JPH0530255B2 - - 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 shutter blades that also serve as aperture blades, shutter blades that are independent of the aperture blades, and shutter blades that are independent of the aperture blades. The present invention relates to a shutter drive device for driving shutter blades, etc. of a Calplane shutter.

Shutter 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, and this type of electrostrictive element drives mechanical members. In order to obtain a sufficient amount of displacement, the electrostrictive element has a bimorph structure.

First, the operating principle of the electrostrictive element 1 having a bimorph structure will be explained with reference to FIG. 1. The electrostrictive element 1 has a structure in which ceramic layers 1b and 1c having a piezoelectric effect are laminated on both sides of a thin metal piece 1a. By applying a voltage to the ceramic layers 1b and 1c, the ceramic layers 1b and 1c are displaced as shown by the dashed line, and even after the current is turned off, the applied voltage is maintained because the charge is retained, and the displaced state is also maintained. 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.

A general formula for obtaining the displacement amount S at the free end of the electrostrictive element having the seed structure is shown in (Formula-1).

S=31 ² Vd/4t ² (Formula-1) However, l: Length of the electrostrictive element V: Applied voltage d: Piezoelectric constant t: Thickness of the electrostrictive element As is clear from the above (Formula-1) In order to increase the amount of displacement S generated at the free end of the electrostrictive element 1, it is required to increase the length l of the electrostrictive element 1 or to increase the applied voltage V.

Therefore, first considering the case where the length l of the electrostrictive element 1 is increased, the following problems arise.

(1) The overall structural dimensions become larger, making it difficult to fit inside the camera.

(2) Since the moment of inertia increases in proportion to the square of the length l, the operating speed decreases.

(3) In order to perform high-speed operation, it is necessary to increase the force P, but to do so, the width b of the electrostrictive element 1 must be increased.
needs to be increased, but doing so will further increase the moment of inertia.

(4) Since the natural frequency of the cantilever-supported piezoelectric element 1 is inversely proportional to the square of its length l, its period approaches the operating time of the shutter mechanism (several hundredths of a second), which is harmful to photography. Bounce occurs due to resonance.

In addition, the general formula for obtaining the force P is (formula-2),
Also, the general formula for obtaining the natural frequency f ₀ is (formula −
3).

P=3btVdE/2l (Formula-2) However, E: Young's modulus Furthermore, when the applied voltage V is increased, the following problem occurs.

(1) Since the amount of displacement per unit length of the electrostrictive element 1 increases, internal stress also increases, which may lead to destruction of the element.

(2) It is necessary to increase the breakdown voltage of the semiconductor used in the control system, making it unsuitable for IC implementation.

The present invention has been made to solve these problems, and provides a shutter that can obtain a sufficient amount of displacement without increasing the length of the electrostrictive element 1 or increasing the applied voltage V. The purpose is to provide a control device.

In summary, the shutter control device of the present invention applies to the electrostrictive element 1 a voltage waveform that is at least approximate to a sine wave and that continuously changes from one peak level to the other peak level. By driving this with the electrostrictive element 1, the effective displacement amount can be doubled while keeping the absolute value of the applied voltage and the effective length of the electrostrictive element 1 constant.
It is designed to stabilize the operating characteristics of the mechanical members from the start of travel to the end of travel.

The shutter control device of the present invention can be widely applied, such as controlling the operation of a lens shutter that also serves as an aperture blade, controlling the operation of a lens shutter independent of the aperture blades, and controlling the operation of the leading and trailing curtains of a focal plane shutter. 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.

FIG. 2 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 an axis 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.

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

In the illustrated state, the electrostrictive element 1 is at 0 potential,
The shutter blade 3 slightly opens the aperture 2a. Then, when the power is turned on, a negative voltage is applied to the electrostrictive element 1, and the transmitter 7 provided at the tip of the electrostrictive element 1 is swung to the left.
Rotate clockwise within the slot 2b around the center to close the aperture 2a. When the shutter button is pressed in this state, the electrostrictive element 1
The applied voltage increases, the electrostrictive element 1 is displaced to the right, and the shutter blade 3 rotates counterclockwise about the shaft 4a to open the aperture 2a.

In the present invention, the displacement of the electrostrictive element 1 in both positive and negative directions is used to drive the light-shielding curtain, so that the amount of displacement of the electrostrictive element 1 in one direction is only half that of the conventional device.

FIG. 3 shows an embodiment of a circuit for applying a voltage to the electrostrictive element 1. In FIG.

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.

The sine wave signal generated by the oscillator 11 is applied to the electrostrictive element 1 via the analog gate 13 to open the shutter blade 3, and the sine wave signal generated by the oscillator 11 is applied to the inverting circuit. Analog gate 15 after being inverted at 14
is applied to the electrostrictive element 1 via the shutter blade 3 to close the shutter blade 3.

