Optical: systems and elements – Lens – With variable magnification
Reexamination Certificate
2000-08-14
2001-06-05
Mack, Ricky (Department: 2873)
Optical: systems and elements
Lens
With variable magnification
C359S699000
Reexamination Certificate
active
06243214
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a lens barrel comprising a cylindrical cam provided with a spiral cam slot for moving a photographing lens system in focusing mode or in zooming mode.
2. Related Background Art
The above-mentioned type of the lens barrel generally contains two or more photographing lens systems disposed therein and performs focusing or zooming by changing the distance between the lens systems.
In the construction for focusing or zooming hitherto generally known, the lens barrel comprises a guide tube in which a member for holding the photographing lens system, for example, a lens frame is mounted. On a part of the guide tube there is formed a linear slot in which a cam pin is engaged. Through the cam pin, the lens frame is supported for movement along the optical axis. Rotatably relative to the guide tube, there is mounted a cylindrical tube on which a spiral cam slot is formed. The spiral cam slot extends circumferentially and inclined to the optical axis. The above-mentioned cam pin is engaged in the spiral cam slot. With the rotation of the cylindrical cam, a force intending to move the lens system forwardly and backwardly in the direction along the optical axis can be transmitted to the lens frame through the cam pin.
The spiral cam slot on the cylindrical cam plays an important role regarding the function to give a lift to the lens system in the direction along the optical axis. For the prior art cylindrical cams made of resin by molding, various methods have been employed to form such spiral cam slot on the cylindrical cam. Some examples thereof are shown in FIGS.
8
through
10
(B).
In the example shown in
FIG. 8
, the cylindrical cam
1
has a cam
2
formed by single surface only.
In another example shown in FIGS.
9
(A) through
9
(E), the spiral cam slot has two side surfaces. One of the two side surfaces is formed by a surface perpendicular to the axis of the cylindrical tube and the other is formed by a surface so inclined as to widen the slot toward the open side.
In a further example shown in FIGS.
10
(A) and
10
(B), a spiral cam slot
2
is formed on the inside surface of the cylindrical cam
1
. The cross-section of the cam slot has a V-form. Engaged in the cam slot is a cam pin
4
which is radially biased by a spring
5
on the side of the lens frame
3
.
SUMMARY OF THE INVENTION
However, the prior art cylindrical cams as shown above, involve some problems, in particular, in connection with the forming of the spiral cam slot
2
on the cylindrical cam
1
made of resin by molding.
For example, in the case of the prior art construction as shown in
FIG. 8
, it is impossible to form any through-slot in the cylindrical cam. Therefore, it is not suitable for the lens barrel of the type in which the element to be moved (lens system) is received in the cylindrical cam. In addition, if the cam
2
has to be formed extending over a wide circumferential area range more than 180° in order to ensure the necessary amount of rotation of the cylindrical cam
1
, it is impossible to form two or more cams
2
simultaneously. Therefore, this example of the prior art construction has a difficulty in attaining the purpose of the smooth guidance of the lens system.
The prior art construction as shown in FIGS.
9
(A) through
9
(E) has also the disadvantage that the range of the extension of the cam slot
2
is limited within a narrow range in view of molding and it is impossible to form the cam slot
2
extending over the rotational range more than 90°.
The last-mentioned prior art construction as shown in FIGS.
10
(A) and
10
(B) has the drawback that it needs a complicated structure and high manufacturing cost. The cam slot
2
of this prior art cylindrical cam has a V-shaped section. Therefore, the cam pin
4
to be engaged in the V-shaped cam slot
2
is needed to be a conical pin. To obtain an exact amount of cam lift, there is required a biasing force intending to push the cam pin
4
against the cam surface thereby removing undesirable gap between the V-shaped cam slot
2
and the conical cam follower
4
. Thus, additional members such as the spring
5
are needed, which leads to complicated construction and cost-up. In the art, therefore, many attempts are being made to solve these problems involved in the prior art.
Accordingly, it is an object of the present invention to provide a lens barrel made of resin and comprising a cylindrical cam having spiral cam slots formed thereon in a simple manner with improved formability.
Another object of the invention is to provide a lens barrel having such spiral cam slots each of which can be formed extending a wide circumferential area range more than 90°.
A further object of the invention is to provide a cylindrical cam provided with spiral cam slots which is resistable against deformation.
It is a further object of the invention to make the cylindrical cam resistable against deformation by forming the spiral cam slots in such manner that the cam slots are distributed about the axis of the cylindrical cam and one side surface of each slot as viewed in the same direction as the axial direction is formed by a surface parallel to the perpendicular to the axis of the cylindrical cam.
In order to attain the above and other objects, the present invention provides a lens barrel comprising a resin cylindrical cam provided with a spiral cam slot for moving a photographing lens system forward and backward in the direction along the optical axis, which is characterized in that the spiral cam slot is composed of a plural number of areas divided around the axis of the cylindrical cam, and that in each of said cam areas, the spiral cam slot has a cam surface and a surface opposite to the cam surface, said cam surface being formed at one side of a section of the spiral cam slot taken along a plane containing a normal line to the axis of the cylindrical cam and orthogonal to the locus along the cam slot and said opposite surface being formed at the other side of said section and inclined to said cam surface providing that these opposite surfaces in adjacent areas be inclined in opposite directions to each other, and that every adjoining part between cam areas includes a first border portion in which said inclined surface is formed by a surface approximately parallel to said cam surface, or a second border portion in which said inclined surface is formed by two oppositely inclined adjacent surfaces, said first and second border portions being disposed alternately in said plural number of cam areas.
The present invention provides also a lens barrel mentioned above which is further characterized in that among said plural number of cam areas constituting the spiral cam slot, those areas in which said inclined surface on the other side is so inclined as to inwardly widen the slot, are formed by groove portions recessed from the inside surface of the cylindrical cam.
According to the invention, by combining together a plural number of divided areas, the spiral cam slots can be formed extending continuously over a wide area range more than 90° on a cylindrical cam. Furthermore, it is possible to moderate the inclination of the spiral cam slot to the optical axis when the amount of movement of the lens system is the same as that in the prior art one. Therefore, the turning force of the cylindrical cam required for moving the lens system can be decreased accordingly. As the result, the driving torque for rotating the cylindrical cam can be reduced substantially.
Further, since one side surface of the cam slot extending over the area more than 90° is formed by a surface extending parallel to the perpendicular to the axis of the cam surface, a straight pin can be used as the cam follower (
14
in FIG.
4
). This makes it possible to exactly transmit the cam lift to the lens system even if there is any play of the pin in the slot in the direction of the plane extending perpendicularly to the optical axis of the lens system in the lens barrel.
These objects and advantages of this in
Mack Ricky
Nikon Corporation
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