JPH0424665A - Electrophotographic recording device - Google Patents

Abstract

PURPOSE:To record an image with multi-gradation and of high quality by disposing a mirror for irradiating with both laser beams the same position on the surface of a photosensitive body, making the beam diameters of the laser beams from a pair of laser light sources and which are formed on the surface of the photosensitive body different from each other, and selectively actuating the pair of laser light sources. CONSTITUTION:A dichroic mirror 4 is disposed between the laser light sources 2 and 3 and the photosensitive body 1, the laser beam from the laser light source 2 is transmitted through the dichroic mirror 4, meanwhile, the laser beam from the laser source 3 is reflected on the dichroic mirror 4, and both laser beams are radiated on the same position on the surface of the photosensitive body 1. That means, the dichroic mirror 4 is provided with the characteristic of high transmissivity with reference to the wavelength of the laser beam of the laser light source 2, and provided with the characteristic of high reflectance with reference to the wavelength of the laser beam of the laser light source 3. And the beam diameters of the laser beams from the laser light sources 2 and 3 and which are formed on the surface on the photosensitive body 1 are different from each other. And the light quantity of the laser beams from the laser light sources 2 and 3 which are selectively actuated can be adjusted. Thus, the image with multi-gradation and of high quality can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electrophotographic recording device, and more particularly to an electrophotographic recording device applied to a laser printer or the like that records images using an electrophotographic method.

[Conventional technology]

Conventionally, in electrophotographic recording devices such as laser printers, the diameter of each dot is fixed depending on the pixel density, so when expressing gradation by area modulation such as dither method,
It is known that resolution decreases. For this reason, a PWM (pulse width modulation) method, a PM (power modulation) method, etc., which are able to express gradations without reducing the resolution by changing the size (area) of each dot, have been adopted.

The PWM method can change the dot size in the main scanning direction, and the PM method can change the dot size in the sub-scanning direction by changing the light intensity of the laser beam. In 2, the dot's variable range was limited. As a solution to this problem, for example, the method described in Japanese Unexamined Patent Publication No. 1-1 (8522) is known, and the method S is a liquid crystal element that electrically drives the diameter of the laser beam By adjusting the diameter of the laser beam on the surface of the photoreceptor, the size of the toe is changed.

[Problem to be solved by the invention]

However, in such conventional electrophotographic recording devices, the size of the dots is changed by an electrically driven liquid crystal element, so it takes a long time to drive the liquid crystal element, and the dots cannot be printed at high speeds. - There was a problem that the size of the gutter could not be changed and the quality of the recorded image deteriorated.

[Purpose of the invention]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an electrophotographic recording apparatus capable of recording a multi-gradation, high-quality image by changing the dots at high speed while expanding the variable range of the dots.

[Structure of the invention]

In order to achieve the above object, an electrophotographic recording apparatus according to the present invention includes a photoconductor and a pair of lasers capable of irradiating the photoconductor with laser beams of different wavelengths to form a latent image on the surface of the photoconductor. It is provided between a light source, a pair of laser light sources and a photoreceptor, and transmits one laser beam of the pair of laser light sources and reflects the other laser beam, so that both laser beams are directed onto the same surface of the photoreceptor. and a mirror for irradiating the light onto the photoreceptor surface, the beam diameters of the laser beams of the pair of laser light sources on the surface of the photoreceptor are different from each other, and the pair of laser light sources are selectively activated. Further, the light intensity of the laser beams from the pair of laser light sources may be adjustable so that the size of the dots constituting the latent image formed on the surface of the photoreceptor is changed.

Hereinafter, the present invention will be specifically explained based on Examples.

1 to 3 are diagrams showing one embodiment of an electrophotographic recording apparatus according to the present invention, and are examples in which the electrophotographic recording apparatus is applied to a laser printer.

First, the configuration will be explained.

In FIG. 1.2, l is a photoreceptor, and 2.3 is a pair of laser light sources. The laser light source 2.3 is composed of, for example, a semiconductor laser (LD), and irradiates the photoreceptor 1 with laser beams of different wavelengths via an optical unit 7, which will be described later, to form a latent image on the surface of the photoreceptor 10. be able to.

