JPS63307419A - Light beam scanner - Google Patents

Abstract

PURPOSE:To form a uniform beam spot in any position on a scanning line by rotating a synchronous slit, which shapes an incident beam in main scanning and subscanning directions, and a deflector as one body. CONSTITUTION:A cylindrical slit member 29 is covered on a pyramidal mirror 24 of a deflector 23, and a beam 28 is reflected on the mirror 24 and is cut into an elliptic light 31 having a major axis (a) and a minor axis (b) by a synchronous slit 51 and is made incident on an image forming lens. Though the mirror 24 is rotated at 90 deg. from the initial position, the beam having the major axis (a) in the main scanning direction and having the minor axis (b) in the subscanning direction is emitted by the slit 51 which is always turned synchronously with the reflection face as one body. This beam is emitted similarly though the deflector 23 is rotated <=90 deg., and the uniform beam spot is formed in any position on the scanning line to improve the quality of image.

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. 5, 6, and 10, a beam diverged from a semiconductor laser 32 serving as a light source is collimated by a collimator lens 33, then shaped by a slit 34, and emitted from the semiconductor laser unit 21. .

Then, this beam is deflected by the first mirror 22! $
The light is incident approximately along the axis of rotation of the pyramidal mirror 24, which has a reflective surface that is obtained by cutting a cylinder forming the reflective surface 23 diagonally.

When the pyramidal mirror 24 rotates under such conditions,
Along with this, it is deflected and proceeds to the fθ lens 25, is connected, the optical axis is bent by the reflection part 3 of the second mirror 26, passes through the toroidal lens 27, and is connected to the outer circumferential surface of the photoreceptor drum 1. imaged.

Note that the optical fiber 35 placed between the fQ lens 25 and the second mirror 26 is guided to a photosensor 36, and these are at the writing position I! This is to extract the synchronous light that determines the

In such an optical system, the slit 34 for beam shaping before the deflection of 1 m23 is connected to the laser unit 21.
This configuration causes the following problems.

As shown in No. 711, the elliptical incident beam LN shaped by the slit 34 (see No. 101!l) is transmitted to the first mirror 2.
2 and enters the pyramidal mirror 24.

Here, as shown in FIG. 7, at a certain rotational position of the pyramidal mirror 24, the diameter a of the incident beam LN is an ellipse of tla having its long axis in the X-axis direction, with the diameter of one reflected beam LO after reflection being in the main scanning direction. Becomes a beam of However, since the incident angle is inclined with respect to the normal direction, when the pyramidal mirror 24 rotates 90 degrees, the diameter of the reflected beam LO changes to the y-axis, which is the sub-scanning direction, orthogonal to the main-scanning direction, as shown in FIG. It becomes an elliptical beam with a diameter a and a long axis in the direction.

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, while the pyramidal mirror 24 rotates 90 degrees, the deflected beam rotates on the photoreceptor l. , 900 rotations, the positions of the major axis and minor axis are reversed between the main scanning direction and the sub-scanning direction.

In light optical systems such as the fO 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 varies depending on the main scanning direction and the sub-scanning direction. Since they differ in the scanning direction, if the diameter of the deflected beam changes as described above, the final spot diameter on the photoreceptor surface varies, resulting in poor image quality.

That is, in a beam positioning 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 incident angle and the reflection angle are approximately 45° is used. In the case where the elliptical beam is deflected by rotation of the deflector.

It is scanned while rotating, and the spot diameter of the focused beam on the scanned surface by the imaging lens is in the main scanning direction.

There was a problem in that it changed in the sub-scanning direction, which in turn had an adverse effect on image quality.

(Purpose) Therefore, the 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, and to maintain the relationship between the angle of incidence and the angle of reflection with respect to the reflecting surface of the deflector, and furthermore, for the deflected elliptical beam, the spot diameter on the scanned surface is the main one. An object of the present invention is to provide a light beam scanning device that does not change in the scanning direction.

(Structure) In order to achieve the above object, the present invention provides a beam diameter in the main scanning direction of an incident beam toward an imaging lens;
*A synchronous slit that shapes the beam diameter in the scanning direction is provided on the optical path, after the reflective surface of the deflector, integrally with the reflective surface.
It is characterized in that it rotates together with the reflecting surface.

