JPH01210919A - Light beam scanner - Google Patents

Abstract

PURPOSE:To form a beam spot whose diameter is not changed on a face to be scanned by providing a circular slit before a deflector and rotating a long slit having a prescribed shape as one body together with the reflection face of the deflector. CONSTITUTION:A circular slit 38S is arranged on an optical path before a deflector 230, and long slits 39S-1 and 37S-2 which shape the beam in the subscanning direction of an arrow (y) are totaled as one body together with a rotary mirror 240. In this constitution, the beam emitted from the rotary mirror is shaped to a circle by the circular slit 38S and is emitted without the change of the diameter. This beam 40 is shaped in the subscanning direction of the arrow (y) by a slit member 39. Consequently, since a beam 41 going toward an ftheta lens 25 always keeps equal beam diameters in the scanning direction of an arrow (x) and the subscanning direction of the arrow (y), the beam spot whose diameter is not changed is formed on the face to the scanned and the image quality is improved.

Description

Detailed Description of the Invention (Technical Field) The present invention relates to a light beam scanning device, and more particularly to a light beam scanning device that can be applied to optical writing systems in laser printers, digital copying machines, facsimile machines, etc. .

(Prior Art) Conventionally, in order to form a beam onto a scanned surface (for example, a photoreceptor) with a required spot diameter necessary for image formation, a beam shaping slit has been provided on the optical path before the imaging lens. An optical beam scanning device is known in which the beam after passing through the slit is incident on a reflecting surface of a deflector at an angle relative to its normal direction, and the reflected light is made incident on the imaging lens as an incident beam. It is being

For example, in FIGS. 10, 11, and 12, a beam diverged from a semiconductor laser 32 serving as a light source is collimated by a collimator lens 33, shaped by a slit 34, and emitted from the semiconductor laser unit 21.

Then, this beam is transmitted to the deflector 2 by the first mirror 22.
The light is incident approximately along the axis of rotation of a rotary mirror 24, which has one reflective surface that is obtained by cutting a cylinder forming the third reflective surface diagonally.

When rotating mirror 24 rotates under such conditions.

Along with this, the beam is deflected and advances to the fθ lens 25, is made to have a constant velocity ratio, has its optical axis bent by the reflection part 37 of the second mirror 26, passes through the toroidal lens 27, and is directed onto the outer peripheral surface of the photoreceptor drum 1. imaged.

Note that an optical fiber 35 placed between the fθ lens 25 and the second mirror 26 is guided to a photosensor 36, and is used to extract synchronized light that determines the writing start position.

In such an optical system, the slit 34 for beam shaping before the deflector 23 is fixed to a fixed member integrally with the laser unit 21, and this configuration has caused the following problems.

As shown in FIG. 13, the elliptical incident beam LN shaped by the slit 34 (see FIG. 10) is reflected by the first mirror 22 and enters the one-rotation mirror 24.

Here, as shown in FIG. 13, at a certain rotational position of the one-rotation mirror 24, the diameter a of the incident beam LN is the diameter a of the one reflected beam LO after reflection, which has its long axis in the X-axis direction, which is the main scanning direction. It becomes an elliptical beam. However, since the incident angle is inclined with respect to the normal direction, when the rotating mirror 24 rotates 90 degrees, the diameter of the reflected beam LO increases in the y-axis direction, which is the sub-scanning direction orthogonal to the main scanning direction, as shown in FIG. diameter a with axis
becomes an elliptical beam.

Of course, in the elliptical beam, the diameter in the minor axis direction perpendicular to the major axis direction also changes in the coordinate axis direction, and as a result, the deflected beam rotates on the photoreceptor 1 while the rotating mirror 24 rotates 906 times, When the image is rotated by 90 degrees, the positions of the major axis and minor axis are reversed between the main scanning direction and the sub-scanning direction.

In the imaging optical system such as the fθ lens 25 and the toroidal lens 27, the imaging diameter is usually determined by the diameter of the beam incident on the lens, and the diameter of the incident beam incident on the lens is determined by the diameter of the incident beam in the main scanning direction. Since it differs in the sub-scanning direction, when the diameter of the deflected beam changes as described above, the final spot diameter on the photoreceptor surface varies, resulting in poor image quality.

