JPS63201636A - Shutter driving device - Google Patents

Abstract

PURPOSE:To improve stability to variation in shutter opening speed with time by using a bimorph for a shutter driving source, charging electrically and deforming this bimorph by a constant-current charging circuit, and connecting a capacitor which cancels the temperature coefficient difference between the bimorph and constant-current charging circuit in parallel to the bimorph. CONSTITUTION:The bimorph Bi is inserted into the collector circuit of a transistor(TR) 3 and the amplification characteristics of the TR that the collector current is nearly constant regardless of the collector voltage when the base current, i.e. base-emitter voltage is constant are utilized to charge the bimorph Bi with a constant current. Further, the capacitor C1 is connected in parallel to the bimorph Bi charged with the constant current and a bimorph charging circuit 27 is so constituted that the temperature coefficient of the total electrostatic capacity of the bimorph Bi and capacitor is equal to the temperature coefficient of the constant-current charging circuit. Consequently, the shutter speed is made stable to temperature variation and time accuracy is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a shutter driving device using a bimorph.

However, prior art shutter drives require exposure accuracy. That is, opening accuracy and time accuracy for reaching a predetermined opening position are required. When driving a shutter using an electrostrictive element that generates a driving force by applying a voltage, such as a bimorph, the required aperture accuracy can be easily achieved by using a photocoupler, etc. However, the time required to reach a predetermined aperture position is Accuracy is that the driving force generated in the bimorph is proportional to the voltage applied to the bimorph, and the voltage applied to the bimorph is proportional to its charging charge.Since the bimorph can be regarded as a capacitor, the charging speed when applying voltage to the bimorph is stable. Depends on degree.

Conventional methods include supplying a bimorph-shaped pulse current as shown in Japanese Patent Application Laid-Open No. 60-149033, and Japanese Patent Application No. 61-1 filed by the applicant of the present application.
As shown in No. 89288 (an invention in which the capacitor C1 is deleted from FIG. 1), charging was performed using a constant current. However, as shown in Figure 3, the capacitance of the bimorph increases as the temperature rises (approximately 7000 ppm/"C).
As shown in FIG. 4, the current in the constant current circuit increases (approximately 3500 ppm/''C) as the temperature rises.

However, since the increasing ratios of the two are different, the charging state of the bimorph changes with temperature changes by the difference in temperature coefficient between the bimorph and the constant current circuit, as shown in FIG.

Therefore, this method has a problem in that if the ambient temperature changes, the shutter speed also changes with the temperature change.

In addition, bimorphs are affected by humidity, and as the humidity increases, leakage current increases.As shown in Figure 6, when charged with the same current, the charging voltage becomes lower, and the apparent capacitance of bimorphs increases. Therefore, as shown in FIG. 7, the shutter speed becomes slow and the exposure amount becomes under-exposure.

C.6 Problems to be Solved by the Invention It is an object of the present invention to stabilize the shutter opening speed of a shutter device using an electrostrictive element against temperature changes.

21 Means for solving the problem In a shutter that uses the mechanical driving force generated in the bimorph by voltage as a driving source, the shutter has a temperature coefficient smaller than or in the opposite direction to the temperature coefficient of the electrostrictive element in parallel with the electrostrictive element. A capacitor was connected so that the electrostrictive element and the capacitor were simultaneously charged by a constant current circuit.

E1 Effect The present invention provides a method for improving the time accuracy of reaching a predetermined opening position in a shutter drive device. The driving force of the bimorph is proportional to the charging voltage. Therefore, in order to improve the time accuracy for reaching a predetermined opening position, it is only necessary to improve the reproducibility of the charging speed of the bimorph.The present invention incorporates a bimorph charging circuit that charges the bimorph with a constant current into the shutter device. In addition, a capacitor with a temperature coefficient smaller than the temperature coefficient of the bimorph or a capacitor with a temperature coefficient in the opposite direction (e.g., a ceramic capacitor) is connected in parallel with the bimorph, and the temperature coefficient of the total capacitance of the bimorph and the capacitor is determined by a constant current circuit. The aim is to improve the stability of the time accuracy for reaching the opening position against temperature changes by keeping the same temperature coefficient (approximately 3500 ppm/'C). In other words, if the rate of change due to temperature in the constant current circuit is always the same as the rate of change due to temperature of the total capacitance of the bimorph and the capacitor, then the change due to temperature in the rate of increase in the voltage applied to the bimorph will be the same as the rate of change due to temperature in the constant current circuit. This is offset by changes due to temperature, and the shutter speed is stabilized against temperature changes, improving time accuracy.

