JPH0462366B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention uses mechanical strain generated in an electrostrictive element by applying a voltage as a driving source to produce a shutter blade that also serves as an aperture blade, a shutter blade that is independent of the aperture blade, and a focus lens. The present invention relates to an exposure control device that drives the shutter blade of a plain shutter or the light-shielding screen of an automatic aperture of a single-lens reflex camera.

Shutter drive mechanisms have been known that use strain generated in an electrostrictive element such as a ceramic piezoelectric element as a driving force source when a voltage is applied to the electrostrictive element.
In this type of drive mechanism, in order to obtain a displacement amount of the electrostrictive element sufficient to drive the mechanical members, the electrostrictive element is configured in a bimorph structure, and one end of the electrostrictive element is supported on a cantilever. When a step voltage is applied to the electrostrictive element, the mechanical member is driven by the strain generated at its free end.

By the way, in order to displace an electrostrictive element with a bimorph structure by 1 mm at its free end, the length of the electrostrictive element must be
It needs to be between 30mm and 50mm, but if the electrostrictive element is supported on a cantilever with this length, its resonant frequency will be:
As shown in the [length-vibration characteristic curve] in Figure 1,
It becomes about several 100Hz.

This resonant frequency of several 100 Hz is approximately equal to the opening/closing time of the shutter when its period is considered, so when a step voltage is applied to the electrostrictive element, the shutter opens as shown in Figures 2 and 3. A problem arises in that accurate exposure cannot be given due to bouncing during opening and closing. Furthermore, Figures 2a and b show the aperture characteristics b when a step voltage a is applied to the lens shutter, and Figures 3a, b, and c show the aperture characteristics b when a step voltage a is applied to the focal plane shutter for front curtain running.
Also, the running characteristics c of the leading and trailing curtains are shown when a step voltage b for running the trailing curtains is applied.

The present invention has been made in view of the current situation, and aims to eliminate the effects of bounce of mechanical members caused by vibrations of the electrostrictive element caused by the influence of the resonant frequency of the electrostrictive element, and to achieve a stable exposure amount. The object of the present invention is to provide an exposure control device that can provide the following.

In summary, the exposure control device of the present invention is an exposure control device that drives a light-shielding curtain using mechanical strain produced in an electrostrictive element by application of a voltage as a driving source, and the peak level thereof is determined by the operation of the light-shielding curtain. By applying a sinusoidal voltage signal that coincides with the end point to the electrostrictive element, bounce is prevented from occurring at the end point of the operation of the light shielding curtain.

The exposure control device of the present invention controls the operation of a lens shutter that also serves as an aperture blade, the operation control of a lens shutter independent of the aperture blades, the operation control of the front curtain and the rear curtain of a focal plane shutter, and the operation control of an automatic aperture of a single-lens reflex camera. etc., and can be widely applied.
In the following, first, an embodiment in which the present invention is applied to control of a shutter blade that also serves as an aperture blade will be described.

First, the operating principle of the electrostrictive element 1 having a bimorph structure will be explained with reference to FIG. 4. The electrostrictive element 1 has a structure in which ceramic devices 1b and 1c having a piezoelectric effect are laminated on both sides of a thin metal piece 1a. By applying a reverse voltage to each of the ceramic layers 1b and 1c, the ceramic layers 1b and 1c are displaced as shown by the dashed-dotted lines, and even after the current is turned off, the applied voltage is maintained and the displaced state is maintained because the charge is retained. . Therefore, by utilizing the distortion that occurs when the voltage applied to the electrostrictive element 1 is varied, the electrostrictive element 1 can be used as a source of mechanical driving force.

FIG. 5 shows an example in which the electrostrictive element 1 is used as a source of driving force for a two-blade lens shutter.
The aperture 2a drilled in the shutter blade 3
The exposure amount is controlled by opening and closing.

To explain in detail the structure and operation of the transmission mechanism for transmitting the displacement of the electrostrictive element 1 to the shutter blade 3, first, the shutter blade 3, which has a slot 3a bored therein, is pivotally supported on a shaft 4a fixed to the substrate 2. It has a structure that allows it to swing around the shaft 4a.

