JPS6186723A - Optical beam scanner - Google Patents

Abstract

PURPOSE:To correct the wobbling and surface inclination of a deflector and to reduce the curvature of field so as to make highly accurate scanning, by converging beams in the auxiliary scanning direction by means of a concave cylindrical half mirror provided between a scanning lens and scanning surface. CONSTITUTION:Light from a laser light source 1 is made incident on a concave cylindrical half mirror 10 provided under a condition where it is elongated in the main scanning direction and converged onto a scanning surface 9 after the light is reflected and deflected by means of a rotary polygon mirror 5 and made incident on a scanning lens 6. The length of the optical path from the lens 6 to the scanning surface 9 is set equally to the focal length of the lens 6 and the light is converged on the surface 9 irrespectively of the wobbling and surface inclination of the polygon mirror 5, and thus, the light makes auxiliary scanning in the direction shown by the arrow C and main scanning in the direction shown by the arrow A. On the other hand, a beam 2b transmitted through the half mirror 10 is condensed on a light condensing bar 12 after passing through a grid 11 and the scanning location is detected by a detector 13. Since the mirror 10 is used, the wobbling and surface inclination of the deflector can be corrected and the curvature of field is reduced, resulting in highly accurate scanning.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of the Invention) The present invention relates to a light beam scanning device that deflects a light beam to scan a scanning surface. This invention relates to a light beam scanning device that can perform uniform, accurate, and highly accurate scanning using one light beam, and obtain a synchronization signal using the other light beam.

(Technical Background of the Invention and Prior Art) In recent years, various systems for reading and/or recording images using light beams have been developed. In such a system, a light beam emitted from a light source is
It is reflected and deflected by a deflector such as a rotating polygon mirror, and sent at a constant speed in a direction perpendicular to the direction of deflection (sub-scanning)
It is designed to scan on a scanning plane. In addition, in the above system, the light beam reflected and deflected by the deflector is split into two light beams by a half mirror, and one light beam is used for reading, while the other light beam is made incident on the grid. Many devices that obtain a synchronization signal are also known. However, in conventional scanning devices, the deflector that reflects and deflects the light beam to perform main scanning is driven at high speed, which tends to cause wobbling due to vibration. There is a risk that the scanning line to be scanned may be distorted in the sub-scanning direction.In addition, especially when a rotating polygon mirror is used as a deflector, each surface of the rotating polygon mirror on which the light beam enters is aligned with the rotation axis. It is technically difficult to make the rotating polygon mirror perfectly parallel to the mirror, and there is a problem in that the pitch of the scanning line becomes uneven due to the tilting of the surface of this rotating polygon mirror.Therefore, in order to correct this tilting of the surface, a cylindrical lens is used. Various scanning devices have been proposed in the past in which optical systems such as the above are provided between a deflector and a scanning surface, and examples thereof will be explained with reference to FIGS. 3 and 4.

A light beam 102 emitted from a laser light source 101 is made into an appropriate thickness by a beam expander 103, passes through a cylindrical lens 104, and is directed to a rotating polygon mirror 105, which is a deflector, along the rotation axis of the rotating polygon mirror. Incident as a perpendicular line image, rotating polygon! 1105 is reflected and deflected as it rotates in the direction of arrow m. FIG. 3 is a schematic diagram of the optical path of the reflected and deflected light beam 102 viewed from a direction parallel to the rotation axis, and FIG. 4 is a schematic diagram of the optical path viewed from a direction perpendicular to the rotation axis. be. First, the main scanning of the deflected light beam 102 as shown in FIG. 3 will be explained.
The light beam 1 reflected and deflected by the rotating polygon mirror 105
02 enters the scanning lens 106 provided on the optical path,
The light beam 102 that has entered the scanning lens 106 as parallel light is further passed through a half mirror 108 that is provided on the optical path and is set to transmit the amount of light beam necessary for scanning and reflect the remaining light beam. The light beam 102a that is incident and transmitted through the half mirror 108 is directed to the scanning lens 1.
The light is focused on a scanning surface 109 provided apart from the scanning lens 106 by a focal length fIOG of 06, and main scanning is repeatedly performed in the direction of the arrow in the range from al to a2. Furthermore, an IC cylindrical lens 107 extending in the main scanning direction is provided between the scanning lens 106 and the half mirror 108, but this focuses the incident light only in the direction perpendicular to the main scanning direction (sub-scanning direction). In FIG. 3, it only transmits the light beam 102. On the other hand, as described above, the rotating polygon mirror 105 often suffers from surface tilt, and a system for correcting this will be explained with reference to Fig. Wi4.

