JPH0625830B2 - Optical scanning device - Google Patents

Description

The present invention relates to an optical scanning device applicable to copiers, printers, facsimiles, and the like.

(Prior Art) A generally used optical scanning device uses a rotary polygon mirror. FIG. 9 shows an example of such a conventional optical scanning device. In FIG. 9, the laser light emitted from the laser light source 21 is guided to the reflecting surface of the rotary polygon mirror 27 via the beam compressor 22, the acousto-optic modulator 23, the beam expander 24, and the cylindrical lens 25. The rotary polygon mirror 27 is rotationally driven by the motor 26, reflects the laser light from the laser light source 21 side, and deflects it within a certain angle range. A toroidal lens 28 and an fθ lens 29 are arranged on the optical path reflected by the rotating polygon mirror 27,
The reflected light from the rotary polygon mirror 27 is imaged on the surface of the photosensitive drum 30. As is well known, the rotation of the rotary polygon mirror 27 causes the light beam to scan the photoconductor drum 30 in the main scanning direction, which is the direction of its rotation axis. An image information signal is carried by the acousto-optic modulator 23 on the light beam, and a predetermined image is formed on the photosensitive drum 30 by rotating the photosensitive drum 30 around its axis to perform sub-scanning. Will be recorded.

(Problems to be Solved by the Invention) According to the optical scanning device using the rotary polygon mirror as described above,
The surface tilt of each reflecting surface of the rotary polygon mirror causes unevenness in the pitch of the scanning lines in the sub-scanning direction to deteriorate the image quality. Therefore, it is required to minimize the surface tilt. Therefore, there is a problem that extremely high processing accuracy of the rotary polygon mirror is required, and a cylindrical lens and a toroidal lens are required to correct the surface tilt, which complicates the configuration of the optical system. Further, since the main scanning angle is 2θ with respect to the rotation angle θ of the rotary polygon mirror, it is necessary to increase the image signal processing speed with respect to the rotation speed of the rotary polygon mirror.
There is a problem that the efficiency of the processing time of the image signal is deteriorated, and the jitter of the drive motor is doubled.

The present invention has been made in order to solve the problems of the prior art, and in principle, there is no problem of surface tilt, and the main scanning angle becomes θ with respect to the rotation angle θ of the light deflection element. It is an object of the present invention to provide an optical scanning device capable of improving the efficiency of image signal processing time.

(Means for Solving the Problems) According to the present invention, a plurality of light deflection elements arranged around a rotation axis deflects an incident light beam parallel to the rotation axis by 90 ° and is parallel to the rotation axis at right angles. An image forming lens configured to emit as a light beam and for forming an image of the light beam emitted from the light deflecting element on an image forming surface is disposed between the light deflecting element and the image forming surface. .

(Operation) A light beam from the light source travels in parallel with the rotation axes of the plurality of light deflection elements and is emitted by the light deflection element as a parallel light beam perpendicular to the rotation axis. When the light deflection element rotates about the rotation axis, the emitted light is deflected in the main scanning direction at the same angle as the rotation angle of the light deflection element. This deflected light is imaged on the image forming surface by the image forming lens.

(Embodiment) An embodiment of the optical scanning device according to the present invention will be described below with reference to FIGS. 1 to 8.

In FIG. 1, reference numeral 3 indicates a rotary prism housing, and the rotary prism housing 3 is rotationally driven about a rotary shaft 7 by a drive motor (not shown). Windows 3a that are long in the rotational direction are formed at regular intervals on the peripheral portion of the upper surface of the housing 3, and a window 3b that is long in the rotational direction is formed on the outer peripheral surface of the housing 3 at a position corresponding to the window 3a. Are formed at regular intervals. A pentagonal prism 4 serving as a light deflecting element is formed in the housing 3 at the positions of the window holes 3a and 3b forming a pair.
Is provided.

As shown in FIG. 2, the pentagonal prism 4 has a light incident surface 4a and a light emitting surface 4d perpendicular to the light incident surface 4a, and reflects the light incident from the incident surface 4a in a direction of about 45 °. 1
And a second reflecting surface 4c for reflecting the light reflected by the reflecting surface 4b in the direction of about 45 ° and for emitting it from the emitting surface 4d. The angle α formed by the two reflecting surfaces 4b and 4c is set to about 45 °.