In this embodiment, the timing of conduction of the analog gate 13 is controlled by the open pulse generation circuit 20 to open the shutter blade 3 at a desired timing, and the timing of conduction of the analog gate 15 is controlled by the close pulse generation circuit 30 to open the shutter blade 3 at a desired timing. The blades 3 are closed 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 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 as a time constant.
The Q output is sequentially transmitted to flip-flops 22 and 23 in synchronization with the reference clock. And the Q output of flip-flop 22 and flip-flop 2
Since the output of AND gate 24 is the AND condition of AND gate 24, the output of AND gate 2 becomes
4 is open and the reference clock passes through AND gate 24 and is applied to analog gate 13.

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 function, the shutter switch 10
When the reference clock is turned on, the reference clock passes through the AND gate 31, and the counters 33 and 34 are thereby incremented. However, since the reference clock is inverted and added to the counter 34, the count value of the counter 34 is the same as the count value of the counter 33. It will always be half a period ahead of the numerical value. 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 S becomes logic 1. The output of this AND gate 37 is then applied to the analog gate 15 as a closing pulse.

Further, 16 indicates a bias power supply that superimposes a voltage corresponding to the negative peak level of the sine wave signal generated by the oscillator 11, and 17 indicates a switch that transmits the level of this bias power supply 16.

Further, 18 is a voltage holding circuit, which holds the peak level of the voltage passing through the analog gate 13 when the shutter is opened by a capacitor 18a.
The charge is discharged when the shutter is closed. Furthermore, 1
9 is a non-inverting amplifier for driving the electrostrictive element 1, and 19a is a variable resistor for adjusting the amplification factor in conjunction with the aperture value.

Next, the operation of the embodiment shown in FIG. 3 will be explained with reference to the above matters and the timing chart of FIG. 4. Incidentally, the alpha-betting symbols in FIG. 4 indicate the signals derived at the points indicated by the corresponding alpha-betting symbols in FIG. 3.

First, when the power is turned on at time t1, the oscillator 11
oscillates at a period corresponding to the maximum shutter hour and second, and a sinusoidal voltage signal is derived at its output point A.
This signal is transmitted to the differentiating circuit 12a and the analog gate 1.
3 and is inverted by an inverting circuit 14 and applied to an analog gate 15.

Therefore, the level at the input point B of the analog gate 15 is an inversion of the sine wave generated by the oscillator 11.

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

Further, at the same time as this power is turned on, the switch 17 is turned on for a short period of time, and the capacitor 18a is charged to a potential whose level corresponds to the negative peak level of the sine wave generated by the oscillator 11. This is amplified by the amplifier circuit 19. is applied to the electrostrictive element 1. Therefore, the electrostrictive element 1 is displaced to the left in FIG. 2, and the shutter blade 3 closes the aperture 2a.

Now, when the switch 10 is turned on in conjunction with the shutter release at time t2, the output at point E rises at the same time, and the one-shot circuit 21 operates using the rising edge as a trigger. It becomes high level within the time T1 determined by the time constant.

Therefore, after the switch 10 is turned on, when the first reference pulse D arrives at time t3, the output point H of the flip-flop 22 rises, and the time
When the second reference pulse D arrives at t4, the output point H of the flip-flop 23 falls.
Then, the AND gate 24 is turned on during the time period after the output point G rises until the output point H falls, and an open pulse is derived from the output point I. Then, the opening pulse derived from this point I is applied to the analog gate 13.
is on while the open pulse I is being applied.

Therefore, at the output point T of the analog gate 13,
Of the sine wave signals added to the input point A,
A component during the time when the open pulse I is on is derived, and this signal is applied to the voltage holding circuit 18, which discharges the negative charge held in the capacitor 18a and charges the capacitor 18a with a positive charge. .

As a result, the output point V of the voltage holding circuit 18 rises while drawing a curve from the negative peak point of the sine wave to the positive peak point, and thereafter maintains the peak level until the capacitor 18a is discharged.

On the other hand, the AND gate 31 is opened at the same time as the switch 10 is turned on, and a count-up clock having the same phase as the reference clock is derived from the output point J of the AND gate 31, and the counter 33 counts up with its negative edge. I will do it. Therefore, pulses such as those shown in FIG. 7 are derived at the output points K, L, and M of the counter 33, respectively.

Further, a count-up clock which is an inversion of the count-up clock derived from the output point J is derived from the output point N of the inverter 32, and the counter 34
will continue to count up based on that negative edge. Therefore, each output point O, P, Q of the count 34
Pulses as shown in O, P, and Q in FIG. 7 are derived, respectively.

