JPS6226733Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to an optical scanning device, and in particular, in an optical beam scanning device that uses a rotating polygonal mirror or the like to reflect a scanning beam, the eccentricity of the rotational axis of the rotating polygonal mirror and the shift of the mirror surface relative to the axis center. The present invention relates to a light beam scanning device including means for optically correcting deviation of a scanning line due to parallelism error.

Optical beam scanning devices using rotating polygon mirrors have a high scanning beam resolution ability and can obtain relatively high scanning speeds, so they are used in film recording devices, laser printers, television image display devices, facsimile devices, etc. It is widely used in various known devices.

In such a light beam scanning device, the spot movement in the direction perpendicular to the scanning line is required to be approximately ±5% to ±10% of the scanning line pitch in view of image quality. For this reason, it is required that the sum of the parallelism error of the mirror surface and the eccentricity error of the rotating shaft with respect to the axis of the rotating polygon mirror is within ±several seconds. A parallelism error of ±several seconds is the limit of current processing technology for polygon mirrors, which results in a very expensive polygon mirror, and if you add in the eccentricity error of the rotation axis of the polygon mirror, it exceeds the allowable error. Several correction devices have been proposed to eliminate such difficulties. Among them,
For example, a method of optically correcting
No. 49315 and Japanese Unexamined Patent Publication No. 48-98844, the devices disclosed in these documents have a restriction that the light beam incident on the correction cylindrical lens must be substantially parallel to the optical axis. This is because when a light beam is incident on a cylindrical lens obliquely with respect to the optical axis, the tangential line of the cylindrical lens by the light beam becomes an elongated circle instead of a circle, resulting in astigmatism, resulting in the curvature of the image plane of the cylindrical lens. This is because the image plane of the condensing lens does not coincide with the image plane of the condensing lens, and therefore the desired converging diameter cannot be obtained. For this reason, in the case of a configuration in which the reflected beam from the rotating polygon mirror is directly incident on the cylindrical lens, the deflection angle of the reflected beam from the rotating polygon mirror becomes extremely small, which has the disadvantage that the scanning line length cannot be made long. Ta. In addition, in the case of a configuration in which the reflected beam from a rotating polygon mirror is incident on a cylindrical lens via a focusing lens, the output light from the focusing lens must be approximately parallel to the optical axis, so the scanning line length must be made long. If this is to be done, the apertures of the focusing lens and cylindrical lens must be made as large as the scanning line length. Such a large-diameter focusing lens has the drawback of being very expensive and practically difficult to manufacture.

The purpose of this invention is to provide a means for optically correcting the deviation of the scanning line using a combination of inexpensive lenses that are usually easily obtained, and to eliminate the drawbacks of the conventional device described above. An object of the present invention is to provide a light beam scanning device that achieves the above goals.

According to this invention, there is provided a light beam generating device, a reflecting device that receives an incident light beam and moves the reflected light beam in a scanning manner, and a reflecting device that directs the incident light beam from the light beam generating device to a reflection point of the reflecting device. a first focusing device that focuses in a direction perpendicular to the scanning direction of the light beam of the reflecting device and collimates in the scanning direction of the light beam of the reflecting device; second and third focusing devices forming a relay system for the light beam incident from the reflecting device; and unidirectional focusing for focusing the incident light beam in a direction perpendicular to the light beam scanning direction of the reflecting device. and a fifth focusing device that focuses the incident light beam at an image height of K·θ (K is a constant) on the scanning plane with respect to the incident angle θ, The fourth focusing device is arranged so that the light beam focusing position of the fourth focusing device is the same as the light beam focusing position of the second focusing device, and the light beam reflected by the reflecting device is A light beam scan characterized in that the light beam passes through a second focusing device, a fourth focusing device, a third focusing device, and a fifth focusing device arranged as described above and is focused on a scanning surface. A device is obtained.

With this invention, a light beam scanning device can be obtained which has a function of correcting the vertical deviation of the scanning line and can scan a long scanning line length by using a combination of small-diameter lenses.

Next, this invention will be explained in detail with reference to the drawings.