In FIG. 1, laser light emitted from a laser light source 1 composed of a semiconductor laser or the like is shown in FIG.
To form a parallel light flux, which travels in parallel with the rotation axis 7 of the plurality of pentagonal prisms 4 as light deflecting elements and is incident on the pentagonal prism 4. The pentagonal prism 4 deflects the incident light beam by 90 ° and outputs it as a parallel light beam perpendicular to the rotation axis 7. The recording drum 6 is arranged in front of the emitted light. The outer peripheral surface of the recording drum 6 is composed of a photoconductor,
This photoconductor surface serves as an image plane. An fθ lens 5 is disposed between the pentagonal prism 4 and the recording drum 6 for focusing the light flux emitted from the pentagonal prism 4 on the imaging surface of the recording drum 6.

Next, the operation of the above embodiment will be described.

The light beam from the laser light source 1 is collimated by the collimator lens 2 and enters a pentagonal prism 4. 5
The prism prisms 4 are attached to the rotating prism housing 3, and the pentagonal prisms 4 are also rotated about the axis 7 by the rotation of the housing 3 about the axis 7, and the incident light beam is deflected in the main scanning direction. To be done. The deflected parallel light flux passes through the fθ lens 5 and reaches the recording drum 6.

Here, the state of the light beam in the main scanning section will be seen. When the pentagonal prism 4 is rotated about the axis 7 by an angle θ from the position shown by the solid line in FIG. 3 to the position shown by the chain line 4A, the incident light beam is deflected by the angle θ in the main scanning direction and emitted. In FIG. 3, a light beam from the laser light source side enters in a direction perpendicular to the paper surface. The light flux is refracted twice when entering and exiting the pentagonal prism 4, and is reflected twice within the pentagonal prism 4. The incident angles on the refracting surface and the reflecting surface are: It does not change during the deflection. Therefore, there is no change in the energy of the light flux.

Next, the state of the light beam in the sub-scan section will be checked. The pentagonal prism 4 has static individual variations due to variations in processing accuracy and dynamic variations. Regarding the dynamic fluctuation, there are a case where the prism 4 moves in parallel as shown by a solid line and a chain line in FIG. 4 and a case where the prism 4 moves rotationally as shown by a solid line and a chain line in FIG. However, the angle formed by the two reflecting surfaces 4b and 4c of the prism 4 is 45 ° as described above, and since the incident light beam is bent at 90 ° and emitted, the prism 4 has the above-mentioned dynamic fluctuation. Even if there is, the light flux emitted from the prism 4 maintains a constant angle in the sub-scan section as shown by chain lines 9A and 9B in FIGS. 4 and 5, but there is no dynamic fluctuation in the prism 4. The emission position is only shifted as compared with the case. Therefore, the prism 4
If the light flux emitted from is parallel to the optical axis of the fθ lens 5, even if there is a dynamic change in the prism 4, the image formation of the recording drum 6 which is always the focus position of the fθ lens 5 is performed. An image can be formed at a predetermined position on the surface.
In principle, this eliminates the surface tilt of the light deflection element.

The static individual variation of the pentagonal prism 4 is
It depends on the processing accuracy of the prism prism 4. Of particular importance are the two surfaces 4b and 4c that form the internal reflection of the pentagonal prism 4.
Is the angle α formed by. If this angle α varies among the individual prisms 4, it appears as uneven pitch of the scanning lines in the sub-scanning direction. However, if the manufacturing process of the individual pentagonal prisms 4 is modified, the static variation of the individual prisms 4 can be eliminated. FIG. 6 shows an example of the manufacturing process, in which a long block which is a prism material is processed to form two surfaces 4a and 4d which become an entrance surface and an exit surface and two surfaces 4b and 4c which serve as an inner reflection surface. After that, the long block is cut into a predetermined length to obtain individual pentagonal prisms 4. 5 cut from one long block
The prism prism 4 is housed in the same prism housing 3 (see FIG. 1). By doing this, a set of pentagonal prisms 4
It is possible to reduce the variation in the angle α formed by the two reflecting surfaces 4b and 4c, and to reduce the uneven pitch of the scanning lines.

