JPH08164634A - Image forming apparatus - Google Patents

Abstract

PURPOSE: To make it possible to form an image in spot diameter suited to a variety of image data. CONSTITUTION: In an image forming apparatus wherein after a beam of light is modulated by light from a laser light source means 12 is deflected by a deflection means 8, light is guided to a scanned surface 10 through an image forming means 9 to form an image, the laser light source means have multiple light sources 2, 3 which have different oscillation wavelengths, of the laser light sources, those having a longer oscillation wavelength are used to form a halftone image, and those having a shorter oscillation wavelength are used to form a character image.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, and more particularly, it uses a plurality of laser light sources (semiconductor lasers) having different oscillation wavelengths, and a beam spot diameter suitable for image information (Spot diameter) will be selected, and the surface to be scanned is optically scanned using the light beam from the laser light source, which is suitable for a device such as a laser beam printer (LBP). Image forming apparatus.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus such as a laser beam printer, an apparatus as shown in FIG. 3 has been used.

In the figure, when a desired image is formed, a semiconductor laser (solid-state laser element) 32, which is a laser light source, is generated by a light emission signal generator 31 based on an image signal (image information) input from the outside (CPU). The light is modulated by blinking (ON, OFF) at a predetermined timing.

Then, the light beam emitted from the semiconductor laser 32 is made into a parallel light beam by the collimator lens 33, and after being deflected and reflected by the deflection surface 34a of the optical deflector 34,
The light is guided onto the surface of the photosensitive drum 36, which is the surface to be scanned, through the imaging lens system 35 having the f-?

By rotating the optical deflector 34 in the direction of arrow A at a constant speed, the surface of the photosensitive drum 36 is optically scanned in the direction of arrow B (main scanning direction), and further the photosensitive drum 3 is rotated.
By rotating 6 in the direction of arrow C (sub-scanning direction) by a predetermined amount, two-dimensional optical scanning is sequentially performed on the surface of the photosensitive drum 36 with a light beam optically modulated by image information, and the image information is written as a latent image. I'm out.

A latent image formed on the surface of the photosensitive drum 36 is visualized by a known electrophotographic process by a developing device, a primary and transfer charging device, a fixing device, a cleaner and the like which are provided around the photosensitive drum 36, which are not shown. Imaged and transferred to a transfer material.

Generally, the spot diameter d ₀ of the light beam on the surface to be scanned is proportional to the product of the F number (FN _O ) of the imaging optical system and the oscillation wavelength λ of the laser light source. That is, the size of the spot diameter d ₀ can be expressed by the following equation.

D ₀ ∝FN _O × λ (1) Generally, the optimum spot diameter d ₀ of the light beam formed on the surface to be scanned differs depending on the type of image information. . For example, when forming image information having a high pixel density, it is preferable to optically scan the surface to be scanned with a light beam having a small spot diameter.

Further, even in the case of forming a character image and a multi-tone image, an output image in which it is preferable to optically scan the surface to be scanned with a light beam having an optimum spot diameter corresponding to each image information is obtained. It is necessary for that. Therefore, an image forming apparatus that can easily change the spot diameter of the light beam according to the type of image information is desired.

In the conventional image forming apparatus, for example, when the oscillation wavelength λ of the semiconductor laser is constant, the F number of the imaging optical system is changed to change the light beam diameter of the light beam or the collimating optical system is zoomed. The size of the spot diameter d ₀ is changed according to the above.

[0011]

In the conventional image forming apparatus, in order to obtain the optimum spot diameter on the surface to be scanned, the F number of the image forming optical system is changed or liquid crystal is used as described above. It was For this reason, the entire device becomes complicated,
In addition, there is a problem that the size tends to be large and it is difficult to perform the process quickly.

Particularly when different types of image information are mixed in the same image, for example, for the purpose of forming a character image and a multi-tone image, the spot diameter can be changed at high speed by mechanical means. Since it is difficult to change the spot diameter of the light beam and the laser light amount at the same time even when using a liquid crystal means or the like, it is very difficult to control both of them with high accuracy.

