Electronically operated magnetic control device for camera

The disclose circuit energizes a magnetic winding of a shutter actuating device. A constant voltage circuit is connected across the magnetic winding, or between the power supply terminal of the magnetic winding and a basic potential to ensure that the response of the armature of the actuating device to the output of a timing circuit is stabilized despite variation in the voltage of an electrical power source. This produces the advantage of substantially improving the accuracy of exposure control, because the closing operation of the shutter is controlled through movement of the armature.

BACKGROUND OF THE INVENTION 
This invention relates to photographic cameras, and more particularly to 
electromagnetic control devices in such cameras. Still more particularly, 
it relates to the stabilization of an electric impulse for energizing a 
magnetic winding of such device. 
Recently, the electromagnetic control devices have found wide use in 
photographic cameras. In still cameras having electrically timed shutters, 
this device is generally constructed to be responsive to the output of a 
timing circuit and arranged to control the closing movement of the 
shutter. In cine cameras, the period of actuation of the shutter drive 
means is controlled by an electromagnetic actuating device. In any case, 
efforts have been made to eliminate inconvenience in handling and 
portability of cameras. To do this it is necessary that the electrical 
power source or battery which is utilized in energizing a magnetic winding 
of the device be of small size so that the resulting output and capacity 
is small. This arises from the restriction of the space which the battery 
is intended to occupy. For this reason, it is of great importance to 
minimize consumption of electrical energy of the battery by the magnetic 
actuating device from the standpoint not only of preventing premature 
consumption of the battery but also of assuring a satisfactory dynamic 
range of exposure control even at lowered temperatures. The internal 
resistance of the battery is increased with decrease in temperature. 
Energization of the magnetic winding continues during the period of 
actuation of the shutter, that is, from the initiation to the termination 
of an exposure. Hence the current flowing through the magnetic winding, 
however small its intensity may be, reaches a considerable level 
particularly when the shutter time is long. To avoid this, mechanical 
subsidiary means have been arranged to be moved away from the armature of 
the magnetic actuating device at an appropriate time interval before the 
termination of duration of an exposure time, while simultaneously 
permitting the start of energization of the magnetic winding. At that 
termination, the magnetic winding is de-energized in response to the 
output of a timing circuit, causing movement of the armature through which 
the shutter is closed. Such shutter arrangement gives rise to the problem 
of increasing the production cost of the camera owing to the resulting 
complicated mechanical construction. At the same time, it involves 
lowering the reliability of exposure control. 
Attempts have been made to overcome the above-mentioned drawbacks by 
employing a permanent magnet in association with the electromagnet, as for 
example, disclosed in U.S. Pat. No. 4,020,433 (issued Apr. 26, 1977). Here 
the permanent magnet is arranged in the magnetic circuit of the device so 
that the armature is attracted by the magnetic flux of the permanent 
magnet. When the magnetic winding is energized, this magnetic flux is 
cancelled to permit movement of the armature under the action of a bias 
spring by which the shutter is driven to operate. Thus, remarkable 
reduction of consumption of the electrical energy can be achieved without 
an unduly large increase in complexity of mechanical construction and 
arrangement of the shutter control. The use of the permanent magnet leads 
to the production of what is called a moving coil type magnetic actuating 
device in which the magnetic winding, upon energization, is moved relative 
to the permanent magnet. Such movement of the magnetic winding is 
translated to control actuation of the shutter, or a trigger for the 
various portions of the camera mechanism. 
With these two conventional types of magnetic actuating devices, though the 
efficiency of usage of the electrical energy is remarkably improved as 
compared with the aforesaid overallperiod power supply type magnetic 
actuating device, the magnetic resistance in the magnetic circuit is 
substantially larger than that in the overall-period power supply type 
because of the permanent magnet or the air gap which is comparatively 
large in the magnetic circuit. In consequence, the required value of 
magnetomotive force exerted in the magnetic winding is increased to an 
amount available from the battery which is adapted for use in the camera 
since the internal resistance of the battery is relatively large. A 
control circuit for the magnetic actuating device is, therefore, designed 
to include a capacitor on which a certain fraction of the electrical 
energy necessary to energize the magnetic winding is previously stored. 
Thus energization of the magnetic winding takes the form of an electric 
pulse or impulse. 
The time lag from the moment at which an actuating signal has been produced 
by the timing circuit to the moment at which the armature or the moving 
coil starts to move varies, depending upon the magnitude of the electric 
impulse. The present inventors have now found from many experiments and 
analysis that, with the moving-coil type actuating device, when the 
voltage of the battery is varied by 2 volts, the variation of the time lag 
reaches 1 millisecond, as shown by a dashed line curve in FIG. 1. With the 
armature type actuating device, the variation of the time lag ranges from 
0.2 to 0.5 milliseconds, as shown by a solid line curve. 
