JPH0519187A - Light beam scanning device - Google Patents

Abstract

PURPOSE:To remove noise light such as multiply reflected lights, arising near a light receiving surface, and to improve the writing position accuracy of a light beam scanning optical system by providing a light diffusing member in front of the light receiving surface of a photodetector. CONSTITUTION:When a light beam for synchronization detection is transmitted through a lens part, it goes toward the light receiving surface 13 by receiving a light condensing action. At this time, the light beam goes toward the light diffusion plate 15 on the behind in the shape of partially cut off by a slit plate 16 in accordance with a scanning time, and then, the light becomes a beam containing a diffusion component while being transmitted through the light diffusing plate 15, and then, it reaches the light receiving surface 13. The energy of the light incident on the light receiving surface 13 is photoelectrically converted so as to be taken out as an electrical signal from the photodetector 10, and in the case of using optimumly selected materials whose transmittivity and diffusion ability are good as the materials for the light diffusing plate 15, the occurrence of the sharp internal reflection light having high intensity near the light receiving surface 13 can be prevented, thus, the intrusion the reflection light to a signal light beam can be reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light beam scanning device using a light receiving element for synchronization detection in a writing scanning optical system such as a laser beam printer.

[0002]

2. Description of the Related Art Conventionally, in a writing / scanning optical system such as a laser beam printer, a part of a scanning beam is used in order to accurately secure a writing position on a photosensitive drum. That is, the reference writing timing can be obtained by detecting the scanning beam immediately before the reference writing start position by the light receiving element installed at a predetermined position.

In other words, the scanning beam that is synchronously detected in the writing optical unit configuration takes into consideration the positional relationship of the light receiving elements and the converging property of the light beam, and then passes through a bending mirror, a lens, etc. At the light receiving surface of the light receiving element. Conventionally, there are cases where an optical fiber is interposed while reaching the light receiving surface, but in many cases it is directly detected by a light receiving element such as a photodiode for the purpose of reducing the number of components.
Based on the signal, the writing start timing in the scanning direction can be obtained.

For example, in a conventional writing optical unit,
As shown in FIG. 9, when the light beam scanned by the polygon mirror 1 is written on the photoconductor 2, the light beam immediately before the start of writing is reflected by the mirror 3 and is received by the light receiving element 5 via the condenser lens 4. To do. FIG. 10 is an enlarged view of the light receiving element portion,
A light receiving surface 6 is provided inside the light receiving element 5, and receives the incident light beam L while being scanned in the arrow direction.

[0005]

However, in the above-mentioned conventional example, since the light-receiving surface 6 made of a silicon semiconductor is generally surrounded by a synthetic resin material or the like, the light-receiving surface 6 and the synthetic resin are not provided. There is a problem that the surface of the material has a reflecting action although it is small.

That is, as shown in FIG. 11, when the light beam L that is synchronously detected is incident on the light receiving surface 6, the light beam L has a sharp converging shape, so that The light that is internally reflected from the surrounding synthetic resin material and wraps around, or the light that is reflected when entering the light-receiving surface 6 and is reflected again on the surface of the synthetic resin material, etc. together with the original light beam L as the period detection light. It will be received.

For this reason, as shown in the time change diagram of the child output of the light receiving element 5 in FIG. 12, a serrated noise component N is included in the originally smoothly changing signal,
This causes a time error in the output level that is electrically recognized as a synchronization detection signal, and reduces the position accuracy at the time of writing in the writing scanning optical system.

The object of the present invention is to solve the above-mentioned problems,
By providing a light diffusing member in front of the light-receiving surface, it is possible to prevent internal reflection by the synthetic resin material around the light-receiving surface or re-reflection by the synthetic resin material around the light-receiving surface, and to provide a light beam scanning device that improves writing position accuracy. To do.

[0009]

A light beam scanning device according to the present invention for achieving the above object is provided on a light receiving surface of a light receiving element used for synchronous detection in a light beam scanning optical system such as a laser beam printer. A light diffusing member is arranged to remove noise light due to multiple reflection of a light beam.

[0010]

In the light beam scanning device having the above-described structure, the light diffusion portion is provided near the light receiving surface of the light beam used for the synchronization detection to perform the synchronization detection.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail with reference to the embodiments shown in FIGS. 1 and 2 show a first embodiment of the present invention, in which a recess 12 is provided in the front surface of a base 11 of a light receiving element 10, a light receiving surface 13 is arranged in the recess 12, and a recess 12 is provided in the recess 12. Light-transmissive synthetic resin 14 is filled.
A light diffuser plate 15 is arranged in front of the light receiving surface 13, and a slit plate 16 is further provided in front of it.

In this structure, as shown in FIG. 3, the light beam L for detecting the synchronization is focused on the light receiving surface 13 by the condensing action when passing through the lens portion. At this time, the light beam L is partially cut off by the slit plate 16 according to the scanning time toward the rear light diffusing plate 15 and is further transmitted through the light diffusing plate 15 to be a beam L'containing a diffusing component.
And reaches the light receiving surface 13.

