JP3189151B2 - Drive device for piezoelectric actuator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric actuator which is very effective when used in a camera.

[0002]

2. Description of the Related Art Hitherto, a piezoelectric element which converts an electric signal into a mechanical displacement has been used as a piezoelectric actuator. This piezoelectric element has a structure in which a thin ceramic substrate formed of a piezoelectric material having a piezo effect is laminated in a multilayer structure. When a voltage of about 100 volts is applied between two electrodes, the piezoelectric element expands and contracts depending on the polarity of the voltage, and its dimensions. Has the property of changing. Although the displacement at this time is relatively small, several tens of microns, a large force of several tens of kilograms is obtained for the volume of the piezoelectric element, so that it is attracting attention as an electromechanical transducer in a small device such as a camera.

[0003]

The piezoelectric actuator having the above-described features utilizes a displacement or a displacement force of the piezoelectric actuator when a rated voltage is applied from a state where no voltage is applied to a mechanical system by using the displacement force. When the piezoelectric actuator is used in a camera, the camera is taken in various postures and shooting is performed.If the direction of operation of the piezoelectric actuator is opposite to the direction of gravity, the load becomes heavy and a regular voltage is applied. It may not be possible to operate even if the voltage is applied. As a countermeasure, the maximum value of the acceleration due to the amount of mechanical displacement that can be taken out of the piezoelectric actuator may be designed to have a sufficient margin for the load. However, the environment of use of a camera or the like ranges from underwater to outer space, and it is not practical to set the characteristics of the piezoelectric actuator corresponding to all of them. Further, due to variations in the characteristics of the piezoelectric actuator itself, variations in the mechanical load, variations in the driving power supply circuit, and the like, those that all vary in the bad direction may not be able to operate even when a normal voltage is applied. Further, not only due to the influence of gravity, but also due to vibration or shock applied to the camera at the time of operation, the force generated in the piezoelectric actuator is canceled and reduced, and the operation may not be possible even if a regular voltage is applied.

[0004]

A mechanical means for performing an operation in accordance with the displacement of a piezoelectric actuator, an end detecting means for detecting that the operation of the mechanical means has been completed, and a mechanical displacement in a predetermined direction to the piezoelectric actuator And a voltage generating means for generating a reverse polarity voltage for generating a mechanical displacement in a direction opposite to a predetermined direction, and generating a forward polarity voltage generated by the voltage generating means. When the end detecting means does not detect the end of the operation of the mechanical means within a predetermined time, a voltage of the opposite polarity generated by the voltage generating means is applied to the piezoelectric actuator for a predetermined time, and then again. A forward polarity voltage is applied. Further, a plurality of voltages having different forward polarity voltage values are generated, and the forward polarity voltage (predetermined voltage value) to be applied again is a voltage value higher than the previous voltage (voltage value larger than the predetermined voltage value). . Further, a predetermined voltage value generated by the voltage generating means is set as a rated drive voltage value of the piezoelectric actuator, and a voltage value larger than the predetermined voltage value is set as a maximum allowable drive voltage value of the piezoelectric actuator.

[0005]

Even if the mechanical means is not completed once the piezoelectric actuator is operated, if the mechanical means is operated again, then the probability that the previous bad condition has been canceled is high, and the mechanical means can be completed. Probability is high. By applying a reverse polarity voltage to drive the piezoelectric actuator in reverse before re-operating, it is possible to obtain more displacement and acceleration of the piezoelectric actuator when a forward polarity voltage is applied again. Is more likely to be completed. If the voltage is set higher than the previous time when the operation is performed again, the operation of the mechanical means can be more reliably completed.

[0006]

FIG. 1 is a block diagram of an electric circuit including a driving device for a piezoelectric actuator according to the present invention, and FIG. 2 is a perspective view for explaining a mechanical structure when the piezoelectric actuator is used for driving a shutter of a camera. In order to understand the operation of the piezoelectric actuator, first, FIG. 2 will be described. In FIG. 2, the piezoelectric actuators 1 and 2 respectively have a shutter front curtain 17,
It is used to control the opening start of the rear curtain 37,
The figure shows the state before the opening of the first curtain. The actuator 1 is fixed to a fixing member 3, and a lever 4 is in contact with an end surface thereof by a spring 5. The lever 4 is rotatably supported around a rotation shaft 6 together with a pin 7 provided thereon. A lever 8 rotatable on the shaft 9 is urged by a spring 10 so that one end of the lever 8 can abut on the pin 7 and the other end forbids rotation of the other lever 11. The lever 11 is rotatable about a shaft 13 and usually has a spring 1.
The rotation of the lever 8 is restricted by the other end of the lever 8. The pin 14 on the lever 11 is a member for directly controlling the operation of the shutter front curtain 17, and the front curtain 17 covers a film surface (not shown) by a known method. Pin 14
The lever 15 provided at an intermediate portion of the switch is located at a position where the switch 16 can be turned on and off. In this case, the switch 16
Is off.

