JPS588B2 - Hikari Bee Mususasouchi - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved optical beam scanning device using a rotating polygon mirror.

In recent years, many devices have been developed that scan light beams such as laser beams to read and record information.

One type of optical deflector used in such devices is a rotating polygon mirror.

Even if a rotating polygon mirror is highly precisely machined, there is some error in the parallelism between the rotation axis and the reflecting mirror surface.

Since this parallelism error deflects the light beam in a direction perpendicular to the direction of light deflection by the rotating polygon mirror, the trajectories of scanning lines drawn by the light beams on the scanning surface by the respective reflecting mirror surfaces of the rotating polygon mirror do not match.

Several methods have been proposed for optically correcting the deviation of the scanning line due to the parallelism error and forming matched scanning lines.

For example, in the invention described in Japanese Patent Application Laid-Open No. 47-33642, the amount of correction for the error in parallelism of each reflecting mirror surface of a rotating polygon mirror is measured in advance and stored in a storage device, and the rotation of the rotating polygon mirror is In synchronization with this, a separately installed optical deflector for correcting parallelism error is driven by a signal from this storage device, thereby removing the deviation of the scanning line of the light beam.

This method has the disadvantage that it requires a complicated device to newly provide an optical deflector and drive it via a storage device.

Furthermore, in the invention described in JP-A No. 48-49315, two cylindrical lenses are used, and the first cylindrical lens is used to direct the light beams parallel to the plane formed by the group of light beams deflected onto the reflecting mirror surface of the rotating mirror. By forming a line image and using a second cylindrical lens to make the deflection point on the reflecting mirror surface and the scanning plane into an object point and image point relationship, deviation of the scanning line due to parallelism error is eliminated.

This method requires two cylindrical lenses, and it is not easy to set them in a predetermined relationship.Also, the light beam incident on the rotating polygon mirror is in the same plane as the plane formed by the group of deflected light beams. Therefore, if an attempt is made to increase the polarization angle, the angle of incidence of the incident light beam with respect to the reflective mirror surface must be increased, which has the disadvantage that the incident light beam is likely to be vignetted by the reflective mirror surface.

SUMMARY OF THE INVENTION An object of the present invention is to provide an improved light beam scanning device that eliminates even-oddity in the direction perpendicular to the scanning direction of the scanning line due to the parallelism error of the rotating polygon mirror.

According to the present invention, the deviation of the scanning line due to the parallelism error of the rotating polygon mirror is eliminated by using one optical element having a major axis and a minor axis having different focal lengths.

Further, according to the present invention, it is very easy to set the optical element to eliminate evenness and oddness of the scanning lines due to parallelism errors of the rotating polygon mirror.

Furthermore, according to the present invention, since it is not necessary to make the incident light beam on the rotating polygon mirror in the same plane as the plane formed by the group of deflected light beams, the angle of incidence of the incident light beam on the reflecting mirror surface can be made small. .

Therefore, the vignetting of the incident light beam can be reduced by the reflective mirror surface, and the effective deflection angle can be increased for the same incident light beam diameter; Since the diameter of the light beam can be increased, the resolution on the scanning plane can be increased.

The present invention provides a light beam scanning device including a rotating polygon mirror, an optical element having a main axis and a minor axis having different focal lengths, and an imaging optical system, in which an incident light beam is transmitted through the rotating polygon mirror by passing through the optical element. A line image perpendicular to the rotation axis is formed on the reflecting mirror surface of the mirror, and the reflected light beam from the reflecting mirror surface is passed through the optical element again, and then a light spot is imaged on the scanning surface by the imaging optical system. By arranging the light spots so that the rotating polygon mirror rotates, the beam corrects the deviation of the scanning line even if there is a parallelism error on the reflecting mirror surface when the light spot scans on the scanning surface. It is a beam scanning device.

In the present invention, an optical element having a major axis and a minor axis with different focal lengths is a general term for optical elements whose focal length in one direction is different from the focal length in a direction perpendicular to the cylindrical lens, a typical example of which is a cylindrical lens. The axis related to the short focal length is the main axis, and the axis related to the long focal length is the secondary axis.

Examples of such optical elements include, in addition to the above-mentioned cylindrical lens, anamorphic lenses, parabolic mirrors, cylindrical mirrors, and the like.

The present invention will be explained below using specific examples.