On the other hand, a groove 6a for sandwiching the transmitter 7 provided at the tip of the electrostrictive element 1 is provided at the driving end of the lever 6 pivotally supported by the shaft 5, and a groove 6a is provided at the driven end of the lever 6. The protrusion 6b passes through a slot 2b formed in the shutter substrate 2 and a slot 3a formed in the shutter blade 3, and protrudes from the back surface of the shutter substrate 2.

Therefore, a voltage is applied to the electrostrictive element 1 supported in a cantilevered manner on the shutter board 2 by the support member 8, and the transmitter 7 provided at the tip of the electrostrictive element 1 is displaced from side to side in the drawing. Then, the lever 6 swings around the shaft 5, and the protrusion 6b provided at the tip of the lever 6 swings the shutter blade 3 around the shaft 4a, so that the shutter blade 3 opens and closes the aperture 2a.

Note that a shutter blade symmetrical to the shutter blade 3 is pivotally supported on the shaft 4b, but is omitted in the drawing.

In the present invention, the shutter blade 3 is driven by the displacement of the electrostrictive element 1 that occurs when a sinusoidal voltage with variable amplitude and period is applied, and by controlling the amplitude, the effective aperture is controlled.
By controlling the period, the effective exposure time is controlled.

FIG. 6 shows an example of a drive circuit that applies a voltage to the electrostrictive element 1. In the figure, reference numeral 11 indicates an oscillator, and this oscillator 11 generates a sine wave voltage at a period corresponding to the maximum shutter time and seconds. 12a is a differentiation circuit that differentiates the sine wave generated by the oscillator 11 to obtain a 90° phase advanced sine wave, and 12b is a differentiation circuit that compares the sine wave output from the differentiation circuit 12a with the ground level to determine its positive region. Each comparator outputs a reference pulse whose logic is 1 and whose negative region is logic 0, and the control shown in FIG. The circuit system works.

Further, 13a is a non-inverting amplifier, and the oscillator 11
The voltage of 1/2 of the generated sine wave is applied to the DC power supply 13b.
biased and always outputs a positive level sine wave. The output of the non-inverting amplifier 13a passes through the analog gate 14 and is used as a voltage for opening the shutter blade 3.

Further, 15a is also a non-inverting amplifier, and the oscillator 11
is generated and biased by the DC power supply 15b with a voltage of 1/2 of the sine wave inverted by the inverting circuit 15c, and a sine wave of a positive level is always output. The output of this non-inverting amplifier 15a is the analog gate 16
is used as a voltage to close the shutter blade 3.

A voltage holding circuit 17 holds the peak level of the voltage passing through the analog gate 14 when the shutter is opened using a capacitor 17a, and discharges the charge when the shutter is closed. Furthermore, 18
is a non-inverting amplifier for driving the electrostrictive element 1, and 18a is a variable resistor for adjusting the amplification factor in conjunction with the aperture value. Note that 19a and 19b indicate diodes for preventing discharge and preventing charging, respectively.

In this embodiment, the opening pulse generating circuit 20 controls the conduction of the analog gate 14 to open the shutter blade 3 at a desired timing.
6 is controlled by a closing pulse generating circuit 30 to close the shutter blade 3 at a desired timing.

First, to explain the open pulse generating circuit 20 in detail, the open pulse generating circuit 20 is composed of a one-shot circuit 21 whose time constant is adjusted to approximately one period of the reference clock, D-type flip-flops 22 and 23, and an AND gate 24. , the flip-flops 22 and 23 constitute a shift register. To describe its operation, when the shutter switch 10 is turned on, using this as a trigger, the one-shot circuit 21 sets its Q output to logic 1 for a period determined by a time constant, and the Q output is sequentially sent to flip-flops 22 and 23 in synchronization with the reference clock. communicated. And the Q of this flip-flop 22
Since the output and the output of the flip-flop 23 are the AND condition of the AND gate 24, the AND gate 24 is open during the period from when the output of the one-shot circuit 21 is transmitted to the flip-flop 22 until it is transmitted to the flip-flop 23, and the reference clock is It passes through AND gate 24 and is applied to analog gate 14 .

