Shutter blade opening and closing device

The camera shutter comprises two shutter blades which have first opening forming portions and second opening forming portions capable of alternatively forming two exposure openings different in area on an exposure aperture. These shutter blades are opened and closed by a shutter blade opening and closing lever which can be retained at a neutral position by a closing spring. The shutter blade opening and closing lever is turned by a motor which starts from the neutral position rotates in one of two directions opposite to each other. The lever is equipped with a opening spring capable of exerting a resilient force in the rotating directions of the opening and closing lever. The resilient force of the opening spring is weaker than that of the closing spring. The first opening forming portions form an exposure opening when the motor is started in a first direction and the second opening forming portions form an exposure opening when the motor is started in a second direction. Sizes of the exposure openings are adjustable by turning an adjustable eccentric stopper. This camera shutter can perform accurate and stable exposure operations though it has a simple construction and can be manufactured at a low cost.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a camera shutter which is capable of 
forming two types of exposure openings different in size from each other 
by reversing the starting directions of a plurality of shutter blades when 
they are to be opened. 
2. Description of the Related Art 
There have been proposed shutters of the type capable of switching between 
two exposure openings different in size for use with low cost still 
cameras. These shutters operate by changing emulsion speed of the film to 
be used with a single shutter speed which is kept unchanged. For example, 
the shutter opens to a certain side for one speed film, but opens to a 
different size for a second speed film. From the viewpoint of 
construction, these shutters are classified into two types: one type uses 
two driving sources, one for operating the shutter blades and the other 
for switching exposure opening diameters respectively. The second type 
uses as a driving source, a single pulse-motor which is reciprocally 
rotated in directions reverse to each other for switching exposure 
openings different in size from one to the other (See Japanese Patent 
Preliminary Publication No. Sho 60-249123). 
The camera shutter of the former constructional type, which is equipped 
with the two driving sources for performing the shutter functions, has a 
defect that it requires a large number of parts, a large number of 
assembly stages, etc., thereby increasing manufacturing cost and 
decreasing the reliability of the shutter itself. On the other hand, the 
camera shutter of the latter constructional type requires rotating the 
pulse motor in both the normal and reverse directions for exposure of film 
and must use a complicated electrical circuit, thereby increasing 
manufacturing cost of the electrical system and this increasing 
manufacturing cost of the shutter itself. 
SUMMARY OF THE INVENTION 
It is therefore a primary object of the present invention to provide a 
camera shutter which has a simple construction and can be manufactured at 
a low cost. 
Another object of the present invention is to provide a camera shutter 
which can accurately perform the opening and closing movement of the 
shutter blades for precise exposure control. 
A further object of the present invention is to provide a camera shutter 
which facilitates fine adjustment of exposure at the assembly stage and is 
free from malfunctions. 
According to the present invention, these objects attained by a first 
opening forming portion and a second opening forming portion in each of 
the plurality of shutter blades. A first exposure opening is generated 
with the first opening forming portions when a motor is driven for moving 
the shutter blades in a first direction. A second exposure opening 
different in area from the first exposure opening with the second opening 
forming portions when the motor is driven for moving the shutter blades in 
a second direction opposite to the first direction. Finally the shutter 
blades are biased and moved by a closing spring for maintaining the 
shutter blades at closed positions thereof when the shutter blades are to 
be closed for terminating the exposure. 
The camera shutter according to the present invention further comprises an 
opening spring which has a resilient force weaker than that of the closing 
spring. The opening spring is so adapted as to exert no resilient force in 
either the first or the second direction when the shutter blades are at 
the closed positions thereof. However, the opening spring exerts a 
resilient force in either of the first or second directions in which each 
of the shutter blades is moved in by the motor. Due to the construction 
described above, the camera shutter according to the present invention 
prevents re-exposure of the film caused by inertia when the shutter blades 
are to be closed. 
The camera shutter according to the present invention further includes a 
stopper which is adjustable in position thereof. The stopper is brought 
into contact with at least one of the shutter blades when the first or 
second exposure opening is to be determined by the shutter blades. This 
stopper permits accurate adjustment of the area of the exposure opening, 
thereby making it possible to accurately control exposure without changing 
the duration of time for supplying current to the driving motor when 
either of the exposure openings is to be used. 