In the above, the synchronous slit is formed on the outer peripheral surface of a cylindrical slit member, and the lower end of the slit member is open at the inner diameter dimension.

A detailed explanation will be given below based on one embodiment of the present invention.8 In FIGS. 1 and 2, a slit member 29 having a cylindrical shape is placed over the pyramidal mirror 24 of the deflector 23. It is attached so that it rotates integrally with the For this attachment, an appropriate method such as gluing, press-fitting, or screwing the slit member 29 to the shaft of the pyramidal mirror 24 is used. Specific means will be described later.

A synchronizing slit 51 according to the present invention is formed on the outer peripheral surface of this slit member 29. Incidentally, regarding the incident beam 28 in this example, the slit 34 (first
It should be noted that the beam (see Figure 0) is a beam emitted from a laser unit that is not in use.

The synchronous slit 51 is formed according to the required beam diameter corresponding to the main scanning direction X, where a is the required beam diameter, and b is the beam diameter corresponding to the sub-scanning direction y.
Further, the position where the slit is formed in the circumferential direction is fixed in accordance with the direction in which the beam enters the pyramidal mirror and is reflected once.

As shown in FIGS. 1 and 2, the incident beam directed toward the synchronization slit 51 after being reflected by the pyramidal mirror 24 is cut by the synchronization slit 51 into an ellipse (or elongated hole shape) with a long axis a and a short axis S. It will go to the fθ lens 25.

The deflected light after the deflector 23 becomes an ellipse of beam system a and b as shown in FIG. will be done.

tt*, reference numeral 28 in FIG. 2 indicates the incident beam directed toward the slit member 29, and reference numeral 31
shows the beam cross section after exiting from the synchronous slit.

With the above configuration, the pyramidal mirror 24
Even when the beam is rotated by 90 degrees from an arbitrary initial position, the beam is always shaped in the main scanning direction xeiM by the synchronizing slit 51 which rotates in physical synchronization with the reflecting surface, and the beam is shaped in the main scanning direction xeiM and scanning direction y. 29 is 9
0@ Long axis as before rotation.

The same thing holds true even when the short axis direction is maintained in the main scanning direction XtlJ and the scanning direction y, and the deflection W23 is rotated within 90e, so an image is formed with the desired spot diameter at any position on the scanning line. .

Normally, the effective scanning angle is ±90 @ (width in the scanning direction is 180
Since it is within @), the spot diameter is uniform on the photoreceptor surface and the image quality is also good.

Next, regarding the size and shape of the incident beam 28 that enters the synchronous slit 3G, the divergence angle from the semiconductor laser 32 is different between the parallel direction (0/) and the perpendicular direction (on θ) to the bonding surface. , 0/=8°~14", θ work=200~36
It is about ＠, and even if lenses, prisms, etc. are used, it will remain elliptical.

Therefore, when shaping this elliptical beam with the synchronization slit 30, even if the synchronization slit 30 is rotated by both effective scanning angles, the incident beam 28 has a size and shape that sufficiently covers the synchronization slit 30 at least within that range. must have.

However, there is a limit because simply increasing the beam diameter will reduce the light utilization efficiency and make it impossible to obtain the necessary power.

Therefore, the required beam shape is determined by balancing both.

It is necessary to determine the size.

Next, FIG. 3 shows a specific means for attaching the slit member 29 to the pyramidal mirror 24 integrated with the motor shaft.
This will be explained with reference to FIG.

As shown in FIG. 3, a groove 24-a for preventing removal and a recess 24-b for rotational positioning are formed in the shaft of the pyramidal mirror 24 in the circumferential direction thereof.

On the other hand, the slit member 29 is provided with a protrusion 29-a on the inside of the cylinder that can be engaged with the groove 24-a, and a convex part 29-b that can be engaged with the concave part 24-b. has been done.

As shown in FIG. 4, the slit member 29 is inserted into the shaft of the pyramidal mirror 24, the protrusion 29-a engages with the groove 24-a, and the convex part 29-b engages with the concave part 24-b. Installed. In order to promote flexibility during insertion, grooves 29-c are formed in the slit member 29 at appropriate intervals in the axial direction.

As another embodiment of the present invention, instead of using the cylindrical slit member 29 as in the above example, a synchronous slit is formed on the back of a plate bent into a U-shape, and this is used as a reflective surface. It may be fixed to the rotating wheel of the pyramidal mirror by covering it.

