JPH03189664A - Laser scanning type image forming device - Google Patents

Abstract

PURPOSE:To obtain an image of high gradation and high quality by dividing laser beam into a multiple number of beams by a light modulation and polarization means and forming an image again in nearby positions to each other on a photosensitive body after the divided beams are converged once at a focal surface. CONSTITUTION:When the laser beam L (incident beam) makes incidence on a multi frequency drive acoustooptical element 7, the multiple number of defracted beams L' are obtained in a direction of a Bragg angle determined by each frequency. Because of this, by varying the frequency of a carrying wave in accordance with an iamge data, a cycle of refractive index variation inside an acoustic medium is varied, and the defraction angle can be varied. That is, dot area on the photosensitive body 4 formed by synthesis of the defracted beam L' can be varied. Because of that, gradation can be expressed by the dot unit, and the image of high gradation and high quality without decreasing of resolution can be easily formed.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a laser scanning image forming apparatus such as a laser beam printer using a semiconductor laser, gas laser, etc. as a light source, and particularly relates to a laser scanning image forming apparatus such as a laser beam printer that uses a semiconductor laser, gas laser, etc. as a light source. This relates to making it variable and improving resolution.

(Prior Art) In general, a laser beam printer converges a laser beam with coherent characteristics emitted from a laser light source using a condenser lens to form a minute spot on a light receiving surface, and a photoreceptor that is electrically charged in a negative manner. The surface is scanned and exposed. By controlling the laser beam using pixel signals, an electrostatic latent image is formed on the surface of the photoreceptor and developed with fine powder toner.

In such laser beam printers, the diameter of the light beam is fixed according to the pixel density, and in order to obtain high-quality images, it is necessary to scan and expose at high density.
Large amounts of image data must be processed at high speed.

For this purpose, for example, by using a plurality of semiconductor lasers as a light source and controlling the intensity of each semiconductor laser, the center position of the combined and imaged light energy can be made variable (Japanese Patent Laid-open No. 6
1-212818), or - one beam is divided into a plurality of beams by a light modulation deflector, and the plurality of beams are selectively used in accordance with a plurality of types of pixel densities (
Several methods have been proposed to obtain partially pseudo high-density images and efficiently form high-quality images, such as Japanese Patent Laid-Open No. 60-182868.

(Problem to be solved by the invention) However, even with these methods, area gradation methods using matrices such as the dither method are mainly used to express gradations, and gradation using such matrices is difficult to achieve. In tone expression, a problem arises in that the resolution decreases.

(Object of the invention) The present invention has been made in view of the above-mentioned circumstances, and includes:
An object of the present invention is to provide a laser scanning image forming apparatus that can easily form high-quality images with high gradation without reducing resolution by varying the size of dots on a dot-by-dot basis.

(Structure and operation) In order to achieve the above object, the present invention scans and exposes a photoreceptor moving in the sub-scanning direction with a recording light signal corresponding to the state of recording pixels to form an electrostatic latent image. A laser scanning image forming apparatus that develops an electrostatic latent image and transfers it onto a recording sheet includes a light modulation deflection means that divides a laser beam emitted from a light source into a plurality of beams according to image data, and a light modulation deflection means that divides a laser beam emitted from a light source into a plurality of beams according to image data. It is provided with a means for converging the divided beams divided by the deflection means once within the focal plane and then refocusing them on positions close to each other on the photoreceptor, so that the diameter of the dots on the photoreceptor can be varied in units of one dot. It is characterized by tightening.

In the present invention, a laser beam emitted as parallel light is divided into a plurality of beams by a light modulation deflection means, and after each of the divided beams is once converged within a focal plane, the image forming means brings them closer to each other on a photoreceptor. The image is formed at the position. The imaging position of each split beam can be varied by controlling the light modulation and deflection means according to the image data, and the dot area on the photoreceptor can be changed, making it possible to easily achieve high gradations without reducing resolution. Form high quality images.

(Example) FIG. 1 shows a basic configuration (a) of the present invention and a schematic diagram (b) showing changes in dot area.

In FIG. 1(a), 1 is a light modulating deflection element, 2 is a lens selected so that the focal plane A is behind the light modulating deflection element 1, 3 is an imaging lens, and 4 is a photoreceptor. In the subsequent drawings as well, common parts are given the same numerical symbols, and the explanation will be omitted since it will be redundant.

In FIG. 1(a), laser light that enters the lens 2 as parallel light from a laser light source (not shown) is divided into a plurality of beams B by the light modulation deflection element 1, and each of the divided beams B is within the focal plane A. After converging once, the images are again focused on the photoreceptor 4 at positions close to each other by the imaging lens 3.

The image formation position of each of the divided beams B can be varied by controlling the light modulation deflection element 1 according to the image data. The dot area can be changed.

In FIG. 1(b), the left side shows the case of one-dimensional deflection, and the right side shows the case of two-dimensional deflection. In the case of -dimensional deflection, the two-dimensional deflection is applied only in one direction (y direction) on the photoreceptor 4. In this case, the dot area can be further changed in both directions (x+y direction) on the photoreceptor 4.