In the current example of operation, the switch 35 interlocked with the shutter speed setting mechanism is connected to the output point M of the counter 33 and the output point Q of the counter 34, and the pulses derived to the output point M are passed through the inverter 36 and The pulse applied to the gate 37 and derived to the output point Q 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 Q of the counter 34 rises, the count-up clock is applied to the counter 34. The output point R of the inverter 36 falls after a half period. Therefore,
The time from when the output point Q of the counter 34 rises until the output point R of the inverter 36 falls, the output point S of the AND gate 37 becomes logic 1. The signal thus derived to the output point S of the AND gate 37 is applied as a closing pulse to the analog gate 15, and the analog gate 15 is turned on while the closing pulse is applied.

Therefore, at the output point U of the analog gate 15,
Of the sine wave signals added to the input point B,
The component during the time when the closed pulse S is on is derived. As a result, the positive charge stored in the capacitor 18a is discharged and the capacitor 18
A is charged with a negative charge, and the output point V of the voltage holding circuit 18 also falls from the positive peak level of the sine wave to the negative peak level.

In this way, the signal derived to the output point V of the voltage holding circuit 18 (i.e., rises from the negative peak level of the sine wave to the positive peak level at the same time as the occurrence of the open pulse, and maintains the positive peak level as it is). , a signal that falls from the positive peak level of the sine wave to the negative peak level at the same time as the closing pulse is generated) is applied to the amplifier 19, and is applied to the amplifier 19 by a variable resistor 19a whose resistance value is determined in accordance with the aperture diameter. The signal is amplified at a set amplification factor and applied to the electrostrictive element 1.

At this time, the peak aperture is varied by varying the amplification factor of the variable resistor 19a 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 19a is set by operating the aperture ring and the switching of the switch 35 is made to follow the brightness of the field, 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 19a 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 19a 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. 3 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 19a becomes unnecessary. Further, the embodiment shown in FIG. 3 can be directly applied to a so-called automatic aperture of a single-lens reflex camera.

In the above embodiment, in the case of a so-called electronic still camera in which a solid-state image sensor is arranged at the focal plane, the shutter release can be synchronized with the vertical synchronization pulse of the solid-state image sensor. When used in a normal camera arranged in be.

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 provided close to the emulsion surface of the film, and after the shutter release, the first curtain opens the screen frame, and the delay time corresponding to the set shutter speed is set. After that, the second curtain closes the above screen frame,
The effective exposure amount is controlled by the width of the slit formed between the leading curtain and the trailing curtain in accordance with 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 The mechanism for transmitting the displacement of the element to the leading curtain and the trailing curtain is described in 2 above.
The electrostrictive element may be interposed between the series of electrostrictive elements and the front curtain and the rear curtain, and the voltage applied to the two series of electrostrictive elements may be controlled.

FIG. 5 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 40a and the circuit system for displacing the electrostrictive element 40b have the same configuration, the circuit system for displacing the electrostrictive element 40a will be described as a representative.

43a is an analog gate, 44a is a capacitor, 45a is a non-inverting amplifier, 46a is a switch linked to the shutter release, 47a is a power source for charging the capacitor 44a with a negative charge before photographing, and 48a is an amplifier. show.

A differentiation circuit 49a determines the conduction of the analog gate 43a, a comparator 50a with the ground level as a threshold level, a switch 51a linked to the shutter release, and an AND gate 52.
It is controlled by a.

Next, the operation shown in FIG. 5 will be explained with reference to the above items and the timing chart shown in FIG. Incidentally, the alpha-betting symbols in FIG. 6 indicate the signals derived at the points indicated by the corresponding alpha-betting symbols in FIG.

First, the oscillator 41 starts oscillating by the shutter release, and the switches 46a and 46b
is turned on for a short period of time, capacitors 44a, b are charged with negative charge, and the output level of non-inverting amplifiers 45a, b is lowered to the negative peak level of the sine wave signal generated by oscillator 41. Therefore, a negative voltage is applied to the electrostrictive elements 40a and 40b, and the shutter curtain waits at the origin.

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

First, the differentiating circuit 49a differentiates the applied sine wave signal and derives a 90° phase-advanced sine wave signal to the output point B, and the comparator 50a compares this with the Gundo level, so that the sine wave signal is outputted to the output point C. 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.

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 D is applied to the differentiating circuit 49b.

And a differentiating circuit 49b and a comparator 50b
has the same configuration as the differentiating circuit 49a and the comparator 50a, so the comparator 50b
A pulse is derived from the output point E of the comparator 50a, which is delayed by a time Ts from the pulse derived from the output point C of the comparator 50a.

