JP3205374B2 - Optical scanning device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning device, and more particularly, to an optical scanning device capable of improving optical scanning efficiency and optical scanning density.

[0002]

2. Description of the Related Art As an optical scanning device, a semiconductor laser is generally used as a light source, and optical scanning is performed using a rotating polygon mirror such as a polygon mirror, a galvano mirror, a hologram disk or the like as an optical deflecting means.

In order to increase the speed of image formation and reading of such an optical scanning device, a method of increasing the rotation speed of a light deflecting means is generally known. Such a method has a problem in that a large torque is required for a motor used for rotation, and durability of a bearing at high speed rotation is problematic, and thus is not suitable for a small optical scanning device.

Accordingly, Japanese Patent Application Laid-Open Nos. 54-158251, 57-54914 and 57-549 have been disclosed.
As disclosed in Japanese Patent No. 23913 or the like, a plurality of semiconductor lasers and a semiconductor laser having a plurality of light emitting points (hereinafter, referred to as a multi-beam semiconductor laser) are independently driven and controlled, and the rotation of the optical deflector is performed. In some cases, the light scanning efficiency is increased by simultaneously scanning a plurality of light beams to form and read images at high speed. According to such an optical scanning device, the size of the entire system can be reduced.

However, the conventional technique of scanning a plurality of light beams has the following problems when forming and reading an image at a high density. That is, when using the plurality of semiconductor lasers described above, each semiconductor laser must be accurately arranged in a row according to the recording density. In this case, the optical characteristics (optical output, optical output, If the radiation angles, astigmatism, etc.) are not uniform, there is a drawback that a plurality of luminous fluxes will vary.

When a multi-beam semiconductor laser having a plurality of light emitting points is used, the distance between the elements constituting each light emitting point is set to a constant distance (for example, about 0.1 mm) in order to avoid thermal interference. There is a drawback that the following cannot be performed, and therefore, it is not easy to cope with an increase in the density of an image. For this reason, for example, in the case of image formation, there is a disadvantage that the light emitting points arranged in a row must be inclined with respect to the scanning direction, and the light emitting timing of each light emitting point must be shifted to form an image.

Further, an optical scanning device using an optical deflecting means is:
Generally, since it is a magnifying optical system, a laser beam of several μm at a light emitting point is expanded to several tens μm to several hundred μm on a scanning surface. The placement error is enlarged on the surface. For this reason, there is a disadvantage that a high-accuracy placement technique is required.

[0008] The above disadvantages are caused by using a plurality of semiconductor lasers or a semiconductor laser having a plurality of light emitting points.

[0009]

In an optical scanning device, it is generally desired to perform high-speed and high-density image formation and reading.

However, as described above, in the conventional apparatus for optical scanning with one scanning line, the optical scanning efficiency is low, and it is difficult to increase the speed of image formation and reading. With an optical scanning device using a multi-beam semiconductor laser, it has been difficult to increase the density of image formation and reading.

The present invention solves the above-mentioned drawbacks of the prior art, and can simultaneously improve the optical scanning efficiency and the optical scanning density, thereby reducing the size of the apparatus and greatly reducing the cost. It is an object of the present invention to provide an optical scanning device capable of performing the above.

[0012]

An optical scanning device according to the present invention comprises:
A laser light source that emits laser light, an optical modulator that turns on and off the optical output of the laser light source, a front hologram that diffracts the laser light emitted from the laser light source, and swings the front hologram A rotating hologram disk having a plurality of holograms in the circumferential direction for diffracting the laser light diffracted by the front hologram, and a scanning surface on which the laser light diffracted by the rotating hologram disk is scanned with the door, front location hologram, a plurality of diffracted light having an emission angle at which the phase different from each other emitted from said rotary hologram disk is exchange the scanning surface
It is swung so as to scan each other , thereby achieving the above object.

[0013]

Preferably, DFB is used as the laser light source.
A semiconductor laser having a single longitudinal mode in a use temperature range such as a laser or a DBR laser is used, and the power of the semiconductor laser is directly driven by the optical modulator to turn on the optical output.
/ OFF.

Preferably, the rotating hologram data is
Post-hologram in the optical path of the diffracted light diffracted by the disk
Is provided.

Preferably, the hologram of the front hologram and the hologram of the rotating hologram disk have interference fringes in which an object wave and a reference wave are respectively recorded by mutual interference of spherical waves.

[0017]

According to the above arrangement, scanning of a plurality of diffracted light beams can be simultaneously performed by one rotation of the rotating hologram disk for the following reason.

