Lens barrel

A lens barrel of a camera has a stationary cylinder and a rotary cylinder which is advanced and retracted relative to the stationary cylinder while it is rotated. A plurality of helical gears as well as a helicoid are formed, along the helicoid, on an outer periphery of the rotary cylinder which is helicoid-coupled to the stationary cylinder and advanced and retracted along the optical axis while it is rotated. A plurality of drive gears which are gear-coupled to the helical gears are formed on the stationary cylinder. At least one of the plurality of drive gears is gear-coupled to the helical gears in a rotation range of the rotary cylinder.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a lens barrel suitable for use in driving 
in and out in a sink barrel type camera, zoom-driving a photographing lens 
system in a zooming camera or focus-driving a photographing lens system in 
an AF camera. 
2. Related Background Art 
In a recent compact camera, a sink barrel type in which a lens barrel is 
driven into a camera body is adopted to meet a requirement of compactness 
and thinness. 
In a lens barrel of such a sink barrel type camera, a rotating drive force 
from a drive source such as an electric motor is transmitted by a drive 
gear to a rotary cylinder which is rotatably held by a helicoid coupling 
in a stationary cylinder on a camera body, and the rotary cylinder is 
driven out along an optical axis while it is rotated so that the lens 
barrel is projected from the front surface of the camera body to be ready 
for photographing, and the rotary cylinder is reversely rotated to drive 
it into the camera body. 
In a recent camera, as a part of multi-functioning of the camera, a zoom 
lens which permits photographing from telescopic range to wide angle range 
has been used. 
In a lens barrel of such a zooming camera, the rotary cylinder is moved 
back and fourth along the optical axis while it is rotated as it is in the 
sink barrel type, and a focal distance of the photographing lens held and 
arranged in the lens barrel in the rotary cylinder is varied in accordance 
with the drive distance so that the photographing at a desired 
magnification is attained. 
Recently, a combination of the zoom lens and the sink barrel type has been 
adopted. In such a combination of the zoom lens and the sink barrel type, 
it is required to increase the rotation angle and the drive distance of 
the rotary cylinder in the lens barrel and the drive distance of the lens 
barrel. 
Further, auto-focusing (AF) which automatically focuses the lens has been 
widely adopted. In this case, again, the rotation and the drive of the 
rotary cylinder in the lens barrel and the drive of the lens barrel are 
done under a predetermined condition by the transmission of the rotating 
drive force from an electric motor to focus the lens system. 
In the sink barrel type, the zoom type and the AF type, a rotation 
transmission unit of a drive gear which imparts a rotating drive force 
from the electric motor to the rotary cylinder usually uses a construction 
as disclosed in Japanese Laid-Open Utility Model Application No. 2-10514, 
in which a helical gear is provided on an outer periphery of the rotary 
cylinder and a stationary cylinder or a drive gear provided on a camera 
body is meshed therewith, and both cylinders are helicoid-coupled while 
the rotary cylinder is rotatably driven in the stationary cylinder so that 
the rotary cylinder is driven out and in along the optical axis. 
However, in the prior art construction described above, in order to 
increase the drive stroke of the rotary cylinder, it is necessary to form 
the helical gear in a certain range along the optical axis on the outer 
periphery of the rotary cylinder because there is only one drive gear on 
the stationary cylinder. In addition, since the rotary cylinder is 
gradually driven out of the lens barrel so that an end thereof is exposed 
externally to form an externally viewable part, it is necessary to form an 
externally viewable part in addition to the gear formation part. 
Accordingly, the larger the drive stroke is, the longer is the length of 
the rotary cylinder along the optical axis. This leads to the increase of 
the size of the lens barrel and hence the entire camera. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a lens barrel which 
prevents the increase of the size of the rotary cylinder and the lens 
barrel to attain a compact camera by improving a transmission unit between 
the rotary cylinder which is driven along the optical axis while it is 
rotated to drive in and out the photographing lens system and the drive 
unit for rotatably driving the rotary barrel. 
In order to meet the above requirement, in the lens barrel of the present 
invention, a helical gear is formed at a portion of an outer periphery of 
the rotary cylinder which is helicoid-coupled to the stationary cylinder 
and driven in and out while it is rotated, and a plurality of drive gears 
which are gear-coupled to the helical gear are formed on the stationary 
cylinder so that at least one of the plurality of drive gears is 
gear-coupled with the helical gear in a rotation range of the rotary 
cylinder and only one of the drive gears is gear-coupled to the helical 
gear in at least one range in the rotation range. 
