JPH06347713A - Lens system for optical scanning - Google Patents

Abstract

PURPOSE:To provide a lens system for optical scanning effectively reducing the influence of striae and the birefringent region of a plastic lens. CONSTITUTION:In an optical scanning device, this lens system is arranged between the starting point of deflection of a light beam by means of an optical deflector 1 and a surface to be scanned 3, includes two and more plastic lenses 10, 12 formed by plastic molding and at least one of the plastic lenses 10, 12 is arranged so that the direction of its gate part 10A is opposed to the direction of the gate part 12A of other plastic lens.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning lens system.

[0002]

2. Description of the Related Art An optical scanning lens system is a lens system provided between an origin of deflection of a light beam and a surface to be scanned in an optical scanning device, and an fθ lens is a typical example thereof. Recently, plastic lenses have been widely used in such optical scanning lens systems due to demands for cost reduction, adoption of special lens surfaces, and the like.

Generally, a plastic lens is manufactured by "injection molding" from the viewpoint of mass productivity, but the inside of the injection-molded plastic lens is a region having a non-uniform refractive index. Often occurs, or the internal stress distribution during molding freezes as a “birefringence region”.

When a plastic lens having such striae and birefringence regions is included in the optical scanning lens system,
There is a problem in that a “spot diameter defect” of a light spot formed on the surface to be scanned occurs and prevents proper light scanning.

The above-mentioned "striation" and "birefringence region" are likely to occur in a portion where the plastic flow is disturbed during the molding of a plastic lens. Specifically, it is necessary for positioning the gate portion and the plastic lens assembly. It is likely to occur in the vicinity of the positioning projection used.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object thereof is to provide a novel optical scanning lens system which effectively reduces the influence of the striae and the birefringence region. To do.

[0007]

The optical scanning lens system of the present invention is a "lens system provided between a deflection origin of a light beam and a surface to be scanned in an optical scanning device".

An optical scanning lens system according to claim 1 includes "two or more plastic lenses formed by plastic molding, wherein at least one of the two or more plastic lenses has a gate portion oriented in another plastic. It is placed in the direction opposite to the direction of the gate part of the lens. "

Each of the two or more plastic lenses in the optical scanning lens system according to claim 1 may have a gate portion protruding in the direction corresponding to the main scanning (claim 2), or both of them may be sub-elements. You may have a gate part which protrudes in a scanning corresponding direction (Claim 3).

The "main scanning corresponding direction" is a virtual linear light obtained by linearly expanding the optical path from the origin of deflection of the light beam to the surface to be scanned along the optical axis of the optical scanning lens system. A direction that corresponds to the main scanning direction in parallel on the road, and a direction that corresponds to the sub scanning direction in parallel on the linear optical path is referred to as a "sub scanning corresponding direction".

When four or more plastic lenses are included in the optical scanning lens system, two or more of them have a gate portion protruding in the main scanning corresponding direction (or the sub scanning corresponding direction), and the other lens is A gate portion protruding in the sub-scanning corresponding direction (or main scanning corresponding direction) may be provided. In such a case, the gate portion of one or more lenses in each of the main and sub-scanning corresponding directions may be connected to the gate of another lens. It can be turned upside down.

According to a fourth aspect of the present invention, there is provided an optical scanning lens system that "includes at least one plastic lens formed by plastic molding and has an adjusting mechanism for adjusting the position of at least one plastic lens in the sub scanning corresponding direction." Characterize.

The optical scanning lens system according to any one of claims 1 to 4 can include one or more glass lenses together with a plastic lens (claim 5).

According to a sixth aspect of the present invention, there is provided an optical scanning lens comprising: "two or more plastic lenses formed by plastic molding, each of the two or more plastic lenses has a projection for positioning, and each plastic lens. The deflected light beam passing near the positioning projection in
The position of the positioning projection in each plastic lens is set so that it passes through the position away from the positioning projections of other plastic lenses. "

In the optical scanning lens system according to the sixth aspect, "two or more plastic lenses formed by plastic molding each have a positioning projection protruding in the sub-scanning corresponding direction" (claim) Item 7).