In other words, in a beam scanning device that makes an elliptical beam incident at a finite angle with respect to the normal direction of the reflecting surface of a deflector and deflects the beam, an optical arrangement in which the angle of incidence and the angle of reflection make about 45 degrees is particularly useful. When scanning, the deflected elliptical beam is rotated and scanned by the rotation of the deflector, and the spot diameter of the focused beam on the surface to be scanned by the imaging lens changes in the main scanning direction and the sub-scanning direction. However, there was a problem in that the image quality was adversely affected.

(Objective) Therefore, one object of the present invention is to maintain the relationship between the angle of incidence and the angle of reflection with respect to the reflecting surface of the deflector without changing from the conventional one.

Moreover, it is an object of the present invention to provide a light beam scanning device in which the spot diameter of a deflected elliptical beam on a surface to be scanned does not change in the main scanning direction and the sub-scanning direction.

(Structure) In order to achieve the above object, the present invention is configured such that the beam incident on the reflective surface of the deflector is irradiated to an arbitrary incident position on the reflective surface that is off the rotation axis of the deflector. A circular slit is placed before the deflector to shape the beam diameter in the main scanning direction, which is the scanning direction of the beam incident on the imaging lens, and a circular slit is placed before the deflector to shape the beam diameter in the sub-scanning direction, which is perpendicular to the main scanning direction. A long slit with an opening greater than the full scanning angle is placed between the deflector and the imaging lens along the main scanning direction, and the shape of this long slit is adjusted to the direction of incidence on the imaging lens. The scanning trajectory of the beam is curved, and the elongated slit is configured to be rotated integrally with the reflecting surface of the deflector.

Hereinafter, a detailed explanation will be given based on one embodiment of the present invention.

In the example below, the reflective surface of the deflector is shown at 240-- in FIG.
It is composed of two mirror surfaces as shown by 1.240-2. And each of these mirror surfaces 240-1.
In order to make the deflection mode of each beam equal by 240-2, each mirror surface 240-1.240-2 has a rotation axis 0-0.
When assuming an arbitrary virtual plane 242 that passes through the plane, the planes are formed evenly distributed at the same inclination angle with this plane as a boundary. Here, a unit including a drive motor for the one-rotation mirror 240 is referred to as a deflector, and is designated by the reference numeral 230.

Such a rotating mirror 240 has a larger number of reflective surfaces than the one described above with a single reflective surface, so high-speed scanning is possible.
Since the rotation axis 0-0 is located on -3, this rotation axis 0-
It becomes meaningless to make the beam incident on the 0-0 axis, and the beam has to be made incident on a position away from the 1-rotation axis 0-0.

In the case of such incident conditions, the irradiation locus of the beam on each reflective surface is as shown in FIG. It becomes a parabola as shown by the imaginary line in Figure 6.

Therefore, since the deflected beam is reflected light starting from such an irradiation locus, the main scanning direction is not a straight line but an arcuate curve.

In this way, a rotating mirror with two reflective surfaces inevitably has a configuration in which the beam is incident at a position off the rotation axis O-0, but even with a rotating mirror with one reflective surface, the rotation When there are circumstances in which it is difficult to make the beam incident on the axis 0-0, the above-mentioned situation also occurs.

Therefore, to explain an embodiment, as shown in FIG. 1, a slit member 38 having a circular slit 38S having the same diameter in the main scanning direction Specifically, it is placed on the optical axis before the rotating mirror 240. In this example, a slit member 38 is arranged within the laser unit 21 in place of the conventional slit 34.

Further, as shown in FIGS. 2, 7, and 8, a cylindrical slit member 39 in which two long slits 395-1. Rotating mirror 240 of deflector 230 along scanning direction
It is fitted onto the shaft and fixed so that it rotates integrally with the shaft.

The vertical width dimension of these elongated slits 39S-1, 395-2 is formed to match the required beam diameter in the sub-scanning direction y, and the longitudinal dimension is larger than the total scanning angle that satisfies the required scanning length of the beam. It is formed with an opening degree of .