Time when a predetermined period of time has elapsed after the shutter release
At t1, the switches 51a and 51b are turned on, and the levels of their output points F and G remain at logic 1 for a predetermined time.
become. During this time, the pulse generated by the comparator 50a passes through the AND gate 52a and is applied to the analog gate 43a as a leading curtain running pulse H.
Further, the pulse generated by the comparator 50b passes through the AND gate 52b and is applied as the trailing curtain running pulse I to the analog gate 43b.

Due to the generation of the front curtain running pulse H, the output point of the analog gate 43a receives the front curtain running pulse H of the sine wave signal applied to the input point A.
The component during the time when is on is derived, and this signal charges the capacitor 44a with positive charge while discharging the negative charge held in the capacitor 44a.

As a result, the output point J of the non-inverting amplifier 45a rises while drawing a curve from the negative peak point of the sine wave to the positive peak point, and thereafter maintains its peak level until the capacitor 44a is discharged.

This signal is then amplified by the amplifier 48a and applied to the electrostrictive element 40a, causing the leading curtain to run.

In this way, after the predetermined delay time Ts has elapsed after the leading curtain has traveled, the trailing curtain traveling pulse I is generated, so that the output point of the analog gate 43b is
Of the sine wave signals added to the input point D,
A component during the time when the trailing curtain running pulse I is on is derived, and this signal is transmitted to the capacitor 44b while discharging the negative charge held in the capacitor 44b.
to charge a positive charge.

As a result, the output point K of the non-inverting amplifier 45b rises while drawing a curve from the negative peak point of the sine wave to the positive peak point, and thereafter maintains its peak level until the capacitor 44b is discharged.

This signal is then amplified by the amplifier 48b and applied to the electrostrictive element 40b, causing the trailing curtain to run.

Thereafter, the capacitors 44b and 44a are sequentially discharged in conjunction with the shutter charge during film winding, and the trailing and leading curtains return to their initial positions.

As explained above, according to the present invention, the electrostrictive element is displaced in the negative direction and then in the positive direction, so if the total displacement position is constant, the amount of displacement on one side can be halved. , Therefore, it becomes possible to reduce the length of the electrostrictive element to about 70.7%. (Formula-
1) Therefore, the width of the electrostrictive element required to obtain the same force is approximately 70.7%, so its area is approximately 50%.
%. (Refer to Equation-2) Furthermore, due to such miniaturization, the moment of inertia is also reduced to about 35% or less, enabling higher-speed operation. Also, due to this miniaturization, the capacitance also decreases.
Since it is less than 50%, charging and discharging can also be accelerated.

Furthermore, when the length of the electrostrictive element becomes 70.7%, its resonance frequency doubles (see formula-3), so the bounce of the mechanical member due to resonance is also reduced.

In addition, since the applied voltage required to obtain the same force is lower, it is easier to implement an IC, and the control system can also be made smaller.

Further, in the present invention, the voltage applied to the electrostrictive element is controlled by a voltage waveform that is at least approximate to a sine wave and continuously changes from one peak level to the other peak level, so that the speed of the mechanical member is gradually increased. Since the speed of the mechanical member is increased to zero and then gradually decreased, the speed of the mechanical member becomes zero at the start and end of the movement, effectively preventing the mechanical member from bouncing, and providing stable operating characteristics.

Moreover, although the above example shows that a positive voltage is applied after applying a negative voltage to the electrostrictive element, it goes without saying that a negative voltage may be applied after applying a positive voltage.

[Brief explanation of the drawing]

Fig. 1 is a diagram of the operating principle of an electrostrictive element, Fig. 2 is a mechanism diagram for driving a shutter with an electrostrictive element, Fig. 3 is a circuit diagram of an embodiment of the present invention, and Fig. 4 is a diagram of the mechanism shown in Fig. 3. FIG. 5 is a circuit diagram of another embodiment of the present invention, and FIG. 6 is a timing diagram of FIG. 1... Electrostrictive element, 11... Oscillator, 16... Bias power supply, 40a, b... Electrostrictive element, 47a, b... Bias power supply.

Claims (1)

[Scope of Claims] 1. A camera shutter comprising an electrostrictive element that distorts in response to an applied voltage, and a shutter blade that opens and closes a photographing optical path by transmitting the distortion generated in the electrostrictive element, comprising: The shutter blade is provided with a sine wave generating means for generating at least approximately a sine wave voltage having a voltage range corresponding to the operating range from the initial position to the forward limit of the shutter blade, the sine wave generating means generating The voltage applied to the electrostrictive element is controlled by a voltage that continuously changes from one peak level corresponding to the initial position of the shutter blade to the other peak level corresponding to the forward limit of the shutter blade. shutter control device.