JPH01912A - Optical device in image forming apparatus - 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 [Object of the Invention] (Industrial Application Field) The present invention relates to an optical device in an image forming apparatus that forms an image of a laser beam in a device that forms an image using a laser beam, such as a laser printer.

(Prior Art) In recent years, image forming apparatuses such as copying machines and printers have frequently used laser beams as means for forming electrostatic latent images on photoreceptors, which are image carriers. That is, in such a device, as shown in FIG. 4, a laser beam (11) oscillated by a laser oscillation unit (10) such as a semiconductor laser is irradiated onto a polygon mirror (12) rotating at high speed, According to the rotation of this polygon mirror (12), the laser beam (11) is reflected so as to scan in the longitudinal direction of the photoreceptor (13), and further the laser beam (11) is reflected to scan in the longitudinal direction of the photoreceptor (13), and the second lens (14a) and the second lens (
An electrostatic latent image is formed on the photoreceptor (13) by uniformly irradiating the laser beam (11) onto the scanning line of the photoreceptor (13) using the imaging lens system (14) consisting of the image forming lens system (14b). be.

However, in such a device, the laser oscillation section (
10) and is scattered while reaching the photoreceptor (13).

Alternatively, if the laser beam reflected from each device becomes stray light and reaches the photoreceptor (13), an unnecessary electrostatic latent image is formed on the photoreceptor (13) in addition to the electrostatic latent image based on actual information. This has the disadvantage that the image quality is significantly degraded. In particular, the adverse effects of stray light caused by reflection on the lens surface are large, for example, in the imaging lens system (14).
The optical axis (17) of the scanning plane (1) of the polygon mirror (12)
2a), the stray light (16) reflected on the surface of the first lens (14a) toward the polygon mirror (1, 2) is transferred to the imaging lens system (12) again by the polygon mirror (12).
According to actual information, the laser beam (
The photoreceptor (13) is irradiated a little later than 11) and on the same scanning line, albeit at a shifted position. Moreover, the optical path of this stray light (16) is the same as the optical path of the laser beam (11) based on actual information.
Since it is located on the scanning plane (2), it is impossible to take preventive measures such as blocking the optical path midway.

Therefore, the second lens (14a) and the second lens (14a)
An anti-reflection film is formed on the surface of the lens (14a).
.

(14b) A device for preventing reflected light on the surface has also been developed, and due to the surface treatment, the lens (14a).

(14b) has become expensive, and surface treatment is difficult, especially for plastic lenses that have been widely used in recent years.
This has the problem of requiring a long manufacturing process, resulting in an increase in cost and, as a result, an increase in the price of the device.

(Problems to be Solved by the Invention) Conventionally, an antireflection film has been formed on the lens surface to prevent stray light due to reflection on the lens surface, but this has led to an increase in the price of the lens.

SUMMARY OF THE INVENTION The present invention aims to eliminate the above-mentioned drawbacks, and is capable of preventing stray light from irradiating an image carrier due to reflection on a lens surface without performing lens surface treatment, thereby improving the optical performance of an image forming apparatus. The purpose is to provide equipment.

[Structure of the invention]

(Means for Solving the Problems) In order to solve the above problems, the present invention provides a laser beam whose optical axis is formed by a polygon mirror so that stray light due to reflection on the lens surface is not irradiated onto the scanning line of the image carrier. An imaging lens system is provided which is not aligned with the scanning plane of the image forming apparatus.

(Function) The present invention uses the above means to guide stray light generated by reflection on the lens surface to a position that is off the scanning line of the image carrier, thereby preventing the harmful effects of stray light on the image and improving the image quality. Since there is no need to perform surface treatment on the lens, it is possible to reduce the cost of the lens and, by extension, the cost of the entire device.

(Example) An example of the present invention will be described below with reference to FIGS. 1 and 2.

Figure 1 shows an optical bag W1 (
19), the laser unit (18) includes an oscillation part (18a) that oscillates a laser beam (20) and a collimator lens (18b) that focuses the laser beam (20) into elliptical parallel light. have.

Further, (21) is a polygon mirror rotated by a motor (21a) at 6000 degrees (7 minutes of rotation), and a laser beam (1) emitted from a laser unit (18) and deflected by 90 degrees by a prism (not shown). Further, (22) is an imaging lens system that constantly focuses the laser beam (20) over the entire length of the longitudinal scanning line of the photoreceptor drum (23), which is an image carrier. , a first lens (22a) and a second lens (22b).In the first lens (22a) of the imaging lens system (22), the light is reflected by the polygon mirror (21). In the optical path of the laser beam (20),
The optical axis (24) is provided so that the inclination angle φ is 1 degree with respect to the scanning plane (21a) of the laser beam (20) by the polygon mirror (21). Nao (22c
) is the center of the imaging lens system, (25a) is the first mirror, (
25b) is the second mirror, (25c) is the dustproof glass, (
27) is stray light generated by reflection at the first lens (22a).

