JPH0448206B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an exposure control device that drives a shutter blade using mechanical strain generated in an electrostrictive element by applying a voltage as a driving source.

Conventionally, exposure control devices have been known in which an electrostrictive element such as a piezoelectric ceramic element is configured in a bimorph structure, and the mechanical strain generated when a voltage is applied to this element is used as a driving source to drive a shutter blade that also serves as an aperture. As exposure control using this type of exposure control device, there are two known methods: (1) applying a pulsed voltage to the piezoelectric ceramic element, and (2) applying the voltage as a sawtooth wave. FIG. 2 shows the voltage applied as a pulse, and FIG. 2 shows the voltage applied as a sawtooth wave.

The amount of strain in an electrostrictive element is theoretically linear with the applied voltage, but in reality, in the example shown in Figure 1, the bounce due to resonance of the electrostrictive element itself is large when it reaches a predetermined diameter. In addition, in the example shown in Figure 2, the direction of movement of the aperture member changes rapidly after reaching a predetermined diameter, causing bounce and overshoot due to collisions within the mechanism for driving the aperture member, and the applied voltage rises. There is a problem in that the time it takes for the aperture member to actually close after it has been lowered is difficult to predict due to variations in various conditions, making it difficult to perform accurate exposure control.

The present invention was made in view of the current situation, and its purpose is to eliminate as much as possible the effects of bounce and overshoot caused by resonance of the electrostrictive element itself and collisions of the driving force transmission mechanism, and to improve accuracy. The purpose of the present invention is to provide an exposure control device that can perform high exposure control.

In summary, the exposure control device of the present invention applies a sinusoidal voltage with a variable period and amplitude to an electrostrictive element that is a source of mechanical driving force, thereby suppressing sudden fluctuations in the motion of mechanical members. In addition to avoiding the effects of bounce and overshoot as much as possible,
By freely controlling the period and amplitude of the applied voltage, the amount of exposure to the photosensitive material can be controlled.To achieve the above purpose, the output of a sine wave oscillator whose frequency varies in accordance with the shutter speed is used. is applied to the electrostrictive element through an amplifier and an analog gate whose amplification degree varies in accordance with the aperture value, and the above voltage is applied to the electrostrictive element for one cycle from the lowest level of the sine wave voltage that first arrives after the shutter button is turned on. The analog gate is turned on.

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings.

First, the operating principle of the electrostrictive element 1 having a bimorph structure will be explained with reference to FIG. 3. 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 reverse voltage to each of the ceramic layers 1b and 1c, the ceramic layers 1b and 1c are displaced as shown by the dashed 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. 4 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 function 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 is provided on the drive shaft of the lever 6, which is pivotally supported on the shaft 5, for sandwiching the transmitter 7 provided at the tip of the electrostrictive element 1, and a groove 6a is provided on 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. 5 shows an example of a drive circuit that applies a voltage to the electrostrictive element 1. In the figure, numeral 11 is a variable resistor, which is linked to the shutter speed. 12 is variable resistor 11
The oscillator 1 shows a sine wave oscillator whose oscillation frequency varies depending on the input voltage determined by the resistance value of the oscillator 1.
The effective exposure time is determined by the frequency of 2.

Further, 13 is a non-inverting amplifier, which is biased by a DC power supply 14 with a voltage of 1/2 of the sine wave generated by the oscillator 12, and always outputs a sine wave at a positive level. Further, 15 is an analog gate, and this analog gate 15 opens for one cycle of the sine wave after the shutter button is turned on. Furthermore, 16 is a non-inverting amplifier for driving the electrostrictive element 1, and 16a
is a variable resistor for adjusting the amplification factor in conjunction with the aperture value.

In this embodiment, opening and closing of the analog gate 15 is controlled by a timing control circuit system 20, so that a sinusoidal voltage is applied to the electrostrictive element 1 for one period.

