybdate (P, M2
O3) and λ. = 63282 (Hs-Ne laser), f0 = 80 MHz, L = 14 sm, and the theoretical values of changes in beam ellipticity ratio and modulation efficiency when changing the beam spot diameter entering the AOM K are shown in Figure 8. Shown below. This figure shows that the beam ellipse ratio can be changed by changing the diameter of the beam spot incident on the AOM.

This is a change when changing factor 21 among the above factors, but the same can be said for other factors.However, when embodied as a device,
The 10th carrier frequency in (5) can be made variable.
Others are fixed f-2 according to specific conditions, and it is difficult to make them freely variable.

For example, as shown in the example in Fig. 5 (, AOM's ultrasonic travel direction (
X direction) and the mechanical deflection direction of the beam by the rotating polygon mirror 5 (in the x-z plane) are orthogonal to each other, the AOM
4, the beam diameter in the X direction is larger than the diameter in the X direction, but since the beam diameter ratio is reversed by the fθ lens 6, the diameter in the y direction is
It is larger than the diameter in the direction. In this case, since the major axis of the elliptical beam is aligned in the direction perpendicular to the main scanning direction, it is compatible with the portrait type output format shown in FIG.

Assuming that the mechanical deflection direction of the beam by the rotating polygon mirror 5 is parallel to the ultrasonic traveling direction of the AOM 4, the beam diameter on the surface of the photoreceptor drum 8 in the y direction is It is smaller than the diameter in two directions. In this case, since the major axis of the Km circular beam in the main scanning direction is the same as the length of the Km circular beam, it is compatible with the landscape type output format shown in FIG.

Therefore, in the case of a portrait type, the ultrasonic travel direction of the AOM and the mechanical deflection direction by the rotating polygon mirror are set to be orthogonal, and in the case of a landscape type, the
If the OM's ultrasonic traveling direction is parallel to the mechanical deflection direction of the rotating polygon mirror, it is possible to form high-quality characters in both portrait and landscape types. As a practical matter, it is quite difficult to create a configuration in which the above-mentioned ultrasonic traveling direction and mechanical deflection direction can be switched.

Therefore, for example, as shown in FIG. 9, A in FIG.
Instead of the OM 4, an AOMlo is provided between the modulation optical systems 3. This AOMiO includes a transducer ioy that transmits ultrasound waves in the y direction, and a transducer 0x that transmits ultrasound waves in the X direction, and both are mounted on the AOM medium in a relationship that is orthogonal to each other.

Furthermore, the input to each of these transducers 0x and 10y is configured to be switched between an image signal 11y to be output in portrait type and an image signal 11x to be output in landscape type.

For example, when writing the image composition code 11x, the changeover switch S1 and the changeover switch S2 are operated in conjunction with each other, and the write input is applied to the transducer 0x. Also, when writing the ::'j image signal iiiy, the write input is applied to the transducer 0y'.

In the figure, reference numeral 11 is an oscillator that oscillates a carrier wave, and reference numeral 1
Reference numeral 2 represents a mixer for mixing an image signal and a carrier wave, and reference numeral 13 represents an amplifier.

In designing the device, the conditions of each member are determined in consideration of the factors (1) to (6) above so as to form an optimal beam shape. Then, on top of that, the carrier frequency is changed by 1° to slightly change the shape of the elliptical beam,
You can also adjust the text quality.

For example, when a mechanical deflector such as a rotating polygon mirror is used as an optical scanning means for scanning a recording medium such as a photosensitive drum with a laser beam, pitch irregularities are inevitable due to tilting of the surface of the mechanical deflector during operation. The pitch unevenness causes black or white streaks on the image and has an adverse effect. In order to avoid such adverse effects, it is necessary to first
For operations such as zero, the effect of changing the carrier frequency fo can be utilized.

[Brief explanation of drawings]

Figure 1 is a diagram explaining the output format in portrait type, Figure 2 is a diagram explaining the output format in landscape type, Figure 3 is a partially enlarged view of Figure 1, and Figure 4 is the same as in Figure 4. 2 is a partially enlarged view, FIG. 5 is a schematic configuration diagram of a laser scanning recording device suitable for implementing the present invention, FIG. 6 is a perspective view of the AOM, FIG. 7 is a diagram of the beam shape of the AOM modulation source, and FIG. The figure is a diagram explaining the relationship between the AOM incident beam diameter and the beam ellipse ratio of the AOM modulated light, etc., Figure 9 is a diagram showing the configuration around the AOM explaining one embodiment of the present invention, and Figure 10 is the sub-scanning pitch and FIG. 3 is a diagram illustrating the relationship with the beam diameter in the sub-scanning direction. Ryo 6 reasons

Claims (1)

[Claims] 1. In a laser scanning recording method using an acousto-optic modulator (hereinafter referred to as AOM) as an external modulator of the laser, the beam diameter in the main scanning direction and the beam diameter in the sub-scanning direction can be adjusted depending on the image output form. A laser scanning recording method characterized by recording by changing the diameter. 2. A laser scanning recording method characterized in that the beam ellipse ratio of the AOM is used to change the beam diameter according to claim 1.