When printing starts, the host system (not shown)
A laser beam (20) is oscillated from an oscillator (18a) in response to a printing signal from a collimator lens (18b) and a prism (not shown).
The light is irradiated onto the polygon mirror (21) through.

Next, the laser beam (20) passes through the polygon mirror (21)
As the light rotates, it is scanned in the longitudinal direction of the photosensitive drum (23) via the imaging lens system (22). - On the first lens (22a) of this imaging lens system (22), when the laser beam (20) passes through, a part of the laser beam (20) is reflected on its surface, and stray light (27 )
becomes. However, the optical axis (
24) is inclined with respect to the scanning surface (21a) of the laser beam (20), so the first lens (22a)
The stray light (27) generated on the surface is reflected through the optical axis (24) so as to be symmetrical with the laser beam (20), as shown by the broken line in Figure 2 (b), and is irradiated again onto the polygon mirror (21). Ru. Also in the polygon mirror (21), the stray light (27) generated by the first lens (22a) is reflected so that the angle of incidence and the angle of reflection are equal, as shown by the broken line in Figure 2 (b). As a result, the reflected light does not reach the photosensitive drum (23) and deviates significantly from the scanning surface (21a) of the laser beam (20).

With this configuration, stray light (27) generated on the surface of the first lens (22a) during scanning is irradiated onto a scanning line (not shown) on the photosensitive drum (23) of the laser beam (20). There was no incident, and stray light (27) caused the photoreceptor drum (23
) An unnecessary electrostatic latent image is not formed on the image and the image is not significantly degraded, and a clear and high-quality image can be obtained.

It should be noted that the present invention is not limited to the above-mentioned embodiments, and can be modified in various ways. For example, in the embodiments, only the first lens of the imaging lens system has its optical axis tilted, but the optical axis of the second lens can also be changed. By tilting the optical axis, it is possible to prevent image contamination due to stray light that is reflected light on the second lens surface, and it is possible to obtain a clearer and better quality image. Further, the inclination angle of each lens of the imaging lens system is not limited as long as the optical characteristics of the lens are acceptable, but it is preferably about 30 [minutes] to 5 [degrees].

Furthermore, in order to prevent the scanning plane of the laser beam from coinciding with the optical axis of the imaging lens system, a polygon mirror (29) of the laser beam (28) is used as shown in another embodiment of FIG.
The first lens (30) is arranged so that the scanning surface (29a) by
) may be moved perpendicularly to the scanning plane (29a). In this way, the stray light (31) of the laser beam (28) that is generated by being reflected on the surface of the first lens (30) is removed from the scanning surface (2) of the laser beam (28), as shown by the dotted line in Figure 3.
9a), and there is no risk of adversely affecting the image on the photoreceptor (32).

〔Effect of the invention〕

As explained above, according to the present invention, the optical axis of each lens is aligned with the scanning plane of the laser beam without having to perform surface treatment such as an anti-reflection film on each lens of the imaging lens system, which increases the cost. By simply installing each lens so that they are offset, you can prevent the negative effects on the image caused by reflected light on the surface of each lens.
Clear, high-quality images can be obtained, and it is also possible to reduce the curvature.

[Brief explanation of drawings]

1 and 2 show one embodiment of the present invention, FIG. 1 is a schematic sectional view thereof, FIG. 2(A) is a developed view as seen from the top, and FIG. 2(B) is a side view 3 shows another modification of the present invention. A) is a developed view seen from the top, (B) is a developed view seen from the side, and FIG. 4 is a conventional device. , (a) is a developed view seen from the top, and (b) is a developed view seen from the side. 18... Laser unit 18a... Oscillation section 20...
・Laser beam, 21...polygon mirror, 21a・
...Scanning plane, 22...Imaging lens system. 22a...first lens, 22b...second lens
lens, 23...photosensitive drum, 24...
・Optical axis, 26...scanning plane, 27...
Stray light.

Claims (1)

[Claims] 1. In an apparatus that forms an electrostatic latent image on an image carrier by irradiating a laser beam, an oscillation unit that oscillates a laser beam, and a device that scans the laser beam on the image carrier. The method includes a polygon mirror, and an imaging lens system provided between the polygon mirror and the image carrier and having an optical axis different from a scanning plane of the laser beam by the polygon mirror and condensing the laser beam. An optical device in a featured image forming apparatus. 2. The imaging lens system includes a plurality of lenses, and the optical axis of at least one of the lenses is different from the scanning plane of the laser beam by the polygon mirror, as set forth in claim 1. An optical device in an image forming apparatus. 3. The optical device in the image forming apparatus according to claim 1, wherein the optical axis of the imaging lens system intersects the scanning plane of the laser beam by the polygon mirror. 4. An optical device in an image forming apparatus according to claim 1, wherein the optical axis of the imaging lens system is parallel to the scanning plane of the laser beam by the polygon mirror.