On the other hand, the other actuator 2 is a fixed member 2
3, and a lever 24 is in contact with an end surface thereof by a spring 25. The lever 24 is rotatably supported around a rotation shaft 26 together with a pin 27 provided thereunder. A lever 28 rotatable by a shaft 29 is urged by a spring 30 so that one end of the lever 28 can abut on the pin 27 and the other end forbids rotation of the other lever 31. The lever 31 is rotatable about a shaft 33 and is normally urged by a spring 32, but its rotation is regulated by the other end of the lever 28. The pin 34 on the lever 31 is a member that directly controls the operation of the shutter rear curtain 37,
The rear curtain 37 is retracted from a film surface (not shown) by a known method. The lever 35 provided at the end of the pin 34 is at a position where the switch 36 can be turned on and off. In this case, the switch 36 is off.

The exposure operation for controlling the rear curtain 17 and the front curtain 37 of the shutter is performed as follows. First, when the actuator 1 is energized and operated, its length is extended in the longitudinal direction (upper right), and the displaced force is transmitted to the lever 4.
The lever 4 rotates clockwise about the rotation axis 6 against the spring 5 and rotates the lever 8 counterclockwise (counterclockwise) about the rotation axis 9 with the pin 7 against the spring 10.
Then, the lever 11, which has been prohibited by the other end of the lever 8, stops rotating by the restoring force of the spring 12,
, The pin 14 also rotates about the rotation shaft 13 and moves in the upper right direction. As a result, the front curtain 17 travels in the upper right direction indicated by the arrow to start exposure. At this time, the switch 16 is turned on by the lever 15 simultaneously with the opening of the front curtain 17.

As described above, when the timing to close the shutter rear curtain 37 comes a predetermined time after the front curtain 17 is opened, the actuator 2 is first energized. Then, the length is extended in the longitudinal direction (upper left), and the force due to the displacement is transmitted to the lever 24. The lever 24 rotates counterclockwise around the rotation shaft 26 against the spring 25, and the pin 27 causes the lever 28 to rotate clockwise around the rotation shaft 29 against the spring 30. Then, the lever 31 which has been prohibited by the other end of the lever 28 from rotating by the restoring force of the spring 32 until then.
However, the prohibition is released, and the pin 34 rotates leftward about the rotation axis 33 and the pin 34 moves to the upper right. With this, the second curtain 37
Travels in the upper right direction similarly to the front curtain 17 to end the exposure. At this time, the switch 36 is turned on by the lever 35 at the same time when the rear curtain 37 is opened. As described above, the exposure operation on the film by the shutter first curtain 17 and the rear curtain 37 is completed. The operation of the front curtain 17 and the rear curtain 37 can be completed by monitoring the states of the switches 16 and 36, respectively. .

Next, an electric circuit for driving the piezoelectric actuator will be described with reference to FIG. Battery 40 supplies power to power supply circuits P1, P2, and P3. Power supply circuit P
1 outputs a voltage of about 5 V and is used as a voltage for a control circuit including a CPU. A power supply circuit P2 outputs a voltage of about 100 V and is used for driving the actuators 1 and 2 and the lamp 43 for liquid crystal display illumination in a normal state. , The power supply circuit P3 is 2
Actuator 1, which outputs a voltage of about 00V,
2 Further used for driving the strobe light emitting tube 44. The operation of the power supply circuit P1 is controlled by turning on a half-press switch 41 which is turned on in conjunction with a shutter button (not shown) of the camera and a transistor Q1 driven by the CPU. Here, the on / off state of the switch 41 is also transmitted to the CPU, and the operation state is grasped. A diode D1 is inserted between the ON state of the transistor Q1 and the ON state of the switch 41 between them. With such a configuration, the switch 4 is released from the shutter button.
The operation of the camera is extended by keeping the transistor Q1 on for a certain period of time after the transistor 1 is turned off. The above configuration is publicly known. The operation of the power supply circuits P2 and P3 is controlled by transistors Q2 and Q3 driven by the CPU, respectively.

