JP2706984B2 - Scanning optical device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a display, an electrophotographic photosensitive member,
The present invention relates to a scanning optical apparatus that scans an object to be irradiated such as a heat-sensitive element, and more particularly to a scanning optical apparatus that has a unit that adjusts the state of condensing or forming an image of a scanning light beam on the object to be irradiated.

[Related Art] In recent years, displays, printers, and the like that scan an object surface with a light beam modulated according to information have become widespread. In such an apparatus, there is a property that the focal position of the scanning light beam changes due to environmental changes such as temperature and humidity. This is not a problem in a scanning optical system having a relatively large F-number and a large light beam spot diameter on an irradiation object, since a focal range (depth) in which a required spot diameter can be obtained is large.

However, in a scanning optical system having a small F-number and a small light beam spot diameter on an irradiation object, the focal position is deviated from the focal depth due to the above-mentioned environmental change because the depth of focus is shallow. Cannot be performed on the irradiation target.

For this reason, it has been proposed to provide an automatic focus adjustment unit for correcting a change in the focus position.

The method includes moving a light source such as a laser light source in the optical axis direction, moving a collimator lens in the optical axis direction, providing a correction lens system after the collimator lens, and moving the correction lens system in the optical axis direction, f There are proposals for moving a θ lens, changing a distance between an f · θ lens and an irradiation target such as a photosensitive drum, and the like.

[Problems to be Solved by the Invention] However, the above method is not practical because the device for moving becomes too large.

In the above methods, the focus adjustment can be performed with a small device, but conversely, the amount of movement of the light source and the like required to adjust the change in the focus position becomes too small, and the Control becomes difficult, the movement control mechanism becomes complicated or expensive.

For example, in the case of a scanning optical system that obtains a spot diameter of 40 μm on an irradiation target using a semiconductor laser having a wavelength of 0.78 μm as a light source,
The depth of focus is about ± 0.8 mm, and the scanning lens (f ·
the F-number of the collimator lens
Assuming that the number is 2.0, a change of ± 0.8 mm on the irradiation object corresponds to a change of ± 2.6 μm in the position of the laser.
In the case of environmental changes that can be considered normally, changes in the focal position are considered to be about ± 5 μm when converted into changes in the laser position.

Therefore, in the above method, it becomes necessary to control the collimator lens or the like with the moving amount in μm unit, and the type of the actuator used as the moving means is limited or a special device is required. is there.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a scanning optical device that enables fine focus position adjustment using focus adjustment means having a relatively simple configuration in view of the above problems.

[Means for Solving the Problems] In the present invention for achieving the above object, a prism means is disposed in an optical path between a light source and an irradiation target to be scanned with a light beam from the light source. The means adjusts the focusing state of the scanning light beam on the irradiation object by moving the scanning light beam at least in a direction different from the optical axis direction.

Specifically, the prism means includes a wedge prism arranged such that one surface is perpendicular to the optical axis and the other surface is adjacent to the surface of another optical member (a lens, another wedge prism, or the like), The prism is moved in a direction different from the optical axis direction (a direction perpendicular to the optical axis, a direction parallel to the adjacent optical member surface, etc.) while maintaining the adjacent optical member surface and the other surface of the prism in parallel. The prism means comprises one or more wedge prisms, lenses.

[Operation] According to the configuration of the present invention described above, the relatively simple and lightweight prism means inserted into the optical path of the scanning optical system is wholly or partially moved in a direction different from the optical axis direction.
The effect of the movement amount on the change in the focal position of the scanning light beam is reduced, and the movement of the prism means can be controlled.

Therefore, the means for moving the prism means is simplified, and the precision of the focal position adjustment is also high.

Embodiment FIGS. 1 to 3 show a first embodiment of the present invention. In FIG. 1 showing the overall configuration of the scanning optical device (on the main scanning surface where the scanning light beam forms over time), reference numeral 1 denotes a semiconductor laser as a light source, and the light beam emitted from the laser 1 is a wedge prism. Then, the light enters the collimator lens 4. The collimator lens 4 is provided with an aperture 4a, and a beam emitted from the collimator lens 4 is converted into a substantially parallel light of a certain size. The parallel light is incident on a rotating polygon mirror 5 rotating at a high speed at a constant speed in the direction of the arrow, where it is deflected and scanned. The light beam subjected to the deflection scanning is corrected in the scanning linearity by the f · θ lenses 6 and 7 and is subjected to a light-condensing action to form an image as a small spot on the surface 8 to be scanned, which is an irradiation object.

