Note: Descriptions are shown in the official language in which they were submitted.
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BA~K~7ROUND OF TH~ INVENTION
Field of the Invention
This invention relates generally to a lens moving apparatus
wherein two lenses are individually moved with a a certain
mutual relationship parallel to the optical axis to effect
zooming and, more particularly, to such lens moving
apparatus that includes a small-size zoom lens unit suitable
for use with a video camera.
Description of the Background
A conventional zoom lens unit for use with a video
camera normally includes a so-called variator lens and a
compensator lens both disposed between a focus lens and a
so-called master lens. The variator lens and the
compensator lens are mounted for individual movement with a
desired mutual relationship parallel to the optical axis to
effect a zooming operation. In such conventional apparatus,
the individual movements of the variator lens and the
compensator lens for such zooming operation are provided by
a helicoid gear incorporated in a cylindrical lens holder.
In the conventional arrangement, the helicoid gear
necessarily has a diameter substantially equal to the
diameter of the focus lens. ~ccordingly, it is a drawback
that the conventional zoom lens unit has a comparatively
large size due to the required presence of the helicoid
gear, even though the individual variator lens and the
compensator lens are of comparatively smaller size.
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Furthermore, where a power zoom system is employed, it is
necessarv to mount the ~oom drive motor on the outside of
the power zoom systeml which also results in the entire lens
unit having a very large size.
One arrangement which attempts to eliminate such
drawbacks is described in U.S. patent No. 4,853,827. In the
optical lens moving mechanism disclosed in that patent, a
plane cam is mounted for pivotal motion in a plane parallel
to the optical axis of the lens system, and first and second
lens groups are individually moved parallel to the optical
axis by means of two cam grooves formed in the plane çam.
In order to increase the stroke or length of movement of the
first lens group in the optical system of that patent, the
size of the plane cam must be increased, which hinders the
efforts in reducing the size of the entire arrangement.
Furthermore, because the two cam grooves are provided on the
common plane cam, steps must be taken to prevent any
interference between the two cams. Accordingly, one
drawback of that disclosed arrangement is that the degree of
freedom in designing the lens system is diminished when it
is required to have two cams on the same flat surface o~ the
plane cam.
Another drawback of known lens systems of this
type is that it is very difficult to realize a structure to
enable movement of only one of the lens groups, while
maintaining the other in a stationary condition, in order to
effect macro photography.
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OBJECTS_AND SUMMARY OF TF.IE INVENTION
Accordingly, it is an object of the present
invention to provide a lens moving apparatus that can
eliminate the deects inherent in the prior art.
Another ob~ect of the present invention is to
provide a lens moving apparatus wherein a zoom lens unit i5
made compact, and a variator lens and a compensator lens can
make independent desired movements for enabling macro
photographic operations.
In accordance with an aspect of the present
invention, there is provided a lens moving apparatus that
comprises a driving or cam disk mounted on a frame of the
lens system for rotation in a plane parallel to the optical
axis of the lens s~stem. A cam groove and an engaging pin
are provided on a top surface of the driving disk, a first
lens holder is supported for movement along the frame
parallel with the optical axis, and a cam follower is
provided thereon for engaging the cam groove on the driving
disk. A second lens holder is also supported for movement
along the frame parallel with the opt~cal axis and a guide
is provided thereon for engagement with th~ engaging pin
formed on the driving disk.
With the lens moving apparatus of the present
invention, only the cam groove for moving the first lens
holder, that is, for moving the so-called ,-ompensator lens,
is provided on the cam disk, so that one cam groove can not
interfere with another cam used for driving the second lens
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holder. The sin~le cam on the cam disk can take forms
differerlt than a groove. Accordingly, the two lenses that
are associated with the first second lens holders can make
individual and independent movements as required.
Furthermore, the first lens holder, on which a compensator
lens may be mounted, can be moved without moving the second
lens holder, on which a variator lens may be mounted,
thereby enabling the lens system to be used in a macro
operation for close-up photography. In addition, the
driving torque for the cam disk can be reduced and,
consequently, further miniaturization of the lens driving
system can be attained.