Figures a and b are a plan view and a front view, respectively, showing a first embodiment of the optical beam scanning device of this invention.
In the figure, a light beam generated by a light beam generator 1 is passed through a rotating polygon mirror 3 by a first focusing device 2.
The light is collimated in the light beam scanning direction of the rotating polygon mirror 3, and is focused and reflected in the direction perpendicular to the light beam scanning direction of the rotating polygon mirror 3, on the reflection point of the rotating polygon mirror 3. The light beam reflected in a scanning manner by the rotating polygon mirror 3 is incident on the reflection point of the rotating polygon mirror 3 into a second focusing device 4 that constitutes a relay system together with a third focusing device 5, and then passing through a fourth focusing device 6 having a focal plane at the same position as the focal plane of the second focusing device 4 and having unidirectional focusing in a direction perpendicular to the light beam scanning direction of the rotating polygon mirror 3; Next, it is collimated by the third focusing device 5, focused on the scanning surface 8 by the fifth focusing device 7, and scanned on the scanning surface 8 as the rotating polygon mirror 3 rotates. In the light beam scanning device of the present invention, the second focusing device 4
and the third focusing device 5 constitute a relay system, so that the light beam incident on the fourth focusing device 6, which is a cylindrical lens, for example, has a unidirectional focusing property.
It is parallel to the optical axis, and there is no curvature of the image plane. or,
In the present invention, the fifth focusing device 7 adjusts the incident light beam to K·θ (K is a constant) with respect to the incident angle θ.
This is a so-called f-theta lens, which focuses the image at a position with an image height of It is known to those skilled in the art that the aperture of the f-theta lens can be designed to be small by increasing the angle formed between the output beam with the maximum angle of view and the optical axis, and the f-theta lens can be made small in aperture. Further, by appropriately shortening the focal lengths of the second focusing device 4 and the third focusing device 5 that constitute the relay system, the aperture of the fourth focusing device 6 can be made small. In the front view of FIG. b, the light beam generator 1 and the first focusing device 2 are omitted. In the front view of FIG. b, in order to explain the correction of the deviation of the scanning line, the optical path of the light beam when the reflective surface of the rotating polygon mirror 3 is tilted with respect to the rotation axis is shown as a dotted line.
Also, intervals are shown to explain the positional relationship between the second focusing device 4, the third focusing device 5, the fourth focusing device 6, and the fifth focusing device 7.

In the figure, f ₂ , f ₃ and f ₄ represent the focal length of the second focusing device 4, the third focusing device 5 and the fourth focusing device 6, respectively. As is clear from FIG. b, the reflected beam from the rotating polygon mirror 3 is incident on the fifth focusing device 7 parallel to the optical axis, regardless of the inclination of the reflecting surface of the rotating polygon mirror 3, so that the scanning surface No deviation of the scan line occurs on 8.

[Brief explanation of the drawing]

Figures 1a and 1b are a plan view and a front view, respectively, showing a first embodiment of this invention. In the figure, 1 is a light beam generator, 2 is a first focusing device, 3 is a rotating polygon mirror, 4 is a second focusing device, 5 is a third focusing device, 6 is a fourth focusing device, and 7 is a rotating polygon mirror. The fifth focusing device, 8, each represents a scanning plane.

Claims (1)

[Scope of utility model registration request] a light beam generator; a reflector that receives an incident light beam and moves the reflected light beam in a scanning manner; and a reflector that directs the incident light beam from the light beam generator onto a reflection point of the reflector. a first focusing device that focuses in a direction perpendicular to the light beam scanning direction and collimates in the light beam scanning direction of the reflecting device; second and third focusing devices forming a relay system for the light beam; and a fourth focusing device having unidirectional focusing ability to focus the incident light beam in a direction perpendicular to the light beam scanning direction of the reflecting device. and a fifth focusing device that focuses the incident light beam at an image height of K·θ (K is a constant) on the scanning plane with respect to the incident angle θ, and the fourth focusing device The light beam focusing position is arranged to be the same as the light beam focusing position of the second focusing device, and the light beam reflected by the reflecting device is transferred to the second focusing device arranged as described above. , a fourth focusing device, a third focusing device, and a fifth focusing device, and the light beam is focused on a scanning surface.