FIG. 1 is a basic layout diagram of an optical system of a first embodiment in which the present invention is applied to a laser recording apparatus.

A parallel laser light beam 10 emitted from a laser light source 100
becomes a light beam 20 that is modulated in time series by the optical modulator 110.

The light beam 20 is connected to a beam expander 12 as necessary.
A light beam 30 whose beam diameter is expanded by 0 is obtained,
It is reflected by the total reflection mirrors 130 and 140 and forms the cylindrical lens 2.
Enter 00.

The light beam 30 is a parallel light beam, but when it passes through the cylindrical lens 200, it becomes a light beam 40 that is parallel to the horizontal direction (direction parallel to the main axis 210 of the cylindrical lens 200) and focused only in the vertical direction.

Cylindrical lens 200 and reflective mirror surface 310 of rotating polygon mirror 300
is set at a focal length f1 related to the principal axis 210 of the cylindrical lens 200, and the principal axis 21 of the cylindrical lens 200 is
By setting 0 and the rotation axis 320 of the rotating polygon mirror 300 perpendicularly, the light beam 40 is focused on the reflecting mirror surface 310 and forms a line image having a length in the direction perpendicular to the rotation axis 320 of the rotating polygon mirror 300. form 50.

When rotating mirror 300 rotates in the direction of arrow 330, the reflected light beam is deflected in the direction of arrow 331.

a reflected light beam 60 at any position within the effective deflection angle;
As a special case, consider reflected light beams 60a and 60b at opposite ends of the effective deflection angle.

Reflected light beam 60 emanates from line image 50 and is parallel in the horizontal direction and diverging in the vertical direction.

However, when it passes through the cylindrical lens 200 again, it becomes a completely parallel light beam 70 (70a at both ends of the effective deflection angle).
and 70b), which is further focused by the imaging lens 400 as a light beam 80 (80a and 80b at both ends of the effective deflection angle), and a light spot is formed on the image plane at a distance of focal length f2 from the imaging lens 400. 90 (90a and 90b at both ends of the effective deflection angle).

When the rotating polygon mirror 300 rotates in the direction of the arrow 330, this light spot scans the image plane from the position 90a to the position 90b for each reflecting mirror surface of the rotating polygon mirror 300, thereby forming a scanning line 91.

A recording material 410 having a recording surface is placed on the image plane, and arrow 411
Information is recorded on this recording material 410 by the above-mentioned scanning lines.

Even if there is a parallelism error in the rotating polygon mirror 300, the deviation of the scanning line in the direction perpendicular to the scanning direction is removed by the light beam scanning device used in the laser recording apparatus described above.

Fig. 2 is a diagram for explaining in detail the state of light beam scanning in the laser recording device of Fig. 1, and Fig. 2a explains the removal of the deviation of the light beam due to the parallelism error of the rotating polygon mirror. FIG. 2 is a side view of the optical system for the purpose of the present invention, and FIG. 2 is a plan view thereof for explaining the scanning of the light beam.

In the side view of FIG.
This results in a light beam 40 that is focused upwards.

The light beam 60 reflected from the reflecting mirror surface 310 and diverging is caused by the parallelism error of the rotating polygonal mirror 300.
If the beam is tilted as shown at 0', it will be deflected in the direction of reflection and will be generated at the position of the light beam 60'.

These reflected light beams 60 and 60' pass through the cylindrical lens 200 again to become parallel light beams 70 and 70'.

Moreover, since the light beams 70 and 70' are parallel to each other, a light spot can be imaged at the same position 90 on the image plane at a distance of focal length f2 by the imaging lens 400, and this image plane In the above, the deviation of the scanning line in the direction perpendicular to the scanning direction due to the parallelism error of the rotating polygon mirror 300 is removed.

In the plan view of FIG. 2, the light beam 40 after the parallel light beam 30 passes through the cylindrical lens 200 is also parallel;
The light beams 60 (60a and 60b at both ends of the effective deflection angle) reflected by the reflective mirror surface 310 are also parallel.

Furthermore, this light beam 70 (70a and 70b at both ends of the effective deflection angle) passes through the cylindrical lens 200 again.
) are also parallel.

However, since the incident angle of the light beam 70 to the imaging lens 400 differs depending on the deflection angle, the position 90 of the light spot imaged on the image plane at a distance of focal length f2 from the imaging lens 400 is determined by the deflection angle. It depends.

