JPH08179230A - Scanning optical device - Google Patents

Abstract

PURPOSE: To prevent the size of a polygon mirror from becoming larger. CONSTITUTION: A light beam transmitted through an fθ lens 1 is condensed at the detection part of a synchronism detection sensor 5 by a condenser lens 2. The gap G between the outermost angle of the lens 1 and the innermost angle of the lens 2 is made small and the angle range deflected by the polygon mirror 9 is made narrow. Thus, the size of the mirror 9 is made small. Besides, the starting time of a motor is shortened and the inclination error of the mirror 9 is made smaller.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to scanning optics, and more particularly to scanning optics used in laser printers.

[0002]

2. Description of the Related Art Generally, a laser printer forms a laser light source, a polygon mirror for deflecting and scanning a light beam emitted from the laser light source, a reflected beam of the polygon mirror on a scanning line, and the beam is equal. It is configured to include an fθ lens that is corrected so as to scan at a speed, and a synchronization detection sensor that outputs a synchronization signal for determining the image writing position.

This conventional scanning optical device is disclosed in, for example, Japanese Patent Application Laid-Open No. 60-183870. As shown in FIG. 2, a laser beam LB from a laser light source (not shown) is reflected by a polygon mirror 9 rotating in the direction of arrow Y, and this reflected beam is reflected by a lens 1 onto a scanning medium 30. It forms an image. Incidentally, reference numeral 5 in the figure is a synchronization detection sensor.

Further, some laser printers are configured to include a condenser lens for condensing the reflected beam of the polygon mirror in the detection portion of the synchronization detection sensor, as disclosed in Japanese Patent Laid-Open No. 2-226219. Some are. As shown in FIG. 3, the condensing lens 2 is provided in order to make the passing beam of the fθ lens composed of the lenses 1a and 1b enter the synchronization detection sensor 5 via the two reflecting mirrors 31 and 32. It is the composition that was set. In addition,
In the figure, 6 is a laser light source, and 80 is a collimator lens.

Incidentally, some laser printers employ a scanning optical device having a structure in which an fθ lens and a condenser lens are integrally molded in order to reduce the cost. This conventional scanning optical device will be described with reference to FIG.

In the figure, the scanning optical device is an fθ lens 1
The synchronous detection sensor 5 is provided at the position on the emission side of the optical axis and for detecting the light beam in a portion other than the image information portion in the beam scanning range of the polygon mirror. A slit 4 is provided in front of this synchronization detection sensor 5,
The light flux passing through other than the effective range of the condenser lens 2 was blocked. In the figure, 7 is a circuit board and 8 is a cylinder lens.

Although the condenser lens 2 is provided on the fθ lens 1, it is difficult to match the curvatures in the design where the two lenses are in contact with each other, and a step is formed on the surface. When the irradiation light beam is applied to this step portion, it scatters, which causes a problem in image quality. Therefore, in this conventional scanning optical device, a sufficiently large gap G is provided between the outermost angle of the fθ lens 1 and the innermost angle of the condenser lens 2.

In FIG. 4, the same parts as those in FIGS. 2 and 3 are designated by the same reference numerals.

[0009]

In the conventional scanning optical device shown in FIG. 4 described above, since the gap G described above needs to be large, the angular range of deflection by the polygon mirror is wide. Therefore, the size of the polygon mirror tends to increase, or the polygon mirror cannot be multifaceted.

As the size of the polygon mirror increases,
There is a drawback that it takes a long time to start the motor for driving the mirror. Further, there is also a drawback that as the size of the polygon mirror increases, the tilt error of the mirror increases.

On the other hand, if the polygon mirror cannot be multi-faced, the number of rotations of the motor for driving the mirror cannot be reduced, and if the rotation speed is increased, the life of the motor is shortened.

The above drawbacks cannot be solved by the inventions disclosed in the above-mentioned publications.

The present invention has been made to solve the above-mentioned drawbacks of the prior art, and an object thereof is to provide a scanning optical device capable of reducing the size of a polygon mirror.

[0014]

A scanning optical device according to the present invention is a scanning optical device for scanning a light beam according to input image information, and a polygon mirror for reflecting and deflecting the light beam for scanning. Synchronization detection means for detecting a light beam in a portion other than the image information portion in the beam scanning range by the polygon mirror and transmitting a synchronization signal for timing the scanning of the light beam, and a beam in the beam scanning range are incident. A first lens that focuses on the image portion, and a second lens that is configured integrally with the first lens and focuses the light beam that has passed through the lens onto the detection unit of the synchronization detection means.
And a lens of.