Furthermore, since the charging characteristics of the capacitor connected in parallel with the bimorph do not change depending on humidity, by connecting the capacitors in parallel, changes in the bimorph's charging curve due to humidity are reduced, as shown in Figure 6.

Embodiment Fig. 2 shows an embodiment of the mechanism of the present invention. This embodiment is a shutter device in which the shutter also serves as an aperture and opens at a constant speed to an aperture value determined by the brightness of the subject. The pair of shutter blades 2.4 are simultaneously rotated in opposite directions by the driving force generated in the single-supported bimorph 14, and the small holes for shutter opening detection provided in the shutter blades 2 and 4 are aligned. It is detected by the rear photodetecting element 1°, and the specified shutter opening position is detected by the number of times the photodetecting element 1o detects light. rta
When the number of times of light detection reaches a predetermined number, it is determined that the shutter opening degree has reached the specified opening degree, and the opening movement of the shutter blades is stopped and the shutter blades are returned to the initial position. It is.

Figure 1 is a control circuit diagram for monitoring and controlling the movement of the shutter described above, in which the bimorph Bi is connected to the transistor Tr3.
When the base current is constant and the voltage between the base and emitter is constant, the collector current is almost constant regardless of the collector voltage. At the same time, a capacitor C1 is connected in parallel to the bimorph Bi, which is charged with a constant current, so that the temperature coefficient of the total capacitance between the bimorph Bi and the capacitor is the same as the temperature coefficient of the constant current circuit. The bimorph charging circuit 27 is the main part of the present invention.

As stated at the beginning, the temperature coefficient of the bimorph is approximately twice that of the constant current circuit. Therefore, if a film capacitor, for example, whose temperature coefficient can be regarded as 0 is used as capacitor C1, and the capacitance of C1 is made equal to that of a bimorph, the total temperature coefficient of both will be half of the original value. It can be matched with the temperature coefficient of the constant current circuit. If a capacitor with a negative temperature coefficient, such as a ceramic capacitor, is used for C1, the required capacitance of C1 may be even smaller.

Bimorphs are affected by humidity, and as humidity increases, the charging voltage when charged with the same current decreases, which is the same as increasing the bimorph's capacitance. Capacitors are not affected by humidity in this way. Therefore, if you connect a capacitor in parallel with a bimorph, you can suppress changes in the charging speed due to humidity, as shown in Figure 6. By setting C1 and C1 to the same capacity, the influence of humidity can be approximately halved. Also, C1
If you use a capacitor that has temperature characteristics in the same direction as the bimorph and has a coefficient smaller than that of the bimorph, you will need a capacitance several times that of the bimorph. It is also possible to suppress the influence to a fraction of that.

Note that the embodiment shown in FIGS. 1 and 2 will be described in detail. In FIG. 2, the shutter blades 2 and 4 are rotatably held on a shaft 8 fixed to a shutter base plate 6, and are symmetrical with respect to a line connecting the center of the exposure opening 6a and the center of the shaft 8. The long holes 2b and 4b provided in the shutter blades 2 and 4 engage with the engagement pins 12a and 12b provided in the opening/closing lever 12, and the engagement pins 12a and 12
The shutter blades 2 and 4 are rotated by the movement of b. The V-shaped notch openings 2a and 4a provided in the shutter blades 2 and 4 open and close the exposure opening 6a by the above rotation. Multiple small holes 2A and 2B in shutter blades 2 and 4
, 2C, 2D, 2E and 4A, 4B, 4C, 4D, 4E
are provided on the same circumference centered on the shaft 8 and symmetrically with respect to a line connecting the center of the exposure opening 6a and the center of the shaft 8, and the small holes are arranged in accordance with the rotation of the shutter blades 2 and 4. At the measurement position 10a of the photodetecting element JO, which has been moved and installed in the notch 6b of the white board, the small holes 2A and 4A are opened immediately before the blade opening, and the small holes 2B and 4B are opened to the minimum diameter aperture, and the small holes 2
E and 4E are arranged so that they overlap when the aperture is opened to the maximum aperture, and the other small holes 2C and 4C, 2D and 4D
are arranged so that they overlap when the shutter blades open to a predetermined aperture between the minimum aperture and the maximum aperture.