Next, the close pulse generation circuit 30 will be described in detail.The close pulse generation circuit 30 includes an AND gate 31 that passes the reference clock, an inverter 32 that inverts the reference clock, binary counters 33 and 34 that have a down edge trigger, and an automatic or manual clock. a switch 35 linked to the shutter speed setting mechanism;
It is composed of an inverter 36 and an AND gate 37. To explain its operation, when the shutter switch 10 is turned on, the reference clock passes through the AND gate 31, and the counters 33 and 34 are thereby incremented. The counted value of is always ahead of the counted value of the counter 33 by half a period. Then, after the count value of the counter 34 reaches the designated shutter speed, the AND gate 37 is turned on for half a cycle until the count value of the counter 33 reaches the designated shutter speed, and the AND gate 37 outputs Point V becomes logic 1. The output of this AND gate 37 is then applied to the analog gate 16 as a closing pulse.

Next, the operation of the embodiment shown in FIG. 6 will be explained with reference to the above matters and the timing chart of FIG. 7. Incidentally, the alpha-betting symbols in FIG. 7 indicate signals derived at the points indicated by the corresponding alpha-betting symbols in FIG.

First, when the power is turned on, the oscillator 11 oscillates at a period corresponding to the maximum shutter time and seconds, and a sinusoidal voltage signal is derived at its output point A. This signal is passed through the differentiating circuit 12a, the non-inverting amplifier 13a, and The signals are respectively applied to the inverting circuit 15c.

The sine wave signal applied to the differentiating circuit 12a is differentiated by the differentiating circuit 12a, and a sine wave signal obtained by leading the phase of the signal at point A by 90° is derived at the output point B of the differentiating circuit 12a, and this signal is Comparator 12
Since it is compared with the ground level at point C, a reference clock that rises at the lowest level of the output waveform of the oscillator 11 is derived at the output point C of the comparator 12b.

Also, since the sine wave signal applied to the non-inverting amplifier 13a has a level of 1/2 of the amplitude superimposed by the DC power supply 13b, the same signal as the signal at point A is sent to the output point D of the non-inverting amplifier 13a. A sine wave signal that is always at a positive level in phase is derived, and the sine wave signal applied to the inversion circuit 15c is inverted by the inversion circuit 15c, and then the amplitude is reduced to 1/2 by the DC power supply 15b.
Since the level of the signal is superimposed and applied to the non-inverting amplifier 15a, a sine wave signal which is an inversion of the signal delivered to the output point D is derived at the output point E of the non-inverting amplifier 15a. The signals at point D and point E are applied to analog gates 14 and 16, respectively.

Now, when the shutter switch 10 is turned on at time t1, the output at point F rises at the same time, and the one-shot circuit 21 operates using the rising edge as a trigger. It becomes high level within T1.

Therefore, after the shutter switch 10 is turned on,
When the first reference pulse C arrives at time t2, the output point H of the flip-flop 22 rises, and at time t3 the second reference pulse C arrives.
When , the output point I of the flip-flop 23 falls. After output point H rises,
The AND gate 24 is turned on during the time until the output point I falls, and an open pulse is derived at the output point J. The opening pulse derived at this point J is applied to the analog gate 14, and the analog gate 14 is turned on while the opening pulse J is being applied.

Therefore, at the output point K of the analog gate 14,
Of the sine wave signals added to the input point D,
The component during the time when the open pulse J is on is derived, and the signal at the output point K is applied to the voltage holding circuit 17 via the diode 19a. As a result, the capacitor 17a is charged, and the output point L of the voltage holding circuit 17 maintains its peak level until the capacitor 17a is discharged.

On the other hand, AND gate 31 is shutter switch 1
0 is turned on, and a count-up clock having the same phase as the reference clock is derived at the output point M of the AND gate 31, and the counter 33
will continue to count up based on that negative edge. Therefore, each output point N, O, P of the counter 33
Pulses as shown in FIG. 7, N, O, and P, are respectively derived.

Moreover, the output point M of the inverter 32 is connected to the output point Q of the inverter 32.
A count-up clock is derived by inverting the count-up clock derived from counter 3.
4 counts up with that negative edge. Therefore, each output point R, S, of the counter 34
Pulses as shown in R, S, and T in FIG. 7 are derived from T, respectively.

