JPH0481810A - scanning optical device - Google Patents

Abstract

PURPOSE:To prevent stray light and to obtain the device having high image quality by providing a light shielding plate off the image forming region on a scanning start side and end side. CONSTITUTION:The laser beams made incident in the form of collimated beams of light are once condensed at the co-focal position of an afocal lens 4a and are thereafter made again into the collimated beams of light which are introduced to an f-theta lens 4b. A microspot is thereby formed on a drum-shaped photosensitive body 5. The light shielding plate 8 is installed in the co-focal position of the condenser lens 4 and off the image forming region on the scanning start side and end side to shield the laser beam in such a manner that the laser beam does not fall onto side plates 6, thereby preventing the generation of the stray light. A synchronous detector 7 is installed in the position conjugate with the photosensitive body 5 and the condenser lens 4 in order to increase the detection sensitivity. The device having the high image quality is obtd. if the microspot is formed in the synchronous detector 7.

Description

[Detailed Description of the Invention] : Industrial Field of Application] The present invention is applicable to image forming devices such as racer beam printers!
The present invention relates to a scanning optical device that raster-scans a photoreceptor with modulated light.

[Prior Art] Conventionally, there is a laser beam printer as a device that forms an image by irradiating a photoreceptor made of a photoconductive substance with laser light as modulated light. The configuration of this device will be explained using FIG. 2. Laser light (modulated light) emitted from the semiconductor laser 1 passes through the collimating lens 2 to become substantially parallel light and enters the rotating polygon mirror 3. The rotating polygon mirror 3 rotates in the direction of the arrow in the figure, and functions as an optical deflector for raster scanning the laser beam. The laser beam reflected by one surface of the rotating polygon mirror 3 is deflected and scanned and guided to the condenser lens 9.

The condensing lens 9 has an f-θ characteristic that converts a beam deflected at a constant rotational speed so that it scans at a constant linear speed on the image plane, and directs the laser beam to the drum-shaped photoreceptor 5. In addition to irradiating with a minute spot, deflection scanning at a constant rotational speed is converted into linear scanning at a constant linear velocity. A two-dimensional electrostatic latent image is formed on the photoreceptor 5 by raster scanning the photoreceptor 5, which rotates around the axis of the drum, with a laser beam modulated according to an image signal. The synchronization detector 7 is located on the scanning start side to take the timing of the image signal. has been done.

The operation of the above configuration is as follows.

The laser beam is modulated in accordance with the image signal by a modulation means (not shown). On the other hand, in order to always align the starting positions of images on the photoreceptor 5, the modulation means sends out image signals at a constant timing after the light is incident on the synchronous detector 7. Since the synchronous detector 7 is installed on a scanning optical path that does not contribute to image formation, the scanning range of the laser beam includes an area that does not contribute to image formation.

Therefore, within one scanning period, there are a period in which the light contributes to image formation and a period in which the light does not contribute to image formation and shines at a constant amount of light.

[Problems to be Solved by the Invention] However, during the period when the light is illuminated with a constant amount of light, the device components such as the side plate 6 may be irradiated with the laser light, and stray light 10 may be generated. The stray light 10 irradiates the photoreceptor 5 as light other than image information, causing density unevenness or fogging, which causes deterioration of image quality.

The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a scanning optical device that has a simple configuration, prevents stray light, and has high image quality.

[Means for Solving the Problems] In order to achieve the above object, the present invention includes an optical deflector that deflects modulated light and performs rask scanning, and a photoreceptor on which an image is formed by being irradiated with the above scanning light. In the scanning optical device, a condensing lens for condensing the scanning light is provided between the optical deflector and the photoreceptor, and a light shielding plate is provided outside the image forming area on the scanning start side and the scanning end side at this condensing position. It has been established.

[Operation] According to the above configuration, the scanning light outside the image forming area on the scanning start side and the scanning end side is blocked, so that no stray light is generated, and the modulated light that does not contain image information outside the image forming area is blocked. is no longer irradiated onto the photoreceptor.

[Example] Hereinafter, an example of the scanning optical device of the present invention will be described using FIG. 1.

In FIG. 1, the same components as in FIG. 2 of the prior art described above are given the same reference numerals, and the explanation thereof will also be referred to.

The condensing lens 4 is composed of an afocal lens 4a and an fθ lens 4b, and is provided between the rotating polygon mirror 3 and the photoreceptor 5 as a pre-assembled optical device. The laser beam that has entered as parallel light is once focused at the confocal position of the afocal lens 4a, and then becomes parallel light again and is guided to the f-theta lens 4b.
Minute spots are formed on a drum-shaped photoreceptor 5. In the above configuration, since the scanning direction on the photoreceptor 5 is reversed with respect to the deflection direction by the rotating polygon mirror 3, the rotation direction of the rotating polygon mirror 3 is reversed so as to match the scanning direction in the prior art described above. There is. The synchronization detector 7 is installed outside the image forming area on the scanning start side of a light shielding plate 8, which will be described later. The light shielding plate 8 is installed at the confocal position of the condensing lens 4 outside the image forming area on the scan start side and end side, and blocks the laser light from hitting the side plate 6.

As described above, stray light is generated during the period of light that does not contribute to image formation and is illuminated with a constant amount of light, so by installing the light shielding plate 8 across the scanning range that contributes to image formation, the generation of stray light can be prevented. However, even if the light shielding plate 8 is installed at a position where the laser light is spreading, it is impossible to shield only the scanning range that does not clearly contribute to image formation due to the overlap of the light beams. On the other hand, if the light shielding plate 8 is provided at the confocal position of the condenser lens 4 as in this embodiment, the light beams will not overlap and can be clearly shielded.

At this time, in order to increase the detection sensitivity, the synchronous detector 7
is installed at a position conjugate to the photoreceptor 5 and the condensing lens 4, and the synchronization detector 7 needs to have a minute groove formed therein. To explain the reason for using minute blemishes, in order to accurately match the writing start position of the image dot by dot, it is necessary to adjust the timing with a time precision shorter than one dot. This is because the synchronization detector 7 sets a threshold value at a constant level of the slope at which the amount of light changes, and sets the timing so that the image is written out after a certain period of time from that point.

Note that the present invention is not limited to the configuration of the above-described embodiment, and various modifications are possible. For example, the light source may be a gas laser or a lamp instead of the semiconductor laser 1, and the rotating polygon mirror 3 may be a galvano mirror. Furthermore, the condenser lens 4
It is not always necessary to use an afocal lens, and a lens that provides the same effect may be used.

[Effects of the Invention] As described above, according to the present invention, the scanning light is once focused between the photoreceptor and the optical deflector, and at that position, a light shielding plate is provided outside the image forming area on the scanning start side and the scanning end side. With the simple configuration of providing, it is possible to prevent the generation of stray light and obtain a scanning optical device with high image quality.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a scanning optical device according to an embodiment of the present invention, and FIG. 2 is a block diagram of a conventional scanning optical device. 1... Semiconductor laser, 3... Rotating polygon mirror, 4...
Condensing lens, 5... Photoreceptor, 7... Synchronization detector, 8
...shading plate.

Claims (1)

[Claims] (1) An optical deflector that deflects the modulated light and performs raster scanning;
In the scanning optical device including a photoconductor on which an image is formed by irradiation with the scanning light as described above, a condensing lens for condensing the scanning light is provided between the optical deflector and the photoconductor, and the condensing lens is provided between the optical deflector and the photoconductor. A scanning optical device characterized in that a light shielding plate is provided outside the image forming area on the scan start side and the scan end side.