According to a sixth aspect of the present invention, there is provided an optical scanning lens system in which "each of two or more plastic lenses formed by plastic molding has a positioning projection protruding in a sub-scanning corresponding direction and a main scanning corresponding direction. And a protruding gate portion, and at least one of the two or more plastic lenses is arranged with the direction of the gate portion opposite to that of the other plastic lens. " (Claim 8)

An optical scanning lens system according to a ninth aspect of the present invention is that "two or more plastic lenses formed by plastic molding are included, and each of the two or more plastic lenses formed by plastic molding is in the sub-scanning corresponding direction. It has a protruding protrusion for positioning and a gate portion protruding in the sub-scanning corresponding direction. The deflected light beam that passes near the positioning protrusion of each plastic lens and near the gate portion is used for positioning other lenses. The position of the positioning protrusion and gate on each plastic lens was set so that it passes through the position away from the protrusion and the gate. ”
It is characterized by

According to a sixth aspect of the present invention, there is provided an optical scanning lens system comprising: "one or more plastic lenses formed by plastic molding are positioned in a sub-scanning corresponding direction and main scanning compatible. It is possible to have an adjusting mechanism for adjusting the tilt state with respect to the direction ”(claim 10).

Further, claim 6 or 7 or 8 or 9
Alternatively, the optical scanning lens system according to the tenth aspect can include one or more glass lenses (claim 11).

[0020]

[Function] "Striae" and "birefringence region" with non-uniform refractive index
Generally tends to occur remarkably on the side of the gate of a plastic lens, and when using two or more plastic lenses with striae and birefringence regions, the direction of the gate of each lens should be aligned on one side. The striae / birefringence region of each plastic lens easily overlaps each other on the gate side, and the light spots in the striae / birefringence region due to the lenses in the regions where the striae / birefringence region overlaps each other. The adverse effect on the diameter etc. is not "additive" but "synergistic".

Therefore, as in the first to third aspects of the present invention, the gate portions of at least one plastic lens are oriented in the other plastic lens without aligning the gate portions of the plurality of plastic lenses on one side. By reversing the direction of the gate, it is possible to reduce the overlap between the striae and the birefringence region.

If at least one of the lenses constituting the optical scanning lens system is a glass lens, since the glass lens has no striae or birefringence region, the overlap between the striae and birefringence region is effective. (Claim 5)

Further, in the optical scanning lens system, a considerable area of the lens is used in the main scanning corresponding direction, but in the case of a plastic lens, the incident position of the deflected light beam on the lens is shifted in the sub scanning corresponding direction. This makes it possible to use a portion of the plastic lens that is less affected by the pulsation / birefringence region (claim 4).

In addition, a "positioning projection" is often formed on the plastic lens for positioning when the plastic lens is assembled to the optical scanning device, and a "positioning projection" is also formed in the vicinity of such a positioning projection. Striae and “birefringence regions” tend to occur. When using two or more plastic lenses with these striae and birefringence regions, the position of the projection for positioning each lens should be seen from the optical axis direction. If they are aligned, the striae / birefringence regions in the vicinity of the protrusions for positioning are likely to overlap each other between the plastic lenses, and the striae / birefringence regions due to the striae / birefringence are overlapped at the portions where the striae / birefringence regions overlap. The adverse effect on the light spot diameter and the like in the area is “synergistic” rather than “additive”.

In a plastic lens having a positioning projection, striae and birefringence regions are generated by the projection and the gate portion. in this case,
It is also possible to make the plastic lens itself larger than the incident area of the polarized light beam and devise the position of the gate part so that the striae and the birefringence area due to the gate part do not cover the incident area. is there. However, even in such a case, it is not always easy to prevent the striae / birefringence regions due to the positioning projections from intensively overlapping in the incident region.

Therefore, in the inventions according to claims 6 and 7,
"Set the position of the positioning projection on each plastic lens so that the deflected light beam passing near the positioning projection on each plastic lens passes through a position away from the positioning projections on other plastic lenses."
By doing so, striae near the protrusion for positioning each plastic lens and “concentrated overlap” of the birefringence region
Is effectively reduced.

Further, in the present invention as defined in claims 8 and 9, striae in the vicinity of the positioning projection in the plastic lens, birefringence region and striae in the vicinity of the gate portion,
Effectively reduce mutual overlap of birefringent regions.