In the current example of operation, the switch 35 linked to the shutter speed setting device is connected to the output point P of the counter 33 and the output point T of the counter 34, and the pulses derived to the output point P are passed through the inverter 36 and The pulse applied to the gate 37 and led out to the output point T is applied directly to the AND gate 37.

As already mentioned, the count-up clock applied to the counter 34 is the inverted version of the count-up clock applied to the counter 33, so after the output point T of the counter 34 rises, the count-up clock is applied to the counter 34. The output point U of the inverter 36 rises after half a cycle. Therefore,
The time from when the output point T of the counter 34 rises until the output point U of the inverter 36 rises, the output point V of the AND gate 37 becomes logic 1. The signal thus derived to the output point V of the AND gate 37 is applied as a closing pulse to the analog gate 16, and the analog gate 16 is turned on while the closing pulse is applied.

Therefore, at the output point W of the analog gate 16,
Of the sine wave signals applied to the input point E,
The component during the time when the closed pulse V is on is derived. As a result, capacitor 17a becomes diode 1
9b, and the output point L of the voltage holding circuit 17 also falls from the peak level in a sinusoidal manner.

The signal thus derived to the output point L of the voltage holding circuit 17 (i.e., rises in a sinusoidal manner at the same time as the opening pulse occurs, maintains its peak level, and falls sinusoidally at the same time as the closing pulse occurs). The signal) is applied to an amplifier 18, which is connected to a variable resistor 18a whose resistance value is determined in accordance with the aperture diameter.
The signal is amplified by an amplification factor set by and applied to the electrostrictive element 1.

FIGS. 8a and 8b show the relationship between the voltage variation a applied to the electrostrictive element 1 and the aperture variation b, and the electrostrictive element 1 is displaced in response to the applied voltage. However, since the shutter blades 3 open and close in response to the displacement of the electrostrictive element 1, the shutter blades also open in a sinusoidal manner at the same time as the opening pulse occurs, maintain the peak aperture, and open in a sinusoidal manner at the same time as the closing pulse occurs. It will be closed in. Therefore, as the shutter blade approaches the opening peak point and as the shutter blade approaches the closing point, the displacement speed of the electrostrictive element and the moving speed of the shutter blade gradually decrease, causing resonance. The impact of bounce can be minimized.

At this time, the peak aperture is varied by varying the amplification factor of the variable resistor 18a by operating the aperture ring, and the effective exposure time is varied by switching the switch 35 by operating the shutter dial. At this time, if the amplification factor of the variable resistor 18a is set by operating the aperture ring and the switching of the switch 35 is made to follow the field brightness, automatic exposure control with aperture priority becomes possible; By switching the shutter speed by operating the shutter dial and making the resistance value of the variable resistor 18a follow the brightness of the field, automatic exposure control that prioritizes the shutter speed becomes possible. Furthermore, if the resistance value of the variable resistor 18a and the switching of the switch 35 are made to correspond to combinations prepared in advance in accordance with the brightness of the field, exposure control by so-called program auto becomes possible.

Note that the counters 33 and 34 are reset by a circuit system (not shown) after the shutter is closed, and the entire system is initialized.

The embodiment shown in FIG. 6 above is an example in which the present invention is applied to a shutter blade that also serves as an aperture blade.
For cameras with independent aperture blades,
The variable resistor 18a becomes unnecessary. Further, the embodiment shown in FIG. 6 can be directly applied to a so-called automatic aperture of a single-lens reflex camera.

In the above example, when the shutter blade 3 is opened and closed, a sinusoidal voltage is applied to the electrostrictive element 1 for half a period (i.e., from the lowest level to the highest level when the shutter blade 3 is opened, and from the highest level to the lowest level when closed). I have shown an example of applying voltage, but when it is open, a sine wave voltage for 1/4 period from the center level to the highest level is applied, and when it is closed, a sine wave voltage for 1/4 period from the highest level to the center level is applied. You may give. In addition, in FIG. 9a and b, 1/
The aperture characteristic b is shown when a voltage a for four cycles is applied.

Next, an example in which the present invention is applied to a focal plane shutter will be shown.

