Iris diaphragm device for a camera

An iris diaphragm device wherein a rocking motion of a movable magnetic member caused by application of a driving electric current corresponding to the brightness of a subject is transmitted to a leaf operating member for opening or closing iris diaphragm leaves through a connecting lever provided at the both end portions thereof with clearances. Because of the clearances, the iris diaphragm leaves open or close in prompt response to the application of the driving electric current and a chattering motion of the movable magnetic member brought about when it stops is completely absorbed, thereby enable a non-flickering exposure.

BCKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to an iris diaphragm device applicable to an 
automatic exposure control system in cameras of various types and, more 
particularly, to an iris diaphragm device which enables iris diaphragm 
leaves to stably open or close without a chattering motion so as to form 
an iris aperture of suitable size according to the brightness of a 
subject, whereby a non-flicker exposure is effected. 
2. Description of the Prior Art 
An iris diaphragm device for use in a video camera, a cinecamera or the 
like generally comprises an iris diaphragm element having a plurality of 
iris diaphragm leaves for forming an iris aperture, and a drive means 
having a construction similar to that of an electric motor which is 
composed of a movable magnetic member and a stationary magnetic member and 
adapted to open or close the iris diaphragm leaves so as to determine 
appropriate exposure according to the brightness of a subject detected by 
means of a photoelectric device such as a charge coupled device (CCD). In 
general, the iris diaphragm device of this type is incorporated in a lens 
barrel or a camera body. 
Various diaphragm devices having such a construction as mentioned above 
have been proposed. For example, the conventional diaphragm device 
disclosed in Japanese Patent Application Public Disclosure No. Sho 
58(1983)-80627 is designed to generate relatively large rotational torque 
even from a feeble electric current corresponding to the brightness of a 
subject so as to reliably open or close the iris diaphragm leaves. This 
prior art device comprises a moving coil as a movable magnetic member 
disposed concentrically relative to magnets as a stationary magnetic 
member circularly arranged around the optical axis and rotatably supported 
by pivot members protruding outwardly from both sides thereof in the 
direction perpendicular to the optical axis, and a leaf operating disc of 
a ring shape which is capable of angularly rotating around the optical 
axis by applying an electric current corresponding to the brightness of 
the subject to the moving coil, to thereby open or close the iris 
diaphragm leaves so as to form an iris aperture of suitable size. In this 
device, a connecting arm integrally fixed on one of side pivot portions of 
the moving coil is used as a means for transmitting a rocking motion of 
the moving coil to the leaf operating disc. That is to say, the connecting 
arm protruding from one of the opposed side pivot portions of the moving 
coil toward the leaf operating disc in the direction perpendicular to the 
pivot members of the moving coil is coupled at the free end thereof with 
the leaf operating disc, whereby the rocking motion of the moving coil is 
directly transmitted to the leaf operating disc so as to effect an opening 
or closing of the iris diaphragm leaves. The diaphragm device enjoys an 
advantage that the rocking motion of the moving coil can be reliably 
transmitted to the leaf operating disc with minimum loss in prompt 
response to application of a driving electric current thereto because 
there is no medium for transmission of motion therebetween except for the 
connecting arm integrally fixed on the moving coil. However, the moving 
coil cannot exactly stop at the magnetic equilibrium point determined by 
the intensity of the electric current applied to the moving coil due to 
the force of inertia. The moving coil thus overshooting the magnetic 
equilibrium point stops and then moves rearwardly by the energizing force 
of a spring which is generally provided in the device of this type and by 
counterelectromotive force generated by overshooting of the moving coil. 
Nevertheless, the moving coil which moves backward will again overshoot 
the magnetic equilibrium point just a little. Consequently, the moving 
coil is repeatedly rocked around the magnetic equilibrium point and gives 
rise to a chattering motion, and then stops at that point in time. As a 
result, the iris diaphragm leaves are unstably moved so as to cause a 
flickering phenomenon which brings about lowering of the optical 
characterisitcs of a camera. The same is true in the case where the 
movable magnetic member is a magnet and the stationary magnetic member is 
of one or more electromagnetic coils. Disadvantageously, if a damper means 
is used to prevent an overshooting motion of the movable magnetic member, 
the iris diaphragm leaves cannot effectively respond to a change in 
brightness of a subject. Instead, if an electrically controlling circuit 
for compensating the force of inertia brought about by the rocking motion 
of the moving coil is adopted, the device is complicated in structure and 
is expensive. 