In the optical scanning lens system, a considerable area of the lens is used in the main scanning corresponding direction, but in the inventions of claims 6 to 9, the incident position of the deflected light beam on the lens corresponds to the sub scanning. By shifting in the direction, it is possible to use a portion of the plastic lens that is less affected by the pulsation / birefringence region (claim 10). Also, in the inventions described in claims 6 to 10, by including at least one glass lens having no striae or birefringence regions, overlap of striae / birefringence regions can be effectively reduced (claim 11). .

[0029]

EXAMPLES Specific examples will be described below. Figure 1
An example of the optical scanning lens system according to claims 1 and 2 is shown. FIG. 1A shows a state in which an optical scanning lens system provided between a deflection start point of a light beam by a deflector 1 (rotary polygon mirror) and a surface to be scanned 3 is viewed from a sub-scanning corresponding direction. . The vertical direction in the figure corresponds to the main scanning direction.

The optical scanning lens system is composed of two plastic lenses 10 and 12. Each of the plastic lenses 10 and 12 has gate portions 10A and 12A protruding in the main scanning corresponding direction, but the plastic lenses 10 and 12 are arranged so that the gate portions 10A and 12A are oriented in opposite directions. ing.

FIG. 1B shows the state of striae 100 in the plastic lens 12, and FIG. 1C shows the state of the birefringent region 110 (photoelastic image) in the lens 12. As shown in FIG. 1B, the striae 100 are likely to occur on the side of the gate portion 12A, and tend to occur long in the main scanning corresponding direction starting from the position of the gate portion.

As shown in FIG. 1C, the gate portion 12A
In the case where is projected in the main scanning corresponding direction, the birefringent region 110 appears at both ends of the lens in the main scanning corresponding direction, but is more likely to occur on the gate portion 12A side.

The tendency of the striae / birefringence region to occur is common when the gate portion projects in the direction corresponding to the main scanning, and the same striae / birefringence also occurs in the case of the plastic lens 10. Areas are likely to occur.

Therefore, the two plastic lenses 1 are arranged so that the projections of the gate portions 10A and 12A are aligned.
When 0 and 12 are provided, both the striae and the birefringence region are likely to be concentrated on the same side of the two lenses, and there is a high possibility that adverse effects synergistically appear on the light spot diameter and the like on this side.

However, as shown in FIG. 1A, if the gate portions 10A and 12A of the plastic lenses 10 and 12 are made to project in mutually opposite directions, striae and birefringence regions of one lens are remarkable. Since this part overlaps with the area with relatively few striae and birefringence areas in the other lens,
The effects on the light spot diameter in the striae / birefringence region are averaged as a whole, and synergistic adverse effects can be effectively reduced.

FIG. 2 shows an embodiment of the optical scanning lens system according to the first and third aspects. In order to avoid complication, the same symbols as those in FIG. 1 are attached to those which are not considered to be confused.

FIG. 2A shows a perspective view of an optical scanning lens system provided between the deflection start point of the light beam by the deflector 1 and the surface 3 to be scanned. The optical scanning lens system is composed of two plastic lenses 11 and 13. Each of these plastic lenses 11 and 13 has gate portions 11A and 13A protruding in the sub-scanning corresponding direction, but in the lens arrangement, the direction of the gate portions 11A and 13A is different between the plastic lenses 11 and 13. They are opposite each other.

FIG. 2B shows the state of the striae 120 in the plastic lens 11, and FIG. 2C shows the state of the birefringent region 130 in the lens 11 (photoelastic image). As shown in FIG. 2B, the striae 120 are likely to occur on the gate portion 11A side, and tend to occur long in the left-right direction in the main scanning corresponding direction starting from the position of the gate portion.

As shown in FIG. 2C, the gate portion 11A
In the case where is projected in the sub-scanning corresponding direction, the birefringent region 130 appears on both side edge portions of the lens in the sub-scanning corresponding direction, but is more likely to occur on the gate portion 11A side.

The tendency of the striae / birefringence region to occur is also common when the gate portion projects in the sub-scanning corresponding direction, and the striae / birefringence also occurs in the case of the plastic lens 13. Areas are likely to occur.