Accordingly, to the present invention, a proper exposure time can be easily 
controlled in accordance with the brightness of an object to be 
photographed, and the shutter can be used as a program shutter by 
selecting any one of the first and second exposure openings and the 
shutter speed. 
These and other objects as well as the features and advantages of the 
present invention will become apparent from the following detailed 
description of the preferred embodiments when taken in conjunction with 
the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Now, a first Embodiment of the camera shutter according to the present 
invention will be described below with reference to FIG. 1 through FIG. 
10. 
In these drawings, the reference numeral 1 represents an exposure aperture 
formed in a shutter base plate P, the reference numeral 2 designates a 
shutter blade which is pivoted about a pin 3 studded on the shutter base 
plate P, and has a first opening forming portion 2a, a second opening 
forming portion 2b and a slot 2c. The reference numeral 4 denotes a second 
shutter blade which is pivoted about a pin 5 studded on the shutter base 
plate P, and has a first opening forming portion 4a, a second opening 
forming portion 4b and a slot 4c. The second shutter blade the reference 
numeral 6 represents a shutter blade opening and closing lever which is 
pivoted about a shaft 7 studded on the shutter base plate P, and equipped 
at a first arm end with a pin 6a inserted commonly into the slots 2c, 4c 
of the shutter blades 2, 4. The shutter blade opening and closing lever 
has a second arm end with a fork portion 6b and at a third arm end with a 
pin 6c. 
The shutter blades 2 and 4 have the same shape and overlap with each other 
in such positional relationship that one is set upside down and the two 
blades are symmetrical with regard to the exposure aperture 1. In other 
words, the first opening forming portions 2a, 4a and the second opening 
forming portions 2b, 4 have shapes so as to form two openings different in 
size concentrically located with the exposure aperture 1 when the shutter 
blades 2, 4 attain to the fully opened positions thereof. 
The reference numeral 8 represents a driving motor such as a DC motor which 
is mounted on the shutter base plate P and is equipped at an eccentric 
location with a magnet rotor having a driving pin 8a fitted into the fork 
portion 6b of the lever 6. The reference numeral 9 designates a shutter 
blade closing spring which is wound around the shaft 7 and stretched so 
that both arms 9a, 9b sandwich the pivot pin 3 for the shutter blade 2 and 
the pin 6a studded on the lever 6 in the shutter blade closed state 
illustrated in FIG. 1. This closing spring 9 is so composed as to be 
capable of retaining the shutter blade opening and closing lever 6 and the 
driving pin 8a at neutral positions thereof, thereby keeping the shutter 
blades 2, 4 at the closed positions thereof. When the driving motor 8 is 
not electrically energized. 
The reference numeral 10 denotes a pole studded on the shutter base plate P 
at such a location that the center of said pole is positioned on a 
straight line traced from the shaft 7 to the pin 6c on the opening and 
closing lever 6 when the opening and closing lever is at the neutral 
position thereof. The reference numeral 11 represents a shutter blade 
opening spring which is wound around the pin 6c and stretched so that both 
arms 11a, 11b sandwich the pole 10. This opening spring 11 has a resilient 
force that is weaker than that of the shutter blade closing spring 9 so 
that the former exerts no rotating force to the opening and closing lever 
6 while the lever 6 is kept at the neutral position thereof. 
The reference numeral 12 designates a stopper planted on the shutter base 
plate P in such a manner that the stopper is rotatable eccentrically and 
engages with the second end of the shutter blade 4 at the fully opened 
positions of the shutter blades 2, 4 when the smaller exposure opening is 
selected, i.e., when the second opening forming portions 2b, 4b form the 
opening. More specifically, the stopper 12 has, as illustrated in FIG. 4, 
a cylindrical head 12a to be engaged with the end of the shutter blade 4 
and a threaded shaft 12b which protrudes at a location eccentric from said 
head 12a and is screwed into the shutter base plate P. A spring washer 
12c, for example, should preferably be interposed between the head 12a and 
the shutter base plate for preventing the stopper 12 from being rotated 
accidentally when the threaded shaft 12b is screwed into the shutter base 
plate P. 
FIG. 5 shows an example of a driving circuit for the driving motor 8. In 
this drawing, the reference symbol E represents a power source, the 
reference symbols r.sub.1, r.sub.2, r.sub.3 and r.sub.4 designate 
transistors, and the reference symbol C denotes a control circuit which 
determines the rotating direction and an energizing time of the driving 
motor 8 so as to perform an exposure adequate for the brightness of an 
object to be photographed, and sensitivity of a film to be used, etc. 