According to the present invention, a plurality of laser light sources (semiconductor lasers) having different oscillation wavelengths are used as laser light source means, and a laser light source having a long oscillation wavelength is used to form a multi-gradation image. However, by forming a character image using a laser light source with an oscillation wavelength shorter than that, an image forming apparatus capable of forming a high quality image by optically scanning the surface to be scanned with a light beam having an optimum spot diameter is formed. For the purpose of provision.

[0014]

According to the image forming apparatus of the present invention, the light beam which has been subjected to the light modulation from the laser light source means is deflected and reflected by the deflecting means, and then is reflected on the surface to be scanned through the image forming means. In an image forming apparatus that guides light to form an image,
The laser light source means has a plurality of laser light sources having different oscillation wavelengths, and a laser light source having a long oscillation wavelength is used to form a multi-gradation image, and the oscillation wavelength is shorter than that. It is characterized in that a character image is formed by using a laser light source.

In particular, the laser light source means is characterized by using a light beam oscillated from at least two laser light sources among the plurality of laser light sources according to image information in one scanning.

[0016]

Embodiment 1 FIG. 1 is a schematic view of the essential portions of Embodiment 1 of the present invention.

In the figure, 11 is a CPU, which controls the operation of the light emission signal generator 1 based on the pixel density of the image information to be formed. The light emission signal generator 1 serves as a laser light source means 12 based on an image signal from the CPU 11 and has two laser light sources (semiconductor lasers) having different oscillation wavelengths
It is determined which of the semiconductor lasers 2, 3 is to emit the light emission signal.

In this embodiment, the pixel density of image information formed as described later is, for example, 400 DPI (dot / inch) and 6
Two types of images of 00 DPI can be arbitrarily selected, and when a character image (binary image) of 600 DPI is formed based on the image signal from the CPU 11, the light emission signal generator 1 oscillates. When a semiconductor laser 2 which emits a light beam having a wavelength of 440 nm is driven to form an image, or when a multi-gradation image (multi-valued image) of 400 DPI is formed, the oscillation wavelength of 6 is generated by the emission signal generator 1.
An image is formed by driving the semiconductor laser 3 which emits a light beam of 60 nm.

The light beams emitted from the two semiconductor lasers 2 and 3 are optically modulated by the same image signal, and image information based on the respective light beams is provided at the same position on the surface of the photosensitive drum 10 as the surface to be scanned. Is imaged.

Numerals 4 and 5 are collimator lenses,
The light beams emitted from the corresponding semiconductor lasers 2 and 3 are substantially parallel light beams.

Reference numeral 7 is a reflecting mirror, which reflects the light beam emitted from the semiconductor laser 3. A half mirror 6 reflects the light beam emitted from the semiconductor laser 2 and transmits the light beam emitted from the semiconductor laser 3. The half mirror 6 may be replaced by a rotatable reflecting mirror.

Reference numeral 8 denotes an optical deflector as a deflecting means, which is composed of, for example, a rotary polygon mirror having a plurality of deflecting surfaces (reflection surfaces), and is indicated by an arrow A by a driving means (not shown) such as a motor.
Is rotating in a predetermined direction.

An image forming means (image forming optical system) 9 having an f-θ characteristic has three lenses 9a, 9b and 9c, and is based on the image information deflected and reflected by the optical deflector 8. The light beam is imaged on the surface of the photosensitive drum 10 as the surface to be scanned.

The photosensitive drum 10 is rotated at a predetermined speed in the sub-scanning direction by driving means (not shown) such as a motor, and image information is written as a latent image on the surface of the photosensitive drum 10. Around the photosensitive drum 10, a developing device, a primary and transfer charging device, a fixing device, and a cleaner, which are not shown, are provided, and the latent image formed on the surface of the photosensitive drum 10 is formed by a known electrophotographic process. It is visualized and transferred to a transfer material.

