JPS6134519A - Optical beam scanning device - Google Patents

Abstract

PURPOSE:To miniaturize a device and to realize uniform scanning even when wobbling and deviation may occur to the surface of a polygon mirror by using optical system composed of scanning lens, beam splitter, cylindrical lens, and image forming lens, etc. CONSTITUTION:When a reflecting mirror 6a shifts to the position of 6a' because of wobbling or deviation, the light route moves as shown by dotted line, but light beams is made incident on a scanning lens 5 and are as parallel beams seeing from the direction of main scanning. These parallel beams 10 are made incident on cylindrical lens 7 through 1/4 wavelength board and polarizing beam splitter 3. This lens 7 refracts the beam 10 as if it is emitted from its focal dis- tance 7', and the beam is focused by lens 8 at the one point on the scanning surface 9. Therefore, stable and uniform scanning is obtained in spite of wobbling and deviation of the polyyon mirror, and the device can be miniaturized.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of the Invention) The present invention relates to a light beam scanning device that scans a surface to be scanned with a light beam, and more particularly, the present invention relates to a light beam scanning device that scans a surface to be scanned with a light beam. The present invention also relates to an improvement in a light beam deflection system in a light beam scanning device that scans a 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 is sent (sub-scanned) in a direction perpendicular to the direction of deflection at a constant speed to scan the surface to be scanned. However, in conventional optical beam scanning devices, since the deflector is driven at high speed, wobbling occurs due to vibration, and as a result, the deflected scanning line that scans the surface to be scanned is distorted in the sub-scanning direction. As a result, there is a problem that uniform reading and recording cannot be performed. In addition, especially when a rotating polygon mirror is used as a deflector, it is not possible to make each surface of the rotating polygon mirror completely parallel to the rotation axis through highly precise processing. Even if there were such a structure, it would be difficult to do so, and there would be a problem in that each deflection/reflection surface would have a surface tilt, and this surface tilt would cause unevenness in the pitch of the scanning lines.

Furthermore, in conventional devices, a light beam with a certain width is incident on a deflector from an oblique direction and is reflected and deflected (when the deflector is at the center angle of the scan, the light beam is vertically Therefore, if the surface of a deflector capable of reflective deflection is made sufficiently thick, there is a problem in that the reflecting mirror of the deflector will inevitably become large.

(Object of the invention).

The present invention was made in view of the above-mentioned problems, and eliminates the positional deviation of the scanning line due to wobbling of the deflector and the pitch unevenness due to surface tilt, and enables uniform scanning using equally spaced parallel straight lines. Another object of the present invention is to provide a light beam scanning device equipped with a deflection system that can sufficiently reflect and deflect even if a relatively small reflecting mirror of a deflector is used.

(Structure of the Invention) The light beam scanning device of the present invention makes a light beam incident perpendicularly to the reflection mirror of the deflector when the deflector is at the center angle of scanning, and this light beam The optical system that combines a plurality of lenses provided on the optical path of the optical beam prevents the deflector from wobbling or collapsing, so that the optical beam is reflected and deflected on almost the same plane as the optical path of the optical beam. It is characterized by being able to scan parallel straight lines at equal intervals without pitch irregularities.

The light beam scanning device of the present invention first makes a linearly polarized light beam enter an input lens system, focuses it at a focusing position only in the main scanning direction, and focuses the light beam into a straight line. A light beam having a direction is incident on a polarizing beam splitter and is reflected. The surface of this polarizing beam splitter through which the reflected light beam passes has a 1/
A 4-wavelength plate is provided, and the light beam that passes through this 1/4-wavelength plate becomes circularly polarized light. Furthermore, the light beam that is focused only in the main scanning direction at the focusing position, such as a straight line, spreads out again after passing the focusing position, and becomes separated by its own focal length -1 from the focusing position on the optical path. The light incident on this person and the incident light enters a deflector installed at a distance from the scan lens in the form of a line image perpendicular to the axis of rotation of the deflector. It is reflected and deflected almost on the same plane as the beam. This reflected and deflected light beam enters the scanning lens again from the opposite direction, and then, at the focusing position, it is again focused only in the main scanning direction and linearly focused. The light beam also enters the polarized beam splitter again, and this light beam is returned to a linearly polarized light beam by the quarter-wave plate provided on the incident surface of the polarized beam splitter. Since the polarization direction of the light beam differs by 90 m from that of the light beam before entering the polarization beam splitter, the polarization beam splitter transmits this light beam. The light beam further enters a concave cylindrical lens provided at a distance from the focusing position by its own focal length, and an imaging lens provided behind the cylindrical lens that connects the focusing position and the surface to be scanned in a conjugate relationship. The surface to be scanned is then scanned.

