JPH08304731A - Optical scanner - Google Patents

Abstract

PURPOSE: To provide an optical scanner capable of obtaining a uniform scan characteristic ranging to the whole scan area. CONSTITUTION: When laser light 21 exists in the vicinity of both ends of a hologram plate 10, a minute spot 22 formed on a scan surface becomes a shape slightly extended in the direction of a sub-scan like 22d, 22e. Further, when the vicinity of the center is irradiated by the laser light 21, since a width of a hologram 32 in the direction of the sub-scan is narrower than the width of the laser light 21 in the direction of the sub-scan, the extended angle of the laser light 22 in the direction of the sub-scan is reduced effectively, and by that a spot size of a laser light spot formed on the scan surface is increased than an essential value like 22a, the spot size in the direction of the sub-scan becomes nearly equal to the light spots 22d, 22e in scan end parts, and the uniform spot size ranging to the whole scan area is obtained.

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 using a hologram.

[0002]

2. Description of the Related Art Conventionally, as an optical scanning device using a hologram, a hologram scanner 100 as shown in FIG.
It has been known. The hologram scanner 100 includes a semiconductor laser 110, a collimator lens 111, a cylindrical lens 113, a hologram disc 117, and a hologram plate 121. The hologram disc 117 has a hologram with one surface having an uneven surface. Is formed by. Similarly, the hologram plate 121 also has a hologram formed on one surface thereof in the shape of an uneven surface. The laser light emitted from the semiconductor laser 110 is collimated by the collimator lens 111, and is then condensed by the cylindrical lens 113 only in the sub-scanning direction which is a direction perpendicular to the scanning direction, and is applied to the hologram disc 117.
Hologram 11 formed on hologram disk 117
The diffracted light from 7 is diffracted by the hologram plate 121,
It is converged and irradiated onto the photosensitive drum 122. The hologram disk 117 is attached to the rotation shaft of the motor 124, and the hologram disk 117 rotates as the motor 124 rotates, so that the diffracted laser light linearly scans on the photosensitive drum 122 in its longitudinal direction. To do. Here, the hologram plate 121 causes the minute laser spot formed on the surface of the photosensitive drum 122 to move linearly on the drum surface, but the moving speed can be kept constant.

[0003]

However, in the hologram plate 121 as described above, as shown in FIG. 11, the width is sufficiently wider than the spot diameter of the laser beam 135 with which the hologram plate 121 is irradiated, and the hatched area is shaded. A hologram 130 as shown is formed. When the laser beam 135 moves on the hologram plate 121 by being deflected by the hologram disc 117, a minute light spot 140a is formed on the surface of the photosensitive drum 122 which is the scanning surface in the vicinity of the scanning center. However, the scan center 140
As the distance from a increases, the influence of aberration increases, and the light spots on the scanning surface are 140 b, 140 c, and 140
In particular, the spot diameter in the sub-scanning direction increases like d and 140e. Further, in general, the hologram 130 has a lower diffraction efficiency as the hologram 130 is closer to the scanning end, and therefore the scanning center 140a.
The intensity of the light spot on the scanning surface decreases with increasing distance from. For this reason, the spot diameter becomes larger and the light intensity becomes weaker toward the scanning end portion, so that there is a problem that the resolution and the contrast fluctuate in the scanning region and the print quality deteriorates.

Further, if the diffraction angle θ _HP in the hologram plate 121 is reduced in order to reduce the aberration, the diffracted light 150 and the undiffracted transmitted light 152 indicated by the dotted line overlap each other as shown in FIG. Separation becomes impossible. As a result, the photosensitive drum 122 is irradiated with the zero-order light in addition to the desired light spot 140, which causes a problem that normal printing cannot be performed.

The present invention has been made in order to solve the above-mentioned problems, and an object thereof is to provide an optical scanning device which can obtain a uniform scanning characteristic over the entire scanning region.

[0006]

In order to achieve this object, in the optical scanning device according to the first aspect of the invention, a laser light source and a light for deflecting and scanning the laser light emitted from the laser light source. Deflection means and a hologram plate on which a hologram is formed for converging the laser light deflected by the light deflection means on the scanning surface, and among the holograms formed on the hologram plate The width of the contributing region in the sub-scanning direction perpendicular to the scanning direction is smaller than the beam diameter of the laser light with which the hologram plate is irradiated in the sub-scanning direction.

According to the optical scanning device of the invention of claim 2,
The width of the hologram formed on the hologram plate in the sub-scanning direction becomes narrower toward the scanning center.