The above and other objects, features, and
advantages of the present invention will become apparent
from the following detailed description of illustrative
embodiments that are to be read in con~unction with the
accompanying drawings~ in which like reference numerals
represent the same or similar elements.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a p~rspective view of a portion of a
zoom mechanism in the optical system of a ~ideo camera
accoraing to the present invention;
FigO ~ is a cross-sectional view of the entire
optical system of the video camera;
Fig. 3 is a bottom plan view showing a driving
system of a zoom mechanism in the optical system of Fig~ 2;
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Fig. 4 is a front elevational view of the optical
system of Fig. 2;
Fig. 5 is a rear elevational view of the optical
system of Fig. 2;
Fig~ 6 is a bottom plan view of the optical system
of Fig. 2 performing a wide-angle operation;
Fig. 7 is a side elevational sectional view of the
optical system of Fig. 6;
Fig. 8 is a bottom plan vlew of the optical system
of Fig. 2 performing a telP-angle operation;
Fig. 9 is a side elevational view in partial
cross-section of the optical system of Fig. 8;
Fig. 10 is a bottom plan view of the optical
system of Fig. 2 performing macro operation; and
Fig. 11 is a side elevational view in partial
cross-section of the optical system of Fig. 10.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Initially, Figs. 2 and 3 represent an optical
system of a video camera that includes a focus lens 10 that
is provided at a forward end of the system and that is
supported on a holding member 11. Focus lens holding member
11 is supported on a frame 14 by means of a pair of guide
rods 12 and 13. A threaded portion 15 is formed on the
inner end of guide rod 12, and the threaded portion is
maintained in threaded engagement with a tapped sleeve lÇ
that is adjacent the frame. A pulley 17 is fitted onto
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the outer surface of sleeve 16 and is coupled b~ a belt (not
shown) with a focus motor (not shown) mounted on frame 1
near pulley 17. In this manner pulley 17 may be driven ~
the focus motor to move focus lens 10 by action o threaded
portion 15 acting like a leacl screw.
A variator lens 20 and a compensator lens 21 are
disposed on frame 14 at the rear of locus lens 10. Lenses
20 and 21 are firmly mounted on a pair of holding members 22
and 23, respectivel~. Holding members 22 and 23 are
supported by means of three guide rods 24, 25, and 26 shown
clearly in Fig.l.
Referring then to Fig. 1, holding member 22, on
which variator lens 20 is mounted, is supported by means of
guide rods 24 and 26, whereas holding member 23, on which
compensator lens 21 is mounted, is supported by means of
guide rods 25 and 26.
Now, a mechanism for moving holding members 22 and
23 on which lenses 20 and 21 ar~ mounted, respectivelyr will
be described with reference to Figs. 1, 2, and 3. The lens
moving mechanism includes a driving or cam disk 30 supported
for rotation on frame 14. A pin 31 is arranged on cam disk
30 for engagement with a cam groove 32 formed on a lower
face of holding member 22 on which variator lens 20 is
mounted. The upper end of cam groove 32 terminates in an
actuate guide face 33, as shown in Fig. 3. A cam follower
pin 34 is provided on a lower face of holding member 23 on
which compensator lens 21 is mounted, and cam ollower pin
34 normally engages with a cam groove 35 formed on cam disk
30.
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A motor 36 i.s moun~ed on one side of frame 14 and
a pulley 37, partially hidden in Fig. 2, is secu.red to an
output power shaft (not shown) of motor 36 and is coupled to
a pulley 38 by means of a be:Lt 39. A worm 40 is mounte~ on
pulley 38 and is held in meshing engagement with a worm
wheel 41. A driving gear 42 is mounted on worm wheel 41 and
is held in meshing engagement with the teeth of a gear ~3
formed on the outer periphery of cam disk 30.
An iris unit 45, the elements of which are not
shown, is disposed at the rear of compensator lens 21. A
cylindrical lens holder ~6 is mounted on frame 14 at the
rear of iris unit 45, and a master lens set, shown generall~
at 47, includes a plurality of lenses and is mounted in
cylindrical lens holder 46. A frame 48 is securel~ mounted
at the rear end of cylindrical lens holder 46, and a charge
coupled device (CCD~ imager 49 is mounted on frame 48. The
relationship among cylindrical lens holder 46, frame 48, and
imager 49 is shown in Fig. 5.
In the operation, particularly a zooming
operation, of the lens moving apparatus as described above,
~or wide-angle operation to widen the angle of view cam disk
30 is rotated counterclockwisel relative to Fig. 6, by motor
36 by way of pulle~ 37, belt 39, pulley 38, worm 40, worm
wheel 41, driving gear 42, and gear 43. Thereupon, holding
member 22 i5 pushed along cam groove 32 by pin 31 on cam
disk 30 to move variator lens 20 toward focus lens 10.
Simultaneouslv, compensator lens 21 is moved toward CCD
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imager 49 by cam grove 35 of cam disk 30 by way of cam
follower 34 affixed to holding member 23. In summary, upon
wide~angle operation, variator lens 20 and compensator lens
21 are moved away from each other.