Next, a laser printer suitable for an embodiment of the present invention will be explained with reference to FIG. 9 and FIG. 1O.

In FIG. 9, a charger 2, a developing unit 3. Transfer charger4. A cleaning unit 5 is arranged at a position I! between the charging unit W2 and the developing unit 3. At 6, a writing optical unit 7 is provided so that a writing beam is incident on the photoreceptor drum l to expose it.

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 located below the photoreceptor drum 1. It is provided below the developing unit 3 and cleaning unit 5.

Further, the transfer charger 4 is arranged above the photosensitive drum 1. A paper feed cassette 8 for feeding transfer paper to a transfer section between the transfer charger 4 and the photosensitive drum 1 is provided further below the optical writing unit 7.

The transfer paper is fed by a feed roller 9 and a flexible roller 1 that presses against the feed roller 9.
The double feed is separated by the pad 10 and the sheets are sent out one by one, making a large U-turn on the side of the developing unit 3, and a pair of registration rollers 11.1 provided above the developing unit 3.
2, the paper is fed to the transfer section at the same timing as the image formed on the photosensitive drum 1.

A fixing unit 13 is provided in the transfer paper path after transfer,
A paper discharge tray 14 is provided on the discharge side.

As shown in FIGS. 9 and 10, in the writing optical unit 7, light that flashes in response to an image information signal emitted from a laser unit 21 is reflected by a first mirror 22, and is deflected by a scanner motor. The light enters a pyramidal mirror 24, which is a mirror integrally attached to the axis of the device 23, and is repeatedly deflected within a certain angular range. The deflected light is corrected by the fO lens 25 so that it forms an image on a straight line at the incident position W16 on the photoreceptor drum 1, and the projection point moves at a constant speed, and then passes through the second mirror 26 and the toroidal lens 27 to the photoreceptor drum. Enter 1.

Main scanning is performed by deflecting the incident light, and the photoreceptor drum 1
Sub-scanning is performed by the rotation of , an image corresponding to one image information signal is written, and an electrostatic 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 a developing unit 3 to form a toner image.

The image is transferred by the action of the transfer charger 4 onto the transfer paper fed by the pair of registration rollers 11 and 12. The transfer paper separated from the transfer detection photoreceptor drum l is transferred to the fixing unit 13.
is fixed and discharged to the paper discharge tray 14.

On the other hand, the toner remaining on the photosensitive drum 1 of the transfer device 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. Like this 1
In rotating polygon mirrors and holo scanners, a problem known as the so-called face tilt problem occurs because multiple mirror surfaces or hologram gratings are involved in the deflection of the light beam.

In order to correct this surface tilt, there is a problem that the optical system becomes 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 one reflected beam by 360 degrees is being proposed. The reflecting medium in such a deflecting means is called a pyramidal mirror.

In addition, in the deflection method using a pyramidal mirror.

Since only one mirror surface is involved in the deflection of the light beam, the above-mentioned surface tilt problem is solved in principle.

(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]

Fig. 1 is an exploded perspective view of a light beam scanning device illustrating an embodiment of the present invention, Fig. 2 is a partial sectional view of the above figure, Fig. 3 is an explanatory diagram of a method for attaching a slit member, and Fig. 4 is a partial cross-sectional view showing the state in which the slit member is installed, and FIGS. 5 and 6 are diagrams each explaining the arrangement of the optical system of the light beam scanning device.
FIG. 7 is a diagram explaining the deflection mode of the pyramidal mirror at any rotational position, and FIG.
FIG. 9 is an explanatory diagram of a laser printer suitable for carrying out the present invention; FIG.
The figure is a diagram illustrating the arrangement of a laser unit and a deflector. 23...deflector, 24...pyramidal mirror,
51...Synchronization slit. 7. Death To I Figure 2 Figure Karasu D Figure 66 Figure - Goichi

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 reflecting surface at an angle with respect to its normal direction, and the reflected light is made incident on the imaging lens as an incident beam, the main scanning direction of the incident beam toward the imaging lens is A synchronized slit for shaping the beam diameter in the direction and the beam diameter in the sub-scanning direction is provided integrally with the reflecting surface on the optical path after the reflecting surface of the deflector, and rotates together with the reflecting surface. Features a light beam scanning device.