JPH05196882A - Optical unit for laser light scanning - Google Patents

Abstract

PURPOSE:To reduce the cost of the optical unit for laser light scanning which uses a pyramidal mirror and improve the precision of the scanning of laser light by composing the optical unit of a mirror member whose reflecting surfaces are not symmetrical about the axis of rotation and a rotary shaft where the mirror member is fixed. CONSTITUTION:This optical unit consists of a mirror member 10 and rotary shaft 12 where the mirror member 10 is fixed. The mirror member 10 has the reflecting surfaces 10a and 10a which are not symmetrical about the axis E of rotation of the rotary shaft 12 and constitutes the pyramidal mirror. The mirror member 10 is constituted by coating a glass or plastic member to a >=80% reflection factor and the reverse surface of the mirror member 10 is tightly fixed on the top surface of the rotary shaft by a fixing means such as an adhesive. In this case, the body formed by fitting the mirror member slantingly to a rotary shaft in a shape close to that of the pyramidal mirror by a fixing method such as adhesion and screwing may be used as the pyramidal mirror.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser beam scanning optical device used in an image forming apparatus such as a digital copying machine or a laser printer.

[0002]

2. Description of the Related Art Conventionally, as disclosed in Japanese Patent Laid-Open No. 63-109411, a scanning optical device of an image forming apparatus such as a laser printer is constructed by using a pyramidal mirror having one or two mirror surfaces. It is known how to do it. By using such a pyranidal mirror, a scanning optical device can be constructed at a lower cost than using a polygon mirror having a configuration in which two to twelve mirror surfaces are provided on the outer peripheral portion of a flat disk.

[0003]

However, since there is a strong demand for low cost in laser printers, further cost reduction is desired even in scanning optics using pyramidal mirrors.

Further, since the pyramidal mirror is asymmetric, there is a problem that it is difficult to align the rotation center of the rotation axis and the mirror surface with the method of separately forming the mirror surface and the rotation axis. Furthermore, if the mirror surface is a curved surface,
Since it is required that the center of rotation and the center of the mirror surface coincide with each other with higher accuracy, the assembling work becomes more difficult and the defect rate tends to increase.

Further, the pyramidal mirrors proposed previously are not shaped like a hexahedron or an octahedron close to the axial symmetry of the rotation axis, but are often formed by obliquely cutting a rod-shaped material. The balance is in a hardened state around the motor axis. Further, since scanning is performed on one surface, it is almost used at 8000 rpm or more, and there is a problem that vibration is likely to occur due to imbalance in rotation of the motor.

In view of the above problems, it is an object of the present invention to achieve further cost reduction and laser beam scanning accuracy improvement in a laser beam scanning optical device using a pyramidal mirror. A specific goal is to provide an inexpensive laser light scanning optical device using a member such as glass or plastic that has been conventionally used, and to match the mirror surface and the rotation axis with high accuracy. That is, the balance of the pyramidal mirror is improved to achieve stable rotation without vibration at high speed rotation.

[0007]

The invention according to claim 1 is
It is composed of a mirror member whose reflection surface is not axially symmetric with respect to the center of rotation, and a rotation shaft to which the mirror member is fixed. The invention according to claim 2 has a structure in which a part of the rotating shaft is provided with a reflecting surface whose shape is not axially symmetric with respect to the rotation center. The invention of the method according to claim 5 is
It is a manufacturing method of the optical device for laser light scanning of Claim 2, Comprising: The cylindrical surface of the said rotating shaft is cut by Compax diamond, and the said reflecting surface is mirror-cut by a single crystal diamond bite by inclining the said rotating shaft. The maximum surface roughness is 0.05 μm or less. Further, the invention according to claim 9 uses a balance weight when rotating against centrifugal force generated from the shape of the mirror member and the rotating shaft according to claim 1 or the rotating shaft having the reflecting surface according to claim 2. The centrifugal force is balanced.