Regarding the timing control circuit system 20, 21a and 21b are differential circuits, 22a and 2 are differentiating circuits, and 22a and 2 are differentiating circuits.
2b indicates a comparator with the ground level as a threshold level, and the phase of the sinusoidal signal generated by the oscillator 12 is determined by differentiating circuits 21a and 2.
After shifting each by 90° in 1b, the differentiating circuit 21a.
The output of 21b is compared with the ground level by comparators 22a and 22b to obtain a pulse whose positive part becomes logic 1, and both comparators 22a and 22b
The pulse outputted by is applied to the AND gate 23. Therefore, by calculating the logical product using the AND gate 23, it is possible to obtain a reference pulse that rises when the sine wave generated by the oscillator 12 is at its lowest level. Therefore, in this embodiment, the reference pulse obtained from this AND gate 23 is used to control the analog gate 1.
A flip-flop 24 for opening and closing 5 is operated.

Note that 25 and 26 indicate an inverter and an AND gate for detecting that the shutter switch 27 is turned on when the reference pulse is a logic 0, and 28 indicates a flip-flop that memorizes that the shutter switch 27 is turned on. Also, 29a is the down edge trigger 4
It is a forward counter, and when two reference pulses are received, its Q2 output is inverted by the inverter 29b and the AND gate 29c is closed.

Next, referring to the above matters and other drawings,
Let us explain the operation of this embodiment.

First, when the power is turned on, the oscillator 12 starts oscillating at the frequency specified by the variable resistor 11 for specifying the shutter speed, and the output point A of the oscillator 12 has a sinusoidal waveform as shown in FIG. 6A. A signal is derived and applied to the differentiating circuit 21a and the non-inverting input terminal of the non-inverting amplifier 13. Since the level of 1/2 of the amplitude of the signal derived from the output point A is superimposed on this non-inverting input terminal by the power supply 14, the output point B of the non-inverting amplifier 13 is
As shown in FIG. 2, a sinusoidal signal with a constant positive level is derived, and this signal is applied to the analog gate 15.

On the other hand, the flip-flop 2
4.28 and the counter 29 have been reset by a circuit system not shown, and the analog gate 15 is closed.

Further, the differentiating circuit 21a differentiates the sinusoidal signal derived from the point A and calculates the phase as shown in FIG. 6C.
A sinusoidal signal shifted by 90° is derived to output point C,
This signal is transmitted to the comparator 22a and the differentiating circuit 21.
added to b. And the comparator 22a is C
Since the signal at the point is compared with the ground level, a pulse is derived at the output point D of the comparator 22a, with the positive region of point C being logic 1 and the negative region of point C being logic 0, as shown in FIG. 6D. and this pulse is applied to one input of AND gate 23.

Further, the differentiating circuit 21b differentiates the sinusoidal signal derived from point C, and derives a sinusoidal signal whose phase is further shifted by 90° as shown in FIG. 6E to output point E. is added to comparator 22b. Since the comparator 22b also compares the signal at point E with the ground level, the comparator 22b also compares the signal at point E with the ground level.
At the output point F of 2b, as shown in FIG.
A pulse is derived in which the positive region of the point is logic 1 and the negative region of point E is logic 0, and this pulse is passed through the AND gate 23.
is added to the other input. Therefore, as shown in FIG. 6G, a reference pulse that rises at the lowest point of the sine wave led to point A is derived from the output point G of the AND gate 23, and this reference pulse is applied to the inverter 2.
5 and the AND gate 29c.

Now, when the shutter switch 27 is pressed at time t1, the flip-flop 2 is pressed as shown in FIG. 6H.
The level of the H point applied to the D input terminal of 4 and one input of the AND gate 26 is the time logic 1 of T1.
become.

Since the reference clock derived from the G point is inverted by the inverter 25 and applied to the other input of the AND gate 26, when the level of the H point becomes logic 1 at time t1, the AND gate 26 At the output point the signal shown in FIG. 6 is derived, so that flip-flop 28 is set at time t1 and its output point J becomes a logic 1 as shown in FIG. 6J.

The level at point J, which is the Q output of flip-flop 28, is applied to one control input terminal of AND gate 29C, and the Q2 output of counter 29a is inverted by inverter 29b to the other control input terminal of AND gate 29c. has been added. In the initial state, the counter 29a is reset, so the AND gate 29c is opened and the G
The reference pulse derived at the point is applied to the AND gate 29c.
is applied to the clock input terminal of flip-flop 24.