As is well known, focal plane shutters have a screen frame close to the emulsion side of the film, and when the shutter is released, the leading curtain first opens the screen frame, responding to the set shutter speed. The rear curtain closes the screen frame after a delay time, and the effective exposure amount is controlled by the width of the slit formed between the front curtain and the rear curtain corresponding to the delay time.

Therefore, when driving a focal plane shutter using the displacement that occurs in an electrostrictive element when a voltage is applied, two series of electrostrictive elements that operate independently are provided, and the two series of electrostrictive elements are A link mechanism for transmitting the displacement of the element to the front curtain and the rear curtain, respectively, is interposed between the two series of electrostrictive elements and the front curtain and the rear curtain, and the voltage applied to the two series of electrostrictive elements is controlled. do it.

FIG. 10 shows an example of a circuit for applying an applied voltage to an electrostrictive element that drives a focal plane shutter. In the figure, 40a indicates an electrostrictive element for driving the leading curtain, and 40b indicates an electrostrictive element for driving the trailing curtain. Further, 41 indicates an oscillator that generates a sinusoidal voltage signal with a period corresponding to the curtain speed, and 42 indicates a delay circuit that delays the sine wave signal generated by the oscillator 41 in accordance with shutter hours and seconds. In this embodiment, the electrostrictive element 40a is displaced by the sine wave generated by the oscillator 41 to cause the front curtain to run, and the electrostrictive element 40a is caused to move by the sine wave output from the delay circuit 42 after a delay time corresponding to the shutter hours and seconds. The rear curtain is caused to run by displacing the element 40b. Since the circuit system for displacing the electrostrictive element 40b and the circuit system for displacing the electrostrictive element 40b have the same configuration with one exception, the electrostrictive element 40
A circuit system for displacing a will be explained as a representative.

Reference numeral 43a designates an analog gate, 44a a capacitor, 45a a non-inverting amplifier, and 46a a shutter reset switch interlocked with the film winding mechanism. The capacitor 44a and the non-inverting amplifier 45a constitute a voltage holding circuit.

A differentiation circuit 47a detects the conduction of the analog gate 43a, comparators 48a and 49a with the ground level as the threshold level, a shutter switch 50, a one-shot circuit 51 which is triggered by the ON of the shutter switch 50, and an SR type circuit which memorizes the ON state of the shutter switch 50. A flip-flop 52, a D-type flip-flop 53a that synchronizes the turning on of the shutter switch 50a with the reference period of the oscillator 41, and an AND gate 5.
4a. The only difference between the circuit system for displacing the electrostrictive element 40a and the circuit system for displacing the electrostrictive element 40b is that the electrostrictive element 4
The circuit system for displacing 0b is AND gate 5
5, and this AND gate 55
At what timing does the shutter switch 51 turn off?
This is to ensure that the front curtain always runs first even if it is turned on. Further, 56a indicates a non-inverting amplifier.

In FIG. 10, the shutter switch 50, one-shot circuit 51, and flip-flop 52 are provided in both the circuit system for displacing the electrostrictive element 40a and the circuit system for displacing the electrostrictive element 40b. Can be used commonly in circuit systems.

Next, the operation shown in FIG. 10 will be explained with reference to the above matters and the timing chart shown in FIG. 11. Incidentally, the alpha-betting symbols in FIG. 11 indicate the signals derived at the points indicated by the corresponding alpha-betting symbols in FIG. 10.

When the power is turned on, the oscillator 41 starts oscillating and derives a sinusoidal voltage signal at its output point A, and this signal at the point A is applied to the differentiating circuit 47a, the comparator 49a, and the delay circuit 42.

First, the differentiating circuit 47a differentiates the applied sine wave signal and outputs a 90° phase advanced sine wave signal to the output point B, and the comparator 48a compares this with the Gundo level, so that the output point C is A pulse signal is derived in which the positive region of point B is logic 1 and the negative region of point B is logic 0. Further, since the comparator 49a compares the output of the oscillator 41 with the ground level, a pulse signal is derived at the output point D, in which the positive region of the point A is logic 1 and the negative region of the point A is logic 0.