Functions of the First Embodiment are described below: 
When a driving current is supplied to the driving motor 8 so as to turn the 
rotor clockwise at a predetermined angle in the state illustrated in FIG. 
1, the driving pin 8a is displaced to the location shown in FIG. 2, 
whereby the opening and closing lever 6 is turned counterclockwise to the 
location shown in FIG. 2 against the resilient force exerted by the arm 9a 
of the shutter blade closing spring 9. This turning of the opening and 
closing lever 6 causes clockwise rotation of the first shutter blade 2 
around the pin 3 and counterclockwise rotation of the second shutter blade 
4 around the pin 5 until these shutter blades are brought to the fully 
opened positions respectively (See FIG. 2). In this case, area of the 
exposure opening is determined by the exposure aperture 1. Since the 
current supplied to the driving motor 8 is stopped upon lapse of a proper 
exposure time, the shutter blade opening and closing lever 6 is rapidly 
turned clockwise by the returning force of the shutter blade closing 
spring 9 which is exerted to the pin 6 by way of the arm 9a, at the same 
time, the shutter blades 2, 4 are returned to the positions shown in FIG. 
1, and set at the closed states thereof, thereby terminating one exposure 
operation. 
In contrast, when a driving current of the polarity reverse to that of the 
driving current described above is supplied to the motor 8 by changing the 
emulsion speed of film to be used, for example, the driving pin 8a is 
rotated counterclockwise at a predetermined angle in the state illustrated 
in FIG. 1. The shutter blade opening and closing lever 6 is thus turned 
clockwise, whereby the first shutter blade 2 is rotated counterclockwise 
around the pin 3 and the second shutter blade 4 is rotated clockwise 
around the pin 5 against the resilient force exerted by the arm 9b of the 
shutter blade closing spring 9 until the shutter blades 2, 4 are brought 
to the fully opened positions thereof (See FIG. 3). In this case, the 
exposure opening is smaller than the exposure aperture 1. When the current 
supply to the driving motor 8 is stopped upon lapse of a proper exposure 
time, the shutter blade opening and closing lever 6 is rapidly turned 
counterclockwise by the returning force of the shutter blade closing 
spring 9 which is exerted to the pin 6a by way of the arm 9b. And at the 
same time, the shutter blades 2, 4 are returned to the positions shown in 
FIG. 1 and set in the closed states thereof, thereby terminating one 
exposure operation which is different from that already described above. 
During both of the exposure operations described above, the returning force 
of the shutter blade closing spring 9, i.e. the closing resilient force 
F.sub.1, varies in conjunction with the opening movements of the shutter 
blades 2, 4, as illustrated in FIG. 6A. The closing resilient force 
F.sub.1 is minimum when the shutter blades are set at the closed states 
(FIG. 1) and maximum when the shutter blades are set at the fully opened 
states (FIG. 2 and FIG. 3). The shutter blade opening spring 11 generates, 
at the neutral position thereof (FIG. 1), a force F acting in the 
direction from the pin 6c to the shaft 7 due to the reaction to the 
resilient forces equal to each other which are exerted by the arms 11a, 
11b toward the center of the pole 10, but this force F does not act as a 
force to turn the shutter blade opening and closing lever 6 because it 
acts directly towards the axis of the shutter blade opening and closing 
lever. When the opening and closing lever 6 is turned counterclockwide as 
shown in FIG. 7, however, said force F produces a component of force 
F.sub.2 which acts to turn said lever 6 counterclockwise. When the opening 
and closing lever 6 is turned clockwise as shown in FIG. 8, said force F 
produces a component of force F.sub.2 which acts to turn said lever 6 
clockwise. This component of force F.sub.2 varies as illustrated in FIG. 
6B during the opening movements of the shutter blades 2, 4. As a result, 
the shutter blade opening and closing lever 6 is rotated against a 
resilient force (F.sub.1 -F.sub.2) for opening the shutter blades 2, 4 and 
turned to the neutral position thereof by the resilient force (F.sub.1 
-F.sub.2) for closing the shutter blades as shown in FIG. 6c. The shutter 
blade opening and closing lever 6 has a tendency not stop at the neutral 
position thereof, but over-runs this position due to the forces of inertia 
of the shutter blades 2, 4 and the opening and closing lever itself. 