SUMMARY OF THE INVENTION 
In view of the above, the object of the present invention is to provide an 
iris diaphragm device of a simple structure, in which the iris diaphragm 
leaves open or close reliably and stably in quick response to application 
of a driving electric current corresponding to the brightness of a 
subject, whereby an iris aperture of suitable size can promptly be formed 
with accuracy without causing a chattering motion and so as to enable a 
non-flickering exposure. 
To attain the above object according to the present invention an iris 
diaphragm device is provided for use in a camera, which comprises one or 
more iris diaphragm leaves capable of opening or closing around the 
optical axis to form an iris aperture, a leaf operating member rotatably 
disposed around the optical axis to operate the iris diaphragm leaves to 
open or close, drive means having a movable magnetic member capable of 
moving rockingly around pivot members extending outward from opposed side 
portions of the movable magnetic member and one or more stationary 
magnetic members, and motion transmitting means composed of an arm member 
extending from one of side portions of the movable magnetic member and a 
connecting lever having one end thereof rotatably coupled with the free 
end portion of the arm member through a clearance and a second end thereof 
rotatably coupled with the leaf operating member through a clearance so as 
to transmit the rocking motion of the movable magnetic member to the leaf 
operating member. 
Each of the coupling means between the connecting lever and the respective 
arm member and leaf operating member may consist of a crank pin and a 
guide slit, for example. In this case, the crank pin has a diameter 
smaller than the width of the guide slit to form a clearance. Preferably, 
the coupling means is designed to bring the crank pin into point contact 
with the inner edge of the guide slit so as to lessen the transmission 
loss of motion. 
The movable magnetic member is driven so as to be rocked by supplying 
thereto a driving electric current corresponding to the quantity of the 
incident light into a lens system of the camera. The first transition 
movement of the movable magnetic member is accelerated due to the two 
clearances formed in the coupling means provided at the both end portions 
of the connecting lever, whereby the iris diaphragm leaves move with 
alacrity. Furthermore, a chattering motion of the movable magnetic member 
which is caused around the magnetic equilibrium point due to the force of 
inertia is completely absorbed by the aforementioned clearances and is no 
longer transmitted to the leaf operating member. Consequently, the iris 
diaphragm leaves promptly move following the brightness of the subject 
without causing a chattering motion even if the brightness is suddenly 
changed, to thereby enable a non-flickering exposure.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
This invention relates to an iris diaphragm device which comprises a base 
member 1, a diaphragm element 10 and a drive means 100 and is incorporated 
into a lens system in a video camera, a cinecamera or the like. 
The base member 1 comprises a cylindrical body 3 having an aperture 2 with 
the center through which an optical axis O passes, and a flange portion 4 
extending outwardly from the circumferential surface of one end of the 
cylindrical body 3. The flange portion 4 is provided in one side surface 
thereof with an annular groove 5 and an annular step portion 6. In a part 
of the flange portion 4, a through hole 7 is bored. 
The diaphragm element 10 which is fixed on the base member 1 comprises a 
leaf operating member 20, a supporting plate 30, a set of iris diaphragm 
leaves 40, and a cover plate 50. 
The leaf operating member 20 is rotatably set in the annular groove 5 
formed in the flange portion 4 of the base member 1 and provided on one 
surface thereof with sliding pins 21 equal in number to the iris diaphragm 
leaves 40 and stopper pins 22 and 23, and on the other surface with a 
connector 24. In this embodiment, the connector 24 is composed of a pair 
of round rods. 
The supporting plate 30 has an outer diameter substantially the same as 
that of the annular step portion 6 formed in the flange portion 4 of the 
base member 1 and arcuate slots 31 through which the sliding pins 21 on 
the leaf operating member 20 are slidably inserted so that the sliding 
pins 21 can move in the circumferential direction by a fixed length. On 
one side of the supporting plate 30, leaf supporting pins 32 for pivotally 
supporting the iris diaphragm leaves 40 are distributed substantially 
equidistantly about the periphery of the iris aperture. The supporting 
plate 30 is further provided with a slot 33 and a notch 34 for admitting 
the corresponding stopper pins 22 and 23 thereinto so as to restrict the 
rotation of the leaf operating member 20 within a limited range. These 
stopper pins 22 and 23, the slot 33 and the notch 34 are not indispensable 
components of the invention. That is to say, instead of these components, 
the restriction of the rotation of the leaf operating member 20 may be 
accomplished merely by means of the sliding pins 21 and the arcuate slots 
31 which are engaged with each other. Further, if the leaf supporting pins 
32 on the supporting plate 30 are provided on the base member 1 and the 
slots 31 and 33 and the notch 34 are formed in the cover plate 50, the 
supporting plate 30 can be omitted. Denoted by 35 are screw fitting holes. 
