Optical: systems and elements – Lens – With support
Reexamination Certificate
1999-08-04
2001-09-25
Mack, Ricky (Department: 2873)
Optical: systems and elements
Lens
With support
C065S037000, C065S039000
Reexamination Certificate
active
06295172
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a molding apparatus for molding an optical element such as a glass-molded lens from a thermally softened glass material by pressing a mold, an optical element molding method, and an optical element and prism as molded products.
Conventionally, to obtain a glass-molded lens, a molding apparatus, the main section of which is shown in
FIG. 1
, is used. In
FIG. 1
, a glass gob
1
having a predetermined weight is placed between lower and upper molds
2
and
3
slidably arranged in a cylindrical mold
4
, and is softened by heating. The lower and upper molds
2
and
3
are made relatively come close to each other to press-mold the glass gob
1
, thereby obtaining a required optical glass element such as a glass-molded lens.
With the molding apparatus having this mold structure, the cavity formed in the cylindrical mold
4
is a closed space partitioned by the molding surfaces of the lower and upper molds
2
and
3
. When the glass-molded lens is obtained by this apparatus, variations in weight of the glass gob directly appear as variations in thickness of the lens to adversely affect the optical characteristics of the lens.
In order to eliminate the influence cased by the variations in weight of the glass gob, a countermeasure for this is proposed. As shown in
FIG. 2
, when press molding is performed with upper and lower molds
7
and
6
so as not to regulate the periphery of the glass material with the inner surface of a cylindrical mold
8
, an excess
5
of the glass gob is allowed to swell from the edges of the molding surfaces and is received in a recess formed in the inner surface of the cylindrical mold
8
.
When the recess is formed in this manner such that the entire periphery of the side surface of the lens to be molded forms an equal swell-out portion, the swell-out portion must be additionally formed with a portion that serves as a reference when incorporating the molded lens in a predetermined holding frame.
In order to avoid this additional formation, a molding apparatus shown in, e.g., Japanese Patent Laid-Open No. 60-171233 is employed. In this apparatus, as shown in
FIGS. 3 and 4
, slide cores
10
L and
10
R that slide laterally are molded at portions that form the side surface of the lens, and are moved forward/backward by actuators
11
L and
11
R. Spaces
9
into which the excess of the glass gob can flow are formed at required portions of the slide cores
10
L and
10
R. Hence, the lens can be molded with positional references, in addition to the glass swell-out portion, in the horizontal direction simultaneously with formation of optical functional surfaces.
In order to form the lens surfaces and the lens positioning references simultaneously, Japanese Patent Publication No. 63-10100 has already proposed a molding apparatus necessary for this. As shown in
FIG. 5
, a side surface regulating portion
17
is formed only on the inner surface of a cylindrical mold
16
which does not positionally regulate swelling from the edge of the molding surface of an upper mold
15
but is in contact with the edge of the molding surface of a lower mold
14
corresponding to the optical functional surface of the lens. Alternatively, as shown in
FIG. 8
, upper and lower upper position regulating members
24
and
23
that form position regulating portions
28
and
27
are formed on the edges of the molding surfaces of upper and lower molds
22
and
21
in a cylindrical mold
25
. The molding apparatus has both a portion that regulates circumferential swelling of the softened glass gob from the edges of the upper and lower molds, and a portion
18
(see
FIG. 5
) or
26
(see
FIG. 8
) that does not regulate the softened glass gob but allows it to swell out.
A molded optical element as the target of the proposed molding apparatus is axially symmetrical. The amount of excessive glass swelling out from the edges of the molding surfaces of the upper and lower molds when performing press molding can be automatically set constant highly precisely if the gap between the edges of the molding surfaces is kept constant.
In the molding apparatus of Japanese Patent Laid-Open No. 60-171233, the actuators
11
L and
11
R for driving the slide cores
10
L and
10
R are needed, leading to a complicated structure. In the molding apparatus of Japanese Patent Publication No.
63-10100,
these actuators are not needed and both the glass regulating portion and portion that allows swelling can be provided. In the latter apparatus, as shown in
FIGS. 6 and 7
, and
9
and
10
, regarding its mold structure, a positional reference
19
, or positional references
30
and
31
are formed on the outer surface of the molded optical element. Simultaneously, a continuous annular swell-out portion
20
or
29
is formed to surround the outer surface of the molded optical element. Conventionally, most optical elements molded by glass molding are axially symmetrical. Even if the swell-out portion
20
or
29
annularly surrounds the side surface of the lens at a certain constant height, no particular problem arises.
In recent years, as the types and variations of optical elements increase, a demand for axially asymmetrical lenses increases. Assume that, as shown in
FIG. 13
, an axially asymmetrical optical element is to be molded (in this case, the lower and upper molds are respectively divided into portions
32
a
to
32
c,
and
33
a
to
33
c,
and horizontal position regulating members
34
and
35
are provided around the portions
32
a
to
32
c,
and
33
a
to
33
c,
respectively, to form a space, between position regulating portions
38
and
39
, into which an excess
37
of the glass gob flows when press molding is performed in a cylindrical mold
36
). As shown in
FIG. 14
, when a swell-out portion
40
corresponding to the glass gob excess is formed around the molded optical element, this swell-out portion
40
is present very close to a portion
45
(part of the optical functional surface) on, e.g., side surfaces
41
and
42
of the optical element. The deformation amount of glass is large in the swell-out portion
40
and the outermost portion of the swell-out portion
40
is not regulated by the mold during molding. This adversely affects the planar precision of the peripheral portion of the swell-out portion
40
.
In this manner, if the edge portion of an optical functional surface
43
, or optical functional surfaces
44
and
45
transferred from the molding surface of the upper or lower mold vertically changes and does not have a constant height, the swell-out portion
40
of the glass gob can degrade the planar precision.
In recent years, as the types and variations of optical elements increase, even in molded optical elements such as glass-molded lenses, a demand for molding one having an axially asymmetrical shape increases. When molding an optical element having a general axially asymmetrical shape, it is naturally molded by using an axially asymmetrical mold. During press molding, deformation of the glass material in the horizontal direction is accordingly axially asymmetrical. Assume that such an optical element is to be molded by using a conventionally used mold structure in which the vertical size of the gap, that defines a glass excess, around the edges of the molding surfaces of the upper and lower molds is kept constant. In this case, depending on the relationship between the shape of the glass material before molding and the mold shape, the softened glass may quickly fill even the corners of the mold during molding to result in cracking or cutout during later press molding. Alternatively, the softened glass may not sufficiently fill the corners of the mold even after press molding. The optical functional surface is not perfectly transferred from the molding surface, leading to a molded product having a cut optical functional surface, i.e., a filling defect.
SUMMARY OF THE INVENTION
The present invention has been made on the basis of the above situation, and has as its first object to provide a molding
Matsumoto Kosei
Nakagawa Nobuyuki
Yamamichi Nobuhiro
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Mack Ricky
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