JPH0248827Y2 - - Google Patents

Description

[Detailed description of the invention] This invention is a photographic aperture control device used in cine cameras, video cameras, etc. In particular, it uses a servo motor as the drive source for control, and when the drive power is turned off, the aperture blades automatically move. The present invention relates to a photographic aperture control device that is moved to a closed position and held at that position. Cine cameras, video cameras, etc. are often equipped with automatic aperture control devices in order to photograph moving subjects with proper exposure, but among these control devices, those that use TTL metering do not allow shooting. The aperture blades must be held in the closed position when not in use, ie, when the camera's power switch is open. This is to prevent the photoelectric conversion element, etc. for detecting field brightness, which is placed behind the aperture blades, from breaking down or becoming fatigued due to external light.

For this reason, in conventional automatic aperture devices, a spring is placed on the rotor of the servo motor that drives the aperture blades, and the restoring force of the spring returns the aperture blades to the closed position when the drive power is cut off. and held in that position. However, this method has the following drawbacks. In other words, (1) it is difficult to mass-produce products that meet certain standards due to variations in the elasticity between springs, (2) the elasticity of the springs tends to change over time, and (3) it is difficult to keep the aperture blades in the closed position. In order to hold the aperture stably, the elasticity of the spring must be made strong, but as a result, the load associated with opening the aperture blades increases as the aperture diameter increases, and drive power consumption increases (in other words, the above-mentioned It has been pointed out that stabilization of holding and reduction of driving power consumption are always incompatible.

In view of the above, the applicant used a permanent magnet rotor and further arranged a soft magnetic material in relation to the rotor,
An application was filed for an automatic diaphragm device in which the diaphragm blades are returned to the closed position by the magnetic attraction force acting between them (Utility Model Application No. 55-105252; Utility Model Application No. 57-28427), but this device has a spring-type On the other hand, since the above-mentioned magnetic attraction force is inversely proportional to the square of the distance, there is a risk that the magnetic attraction force will not work satisfactorily in a position where the aperture blades are wide open.
In order to avoid this, there was a problem in that the magnetic attraction force had to be increased at the expense of reducing drive power consumption.

The present invention eliminates the drawbacks of the method using only magnetic force as described above, and also eliminates the drawback (3) among the drawbacks of the method using only springs, and furthermore (1) and (2).
In order to greatly improve the shortcomings of
The rotor of the servo motor is configured to be able to rotate by less than 90 degrees while the aperture moves from the throttle end position to the fully open position, and a soft magnetic material is provided near the permanent magnet of the rotor in the throttle end position. Furthermore, a spring is tensioned to bias the aperture to the aperture end position, and the aperture is brought to the aperture end position by the combined force of the magnetic force acting between the permanent magnet and the soft magnetic material and the elastic force of the spring. , it is an object of the present invention to provide a photographing aperture control device which is configured to hold the photographic aperture at this position.

First, the structure of the present invention will be explained with reference to the drawings (FIGS. 1 to 3) showing preferred embodiments of the present invention. First, in FIG. 1, reference numeral 1 denotes an aperture device having a known structure, in which aperture blades 2 are opened and closed by rotating an aperture ring (not shown) left and right. Reference numeral 3 denotes an operating rod embedded in the aperture ring, and has an elongated hole 3a. The pin 6a of the rotor of the servo motor 4 is inserted into the long hole 3a.
(described later) is fitted therein, and when the servo motor 4 rotates, the aperture ring rotates via the pin 6a, and the aperture blades 2 open and close. A spring e is stretched between the fixed plate P and the operating rod 3, and applies biasing force to the aperture ring in the counterclockwise rotation direction, that is, toward the aperture cutting position.