The lens barrel of the present invention comprises a rotary cylinder having 
a second helicoid on an inner periphery thereof, the second helicoid being 
helicoid-coupled to a first helicoid on an outer periphery of the lens 
cylinder for holding a photographing lens system, the second helicoid 
being rotatably arranged externally of the lens cylinder and having a 
third helicoid on an outer periphery thereof; a stationary cylinder having 
a fourth helicoid coupled to a third helicoid and rotatably holding the 
rotary cylinder; a key ring having a first straight drive key engaged with 
a portion of the lens cylinder to guide the lens cylinder only along an 
optical axis and rotatably held by the rotary cylinder; and a second 
straight drive key engaged with a portion of the key ring and formed on 
the stationary cylinder to movably hold the key ring only along the 
optical axis. A helical gear is formed on the outer periphery of the 
rotary cylinder along the third helicoid and a plurality of drive gears 
gear-coupled to the helical gear are formed on the stationary cylinder. At 
least one of the plurality of drive gears is gear-coupled to the helical 
gear in a rotation range of the rotary gear, and only one of the drive 
gears is gear-coupled to the helical gear in at least one range in the 
rotation range. 
In accordance with the present invention, the rotary cylinder is gradually 
driven in and out while it is rotated by the transmission of rotation from 
the gear of the drive gears which is gear-coupled to the helical gear of 
the rotary cylinder, and when the gear-coupled drive gear reaches the end 
of the helical gear as the rotary cylinder is rotated, another drive gear 
is gear-coupled to the helical gear so that the gear-coupled gears are 
sequentially relayed to share the entire drive stroke of the rotary 
cylinder. As a result, the range of formation of the gears on the rotary 
cylinder can be narrowed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIGS. 1 to 6 show one embodiment of the lens barrel of the present 
invention. In the present embodiment, the lens barrel is a zoom lens in a 
sink barrel type camera. 
In FIGS. 1 to 3, numeral 1 denotes a photographing lens system which 
comprises a first group of lenses 1a and a second group of lenses 1b and 
which forms a zoom lens system. A lens shutter mechanism 2 is arranged 
around the first group of lenses 1a and it is fixedly held in the lens 
cylinder 3. Numeral 4 denotes a lens cylinder which holds the second group 
of lenses 1b and it is advanced and retracted by a drive mechanism, not 
shown, along an optical axis L relative to the shutter mechanism 2 and the 
first group of lenses 1a held thereby. 
A first helicoid 3a is provided at a portion of the outer periphery of the 
lens cylinder 3 and it is helicoid-coupled to a second helicoid 5a 
provided on the inner periphery of the rotary cylinder 5 as a double 
helicoid cylinder fitted to and arranged around the lens cylinder 3. 
As seen from FIGS. 1 and 4, third helicoids 5b and 5c are provided at two 
points on the outer periphery of the rotary cylinder 5, and helical gears 
20a and 20b to be described hereinlater are formed along the third 
helicoids 5b and 5c. FIG. 4 et seq show the development of the outer 
periphery of the rotary cylinder 5. 
Numeral 6 denotes a stationary cylinder which serves as a dark box and 
which is arranged to encircle the lens barrel in a camera body 7. The 
third helicoids 5b and 5c of the rotary cylinder 5 are helicoid-coupled to 
a fourth helicoid 6a formed on the entire inner periphery of the 
stationary cylinder so that the rotary cylinder 5 is driven in and out 
along the optical axis while it is rotated. 
A film transport path, not shown, is formed on a back side of a member 8 
which is arranged on a back side of the camera body 7 to form an aperture 
8a. 
Numeral 9 denotes a key ring rotatably built in and held on an inner 
periphery at a rear portion of the rotary cylinder 5. A first key 9a which 
extends forward of the camera from a portion of the key ring 9 engages 
with a key groove 3b formed at a portion of the inner periphery of the 
lens cylinder 3 so that the lens cylinder 3 and the key ring 9 are driven 
in union in the rotation direction and the lens cylinder 3 can freely 
advance and retract along the optical axis relative to the key ring 9. 
Numeral 5d denotes a flange provided at a rear end on the inner periphery 
of the rotary cylinder, and numeral 5e denotes a thread formed at a rear 
end of the flange 5d. An inner periphery thread 10a of a retainer ring 10 
is threadedly coupled to the thread 5e to hold the key ring 9 rotatably 
between the retainer ring 10 and the flange 5d. 
