JPS6230006Y2 - - 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 a rotating polygon mirror or the like have a high resolution of the scanning beam and can achieve a relatively high scanning speed, and therefore are widely used in various well-known devices such as film recording devices, laser printers, television image display devices, and facsimile 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 ellipse instead of a circle, resulting in astigmatism, and as a result, 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, resulting in 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 generator, a reflection device that receives an incident light beam and moves the reflected light beam in a scanning manner, and a first focusing device that focuses the light beam that enters from the light beam generator. a second and third focusing device forming a relay system for the light beam incident from the reflection device with the reflection point of the reflection device approximately at the focal point on the incident side; A fourth focusing device has a unidirectional focusing property that focuses the incident light beam in a direction perpendicular to the scanning direction of the light beam, and a fourth focusing device has a unidirectional focusing property that focuses the incident light beam in a direction perpendicular to the scanning direction of the light beam. a fifth focusing device that focuses the light beam at a position at the image height, and causes the light beam incident from the first focusing device to pass through the fourth focusing device and the second focusing device to reach the reflection point of the reflecting device. A first focusing device is disposed above so that the light beam is focused in a direction perpendicular to the scanning direction of the light beam of the reflecting device, collimated in the scanning direction of the light beam of the reflecting device, and is incident on the reflection point of the reflecting device. , 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.

FIGS. 1a and 1b are a plan view and a front view, respectively, showing a first embodiment of the light beam scanning device of this invention. In the figure, a light beam generated by a light beam generator 1 is focused by a first focusing device 2, has its optical path bent by a mirror 9, and passes through a fourth focusing device 6 and a second focusing device 4. The light is collimated in the light beam scanning direction of the rotating polygon mirror 3, is focused in a direction perpendicular to the light beam scanning direction of the rotating polygon mirror 3, and is incident on the reflection point of the rotating polygon mirror 3, and is reflected. The light beam reflected in a scanning manner by the rotating polygon mirror 3 is
The reflection point of the rotating polygon mirror 3 is incident on the second focusing device 4 which constitutes a relay system together with the third focusing device 5, and the focal plane is then set at the same position as the focal plane of the second focusing device 4. The light beam passes through a fourth focusing device 6 having a unidirectional focusing property in a direction perpendicular to the scanning direction of the light beam of the rotating polygon mirror 3, is then collimated by a third focusing device 5, and is then focused into a fifth focusing device. The device 7 focuses the light onto the scanning surface 8 and scans the scanning surface 8 as the rotating polygon mirror 3 rotates. In the light beam scanning device of the present invention, since the second focusing device 4 and the third focusing device 5 constitute a relay system, it has unidirectional focusing ability. The light beam incident on the fourth focusing device 6, for example a cylindrical lens, is parallel to the optical axis and no field curvature occurs. Further, in the present invention, the fifth focusing device 7 focuses the incident light beam at an image height of K·θ (K is a constant) with respect to the incident angle θ. Although it is a so-called f-theta lens,
Since it is not necessary to have telecentric characteristics, in such a case, the incident position should be moved closer to the entrance of the f-theta lens, and the angle between the output beam of the maximum screen of the f-theta lens and the optical axis should be made large. It is known by those skilled in the art that the -theta lens can be designed with a small aperture, allowing the f-theta lens to have a small 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. 1b, the light beam generator 1 and the first focusing device 2 are omitted. 1st
In the front view of Figure 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, and The intervals are shown in order to explain the positional relationship of the 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. Figure 1b
As is clear from the above, the reflected beam of the rotating polygon mirror 3 is
Regardless of the inclination of the reflective surface of the rotating polygon mirror 3, the light enters the fifth focusing device 7 parallel to the optical axis, so no deviation of the scanning line occurs on the scanning surface 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. A fifth focusing device, 8 represents a scanning surface, and 9 represents a mirror.

Claims (1)

[Scope of utility model registration request] a light beam generator; a reflection device that receives an incident light beam and moves the reflected light beam in a scanning manner; a first focusing device that focuses the light beam incident from the light beam generator; and the reflection device. second and third focusing devices constituting a relay system for the light beam incident from the reflection device with the reflection point of approximately at the incident-side focal position; a fourth focusing device having a unidirectional focusing property that focuses in the vertical direction; and a fourth focusing device that focuses the incident light beam to a position on the scanning plane at an image height of K·θ (K is a constant) with respect to the incident θ. a fifth focusing device, the light beam incident from the first focusing device is passed through a fourth focusing device and a second focusing device to scan the light beam of the reflecting device on a reflection point of the reflecting device; A first focusing device is disposed such that the light beam is focused in a direction perpendicular to the direction of the light beam, and is collimated in the scanning direction of the light beam of the reflecting device so that the light beam is incident on the reflection point of the reflecting device, and the fourth focusing device is used to The second focusing device is arranged so that the beam focusing position is the same as the light beam focusing device, and the light beam reflected by the reflecting device and the second focusing device arranged as described above are connected to the second focusing device. A light beam scanning device characterized in that a light beam passes through a fourth focusing device, a third focusing device, and a fifth focusing device and is focused on a scanning surface.