[0008]

EXAMPLES Examples of the present invention will be described below. 1 and 2 are respectively a front view and a plan view showing an inexpensive laser beam scanning optical device using a member such as glass or plastic. The laser beam scanning optical device 1 shown in FIG. 1 includes a conventionally used mirror member 10 made of a material such as glass or plastic, and a rotary shaft 12 to which the mirror member 10 is fixed. The mirror member 10 is the rotating shaft 1.
The shapes of the reflecting surfaces 10a and 10a are not axially symmetrical with respect to the rotation center E of 2 and form a pyramidal mirror. The arrow L in the figure indicates the incident laser beam. Mirror member 10
Is a glass or plastic lens coated with a reflectance of 80% or more. As shown in FIG. 3, the lower surface 10b of the mirror member 10 is firmly fixed to the upper surface 12a of the rotary shaft 12 by a fixing means such as an adhesive. To be done. in this case,
As shown in FIG. 4, a mirror member 10 may be obliquely attached to the rotary shaft 14 having a shape close to a pyramidal mirror by a fixing method such as bonding or screwing, and may be used as a pyramidal mirror.

A concave spherical surface as shown on the right side of FIG.
The mirror member 1 having a convex spherical surface or an aspherical surface shown on the left side.
6 and 18 are shown in plan view in FIG.
You may attach by. In the embodiment shown in FIG. 5, the description has been made assuming that the mirror members 16 and 18 have only one reflecting surface. However, like the embodiment shown in FIG.
Providing curved surfaces such as both spherical surfaces or aspherical surfaces on the two front and back surfaces,
You may use them as a reflection mirror.

The shape of the mirror member has a curved surface portion 22 and an outer peripheral portion 24 as shown in FIG.
The stepped shape facilitates attachment to the rotary shaft 12 with the attachment member 26 that surrounds the outer peripheral portion 24.
In other words, the outer peripheral portion 24 is provided outside the curved surface portion 22 necessary for laser beam scanning in consideration of fixing to the rotating shaft 12. In order to facilitate the attachment of such an outer peripheral portion 24, a more stable fixing becomes possible by forming the outer surface into a flat shape as shown in FIG. In FIG. 8, the upper diagram is a plan view of such a two-step type mirror member 30, and the lower diagram is a view seen from the side on which the laser beam is incident. As described above, according to the present embodiment, since the mirror member and the rotary shaft 12 are processed separately, the rotary shaft 12 does not need to have both rigidity and mirror surface workability. Any material can be used as long as it can solve the problem of rigidity such as time deformation, and there is an advantage that the cost of the rotary shaft 12 can be significantly increased. Further, since the mirror member may be a glass or plastic lens or a chip-shaped member, it can be manufactured by a conventional processing method, and the unit price per piece is extremely low. Further, in the case of a spherical or aspherical reflection mirror, it is sufficient to coat an ordinary lens-formed product as a reflection mirror, and there is an advantage that no special mounting member is required.

Next, an embodiment will be described in which the balance of the pyramidal mirror is improved to achieve stable rotation without vibration at high speed rotation. FIG. 9 shows the configuration of the cylindrical pyramidal mirror 34 and the rotary shaft 12. In FIG. 9, since the mirror portion 36 is inclined, the upper portion 38 (shown by diagonal lines) of the mirror portion 36 has an asymmetric shape with respect to the motor axis E. Here, when the pyramidal mirror 34 is rotated, a centrifugal force F1 (vector) is generated by the upper portion 38, as shown in FIG. FIG. 10 is a plan view and a front view showing a balance weight 40 and a mounting washer 42 for canceling the centrifugal force F1 (vector). Both the balance weight 40 and the washer 42 have a cylindrical outer shape.
0 is a shape obtained by obliquely cutting a cylindrical shape. Both the balance weight 40 and the washer 42 are provided with a circular hole 44 having the same size as the diameter of the pyramidal mirror 34 inside. Therefore, as shown in FIG. 11, the balance weight 40 is attached to the outer peripheral portion of the pyramidal mirror 34 with a washer 42 by a method such as bonding or screwing.
Can be attached to 2.