In this embodiment, the iris diaphragm leaves 40 arranged in a circular 
form are adopted, whereas the shape and number of the iris diaphragm 
leaves are not specifically limited. For example, one or more leaves may 
be disposed at equal distances around the aperture and simultaneously, the 
sliding pins 21 on the leaf operating member 20 and the arcuate slots 31 
and the leaf supporting pins 32 on the supporting plate 30 should be equal 
in number to the diaphragm leaves 40. Each of the iris diaphragm leaves 40 
has a pivot hole 41 for receiving the corresponding leaf supporting pin 32 
fixed on the supporting plate 30 and a cam slot 42 into which the 
corresponding sliding pin 21 fixed on the leaf operating member 20 is 
slidably admitted. 
The relationship between the pivot hole 41, the cam slot 42 formed in the 
iris diaphragm leaf 40 and the leaf operating member 20 will be explained 
with reference to FIG. 2. The iris diaphragm leaf 40 is swung around the 
leaf supporting pin 32 within the range of the angle .theta., that is, 
from the open state in which the iris diaphragm leaf 40 is completely 
opened out to form the entire aperture as illustrated by the full line in 
FIG. 2 to the close state in which the iris diaphragm leaf 40 is closed to 
cause the aperture to disappear as illustrated by the chain line in FIG. 
2. The required range within which the diaphragm leaf should be swung and 
the required length L of the cam slot 42 cannot be specified because they 
depend on the inclination of the cam slot 42 relative to the pivot hole 
41, for example. Although the orbit t along which the sliding pins on the 
leaf operating member 20 rotatably move is placed outside the pivot holes 
41 in the illustrated embodiment, the orbit may nevertheless be located 
inside the pivot hole 41. 
The cover plate 50 is adapted to cover the leaf operating member 20, the 
supporting plate 30, and the iris diaphragm leaves 40 which are contained 
within the annular groove 5 in the base member 1 and is provided with 
guide recesses 51 for guiding the aforementioned sliding pins 21 and 
bearing holes 52 for pivotally supporting the leaf supporting pins 32. The 
cover plate 50 is attached to the base member 1 by use of screw means 54 
to be inserted through fitting portions 53. 
In this embodiment, the drive element 100 comprises a movable magnetic 
member 110 formed in a noncircular shape having its center which is 
substantially in agreement with the optical axis O and a pair of 
stationary magnetic members 120 disposed inside the movable magnetic 
member 110 and opposed to each other across the aperture as shown in FIG. 
3. The movable magnetic member 110 is an electromagnetic coil which is 
excited by supplying an electric current thereto and the stationary 
magnetic members 120 are arcuate permanet magnets. In general, the 
electromagnetic coil for use in the diaphragm device of this type has a 
double coil structure composed of a coil for generating rotational moment 
and a damping coil. 
In the drive means 100, a yoke 140 adapted to support the movable magnetic 
member 110 and the stationary magnetic member 120 comprise a base plate 
141 having an aperture and arcuate inner and outer walls 142 and 143 
extend vertically relative to the base plate 141 from the inner and outer 
edge portions of the base plate 141. The stationary magnetic members 120 
are held in position within the space 10 defined between the opposed inner 
and outer walls 142 and 143 in a state of intimate contact with either the 
inner walls or the outer walls. The movable magnetic member 110 is 
pivotally supported between the respective stationary magnetic members 120 
and either the outer walls 143 or the inner walls 142 which are separated 
from the stationary magnetic members. Though the movable magnetic member 
110 in this embodiment assumes a substantially elliptical shape, it may be 
formed in a circular or polygonal shape. Though the movable magnetic 
member 110 is kept energized by a spring 112 in one direction so as to 
close the iris diaphragm leaves 40 when the camera is out of use, the 
spring 112 is not an indispensable component for the diaphragm device of 
the invention. To the opposed side portions of the movable magnetic member 
110, there are respectively attached pivot fixing seats 113 and 114 each 
having the pivot pin 111 extending outwardly therefrom. The pivot pins 111 
formed integrally on the respective pivot fixing seats are pivotally 
supported by supporting frames 147 and 148 of the yoke 140 by the means of 
bearing members 145 and 146. Through lead wires 149 a driving electric 
current corresponding to the brightness of the subject is supplied to the 
movable magnetic member 110. The movable magnetic member 110 is excited by 
application of the electric current and then angularly rotated around the 
pivot pins 111 by the electromagnetic interaction between the movable 
magnetic member which is a moving coil and the stationary magnetic member 
120 which is composed of magnets in this embodiment. 