First, when light emitted from a semiconductor laser, which is a laser light source, is incident on a front hologram, which is a fixed hologram, incident light is emitted at a certain diffraction angle in accordance with the pitch of the front hologram. At this time, if the angle of the front hologram is changed in a direction perpendicular to the optical axis with respect to the plane including the hologram, the emission angle also changes. At the same time, the angle at which the light emitted from the front hologram enters the rotating hologram disk also changes. That is, the light emitted from the rotating hologram disk also changes the diffraction angle.

As described above, by changing the angle of the front hologram, the diffracted light from the rotating hologram disk can be changed. That is, when the position of the front hologram is periodically fluctuated with the same amplitude and the rotating hologram disk is rotated, the laser light also changes with a constant amplitude and period on the scanning surface.

[0020]

[0021]

[0022]

[0023]

[0024]

[0025]

[0026]

[0027]

[0028]

[0029]

[0030]

[0031]

[0032]

[0033]

Embodiments of the present invention will be described below.

FIG. 1 shows a laser beam printer according to an embodiment of the present invention. The laser beam printer 1 includes a semiconductor laser 3 and a pattern, characters,
And a drive control circuit 2 driven by a recording signal of a figure or the like. A hologram disk (rotating hologram disk) 4 is rotatably provided on the front surface of the semiconductor laser 3 and scans a laser beam from the semiconductor laser 3 by its rotation operation.

The drive control circuit 2, the semiconductor laser 3, and the hologram disk 4 constitute an exposure device of the laser beam printer 1.

In addition, this laser beam printer 1
The photosensitive drum 5 is provided on the side where the laser beam from the semiconductor laser 3 is emitted from the hologram disk 4. Around the photosensitive drum 5, a charger 6, a static eliminator 7, and a cleaner 8 are provided.

In this laser beam printer 1,
An electrostatic latent image is formed on the photosensitive drum 5 using a photoconductive phenomenon caused by a laser beam scanned by the hologram disk 4. In this embodiment, a negative latent image is formed, and an image portion to be obtained is exposed.

The laser beam printer 1 further includes a developing unit 9 and a transfer unit 10 around the photosensitive drum 5.
Further, a fixing device 11 is provided downstream of the transfer device 10 (downstream of the recording paper 50 in the conveying direction). The developing device 9 forms a toner image by depositing the toner 51 on the photosensitive drum 5, and the transfer device 10 transfers the toner image to the recording paper 50 conveyed to this position. The recording paper 50 to which the toner image has been transferred is conveyed to the position of the fixing device 11, where the fixing process is performed. The recording paper 50 on which the toner image has been fixed is discharged outside the apparatus.

FIG. 2 shows an optical system of the laser beam printer 1. On the front surface of the semiconductor laser 3, there is provided a collimator lens 14 for converting a laser beam emitted from the semiconductor laser 3 into a parallel beam. A hologram (front hologram) 41 is provided behind the collimating lens 14.
The hologram 41 diffracts the incident laser light and makes the diffracted light incident on the hologram disk 4 at a predetermined incident angle.

The hologram disk 4 is formed by arranging a plurality of arc-shaped holograms 12 in the circumferential direction of a disk-shaped substrate 13. The center of the substrate 13 is connected to the output shaft of the motor 7 and is rotated around the central axis by the rotation of the motor 7. The rotation direction of the substrate 13, ie, the holograms 12, 12,... Changes the diffraction direction of the incident laser light. Therefore, the laser beam is scanned as the hologram disk 4 rotates.

The scanning light beam 44 scanned by the hologram disk 4 is reflected by the mirror 42, subsequently enters the hologram 43 provided later, is diffracted again and condensed on the photosensitive drum 5, which is the scanning surface. . The optical characteristics such as the bending of the scanning line 6 focused on the line on the photosensitive drum 5, the pitch with respect to the rotation angle (constant speed of the scanning line), the spot diameter of the laser beam, etc. 43 are determined by the overall characteristics of the three holograms. Specifically, the spherical waves (specifically, the positions of the reference light and the object light), which are the reference wave and the object wave, are obtained by optimizing the positions using the computer hologram. Can be In this embodiment, as typical optical characteristics, the scanning width is 210 mm, the scanning line bending is ± 0.2 mm, and the laser beam spot diameter is 80 μm.
m is selected.

When the post-hologram 43 is provided as described above, the functions can be shared among the three types of holograms 41, 12, and 43.
Reference numerals 2 and 43 may be basically fringes due to interference of two light beams of a spherical wave or a plane wave or concentric fringes, and do not require a complicated aberration wave. Therefore, there is an advantage that the production of the hologram becomes easy and the cost can be reduced.