According to the optical scanning device of the invention of claim 3,
The surface of the hologram plate is provided with a light blocking unit that increases the light blocking amount toward the scanning center.

According to the optical scanning device of the invention of claim 4,
A slit is provided in the vicinity of the hologram plate, and the width of the slit is formed so as to become narrower toward the scanning center. Further, in the optical scanning device of the fifth aspect of the invention, the optical deflecting means has a hologram.

[0010]

According to the optical scanning device of the first aspect of the present invention having the above structure, the laser beam emitted from the laser light source is deflected by the optical deflecting means and further converged as a minute spot on the scanning surface by the hologram plate. To be done. Here, at least at the scanning center, the width in the sub-scanning direction of the region of the hologram formed on the hologram plate that contributes to the diffraction of the laser light is smaller than the beam diameter of the laser light applied to the hologram plate in the sub-scanning direction. Is also narrowed. That is, since the numerical aperture when the hologram plate is imitated as a lens becomes small, the spot diameter of the light spot on the scanning surface in the sub-scanning direction increases.
Moreover, since the width of the hologram is narrow, part of the laser light with which the hologram plate is irradiated is not diffracted, and the light spot intensity on the scanning surface is reduced.

In the optical scanning device of the present invention, the width of the hologram formed on the hologram plate in the sub-scanning direction becomes narrower toward the scanning center, so that the width of the region contributing to the diffraction of the laser light is scanned. The center becomes narrower.

As a result, since the beam diameter in the sub-scanning direction increases toward the scanning center and the light intensity decreases, a light spot having a uniform spot diameter and light intensity in the sub-scanning direction extends from the scanning center to the scanning end. can get.

In the optical scanning device of the third aspect of the present invention, since the light shielding means is provided on the surface of the hologram plate, and the light shielding amount is larger toward the scanning center, the width of the region contributing to the diffraction of the laser light is narrower toward the scanning center. Become.

In the optical scanning device of the fourth aspect of the present invention, since the slit width provided near the hologram plate is narrower toward the scanning center, the width of the region contributing to the diffraction of the laser light is narrower toward the scanning center. .

In the optical scanning device of the fifth aspect of the invention, the change in the condensing characteristic of the hologram plate due to the change in the laser wavelength is compensated by the hologram of the optical deflecting means.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described below with reference to the drawings.

The optical scanning device 1 to which the present invention is preferably applied includes:
As shown in FIG. 1, a semiconductor laser 2 serving as a laser light source has an exit opening through which a collimating lens 3 for collimating laser light emitted from the semiconductor laser 2, a hologram disc 5, and a collimating lens 3 are provided. The cylindrical lens 4 that converges the parallel light in the direction perpendicular to the scanning direction, that is, the sub-scanning direction and focuses it on the hologram disk 5, and the laser light 21 diffracted by the hologram disk 5 on the scanning surface, that is, the photosensitive drum. 7 and a hologram plate 10 for condensing light on the surface. Then, the laser beam 22 diffracted by the rotation of the hologram disk 5 by the rotation driving of the motor 8 as the rotation driving means linearly scans the photosensitive drum 7 in its longitudinal direction, that is, in the scanning direction. .

The hologram disk 5 is composed of a transparent disk-shaped substrate, the center of which is fixed to the rotation shaft of the motor 8 and can rotate as the motor 8 is driven to rotate. The hologram disk 5 and the motor 8 constitute the light deflecting means of the present invention.

The hologram plate 10 is composed of a transparent plate-shaped substrate, and as shown in FIG.
A hologram 32 is formed on the surface of the area in the shaded area. The hologram 32 is formed such that the width thereof in the sub-scanning direction becomes narrower as it is closer to the center of the hologram plate in the longitudinal direction which is the main scanning direction, that is, the scanning center.

As the material of the hologram disc 5 and the hologram plate 10, a substrate made of resin such as polycarbonate, PMMA, polyimide, amorphous polyolefin or the like can be used. Also,
Other than resin, glass or ceramic may be used. In this case, irregularities may be directly formed on the glass or ceramic substrate to form a hologram. Further, a hologram may be formed of resin or the like on these substrates.