(Embodiments) Hereinafter, a light beam scanning device of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a perspective view showing an overview of one embodiment of the present invention, and FIGS. 2(a), (b), and (C) each illustrate a part of the optical path and optical system shown in FIG. Arrow a in figure 1,
FIG. 3 is a schematic view seen from directions b and c, and is for explaining the optical path and optical system of the light beam emitted from the light source until it enters the deflector.

The light beam 10 emitted from the semiconductor laser 1 is linearly polarized in a plane that includes the optical path and is parallel to the main scanning direction, and is focused only in the main scanning direction by the incident lens system 2.
It is focused in a straight line at the focusing position indicated by A. After this light beam 10 is focused at the focusing position A-A, a light beam with a polarization direction perpendicular to the plane containing the incident reflected light is reflected, and a light beam with a polarization direction in a direction parallel to the plane is reflected. The light beam 10 enters the polarizing beam splitter 3, which has the property of transmitting the light, is reflected by the polarizing beam splitter 3 to change its optical path, and the reflected light beam 10 becomes the polarized light that passes when exiting the polarizing beam splitter 3. The 1/4 wavelength plate 4 provided on the surface of the beam splitter 3 converts the light into circularly polarized light.

Further, the light beam 10 is directed to a scanning beam provided on the optical path so that the sum of the distance from the focusing position to the reflection position of the polarizing beam splitter and the distance from this reflection position to the own position is equal to its own focal length f. The light enters the lens 5 and is focused only in the direction perpendicular to the main scanning direction onto the reflecting mirror 6a of the rotating polygon 16, which is provided at a distance of focal length f from the scanning lens 5. Therefore, a linear light beam 10 of a constant length parallel to the main scanning direction is always on the C reflection mirror 6a.
This light beam 10 is designed to be incident perpendicularly to the reflecting mirror 6a when it is at the center angle of scanning.

The light beam 10 emitted from the light source 1 in this way enters the rotating polygon mirror 6 and is deflected.
A third view of Figure 1 and Figure 1 viewed from the sub-scanning direction (direction of arrow C in the diagram) and the main scanning direction (direction of arrow a in the diagram), respectively.
With reference to FIGS. (a) and (b), the optical system and its operation until the light beam 10 reflected and deflected by the rotating polygon mirror 6 scans the surface to be scanned will be described.

First, to explain the optical path of the light beam 10 and the state of the optical system in the main scanning direction with reference to FIG. After being reflected and deflected, it enters the scanning lens 5, and from the scanning lens 5 the focal length f of this scanning lens 5.
It focuses only in the main scanning direction at each position on line B-8, which is separated by 6.

Furthermore, this light beam 10 enters the polarizing beam splitter 3 before being converged, but the light beam 10 first passes through a 1/4 wavelength plate 4 provided on the incident surface of the polarizing beam splitter 3 and becomes linearly polarized again. will be returned to. In other words, the light beam 10, which was linearly polarized in a direction perpendicular to the plane containing the incident reflected light when emitted from the light source, has its polarization direction rotated by 90 degrees, so that the polarization direction changes within the plane containing the incident reflected light. , and the polarizing beam splitter 3 splits this light beam 1
This will allow 0 to pass through. After passing through the scanning lens 5 and the polarizing beam splitter 3, the focused light beam 10 spreads out again, and its own focal length f from the focusing position is
Concave cylindrical lens 7 located far apart
incident on . This cylindrical lens 7 is shown in FIG.
) and (b), the light beam 10 is transmitted as it is in the main scanning direction, and is made into a light beam in the sub-scanning direction as if it were emitted from the focal point of the cylindrical lens 7. Therefore, in the optical path of the light beam 10 shown in FIG. 3(a), the cylindrical lens 7
only transmits the light beam 10, and the light beam 10 that passes through the cylindrical lens 7 is incident on the imaging lens 8 and then on the surface to be scanned 9. The focal length of this imaging lens 8 is f9, the distance from the line BB to the imaging lens is 81, and the distance from the imaging lens to the surface to be scanned is b, then 1/a + 1/b 71 / f9
It is placed in a position that satisfies the requirements. Therefore, the light beam 10 forms a point image on the surface to be scanned 9 and travels from 9' to 9'' on the surface to be scanned.
Repeat scanning over

By the way, as mentioned above, the rotating polygon mirror 6 often causes wobbling and surface tilting, so the system that corrects these using the optical system described above is suitable for use when optical path blurring due to wobbling and surface tilting is observed. This will be explained with reference to FIG. 3(b) as seen from the scanning direction.

The light beam 10 reflected by the rotating polygon mirror 6 enters the scanning lens 5 and the polarizing beam splitter 3.