FIG. 2 shows a configuration diagram of the first embodiment of the present invention, and 3' in FIG. A lens is provided to suppress the spread between the divided beams 8, 5 is a deflection plate, 6 is an optical scanner such as a rotating polygon mirror, and the direction of the arrow indicates the direction of deflection by the deflection plate 5.

Further, the multi-frequency drive acousto-optic element 7 shown in FIG. 4 is driven and controlled by a drive control section 8, and the drive control section 8 receives gradation control signals F, F2, . . . , Fm and a carrier frequency f□.

Mixer 81, 8□...8 for mixing f2...fm
n, a coupler 8C that couples the mixer output, and a power amplifier 8 that excites the multi-frequency drive acousto-optic element 7.
Consists of A.

When the multi-frequency drive acousto-optic element 7 is driven by a carrier wave f of a certain frequency, an ultrasonic wave is excited in the acoustic medium, and a periodic refractive index change in the medium due to the ultrasonic wave generates laser light. It is an element that can perform optical deflection and optical modulation using the phenomenon of diffraction of multiple different carrier waves f.
1. When driven at the same time by f,...fm, multiple different periods of refractive index changes determined by each frequency occur simultaneously in the element, and when laser light L (incident beam) is incident on this, the refractive index changes are determined by each frequency. A plurality of diffracted beams L' are obtained in the direction of the Bragg angle.

Therefore, by changing the frequency of the carrier wave according to the image data, it is possible to change the period of change in the refractive index in the acoustic medium, change the diffraction angle, and change the convergence position of each diffracted beam. That is, the diffracted beam L'
The dot area on the photoreceptor 4 formed by the synthesis of the dots can be changed. Further, the deflection plate 5 is set so that the deflection angles of adjacent divided beams B are shifted by 90 degrees.
It plays the role of reducing the interference effect between each diffracted beam L'.

FIG. 3 shows a configuration diagram of a second embodiment of the present invention, in which a multi-frequency drive acousto-optic element 7 is used as a light modulation deflection element in the same way as in the first embodiment, but the first embodiment In the case of , a composite dot of only the diffracted beam L' by the multi-frequency driven acousto-optic element 7 was formed (-dimensional deflection in Fig. 1(b)).
. On the other hand, in the second embodiment, a dot is formed by using a zero-order beam (transmitted beam) as a fundamental beam and converging a diffracted beam L' around it (first
(two-dimensional deflection in Figure (b)), so the center of intensity of the beam is always on the scanning line, making it possible to obtain a stable image. 5' in Figure 3 is a deflection plate that rotates the deflection angle of the 0th-order beam by 90 degrees, and also serves to attenuate the 0th-order beam intensity so that it does not become too strong compared to the intensity of the diffracted beam. We are prepared.

As a result, the zero-order beam can be used as a fundamental beam without interfering with the diffracted beams, and the dot area can be varied depending on the imaging position of the surrounding diffracted beams.

Furthermore, the multi-frequency drive acousto-optic element 7 used here is not limited to the one shown in FIG. 4, but may also have the configuration shown in FIG. 5, for example. 7 from mutually orthogonal directions by the drive control units 8, 8, it is possible to drive not only in one direction as shown on the left side of FIG. 1(b) but also in both directions as shown on the right side of FIG. 1(b), that is, two-dimensionally. The dot diameter on the photoreceptor can be changed accordingly.

Furthermore, although only multi-frequency driven acousto-optic elements are discussed here as optical modulation deflection elements, the high-order diffraction beams may be used in general single-frequency acousto-optic elements, or other devices other than acousto-optic elements may be used. However, a light modulation deflection element that can be controlled at high speed, such as a deflection element that applies an electro-optic effect, may also be used.

(Effects of the Invention) As explained above, according to the present invention, the dot area on the photoreceptor can be changed in units of one dot.

Therefore, it is possible to express gradation with one dot, and it is possible to easily form a high-quality image with high gradation without reducing resolution.

[Brief explanation of drawings]

FIG. 1(a) is a basic configuration diagram of the present invention, FIG. 1(b) is a schematic diagram showing changes in dot area, FIG. 2 is a configuration diagram of the first embodiment of the present invention, and FIG. FIGS. 4 and 5 are block diagrams of a second embodiment of the present invention, showing the block diagrams of a multi-frequency driven acousto-optic element used in this embodiment and serving as a light modulation deflection element. 1... Light modulation deflection element, 2, 3'... Lens, 3... Imaging lens, 4... Photoreceptor, 5
... Deflection plate, 6 ... Optical scanner, 7 ... Multi-frequency drive acousto-optic element, 8 ... Drive control section, 81,8
□...8n...Mixer 8A...Power amplifier, 8C...Coupler.

Claims (1)

[Claims] Laser scanning scans and exposes a photoreceptor that moves in the sub-scanning direction with a recording light signal corresponding to the state of recording pixels to form an electrostatic latent image, and develops this electrostatic latent image to transfer and record it on recording paper. In a type image forming apparatus, a light modulation deflection means splits a laser beam emitted from a light source into a plurality of beams according to image data, and each split beam split by the light modulation deflection means is split once within a focal plane. 1. A laser scanning image forming apparatus comprising means for refocusing the images at positions close to each other on the photoreceptor after convergence, and making the diameter of the dots on the photoreceptor variable in units of one dot.