For tele-angle ope:ration to narrow the angle of
view, cam disk 30 is rotated in the clockwise direction,
relative to Fig. 8, so that holding member 22 is moved
rearwardly by pin 31 cooperating with cam groove 35 on disk
30 to move variator lens 20 back to a position directly in
front of the compensator lens 21, as shown in Figs. 8 and 9.
In summary, variator lens 20 and compensator lens 21 are
both moved away from the locus lens 10 while narrowing the
field of view, as in so-called tele-angle operation,
In a macro operation for close-up photography,
with reference to Figs. 10 and 11, cam disk 30 is rotated
farther in the counterclockwise direction than the most
wide-angle position thereof. ~hereupon, pin 31 on cam disk
30 is disengaged from cam groove 32 of holding member 22 and
is brought into engagement with arcuate guide face 33 that
is contiguous to cam groove 32. It should be noted that in
this case variator lens 20 is not moved paral~el to the
optical axis, because here the arcuate guide face 33 has a
profile which coincides with a locus of the turning movement
of pin 31. While variator lens 20 remains stationary,
holding member 23, on which compensator len~ 21 is mounted,
is advanced a short distance toward focus lens 20 b~ an end
portion of cam groove 35 on cam disk 30. In this manner,
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only compensator lens 21 is moved, while variator lens 20
remains in a stationary condition, thereby enabling a macro
operation of the optical system for close-up photography,
that is, close-up video pictures with a video camera.
With the lens movi:ng apparatus describea above, it
is possible to move compensator lens 21 directly hy cam
groove 35 formed in cam disk 30 and, also, to move variator
lens 20 along a path parallel to the optical axis through
engagement of pin 31 mounted on cam disk 30 with cam groove
32 formed in holding member 22, as described hereinabove.
Holding members 22 and 23 for the two lenses 20 and 21,
respectively, are guided for movement parallel to the
optical axis by three guide rods 24 to 26. ~ccordingly, the
æoom lens unit does not require a cylindrical lens holder,
and it is possible to place the driving system, such as disk
driving motor 36, in the space that is provided by the
elimination of such a cylindrical lens holder. As a result,
miniaturization of the optical system of the video camera,
particularly the æoom lens unit thereof, is enabled.
Holding member 11 for focus lens 10 is guided by
two guide rods 12 and 13, and focus lens 10 is moved
parallel to the optical axis by threaded portion 15 of guide
rod 12 to effect focusing of the optical system. Because
the driving mechanism for focus lens 10 is also disposed in
the surplus spacing around the outer periphery of the zoom
lens unit, no component of the driving system will extend
outwardly beyond the outer peripher~ of focus lens 10.
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Furthermore, as shown in Fig. ~, the upper and
lower end portions of focus lens 10 are cut off in order to
reduce the vertical dimension of the locus lens 10. Because
mounting of focus lens 10 is attained not by means of a ring
nut or threaded ring but by means of fastening screws 5~
mounted at four corners of holding member 11, as shown in
Fig. 4, it is possible to assure a comparatively large
opening for focus lens 10. Bv the combination of these
structures it is possible to accommodate all of the
mechanism, even including the electric driving system,
within a space not greater than the outer diameter of focus
lens 10, which has the upper and lower portions thereof cut
off as described above, and consequently to make the entire
lens arrangement compact.
In the structure according to the present
embodiment, variator lens 20 is moved as holding member 22
is driven by cam groove 32 cooperating with pin 31.
Accordingly, even if cam disk 30 is rotated to a position in
which a radial line passing through pin 31 extends parallel
to the optical axis, a high load will not be applied to cam
disk 30. If the variator lens is moved by a cam groove that
is also formed on the disk in addition to the cam groove
provided for the compensator lens, a high lateral pressure
will be applied to the cam depending upon the rotational
position of the disk, caused in part ~y the binding due to
intersection of moving two separate elements. This high
lateral pressure means that a very high driving toraue will
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be re~uired to rotate the cam disk. On the contrary, with
the apparatus according to the present embodiment such high
lateral pressures are eliminated, and it is possible to
rotate cam disk 30 wikh a lower torque, so as to move the
two lenses 20 and 21 smoothly in the direction of the
optical axis to effect an accurate zooming operation.
In this embodiment the cam on the cam disk is
formed as a groove and the cam follower is a pin, however,
the invention is equally applicable to other forms of cams
and cam followers.
The above description is given on a single
preferred embodiment of the invention, but it will be
apparent that many modifications ancl variations could be
effected by one skilled in the art without departing from
the spirit or scope of the novel concepts of the invention,
which should be determined by the appended claims.
