Lens barrel

Details Lens barrel Lens barrel

2003-03-26

2004-09-21

Epps, Georgia (Department: 2873)

Optical: systems and elements

Lens

With support

C359S699000, C359S700000

Reexamination Certificate

active

06795259

ABSTRACT:

This application claims the benefit of Japanese Patent applications No. 2002-091717 and No. 2002-219461 which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a lens barrel structured to extract a straight advancing motion from a rotary motion of a frame member and to perform an operation such as a lens extension, etc.
2. Related Background Art
In this type of lens barrel, a lens extension-and-reduction mechanism has hitherto been constructed of a multi-thread screw called a helicoid or a cam mechanism configured by cam pins and cam grooves.
FIG. 13
is a view showing the helicoid in development in one conventional lens barrel.
In this conventional lens barrel, a female helicoid member
10
having a female helicoid includes a first guide groove
10
a
for moving back and forth in the optical-axis directions corresponding to rotations, and a second guide groove
10
b
(a lead-0 portion) defined as a groove formed in a circumferential direction in continuation with the first guide groove
10
a.
FIG. 14
is a partially enlarged view of FIG.
9
.
A male helicoid member
20
having a male helicoid engaging with the female helicoid of the female helicoid member
10
, has a guide protruded portion
200
configured by surfaces
20
a
,
20
b
facing to the first guide groove
10
a
, and surfaces
20
c
,
20
d
facing to the second guide grooves
10
b
(the lead-0 portion).
The male helicoid member
20
, when making the relative rotary motion to the female helicoid member
10
by the rotation of the female helicoid member
10
, through engaging with the first guide groove
10
a
, moves in the optical-axis direction corresponding to the rotation. In an area of the second guide groove
10
b
(the lead-0 portion), the relative movement in the direction of rotation is made, however, no movement in the optical-axis direction is made. The function of the second guide grove
10
b
is, as disclosed in, for example, Japanese Patent Application Laid-Open No.11-23937, utilized for opening and closing a lens barrier.
FIGS. 15 through 17
are views showing a helicoid of another conventional lens barrel in development.
In this conventional lens barrel, a female helicoid member
10
having a female helicoid includes a helical groove
10
a
for moving back and forth in the optical-axis directions corresponding to rotations, and a circumferential groove
10
b
defined as a groove formed in the circumferential direction in continuation with the helical guide groove
10
a.
A male helicoid member
20
, when making the relative rotary motion to the female helicoid member
10
by the rotation of the female helicoid member
10
, through engaging with the first guide groove
10
a
, moves in the optical-axis direction corresponding to the rotation. In the circumferential groove lob, the relative movement in the direction of rotation is made, however, no movement in the optical-axis direction is made.
What is required of the conventional lens barrel described above is a contrivance for preventing the operation from becoming unstable due to interference with the helical groove
10
a
when the protruded portion of the male helicoid member
20
passes through the circumferential groove
10
b.
Further, it is also required that an incorrect helical engagement with an adjacent groove different from the predetermined position be avoided.
For meeting these requests, there has hitherto been adopted a configuration that the number of grooves is restricted, and the grooves are thinned out.
Moreover, the helicoid engagement is established by decreasing a length (an angle of rotation) of the circumferential groove
10
b.
Accordingly, the helicoid is unable to be disposed along the entire periphery, and an engaging area is reduced, resulting in a drop of engaging force. When receiving an external force, the helicoid might come off the engagement thereof.
Further, in an area where the helicoid engagement is attained, it is possible to shield the light that is to leak through a gap between the female helicoid member
10
and the male helicoid member
20
. In an area where the helicoid engagement is not attained, however, a problem arises, wherein the light-shielding can not be performed, and a light shielding means is needed.
A further problem is that a non-groove area of the inner periphery of the female helicoid member
10
expands, and, when a beam of light is projected on this area, an intensive reflection occurs to cause a flare.
A still further problem is that the helicoid engaging areas can be provided merely in approximately three directions on the circumference because of the configuration of thinning out the helicoid grooves, and ununiform rotations are caused due to sinking in a recessed portion, etc. necessary for a secant relief of a die assembly, which is provided in the inner periphery of the female helicoid member
10
.
A yet further problem is that the priority given to establishing the small number of engaging areas conduces to a restraint in terms of design.
SUMMARY OF THE INVENTION
It is a primary object of the present invention to provide a lens barrel capable of being formed with a multiplicity of grooves, attaining a stable helical engagement, obtaining a high engagement force, exhibiting an excellent light shielding characteristic and making difficult occurrences of the caused-by-stray-light flare, ghost, etc.
To accomplish the above object, according to one aspect of the present invention, a lens barrel includes a first cylindrical member having an inner peripheral surface, and a second cylindrical member internally fitted to the first cylindrical member and having an outer peripheral surface that facing in a radial direction to the inner peripheral surface of the first cylindrical member, wherein any one of the inner peripheral surface and the outer peripheral surface is formed with first and second grooves taking a helical shape and extending in an axial direction in parallel with each other, and a third groove extending in only a circumferential direction continuously from one side ends of the first and second grooves, the other of the inner peripheral surface and the outer peripheral surface are formed with first and second protruded portions engaging respectively with the first and second grooves in alignment in the circumferential direction and enabling relative rotations between the first and second cylindrical members and relative movements in the axial direction therebetween, the first and second protruded portions engage respectively with the first and second grooves with the result that the first and second cylindrical members make the relative rotations and the relative movements in the axial direction, and, when reaching the third groove, move through within the third groove, and the first and second cylindrical members are allowed to make only the relative rotations without moving in the axial direction, and the third groove includes a guide portion, formed in continuation from the first groove, for guiding the first protruded portion into the first groove.
In the lens barrel according to the present invention, preferably the second groove includes a portion, formed adjacent to the third groove, for inhibiting the first protruded portion from entering.
In the lens barrel according to the present invention, preferably a height of the first protruded portion is larger than a height of the second protruded portion, and the entrance inhibiting portion of the second groove has a depth set to permit the second protruded portion to pass through and to inhibit the first protruded portion from passing through.
In the lens barrel according to the present invention, preferably the guide portion is a groove bottom portion formed, in the third groove, having a depth set to permit the second protruded portion to pass through and to inhibit the first protruded portion from passing through.
In the lens barrel according to the present invention, preferably a length of the first protruded portion in an extending direction of th

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