The angle formed by the incident light flux and the outgoing light flux on the pentagonal prism 4 should be 90 °. For this purpose, the angle α formed by the two reflecting surfaces 4b and 4c of the pentagonal prism 4 must be 45 °. I have to. If the angle formed by the incident light beam and the emitted light beam is other than 90 °, the scanned light beam draws a conical locus called a fan beam and the recorded image is distorted.

According to the embodiment described above, the pentagonal prism 4 is used to bend the outgoing luminous flux by 90 ° with respect to the incident luminous flux by two reflections in the sub-scanning plane. Thus, the direction of the emitted light flux is constant. Therefore, the factor of changing the angle of the light beam in the sub-scanning direction is only the variation in the angles of the reflecting surfaces of the plurality of pentagonal prisms 4. However, if the pentagonal prism 4 is manufactured by a method in which a long block is processed and then cut into a predetermined length, it is possible to eliminate variations in the individual pentagonal prisms 4 and obtain sufficient accuracy. , It is possible to extremely reduce the pitch unevenness of the scanning lines. Further, since the rotation angle of the pentagonal prism 4 is equal to the deflection angle in the main scanning direction, the processing speed of the image signal with respect to the rotation speed of the light deflection element may be slower than that of the conventional optical scanning device, and the performance can be reduced at a low cost. A high optical scanning device can be provided.

As the light deflection element, a triangular prism as shown in FIGS. 7 and 8 may be used instead of the pentagonal prism in the above embodiment. In the example of FIG. 7, one triangular prism 10 is used to bend the outgoing light beam 12 by 90 ° with respect to the incoming light beam 11. In the example shown in FIG. 8, two triangular prisms 13 and 14 are used to bend the outgoing light beam 16 by 90 ° with respect to the incoming light beam 15. In any case, a plurality of the prisms that constitute the light deflection element are used, and these prisms are attached to the rotating prism housing and driven to rotate about the shaft 7. When the triangular prism as described above is used, the stability of the swing angle is improved by bending the light beam near the minimum deviation angle.

(Effects of the Invention) According to the present invention, a plurality of light deflecting elements arranged around a rotation axis are used to deflect an incident light flux parallel to the rotation axis by 90 ° and to form a parallel light flux perpendicular to the rotation axis. Since it is configured to be emitted as, the direction of the emitted light beam is constant with respect to the dynamic fluctuation of the light deflection element, and it is possible to form an image at a predetermined position on the image forming surface by the image forming lens. It is possible to provide an optical scanning device which does not have trouble and has less unevenness of the scanning line pitch. Further, since the rotation angle of the light deflection element and the deflection angle in the main scanning direction are equal, the processing speed of the image signal with respect to the rotation speed of the light deflection element may be slower than that of the conventional light scanning device, and the cost is high and the performance is high. An optical scanning device can be provided.

[Brief description of drawings]

FIG. 1 is a perspective view showing an embodiment of an optical scanning device according to the present invention, FIG. 2 is a perspective view of an optical deflecting element in the above embodiment, and FIG.
FIG. 4 is a plan view showing the operation of the optical deflecting element in the main scanning section, FIG. 4 is a side view showing the operation of the optical deflecting element in the sub scanning section, and FIG. 5 is a sub scanning section of the optical deflecting element. FIG. 6 is a side view showing another operation of the optical deflecting element, FIG. 6 is a perspective view showing an example of a method for manufacturing the optical deflecting element, and FIG. 7 is a side view showing a modified example of the optical deflecting element applicable to the present invention. FIG. 9 is a side view showing still another modification of the light deflection element, and FIG. 9 is a perspective view showing an example of a conventional optical scanning device. 4, 10, 13, 14 ... Optical deflection element 5 ... Imaging lens, 7 ... Rotation axis, 8, 11, 15 ...
Incident light flux, 9, 12, 16 ... Outgoing light flux

Claims (1)

[Claims] 1. An optical scanning device comprising a plurality of light deflection elements arranged around a rotation axis, wherein the light deflection element deflects an incident light beam parallel to the rotation axis by 90 °. The light is emitted as a parallel light beam perpendicular to the rotation axis, and an image forming lens for forming an image of the light beam emitted from the light deflecting element on the image forming surface is arranged between the light deflecting element and the image forming surface. Optical scanning device.