Therefore, the two plastic lenses 1 are arranged so that the projections of the gate portions 11A and 13A are aligned.
When 1 and 13 are provided, both the striae and the birefringence region are likely to be concentrated on the same side of the two lenses, and adverse effects are likely to appear synergistically on the light spot diameter and the like on this side.

However, as shown in FIG. 2A, if the protruding directions of the gate portions 11A and 13A of the plastic lenses 11 and 13 are made opposite to each other, striae and birefringence regions of one lens are remarkable. Since this part overlaps with the area with relatively few striae and birefringence areas in the other lens,
The effects on the light spot diameter in the striae / birefringence region are averaged as a whole, and synergistic adverse effects can be effectively reduced.

FIG. 3 shows an embodiment of the optical scanning lens system according to the fourth and fifth aspects. In this figure as well, the same reference numerals as those in FIG. 1 are used for those which are not considered to be confused.

FIG. 3A shows a state in which the optical scanning lens system provided between the deflection beam starting point of the deflector 1 and the surface to be scanned 3 is viewed from the sub-scanning corresponding direction. The optical scanning lens system is composed of one plastic lens 14 and one glass lens 16.

Since the plastic lens 14 has the gate portion 14A protruding in the main scanning corresponding direction, striae 100A are generated on the gate portion 14A side and the birefringent region 120A is gated as shown in FIG. 3B. Remarkably appears on the side of the portion 14A.

However, of the two lenses, the lens 16
Is a glass lens, there is no overlap between striae and birefringence in the combination of these two lenses. Therefore, "synergistic" to the light spot diameter due to "overlap of striae and birefringence" There is no “adverse effect” (Claim 5).

Further, the three positions 14-1, 14-2, 14-3 shown in FIG. 3B as incident positions of the deflected light beam on the plastic lens 14 (since the light beam is deflected, the incident positions are (It becomes a straight line parallel to the main scanning corresponding direction), striae 10 at the incident position 14-1.
The influence of 0 A is great, and the influence of the birefringence region 120 A is strong at the incident position 14-3. However, at the incident position 14-2, the influence of the striae 100A and the birefringence region 120A is small.

Therefore, as shown in FIG. 3A, the position of the plastic lens 14 is adjusted in the sub-scanning corresponding direction by the adjusting mechanism 15 so that the incident position of the deflected light beam becomes as shown in FIG.
By setting the incident position 14-2 in (b), it is possible to further reduce the influence of the striae / birefringence region and perform optical scanning.

As the adjusting mechanism 15, a known appropriate one can be used. For example, the one shown in FIG. 3C can be used. That is, the plastic lens 14 is arranged in the frame 150, the leaf springs 151 and 152 exert an upward elastic force on the lens end face in the sub-scanning corresponding direction, and the adjusting screws 153 and 154 are provided on the opposite end face.
Abut the tip. By adjusting the adjusting screws 153 and 154, the displacement of the plastic lens 14 can be adjusted in the sub scanning corresponding direction.

Even in the case where the gate portion is a plastic lens projecting in the sub-scanning direction, the displacement of the plastic lens is adjusted in the sub-scanning corresponding direction so that the deflected light beam is made incident on a portion less affected by the striae / birefringence region. To get the figure 2
It will be easily understood from the appearance of the striae / birefringence region in (b).

Therefore, adjusting the displacement of the plastic lens in the sub-scanning corresponding direction so that the deflected light beam is incident on the portion less affected by the striae / birefringence region is also applicable to the embodiments of FIGS. it can. In this case, the displacement may be adjusted by one of the two plastic lenses or both of them. Furthermore, two or more plastic lenses are used,
When one or more of them are adjusted for displacement in the sub-scanning corresponding direction, the directions of the gate portions may be the same for all plastic lenses.

FIG. 4 shows an embodiment of the optical scanning lens system according to the sixth and seventh aspects. In order to avoid complication, the same reference numerals as those in FIG. 1 are used in FIGS.

FIG. 4A is a perspective view showing a state in which an optical scanning lens system is provided between the deflecting origin of the light beam by the deflector 1 (rotary polygon mirror) and the surface 3 to be scanned. .

The optical scanning lens system is composed of two plastic lenses 11 'and 13'. Each of the plastic lenses 11 'and 13' is a projection 1 for positioning, which projects in the same direction (downward in the figure) in the sub-scanning corresponding direction.
It has 1A 'and 13A'.