Since the response of the composite magnet depends upon the various 
parameters such as magnetic permeability and saturation flux density 
characteristic of the magnetic circuit, and the response of the driven 
mechanism depends upon the force of the spring means, the inertia and the 
like, the range of variation of the time lag can be reduced to some extent 
by proper selection of these design parameters. Because of the presence of 
the comparatively large air gap of the permanent magnet in the magnetic 
circuit, and, therefore, of the creation of the extremely large magnetic 
resistance as compared with the overall-period power supply type magnetic 
actuating device, the degree of freedom of parameter-selection is 
extremely restricted. This makes it difficult to maintain the response of 
the entire system at a certain constant level as the actual voltage of the 
battery varies. 
This problem becomes serious when a highly accurate exposure control is 
desired even at faster shutter speeds, or when such magnetic control 
device is utilized in adjusting the size of diaphragm aperture. 
Particularly with a camera having various electronic control devices 
supplied with electrical power from a common battery, various photographic 
conditions which may be encountered result in a large difference in the 
amount of electrical energy used up at a time. This leads to a large range 
of variation of the voltage across the terminals of the battery due to the 
internal resistance thereof. Further, this internal resistance is varied 
with ambient temperature, thus the accuracy of exposure control is 
substantially decreased. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide an electromagnetic control 
device for use in a photographic camera. 
Another object is to provide an electromagnetic control device for 
actuating a portion of the camera mechanism while limiting the consumption 
of electrical energy to a minimum. 
Another object is to provide an electric impulse stabilizing circuit for 
energizing a magnetic winding of such device. 
Another object is to provide an electromagnetic actuating device for 
controlling movement of members of a camera shutter with high accuracy and 
reliability. 
These and other objects and features of the present invention will become 
apparent from the following detailed description of the preferred 
embodiments thereof taken in conjunction with the accompanying drawings in 
which:

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIGS. 2 and 6, show one embodiment of an electromagnetic actuating device 
according to the present invention, which is adapted to control closing of 
a camera shutter not shown. In FIG. 2, a timing and switching circuit and 
an impulse forming and stabilizing circuit are supplied with electrical 
power from a common battery 1. In the timing circuit a first variable 
resistor 3 has a resistance value related to the adjusted value of the 
shutter speed and is connected through a normally open power supply 
control switch 2 to the positive terminal of the battery 1. A second 
variable resistor 4 connected in series with the first resistor 3 
compensates for the difference in response characteristics of different 
shutter arrangements. A timing capacitor 5 is connected between the 
resistor 4 and the negative terminal of the battery 1, and a switch 6 is 
connected across the capacitor 5 and arranged to be opened during the 
opening operation of the shutter performs. In the switching circuit a 
reference voltage source or voltage divider is composed of resistors 7 and 
8 connected in series to each other between the switch 2 and the negative 
bus. A comparator 9 is connected at one input (+) to the output of the 
voltage divider and at another input (-) to the output of the timing 
circuit. 
The impulse forming circuit for energizing a magnetic winding 10 of the 
actuating device comprises a storage capacitor 12 connected at one pole to 
the positive terminal of the battery 1 through a charging resistor 11 and 
at the opposite pole to the negative bus A. The magnetic winding 10 is 
connected between the output of the comparator 9 and a point between the 
resistor 11 and the capacitor 12. The impulse stabilizing circuit is 
constructed in the form of a constant voltage circuit composed of a single 
voltage regulating element, in this instance, a Zener diode 20 with its 
anode connected to the output of the comparator 9 and with its cathode 
connected to the positive pole of the storage capacitor 12. In other 
words, the Zener diode 20 is connected in a normal direction across the 
magnetic winding 10. The Zener diode is adjusted in breakdown point to 3 
volts, for example, as is determined on assumption that the acceptable 
accuracy of operation of the timing circuit is secured with the battery 1 
of a voltage ranging from 5 to 3.5 volts. 
FIG. 6 shows a schematic example of the mechanical part of the 
electromagnetic actuating device which is of the fixed-coil 
moving-armature type. The magnetic winding 10 of FIG. 2 is formed around 
two arms 60 and 61 of a yoke with a permanent magnet 62 sandwiched between 
the arms 60 and 61. Positioned adjacent the forward ends of the arms 60 
and 61 is an armature 63 of triangular shape. When the magnetic winding 10 
remains de-energized, the armature 63 is attracted by the magnetic force 
of the permanent magnet 62 against the force of a drive spring 64. When 
the winding 10 is energized to cancel the magnetix flux of the permanent 
magnet 62, the armature 63 is moved away from the yoke to actuate a 
control member not shown for the closing operation of the shutter. 