Next, a method of canceling the centrifugal force F1 (vector) due to the asymmetry of the pyramidal mirror 34 will be described. As for the centrifugal force of the upper portion 38, the moment of inertia I1 is obtained from the minute mass ma of the mirror and the distance r from the central axis E, and I1 = ma · r1 ² + ma · r2 ²
+ ... + ma · r (n−1) ² + ma · rn ² . However, for this moment of inertia, F1 (vector) is 1
Therefore, if a balance weight having an inertia moment I2 equal to I1 can be provided, the centrifugal force F1 (vector) can be canceled. That is, F1
It suffices to create a balance weight having an inertia moment that generates F2 (vector) such that (vector) + F2 (vector) = 0. In the present embodiment, the inertial moment I2 of the balance weight is set to I2 = mb · r1 ² + mb · r2 ² + ... + mb · r in the direction such that F1 (vector) + F2 (vector) = 0 in advance in terms of processing cost. (N-
1) ² + mb · rn ² , (where mb represents a minute mass of the balance weight), the ring shown in FIG. 10 is obliquely cut. In this case, the balance weights of the pyramidal mirrors 34 of various shapes can be easily made by adjusting the angle of oblique cutting. Further, while the pyramidal mirror 34 is near the rotation center E with respect to the rotation center E, the balance weight 40 is farther than the pyramidal mirror 34, and therefore the same effect as the upper portion 38 can be obtained with a small weight. A centrifugal force F2 (vector) is generated. for that reason,
By setting the mass of the balance weight 40 to be slightly heavier, not only can the balance of the pyramidal mirror 34 be adjusted, but also the rotation of the motor can be stabilized during high-speed rotation, and high-precision optical scanning can be realized.

Finally, an embodiment in which the mirror surface of the asymmetrical pyramidal mirror and the rotation axis can be aligned with high precision will be described. FIG. 12 shows the configuration of the laser beam scanning optical device 50 according to the present embodiment. The laser light scanning optical device 50 according to the present embodiment includes a pyramidal mirror portion 52 in which a cylindrical column is obliquely cut, and the cut surface is a mirror surface, and a slide bearing portion 54 of the pyranidal mirror portion 52. It is composed of a rotor portion 56 which is a drive source. The laser beam scanning optical device 50 is made of brass containing no hard substance such as Si.

Next, a method of manufacturing the laser beam scanning optical device 50 will be described. First, a cylindrical brass having a predetermined size is prepared. The rotor portion 56 is configured by embedding a magnetic resin 58 in the rotating shaft made of brass alternately in the circumferential direction with S poles and N poles. FIG. 13 is a view of the rotor portion 56 as seen from the lower surface. After that, the surface of the cylinder is cut with a Compax diamond tool with an ultra-precision lathe to have a surface roughness of about 0.2 to 0.3 μm or less. At this time, the magnetic resin 58 is similarly processed. Then, after tilting 45 ° with respect to the rotation axis of the lathe, the mirror surface 60 of the piranidal mirror portion 52 is cut with a Compax diamond bite, and then mirror surface cutting is performed with a single crystal diamond bite to obtain the maximum surface roughness. 0.0
5 μm or less. Then, the reflectance of the mirror surface 60 is set to 8
In order to achieve 0% or more, as shown in the enlarged view in FIG. 14,
Aluminum coat film 6 of about 750 Å
2 is formed, and a SiO (silicon oxide) coat film 64 having a thickness of λ / 2 is formed thereon. Note that λ is the wavelength of the laser used.