In addition, the longitudinal direction of the long slits 39S-1 and 395-2 (
The shape in the main scanning direction is an arcuate shape similar to the scanning locus of the beam. In other words, as shown in FIG. 7, the height changes from the longitudinal center to both sides.

This means that the irradiation trajectory 240-IT on one reflecting surface 240-1 is the axis of rotation 0, as described above with reference to FIGS. 5 and 6.
Since the height h in the direction of the rotation axis 0-0 changes as it goes from -0 to both sides, the deflected beam naturally draws an arc in the scanning direction accordingly, so this was done.

The specific shape of the long slit 395-1.395-2 is precisely determined by the inclination angle of the reflecting surface 240-1.240-2 and the position of the beam incident thereon.

With the above configuration, even if the rotating mirror 240 rotates, the diameter of the beam emitted from the rotating mirror in the main scanning direction is the same because the beam incident on the mirror is shaped into a circle by the circular slit 385. Slit member 39 remains unchanged
Head to.

As shown in FIG. 8, the incident beam 40 heading toward the slit member 39 is always shaped in the sub-scanning direction y by the elongated slits 395-1 (395-2) in the effective scanning area, and is directed toward the fθ lens 25. As shown in Figure 3, the incident beam shape 41-1 is always the same in the main scanning direction
Maintain the beam diameter in the scanning direction y. Note that the locus of the beam that has passed through the elongated slit 39S-1 (395-2) naturally draws an arc, but such a change in the scanning height of the beam is corrected by the toroidal lens 27.

In the above example, two long slits are formed to match the two reflecting surfaces of the rotating mirror 240. Therefore, if the number of nine reflecting surfaces increases further, the elongated slits are formed to face each reflecting surface according to the number n. form n pieces.

As described above, a desired fixed spot is imaged on the photoreceptor drum 1, and image quality can be improved.

Next, a laser printer suitable for an embodiment of the present invention will be explained with reference to FIG.

In FIG. 9, a charger 2, a developing unit 3, a transfer charger 4, and a cleaning unit 5 are arranged on the circumferential surface of the photoreceptor drum 1 in the order of the rotation direction indicated by an arrow. A writing optical unit 7 is provided so that a writing beam enters and exposes the photosensitive drum 1 at a position 6 between the writing optical unit 7 and the photosensitive drum 1 .

In the apparatus of this embodiment, the charger 2 and the optical writing position 6 are arranged below the photoreceptor drum 1, and the optical writing unit 7 is arranged below the photoreceptor drum 1, the developing unit 3, and the cleaning unit 5. ing.

Further, the transfer charger 4 is arranged above the photosensitive drum 1. A paper feed cassette 8 for feeding transfer paper to the transfer section between the transfer charger 4 and the photosensitive drum 1 is provided further below the optical writing unit 7, and the transfer paper is fed by a feed roller 9 and a friction member that presses against the feed roller 9. The double feed is separated by the pad IO, and the sheets are sent out one by one, making a large U-turn on the side of the developing unit 3, and then being transferred to the photosensitive drum 1 by a pair of registration rollers 11 and 12 provided above the developing unit 3.
The paper is fed to the transfer section at the same timing as the image formed above. A fixing unit 13 is provided on the transfer paper path after transfer, and a paper discharge tray 14 is provided on the discharge side thereof.

The writing optical unit 7 is constructed by replacing the deflector 23 in FIGS. 10, 11, and 12 with the one shown in FIGS. 2, 7, 8, etc., and the laser unit The light that flashes in response to the image information signal emitted from the scanner 21 is reflected by the first mirror 22, and is incident on a rotating mirror 240 that is integrally attached to the shaft of a deflector 230 driven by a scanner motor, and is reflected within a certain angular range. Deflect repeatedly.

The deflected light is corrected by the fO lens 25 so that it forms an image on a straight line at the incident position 6 on the photoreceptor drum 1, and the projection point moves at a constant speed. The light enters the photoreceptor drum 1 through the toroidal lens 27, main scanning is performed by deflection of the incident light, sub-scanning is performed by rotation of the photoreceptor drum 1, and an image corresponding to one image information signal is written. Quiet?
! ! A latent image is formed. The components of the writing optical unit 7 are mounted directly on the base cover 280 of the device.