Also, at least the holograms 41 and 12
If the object wave and the reference wave each have interference fringes recorded by mutual interference of spherical waves (divergence or convergence), the fabrication is also easy in this respect, which can greatly contribute to cost reduction.

Further, when a semiconductor laser having a single longitudinal mode within a working temperature range such as a DFB laser (distributed feedback laser) or a DBR laser (distributed reflection laser) is used as the semiconductor laser 3, high-speed direct Since the oscillation spectrum width has a very narrow characteristic under modulation, there is an advantage that the scanning density can be improved.

The hologram 41 is oscillated by an actuator 41c whose details are shown in FIG. That is, the holder 41a on which the hologram 41 is formed is swingably supported around a rotation shaft 41b connected to one end thereof. An actuator 41 is provided at an end of the hologram 41 on the opposite side to the rotation axis 41b.
c is attached. With such a configuration, when the actuator 41c is driven, the hologram 41 moves by L in the illustrated x direction.

FIG. 3B shows an xz section in an xyz three-dimensional orthogonal coordinate system whose direction is shown in FIG. 3A. In FIG. 3B, light incident on the hologram 41 at an incident angle θ _in is output from the hologram 41 by an output angle θ.
_out , and subsequently incident on the hologram 12 to output θ _out ″
Then, the light is reflected by the mirror 42 and reaches the scanning surface of the photosensitive drum 5.

Here, when the actuator 41c is driven, the hologram 41 is displaced from the position A shown in the drawing to the position B. At this time, since the incident angle θ _in is constant, the output angle from the hologram 41 _changes from θ _out to θ with the displacement L.
_out '. Further, the angle θ _out ′ incident on the hologram 12 also changes, and the output angle θ _out ″ from the hologram 12 changes.
Therefore, the position change on the scanning surface after being reflected by the mirror 42 changes from A ′ to B ′.

In the above configuration, the actuator 41
If the movement amount L of c is smoothly changed, the scanning line 6 on the scanning surface can also be moved up and down smoothly. FIG. 4 shows the movement of the scanning line 6 at this time in detail .

Next, when the hologram 41 is changed (swung) by sin function, method input of a recording signal to the scanning optical system that moves by sin function even on the scanning lines 6, i.e., how to hologram recording signal Whether the scanning light is divided into a plurality of scanning lights by one rotation of 41 will be specifically described. FIG. 5 shows a system configuration of the scanning optical system. The operation will be described below.

First, data consisting of patterns, figures, characters, and the like is input to an interface circuit 20 provided in the laser beam printer 1. The input data is processed by the interface circuit 20. Specifically, this data processing analyzes character and graphic data, generates data (DATA) for each scan (one line), and generates a signal (SYNC) for synchronizing the writing start of one line. The generated data is sent to the modulator 21 and the generated signal bar S
YNC is input to the drive circuit 22 of the actuator 41c.

The actuator 41c is driven according to a SYNC signal applied to the drive circuit 22. Thereby, the hologram 41 is swung, and finally the scanning line 6
Changes on the scanning plane as shown in FIG. At this time, the waveform for driving the actuator 41c is the above-described and illustrated sin function, and the amplitude of the sin function is A ₁ and the angular frequency is ω ₁ . The sin function is also input to a quantization circuit 23 that generates a latch signal (LATCH) when the phase is 90 ° or 270 ° based on this waveform. The latch signal LATCH is provided to the modulator 21.

Now, the n-th DATA of the signals output from the interface circuit 20 is
.. Related to N / OFF, and similarly, the (n + 1) th DATA is represented by a binary number 1011110.

The modulator 21 internally has a circuit for generating a clock signal having a cycle (twice the frequency) that is 1/2 the period of the DATA signal. As shown in FIG. When the LATCH signal provided from the above corresponds to the 90 ° phase, modulation is performed with the n-th DATA bit string 110101.
When the phase corresponds to the phase of 70 °, the modulation is performed by the bit string 1011110 of the (n + 1) th DATA. By this modulation, an LDON signal which is a drive signal for turning on / off the semiconductor laser 3 is generated.
(B)).

This LDON signal is input to the drive control circuit 24, and the semiconductor laser 3 is turned on / off in response to this.
Is done. Here, if this ON / OFF is made to correspond to the position of the laser beam on the scanning surface shown in FIG. 4, the data of the n-th line is at the position of A ', and the data of the (n + 1) -th line is B' Are turned ON / OFF respectively.

That is, according to such a configuration, the data of the n-th and (n + 1) -th two lines is
Writing can be simultaneously performed on the scanning surface in one scan corresponding to rotation.

In the above embodiment, the phase of the sine function is set to 2
By dividing and modulating the data, the data of two lines is simultaneously written on the scanning surface.
When the data is divided into a plurality of lines, data of lines corresponding to the number of divided lines can be written simultaneously.