Numeral 11 denotes a second key extending forward of the camera from the 
member 8. The second key 11 engages with an engagement groove, not shown, 
formed at portions of the key ring 9 and the first key 9a to hold the key 
ring 9 movably only along the optical axis. Accordingly, by the action of 
the second key 11 and the first key 9a, the lens cylinder 3 can also be 
driven only along the optical axis through the key ring 9. 
In accordance with the present invention, in the lens barrel constructed in 
the manner described above, helical gears 20a and 20b are formed along the 
third helicoids 5b and 5c at a portion of the outer periphery of the 
rotary cylinder 5 which is helicoid-coupled to the stationary cylinder 6 
and advanced and retracted along the optical axis, and a plurality of (two 
in the present embodiment) drive gears 21 and 22 which are gear-coupled to 
the helical gears 20a and 20b are provided on the stationary cylinder 6 
coaxially and in phase. At least one of the drive gears 21 and 22 is 
gear-coupled to the helical gears 20a and 20b in the rotation range of the 
rotary cylinder 5. 
As seen from FIGS. 4 to 6, the helical gears 20a and 20b are formed at two 
points between the third helicoids 5b and 5c at the rear end of the outer 
periphery of the rotary cylinder 5. On the other hand, plays 6b are formed 
at two points (see FIG. 2) in a formation area of the fourth helicoid 6a 
on the inner periphery of the stationary cylinder 6 to prevent 
interference with the helical gears 20a and 20b on the rotary cylinder 5. 
A support 6c is formed at a portion of the periphery of the stationary 
cylinder 6, and a support shaft 23 for integrally coupling the two drive 
gears 21 and 22 is rotatably supported by the support 6c. Thus, the drive 
gears 21 and 22 are held coaxially and in phase. While the drive gears 21 
and 22 are held coaxially and in phase in the present embodiment, they may 
be in different axes and different phases. Drive gear chains, not shown, 
are gear-coupled to the drive gears 21 and 22 to receive the transmission 
of the rotation from a drive source such as an electric motor. 
In FIG. 1, numerals 25a and 25b denote finder gears which are supported by 
a support 6d provided on the outer periphery of the stationary cylinder 6 
at a different position from the drive gears 21 and 22 (at the facing 
position in the present embodiment). The finder gears 25a and 25b are also 
integrally coupled to the support shaft 25c and rotatable coaxially and in 
phase. The finder gears 25a and 25b take out the rotation of the rotary 
cylinder 5 on the lens barrel by selectively being meshed with the gears 
20a and 20b and transmit the rotation to a variable finder magnification 
gear, not shown. 
In the present embodiment, the rotary cylinder 5 is gradually driven in and 
out along the optical axis while it is rotated by the transmission of the 
rotation from the gear 21 of the drive gears 21 and 22 which is 
gear-coupled to the helical gears 20a and 20b of the rotary cylinder 5, 
and when the drive gear 21 which is gear-coupled reaches the end of the 
helical gear 21a as the rotary cylinder 5 is rotated, the other drive gear 
22 is gear-coupled to the other helical gear 20b. In this manner, the gear 
coupling is sequentially relayed and distributed over the entire drive 
stroke of the rotary cylinder 5. As a result, the range of formation of 
the gears 20a and 20b on the rotary cylinder 5 can be reduced compared to 
the prior art. 
The above operation is now explained in conjunction with the driven-out 
position shown in FIG. 1 and the sink position shown in FIG. 3. 
The lens cylinder 3 and the rotary cylinder 5 are advanced and retracted 
along the optical axis between the driven-out position (FIG. 1) and the 
sink position (FIG. 3). As the lens barrel is driven, the lens cylinder 4 
which holds a second group of lenses 1b is advanced or retracted relative 
to a shutter mechanism 2 by a control unit, not shown, to conduct a 
required zooming operation. 
FIG. 4 shows a positional relation on the cylinder 5 among the drive gears 
21 and 22 and the finder gears 25a and 25b in the sink position shown in 
FIG. 3, FIG. 5 shows a positional relation in an interim position from the 
sink position to the driven-out position, and FIG. 6 shows a positional 
relation in the driven-out position shown in FIG. 1. 
In the sink position shown in FIG. 4, the drive gear 21 is gear-coupled to 
a portion of the gear 20a. At this time, the drive gear 22 is at a 
position not to gear-couple to the gears 20a and 20b. 
Similarly, the finder gear 25a is gear-coupled to the gear 20b while the 
finder gear 25b is at a position having nothing to do with the gears 20a 
and 20b and is not gear-coupled thereto. 