The electrostatic latent image formed on the photosensitive drum 1 is developed by the developing unit 3 to form a toner image, which is transferred by the action of the transfer charger 4 onto a transfer paper fed by a pair of registration rollers 11 and 12. Ru.

After the transfer, the transfer paper separated from the photosensitive drum 1 is fixed by the fixing unit 13 and discharged onto the paper discharge tray 14.

On the other hand, the toner remaining on the photosensitive drum 1 after the transfer is cleaned by the cleaning unit 5 and prepared for the first image formation.

Conventionally, single-rotation polygon mirrors and holo scanners are known as means for deflecting light beams. In these rotating polygon mirrors and holo scanners, a light beam is deflected multiple times by a plurality of mirror surfaces or a plurality of hologram gratings during one rotation of the polygon mirror or hologram. in this way,
In rotating polygon mirrors and holoscanners, a problem known as the so-called surface tilt problem occurs because multiple mirror surfaces and hologram gratings are involved in the deflection of the light beam.In order to correct this surface tilt, optical There was a problem that the system became complicated.

In view of this problem, the mirror surface of a reflective medium that can be rotated once is tilted with respect to the rotation axis, and the light beam to be deflected is incident along the rotation axis and reflected by the mirror surface. , deflection means for deflecting a reflected beam by 360 degrees are being proposed. The reflecting medium in such a deflecting means is called a pyramidal mirror.

In the deflection method using pyramidal mirrors, only a very small number of mirror surfaces are involved in deflecting the light beam.
The rotating mirror 240 in this example, in which the above-mentioned problem of surface sagging has been solved in principle, is based on the above-mentioned pyramidal mirror.

(Effects) According to the present invention, changes in beam spot diameter due to rotation of the elliptical beam on the scanning line are eliminated, and a uniform beam spot can be formed on the scanned surface, thereby improving image quality. This is advantageous because it can improve the performance.

[Brief explanation of the drawing]

FIGS. 1 and 2 are configuration diagrams of a light beam scanning device explaining an embodiment of the present invention, and FIG. 3 is an embodiment of the present invention.
Figures 4 to 6 are perspective views of a rotating mirror as an embodiment of the present invention, and Figures 7 and 8 are diagrams explaining the shape of the beam heading toward the imaging lens. 9 are explanatory diagrams of a laser printer according to the embodiment of the present invention. Figures 10 to 12 are diagrams explaining the main part configuration of a conventional light beam scanning device, Figure 13 is a diagram explaining the deflection mode of the rotating mirror at any rotational position, and Figure 14 is the state of the same as the above figure. FIG. 4 is a diagram illustrating a deflection mode when the beam is rotated by 90 degrees. 230...deflector, 240...rotating mirror, 2
40-1. 240-2... Reflective surface, 38S... Circular slit, 39S-1. 3O5-2... Long slit, 0-O... Rotating shaft. Tassel b Matagata 4 Figure 2 Blue〉 Zo b [≧] Horse 74 Figure

Claims (1)

[Claims] In order to image the beam with the required spot diameter necessary for image formation on the scanned surface, a slit for beam shaping is provided on the optical path before the imaging lens, and the beam after passing through the slit is directed to the deflector. In a light beam scanning device in which light is incident on a reflective surface at an angle with respect to its normal direction, and the reflected light is incident on the imaging lens as an incident beam, the beam that is incident on the reflective surface of the deflector. is set so that it is irradiated to an arbitrary incident position on the reflective surface that is off the rotation axis of the deflector, and the beam diameter in the main scanning direction, which is the scanning direction of the incident beam to the imaging lens. A circular slit that shapes the beam diameter in the sub-scanning direction perpendicular to the main scanning direction is placed before the deflector, and a long slit with an opening greater than the full scanning angle is placed between the deflector and the imaging lens. The long slit is arranged along the main scanning direction between the lenses, and the shape of the long slit is curved to match the scanning locus of the incident beam to the imaging lens, and the long slit is integrated with the reflecting surface of the deflector. A light beam scanning device characterized in that it is configured to be rotated.