As already mentioned, the level of the H point is applied to the D input terminal of the flip-flop 24, but when the first reference clock is applied to the flip-flop 24 at time t2, the level of the H point is logic 1. Therefore, the level at point K, which is the Q output of flip-flop 24, becomes logic 1 at time t2 as shown in FIG. 6K, and therefore analog gate 15 also opens at time t2.

After that, when time T2 passes and time t3 arrives,
Second reference clock G on flip-flop 24
However, at time t3, the level of the H point applied to the D input terminal of the flip-flop 24 has fallen to logic 0, so the flip-flop 24 stores this and outputs its Q output K.
The level of the point becomes logic 0 at time t3, as shown in FIG. 6K. Therefore, analog gate 15 also closes at time T3.

Therefore, the output point L of the analog gate 15 is connected to the output point B of the non-inverting amplifier 13 as shown in FIG.
Of the sine wave derived at the output point B, a portion of time T2 (i.e., one period from the lowest level to the next lowest level of the sine wave derived to the output point B) is derived. Become.

The sine wave for one period derived from this output point L is applied to the amplifier 16 and amplified by the amplification factor set by the variable resistor 16a interlocked with the aperture ring, as shown in FIG. 6M. The signal is electrostrictive element 1
will be applied to

The displacement of the electrostrictive element 1 caused by the application of a sinusoidal voltage in this way is transmitted to the shutter blade 3 by the mechanism shown in FIG.
The electrostrictive element 1 also operates in accordance with the displacement of the electrostrictive element 1 due to the application of this sinusoidal voltage.

Note that since the counter 29a counts up at the down edge of the reference clock G, its Q2 output becomes logic 1 at the down edge of the second reference clock that has passed through the AND gate 29c. This Q2
The output is sent to the AND gate 2 via the inverter 29b.
Since the reference clock is added to AND gate 29c and closes it, the reference clock will not pass through AND gate 29c three times or more consecutively.

Then, at time t4 after the shutter blade 3 closes, the flip-flops 24 and 28 and the counter 2
9a is reset by a circuit not shown, and the entire system returns to its initial state.

FIG. 7 shows the relationship between one cycle of the sine wave signal applied to the electrostrictive element 1 and the opening characteristics of the shutter. In this case, the speed of the shutter blade 3 logically becomes zero at each of the following times: (1) the shutter opening start time Ts, (2) the shutter opening peak time Tp, and (3) the shutter closing time Te. Overshoot of the blades 3 and mechanical collisions are effectively prevented, and extremely stable operating conditions can be obtained.

Note that FIG. 8 shows an example in which the resistance value of the variable resistor 16a is varied, and if the resistance value of the variable resistor 16a is varied, the amplitude of the sine wave applied to the electrostrictive element 1 is varied. Aperture F varies. Furthermore, FIG. 9 shows an example in which the resistance value of the variable resistor 11 is varied, and if the resistance value of the variable resistor 11 is varied, the period T2 of the sine wave is varied, so the effective exposure time T2' is fluctuate.

Also, at this time, the resistance value of the variable resistor 11 is set by the shutter dial, and the resistance value of the variable resistor 16a is set by the shutter dial.
If the resistance value of variable resistor 1 follows the field brightness, automatic exposure control that prioritizes shutter becomes possible.
If the resistance value of the variable resistor 11 is set by the aperture ring and the resistance value of the variable resistor 11 is made to follow the field brightness, aperture-priority automatic exposure control becomes possible. Furthermore,
If the resistance values of the variable resistors 11 and 16a are made to correspond to a combination prepared in advance in accordance with the brightness of the field, automatic exposure control by program auto becomes possible.

Note that various circuits other than those described above can be considered to satisfy the essential element of the present invention, which is to apply a sinusoidal voltage for one cycle to the electrostrictive element 1. For example, a signal equivalent to the reference clock G can be easily obtained by providing a one shot triggered by the rising edge of the output D of the comparator 22a in place of the differentiating circuit 21b, the comparator 22b, and the AND gate 23.