This spot is scanned on the scanned surface 8 at a constant speed in the direction of the arrow. Here, a beam diameter detector 9 is provided near the effective scanning section, and this detector 9 is linked with the prism driving device 3. That is, the prism driving device 3 operates based on the signal from the detector 9 that receives the scanning light beam, thereby controlling the position of the wedge-shaped prism 2 and condensing or imaging the scanning light beam on the surface 8 to be scanned. The state is optimized.

FIG. 2 is a diagram for explaining the automatic adjustment of the beam diameter by the wedge prism. In FIG. 2 (a), a light beam emitted from the semiconductor laser 1 passes through a wedge prism 2, passes through a collimator lens 4, further passes through an aperture stop 4a, and is converted into substantially parallel light having the size of the stop 4a. Proceed in the direction of the broken line.

Here, the center layer of the wedge prism 2 is
D ₁ , the angle of the wedge, that is, the apex angle is θ, and the refractive index is N.

Next, as shown in FIG.
Only in the direction perpendicular to the optical axis. At this time, the center thickness of the prism 2 on the optical axis changes by ΔD = Xtanθ and D ₂ =
D ₁ + Xtan θ, and the positional relationship between the laser 1 and the collimator lens 4 does not change. Therefore, the optical path length between the laser 1 and the collimator lens 4 changes, and focus adjustment on the surface 8 to be scanned becomes possible.

 The change Z in the optical path length is approximately expressed as Z = Xtan θ · (1 / N−1).

Here, as shown in FIG. 2, one surface of the prism 2 is inclined from the position perpendicular to the optical axis by substantially the angle θ.
Increases, optical aberrations, particularly coma, increase. Therefore, better performance can be obtained by using the apex angle θ in the range of 0 to 5 degrees.

Also, since the influence of coma aberration increases when the F-number of the collimator lens 4 used decreases, it is better to use the F-number at 1.8 or more.

Further, the wedge prism 2 arranged as shown in FIG. 2 causes some astigmatism. However, since the semiconductor laser 1 as a light source also has astigmatism or astigmatism, the astigmatism is generally reduced. If the short-side direction of the light-emitting portion of the semiconductor laser 1 is arranged in a direction to cancel the astigmatism, that is, in a cross-section (cross-section shown in FIG. 2) of the wedge prism 2 having the wedge angle θ, the semiconductor laser The astigmatism of the light source section from 1 to the collimator lens 4 can be reduced.

Here, a specific design example is shown. In FIG. 2, the wavelength λ of the light source 1 is 780 nm, and the vertex angle θ of the wedge prism is 1
Degree, D ₁ = 2 mm, N = 1.51072, first collimator lens 4
Radius of surface (prism side) R ₁ = ∞, radius of second surface R ₂ = −6.
066, assuming that the refractive index is 1.78569, and the stop diameter of the stop 4 is φ
1.7.

By moving the wedge prism 4 in the direction perpendicular to the optical axis by X = 5 mm, △ D = 0.08728 mm, and thus the change Z in the optical path length is 0.0295 mm. Therefore, the prism 4
Moving the lens in a direction perpendicular to the optical axis by 5 mm is equivalent to moving the light source 1 and the collimator lens 4 by 0.0295 mm. Therefore, the former has a higher moving sensitivity than moving the lens or the like in the optical axis direction. Becomes 1 / 169.5 and low sensitivity. In this way, the movement of the prism 4 can be controlled accurately with a simple and inexpensive mechanism.

In the first embodiment, a single wedge-shaped prism means is arranged in the optical path of the non-parallel light beam between the light source and the collimator lens, but this prism is used between other optical elements or members,
It may be arranged between the optical elements of the scanning optical device having a tilt correction function (a function to always converge a light beam on the same scanning line even if the deflection reflecting surface of the polygon mirror is tilted).

FIG. 3 shows a second embodiment. In the second embodiment, the prism means is replaced with a wedge-shaped prism, and a wedge member having a structure in which the apex angle of a wedge through which a light beam passes or a position of a wedge into which the light beam enters changes by rotation.
Consists of twelve. The principle of adjusting the spot diameter on the surface 8 to be scanned is the same as in the first embodiment.

FIG. 4 shows a third embodiment. In the third embodiment, the prism means is composed of two wedge prisms 20 and 21 made of different kinds of glass materials bonded to each other to form one wedge prism 22. With this configuration, achromatism is exhibited and the bending of the light beam is adjusted. In the third embodiment, as in the first embodiment, the prism 22 is moved in a direction perpendicular to the optical axis.