In this position, it is assumed that the drive gears are rotated rightward 
(as viewed from the front) when the motor is driven by the control unit, 
not shown, and the rotating motive force is transmitted to the drive gears 
21 and 22 through the drive gear chain. Then, the rotation of the drive 
gears 21 and 22 is transmitted from the gear 21 to the gear 20a to rotate 
the rotary cylinder 5 leftward (as viewed from the front). 
As the rotary cylinder 5 is rotated leftward, the rotary cylinder 5 is 
driven out in the direction of the arrow shown in FIG. 4 while it is 
rotated by the helicoid coupling with the fourth helicoid 6a on the 
stationary cylinder 6. 
As it is rotated under this condition, the drive gear 21 reaches an end 
20a1 of the gear 20a as shown in FIG. 5 so that the gear coupling is 
broken. However, slightly before that, the gear 20b which has been being 
driven out while it is rotated starts the gear coupling to the drive gear 
22 so that the operation is continued by the gear coupling of the gear 20b 
and the drive gear 22 even after the gear coupling of the gear 20a and the 
drive gear 21 has been broken. 
The drive is continued by the transmission of the rotation from the drive 
gear 22 to the gear 20b and it is stopped in the driven-out position shown 
in FIG. 6. 
In the interim position shown in FIG. 5, the right chain line shows the 
sink position and the left chain line shows the driven-out position. The 
movement of the rotary cylinder 5 by the rotational drive of the drive 
gears 21 and 22 will be readily understood. 
On the other hand, when a start of sink command is issued from the control 
unit, the drive gears 21 and 22 are rotated leftward (as viewed from the 
front) and the lens barrel returns to the sink position of FIG. 4 from the 
position of FIG. 6 in the opposite route to that for the drive-out 
operation. 
In the above series of operations, the finder gears 25a and 25b are also 
sequentially gear-coupled to the gears 20b and 20a and the finder gears 
25a and 25b are rotated rightward (as viewed from the front) as the rotary 
cylinder 5 is rotated leftward (as viewed from the front) to drive the 
variable finder magnification gear, not shown, gear-coupled thereto to 
drive the variable magnification finder to a required position. 
In this case, the gear coupling is relayed between the finder gears 25a and 
25b and the gears 20b and 20a in the interim position to continue the 
rotation in the same manner as that for the drive gears 21 and 22, and the 
detail thereof is omitted here. 
It should be readily understood that the present invention is not limited 
to the above embodiment and the shape and the structure of the parts of 
the lens barrel may be modified or changed as desired and various 
modifications may be made. For example, while the above embodiment uses 
the two helical gears 20a and 20b on the rotary cylinder 5 and rotatably 
drives the rotary cylinder 5 by coupling the two drive gears 21 and 22 by 
the support shaft 23, the present invention is not limited thereto but a 
plurality of gears may be formed on the rotary cylinder 5 and a plurality 
of drive gears which are selectively coupled thereto may be provided as 
required. 
In the above embodiment, the finder gears 25a and 25b for driving the 
variable magnification finder are provided in parallel to the drive gears 
21 and 22. This may be applied to a control encoder of the lens barrel. 
The lens barrel of the present invention is not limited to the sink barrel 
type zoom lens of the embodiment but it may be equally applicable to a 
transmission unit of the rotary cylinder and the drive system which 
receives the transmission of the rotation from the drive gears to drive in 
and out the rotary cylinder in the lens barrel of the sink type, zoom type 
and the AF type. 
In accordance with the lens barrel of the present invention, the helical 
gears are formed at a portion of the outer periphery of the rotary 
cylinder which is helicoid-coupled to the stationary cylinder and advanced 
and retracted along the optical axis while it is rotated, and a plurality 
of drive gears which are gear-coupled to the helical gears are provided on 
the stationary cylinder. At least one of the plurality of drive gears is 
gear-coupled to the helical gear in the rotation range of the rotary 
cylinder and only one of the drive gears is gear-coupled to the helical 
gear in-at least one range in the rotation range. Accordingly, the range 
of formation of the gears on the outer periphery of the rotary cylinder 
along the optical axis is minimized in spite of the simple structure so 
that the length along the optical axis of the rotary cylinder and the lens 
barrel arranged therein is shortened and a thin and compact camera is 
provided. 
In accordance with the present invention, the range of formation and the 
angle of inclination of the helical gears on the rotary cylinder and the 
position of arrangement of the drive gears which selectively mesh with the 
helical gears and the pitch of the coaxial arrangement thereof are 
appropriately selected while taking the relation with the helicoids which 
couple both cylinders into account so that drive by a stable power 
transmission is attained while the drive stroke of the rotary cylinder 
along the optical axis is maintained at the required level and the 
reliability of the operation is improved.