In this embodiment, the plastic lenses 11 'and 13' are both in the incident area of the deflected light beam, that is, the deflection area is "crossed" by the plastic lenses 11 'and 13'. It is assumed that the striae / birefringence region due to the gate portion does not affect the deflected light beam.
Are not shown.

FIG. 4 (b) shows the positional relationship of the two plastic lenses 11'13 'of the optical scanning lens system as seen from the optical axis direction, shifted vertically. The positioning projections 11A ′ and 13A ′ both project in the same direction in the sub-scanning corresponding direction (vertical direction in the drawing), but with respect to the main scanning corresponding direction (horizontal direction in the drawing), with respect to the common optical axis, They are on the opposite side of each other.

That is, the positioning projections 11A ', 13
The position of A ′ is “the deflected light beam passing near the positioning projection 11A ′ on the plastic lens 11 ′ is
Protrusion 13A 'for positioning the plastic lens 13'
It is set to "pass a position away from".

Taking the plastic lens 11 'as an example, the state of the striae 120' by the positioning projection 11A 'is as shown in FIG. 4 (c), and the birefringent region 130' is shown in FIG. 4 (d). As shown in FIG.
It occurs near A '.

With respect to the plastic lens 13 ', the same type of "stria / birefringence region" has the projection 13 for positioning.
Although it occurs in the vicinity of A ′, as shown in FIG. 4B, the positioning projections 11A ′ and 13A ′ are positioned on the opposite side in the main scanning corresponding direction with respect to the optical axis. There is little overlap between the striae / birefringence regions 11 'and 13', and the striking / birefringence region in one lens is notable and the striae / birefringence region in the other lens is relatively small. Since they overlap, the effect on the light spot diameter in the striae / birefringence region is averaged as a whole,
It is possible to effectively reduce synergistic adverse effects.

FIG. 5 is a diagram for explaining one embodiment of the optical scanning lens system according to the eighth aspect. The optical scanning lens is composed of two plastic lenses 12 'and 14', and is arranged between the deflection start point of the light beam by the deflector and the surface to be scanned, as in FIG. 4A. The plastic lens 12 'is on the deflection starting point side, and the plastic lens 14' is on the scanned surface side.

FIG. 5A shows a plastic lens 12 '.
The positional relationship of 14 'when viewed from the optical axis direction is shown shifted in the vertical direction. Positioning projections 12A ', 14A'
Both project in the same direction (downward in the figure) in the sub-scanning corresponding direction (vertical direction in the figure), but in the main-scanning corresponding direction (horizontal direction in the figure), they are opposite to each other with respect to the common optical axis. is seperated. Also, plastic lens 12 '
, The gate portion 12B ′ projects rightward at the right end in the main scanning corresponding direction, whereas in the plastic lens 14 ′, the gate portion 14B ′ extends leftward at the left end in the main scanning corresponding direction. Protruding to.

That is, in this example, the plastic lens 1
2'and 14 'are striae and birefringence regions by the positioning projections 12A' and 14A 'and striae and birefringence regions by the gate portions 12B' and 14B 'with respect to the incident region of the deflected light beam. However, the size is large enough to affect.

In this case, the striae / birefringence region due to the gate portion will be described by taking the plastic lens 14 'as an example. As shown in FIG. 5B, the gate portion 14B' projects in the main scanning corresponding direction. If you have a striae 100 '
Is easily generated in the main scanning corresponding direction on the gate portion side from the position of the gate portion, and the birefringent regions 110 ′ appear at both ends of the lens in the main scanning corresponding direction, but on the gate portion 14B ′ side. In, it is more likely to occur.

In the case of the plastic lens 12, there is a high possibility that similar striae and birefringence regions will be generated.

Therefore, when the two plastic lenses 12 'and 14' are arranged so that the projections of the gate portions 12B 'and 14B' are aligned, two striae and birefringence regions due to the gate portions are provided. It is easy to concentrate on the same side of the lens, and there is a high possibility that adverse effects such as the light spot diameter will appear synergistically on this side.