In the above embodiment, the plane on the light most incident side or the quantity emission side of the prism means was slightly inclined from a position perpendicular to the optical axis. Hereinafter, all such planes of the prism means are perpendicular to the optical axis. The following shows an embodiment.

FIG. 5 shows that the prism means is the first prism 30 on the light source 1 side.
A fourth embodiment comprising a second prism 31 on the side of the collimator lens 4 is shown. In the fourth embodiment, two prisms 30,
31 have the same apex angle θ, the spacing is kept at zero and the prism
Numerals 30 and 31 are placed in the divergent light beam in a form having the same function as the parallel plate. In addition, the plane on the light source side of the first prism 30 and the second
Both planes of the prism 31 on the collimator lens side are perpendicular to the optical axis O of the collimator lens 4.

In the fourth embodiment, the prism 30 is moved in a direction parallel to the contact surfaces of the two prisms 30 and 31 to change the optical path length between any two points A and B on the optical axis O. I have. The amount of change ΔAB is ΔAB = Xtan θ · (1 / N−1), as can be seen from the description of the first embodiment. Here, the refractive index of both prisms 30 and 31 is N, the vertex angle is θ, and the amount of movement of the first prism 30 in a direction perpendicular to the optical axis O is X.

When the refractive index N is set to 1.51072 and the apex angle θ is set to 1, 5, and 20 degrees, how the thickness t of the prism means and the change in the optical path length ΔAB change with respect to the moving amount X is as follows. Table 1,
2 and 3 show.

In the present embodiment, since there is no restriction on the vertex angle θ and the like to the left, the amount of movement of the prism required to cancel the environmental fluctuation is arbitrarily set by appropriately selecting the vertex angle of the prism, the refractive index, and the like. As a result, the range of selection of the actuator as the moving means becomes extremely wide.

In addition, since the optically non-refractive surface is changed, the fluctuation of aberration is reduced.

Also in the fourth embodiment, the principle of the focus adjustment is the same as that of the above-described embodiments, and the sixth embodiment moves the second prism 31.
This will be described with reference to the example of FIG. As shown in FIG.
If the apparent thickness of the parallel plate composed of 30 and 31 is reduced (the prism 31 is moved in the P direction from the state shown in FIG. 6A), the collimator lens 4 and the prism means 30 and 31 are moved.
Of the collimator lens system is considered to consist of back focus (distance to the focal point I ₀ of the light source-side surface and the incident surface of the first prism 30) is longer consist l _a to l _b (l _b>
l _a ).

Conversely, when the thickness of the parallel flat plate by moving the second prism 31 in the direction Q as the FIG. 6 (c) is increased, the l _c from l _a the back focus is shortened (l _c <l _a ).

If the light source 1 is placed in the position of l _a, FIG. 6 (a)
6B, a collimated light beam is emitted from the collimator lens 4, at the position shown in FIG. 6B, a divergent light beam is emitted from the collimator lens 4, and at a position shown in FIG. 6C, a convergent light beam is emitted from the collimator lens 4. coming out. Therefore, when the focal position of the scanning light beam is in front of the surface 8 to be scanned, the state shown in FIG. 6B is set so that the divergent light beam is emitted from the collimator lens 4. Adjustment is made so that it comes to the top, and in the opposite case, the state shown in FIG.

In the case of a normal laser scanning system, a change in the focal position due to an environmental change corresponds to a movement of the laser light source by about ± 5 μm. Therefore, in the case of the example of FIG.
If it can be moved by 10 μm, it is possible to correct the change of the focal position due to the environmental change.

When the prism 31 is made of glass having a refractive index N = 1.51072, the vertex angle θ of the prism 31 when the back focus changes by 10 μm, the movement amount X measured in a direction perpendicular to the optical axis, and the actual movement amount of the prism 31 Table 4 shows the relationship of (distance measured along the moving direction) u.

Table 5 shows the case where the prism 31 is made of glass with N = 1.78569.

Hereinafter, some more embodiments will be described.

FIG. 7 shows an example in which a gap is provided between the two prisms 32, 33, and the prism 32 is moved in a direction parallel to the facing surface forming the gap.

FIG. 8 shows an example in which a gap is provided between the two prisms 34 and 35, but the prism 34 is moved in a direction perpendicular to the optical axis.

FIG. 9 shows an example in which the two prisms 36 and 37 are moved together.