Since the hologram rate 10 has power in the sub-scanning direction, the diffracted laser light 21 that is diffracted by the hologram disk 5 and becomes divergent light is focused on the photosensitive drum 7 as a minute light spot. Further, with respect to the main scanning direction, which is a direction parallel to the longitudinal direction of the photosensitive drum 7, the laser light incident on the hologram disk 5 is parallel light, and the diffracted laser light 21 is also sub-scanned by the hologram plate 10. Is focused with a power different from that of, and focused as a minute light spot 22. Note that, due to the converging action of the hologram plate 10 as described above, it is possible to compensate for eccentricity, surface wobbling of the hologram disk 5, and variations in the diffraction angle due to variations in the wavelength of the semiconductor laser 2.
That is, the diffraction angle in the hologram 32 changes depending on the wavelength. Therefore, if the hologram plate 10 is used alone, the scanning characteristics change when the wavelength changes. Therefore,
By using the hologram disk 5 as the light deflecting means in addition to the hologram plate 10 so as to cancel out the influence of the wavelength fluctuation, it is possible to perform stable optical scanning in which the influence of the wavelength fluctuation is small.

The image forming relationship in the sub-scanning direction by the hologram plate 21 is shown in FIG. Spot diameter φ of a minute light spot formed on the surface of the photosensitive drum 7 which is the scanning surface
Is given by

Φ = K · λ / NA (1) Here, K is a constant and λ is a wavelength. NA is the numerical aperture when the hologram plate 10 is imitated as a lens,
As shown in FIG. 3, when the spread angle of the diffracted laser beam 22 is θ, NA = sin θ (2) can be obtained. From these relationships, the spot diameter φ
Becomes larger as the NA is smaller, and NA is the diffracted laser beam 2
The smaller the spread angle θ of 2, the smaller the spread angle θ. The width of the hologram 32 formed on the hologram plate 10 in the sub-scanning direction becomes narrower toward the scanning center. That is, in the hologram plate 10, the region that contributes to the diffraction and convergence of the laser light 21 is only the region in which the hologram 32 is formed, and that region is narrowed toward the scanning center.
This is because when the width of the hologram 32 in the sub-scanning direction is narrower than the spot diameter of the laser light 21 with which the hologram plate 10 is irradiated in the sub-scanning direction at least at the scanning center, the laser beam focused on the scanning surface 7 is used. This corresponds to the divergence angle θ of the light 22 being narrowed as θ2 at least near the scanning center. Therefore, near the scanning center,
The spot diameter φ of the laser beam 22 increases by the amount that becomes smaller to θ2 compared to the value obtained when the spread angle is the original θ.

FIG. 4 schematically illustrates the above relationship. That is, when the laser beam 21 applied to the hologram plate 10 is present at the scanning end, that is, near both ends of the hologram plate 10, the minute spots 22 formed on the scanning surface 7 are in the sub-scanning direction like 22d and 22e. It has a slightly expanded shape. In general, the hologram 32 has a smaller aberration as it gets closer to the center, so that the spot diameter of the laser light spot formed on the scanning surface 7 becomes smaller. However, since the width of the hologram 32 in the sub-scanning direction is narrower than the width of the laser light 21 in the sub-scanning direction when the laser light 21 is applied to the scanning center, that is, near the center of the hologram plate 10. The divergence angle of the laser light 22 in the sub-scanning direction is effectively reduced, the spot diameter of the laser light spot 22 formed on the scanning surface 7 is increased as indicated by 22a, and the spot diameter in the sub-scanning direction is at the scanning end portion. It is almost equal to the light spots 22d and 22e.

Further, by gradually changing the width of the hologram 32 from the scanning end to the scanning center so as to correct the unnecessary reduction of the spot diameter due to the reduction of aberration, the light spot is 22d in the entire scanning region. , 22
Like b, 22a, 22c, and 22e, the spot diameters in the sub-scanning direction become substantially uniform. As a result, uniform resolution can be realized in the entire scanning area.

Further, in the hologram 32, generally, the closer to the center, the higher the diffraction efficiency, so that the light intensity of the laser light spot 22 formed on the scanning surface 7 increases. However, when the laser beam 21 is applied to the scanning center, that is, near the center of the hologram plate 10, the width of the hologram 32 in the sub-scanning direction is narrower than the width of the laser beam 21 in the sub-scanning direction. Of the light 21, the laser light of the portion protruding from the hologram 32 is not diffracted and is not focused on the light spot 22a.
The intensity of a is effectively reduced and becomes substantially equal to the intensity of the light spots 22d and 22e at the scanning end. Further, by gradually changing the width of the hologram 32 from the scanning end to the scanning center, the increase in the light intensity due to the increase in the diffraction efficiency is corrected, and the intensity of the light spot becomes substantially uniform in the entire scanning region. In this way, by narrowing the width of the hologram 32 formed on the hologram plate 10 in the sub-scanning direction toward the center, the scanning characteristics such that the spot diameter and the light intensity in the sub-scanning direction become uniform over the entire scanning region. Can be realized.