However, as shown in FIG. 5A, the gate portions 12B ', 1 of the plastic lenses 12', 14 'are
If the protruding directions of 4B ′ are made opposite to each other, a striking portion of the striae / birefringence region of one lens overlaps with a relatively small region of the striae / birefringence region of the other lens. The influence on the light spot diameter of the birefringence region is averaged as a whole, and the synergistic adverse effect can be effectively reduced.

Striae / birefringence regions are also generated by the positioning projections 12A 'and 14A'. The striae / birefringence region in this case corresponds to the striae 12 described with reference to FIGS. 4C and 4D in accordance with the protrusions 12A ′ and 14A ′.
It will be readily understood that 0'will be similar to the birefringent region 130 '.

In the striae / birefringence region formed by the positioning projections 12A 'and 14A', the projections 12A 'and 14A' are positioned apart from each other on the opposite side in the main scanning corresponding direction with respect to the optical axis. , Each plastic lens 12 ', 1
The striations / birefringence regions do not overlap with each other due to the 4'positioning projection, and a striking portion of the striae / birefringence regions in one lens overlaps the region in which the striae / birefringence region in the other lens is relatively small. Therefore, the influence on the light spot diameter in the striae / birefringence region is averaged as a whole, and the synergistic adverse effect can be effectively reduced.

That is, in the embodiment of FIG. 5, the concentrated overlap of striae and birefringence regions associated with the gate portion and the positioning projections is alleviated and averaged. Adverse effects can be effectively reduced.

FIG. 6 is a view for explaining a characteristic part of two examples of the embodiment of the optical scanning lens system according to claim 9, FIG.
It is a figure drawn after.

In the embodiment shown in FIG. 6A, the optical scanning lens system is composed of two plastic lenses 113 and 115 formed by plastic molding, both of which have the same sub-scanning corresponding direction. Orientation (downward in the figure)
Positioning projections 113A and 115A that project inward, and a gate portion 113 that projects in opposite directions in the sub-scanning corresponding direction.
B, 115B. The protrusions 113A and 115A are
When viewed from the optical axis direction, they are set apart from each other on the left and right sides of the optical axis (corresponding to the main scanning direction), and the gate portions 113B and 115B are opposite to each other in the sub scanning corresponding direction (vertical direction in the figure) at the optical axis position. The deflected light beam, which is positioned so as to project in the vicinity of the projection 113A for positioning the plastic lens 113 and the vicinity of the gate portion 113B, is separated from the projection 115A for positioning the plastic lens 115 and the gate portion 115B. It is designed to pass through.

Both the striae / birefringence regions formed by the positioning projections 113A and 115A and the striae / birefringence regions formed by the gate portions 113B and 115B are the same as those shown in FIGS. 4 (b) and 4 (c). The projections 113A and 115
Since the "concentrated overlap" of the striae / birefringence regions due to A and the gate portions 113B and 115B is mitigated and averaged, synergistic adverse effects on the light spot diameter and the like can be effectively mitigated.

In this example, the gate portions 113B and 115B are set at the optical axis positions in the main scanning corresponding direction when viewed from the optical axis direction, but they are distributed to both sides of the optical axis in the main scanning corresponding direction. May be deployed.

In the embodiment shown in FIG. 6B, the optical scanning lens system is composed of two plastic lenses 213 and 215 formed by plastic molding, both of which have the same sub-scanning corresponding direction. Orientation (downward in the figure)
Positioning projections 213A and 215A that project inward and a gate portion 213 that projects in opposite directions in the sub-scanning corresponding direction.
B, 215B. The protrusions 213A and 215A and the gate portions 213B and 215B are all set apart from each other on the left and right of the optical axis (main scanning corresponding direction) when viewed from the optical axis direction, and are the same in the sub scanning corresponding direction (vertical direction in the drawing). The deflected light beam, which is formed so as to project in the direction (downward in the drawing) and passes near the positioning projection 213A of the plastic lens 213 and near the gate portion 213B, generates the projection 215A for positioning the plastic lens 215 and the gate. It is designed to pass through a position away from the portion 215B.

The striae / birefringence regions formed by the positioning projections 213A and 215A and the striae / birefringence regions formed by the gate portions 213B and 215B are the same as those shown in FIGS. 4 (b) and 4 (c). And the protrusions 213A and 215
A, the “concentrated overlap” of striae / birefringence regions due to the gate portions 213B and 215B is mitigated and averaged, so that a synergistic adverse effect on the light spot diameter and the like can be effectively mitigated.