In the mounting work, since the rotary shaft rotates at a high speed of several thousand revolutions, the slide bearing portion 54 is made of a material softer than the rotary shaft so as not to wear with the rotary shaft of the pyranidal mirror portion 52, for example, a fluororesin slide bearing. (PTFE)
Etc. are used. At present, PTFE-based resins with improved wear resistance and mechanical strength are commercially available.
It can withstand rotation of about m. Further, by embedding the magnetic resin 58 in the rotary shaft, it is possible to perform cutting work together with the rotary shaft, and the rotary shaft can also serve as a rotor of the motor, which enables downsizing. Also, by using brass as the material used,
The rotary shaft and the mirror surface 60 can be collectively cut, and the processing efficiency is improved. Further, since the reflecting surface can be cut into a mirror surface, aluminum and SiO can be thinly coated, and a highly accurate mirror surface can be obtained. Therefore, according to this embodiment, it is possible to provide a laser beam scanning optical device which is easy to assemble and has high precision.

[0016]

As described above, according to the present invention, in the laser light scanning optical device using the pyramidal mirror, it is possible to reduce the cost and improve the accuracy of the laser light scanning. .

[Brief description of drawings]

FIG. 1 is a front view showing a laser beam scanning optical device according to the present embodiment.

FIG. 2 is a plan view of a laser beam scanning optical device according to the present embodiment.

FIG. 3 is a diagram showing a method of assembling the laser light scanning optical device according to the present embodiment.

FIG. 4 is a diagram showing an example in which a mirror member is bonded to a rotation shaft having an asymmetrical shape close to a pyramidal mirror.

FIG. 5 is a diagram showing an example in which a mirror member that is not flat is used.

FIG. 6 is a plan view showing a method of attaching a mirror member to a rotary shaft.

FIG. 7 is a plan view showing an embodiment in which a two-step type mirror member is attached to a rotary shaft.

FIG. 8 is a diagram showing the shape of a two-stage mirror member.

FIG. 9 is a diagram for explaining a centrifugal force generated from an asymmetrical shape of a pyramidal mirror.

FIG. 10 is a diagram showing a balance weight and a washer.

FIG. 11 is a diagram showing a laser beam scanning optical device that achieves stable rotation without vibration during high-speed rotation.

FIG. 12 is a diagram showing a configuration of a laser light scanning optical device capable of accurately matching a mirror surface of an asymmetrical pyramidal mirror with a rotation axis.

FIG. 13 is a view of the rotor section as seen from the lower surface.

FIG. 14 is an enlarged view of a mirror surface of a pyranidal mirror unit.

[Explanation of symbols]

 10 mirror member 12 rotating shaft 40 balance weight 42 washer 50 laser beam scanning optical device

Claims (9)

[Claims] 1. A laser beam scanning optical device comprising a mirror member whose reflection surface is not axially symmetric with respect to a rotation center, and a rotation shaft on which the mirror member is fixed. 2. An optical device for scanning laser light, characterized in that a reflecting surface which is not axially symmetric with respect to the center of rotation is provided on a part of the rotating shaft. 3. The laser beam scanning optical device according to claim 2, wherein the rotating shaft is brass which is a free cutting material. 4. The aluminum coating is applied to the reflecting surface so that the reflectance is 80% or more, and the silicon oxide coating is applied on the aluminum coating for corrosion resistance. 2. An optical device for laser light scanning according to item 2. 5. The maximum surface roughness Rmax is obtained by cutting the cylindrical surface of the rotating shaft with Compax diamond and mirror-cutting the reflecting surface with a single crystal diamond tool with the rotating shaft inclined. The method for manufacturing an optical device for laser light scanning according to claim 2, wherein the optical device has a diameter of 0.05 μm or less. 6. The laser beam scanning optical device according to claim 2, wherein a magnetic resin is embedded in the rotating shaft to form a rotor. 7. The laser beam scanning optical device according to claim 1, wherein the reflecting surface is a convex surface. 8. The laser beam scanning optical device according to claim 1, wherein the reflecting surface is a concave surface. 9. The centrifugal force generated by the balance weight is balanced during rotation with respect to the centrifugal force generated from the shape of the mirror member and the rotating shaft according to claim 1 or the rotating shaft having the reflecting surface according to claim 2. An optical device for scanning laser light, which is characterized in that