A moving-coil type actuating device is shown in FIG. 7 wherein the same 
reference numerals have been employed to denote similar and like parts of 
FIG. 6. A coil 10 equivalent to the magnetic winding 10 of FIG. 6 is 
mounted on a movable support 67. This assembly is arranged within a space 
provided in a yoke 60 so as to surround a central section thereof. The 
support 67 is biased by a spring 64 connected between the camera housing 
not shown and a projection 67a, the latter extending through and outwardly 
beyond a hole 66a provided through the wall of an upper panel 66. A buffer 
spring 65 is positioned between the support 67 and the upper panel 66. The 
forward end 67b of the projection 67a is formed as an armature having the 
same function as that of FIG. 6. 
The operation of the electromagnetic actuating device is as follows. Let us 
now assume that the actual voltage of the battery 1 is, for example, 5 
volts, above a satisfactory operating level. Prior to the making of an 
exposure, the operator need to set a desired value of shutter speed in the 
variable resistor 3. It is further assumed that the second variable 
resistor 4 is appropriately adjusted to enable a particular actuating 
device to perform in an optimum manner with a particular shutter 
mechanism. 
When a shutter release button not shown is depressed to close the power 
supply control switch 2, so the shutter control circuit is rendered 
operative. Then, a diaphragm in a lens mount not shown is closed down to a 
preset value, and then a reflex mirror not shown, is flipped upward. Such 
movement of the mirror causes opening operation of the shutter to start 
with the initiation of an exposure. At this time, the count start switch 6 
is opened so that the timing capacitor 5 is charged through the resistors 
3 and 4. The voltage on the capacitor 5 is increased, and reaches a level 
coincident with the reference voltage when the duration of the time 
interval set in the resistor 3 is terminated. Hence the output voltage of 
the comparator 9 changes to zero potential. This causes the magnetic 
winding 10 to be energized by an electric pulse or impulse with power 
mainly from the storage capacitor 12. The charge on the capacitor 12 is 
suddenly discharged through the magnetic winding 10 and the comparator 9 
to the negative bus A, while the voltage across the magnetic winding 10 
regulated to 3 volts. Accordingly, the armature 63 or 67b of FIG. 6 or 7 
respectively is abruptly moved by the spring 64 with an improved accuracy 
in response to the occurrence of the impulse. A rear curtain of the 
shutter not shown is then released from the cocked position to terminate 
the exposure. 
Alternately assuming that the actual voltage of the battery 1 is lowered to 
about 3.5 volts. Even in this case, the voltage appearing across the 
magnetic winding 10 is maintained at the same level as that when the 
battery 1 provides 5 volts. Therefore, the response of the armature 63 or 
67b remains unchanged. This makes it possible to achieve a high accuracy 
of exposure control regardless of the variation of the voltage of the 
battery 1. After the shutter release button returns to the initial 
position, the switch 2 is opened to cut off the power supply from the 
timing and switching circuit. By subsequent operation of a film winding 
and shutter cocking mechanism not shown, the switch 6 is closed, and the 
armature 63 or 67b is moved backward to the initial position shown in FIG. 
6 or 7. 
FIG. 3 shows another example of the impulse stabilizing circuit as 
constructed by replacing the Zener diode 20 of FIG. 2 by a string of 
light-emitting diodes 30 and 31. These diodes 30 and 31 are connected in a 
forward direction across the magnetic winding 10 to provide an almost 
constant voltage drop regardless of the variation of the voltage of the 
battery 1. The diodes 30 and 31 are arranged to be visible either from the 
outside of the camera housing, or in the viewfield of the finder. 
FIG. 4 shows still another example of the impulse stabilizing circuit as 
constructed by substituting a string of commonly available diodes 40, 41 
and 42 for the light-emitting diodes 30 and 31 of FIG. 3. In this case 
also, the magnetic winding 10 is energized at a constant voltage 
thereacross. 
FIG. 5 shows a further example of the impulse stabilizing circuit of the 
invention. Here a Zener diode 50 has a cathode connected to the connection 
between the resistor 11 and the storage capacitor 12. An npn transistor 51 
with a collector connected to the anode of the Zener diode 50. The emitter 
of transistor 51 connected to the negative pole of the storage capacitor 
12, and the base connected through a resistor 52 to the common power 
supply control switch 2 of the timing circuit. When the shutter release 
button is depressed to close the switch 2, a base current flows to the 
transistor 51 to clamp the voltage on the storage capacitor 21 at the sum 
of a reverse blocking voltage of the Zener diode 50 and an 
emitter-collector voltage Vce of the transistor 51. Thus the voltage 
appearing across the magnetic winding 10 at the time of application of an 
impulse from the storage capacitor 12 is adjusted to a constant level, 
even when the actual voltage of the battery 1 is varied. 
It is of course possible to factor the voltage loss into an otherwise 
constructed electronic device associated with the timing circuit. In this 
case, however, a high unit cost production technique must be employed as 
compared with the present invention. 
While embodiments of the invention have been described in detail, it will 
be evident to those skilled in the art that the invention may be practiced 
otherwise without departing from its spirit and scope.