Claims 6 to 9 described with reference to FIGS.
Also in the optical scanning lens system described above, as in the optical scanning lens system according to claim 4, "adjustment for adjusting the position of at least one plastic lens formed by plastic molding in the sub-scanning corresponding direction" A mechanism "(claim 10).

The plastic lens 1 shown in FIG. 4 (d).
1 ′ will be described as an example. Since the plastic lens 11 ′ has a positioning protrusion 11A ′ that protrudes in the sub-scanning corresponding direction, as shown in the figure, the protrusion 11A
In the vicinity of A ′, the birefringent region 130 ′ remarkably appears on the side of the protrusion 11A ′.

The three positions 11-1, 11-2, 11-3 shown in FIG. 4 (d) for the incident position of the deflected light beam on the plastic lens 11 '(since the light beam is deflected, the incident position is Considering a straight line parallel to the main scanning corresponding direction), the birefringence region 130 ′ is largely affected at the incident positions 11-1 and 11-3, but the incident position 11-
In Fig. 2, the influence of the birefringent region 130 'is also affected by striae 120' (Fig. 4).
(C)) is small.

Therefore, the position of the plastic lens 11 'is adjusted in the sub-scanning corresponding direction by the adjusting mechanism so that the incident position of the deflected light beam becomes the incident position 11-2 in FIG. 4 (d). The optical scanning can be performed while reducing the influence of the striae / birefringence region.

As the "adjustment mechanism" for adjusting the displacement of the plastic lens 11 'in the sub-scanning corresponding direction, one as shown in FIG. 7 can be used. That is, the plastic lens 11 'is arranged in the frame 1500, the leaf springs 1510 and 1520 exert an upward elastic force on the lens end face in the sub-scanning corresponding direction, and the adjusting screws 1530 and 1540 are provided on the opposite end face. Abut the tip. Adjustment screw 1
Plastic lens 1 by adjusting 530 and 1540
It is possible to adjust the displacement of 1'in the sub scanning corresponding direction.

Since the adjustment screws 1530 and 1540 can be adjusted independently, the held plastic lens 11 'is adjusted in the sub scanning corresponding direction and the plastic lens 11' is tilted in the main scanning corresponding direction. It is also possible to adjust the tilt position so that the deflected light beam passes through a place where the striae / birefringence region of the plastic lens is less affected.

The reduction of the influence on the optical scanning of the striae / birefringence region by the displacement adjustment of the plastic lens can be performed on the other plastic lenses shown in FIGS. When the lens system for use includes three or more plastic lenses, it can be applied to two or more of them.

Further, when two or more plastic lenses are used and one or more of them are subjected to displacement adjustment in the sub-scanning corresponding direction, the direction of the gate portion may be the same for all the plastic lenses. .

Further, in the optical scanning lens system according to claims 6 to 10, "one or more glass lenses" can be included in the optical scanning lens system (claim 11).
If at least one of the lenses constituting the optical scanning lens system is a glass lens, since the glass lens has no striae or birefringence regions, it is possible to effectively reduce the overlap between the striae and birefringence regions. In particular, in the optical scanning lens system according to claim 10, if one or more lenses are glass lenses,
Similar to the optical scanning lens system according to claim 5, there is no overlap between striae and birefringence regions between the glass lens and the plastic lens, and therefore, due to "overlap between striae and birefringence regions". "Synergistic adverse effect" on the light spot diameter can be reduced, and by adjusting the position of the plastic lens in the sub-scanning corresponding direction and the tilt position with respect to the main scanning corresponding direction, the light spot in the striae / birefringence region can be adjusted. The effect on the diameter can be further reduced.

In the case of the embodiment of FIG. 3 in which the optical scanning lens system is composed of one plastic lens and one glass lens, the plastic lens 14 in FIG.
It can be replaced with one of the plastic lenses shown in FIGS.

[0086]

As described above, according to the present invention, a novel optical scanning lens system can be provided. Since the optical scanning lens system of the present invention according to claims 1 to 5 is configured as described above, the optical scanning is performed by effectively reducing the adverse effects of the striae and the birefringence region due to the gate portion in the plastic lens. I can do it.