[0015]

Operation: The polygon mirror reflects the light beam to perform deflection scanning. A synchronization detection sensor detects a light beam in a portion other than the image information portion in the beam scanning range of the polygon mirror, and sends a synchronization signal for timing the scanning of the light beam. The beam in the beam scanning range is focused on the image portion by the fθ lens. A condensing lens that condenses the light beam that has passed through the fθ lens on the detection unit of the synchronous detection sensor is configured integrally with the fθ lens.

[0016]

Next, the present invention will be described with reference to the drawings.

FIG. 1 is a schematic configuration diagram of an embodiment of a scanning optical device according to the present invention. The same parts as those in FIGS. 2 to 4 are designated by the same reference numerals and the description thereof will be omitted.

In the figure, the scanning optical device according to one embodiment of the present invention is similar to that of FIG. 4 in that the fθ lens and the condenser lens are integrally formed, but one of the surfaces of the fθ lens is shown. 4 is different from the configuration in FIG. 4 in that the light beam passing through the fθ lens 1 is input to the synchronization detection sensor 5 by the condenser lens 2 instead of providing a condenser lens in the portion.

More specifically, the light beam passing through the fθ lens 1 is reflected by the reflection mirror 3 and the reflected beam is made incident on the condenser lens 2. Then, the reflection mirror 3 causes the light beam of the portion other than the image information portion (image range) of the light beam that has passed through the fθ lens 1 to enter the condenser lens 2.

As described above, since the condenser lens is not provided on part of the surface of the fθ lens 1, the gap G between the outermost angle of the fθ lens 1 and the innermost angle of the condenser lens 2 should be reduced. Can be done.

In this structure, the light beam emitted from the laser light source 6 passes through the cylinder lens 8 and is deflected and scanned by the polygon mirror 9 rotating in the direction of arrow Y. The scanned light has a constant angular velocity, but is corrected by the fθ lens 1 so that scanning with the same linear velocity is performed on the scanning line, and is converged to a constant spot diameter.

The fθ lens 1 on the scanning start side and outside the image range
The light flux that has passed through is reflected by the reflection mirror 3 and f
The light enters the condenser lens 2 that is integrally formed with the θ lens 1. This incident light is condensed by the condenser lens 2 on the detection portion of the synchronization detection sensor 5. It should be noted that the light flux that has passed through a range other than the effective range of the condenser lens 2 is blocked by the slit 4 and does not enter the synchronization detection sensor 5.

With the above construction, the gap G between the outermost angle of the fθ lens 1 and the innermost angle of the condenser lens 2 can be reduced, and the deflection angle range of the polygon mirror can be made smaller than that of the conventional device. Can also be narrowed.
As a result, the size of the polygon mirror can be reduced, the motor start-up time can be shortened, and the mirror tilt error can be reduced.

Further, the polygon mirror can be multifaceted, the number of rotations of the motor for driving the mirror can be reduced, it is not necessary to increase the rotation speed, and the life of the motor is not shortened. .

[0025]

As described above, according to the present invention, the light beam after passing through the first lens is focused on the detecting portion of the synchronization detecting means by the second lens. Since the gap between the outermost angle of the lens and the innermost angle of the second lens can be reduced, the angular range of deflection by the polygon mirror can be narrowed and the size of the polygon mirror can be reduced. The effect is that you can do it. As a result, the motor startup time can be shortened and the mirror tilt error can be reduced.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a scanning optical device according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a conventional scanning optical device.

FIG. 3 is a block diagram showing another configuration of a conventional scanning optical device.

FIG. 4 is a block diagram showing still another configuration of the conventional scanning optical device.

[Explanation of symbols]

 1 fθ lens 2 condenser lens 3 reflection mirror 4 slit 5 synchronization detection sensor 6 laser light source 7 circuit board 8 cylinder lens 9 polygon mirror

Claims (3)

[Claims] 1. A scanning optical device for scanning a light beam according to input image information, comprising a polygon mirror for reflecting and deflecting the light beam for scanning, and the image information portion in a beam scanning range by the polygon mirror. A synchronization detecting means for detecting a light beam in a portion other than the above and transmitting a synchronization signal for timing the scanning of the light beam; and a first beam for which a beam in the beam scanning range is incident and focused on the image portion.
And a second lens that is integrally formed with the first lens and that condenses the light beam passing through the lens onto the detection unit of the synchronization detection means. 2. The scanning optical device according to claim 1, further comprising a reflection mirror that reflects the light passing through the first lens and makes the light incident on the second lens. 3. The reflection mirror according to claim 2, wherein a part of the light beam passing through the first lens other than the image information part is made incident on the second lens. Scanning optics.