On the other hand, the delay circuit 42 is linked to an automatic or manual shutter speed setting mechanism, and outputs a sine wave signal obtained by delaying the sine wave signal derived from point A by a delay time Ts corresponding to the set shutter time and seconds. The signal at point E is derived to point E, and the signal at point E is applied to differentiating circuit 47b and comparator 49b.

And a differentiating circuit 47b and a comparator 48
b, 49b are the differentiation circuit 47a and the comparator 4
Since they are configured the same as 8a and 49a,
Pulses derived from the output points C and D of the comparators 48a and 49a are delayed by the delay time Ts, respectively, to the output points F and G of the comparators 48b and 49b.

Now, when the shutter switch 50 is turned on at time t1, the one-shot circuit 51 outputs a pulse to its output point H, and the flip-flop 52 is set by this pulse to memorize that the shutter switch 50 is turned on. Therefore, the level at input point I of flip-flop 53a rises to logic 1.

Thereafter, at time t2, when the output of the comparator 48a rises, the flip-flop 53
a stores the output of the flip-flop 52, derives a logic 1 to its output point J, and outputs the AND gate 54a.
And the AND gate 55 is made conductive. Therefore, during the time period from when the output of the comparator 49a rises at time t3 to when the output of the comparator 48a falls at time t4, the level of the output point K of the AND gate 54a becomes logic 1, and the output of the AND gate 54a is added to the analog gate 43a as a leading curtain running pulse, and during this time the analog gate 4
3a is conductive.

Therefore, the sine wave signal applied to the input point A of the analog gate 43a passes through the analog gate 43a and charges the capacitor 44a, and the capacitor 44a maintains its peak level until it is discharged, so that the signal is not inverted. The output point L of the amplifier 45a rises like a sine wave and maintains its peak level. The signal thus derived to the output point L of the non-inverting amplifier 45a is amplified by the amplifier 56a and applied to the electrostrictive element 40a for leading curtain running, and the electrostrictive element 40a responds to level fluctuations of the applied signal. and is displaced.

Incidentally, the flip-flop 52a is reset by the front curtain running pulse K, and the flip-flop 52a is initialized.

On the other hand, at time t2, the flip-flop 53
As the output point J of a rises, the output point M of the AND gate 55 becomes logic 1, and when the output of the comparator 48b rises at time t5, the output point N of the flip-flop 53b becomes logic 1. A logic 1 is derived, allowing AND gate 54b to conduct. Therefore, the time from when the output of the comparator 49b rises at time t6 until the output of the comparator 48b falls at time t7,
The level of output point 0 of the AND gate 54b is logic 1
The output of the AND gate 54b is applied to the analog gate 43b as a trailing curtain running pulse, and during this period the analog gate 43b is conductive.

Therefore, the sine wave signal applied to the input point E of the analog gate 43b passes through the analog gate 43b and charges the capacitor 44b, and the capacitor 44b maintains its peak level until it is discharged, so that the signal is not inverted. The output point P of the amplifier 45b rises like a sine wave and maintains its peak level. The signal thus derived to the output point P of the non-inverting amplifier 45b is amplified by the amplifier 56a and applied to the electrostrictive element 40b for trailing curtain running, and the electrostrictive element 40b responds to level fluctuations of the applied signal. Displaced.

Thereafter, when the shutter reset switches 46b and 46a are sequentially turned on in conjunction with the film winding mechanism, the electric charges held in the capacitors 44b and 44a are removed from the shutter reset switches 46b and 46a.
Since the capacitance stored in the electrostrictive elements 40b and 40a is also lost, the electrostrictive element 40
b, 40a return to the initial state. Incidentally, the reason why the capacitor 44b is discharged first at this time is to prevent it from being exposed to light during the shutter reset.

Figure 12 a, b, and c are electrostrictive elements 40a and 40b.
This shows the relationship between the fluctuation of the applied voltage to ) gradually decreases, and when the shutter curtain travels to the vicinity of the screen frame, which is the end point of its operation, its speed becomes almost 0, and stable running characteristics are obtained without the effects of bounce or the like.