Here, the light energy incident on the light receiving surface 13 is photoelectrically converted and taken out as an electric signal from the light receiving element 10. Although various materials are used for the light diffusing plate 15, the light transmittance is lowered so much. It is important to select and use the diffusivity appropriately so that it does not become too much. For example,
When using simple ground glass, the surface roughness is # 12.
It is preferable that the number is about 00 in terms of transmitted light amount and diffusivity. It is preferable that the thickness of the diffuser plate 15 is also thin within a range allowable in terms of strength. With this configuration,
It is possible to suppress the generation of sharp internally reflected light having a high intensity in the vicinity of the light receiving surface 13, and as a result, the reflected light is less likely to be mixed with the signal light.

FIG. 4 is a sectional view of the light receiving element of the second embodiment. The light diffusion plate 15 in the previous embodiment is omitted, and the surface of the light transmissive synthetic resin 14 is treated by chemical etching or the like to form the rough surface portion 17.

The light beam detected synchronously is the slit plate 16
When it passes through the rough surface portion 17, it is subjected to the light diffusion effect and reaches the light receiving surface 13. In this embodiment, by diffusing the light beam L and guiding it to the light receiving surface 13, it is possible to prevent a decrease in S / N due to the influence of multiple reflected light, etc.
Can be made compact.

FIG. 5 is a sectional view of the light receiving element of the third embodiment. On the front surface of the light transmissive synthetic resin 14, a slit portion 18a having a light diffusing property is provided in the central portion as shown in FIG. A light diffusion sheet 18 having a light shielding portion 18b around the periphery is attached.

The light beam L that is synchronously detected passes through the slit portion 18a of the light diffusion sheet 18 and reaches the light receiving surface 13 while being diffused. The light diffusion sheet 18 used here may be a synthetic resin such as thin vinyl, and the slit portion 18a and the light shielding portion 18b may be adjusted by using a dye or the like. The light diffusion sheet 18 is made by printing a dye on a synthetic resin material,
By processing it into a sheet shape later, it is possible to mass-produce small-sized ones having no variation in specifications, which is also advantageous in terms of cost.

In this embodiment, since it is in the form of a sheet, it can be easily attached to the light receiving element 10 and does not require space, and the light diffusion effect can be easily obtained regardless of the type of the light receiving element 10. Therefore, mass production and cost reduction can be achieved.

7 and 8 show a fourth embodiment, FIG. 7 is a perspective view of a light receiving element, and FIG. 8 is a horizontal sectional view. On the surface of the light-receiving surface 13 of the light-receiving element 10, a light-transmitting synthetic resin 19 in a cloudy state is integrally molded by previously mixing a dye such as a white dye.

The light transmissive synthetic resin 19 enables the light diffusing action of the incident light, and the light beam L is subjected to a certain light diffusing action before reaching the light receiving surface 13 and is synchronously detected. In the fourth embodiment, the light-transmissive synthetic resin 19 is caused to perform a light diffusion action, so that external parts are unnecessary and compact.

By providing such a light diffusing layer, the intensity of the sharp noise light is averaged by the diffusing action, but on the other hand, the wraparound diffused light from the outside with respect to the light receiving surface 13 is also increased. The light diffusion layer in the peripheral space of the light receiving surface 13 in the main scanning direction of the light beam L should not be unnecessarily wide.

For example, in FIGS. 7 and 8, it is preferable that the light beam L is cut off in the vicinity of the light receiving surface 13 by using a lens or a slit in order to prevent the light diffusion layer from being widened. Therefore, the thickness of the light-transmitting synthetic resin 19 having a light diffusing property is also preferably made as thin as possible. However, if a general-purpose light receiving element is used as a base for cost reasons, a light diffusion effect close to the desired one can be obtained even if only the light diffusion layer is added. Good to choose.

[0023]

As described above, in the light beam scanning device according to the present invention, the light diffusing member is provided in front of the light receiving surface of the light receiving element, so that noise light such as multiple reflection light generated near the light receiving surface is generated. Can be eliminated, and the writing position accuracy of the light beam scanning optical system is improved.

[Brief description of drawings]

FIG. 1 is a sectional view of a first embodiment.

FIG. 2 is a perspective view.

FIG. 3 is an operation explanatory view.

FIG. 4 is a sectional view of a second embodiment.

FIG. 5 is a sectional view of a third embodiment.

FIG. 6 is a perspective view of a light diffusion sheet.

FIG. 7 is a perspective view of a fourth embodiment.

FIG. 8 is a sectional view.

FIG. 9 is a perspective view of a conventional writing optical unit.

FIG. 10 is a perspective view of a light receiving element portion.

FIG. 11 is a sectional view of a light receiving element portion.

FIG. 12 is a diagram showing a temporal change in the output of the light receiving element.

[Explanation of symbols]

10 Light receiving element 11 Base 12 recess 13 Light receiving surface 14, 19 Light-transmissive synthetic resin 15 Light diffusion plate 16 slits 17 rough surface 18 Light diffusion sheet

Claims (5)

[Claims] 1. In a light beam scanning optical system such as a laser beam printer, a light diffusing member is arranged on the light receiving surface of a light receiving element used for synchronous detection, and noise light due to multiple reflection of the light beam is removed. Light beam scanning device. 2. The light beam scanning device according to claim 1, wherein a slit is provided near the light diffusing member. 3. The light beam scanning device according to claim 1, wherein the light diffusing member has a rough surface portion formed on a surface of a light transmitting synthetic resin. 4. The light beam scanning device according to claim 1, wherein the light diffusing member is a sheet for diffusing light. 5. The light beam scanning device according to claim 1, wherein the light diffusing member has a light diffusing function by clouding a light transmitting synthetic resin.