Note that an appropriate number of small holes may be provided at appropriate positions corresponding to the aperture value to be detected.The shutter plate 6 has an exposure opening 6a and a notch 6blF for installing the photodetecting element 10.
A long hole 6c to prevent the pins 12a and 12b set on the I-close lever 12 from coming into contact and interfering with the movement of the lever;
6d is provided. The shutter opening/closing lever 12 is rotatably held by a shaft 16 on the shutter base plate 6, and a long hole 12e is provided at the right end in the figure so as not to contact the shaft 8.
and a pin 12a that engages with the long holes 2b and 4b of the shutter blade.
, 12b are provided almost symmetrically with respect to the elongated hole 12e, and pins 12c and 12d are provided at the U-shaped tip at the left end in the figure so as to sandwich the tip of the bimorph 14. The bimorph 14 has one end connected to the pins 12c, 12.
d, and the other end is fixed by a holding plate 18.

When a voltage is applied to the bimorph 14 in the shutter closed state shown in FIG.
One end on the side 8 is fixed and rotated in a clockwise direction, thereby generating a driving force.

When the opening/closing lever 12 is rotated clockwise by the driving force, the long holes 2b and 4b of the shutter blades 2 and 4 are pushed by the pins 12a and 12b, and the shutter blades 2 and 4 are mutually opened. It can be rotated in the direction.

As the shutter blades 2 and 4 rotate, the small holes 2A and 4A, 2
The photodetecting element 10 is located at the measurement position 10a, where B and 4B, 2C and 4C, 2D and 4D, and 2E and 4E overlap each other in sequence.
The control circuit detects the overlap and outputs a signal, and when the number of outputs of the detection signal reaches a predetermined number of times, the control circuit determines that the specified shutter opening degree has been reached, and the bimorph 1
4, the opening movement of the shutter blades 2 and 4 is stopped, and an operation is performed to return the shutter blade 2.4 to its initial position.

Returning to FIG. 1, 21 is a photometric circuit that measures the brightness Bv value of the subject, 22 is a film sensitivity reading circuit that reads the film sensitivity Sv value, and 23 is an aperture in which the photodetecting element 10 of FIG. 2 is incorporated into the circuit. This is a position detection circuit. 24 is an arithmetic circuit which calculates an exposure value Ev from the brightness Bv value and film sensitivity Sv, and outputs it to the exposure control circuit 25. The exposure M control circuit 25 includes a switch S that is closed by shutter release operation.
By opening 2, the bimorph B is loaded into the bimorph charging circuit 27.
i, and when the number of pulse signals inputted from the aperture position detection circuit 23 to the exposure control circuit 25 reaches the number corresponding to the exposure value Ev, the charging signal is stopped and the bimorph charge is discharged. Output a signal. The bimorph charging circuit 27 charges the bimorph Bi and the capacitor C1 based on the control signal from the exposure control circuit 25.
This is a circuit that charges the battery with a constant current or instantly discharges the charged charge. The booster circuit 26 is a booster circuit that boosts the battery voltage to the maximum voltage required for bimorph charging, and the booster circuit used in electronic flash devices is commonly used. In addition, as shown in FIG. 1(B), the bimorph 14 (Bi) has a center electrode connected to the booster circuit side, both side electrodes connected to the collector side of the transistor Tr3, and a positive voltage between the center electrode and both side electrodes. By applying a voltage, the second
In Figure (A), one end on the side of the holding plate 18 is set as a fixed end and is rotated clockwise.