The light beam 102 reflected by the rotating polygon mirror 105 enters the scanning lens 106, passes through the scanning lens, and the light beam 102 is slightly expanded onto the scanning surface 109 in the sub-scanning direction, parallel to the plane of the drawing in FIG. The light is incident on the cylindrical lens 107, which focuses the light only in one direction. At this time, if the rotating polygon mirror 105 has no surface tilt etc. and is being driven, the light beam will pass through the optical path shown by the solid line in the figure, but if the rotating polygon mirror 105 has a surface tilt etc. If the mirror 105a is shifted in the direction of 105a', the optical path will move to the optical path shown by the dashed line in the figure. However, since both the light beam in the optical path indicated by the solid line and the light beam in the optical path indicated by the dashed-dotted line are emitted from the same point on the reflecting mirror 105a, the cylindrical lens 107 allows the light beam indicated by the solid line to Since both the light beams indicated by the chain lines can be focused on the same position a3 on the scanning surface 109, even if the optical path of the light beam shifts in the vertical direction in FIG. 4 due to surface tilt, etc., it is possible to correct the shift. Become. The light beam 102a whose surface tilt has been corrected in this manner main scans in the direction of the arrow on the scanning surface 109 which is sub-scanned in the direction of the arrow C. Also, among the light beams 102, the light beam 1 reflected by the half mirror 108
In FIG. 4, the light beam 02b is focused below the half mirror 108 and is incident on a grid (not shown) extending in the sub-scanning direction for obtaining a synchronization signal, and the light beam passing through the grid is detected by photodetection. detected by a device (not shown).

However, in the scanning device that uses the optical system described above to correct for deflector surface tilt, etc., a cylindrical lens is used for correction, so in reality, all the light beams are accurately positioned on the scanning surface. There is a problem in that instead of forming an image, the locus of the image forming position curves as shown by the broken line B in FIG. This field curvature can be corrected to a considerable extent by increasing the number of lenses in the scanning lens, but this method is not practical from a cost standpoint, and the number of lenses in the scanning lens is reduced. If the number of lenses is kept to a realistic number (for example, three), it is difficult to significantly reduce the curvature of field, and there is a disadvantage that highly accurate scanning cannot be performed. In addition, in the above-mentioned scanning device, the optical system becomes complicated by providing a cylindrical lens in addition to a half mirror for splitting the light beam, and there are also problems such as an increase in cost.

(Object of the Invention) The present invention has been made in view of the above-mentioned problems, and it is possible to correct wobbling and tilting of the deflector without using a complicated optical system, and to correct the wobbling and tilting of the deflector without using a complicated optical system. It is an object of the present invention to provide a light beam scanning device that can perform uniform, accurate, and highly accurate scanning by reducing the curvature of field.

(Structure of the Invention) The light beam scanning device of the present invention provides a scanning lens between a deflector and a scanning surface in the optical path of the light beam, and further directs the light beam onto the optical path between the scanning lens and the scanning surface. The present invention is characterized in that a concave cylindrical half mirror is provided that splits the light beam into two light beams and focuses one of the light beams on the scanning surface only in the sub-scanning direction.

The light beam emitted from the laser light source is made to enter the deflector as a line image perpendicular to the drive axis of the deflector by an incident optical system consisting of a cylindrical lens, etc., and the light beam reflected and deflected by the deflector is The scanning lens and the concave cylindrical half mirror focus the light onto the scanning surface and perform scanning. On the other hand, the other light beam split by the cylindrical half mirror enters a grid provided on the optical path, and the light beam passing through the grid is detected by a light detection means provided behind the grid. Generate a synchronization signal.

(Embodiments) Hereinafter, an actual 11MM embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a perspective view showing an outline of a light beam scanning device according to an embodiment IIIA of the present invention.