In this embodiment, with such a configuration, the pixel density setting of the image information formed by the CPU 11 is first recognized, and for example, when a multi-gradation image having a pixel density of 400 DPI is formed, the light emission signal generator 1 On the basis of the image signal from the CPU 11 blinks (ON, OFF) the semiconductor laser 3 having an oscillation wavelength of 660 nm at a predetermined timing to perform optical modulation. Further, when forming a character image with a pixel density of 600 DPI, the light emission signal generator 1 blinks (ON, OFF) the semiconductor laser 2 having an oscillation wavelength of 440 nm at a predetermined timing based on the image signal from the CPU 11 to perform optical modulation. There is.

Then, the light beams emitted from the semiconductor lasers (2, 3) selected based on the image information are made into parallel light beams by the corresponding collimator lenses (4,5),
After being deflected and reflected by the deflection surface 8a of the optical deflector 8 via the reflection mirror 7 or the half mirror 6, the light is guided to the surface of the photosensitive drum 10 through the imaging lens system 9.

By rotating the optical deflector 8 in the direction of arrow A, the surface of the photosensitive drum 10 is optically scanned in the direction of arrow B (main scanning direction), and the photosensitive drum 10 is further moved in the direction of arrow C (sub scanning direction). The photosensitive drum 10 is sequentially rotated by a light beam that is optically modulated by image information by rotating by a predetermined amount.
The surface is two-dimensionally optically scanned and image information is written as a latent image.

The latent image formed on the surface of the photosensitive drum 10 is visualized by a known electrophotographic process by means of a developing device, a primary and transfer charging device, a fixing device, a cleaner, etc., which are arranged around the photosensitive drum 10. Imaged and transferred to a transfer material.

In this embodiment, when the light emission signal generator 1 switches the semiconductor laser according to the image information from the CPU 11, the rotation speed of the optical deflector 8 and the timing of the image signal are also switched at the same time according to the image information. ing.

As described above, in this embodiment, among the plurality of laser light sources 2 and 3 having different oscillation wavelengths as described above, for example, when a multi-gradation image having a pixel density of 400 DPI is formed, the oscillation wavelength is 660 nm. When an image is formed by using the light-modulated light beam from the semiconductor laser 3, and when a character image having a pixel density of 600 DPI is formed, the light-modulated light beam from the semiconductor laser 2 having an oscillation wavelength of 440 nm is used. By performing image formation by using the image formation method, it is possible to form an image with a spot diameter suitable for the image.

In the present embodiment, a cylindrical lens is arranged between the collimator lens (4, 5) and the optical deflector 8 in order to correct the surface tilt of the optical deflector, or optical shaping such as beam shaping is performed. An optical system having a mechanical effect may be arranged in the optical path.

FIG. 2 is a schematic view of the essential portions of Embodiment 2 of the present invention. In the figure, the same elements as those shown in FIG. 1 are designated by the same reference numerals.

In this embodiment, the semiconductor laser that emits light during one scan is appropriately switched for each pixel according to the image information to change the spot diameter during the same scan.
For example, the print quality is improved by mixing and printing a plurality of spot diameters of different sizes in a character font formed as an image.

That is, in the figure, reference numeral 23 denotes an image signal distributor, which processes the image signal and sends it to one of the two light emission signal generators 21 and 22 according to the value of the image signal from the CPU 11. . Each of the light emission signal generators 21 and 22 blinks (ON, OFF) the corresponding semiconductor lasers 2 and 3 at a predetermined timing based on the processing signal sent from the image signal distributor 23 to perform optical modulation. . Then, the semiconductor laser (2,
The light beam emitted from 3) is used to guide light onto the surface of the photosensitive drum 10 through each optical element to form an image.