In the above circuit configuration, the main switch (not shown) is
When it is N, power is supplied to the boost circuit 26 of the electronic flash device, and the boost circuit 26 supplies the main capacitor C2.
is charged to a predetermined voltage. Next, by pressing the first stage of the release button (not shown), a switch (not shown) is turned on.
I, power supply V1 is performed to other circuits except the booster circuit 26. This causes the photometry circuit 21 to operate and measure the brightness of the subject by Bv.
It is output to the arithmetic circuit 24 as a value. The film sensitivity reading circuit 22 automatically reads the film sensitivity from the DX code on the film cartridge, and outputs it as an Sv value to the calculation circuit 24.
Output to. The arithmetic circuit 24 calculates an exposure value Ev from the input luminance Bv value and film sensitivity Sv, and outputs it to the exposure control circuit 25. At this stage, the exposure control circuit 25 is outputting high level signals to both output terminals a and b.
As shown in FIG. 1(C), transistors Tri, Tr
Therefore, the transistors Tr3 and Tr4 for operating and initializing the bimorph BigA are in an OFF state, and the charge of the bimorph Bi is O.

As shown in Figure B, the bimorph Bi has a configuration in which the central electrode is connected to the booster circuit side, and the electrodes on both sides are connected to the collector of the transistor Tr3.

Next, in order to take a picture, the release button (not shown) is pressed to the second stage (first stage).
When the release switch S2 is pressed down to a stroke deeper than the stroke, the release switch S2 is turned on. As a result, the exposure control circuit 25 outputs a 0 level signal to the output terminal a and a high level signal to the terminal A, and as shown in FIG. Turn on. Transistor Tr3 is a constant current transistor.

A diode D1 is connected between the base and the emitter in order to cause the current to flow, and a constant current is caused to flow through the diode D1 by a constant current power supply I.

Therefore, the base-emitter leap voltage of the transistor Tr3 is kept constant, and the collector current 11 of the transistor Tr3 is kept constant. Note that VR is a variable resistor for adjusting the constant current 11. As described above, when the bimorph Bi is charged by the constant current 11, a driving force proportional to the charging voltage is generated in the bimorph Bi. This driving force causes the shutter to open as described above. As the shutter opens, pulses are sequentially output from the opening position detection circuit 23 to the exposure control circuit in accordance with the opening of the shutter. When the exposure control circuit 25 receives the number of pulses corresponding to the calculated exposure value Ev, it outputs a high level signal to the output terminal a and a 0 level signal to the output terminal, as shown in FIG. 1C. Turn transistor Tr2 ON and turn transistor Tr3 OFF.
F, then C.

The Yutter opening is stopped, and at the same time, the transistor Tri that controls shutter closing is set to 0FFL, and the transistor Tr4 is turned on for a short time to short-circuit the bimorph Bi. Due to this short circuit, the bimorph Bi moves to return to its initial position and closes the shutter.

According to the present invention, the temperature characteristics of the bimorph and the bimorph charging circuit can be corrected simply by connecting a capacitor in parallel with the bimorph, and stable shutter speed control against temperature changes can be performed. Connecting a capacitor also has the effect of controlling changes in the charging speed of the bimorph due to humidity, so a high-precision shutter mechanism using the bimorph can be realized with the double effect of killing two birds.

[Brief explanation of the drawing]

Figure 1 shows the circuit configuration of an embodiment of the present invention, (A) is a circuit diagram, (B) is a bimorph wiring diagram, (C) is a time chart of circuit operation, and Figure 2 is a circuit diagram. The mechanical part of the above embodiment is shown in the same figure (A> is a plan view. Figure (B) is a cross-sectional view, Figure 3 is a temperature characteristic graph of a bimorph, Figure 4 is a temperature characteristic graph of a constant current circuit, and Figure 5 is a graph of temperature characteristics of a constant current circuit. 6 is a graph of bimorph charging characteristics, FIG. 6 is a graph of humidity characteristics of bimorph voltage, and FIG. 7 is a graph of humidity characteristics of shutter aperture. 21...Photometering circuit, 22... Film sensitivity reading circuit. 23. ... Opening position detection circuit, 24 ... Arithmetic circuit. 25 ... Exposure control circuit, 26 ... Boosting circuit. 27 ... Charging circuit.

Claims (1)

[Claims] It uses a bimorph as a shutter drive source, and has a configuration in which this bimorph is charged and deformed by a constant current charging circuit,
A shutter driving device characterized in that a capacitor is connected in parallel with the bimorph to offset a temperature coefficient difference between the bimorph and the constant current charging circuit.