The light beam 2 emitted from the laser light source 1 passes through the beam expander 3 and the cylindrical lens 4, and then enters the rotating polygon 1t5 rotating in the direction of the arrow m as a line image perpendicular to the rotation axis of the rotating polygon mirror 5. Reflected and deflected. The reflected and deflected light beam 2 enters a scanning lens 6 formed by combining a plurality of lenses, and then enters a concave cylindrical half mirror 0 provided on the optical path extending in the main scanning direction. In this cylindrical half mirror, 0 is the world light beam 2a necessary for scanning among the incident light beams 2.
is reflected, the remaining light beam 2b is transmitted, and the reflected light beam 2a is focused on the scanning surface 9 only in the sub-scanning direction. Also, the distance a from the scanning lens 6 to the concave cylindrical half mirror 0
The sum of the distance from the concave cylindrical half mirror 0 to the scanning surface 9 is equal to f6, which is the focal length of the scanning lens 6. Therefore, the light beam 2 is focused on the scanning surface 9 regardless of the presence or absence of wobbling or surface inclination of the rotating polygon 15, and the scanning surface 9 is sub-scanned in the direction of arrow C.
Main scan the top in the six directions of the arrows.

By the way, the light beam that should be accurately focused on the scanning surface is actually curved when passing through the lens as described above, but instead of the conventional cylindrical lens, a concave cylindrical half mirror was used. The effect of reducing field curvature of the present invention when used will be explained using FIG. 2.

The rotating polygon J15 rotates the light beam 2 by 40° (±20°
), and the deflected light beam passes through an fθ lens consisting of three lenses with a focal length f6 = 544 mm, and then reaches a distance of 380 m (±19
In a scanning device that is set to perform main scanning on the scanning surface 9 that is distant from the cylindrical lens or half mirror in the range of The distance wIC from the scanning plane 9 to the imaging position at both ends of the curve is 4.7 m. Furthermore, if the rotating polygon mirror has a surface tilt of ±60'' at this time, the pitch unevenness of the scanning line will be 10 μm, and the correction accuracy of the pitch unevenness will also decrease.On the other hand, as in the present invention, the cylindrical lens If a concave cylindrical half mirror is used instead, the curvature of field will be greatly reduced to C-0.5m.Also, if the same tilting as described above occurs, the pitch unevenness of the scanning line will be reduced. The thickness is 1.4 μm, which significantly improves the accuracy of correcting patch unevenness due to one side tilt.

On the other hand, the light beam 2b transmitted through the concave cylindrical half mirror 10 is incident on a grid 11 provided on the optical path. The light beam passing through the grid 11 is focused by a focusing bar 12 provided behind the grid 11, and the focused light is detected by photodetectors 13 provided at both ends of the focusing bar. A scanning position is detected by a photodetecting means consisting of a condensing bar and a photodetector, and a synchronization signal is obtained. In the grid 11, dirt, dust, etc. can easily enter between the grids, and if this dirt or dust blocks the spaces between the grids, it may become impossible to detect the light beam at that position. However, in the scanning device of the present invention, Due to the action of the scanning lens 6 and the concave cylindrical half mirror 0, the light beam 2b incident on the grid 11 becomes an elliptical image whose longitudinal direction is parallel to the lattice of the grid 11. Even if it is attached to the grid, its detection will not be hindered. Note that the photodetection means is not limited to one consisting of a condensing bar and a photodetector as described above; for example, a photodetector consisting of a large number of photodetection elements arranged in series may be provided directly behind the grid. It may be something like this.

In this embodiment M, a cylindrical lens is used to make the light beam enter the rotating polygon mirror as a line image, but this cylindrical lens can also be replaced with a cylindrical mirror.

Furthermore, in this embodiment, the light beam that enters the rotating polygon mirror as a line image is oriented and enters the scanning lens as parallel light in the main scanning direction, but this deflected light beam is not necessarily parallel light. It is not necessary, and if the light beam is not parallel, the scanning lens is not placed at a distance of its focal length from the scanning surface, but is placed at a suitable position to focus the light beam onto the scanning surface. Just do it. Furthermore, it goes without saying that a galvanometer mirror or the like other than a rotating polygon mirror can be used as the deflector.