Although one embodiment of the present invention has been described in detail above with reference to FIGS. 1 to 4, the present invention is not limited to the embodiment described above in detail, and within the scope of the invention. Various changes can be made.

For example, in the previous embodiment, the width of the hologram 32 formed on the hologram plate 10 was narrowed toward the scanning center, but the present invention is not limited to this. The width of the region that contributes to light collection is the hologram plate 1
The same effect can be obtained if the spot diameter of the laser light 21 radiated to 0 is made narrower. Therefore, instead of narrowing the width of the hologram 32 itself as shown in FIG. 2, a light shield of a predetermined shape may be formed on the hologram plate 10 as shown in FIG. Here, since the laser beam 21 does not pass through the light shield 40, even if the hologram 32 is formed in the region where the light shield 40 is provided, it does not contribute to the diffraction, and the sub-scanning similar to the previous embodiment is performed. The effect of making the directional spot diameter and the light intensity uniform can be obtained. Here, the light shield 40
As, Al, Cr, Cu, Au, Ni, Ta, Fe
Metals such as the above, various alloys, metal oxides, nitrides, and sulfides can be used. Further, a material having a large light absorption such as carbon, a pigment, or a paint may be used. The same effect can be obtained regardless of whether the light shield 40 is provided on the surface of the hologram plate 10 on which the hologram 32 is formed or on the opposite surface. Also, it may be provided in the substrate of the hologram plate 10.

Further, by providing such a light shield 40, even if the diffraction angle is made small, as shown in FIG. 6, the focus position of the diffracted light 22 shown by the solid line and the diffraction shown by the dotted line are not generated. It is possible to separate the transmitted light 43 that travels straight.
That is, when the light shield 40 is not provided, the transmitted light 44 shown by the alternate long and short dash line in FIG. 6 and the diffracted light 22 overlap and normal exposure cannot be performed. Generally, when the diffraction angle is reduced,
The overall aberration is reduced and the spot diameter is reduced. For this reason, the spot diameter at the scanning end can also be reduced, and the overall resolution can be improved.

Further, as shown in FIG. 7, a similar effect can be obtained by using a slit 60 instead of the light shield 40.
The slit 60 is arranged near the hologram plate 10. As the slit 60, Fe, Cr, Ni,
Cu, Au, Al and other metals, stainless steel and other alloys,
Any material having a light shielding property such as resin or ceramic can be used. The slits 60 may be arranged on either the photosensitive drum 7 side of the hologram plate 10 or the hologram disc 5 side.

The shape of the region of the hologram plate 10 that contributes to the diffraction is particularly limited as long as it is narrower at least in the scanning center than the beam diameter of the laser beam 21 with which the hologram plate 10 is irradiated in the sub-scanning direction. Instead, for example, it may be linearly changed like the hologram 80 shown in FIG. 8A under the condition that the variation of the spot diameter is within the allowable range. Further, it may be changed stepwise like the hologram 82 shown in FIG. Further, the diffraction efficiency may be gradually changed in the sub-scanning direction as in the hologram 84 shown in FIG.

The basic structure of the optical scanning device is shown in FIG. 1, but the invention is not limited to this.
As shown in FIG. 9, timely reflecting mirrors 71, 72, 73,
The optical scanning device 1 may be miniaturized by inserting 74 or the like and bending the optical path.

Further, the hologram formed on the hologram disk 5 and the hologram plate 10 may be of a so-called relief type in which the hologram 17 is formed in the shape of concavities and convexities on the surface thereof. Moreover, the present invention is not limited to this, and for example, a volume hologram in which a hologram is recorded in the form of phase change of a medium may be used.

As the light deflecting means, means other than the hologram disk may be used. For example, a polygon mirror, a galvano mirror or the like may be used.

Further, the optical scanning device 1 may have a configuration other than that shown in the embodiment, and optical components required may be added at appropriate times. Further, the lens or the like may be replaced with a hologram.

