JPH0368912A - Optical writing optical system of image forming device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a light source for an image forming apparatus such as a copying machine, a printer, or a facsimile machine that writes an image on an image carrier based on written data and forms an image. It relates to a writing optical system.

In conventional optical writing optical systems for image forming devices such as printers that use laser beams, there is no technology to obtain gradations by controlling the laser power in units of 1 pixel during 1 scan. The laser beam power was constant throughout the scan. Therefore, both the vertical and horizontal diameters of the beam projected onto the photoreceptor remained constant during scanning.

This type of device does not have any particular problem with gradation when forming an image similar to a general sentence that can be expressed by a combination of vertical lines, horizontal lines, and dots, but it is necessary to express halftones such as in photographs. In some cases, it is extremely inadequate. In response to this, in the past, halftone dot methods and spiral methods have been devised for dot matrix, but since the pixel size of one dot is constant as described above, sufficient gradation cannot be obtained. In addition, in order to express gradation more finely, there is a method of increasing the size of the matrix and reducing the size of one pixel, but reducing the size of a pixel is technically difficult in optical systems.

Problems to be Solved by the Invention The present invention solves the above-mentioned problems in the prior art, and provides an optical writing optical system for an image forming apparatus that is capable of forming images with good gradation by imparting gradation to each pixel. The challenge is to provide the following.

Means for Solving the Problems In order to solve the above problems, the present invention generates a laser beam in an optical writing optical system of an image forming apparatus that writes an image on an image carrier based on written data to form an image. a plurality of laser diodes, and an output control means for setting different outputs to the plurality of laser diodes, and the projection axes of the laser beams generated from the plurality of laser diodes onto the image carrier are mutually arranged. The plurality of laser diodes are arranged so as to coincide with each other, and the plurality of laser diodes are selectively turned on based on the write data.

According to the present invention, different outputs are set for each of the plurality of laser diodes by the output control means, and the laser beams generated from each laser diode perform optical writing on the image carrier so that their projection axes coincide with each other. Place the optical system,
Since multiple laser diodes are selectively turned on based on written data, multiple pixel dimensions can be obtained for one pixel, and each pixel dimension can be combined, so that at least four gradations can be achieved in one pixel. This means that multiple gradations can be obtained.

Embodiment FIG. 1 shows an example of a control circuit for a laser diode constituting an optical writing optical system of a laser beam printer, which is an example of an image forming apparatus, and FIG. 2 shows a schematic configuration of this optical writing optical system. The optical writing optical system will be explained with reference to FIG.

A laser beam emitted according to written data from a multi-beam laser diode 1 consisting of four beams, which is an example of a plurality of laser diodes, is shaped by an aperture member 2, passes through a first cylindrical lens 3, and is sent to a polygon motor. The light is incident on the mirror surface of the polygon mirror 4 which is rotated at high speed. The rθ characteristic of the laser beam reflected by this mirror surface is corrected by the fθ lens group 5 so that the image forming point moves at a constant speed on a straight line on the photoreceptor belt 8, which is an example of an image carrier. 6. The image is formed onto the photoreceptor belt 8 via the second cylindrical lens 7.

Note that although a multi-beam is used as the light emitting source in the above description, a plurality of single-beam laser diodes may be used.

In FIG. 1, each diode 1-1.1-2.1-3 of a multi-beam laser diode l as a light emitting source
．． Set different powers for 1-4. This power setting is done using conventional technology such as AP as output control means.
The C (Auto, Power Control) circuit is used. That is, if the power of the first laser diode 11 of the multi-beam laser diode 1 is 1, then the power of the second, third, and fourth laser diodes 1-2, 1-3
, l-4 outputs are respectively 1.1, 1.2,
1.3, multi-beam laser diode I
The power detect sensor 1-5 built in detects the emitted light power, and the signal is sent to A via AMP 10.
The constant current controllers 12-1 to 12-4 are controlled by the APC control line 11. Also, write data WDT1 to WDT4 are coupled to the drive lines of the diodes I-1 to I-1-4, respectively, and one or more laser diodes are turned on in response to the write data. There is.

FIG. 3 is a diagram showing the size of a pixel according to the output when each of the laser diodes 1-1-1-4 lights up for one pixel separately. As shown in the figure, even when the same one pixel is lit, as the output increases, both the vertical and horizontal dimensions increase, and four different types of pixels can be expressed.

In contrast, conventionally, it has been impossible to change the pixel size not only in one main scanning direction but also within one page. In other words, in order to change the pixel dimensions using the conventional method, the constant current AI11 control circuit shown in Figure 1 needs to have a response characteristic of several hundred ns, but it is difficult to achieve such a response characteristic. This is because it was.

FIG. 4 shows the relationship between the emission power of the laser diode and the pixel size. It is a known fact that increasing the current supplied to the laser diode increases the diameter of the beam projected onto the photoreceptor, and the present invention applies this fact.

If it is possible to obtain pixel dimensions of 4 gradations during one scan as in this example, if this is applied to the conventional technique of halftone method or spiral method expressed by a 2 x 2 matrix, even finer gradations can be obtained. can be expressed.

For example, among the pixel dimensions shown in Figure 3, the output is 0136m.
Small pixel and 0.468mw (0.36mw
Even if there are only two types of large pixels (1.3 times larger than
+2' = 30, that is, 300 gradations are obtained. In other words, 300 gradations can be expressed compared to the conventional 4 gradations.

Effects As described above, according to the present invention, by providing output control means for setting different outputs to a plurality of laser diodes, it is possible to set different outputs and obtain a plurality of pixel dimensions for one pixel. It is also possible to combine those of each pixel size, and at least 4 in one pixel.
A plurality of gradations higher than the gradation can be obtained, and an image with gradation can be formed.

[Brief explanation of drawings]

FIG. 1 is a control circuit diagram of a laser diode showing an embodiment of the present invention, and FIG. 2 is a schematic diagram of an optical writing optical system of the embodiment.
Figure 3 is a schematic diagram showing the size of a pixel when one pixel is lit;
FIG. 4 is a schematic diagram showing the relationship between light emitting power and pixel size, and FIG. 5 is a diagram showing the gradation when small pixels and large pixels are combined in a 2×2 matrix. 1...Multi-beam laser diode (plural laser diodes) 8...Photoreceptor belt (image carrier) 9...APC (output control means) Fig. 1 Fig. 2 Fig. 1aI 3rd ・Yosj, &Ya ■Bun Pixel

Claims (1)

[Claims] In an optical writing optical system of an image forming apparatus that writes an image on an image carrier based on writing data to form an image, a plurality of laser diodes that generate a laser beam and a plurality of laser diodes each have a plurality of laser diodes. output control means for setting different outputs, the laser diodes are arranged so that projection axes of the laser beams generated from the plurality of laser diodes onto the image carrier coincide with each other, and the laser beams are arranged so that the projection axes of the laser beams generated from the plurality of laser diodes coincide with each other, and An optical writing optical system for an image forming apparatus, characterized in that the plurality of laser diodes are selectively turned on.