The rocking motion of the movable magnetic member 110 is transmitted to the 
aforementioned leaf operating member 20 by means of a motion transmitting 
means 150. The motion transmitting means 150 comprises an arm member 151 
fixed on the pivot fixing seat 113 of the movable magnetic member 110 and 
provided at its free end portion with a crank pin 152, and a connecting 
lever 153 provided at one end portion thereof with a guide slit 154 for 
slidably receiving the crank pin 152 of the arm member 151 to constitute a 
first coupling means and at the other end portion thereof with a crank pin 
155 which is coupled with the connector 24 disposed on the lower surface 
of the leaf operating member 20 to constitute a second coupling means. The 
connecting lever 153 is rotatably supported by a support pin 156 which is 
eccentrically disposed relative to the pivot 111 extending from the 
movable magnetic member 110. The eccentricity of the pivot 111 relative to 
the support pin 156 and the lever ratio of the connecting lever 153 depend 
on the required amount of angular rotation of the leaf operating member 20 
for opening or closing the iris diaphragm leaves 40 in order to determine 
the optimum aperture. Preferably, the length from the support pin 156 to 
the guide slit 154 is made shorter than that from the support pin 156 to 
the crank pin 155 to thereby gain larger momentum. If the aforementioned 
lever ratio is changed, the amount of rotation T, of the leaf operating 
member 20 can be suitably determined. 
The diameter of the crank pin 152 provided on the free end portion of the 
arm member 151 is made smaller than the width of guide slit 154 so as to 
form a clearance. Similarly, the the crank pin 155 provided on one end 
portion of the connecting lever 153 is made smaller than the gap between 
the opposed rods constituting the connector 24 in this embodiment to form 
a clearance. 
Denoted by 160 is a cover which is attached to the yoke 140 by the medium 
of spacers 161 to define a space for accommodating the movable magnetic 
member 110 and the stationary magnetic member 120. 
The operation of the embodiment described above will be explained 
hereinbelow. 
The movable magnetic member 110 which is an electromagnetic coil is applied 
with a fixed bias current while in use. The electric current to be 
supplied from a power source b to the movable magnetic member 110 is 
varied in quantity or changed in its polarity to reverse the direction of 
the magnetization thereof by means of a controller c in accordance with 
the quantity of the light incident upon an photoelectric element e. This 
diaphragm device can utilize any of conventional controlling circuits as a 
controller for controlling the electric current to be applied to the 
movable magnetic member. Thus, the movable magnetic member 110 is 
swingingly moved. The swinging motion of the movable magnetic member 110 
is transmitted to the leaf operating member 20 through the medium of the 
connecting lever 130 and the connector 24 attached to the leaf operating 
member 20 to thereby cause opening or closing motion of the iris diaphragm 
leaves 40 so as to determine the appropriate exposure. 
The operation of the motion transmitting means in the initial state will be 
described below with reference to FIG. 5(A). 
The movable magnetic member 110 rests at the initial position I illustrated 
by the solid line in FIG. 5(A) due to the energizing force of the spring 
112. The movable magnetic member 110 when applied with a driving electric 
current generates rotational torque in the clockwise direction in the 
illustrated embodiment so as to begin to move. However, the rotational 
motion of the movable magnetic member 110 is not transmitted to the 
connecting lever 153 because of the clearance in the first coupling means 
constructed by the crank pin 152 and the guide slit 154 formed in the 
connecting lever 153. At this time, because the movable magnetic member 
110 moves under no load, the rotational motion thereof is accelerated. 
Therefore, when the movable magnetic member 110 reaches the position II, 
the crank pin 152 provided on the arm member 151 contacts with one side 
edge of the guide slit 154 at high speed. Because the load applied on the 
movable magnetic member 110 by bringing the crank pin 152 into collision 
with the side edge of the guide slit is slight, the connecting lever 153 
is swung to bring the crank pin 155 into contact with the connector 24 at 
high speed to move the leaf operating member 20 when the movable magnetic 
member 110 reaches the position III. Thus, the movable magnetic member 110 
can be moved with sufficient acceleration due to the clearances formed in 
the first and second coupling means at the opposed end portions of the 
connecting lever 153 and offers an ample driving force for operating the 
leaf operating member 20 and the iris diaphragm leaves 40 with alacrity in 
opposition to the static load of the leaf operating member 20. 