(Effects of the Invention) As explained above, according to the optical beam scanning device of the present invention, by using a cylindrical half mirror, wobbling and surface tilt of the deflector can be corrected, and
Since field curvature can be greatly reduced, highly accurate scanning can be performed. In addition, since a concave cylindrical half mirror is used and the reflected light from the half mirror is used for scanning, it is possible to prevent interference patterns of light beams caused by reflections on the front and back surfaces when using a cylindrical lens, as well as to prevent variations in wavelength such as those caused by semiconductor lasers. If a certain amount of light is used, chromatic aberration can be reduced. In other words, when using a cylindrical lens, it is desirable to correct chromatic aberration in both the fθ lens and the cylindrical lens, but it is not possible to configure a cylindrical lens with a length longer than the scanning length other than a single lens in order to eliminate chromatic aberration. In contrast, with a concave cylindrical half mirror, it is not necessary to correct chromatic aberration, so it is possible to obtain images of good quality. Also, from a cost perspective, cylindrical lenses use lens materials and require processing on both sides, whereas concave cylindrical half mirrors
It is sufficient to deposit a refractory film on one side, and the same focal length f
The radius of curvature R1 of the lens is R
IL=, f/2, whereas the radius of curvature R2 of the mirror
is R2 yoke 2f, and is a concave cylindrical half mirror.
It is easier to process, and costs can be reduced. Furthermore, in the past, it was necessary to provide a cylindrical lens and a half mirror to correct surface tilt and split the light beam, but with the present invention, only one cylindrical half mirror is required. Therefore, the optical system can be simplified and costs can be reduced. Furthermore, since the light beam transmitted through the cylindrical half mirror becomes a long image in the lattice direction of the grid when it enters the grid to obtain the synchronization signal,
Its practical value is extremely great, as even if dirt, dust, etc. are attached to the grid, it can be reliably detected.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an overview of a light beam scanning device according to an embodiment of the present invention, FIG. 2 is a schematic diagram for explaining field curvature of a light beam, and FIG. 3 is a conventional scanning device. FIG. 4 is a schematic diagram of the optical path of a light beam viewed from a direction parallel to the drive axis of the deflector. FIG. 4 is a schematic diagram of the optical path of a light beam in a conventional scanning device viewed from a direction perpendicular to the drive axis of the deflector. 1...Laser light source 2...Light beam 5.
...Rotating polygon 1 6...Scanning lens 9...
Scanning surface 10...concave cylindrical half mirror, 1...
Grid Figure 2 (Autopsy Procedures Amendment Letter To the Commissioner of the Patent Office, November 1982)
Patent Application No. 59-208834 dated May 8, 2008, Title of the invention: Optical beam scanning device 3, Relationship with the amended person's case Patent applicant Location: 210 Nakanuma, Minamiashigara City, Kanagawa Prefecture Name:
Fuji Photo Film Co., Ltd. 4, Agent 5-2-1-6 Roppongi, Minato-ku, Tokyo Number of inventions to be increased by the amendment None 7 Subject of the amendment ``Detailed description of the invention'' column 8 of the specification; Contents of the amendment 1) On page 14, line 20 of the specification, "on one side" is corrected to "processed on one side." 2) Page 15, line 4

Claims (1)

[Claims] On the scanning surface that is continuously sent in the sub-scanning direction at a constant speed,
In a light beam scanning device that scans a light beam that has been reflected and deflected by a deflector in the main scanning direction, the light beam emitted from a beam source is incident on the deflector as a line image perpendicular to the drive axis of the deflector. a scanning lens provided on the optical path of the light beam deflected by the deflector; and a scanning lens provided on the optical path between the scanning lens and the scanning surface, which directs the light beam passing through the scanning lens into two directions. a concave cylindrical half mirror that splits the light beam into two light beams and focuses one of the light beams on the scanning surface only in the sub-scanning direction; a grid provided on the optical path of the other light beam split by the concave cylindrical half mirror; , a light beam scanning device comprising a light detection means provided behind the grid and detecting a light beam passing through the grid.