Therefore, by rotating the rotating mirror 300 in the direction of the arrow 330, the light spot 90 on the image plane for each reflecting mirror surface moves between the positions 90a and 90b at both ends of the effective deflection angle as indicated by the arrow 330.
Scan repeatedly in the 2 directions.

In this embodiment, as shown in FIG. 2a, a rotating polygon mirror 300
Since the light beam 40 directed to is not perpendicular to the rotation axis 320 of the rotating polygon mirror 300, an angle α is created between the incident light beam 40 and the reflected light beam 60 (the value of α is determined by the reflection of the rotating polygon mirror 300). If there is a parallelism error on the mirror surface, it will be slightly distorted).

Further, when the value of α becomes large, the deflected beam 70 passes through the periphery of the imaging lens 400.

Therefore, the deflected light beam 70 is at both ends 7 of the effective deflection angle.
There is a possibility of being eclipsed by the imaging lens 400 in the vicinity of 0a and 70b, or receiving large aberrations around the imaging lens 400.

In this case, it is preferable to install the imaging lens at a position of 400' and use the central part of the imaging lens 400.

FIG. 3 is a side view of a second embodiment in which a light beam deflected by a rotating polygon mirror passes through a plane including the optical axes of a cylindrical lens 200 and an imaging lens 400.

In this case, the rotation axis 320 of the rotating polygon mirror 300 is tilted by α/2 with respect to the vertical direction as shown in the figure.

Then, the light beam 40 directed toward the reflective mirror surface 310 of the rotating polygon mirror 300 and the reflected light beam 60 form an angle α (α
If the reflecting mirror surface of the rotating polygon mirror 300 has a parallelism error such as 310/, the reflected light beam will be 60'.
)

The reflected light beam 60 that is deflected by the rotation of the rotary polygon mirror 300 is within a plane that includes the optical axis of the cylindrical lens 200, and the light beam 70 that has passed through the cylindrical lens 200 and has become parallel is also reflected by the imaging lens 400. is deflected in a plane that includes the optical axis of.

The light beam 70 is directed from the imaging lens 400 to its focal length f2
A light spot 90 is focused on the image plane at a distance of .

Since the reflecting mirror surface is tilted at 310', there is a parallelism error, and even if the reflected light beam is generated at the 60' position, a light spot is generated at the 90' position on the image plane, resulting in scanning of the scanning line due to the parallelism error. Similar to the first embodiment, the deviation in the direction perpendicular to the direction is removed.

In this embodiment, the light beam deflected by the rotation of the rotating polygon mirror 300 is transmitted through the cylindrical lens 200 and the imaging lens 40.
Since it is in a plane that includes the optical axis 0, it is less susceptible to the effects of aberrations of these lenses, and the deflected light beam can be prevented from being eclipsed by the imaging lens 400.

FIG. 4 is a side view of a third embodiment in which the light beam 40 directed toward the rotating polygon mirror 300 is perpendicular to the rotation axis 320 of the rotating polygon mirror 300.

In this case, the parallel light beam 30 is reflected by the semi-transparent mirror 141 and further passes through the cylindrical lens 200 to be incident at right angles to the rotation axis 320 like the light beam 40.

The light beam 60 reflected by the reflective mirror surface 310 travels in the opposite direction to the light beam 40 and passes through the semi-transparent mirror 141, becoming a parallel light beam 70 and forming a light spot 90 on the image plane by the imaging lens 400. form.

The manner in which the deviation in the scanning direction of the scanning line due to the parallelism error of the rotating polygon mirror 300 is removed is the same as in the previous two embodiments.

In this embodiment, the light beam reflects and passes through the semi-transparent mirror 141 once each before reaching the image plane, so the amount of light used is typically reduced to 1/4, but the light beam always passes through the cylindrical lens 200 and the image forming surface. Since the light passes through a plane that includes the optical axis of the lens 400, it has the advantage of being less susceptible to the effects of aberrations of these lenses.

In the three embodiments described so far, a cylindrical lens was used as an optical element having a major axis and a minor axis with different focal lengths, but any optical element that meets the above definition can be used in the present invention. can.

FIG. 5 is a diagram for explaining an optical system of a fourth embodiment using an anamorphic lens as an optical element having a major axis and a minor axis having different focal lengths.