Incidentally, an example in which the circuit system from the flip-flop 24 to the AND gate 29c in FIG. 5 is modified is shown in FIGS. 10 and 11.

First, in FIG. 10, the counter 4 is set in the initial state.
0 is set to [2], its Q2 output becomes logic 1, and the T-type flip-flop 41
has been reset. Reference clock G is logic 0
When shutter switch 27 is turned on at this time, the output of AND gate 26 rises, counter 40 is reset, and its Q2 output becomes logic 0. Since this is inverted by inverter 42 and applied to AND gate 43, AND gate 43 is opened and reference clock G is applied to the T input terminal of flip-flop 41. Therefore, the flip-flop 41 is inverted at the rising edge of this reference clock, and the Q output led to the K point becomes logic 1, so the analog gate 15 shown in FIG. 5 opens at this point and the sinusoidal voltage becomes electrostrictive. applied to element 1. Then, when the second reference clock G is applied, the flip-flop 41 is inverted again and the analog gate 15 is closed.

Further, the Q2 output of the counter 40 becomes logic 1 at the down edge of the second reference clock, closes the AND gate 43, and returns to the initial state.

Next, in FIG. 11, the counter 44 is set to [2] in the initial state, and its Q2 output is a logic 1.
Along with this, D type flip-flop 4
5 has been reset. When the shutter switch 27 is turned on when the reference clock G is logic 0, the output of the AND gate 26 rises and the counter 44
is reset and its Q2 output becomes a logic zero.
Since this is inverted by the inverter 46 and applied to the AND gate 47, the AND gate 47
The first reference clock G is applied to the clock input terminal of the open flip-flop 45. Since the shutter switch 27 is on at this time, the flip-flop 45 stores this and makes its Q output derived to the K point logic 1. Therefore, the analog gate 15 shown in FIG. 5 is opened at this point, and a sinusoidal voltage is applied to the electrostrictive element 1. Since the shutter switch 27 is already off when the second reference clock G is applied, the Q output of the flip-flop 41 led to the K point becomes logic 0 at this point, closing the analog gate 15.

Further, the Q2 output of the counter 44 becomes logic 1 at the down edge of the second reference clock, closes the AND gate 47, and returns to the initial state.

As explained above, according to the present invention, overshoot of the shutter blade and mechanical collision can be effectively prevented, making it possible to perform stable exposure control, and furthermore, vibration accompanying shutter release can be reduced. Problems such as so-called camera shake can also be reduced.

In the above, an example is shown in which the present invention is applied to a shutter that also serves as a diaphragm blade, but if the shutter has an independent diaphragm blade, the variable resistor 16a becomes unnecessary.

[Brief explanation of the drawing]

Figures 1 and 2 are characteristic diagrams when the shutter is controlled by a conventional control device, Figure 3 is a diagram of the operating principle of the electrostrictive element, and Figure 4 is a diagram of the operating principle of the electrostrictive element for driving the shutter. 5 is a digital circuit diagram of one embodiment of the present invention, FIG. 6 is a timing diagram of one embodiment of the present invention, and FIGS. 7, 8, and 9 are digital circuit diagrams of one embodiment of the present invention. FIG. 10 and FIG. 11 are digital circuit diagrams of other embodiments of the present invention; FIG. 1... Electrostrictive element, 11... Variable resistor, 12...
Oscillator, 13... Inverted amplifier, 14... Power supply,
15...analog gate, 20...gate control circuit.

Claims (1)

[Scope of Claims] 1. In an exposure control device that drives a shutter blade using mechanical strain generated in an electrostrictive element due to the application of voltage as a drive source, there is provided a sine wave generation circuit that generates a sine wave voltage signal; an analog gate that passes the sinusoidal voltage signal during a period from the peak level of the sinusoidal voltage signal to a peak level one cycle after the shutter button is turned on; and the sinusoidal voltage signal that has passed through the analog gate. an amplification circuit that amplifies and applies the amplified signal to the electrostrictive element. 2. The exposure control device according to claim 1, wherein the frequency of the sine wave generation circuit is made variable. 3. The exposure control device according to claim 1 or 2, wherein the amplification factor of the amplifier circuit is variable.