As described above, in the present embodiment, a semiconductor laser that oscillates a light beam having a wavelength corresponding to various image information among the plurality of semiconductor lasers 2 and 3 that oscillates light beams having different oscillation wavelengths is suitable. By switching to, for example, the spots of different sizes are mixed and printed in the character font to improve the print quality. Further, in this embodiment, since the spot diameter can be changed during one scanning, a high quality output image can be obtained at high speed without lowering the printing speed.

Further, in this embodiment, when a character image and a multi-tone image are mixed in the same image, a good output image can be obtained.

That is, in the case of printing a character image among a plurality of semiconductor lasers 2 and 3 having different oscillation wavelengths, a semiconductor laser 2 having an oscillation wavelength of 440 nm that can form a spot diameter smaller than a normal spot diameter is used. Further, when printing a multi-gradation image, image formation is performed by using a semiconductor laser 3 having an oscillation wavelength of 660 nm that can form a spot diameter larger than a normal spot diameter. As a result, even when a character image and a multi-tone image are mixed in the same image, an output image with good print quality is obtained.

As described above, in the present embodiment, even when the resolution is switched within the same image, the spot diameter can be modulated to the optimum spot diameter for each resolution. For example, if the spot diameter corresponds to the pixel size of 400 DPI, By changing the spot diameter corresponding to the pixel size of 600 DPI, it is possible to obtain an image without deterioration in which moire is locally generated and gradation continuity is not lost even when the resolution is switched.

Furthermore, for example, it is most suitable for performing the brightness modulation or the pulse width modulation suitable for reproducing the spot diameter and the halftone which are optimum for the binary output suitable for reproducing the characters and the like. High-quality images can be obtained by changing the spot diameter.

In this embodiment, the laser light source means is constructed by using two semiconductor lasers having different wavelengths. However, for example, if the laser light source means is constructed by three or more semiconductor lasers having different wavelengths. Further favorable image formation becomes possible.

Further, in each of the embodiments, the semiconductor lasers 2 and 3 are composed of separate supports using the half mirror 6 and the reflection mirror 7, and the light beams emitted from the semiconductor lasers 2 and 3 are emitted. Although the respective elements are configured so that their axes coincide with each other, the present invention can be applied in the same manner as in the above-described embodiments even if a plurality of semiconductor lasers are configured by the same support.

[0042]

According to the present invention, as described above, a plurality of laser light sources (semiconductor lasers) having different oscillation wavelengths are used, and among the plurality of laser light sources, a laser light source having a long oscillation wavelength is used for multi-gradation. By forming an image and using a laser light source with an oscillation wavelength shorter than that to form a character image, it is possible to form an image with a spot diameter suitable for the image, and to achieve high-quality printing without lowering the printing speed. It is possible to achieve an image forming apparatus that can easily obtain the output image of

[Brief description of drawings]

FIG. 1 is a schematic view of a main part of a first embodiment of the present invention.

FIG. 2 is a schematic view of the essential portions of Embodiment 2 of the present invention.

FIG. 3 is a schematic view of a main part of a conventional image forming apparatus.

[Explanation of symbols]

 1,2,22 Light emission signal generator 2,3 Semiconductor laser 4,5 Collimator lens 6 Half mirror 7 Reflection mirror 8 Deflection means 9 Imaging means 10 Scanned surface 11 CPU 12 Laser light source means 23 Image signal distributor

Claims (2)

[Claims] 1. An image forming apparatus for forming an image by deflecting and reflecting a light beam, which has been subjected to light modulation from a laser light source means, by a deflecting means and then guiding the light beam onto a surface to be scanned through an image forming means. The laser light source means has a plurality of laser light sources with different oscillation wavelengths, and a laser light source with a long oscillation wavelength is used to form a multi-gradation image An image forming apparatus characterized in that a character image is formed using a short laser light source. 2. The laser light source means uses a light beam oscillated from at least two laser light sources among the plurality of laser light sources according to image information in one scan. 1. The image forming apparatus of 1.