JPS63104013A - Laser beam scanning device - Google Patents

Abstract

PURPOSE:To form a light quantity distribution on the scanning surface of a photosensitive drum, etc., to a real circle by a simple constitution, by providing a concave cylindrical surface mirror for moving along the optical axis direction, and adjusting the light quantity distribution in the sub-scanning direction by the concave cylindrical surface mirror, while keeping the light quantity distribution in the main scanning line direction at constant as it is. CONSTITUTION:A concave cylindrical surface mirror 6 for moving along the optical axis direction is provided between a polygon mirror 2 and the scanning surface of a photosensitive drum 7, etc., so that a light quantity distribution in the sub-scanning direction can be adjusted by the concave cylindrical surface mirror 6 while keeping the light quantity distribution in the main scanning line direction at constant as it is. Accordingly, it can be suppressed that in a still state, the light quantity distribution of a true circle becomes a light quantity distribution of an ellipse in which the diameter in the main scanning direction is large, since an image forming position on the scanning surface of the photosensitive drum 7, etc., moves in the main scanning direction. In this way, the light quantity distribution on the scanning surface of the photosensitive drum, etc., can be formed to the real circle by a simple constitution.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a laser beam scanning device that has a simple configuration and can make the light intensity distribution on a scanning surface of a photoreceptor drum or the like perfectly circular.

[Conventional technology]

As a conventional laser beam scanning device, for example, JP-A-58-
There is one shown in Publication No. 179054. FIG. 6 shows this laser beam scanning device, which includes a focusing lens 20 that focuses the laser beam from the laser light source 10, and a polygon mirror 3 that deflects the focused laser beam onto a predetermined main scanning line.
0, a photosensitive drum 40 exposed to laser light deflected by a polygon mirror 30, and a focusing lens 20.
and the polygon mirror 30, and the motor 73.7
Slit plates 72, 7 whose inclination angles are changed by rotation of 6.
5 (having an open lower 1° 74), and a slit plate 72.
It consists of a control section 70 that controls the effective diameter of the open lower 1° 74 of the 75.

In the above configuration, when a laser beam is emitted from the laser light source 10, the laser beam focused by the focusing lens 20 passes through the open lower 1° 74 of the slit plate 72, 75, and is reflected by the rotating polygon mirror 30. The light is reflected by the reflective surface and is scanned along the main scanning line of the photoreceptor drum 40. At this time, the control 1 wholesaler 70 controls the rotation angles θX and θ of the motors 73 and 76.
By controlling y and adjusting the effective diameter of the open lower portion 1.74, the beam shape in the sub-scanning direction can be made into a shape according to the resolution.

[Problem that the invention seeks to solve]

However, according to the conventional laser beam scanning device, since the slit plates 72, 75 are individually controlled by the rotation of the motors 73, 76, there are disadvantages in that the configuration is complicated and control is difficult.

[Means for solving problems]

The present invention has been made in view of the above, and in order to make the light intensity distribution (beam shape) on the scanning surface of the photoreceptor drum, etc., a perfect circle with a simple configuration, the present invention uses a polygon mirror and the scanning surface of the photoreceptor drum, etc. A laser beam scanning device in which a concave cylindrical mirror that moves along the optical axis is provided in between, and the concave cylindrical mirror adjusts the light intensity distribution in the sub-scanning direction while keeping the light intensity distribution in the main scanning direction constant. It provides:

This prevents a perfectly circular light intensity distribution in a stationary state from becoming an oval light intensity distribution with a large diameter in the main scanning direction due to the image formation position on the scanning surface of the photoreceptor drum moving in the main scanning direction. can do.

Hereinafter, the laser beam scanning device of the present invention will be explained in detail.

〔Example〕

FIG. 1 shows a first embodiment of the present invention, which includes a cylinder lens 1 that focuses laser light (wavelength 790 nm) modulated according to an image signal emitted from a semiconductor laser light source 10 in the sub-scanning direction; A polygon mirror 2 having a deflection surface near its focal point and an imaging lens 3 for forming an image of the laser beam deflected by the polygon mirror 2 return the optical path and move integrally in the optical axis direction. It consists of a plane mirror 4 and a concave cylindrical mirror 6, which adjust the spot diameter in the sub-scanning direction on the imaging surface 5 on the photoreceptor drum 7.

2(a) and 2(b) show the optical path diagram of FIG. 1, showing a plane mirror 4 and a concave cylindrical mirror 6 that move according to the resolution. The interval between the plane mirror 4 and the concave cylindrical mirror 6 is kept constant, and the scanning interval is 25 μm at high resolution.
, 50 μm at low resolution. The beam diameter at the imaging surface 5 of the photoreceptor drum 7 is 1/1 when the light intensity is at its maximum value.
e 2, and when the polygon mirror 2 is stationary, the beam diameter is 40 μm in the main scanning direction and 11 μm in the sub-scanning direction at high resolution (Fig. 2 (a)).
It has become 00Ii. Adjustment of the light amount distribution in the sub-scanning direction is performed based on the position of the concave cylindrical mirror 6. In FIGS. 2(a) and 2(b), the moving distance of the plane mirror 4 and the concave cylindrical mirror 6 is about 7 mm.

