JP2712034B2 - Scanning optical device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a scanning optical device used in a laser beam printer, a laser aligner, a bar code reader, and the like, and deflects and scans a laser beam by an optical deflecting unit. .

(Prior Art) Conventionally, in a scanning optical device, a rotary polygon mirror has been widely used because of its rotational stability and high speed. This very advantageous rotary polygon mirror also has a problem that the scanning position varies due to the tilt of the rotating surface due to the inclination when the mirror is mounted on the flange. In particular, in a laser beam printer that forms an electrostatic latent image with high resolution modulated according to recording information on a moving photosensitive drum, pitch unevenness occurs in which the scanning line interval varies, and the recorded image deteriorates. Such pitch unevenness appears accurately in one rotation cycle of the rotating polygon mirror, and as a means of preventing this, an optical system that reduces the effect of the rotating polygon mirror by using a tilt correction optical system is used. A system is being developed.

(Problems to be Solved by the Invention) However, the means for optically correcting the tilt of the rotating polygon mirror (polygon mirror) requires a complicated optical system and a high-precision frame for holding the same, which increases the cost. Was a factor. The conventional tilt correction optical system uses a cylindrical lens disposed in front of the polygon mirror and a toric lens disposed behind the polygon mirror, and a cylindrical lens disposed in front of the polygon mirror and another disposed near the photosensitive drum surface. Two main types of means, one using a single cylindrical lens, are in practical use. Each of these means has a problem that it is complicated and expensive, and it takes time to adjust.

FIG. 4 shows a conventional example of a tilt correction scanning optical apparatus, in which 2 is a rotary mirror (polygon mirror).
Reference numeral 9 denotes a motor for rotating and driving the laser, 3 denotes a laser device serving as a light source, 7 denotes a cylindrical lens, and 8 denotes an imaging lens group including a toric lens. Reference numeral 5 denotes a photosensitive drum, and reference numeral 6 denotes a horizontal synchronization signal detector provided on the scanning start side.

In addition, a conventional laser beam printer mainly prints at about eight pages per minute, and when the number of polygon mirror surfaces is six and the image density is 300 DPI, the rotation speed of the polygon mirror driving motor is about 5500 rpm. Had become. But,
When the number of prints reaches about 4 per minute,
The rotation speed of the polygon motor is 2750 rpm, and the rotation speed of the polygon motor is low and rotation unevenness is likely to occur.Therefore, a high-precision rotation control circuit and a rotor having high inertia are required, resulting in an increase in cost. is there.

The applicant of the present invention has previously proposed in Japanese Patent Application No. 62-19915 a scanning optical device which solves such a falling problem and has a large degree of freedom in designing the process speed of a laser beam printer. In this Japanese Patent Application No. 62-19915, a use section used for light deflection and a light use section not used for light deflection are provided around a rotary polygon mirror.

The present invention is a further improvement of Japanese Patent Application No. 62-19915, firstly, a rotating mirror provided with a working hole, secondly, a rotating mirror having an increased hardness of a mounting reference surface, and Thirdly, it is an object of the present invention to provide a scanning optical device having any one of the rotating mirrors provided with a reference seat having a diameter equal to or less than the diameter of the inscribed circle of the mirror surface.

(Means for Solving the Problems) The invention for achieving the first object is a scanning optical device which deflects a light beam emitted from a light beam generating means by a rotating mirror. It is characterized in that it has a used surface portion used for deflection and a non-used surface portion not used for light deflection, and that a through-hole is provided on a straight line passing from the non-used surface portion to substantially the center of rotation of the rotating mirror.

According to a second aspect of the present invention, there is provided a scanning optical device for deflecting a light beam emitted from a light beam generating means by a rotating mirror, wherein the rotating mirror is provided around a surface used for light deflection and a light deflecting device. The rotating mirror has a reference surface for mounting the rotating mirror orthogonal to the surface of the used surface portion, and the reference surface is processed to be harder than the surface hardness of the material of the rotating mirror. It is characterized by having done.

According to a third aspect of the present invention, there is provided a scanning optical apparatus for deflecting a light beam emitted from a light beam generating means by a rotating mirror, wherein the rotating mirror is provided with a use surface portion used for light deflection and a light deflecting surface. The rotating mirror has a reference surface for mounting the rotating mirror orthogonal to the surface of the using surface portion, and the reference surface is centered on the rotation center of the rotating mirror, and is located inside the using surface portion. It is characterized by having a circular shape that is equal to or smaller than the diameter of the tangent circle.

(Operation) According to the first aspect of the invention, by providing the through-hole on a straight line that passes from the non-use surface portion to substantially the center of rotation of the rotating mirror,
If this through hole is used as a working hole, it does not affect the processing accuracy of the mirror surface.

In the second invention, by processing to be harder than the surface hardness of the material of the rotating mirror of the mounting reference plane,
Damage to the reference mounting surface is prevented.