Next, FIG. 13 shows a modification of the example in FIG. 10, and redundant explanation will be avoided regarding elements that overlap with the example in FIG. 10. In the example in FIG. The output of the amplifier 45a is delayed by a delay circuit 57 and applied to the electrostrictive element 40b for running the trailing curtain. According to the example shown in FIG. 13, since the delay time by the delay circuit 57 can be set regardless of the period of the oscillator 41, it is possible to cope with so-called long-time exposure.

In the focal plane shutter control described above, an example has been shown in which the leading and trailing curtains return to their initial positions by shutter reset associated with film winding, and the leading and trailing curtains sequentially travel by shutter release. When the front and rear curtains run due to the shutter release, the front and rear curtains are kept in the same position as they are, and when the shutter is released next, the rear and rear curtains are run in the opposite direction in that order. Alternatively, the next film surface may be exposed.

As explained above, according to the present invention, a sinusoidal voltage signal whose peak level coincides with the operation end point of a light-shielding screen such as a shutter blade, shutter curtain, or aperture blade is applied to the electrostrictive element. Therefore, as the light-shielding curtain approaches its operation end point, the displacement speed of the electrostrictive element and the moving speed of the light-shielding curtain gradually decrease, and the effect of the electrostrictive element's own bounce due to resonance of the electrostrictive element. It is possible to eliminate the effects of bounce of mechanical parts and mechanism members, enabling more accurate exposure control and reducing troubles such as camera shake.

[Brief explanation of drawings]

Figure 1 is a characteristic diagram showing the relationship between the length of the electrostrictive element and its resonant frequency, Figure 2 is a characteristic diagram showing the aperture characteristics when a step voltage is applied to the electrostrictive element that drives the lens shutter, and Figure 3 is a characteristic diagram showing the aperture characteristics when a step voltage is applied to the electrostrictive element that drives the lens shutter. A characteristic diagram showing the running characteristics when a step voltage is applied to the electrostrictive element that drives the focal plane shutter. Fig. 4 is a diagram of the operating principle of the electrostrictive element. Fig. 5 shows the driving of the lens shutter with the electrostrictive element. FIG. 6 is a digital circuit diagram of one embodiment in which the present invention is applied to control a lens shutter, FIG. 9 is an aperture characteristic diagram when a lens shutter is driven using a modified example of the circuit in FIG. 6, and FIG. 10 is an aperture characteristic diagram when the present invention is applied to focal plane shutter control. A digital circuit diagram of the embodiment, FIG. 11 is a timing diagram of the circuit of FIG. 10,
12 is a running characteristic diagram when a focal plane shutter is driven by the circuit shown in FIG. 10, and FIG. 13 is a digital circuit diagram showing a modification of the circuit shown in FIG. 10. 1... Electrostrictive element, 11... Oscillator, 14, 16
... Analog gate, 20 ... Open pulse generation circuit, 30 ... Closed pulse generation circuit, 40a, 40b
... Electrostrictive element, 41 ... Oscillator, 42 ... Delay circuit, 43a, 43b ... Analog gate.

Claims (1)

[Scope of Claims] 1. An exposure control device that drives a light-shielding curtain using mechanical strain produced in an electrostrictive element by voltage application as a drive source, comprising: a sine wave generation circuit that generates a sine wave-like voltage signal; a first voltage signal to which the sinusoidal voltage signal or a voltage signal having the same frequency as the sinusoidal voltage signal is supplied;
and a second analog gate, which is shorter than 1/2 cycle of the sinusoidal voltage signal supplied to the first analog gate after the shutter button is turned on, and one peak of the sinusoidal voltage signal. an opening pulse generation circuit that opens the first analog gate for a period ending at a level of 0.05; and after the opening pulse generation circuit activates the first analog gate, the second analog gate a closed pulse generation circuit that opens the second analog gate for a period that is shorter than 1/2 period of the sinusoidal voltage signal supplied to the voltage signal and that ends at the other peak level of the sinusoidal voltage signal; a voltage holding circuit that is charged by the output of the first analog gate and discharged by the output of the second analog gate; and an amplifier circuit that amplifies the holding voltage of the voltage holding circuit and applies it to the electrostrictive element. An exposure control device comprising: 2. The exposure control device according to claim 1, wherein the amplification factor of the amplifier circuit is variable.