At this time, if the rotating polygon mirror 7 is driven without tilting its surface and causing wobbling, the light beam 10 will pass through the optical path shown by the solid line in the figure. Reflection mirror 6 of rotating polygon mirror
If a is shifted to a position of 6 a', the optical path will move to the position shown by the broken line in the figure. However, both the light beam in the optical path shown by the solid line and the light beam in the optical path shown by the broken line are incident on the scanning lens 5 from the same point, which has a focal length of 11t f s (), which is the focal length of the scanning lens 5. 6 refracts the light beam on any optical path so that it becomes a parallel light beam in FIG. 3(b).

This parallel light beam 10 passes through the quarter-wave plate and the polarizing beam splitter 3, and then enters the cylindrical lens 7.

This cylindrical lens 7 refracts a light beam 10, which is parallel to the sub-scanning direction perpendicular to the scanned surface 9, so as to take an optical path as if it were a light beam emitted from its own focal point 7'. and this focal point 7' is
Since it is on line B, the light beam 10 that has passed through the cylindrical lens 7 is at the aforementioned position (1/ a + i / b =
A light beam 10 incident on an imaging lens 9 provided at an angle of 1/f s is focused on a single point on the scanning surface 9 . As seen from the direction (main scanning direction) shown in FIG. 3(b), the light beam 10 made parallel by the scanning lens 5 is used in combination with the cylindrical lens 7 and the imaging lens 8. Since the image is focused on a single point on the surface to be scanned 9, even a light beam whose optical path is shifted due to wobbling or falling can be caused to scan at the same position as a light beam that has passed through an optical path with no shift. Done, arrow C
By sub-scanning the surface to be scanned at a constant speed in the direction, it becomes possible to scan parallel straight lines at equal intervals.

In the embodiment described above, a rotating polygon mirror is used as a deflector, and its wobbling and tilting are corrected. However, even when a galvanometer mirror is used as a deflector, the wobbling of the galvanometer mirror can be corrected by the apparatus of the present invention. correction is possible.

(Effects of the Invention) As described above in detail, according to the light beam scanning device of the present invention, wobbling or falling occurs in the deflector, and as a result, the optical path of the light beam is shifted in the direction perpendicular to the main scanning direction. However, the deviation can be corrected by an optical system provided in the optical path to the surface to be scanned, and scanning can always be performed in parallel and equally spaced straight lines. Furthermore, in the present invention, by using a beam splitter, the light beam is made to enter the reflection mirror of the deflector perpendicularly when the deflector is at the center angle of scanning, so that the reflection mirror can be used effectively during deflection. can be used, and its miniaturization can be realized. In particular, the present invention allows the above-mentioned two improvements to be made using the same optical system, and has extremely great practical value.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an overview of one embodiment of the present invention, and FIG. 2 is a schematic diagram showing the optical path of the light beam from the light source to the deflector and the optical system in the actual 1sM mode shown in FIG. 1. , FIG. 3 is a schematic diagram showing the optical path of the light beam from the deflector to the surface to be scanned and the optical system in the embodiment shown in FIG. 1. 1... light if! 2...Incidence lens, system 3...Polarizing beam splitter 4...1/4 wavelength plate 5...Scanning lens 6...Rotating polygon mirror 7
...Cylindrical lens 8...Imaging lens 9.
... Surface to be scanned 10 ... Light beam (Written amendment of self-procedural procedure Mr. Commissioner of the Patent Office, October 1982, 231, Title of invention: Light beam scanning device 3, Relationship with the case of person making the amendment. Appointment of patent applicant. 210 Nakanuma, Minamiashigara City, Kanagawa Prefecture Name
Fuji Photo Film Co., Ltd. 4, Agent 6, Number of inventions increased by amendment None 7, Subject of amendment Column 8 of “Detailed Description of the Invention” of the specification, Contents of the amendment 1) Page 7 of the specification Delete line 18, "Includes optical path." 2) Correct "in parallel planes" to "in parallel directions" on the same page.

Claims (1)

[Claims] A beam light source that emits a linearly polarized light beam in a light beam scanning device that scans a light beam reflected and deflected by a deflector in the main scanning direction on a scanned surface that is continuously sent at a constant speed in the sub-scanning direction. , an input lens system provided at a position to receive this light beam and focus the light beam to a linear focusing position; /4
a polarizing beam splitter with a wavelength plate; a scanning lens provided on the optical path of the reflected light beam at a distance of its own focal length from the focusing position of the light beam; a deflector that is provided at a distance and reflects and deflects the light beam onto substantially the same plane as the optical path before it enters; a focusing position where the light beam reflected and deflected by this deflector re-enters the scanning lens and focuses it; A light beam scanning device comprising: a cylindrical lens that is separated by the focal length thereof; and an imaging lens that focuses the light beam that has passed through the polarizing beam splitter and the cylindrical lens onto a surface to be scanned. .