Plastic lens, method for manufacturing the same, and imaging device using the same
View Patent ↗A plastic lens 1 has a lens 2 that effectively functions as a lens at a center and an annular flange 3 that does not act as a lens along a circumference of the lens. A gate 4 serving as a flow channel through which molten plastic is to be poured during molding is formed on a circumference of the flange. The gate is cut and taken away at an angle of inclination so as to include a point of intersection between the gate 4 and the circumferential flange 3 , whereby a circumferential flange having a given thickness or more is formed.
1. A method for manufacturing an imaging device including a plastic lens, the method including:
steps of injecting a resin by a gate of dies and injection-molding a plastic lens having a main body constituting an effective optical region, an annular flange formed integrally on an outer circumference of the main body, and a gate made up of a projection formed on a circumference of the flange from the gate of the dies, the annular flange including a tubular first circumferential surface that is parallel to an optical axis of the main body, and a tubular second circumferential surface that is parallel to the optical axis of the main body and is formed continuously from the first circumferential surface;
a cutting step of cutting the gate from the injection-molded plastic lens, together with a part of the second circumferential surface, along a cut plane including a point of intersection between the gate and the flange at an angle of inclination 0≦α 1 ≦θ≦α 2 , the angle of inclination θ being an acute angle made by the cut plane and the optical axis; and
a fixing step of, after the cutting step, anchoring the plastic lens to a lens holder by means of thermal caulking,
wherein, provided that an outer diameter of the flange is taken as D; that an entire length of the tubular first circumferential surface in its thicknesswise direction is taken as H 1 ; that a height and a width of the gate for representing a size of the gate are H 2 and W, respectively, that an entire length of the flange before cutting the gate achieved in a direction of an optical axis is taken as H 3 ; that a point of intersection between the cut plane of the gate and the flange is taken as Q 1 ; a point of intersection between the gate and the circumferential flange is taken as Q 2 (Q 2 ′); and that a vertical distance from a straight line passing through the points Q 2 and Q 2 ′ to a line parallel to the optical axis passing through the point Q 1 is taken as δ, a minimum angle of inclination α 1 and a maximum angle of inclination α 2 for obtaining an circumferential flange having a given thickness or more are set so as to fulfill Expressions (2), (3), (4), (5) and (6) provided below:
[
Mathematical
Expression
1
]
α1
=
arctan
(
δ
(
H
3
-
H
1
-
H
2
)
)
,
(
2
)
(
D
2
-
δ
)
2
+
(
W
2
)
2
=
(
D
2
)
2
,
(
3
)
α1
=
arctan
(
D
-
D
2
-
W
2
2
×
(
H
3
-
H
1
-
H
2
)
)
,
(
4
)
a
2
=
arctan
(
D
-
d
2
×
(
H
3
-
H
1
)
)
,
and
H
1
>
H
3.
(
5
)
2. The method of claim 1 , wherein after the cutting step, the second circumferential surface includes a partially tubular surface that is parallel to the optical axis of the main body and an inclined surface that obliquely cuts the flange from a first point on the first circumferential surface toward a back of the main body with respect to the direction of the optical axis.
3. The method of claim 1 , wherein after the cutting step, no gate residue remains in the flange.
4. An imaging device, comprising:
a first surface lens including a plastic lens;
a group of lenses disposed inside the first surface lens;
a lens holder supporting the first surface lens and the group of lenses; and
an imaging element forming an image from entrance light passing through the first surface lens and the group of lenses, wherein:
the plastic lens comprises:
a main body constituting an effective optical region; and
an annular flange integrally formed on a circumference of the main body,
the flange has a tubular first circumferential surface that is parallel to an optical axis of the main body, and a second circumferential surface including a partially tubular surface that is parallel to the optical axis of the main body and an inclined surface that obliquely cuts the flange from a first point on the first circumferential surface toward a back of the main body with respect to the direction of the optical axis, the tubular surface of the second circumferential surface being formed continuously from the first circumferential surface,
no gate residue exists on the flange,
the inclined surface is located closer to the back of the main body than a front of the main body,
a thickness of the tubular first circumferential surface is one half or more of a thickness of the flange, and
the lens holder and the first surface lens are anchored by means of thermal caulking.
5. The imaging device according to claim 4 , wherein an angle of inclination θ of the inclined surface with respect to the optical axis satisfies the following expression (1):
θ≧arctan(( D−d )/( H 1/2)) (1), where:
D: outer diameter of a flange,
d: radius of main body, and
H 1 : entire length of flange in its thicknesswise direction.
6. The imaging device according to claim 4 , wherein the plastic lens is manufactured by injection molding.
7. The imaging device according to claim 4 , further comprising a sealing member fitted to the flange.