Fig. 5a is a side view thereof, and Fig. 5a is a plan view thereof.

Optical element 20 having major and minor axes with different focal lengths
0, consider an anamorphic lens with focal lengths fl and f1' associated with the major and minor axes, respectively.

According to the above definition, fl<f,' f1'=f1+a1 (al>O) (1).

The main axis of the anamorphic lens 200 is rotated by a polygon mirror 3.
The reflective mirror surface 3 of the anamorphic lens 200 and the rotating polygon mirror 300
10 is set equal to the focal length f1 relative to the principal axis of the anamorphic lens 200.

Parallel beam 30 as depicted in the side view of Figure 5a
is a rotating polygon mirror 3 using an anamorphic lens 200.
00 is focused onto the reflective mirror surface 310.

The light beam 60 reflected and deflected by the rotating polygon mirror is
By passing through the anamorphic lens 200 again, a parallel light beam 70 is formed and leaves the anamorphic imaging lens 400 with a focal length f2' related to its minor axis.
A light spot 90 is imaged onto the image plane at a distance of .

Even if there is a parallelism error in the rotating polygon mirror and the reflecting mirror surface is tilted like 310', the reflected light beam 60' becomes a parallel light beam 70' when it passes through the anamorphic lens 200, which is a parallel light beam 70'. Since it is also parallel to the beam 70, it is focused on the same position as the light spot 90 on the image plane, and the deviation in the direction perpendicular to the scanning direction of the scanning line due to the parallelism error of the rotating polygon mirror is eliminated.

In the plan view of FIG. 5, the parallel light beam 30 passes through the anamorphic lens 200 and becomes the slowly converging light beam 40, and the light beam reflected and deflected by the rotating polygon mirror is reflected from the reflective mirror surface 310 into the al focused at a distance of

Now, if the reflected light beams at both ends of the effective deflection angle are 60a and 60b, they are focused on points a and b, respectively.

When light beams 60a and 60b pass through anamorphic lens 200, they form virtual image points a' at points a and b, respectively.
and b', resulting in light beams 70a and 70b that diverge.

If the positions of virtual image points a' and b' are set to the distance a2 in front of the anamorphic lens 200, the following relationship holds.

Light beams 70a and 70b have a focal length f2 relative to the principal axis of anamorphic imaging lens 400;
When the distance between the anamorphic lens 200 and the imaging lens 400 is a2', the focal length f2. By selecting f2', light spots 90a and 90b are formed on the image plane.

In this embodiment, the rotation direction 330 of the rotating polygon mirror 300 and the scanning direction 332 on the image plane are opposite to each other.

Fig. 6 shows an optical system using a reflective optical element as an optical element having a main axis and a sub-axis with different focal lengths, and Fig. 6a shows a fifth embodiment using a parabolic cylindrical mirror. FIG. 6 is a side view of a sixth embodiment using a cylindrical mirror.

In FIG. 6a, when a parallel light beam 30 is made incident parallel to the optical axis of the parabolic tube mirror 200, the light beam 40 reflected from the parabolic tube mirror 200 forms a line image 50 at its focal point.

If the distance between the parabolic tube mirror 200 and the reflecting mirror surface 310 of the rotating polygon mirror 300 is arranged so that the focal length f1 of the parabolic tube mirror 200 is reached, the light beam 60 reflected by the reflecting mirror surface 310 will be reflected by the parabolic tube mirror. 200 and becomes a parallel light beam 70 parallel to the optical axis of the parabolic tube mirror.

The light beam 70 is passed through the imaging lens 400 to its focal length f
A light spot 90 is imaged onto the image plane at a distance of 2.

Even if there is a parallelism error in the reflecting mirror surface 310 and the light beam 60' reflected there is shifted from the light beam 60, the light beam 70' reflected by the parabolic cylinder mirror is parallel to the light beam 70. The light beam becomes a light beam, and a light spot is imaged at a position 90 on the image plane by the imaging lens 400, thereby eliminating the deviation of the scanning line in the direction perpendicular to the scanning direction due to the parallelism error of the rotating polygon mirror 300.

In this embodiment, the angle α between the incident light beam 40 and the reflected light beam 60 on the reflective mirror surface 310 may be large.