According to the third aspect of the invention, the machining accuracy is improved by making the mounting reference surface a circle having a diameter equal to or less than the diameter of the circle inscribed in the rotary mirror.

(Example) The following invention is explained based on an illustrated example. FIG. 1 is a schematic view showing a laser beam printer to which an embodiment of the present invention is applied. 1 is a rotating mirror, 2 is a driving motor for driving the rotating mirror 1, and 3 is a laser which is a light beam generating means. A light source generates a laser beam modulated in accordance with recording information. 4 is an fθ lens, 5 is a photosensitive drum, 6
Is a synchronization signal detector for obtaining a horizontal synchronization signal. The rotary mirror 1 has two use surface portions (hereinafter, referred to as mirror surfaces) used for light deflection of 1a and 1b, and 1c and 1d are non-use surface portions which are not mirror-finished and have a curved shape. .

The laser beam emitted from the laser light source 3 and modulated in accordance with the information to be recorded is scanned in the main scanning direction (the direction of arrow B) by the rotation of the rotary mirror 1 and in the sub-scanning direction of the moving direction of the photosensitive drum 5. Line scanning is performed in the direction of arrow c.

The laser beam at a specific position outside the effective scanning area of the photosensitive drum 5 is received by the synchronizing signal detector 6, and the synchronizing signal is used to determine the start of modulation of the laser light source.

Around the photosensitive drum 5, a charging device, a developing device, a transfer device,
Unillustrated process means such as a cleaning device are arranged.

Reference numerals 1e and 1f denote through holes, which are provided in the vicinity of the non-use surface portion in axisymmetric manner with respect to the rotation axis of the rotary mirror 1. The holes 1e and 1f are equal in size, are opposed to each other by 180 degrees on a radius around the rotation axis, and are provided so as not to impair the dynamic balance. Further, since it is far from the high-precision mirror surface, even if a slight force is applied as a working hole, the mirror surfaces 1a and 1b are not affected at all. As an advantage of the hole being a through hole,
Since multiple rotating mirrors can be stacked and machined or coated by skewing this through hole, a large number of rotating mirrors can be processed at one time, cost reduction is possible, and variation in processing accuracy Less.

Such through holes 1e and 1f are convenient when a plurality of rotating mirrors are stacked, and are preferably formed in parallel with the mirror surface. In the rotating mirror 1, the facing distance between the mirror surfaces 1a and 1b is shorter than the facing distance between the non-use surface portions 1c and 1d, thereby enabling the rotating mirror to have a large scanning angle even though it is compact. Here, the size of the rotating mirror 1 is determined optimally based on processing accuracy, processing method, deformation, and the like, and cannot be unnecessarily reduced.

FIG. 2 shows an example of an effective rotating mirror, to which an effect of preventing air resistance and turbulence generated at a corner (two-sided joint) when the number of surfaces of the rotating mirror 1 is small is added. is there. That is, the distance between the mirror surfaces 1a and 1b of the rotating mirror 1 is about 14 mm, the length of the mirror surface in the scanning direction is about 14 mm, and the rotating mirror 1 is continuously connected to the non-use surface portions 1c and 1d. The radius of curvature changes continuously from the mirror surfaces 1a, 1b to the non-use surfaces 1c, 1d. This is a rotating mirror 1
The air flow generated when rotating at high speed causes turbulence near the intersection of the mirror surfaces 1a, 1b and the non-use surface portions 1c, 1d, and the mirror surfaces 1a, 1b
The purpose of this is to prevent dust in the air from easily adhering to the corners. By providing a smooth curvature change from the mirror surfaces 1a, 1b to the non-use surface portions 1c, 1d, it becomes possible to prevent turbulence near the mirror surfaces 1a, 1b.

The distance between the non-use surface portions 1c and 1d has a curvature of about 20 mm, and the diameter of the reference mounting surface of the rotary mirror 1 is preferably equal to or slightly smaller than the distance between the mirror surfaces, and is about 13 mm in diameter. . For these reasons, a hole having a diameter of about 2 mm is formed at a position with a radius of 8 mm. This is because, if the through-hole is provided outside the mounting reference plane, the influence of distortion that tends to occur near the through-hole is not transmitted to the reference plane. That is, FIG.
FIG. 1g is a view showing a reference mounting surface to the drive motor 2; reference numeral 1g denotes a mounting reference surface having a circular shape inscribed in the mirror surfaces 1a and 1b of the rotary mirror 1 or a smaller circular shape.

If this mounting reference surface 1g is a reference surface with a diameter larger than the inscribed circle diameter, when cutting the reference surface with a lathe, cutting is interrupted below the mirror surface, resulting in so-called intermittent cutting. The cutting tool causes chattering vibration and the plane accuracy is deteriorated. If the reference surface 1g is formed into a circular shape smaller than the inscribed circle diameter of the mirror surfaces 1a and 1b of the rotary mirror 1, the cutting can be continuously performed without cutting during the processing of the reference surface 1g, and the processing accuracy of the reference surface 1g. Is improved.