FIG. 2 is a simplified representation of the cross-sectional structure of the servo motor 4, in which 5 is a cylindrical permanent magnet;
6 is an intermediate member having a pin 6a, 7 is a rotating shaft,
These three members are integrally molded, for example, by molding the intermediate member 6 to constitute a rotor. 8 and 9 are drive coils and control coils, and 10 and 11 are pieces of soft magnetic material such as pieces of soft iron. The soft magnetic piece is the third
As shown in the figure, two permanent magnets are provided facing each other on an extension of the center line of the permanent magnet 5 of the rotor. The rotor of the servo motor is configured to rotate less than 0° to less than 90° while the aperture ring of the aperture device 1 moves from the closed position (or aperture cut position) to the fully open position of the aperture blades. and when the aperture blades are in the closed position (aperture cut position), the N and S poles of the permanent magnet 5 are connected to the soft magnetic pieces 10 and 11 within a rotatable range of the permanent magnet 5.
It is designed to be the closest. Next, an example of a conventionally known drive circuit used in the present invention will be explained with reference to FIG. In the figure, E ₀ is a power supply, and S ₀ is a power switch. OP ₁ and OP ₂ are operational amplifier circuits that constitute the servo amplifier circuit, and R ₁ , R ₃ and R ₂ ,
_R4 is the input resistance and negative feedback resistance of the operational amplifier circuits _OP1 and _OP2 . Drive coil 8 is operational amplifier circuit OP ₁
and connected between both output terminals of OP ₂ . P _R is a photoelectric conversion element such as a CDS for automatic aperture control, and is arranged so as to be able to receive the light that has passed through the aperture device 1 . _R5 is a resistor, which together with the photoelectric conversion element _PR constitutes one input circuit of the servo amplifier circuit. _R6 ,
_R7 is also a resistor and constitutes another input circuit (reference voltage generation circuit) of the servo amplifier circuit. By using such a drive circuit, during photography, the light from the subject that passes through the aperture generates a voltage in the photoelectric conversion element installed after the aperture device, which corresponds to the intensity of the light. This excites the drive coil of the servo motor, rotates its rotor by a predetermined angle, and automatically corrects the aperture diameter as needed. If we explain this again based on the drawing,
The set voltage V _x (V _x = R ₇ / R ₆ + R ₇ · Vcc, where Vcc: voltage of power supply E ₀ ) given by the voltage divider circuit consisting of resistors R ₆ and R 7 is applied to the photoelectric conversion element _P. When V _X is larger than the variable voltage V _Y determined by the variable output of _R and resistor R ₅ , the operational amplifier
The output of OP ₁ becomes larger than the output of OP ₂ , current flows in the drive coil 8 in the direction of arrow A, and the servo motor 4 drives the diaphragm blades 2 of the diaphragm device 1 in the direction of opening, and vice versa. When voltage V _Y is greater than voltage V _X , the output of operational amplifier circuit OP ₂ is greater than the output of OP ₁ , so arrow A
Current flows in the opposite direction, and the servo motor 4 drives the diaphragm blades 2 of the diaphragm device 1 in the direction of closing. In either case, the drive of the servo motor 4 is formed by operational amplifier circuits OP ₁ and OP ₂ . It continues in the direction where the bridge circuit is balanced, _that is _, until _the set voltage _V , a predetermined aperture aperture is set according to the brightness of the subject.

Next, the effects of the conventional example will be described, and the effects of the present invention will be explained in comparison with these.

Figure 5 shows the aperture blades in an aperture control device using the control circuit described above, in which no aperture cutting means, that is, any biasing means such as a spring for bringing the aperture blades to the aperture cutting position, is provided. It shows the relationship between displacement and servo motor operating current.
In other words, in this case, as shown in the diagram, the above operating current is equal to or less than 100%, except for the rise when the servo motor is started and the rise that occurs when the drive of the servo motor is forcibly blocked at the fully open position of the aperture blades. A horizontal waveform is drawn over almost the entire displacement of the aperture blades 2 (aperture diameter). Below this 5th
The waveform shown in the figure is considered to be the minimum current waveform for driving the aperture blades, and in this sense, it will be hereinafter referred to as the operating limit current (waveform). FIG. 6 shows the relationship between the displacement of the aperture blades and the operating current of the servo motor in the above-mentioned automatic aperture control device using only a spring as the aperture cutting means.
In this case, the restoring force of the spring acts as a load for the opening drive by the servomotor, so if this is represented as a load current by a broken line, it will always be above the solid line (the operating limit current), which is on the upper right. It becomes a straight line. This is because, when the power switch is turned off, the aperture blades must always be displaced to the aperture-closed position (by the spring force). Therefore, in this method, the actual drive current for driving the servo motor is the above operating limit current plus the load current due to the spring, as shown by the solid line α (hereinafter this kind of current will be referred to as the total drive current). becomes. According to this waveform α, in the method using only springs, the total drive current value is generally high, and its peak value is large, so the power consumption is large.
Also, the operational amplifier circuit in the circuit (Fig. 4)
It can be seen that the capacity of OP ₁ and OP ₂ must be increased. Next, FIG. 7 shows the relationship between the operating current of the aperture blades and the servo motor in the automatic aperture control device which performs aperture cutting only by the magnetic attraction force. In this case, when the magnetic attraction force is expressed as a load current, it becomes like a broken line (for the same reason as above, the broken line must always be located above the operating limit current). The drive current is represented by a waveform of a solid line β.
From this, it can be seen that in the method using only magnetic attraction force, the total drive current value is generally high, and its peak value is large, so the power consumption is large, so the capacity of the operational amplifier circuits OP ₁ and OP ₂ in Fig. 4 is increased. It is clear that this must be done.