[0036]

As is apparent from the above description,
According to the optical scanning device of the present invention described in claim 1, among the holograms formed on the hologram plate,
The width in the sub-scanning direction of the region that contributes to the diffraction of the laser light is narrower than the beam diameter of the laser light with which the hologram plate is irradiated in the sub-scanning direction. That is, since the numerical aperture when the hologram plate is imitated as a lens becomes small, the spot diameter of the light spot on the scanning surface in the sub-scanning direction increases. Also, because the width of the hologram is narrow,
Since a part of the laser light with which the hologram plate is irradiated is not diffracted, the light spot intensity on the scanning surface is reduced.
This makes it possible to make the beam diameter and the light intensity of the laser light spots at the scanning end portion and the scanning center portion in the sub-scanning direction substantially uniform, so that the scanning characteristics that the resolution and the light intensity are substantially uniform over the entire scanning region. Is obtained.

According to the optical scanning device of the second aspect of the present invention, the width of the hologram formed on the hologram plate in the sub-scanning direction becomes narrower toward the scanning center, so that the diffraction of the laser beam is reduced. The width of the region that contributes to becomes narrower toward the scanning center. As a result, since the beam diameter in the sub-scanning direction increases toward the scanning center and the light intensity decreases, a light spot with a uniform spot diameter and light intensity in the sub-scanning direction can be obtained from the scanning center to the scanning end portion. As a result, more uniform scanning characteristics can be realized over the entire scanning area.

Further, according to the optical scanning device of the present invention as defined in claim 3, the light shielding means is provided on the surface of the hologram plate, and the light shielding means increases the light shielding amount toward the scanning center. As a result, it is possible to realize uniform scanning characteristics over the entire scanning area, as compared with the optical scanning device according to the first aspect.

According to the optical scanning device of the fourth aspect, a slit is provided in the vicinity of the hologram plate, and the width of the slit is narrowed toward the scanning center. It becomes narrower toward the center of scanning.
As a result, it is possible to realize uniform scanning characteristics over the entire scanning area, as compared with the optical scanning device according to the first aspect.

According to the optical scanning device of the fifth aspect of the invention, since the light deflecting means has a hologram, a change in the condensing characteristic of the hologram plate due to a change in the laser wavelength is compensated by the hologram disk of the light deflecting means. be able to.

[Brief description of drawings]

FIG. 1 is a side view of an essential part showing an embodiment embodying the configuration of an optical scanning device of the present invention.

FIG. 2 is a schematic plan view showing a hologram plate.

FIG. 3 is an explanatory diagram showing an image forming relationship of a hologram plate.

FIG. 4 is a schematic diagram showing a light condensing characteristic of a hologram plate.

FIG. 5 is a schematic view showing a hologram plate in another embodiment of the optical scanning device of the present invention.

FIG. 6 is an explanatory diagram showing an image forming relationship of a hologram plate in another embodiment of the optical scanning device of the present invention.

FIG. 7 is a side view of essential parts showing another embodiment of the optical scanning device of the present invention.

FIG. 8 is a schematic view showing a hologram plate in another embodiment of the optical scanning device of the present invention.

FIG. 9 is a cross-sectional view of essential parts showing another embodiment of the optical scanning device of the present invention.

FIG. 10 is a side view of essential parts showing the configuration of a conventional optical scanning device.

FIG. 11 is a schematic diagram showing a light condensing characteristic of a hologram plate of a conventional optical scanning device.

FIG. 12 is a schematic diagram showing an image formation relationship by a hologram plate of a conventional optical scanning device.

[Description of Codes] 1 Optical Scanning Device 2 Semiconductor Laser (Laser Light Source) 5 Hologram Disk (Light Deflection Means) 7 Scanning Surface 8 Motor 10 Hologram Plate 21 Laser Light 32 Hologram 40 Light Shielding Means 60 Slit

Claims (5)

[Claims] 1. A laser light source, an optical deflecting means for deflecting and scanning the laser light emitted from the laser light source, and a laser light deflected by the optical deflecting means for converging on the scanning surface. Of the hologram formed on the hologram plate, the optical scanning device having a hologram plate on which a hologram is formed has a width in a sub-scanning direction perpendicular to a scanning direction of a region that contributes to diffraction of laser light. The optical scanning device is characterized in that the beam diameter of the laser light with which the hologram plate is irradiated is smaller than the beam diameter in the sub-scanning direction. 2. The optical scanning device according to claim 1, wherein the width of the hologram formed on the hologram plate in the sub-scanning direction is narrower toward the scanning center. 3. The optical scanning device according to claim 1, wherein the hologram plate is provided on the surface thereof with a light shielding unit having a larger light shielding amount toward a scanning center. 4. The optical scanning device according to claim 1, wherein a slit is provided in the vicinity of the hologram plate, and the width of the slit is narrowed toward a scanning center. 5. The optical scanning device according to claim 1, wherein the light deflector has a hologram.