Further, since the optical scanning lens system according to the present invention has the above-mentioned constitution, the striation / birefringence region by the positioning projection of the plastic lens or the positioning projection is formed. Optical scanning can be performed by effectively reducing the adverse effect of the striae / birefringence region due to the gate portion.

[Brief description of drawings]

FIG. 1 is a diagram for explaining one embodiment of the invention described in claims 1 and 2.

FIG. 2 is a diagram for explaining one embodiment of the invention described in claims 1 and 3;

FIG. 3 is a diagram for explaining one embodiment of the invention described in claims 4 and 5.

FIG. 4 is a diagram for explaining one embodiment of the invention according to claims 6 and 7;

FIG. 5 is a diagram for explaining one embodiment of the invention according to claim 8;

FIG. 6 is a diagram for explaining two examples of the invention according to claim 9;

FIG. 7 is a diagram for explaining a characteristic part of the embodiment of the invention described in claim 10;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Optical deflector 3 Scanned surface 10, 12 Plastic lens which comprises the lens for optical scanning 10A, 12A Gate part 11A ', 13A' Positioning protrusion 100 Striae 120 Birefringence area | region

Claims (11)

[Claims] 1. A lens system provided in an optical scanning device between a deflection origin of a light beam and a surface to be scanned, the lens system including two or more plastic lenses formed by plastic molding. An optical scanning lens system, wherein at least one of the lenses is arranged such that the direction of the gate portion is opposite to the direction of the gate portion of another plastic lens. 2. The optical scanning lens system according to claim 1, wherein each of two or more plastic lenses formed by plastic molding has a gate portion protruding in a main scanning corresponding direction. Lens system. 3. The optical scanning lens system according to claim 1, wherein each of the two or more plastic lenses formed by plastic molding has a gate portion protruding in the sub-scanning corresponding direction. Lens system. 4. A lens system provided in an optical scanning device between a deflection origin of a light beam and a surface to be scanned, comprising one or more plastic lenses formed by plastic molding. An optical scanning lens system having an adjusting mechanism for adjusting the position in the sub-scanning corresponding direction. 5. The optical scanning lens system according to claim 1, 2 or 3 or 4, comprising one or more glass lenses. 6. A lens system provided in an optical scanning device between a deflection origin of a light beam and a surface to be scanned, the lens system including two or more plastic lenses formed by plastic molding. Each of the lenses has a projection for positioning, and each plastic lens is so arranged that the deflected light beam passing near the positioning projection of each plastic lens passes through a position away from the positioning projections of other plastic lenses. An optical scanning lens system characterized in that the position of a positioning projection on a lens is set. 7. The optical scanning lens system according to claim 6, wherein each of the two or more plastic lenses formed by plastic molding has a positioning protrusion protruding in the sub-scanning corresponding direction. Optical scanning lens system. 8. The optical scanning lens system according to claim 6, wherein each of the two or more plastic lenses formed by plastic molding has a positioning protrusion protruding in the sub-scanning corresponding direction and a main scanning corresponding direction. A projecting gate portion, and at least one of the two or more plastic lenses is arranged such that the direction of the gate portion is opposite to the direction of the gate portion of the other plastic lens. Optical scanning lens system. 9. A lens system arranged between an origin of deflection of a light beam and a surface to be scanned in an optical scanning device, comprising two or more plastic lenses formed by plastic molding, and formed by plastic molding. Each of the two or more plastic lenses has a positioning protrusion protruding in the sub-scanning corresponding direction and a gate portion protruding in the sub-scanning corresponding direction, and the vicinity of the positioning protrusion of each plastic lens and the gate portion. The positions of the positioning protrusion and the gate portion of each plastic lens are set so that the deflected light beam that passes near the lens passes through the position away from the other lens positioning protrusion and the gate portion. Optical scanning lens system. 10. The optical scanning lens system according to claim 6, 7 or 8 or 9, wherein at least one or more plastic lenses formed by plastic molding are positionally adjusted in the sub-scanning corresponding direction, and An optical scanning lens system having an adjusting mechanism for adjusting an inclination state with respect to a scanning corresponding direction. 11. The optical scanning lens system according to claim 6, 7 or 8 or 9 or 10, wherein the optical scanning lens system includes one or more glass lenses.