As already mentioned, the aperture control device of the present invention was developed to eliminate the drawbacks of the above-mentioned conventional methods, but the relationship between the displacement of the aperture blades 2 (of the present invention) and the operating current of the servo motor 4 was FIG. 8 shows this. In the same figure, the solid line a is the operating limit current waveform, the solid line b is the load current waveform due to the spring e (Fig. 1), and the solid line c is the waveform of the load current caused by the rotor permanent magnet 5 (Figs. 2 and 3). Soft magnetic piece 10,1
The load current waveform due to the magnetic attraction force acting during the period 1, and the dashed dotted line d shows a composite load current waveform obtained by combining the above two load current waveforms.

As is clear from the figure, in the spring force/magnetic force combination method of the present invention, the load current due to the spring force and magnetic force individually is considerably smaller than that of the previous two conventional examples, and the displacement of the aperture blade is The operating limit current is below the operating limit current in almost the entire displacement range, and therefore the aperture blades cannot be displaced to the aperture cut-off position.However, the composite load current that combines these two draws a nearly horizontal waveform and the operating limit current is lower than the operating limit current in the entire displacement range. When the aperture exceeds a certain value and the power switch _E0 is opened, the aperture blades smoothly move to the aperture-closed position and are safely held in that position (mainly by magnetic force). . The total drive current in this case is represented by a waveform γ that is a combination of the composite load current and the operating limit current. From this, it can be seen that in addition to the above-mentioned features, the system of the present invention has a lower total drive current and a smaller peak value than the two conventional examples. Therefore, the aperture control device of the present invention consumes less power when driving the servo motor 4 than the two conventional examples described above, and furthermore, the aperture control device of the present invention consumes less power when driving the servo motor 4.
This has the advantage that relatively small capacities can be used for OP ₁ and OP ₂ . In addition, in the drawing device of the present invention, it is possible to use a spring e with a small (elastic force), so it is possible to minimize variations in elasticity between each spring in mass production, and also to minimize the effects of spring deterioration over time. (in this case, especially with the help of the effect of magnetic attraction).

[Brief explanation of the drawing]

Fig. 1 is a front view of an embodiment of a servo aperture device equipped with the control device of the present invention, Fig. 2 is a sectional view of a servo motor used in the drive unit of the present invention, and Fig. 3 is a rotation of the same servo motor. FIG. 4 is a wiring diagram of an example of an automatic diaphragm control circuit, FIGS. 5 to 7 are displacement-current characteristic curve diagrams of a conventional automatic diaphragm control device, and FIG. The figure is a displacement-current characteristic curve diagram in the embodiment of the present invention. DESCRIPTION OF SYMBOLS 1...Aperture device, 2...Aperture blade, 3...Operation rod, 4...Servo motor, 5...Permanent magnet, 6...
...Intermediate member, 7...Rotating shaft, 8...Drive coil,
9... Control coil, 10, 11... Soft magnetic material, e
...Spring, P _R ...Photoelectric conversion element, E ₀ ...
Power supply, _S0 ...power switch, _OP1 , _OP2 ...operational amplifier circuit, _R1 to _R7 ...resistance.

Claims (1)

[Claim for Utility Model Registration] It consists of a drive coil and a permanent magnet, and is capable of reciprocating rotation to drive and control the aperture blades between a fully apertured position and a fully open position. The magnetic attraction force generated between the rotor, which is set to be less than 90 degrees, and the permanent magnet, which is located close to the throttle-cut position, gives the rotor a rotational habit toward the throttle-cut position. a servo motor having a soft magnetic material; and a spring that cooperates with the magnetic attraction force to bring the aperture blades to the aperture cut-off position and bias the aperture blades to hold the aperture blades at that position. Shooting aperture control device.