In the above configuration, the operation will be explained as follows. When a laser beam modulated according to an image signal is emitted from the laser light source 10, it is deflected by the polygon mirror 2 rotating at a predetermined speed, reflected by the concave cylindrical mirror 6 and the plane mirror 4, and is emitted from the photoreceptor drum 7. The imaging plane 5 is scanned.

At this time, since the imaging position moves in the main scanning direction according to the scanning speed of the polygon mirror 2, the beam shape of the imaging surface 5 becomes longer in the main scanning direction compared to when it is stationary.
50μm in both main scanning and sub-scanning directions at high resolution
Therefore, at low resolution, the main scanning direction is 90 μm and the sub-scanning direction is 100 μm (FIG. 3(a)).

In this way, exposure with a perfect circular or nearly perfect circular light amount distribution is performed. Thereafter, the image is recorded by developing, transferring, and fixing operations.

In general, when a laser beam is used to scan a photoreceptor over a photoreceptor, the light intensity distribution on the photoreceptor can be considered to be a Gaussian distribution or sufficiently close to it. At this time, if the beam diameter on the photoreceptor is set to an outer diameter such that the light intensity is 1/e2 of the maximum value, the optimal beam diameter in the sub-scanning direction is determined in proportion to the scanning line interval (proportional (The constant is determined by the development method, etc.) Furthermore, although the beam diameter in the scanning direction varies depending on the modulation method, there is usually no problem if it is 0.8 times or less the diameter in the sub-scanning direction. In the above embodiment, two levels of resolution have been described, but the invention is not limited to this.

As mentioned above, the concave cylindrical mirror 6 was moved about 7 mm along the optical axis between high resolution and low resolution, but this caused a depth shift and changed the beam diameter. Become.

FIGS. 5(a) and 5(b) show a second embodiment of the present invention,
The plane mirror 4 is replaced with a folding prism 8, and the concave cylindrical mirror 6
The only difference is that the configuration is arranged at the position of the reflection optical path of the folding prism 8, but the rest is the same as the first embodiment. At the time of resolution.

In the above embodiments, the laser light source was directly modulated according to the image signal, but it is also possible to apply an indirect modulation method using an acousto-optic modulation element or the like.

〔Effect of the invention〕

As explained above, according to the laser beam scanning device of the present invention, a concave cylindrical mirror that moves along the optical axis direction is provided between the polygon mirror and the scanning surface of the photoreceptor drum, etc., and the amount of light in the main scanning line direction is Since the light intensity distribution in the sub-scanning direction is adjusted using a concave cylindrical mirror while keeping the distribution constant, the light intensity distribution (beam shape) on the scanning surface of the photoreceptor drum etc. can be made perfectly circular with a simple configuration. Out.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the first embodiment of the present invention, and FIG. 2 (
a) and (b) are explanatory diagrams of the first embodiment at high resolution and low resolution, and Fig. 3 (a) and (b) are illustrations of the rotating polygon mirror at rest and deflection at high resolution. Explanatory diagram showing the beam shape of
Figures (a) and (b) correspond to Figures 3 (a) and (b) and are explanatory diagrams showing beam shapes at low resolution, Figures 5 (a) and (b)
FIG. 6 is an explanatory diagram of a second embodiment of the present invention at high resolution and low resolution, and FIG. 6 is an explanatory diagram showing a conventional laser beam scanning device. Explanation of symbols■・−・−・Cylinder lens 2-1・・−・−Polygon mirror 3・・−−−One imaging lens 4・−・One plane mirror 5
−・−・−Imaging surface (main scanning line) 6−・−・Concave cylindrical mirror 7・・・・−・Photosensitive drum 10・・・−・−・Laser light source patent applicant Fuji Xerox Co., Ltd. agent patent attorney Taira 1) Tadashi separation 1vA l'' / Rintarunsu 1 2 times l Yunchinmensoe 3 Itoiro 4 East 1feruns 4 Miku for bamboo fLt 5 I1-; Surface 6 Cylinder Mifu Fig. 2 (a) 8N medical arithmetic 3rd FI (a) (b) Fig. 4 rσ (b) Stationary 8-call bowcon technique - rotating field) Fig. 5

Claims (1)

[Scope of Claims] A laser beam scanning device that deflects a laser beam with a polygon mirror to scan a flying spot along a main scanning line on a scanning surface, wherein the laser beam is located between the polygon mirror and the scanning surface, and has an optical axis. 1. A laser beam scanning device comprising a light amount distribution adjusting means having a concave cylindrical mirror that adjusts the light amount distribution of the laser beam in the sub-scanning direction based on the movement in the direction.