FIG. 10 shows an example in which the lens 38 and the prism 39 are formed as a single plano-convex lens when viewed as a unit.
Has a curved surface on one side and a plane inclined on the other side from a position perpendicular to the optical axis by the vertex angle of the prism 39. The prism 39 is moved along the inclined plane.

FIG. 11 shows an example in which a gap is provided between the lens 40 and the prism 41.

FIG. 12 shows an example in which the configuration of the collimator lens 42 is three pieces. The two prisms move one or both.

FIG. 13 shows a prism means similar to the example of FIG.
This is an example in which the lens 43 and the movable prism 44 are provided, and when each lens and the prism 44 are viewed integrally, it can be regarded as an example having a collimator lens system having a flat incident surface.

FIG. 14 shows that two prisms 46 and 47, which can be regarded as a parallel plate when the two lenses are combined, are arranged between the entrance lens and the exit lens of the collimator lens system 45 composed of a plurality of lenses. By way of example, one or both prisms are movable.

FIG. 15 shows an example in which a collimator lens system is composed of a plurality of lenses, and a movable prism 48 is disposed between an entrance surface and an exit surface. One surface is a plane inclined by a vertical angle of the prism 48 from a position perpendicular to the optical axis.

[Effects of the Invention] As described above, according to the configuration of the present invention, the prism means is inserted into the optical path of the scanning optical system, and the prism means is moved, in whole or in part, in a direction different from the optical axis. Since the length is changed, thereby adjusting the focusing state of the scanning light beam on the illuminated pair, the movement sensitivity of the prism means can be reduced, and the movement of the prism means can be accurately controlled by an inexpensive and simple movement means. .

[Brief description of the drawings]

FIG. 1 is a schematic structural view of a first embodiment of the present invention, FIG. 2 is an enlarged view of a portion of the first embodiment having a prism, and FIG.
FIG. 4 is a view for explaining an embodiment, FIG. 4 is a view for explaining a third embodiment, FIG. 5 is a view for explaining a fourth embodiment, and FIG. 6 is a modified example of the fourth embodiment. FIGS. 7 to 15 are diagrams showing other embodiments, respectively. 1. Light source, 2, 20, 21, 30-37, 39, 41, 44, 46, 4
7, 48 ... wedge prism, 3 ... prism driving device, 4 ... collimator lens, 8 ... scanned surface, 12, 3
8, 40, 43, 49 …… Prism means

Claims (14)

(57) [Claims] In a scanning optical apparatus for scanning a light beam from a light source onto an object to be irradiated, a prism means is disposed in an optical path between the light source and the object to be irradiated, and the prism means is disposed at least in a part in an optical axis direction. A scanning optical device, wherein the scanning light beam is adjusted in a different direction from the scanning light beam so as to adjust the focusing state of the scanning light beam on the irradiation object. 2. The prism means includes a wedge prism arranged so that one surface is perpendicular to the optical axis and the other surface is adjacent to another optical member surface. The scanning optical device according to claim 1, wherein the prism is moved in a direction different from the optical axis direction while the surface remains parallel. 3. The scanning optical device according to claim 2, wherein said optical member is a lens. 4. The scanning optical device according to claim 2, wherein said optical member is another wedge prism having the same apex angle as said prism. 5. The scanning optical device according to claim 2, wherein the prism is moved in a direction parallel to the surface of the adjacent optical member. 6. The scanning optical device according to claim 2, wherein said prism is moved in a direction perpendicular to an optical axis. 7. The scanning optical device according to claim 2, wherein a distance between said prism and said another optical member is zero. 8. The scanning optical device according to claim 2, wherein said prism and said another optical member have the same refractive index. 9. The scanning optical device according to claim 4, wherein both of said two prisms are moved. 10. The scanning optical device according to claim 1, wherein said prism means comprises a group of wedge prisms. 11. The scanning optical device according to claim 10, wherein an apex angle of said wedge prism is 5 degrees or less. 12. The scanning optical apparatus according to claim 10, wherein an effective F-number of a light beam passing through said prism on a plane inclined with respect to an optical axis of said prism is 1.8 or more. 13. The light source is a semiconductor laser, and a positional relationship between the laser and the prism is determined so that astigmatism of the semiconductor laser and astigmatism generated by the wedge-shaped prism cancel each other. Claim 10
The scanning optical device according to claim 1. 14. A scanning optical apparatus according to claim 1, wherein said prism means is disposed in an optical path in which a light beam between said light source and an exit surface of a collimator lens system is not a parallel light.