[0057]

According to the optical scanning apparatus of the present invention described above, the laser light output as a single light beam from the semiconductor laser is scanned by a plurality of diffracted lights having different emission angles obtained by the swing of the front hologram. Are simultaneously scanned, so that the optical scanning efficiency is high as in the case of using a plurality of conventional semiconductor lasers or the case of using a multi-beam semiconductor laser.

In addition, in the optical scanning device of the present invention, since a single semiconductor laser outputs a single light beam, the distance between a plurality of scanning lines is different from that in the case where a plurality of conventional semiconductor lasers are used. Does not need to be performed using a high-precision arrangement technique in the light source, and the setting of the distance interval is performed by selecting the amplitude and angular frequency of the waveform that swings the front hologram. Therefore, according to the optical scanning device of the present invention, the distance between the plurality of scanning lines can be easily reduced.

Further, it is not necessary to increase the capability of the rotation drive mechanism as in the case of increasing the light scanning capability by speeding up the rotation of the conventional rotating hologram disk. Therefore, according to the optical scanning device of the present invention, it is possible to realize a scanning optical system which has a relatively simple and small structure, has a high optical scanning efficiency, and can easily improve the optical scanning density by using a relatively simple technique. There are advantages. Therefore, the manufacturing efficiency can be improved and the cost can be significantly reduced.

Further, if such a scanning optical system is used, it is possible to shorten the optical scanning time and to improve the optical scanning density. Therefore, an image forming apparatus or an image reading apparatus capable of high-density and high-speed processing can be compared. There is an advantage that can be realized at very low cost.

According to the optical scanning device of the second aspect, the production of the hologram is facilitated, so that there is an advantage that the cost can be greatly reduced.

Further, according to the optical scanning device of the third aspect, the laser light source has a characteristic that the oscillation spectrum width is extremely narrow under high-speed direct modulation. Therefore, in this respect, there is an advantage that the scanning density can be improved. is there.

According to the optical scanning device of the fifth aspect, the functions can be shared among three types of holograms. Therefore, each hologram is basically a stripe or concentric circle due to interference of two light beams of a spherical wave or a plane wave. The upper stripe is good,
There is no need for complicated aberration waves. Therefore, also in this respect, there is an advantage that the production of the hologram is further facilitated and the cost can be further reduced.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing the overall configuration of a laser beam printer according to one embodiment of the present invention.

FIG. 2 is a perspective view showing a scanning optical system of the laser beam printer of FIG.

3A and 3B are a perspective view and a cross-sectional view illustrating a diffraction phenomenon when a front hologram is swung.

FIG. 4 is a diagram illustrating the principle of the optical scanning device of the present invention.

FIG. 5 is a block diagram schematically showing a signal processing system provided in the scanning optical system of the laser beam printer of FIG. 1;

FIG. 6 shows a bar LDO generated by modulating an optical modulator.
FIG. 6 is a signal waveform diagram showing N.

[Explanation of symbols]

 Reference Signs List 1 laser beam printer 2 drive control circuit 3 semiconductor laser 4 hologram disk (rotating hologram disk) 5 photosensitive drum 6 scanning line 7 motor 12 hologram 13 substrate 20 interface circuit 21 modulator 22 drive circuit 23 quantization circuit 41 hologram (prefix) Hologram) 41c Actuator 43 Hologram (Post-hologram)

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G02B 26/10 106 H04N 1/113

Claims (4)

(57) [Claims] A laser light source for emitting laser light; an optical modulator for turning on / off an optical output of the laser light source; a front hologram for diffracting the laser light emitted from the laser light source; An actuator for swinging the hologram; a rotating hologram disk having a plurality of holograms in a circumferential direction for diffracting the laser light diffracted by the front hologram; and a laser beam diffracted by the rotating hologram disk. and a scanning surface to be scanned, said front location hologram, a plurality of diffracted light having an emission angle at which the phase different from each other emitted from said rotary hologram disk is swung so as to scan the scanning surface alternately Optical scanning device. 2. The laser light source according to claim 1, wherein said laser light source is a semiconductor laser such as a DFB laser or a DBR laser which operates in a single longitudinal mode in a use temperature range. 2. The optical scanning device according to claim 1, which is turned on / off. 3. The optical scanning device according to claim 1, wherein a post-hologram is provided in an optical path of the diffracted light diffracted by the rotating hologram disk. 4. The optical scanning device according to claim 3, wherein the hologram of the front hologram and the hologram of the rotating hologram disk have interference fringes in which an object wave and a reference wave are respectively recorded by mutual interference of spherical waves.