However, since said resilient force (F.sub.1 -F.sub.2) is the maximum at 
the neutral position, i.e., the shutter blade closed state, as shown in 
FIG. 6c, the forces of intertia of the shutter blades 2, 4 and the opening 
and closing lever 6 are remarkably cancelled at the neutral position, 
thereby suppressing the over-running of the opening and closing lever 6. 
Thus the opening and closing lever 6 tends to return to the neutral 
position thereof under the reaction and, also in this course, over-running 
is suppressed under the action of the resilient force (F.sub.1 -F.sub.2). 
Consequently, the shutter blade opening and closing lever 6 and the 
shutter blades 2, 4 can be stopped at the neutral positions thereof in a 
short time without over-running at the final stage of the exposure 
operation as illustrated in FIG. 9. That is to say, the camera shutter 
according to the present invention can completely prevent re-exposure due 
to the over-running of the shutters. 
In addition, when the smaller exposure opening is selected in the first 
Embodiment described above, the end of the shutter blade 4 contacts at the 
fully opened position thereof, with the stopper 12 as illustrated in FIG. 
3. Accordingly, the shutter blades 2, 4 are stopped at the fully opened 
positions without fail. As a result, the first Embodiment assures a 
constant area of the opening which is consistent for stable exposures. 
Since the location of the stopper to be engaged with the shutter blade 4 
is adjustable by turning the stopper 12 with a screwdriver or the similar 
means, the first Embodiment permits adjusting the area of the opening or 
exposure between a maximum value Max and a minimum value Min thereof as 
shown in FIG. 10. Consequenctly, the first Embodiment permits controlling 
the exposure accurately as predetermined without changing the time for 
supplying a current to the driving motor even when the larger and smaller 
exposure openings are switched from one to the other, and simplifying the 
composition of the motor driving circuit. The stopper 12 may be so 
constructed as to be engaged with the shutter blade at the fully opened 
position thereof which corresponds to the larger exposure opening, or the 
fully opened positions which correspond to both the larger exposure 
opening and the smaller exposure opening. 
FIG. 11 illustrates a second Embodiment of the camera shutter according to 
the present invention. The second Embodiment is different from the first 
Embodiment in that the second embodiment has shutter blades which are 
modified in shape as compared to the shape of the first embodiment, 
especially in the shape of second opening forming portions 2b', 4b'. The 
second embodiment is also different regarding the mounting of the shutter 
blade closing spring 9, which is wound around a pole 13 studded on the 
shutter base plate P. As shown in FIG. 11, however, the second Embodiment 
is the same as the first Embodiment in the other constructional points as 
well as the functions and advantages. Therefore, the members and parts of 
the second Embodiment which are the same or similar as or to those of the 
first Embodiment are represented by the same reference numerals in FIG. 11 
and will not be described in particular. 
Though each of the embodiments described above uses the two shutter blades, 
it is possible, needless to say, to use three or more shutter blades. 
Further, though the shutter blade closing spring 9 is set so as to 
intersect the arms 9a, 9b in the "X" shape with each other in each of the 
embodiments, these arms 9a, 9b may be stretched parallel with each other 
so as to sandwich the driving pin 6a. In this case, the arms 9a and 9b 
tend to be apart from each other toward the ends thereof, but this 
tendency can be compensated by changing the thickness of the pin to be 
sandwiched between the arms. Furthermore, it is possible to modify the 
embodiments so as to permit controlling exposure time at various spans for 
one exposure operation by stopping the current supply to the driving motor 
before the shutter blades reach the fully opened positions thereof or 
changing the time interval for changing polarity. 
Moreover, the shutter blade closing spring 9 may be stretched in such a 
manner that the arms 9a, 9b thereof sandwich the driving pin 8a so as to 
retain it at the neutral position thereof, thereby retaining the rotor of 
the driving motor 8 at the neutral position thereof, and the shutter 
blades 2, 4 may be pivoted by a common shaft on the shutter base plate P 
and pin-slot connected respectively to the shutter blade opening and 
closing lever 6. In the latter case, the pin-slot connection may be 
realized, for example, by forming plastic moldings of the shutter blades 
incorporating pins and fitting these pins into two slots formed in the 
shutter blade opening and closing lever 6.