A so-called dichroic mirror 4 is provided between the laser beam a2.3 and the photoreceptor 1, and the dichroic mirror 4 transmits the laser beam from the laser light source 2 and reflects the laser beam from the laser light source 3, so that both The laser beams are irradiated onto the same position on the surface of the photoreceptor 10. That is, the dichroic mirror 4 has a characteristic of high transmittance with respect to the wavelength of the laser beam of the laser light source 2, and a characteristic of high reflectance with respect to the wavelength of the laser beam of the laser light a3. The beam diameters of the laser beams of laser light #2.3 on the surface of the photoreceptor 1 are different from each other, and the beam diameter of the laser light source 3 is set to 200 μm. Also, laser light #, 2.3
is selectively activated. That is, as shown in Figure 3,
When the diameter of the dots required for gradation expression is small,
For example, divide the range from 600 to 200 dpi into two, and when the dot diameter is in the smaller range, the laser light source 2 is activated, and when the required dot diameter is in the larger range, the laser light source 3 is activated. I try to let them do it.

On the other hand, this embodiment is an example applied to the above-mentioned well-known PM laser printer, in other words, in this printer, the size of the dots constituting the latent image formed on the surface of the photoreceptor 1 changes. As such, the laser light source 2.3 has a function of adjusting the amount of laser beam of the laser light source 2.3. Specifically, the control unit of the printer adjusts the amount of electricity supplied to the laser light source 2.3 to adjust the amount of emitted laser beam.

Therefore, by adjusting the intensity of the laser beam a2.3 that is selected and activated, it is possible to change the size of the dot in each laser beam of the selected laser light source 2.3.

Here, the optical units provided between the laser light source 2.3 and the dichroic ink mirror 4 and between the dichroic ink mirror 4 and the photoreceptor 1 will be briefly described. Note that this optical unit is a known one.

5.6 is a collimating lens that converts the laser beam emitted from the laser light source 2.3 into parallel light; 7.8 is an aperture having a slit corresponding to the size of the dot of the beam to be formed; 9 is a main scanning beam a cylinder lens 10 that focuses light into a predetermined shape and size on the surface of the photoreceptor 1;
11 is a polygon mirror that scans the focused laser beam in the main scanning direction, that is, the longitudinal direction of the photoreceptor 1; 11 is an Fθ lens that converts the uniform angular motion of beam scanning into uniform velocity motion to correct field curvature; and 12 is a A mirror that changes the irradiation angle of the beam; 13 is a cylinder lens that focuses the beam in the sub-scanning direction, that is, the rotation direction of the photoreceptor 10; 14, 15, and 16 are mirrors and cylinder lenses for synchronizing the main scanning direction; It is a light receiving element.

According to the above configuration, the laser light source 2.3 can be selectively activated to irradiate the same position on the surface of the photoreceptor 1 with beams having different diameters, thereby expanding the variable range of dots. can do.

Furthermore, since this embodiment is particularly applied to a PM method in which the variable range of dots is small, the control range of PM control can be expanded compared to the conventional PM method.

Furthermore, the laser light source 2 is
．． 3, the beam diameter can be changed at high speed, so the size of the dot can be changed at high speed.

Furthermore, compared to conventional devices that use electrically driven liquid crystal elements, the configuration and control are simpler.
Cost can be reduced.

Therefore, a multi-gradation, high-quality image can be provided at low cost.

〔effect〕

According to the present invention, it is possible to selectively operate a pair of laser light sources to irradiate beams with different diameters to the same position on the surface of the photoreceptor, thereby expanding the range of dot variation. .

Further, since the beam diameter can be changed simply by selectively operating the pair of laser light sources using a mirror, the size of the dot can be changed at high speed.

Furthermore, when the size of the dot is changed by adjusting the amount of light of the laser beam, that is, when applied to a PM system, the variable range of the dot can be expanded compared to the conventional system.

Therefore, a multi-gradation, high-quality image can be provided.

[Brief explanation of drawings]

1 to 3 are diagrams showing an embodiment of an electrophotographic recording device according to the present invention, in which FIG. 1 is a perspective view thereof, FIG. 2 is an enlarged perspective view of its main parts, and FIG. 3 is an operation thereof. It is an explanatory diagram. 1...Photoreceptor, 2.3...--Pair of laser light sources, 4...
Dichroic ink mirror (mirror). Diagram

Claims (2)

[Claims] (1) Between a photoconductor, a pair of laser light sources that can irradiate the photoconductor with laser beams of different wavelengths to form a latent image on the surface of the photoconductor, and the pair of laser light sources and the photoconductor. a mirror that is provided to transmit one laser beam of the pair of laser light sources and reflect the other laser beam to irradiate both laser beams to the same position on the surface of the photoreceptor; An electrophotographic recording apparatus characterized in that the beam diameters of the laser beams of the laser light sources on the surface of the photoreceptor are different from each other, and the pair of laser light sources are selectively operated. (2) The light intensity of the laser beams of the pair of laser light sources can be adjusted so that the size of the dots constituting the latent image formed on the surface of the photoreceptor is changed. The electrophotographic recording apparatus according to claim 1.