The movable magnetic member 110 which has moved at high speed by the 
application of the driving electric current corresponding to the 
brightness of the subject does not stop at the magnetic equilibrium point 
IV which is determined by the intensity of the driving electric current to 
be applied thereto due to the force of inertia and somewhat overshoots 
point IV to the point V as shown in FIG. 5(B). However, the movable 
magnetic member 110 thus overshooting turns back from the point IV due to 
counterelectromotive force generated by the overshooting of the movable 
magnetic member 110 and then again overshoots the magnetic equilibrium 
point. As a result, the movable magnetic member 110 is repeatedly rocked 
around the magnetic equilibrium point V as it vibrates as shown by the 
bidirectional arrow in FIG. 5(B) and then stops at the magnetic 
equilibrium point in time. However, according to this invention, the 
rocking movement of the movable magnetic member 110 is completely absorbed 
by the clearances formed in the coupling mechanisms at the both end 
portions of the connecting lever 135 and therefore, can no longer be 
transmitted to the leaf operating member 20, thereby completely preventing 
a chattering motion of the iris diaphragm leaves 40. 
Though the connecting lever 153 is made straight in the foregoing 
embodiment, a hook-shaped lever 253 rotatably supported by a support pin 
156 as shown in FIG. 6 may be used instead of the connecting lever 153. In 
the embodiment shown in FIG. 6, those elements denoted by the same 
reference numerals as those in the foregoing embodiment are equivalent in 
function to those in the former embodiment. The construction in this 
embodiment provides an advantage in that a space factor of the motion 
transmitting means relative to a cover 160 in which the drive means 100 is 
incorporated is somewhat improved. 
There is a possiblility that the loss caused in transmitting the rocking 
motion of the movable magnetic member 110 to the leaf operating member 20 
is increased when the crank pin 155 fixed on the connecting lever 153 
assumes a great angle relative to the connector 24 mounted on the leaf 
operating member 20. To lessen the transmission loss thus caused, it is 
appropriate to decrease the area of contact between the crank pin 155 and 
the connector 24. Accordingly, the pair of round rods constituting the 
connector 24 in the foregoing embodiment may assume a polygonal shape in 
cross section. For example, each cross section of rods constituting the 
connector 24 may be formed in a diamond shape as shown in FIG. 7(A) or a 
triangle shape, or a wedge shape as shown in FIG. 7(B). Otherwise, the 
connector 24 may have a C-shaped cross section as shown in FIG. 7(C), to 
thereby improve the intensity of thereof and hold the crank pin 155 in 
position. Conversely, the crank pin 155 on the connecting lever 153 may be 
constituted by a pair of pin rods and the connector 24 may formed of one 
pin which is put between the pin rods of the connecting lever 153 as shown 
in FIG. 7(D). 
Further, the aforementioned embodiments are explained using an 
electromagnetic coil as a movable magnetic member 110 and one or more 
permanent magnets as a stationary magnetic member 120. Nevertheless, it 
would be obvious that the movable magnetic member 110 may be made of a 
permanent magnet ring and the stationary magnetic member 120 may be formed 
of one or more electromagnetic coils from a standpoint of reversibility of 
an electromagnetic circuit system of this type. Also, though the drive 
means in these embodiments adopts at least one permanent magnet, it goes 
without saying that an electromagnet can obviously substitute for a 
permanent magnet. Furthermore, there may be adopted a construction in 
which a pivot hole is bored in the respective pivot seats 113 and a pivot 
pin is provided on the respective bearing members 145 and 146 instead of 
the pivot structure having the pivots 111 extending from the pivot seats 
113 as in the illustrated embodiment. 
As is evident from the foregoing description, the iris diaphragm device 
according to this invention is simple in structure, and is reliable and 
stable in opening or closing operation of the iris diaphragm leaves 
without entailing a chattering motion even when the brightness of a 
subject is suddenly changed, whereby a non-flickering exposure can be 
effected. 
Obviously, many modifications and variations of the present invention are 
possible in light of the above teachings. It is therefore to be understood 
that within the scope of the appended claims, the present invention may be 
practiced otherwise than as specifically described herein.