Further, by subjecting at least this reference surface 1g to a surface treatment such as hard chromium or nickel plating or alumite treatment, the reference surface 1g can be hardened and scratches can be prevented.

The rotating mirror of this embodiment is described in Japanese Patent Application No.
As proposed in the above issue, the mirror surface is adjusted so as to be arranged along the inclination of the rotating mirror mounting flange of the polygon mirror, and the adjustment method is to rotate the two mirror surfaces so as to minimize the tilt while measuring the tilt. This is for adjusting the rotation phase between the mirror and the flange. However, if dust enters between the rotating mirror and the flange during these adjustments, the mounting reference surface of the rotating mirror is damaged, and the periphery of the wound rises, making it impossible to adjust the rotational phase. In addition, since the rotating mirror is made of aluminum and is soft and easily scratched, even if it does not bite dust, it only contacts the flange, and even fine irregularities on the flange surface may be scratched, and the scratch is crushed when pressure is applied Therefore, each time the rotating mirror is attached to or detached from the flange in order to adjust the rotation phase of the rotating mirror, the flaw changes and the inclination of the rotating mirror changes. In this way, it is possible to take care not to bite dust when attaching or detaching the rotating mirror.However, if the reference surface for attaching the rotating mirror is soft, even if you do not bite dust, it will be damaged by attachment and detachment and adjustment will not be possible. It will be lost.

In the conventional rotary mirror, after the rotary mirror is fixed along the flange of the polygon motor, it hardly moves, and even if the reference surface has fine irregularities, the mounting reference surface of the rotary mirror is deformed accordingly. Since the tilt of the rotating mirror is not affected, it is sufficient to attach the rotating mirror to the flange so that dust does not bite between the rotating mirror and the flange. Did not.

In order to avoid the above-mentioned drawbacks, if the reference surface of the rotating mirror is hardened so as not to be easily damaged, not only the rotational phase can be easily adjusted, but also the change over time of the inclination of the rotating mirror can be reduced. Can also.

In this way, a reference mounting surface 1g without damage is obtained, and the mounting accuracy on the drive motor 2 is improved.

(Effects of the Invention) As described above, according to the present invention, a hard reference surface having no damage and having a working hole which does not affect the mirror surface accuracy by devising the shape of the rotating mirror has high accuracy. The rotating mirror provided with the reference surface has an effect that high-quality image recording becomes possible.

[Brief description of the drawings]

1 is a schematic view of a laser beam printer to which one embodiment of the present invention is applied, FIG. 2 is a perspective view showing another embodiment of the rotating mirror, and FIG. 3 is a perspective view showing another embodiment of the rotating mirror. FIG. 4 is a schematic view showing a conventional laser beam printer. DESCRIPTION OF SYMBOLS 1 ... Rotating mirror, 1a, 1b ... Used surface 1c, 1d ... Unused surface 1e, 1f ... Through hole, 1g ... Mounting reference surface 2 ... Drive motor 3 ... Laser light source (light Beam generating means) 4... Fθ lens, 5... Photosensitive drum 6... Synchronization signal detector

Claims (6)

(57) [Claims] 1. A scanning optical device for deflecting a light beam emitted from a light beam generating means by a rotating mirror, wherein the rotating mirror has a used surface portion used for light deflection and a non-used surface portion not used for light deflection. And a through-hole is provided on a straight line passing substantially from the non-use surface to the center of rotation of the rotating mirror. 2. The scanning optical device according to claim 1, wherein said through hole is provided substantially parallel to a rotation axis of said rotary mirror. 3. The scanning optical device according to claim 1, wherein the through-hole is provided at a position symmetrical to a rotation axis on a predetermined radius from a rotation center of the rotating mirror. 4. A scanning optical device for deflecting a light beam emitted from a light beam generating means by a rotating mirror, wherein the rotating mirror has a used surface portion used for light deflection and a non-used surface portion not used for light deflection. Wherein the rotating mirror has a reference surface for attaching the rotating mirror orthogonal to the surface of the used surface portion, and the reference surface is processed so as to be harder than the surface hardness of the material of the rotating mirror. Scanning optics. 5. A scanning optical apparatus for deflecting a light beam emitted from a light beam generating means by a rotating mirror, wherein the rotating mirror has a used surface portion used for light deflection and a non-used surface portion not used for light deflection. Wherein the rotating mirror has a mounting reference surface of the rotating mirror orthogonal to the surface of the use surface portion, and the reference surface is equal to a diameter of a circle centered on the rotation center of the rotary mirror and inscribed in the use surface portion. A scanning optical device having a small circular shape. 6. The scanning optical device according to claim 1, wherein said through hole is provided outside a reference mounting surface of said rotary mirror.