If the distance between the cylindrical mirror 200 and the reflecting mirror surface 310 in FIG. 6 is arranged so as to match the focal length of the cylindrical mirror 200, it will be the same as in the case of the embodiment using the parabolic cylindrical mirror explained in FIG. 6a. By doing so, it is possible to remove the deviation of the scanning line in the direction perpendicular to the scanning direction due to the parallelism error of the rotating polygon mirror.

In this embodiment, the light beam 40 incident on the reflective mirror surface 310
Since the angle α between the cylindrical mirror 2 and the reflected light beam 60 is small, the cylindrical mirror 2
It is necessary to use only the vicinity of the optical axis of 00.

In the above description, the light beam incident on the light beam scanning device of the present invention is a parallel light beam, but such a light beam is created by various known light sources and optical systems.

Further, this incident light beam does not necessarily have to be a parallel light beam.

For example, instead of starting a parallel beam of light into an optical element having major and minor axes of different focal lengths, the parallel beam of light passes through an imaging optics to form a spot on an image plane. It is also possible to allow a beam to enter.

To do this, an arbitrary light beam is converged at a position separated by its focal length from the imaging optical system, and then the parallel light beam is made incident on the optical element by passing it through the imaging optical system. I can do it.

Further, the position where the light beam is converged can be adjusted to an appropriate position by using a reflecting mirror.

As is clear from the six embodiments described above, according to the present invention, even if there is a parallelism error in the rotating polygon mirror, the deviation in the direction perpendicular to the scanning direction of the scanning line can be removed.

Moreover, in the present invention, only one optical element having a main axis and a sub-axis with different focal lengths needs to be used, so the optical system is simplified and inexpensive.

Furthermore, in the device using two cylindrical lenses described in JP-A No. 48-49315, each of the two cylindrical lenses is installed at a position and orientation determined in relation to the reflecting surface of the rotating polygon mirror. In contrast, in the present invention, only one optical element having a main axis and a sub-axis with different focal lengths needs to be installed at a position and orientation determined in relation to the reflecting mirror surface of the rotating polygon mirror, and the optical system The settings become easier.

Furthermore, in the device described in JP-A-48-49315, since the incident light beam to the rotating polygon mirror is in the same plane as the deflecting plane, the angle of incidence of the incident light beam with respect to the reflecting mirror surface is However, in the present invention, the incident light beam to the rotating polygon mirror does not need to be in the same plane as the deflecting surface, so the incident angle beam is easily vignetted by the reflecting mirror surface. The angle of incidence of the light beam on the reflecting mirror surface can be made small,
Therefore, the vignetting of the incident light beam due to the reflective mirror surface can be reduced.

This means that for the same incident light beam diameter, the effective deflection angle can be made larger when using the present invention, and for the same effective deflection angle, when using the present invention, the effective deflection angle can be made larger. Since the diameter of the incident light beam can be increased, the resolution on the image plane can be increased.

As described above, the light beam scanning device of the present invention is significantly improved over the conventional one, and its practical value is extremely high.

[Brief explanation of the drawing]

FIG. 1 is a layout diagram of the optical system of the first embodiment of the present invention, and FIG.
Figures a and b are a side view and a plan view, respectively, showing the state of the light beam in the first embodiment of the present invention, and Figure 3 shows the state of the light beam in the second embodiment of the present invention. Side view, 4th
The figure is a side view showing the state of the light beam in the third embodiment of the present invention, and FIGS. 5a and 5b are side views showing the state of the light beam in the fourth embodiment of the invention. Plan, 6th
Figure a is a side view showing the state of the light beam in the fifth embodiment of the present invention, and Figure 6 is a side view showing the state of the light beam in the sixth embodiment of the present invention. 100: Light source device, 200: Optical element having a main axis and a sub-axis with different focal lengths, 300: Rotating polygon mirror, 400
: Imaging optical system.

Claims (1)

[Claims] 1. In a light beam scanning device including a rotating polygon mirror, an optical element having a main axis and a minor axis with different focal lengths, and an imaging optical system, an incident light beam is reflected by the rotating polygon mirror by passing through the optical element. A line image perpendicular to the rotation axis is formed on the surface, and the reflected light beam from the reflecting mirror surface is passed through the optical element again, and then a light spot is imaged on the scanning surface by the imaging optical system. A light beam scanning device characterized in that each of these is arranged.