Further, a circuit block having the following input / output functions is connected to the CPU. Photometric circuit LM
, A subject luminance signal is input to the CPU. The display circuit DSP visually or audibly outputs shutter time information to be controlled and various warning signals based on a signal from the CPU so that the photographer can determine the shutter time information. The aperture control circuit AP controls the in-lens aperture according to a signal from the CPU so that an appropriate aperture is obtained. Film sensitivity signal reading circuit FM
Reads the film sensitivity data provided on the side wall of the film cartridge in a known manner and outputs it to the CPU. The humidity detection circuit HMD detects the humidity in the camera and transmits the signal to the CPU. The humidity sensor in this case is
Any position may be used as long as the humidity of the piezoelectric actuator itself provided inside the camera can be determined. Ideally, if the piezoelectric actuator is adhered to the actuator, accurate humidity can be detected. The switch group SW includes an exposure start command release switch interlocked with a shutter button, a switch for detecting completion of film winding, a rear curtain first curtain running completion detection switch 16, 36, and the like. Although the wiring is omitted, each of the above circuit blocks operates by power supply from the power supply circuit P1.

On the other hand, the power supply from the power supply circuit P2 is also supplied to the illumination circuit EL, and when the transistor Q13 is turned on by the CPU, the lamp 43 serving as a backlight is turned on and the liquid crystal display in the above-mentioned liquid crystal display circuit DSP is turned on. Illuminates the element. Here, since the lamp 43 is made of electroluminescence, the output voltage of the power supply circuit P2 becomes about 100 V, and the same voltage output can be shared by the actuators 1 and 2 as described later. On the other hand, the output voltage from the power supply circuit P3 is supplied to the strobe circuit SB. Strobe light emitting tube 44
Can be emitted when the CPU turns on the transistor Q14 when the shutter is opened. This power supply output is also used when it is used to drive the actuator when an abnormal situation occurs, as described later. The circuit blocks 46 and 47 are driving circuits for the actuators 1 and 2, respectively. However, since the circuit contents are the same, the following description will be made only for the actuator 1 and the description for the actuator 2 will be omitted.

The upper terminal of the actuator 1 is supplied with a voltage from the power supply circuit P2 via a transistor Q5 and a voltage from the power supply circuit P3 via a transistor Q6. Also C
It is grounded by a transistor Q11 directly driven by PU. Here, the transistors Q5 and Q6 are respectively CPU
Are controlled by transistors Q8 and Q10 driven by. The lower terminal of the actuator 1 is grounded by a transistor Q9 driven by the CPU, or a voltage from the power supply circuit P2 is applied via the transistor Q7. Here, the transistor Q7 is controlled by the transistor Q12 driven by the CPU. Further, the upper terminal of the actuator 1 is applied with the voltage of the power supply circuit P1 via the transistor Q4, the diode D2 and the resistor R1, and is grounded via the resistors R2 and R3. The resistance R
The midpoint between R2 and R3 is applied to one input terminal of the comparator C, compared with the voltage source 45, and the result is transmitted to the CPU. On the other hand, a surge absorber 42 is connected in parallel between both terminals of the actuator 1. A peripheral circuit having a similar configuration is prepared for the actuator 2 in the circuit 47.

The driving of the above circuit is performed as follows. First, when the power supply circuit P1 starts supplying power and the CPU starts operating, the photometric circuit LM and the film sensitivity detection circuit FM
Calculate the appropriate exposure condition by calculating both input signals. The result is displayed on the display circuit DSP, or a warning is issued in addition to the display when the condition is inappropriate. At the same time, the power supply circuits P2 and P3 are operated to generate two types of high voltages, and the lighting lamp 43 for the liquid crystal display element in the display circuit DSP connected to the power supply circuit P2 is turned on by turning on the transistor Q13. The voltage of the power supply circuit P3 is stored in a capacitor (not shown) for operating the flash circuit SB. Next, the humidity detecting circuit HMD is operated to detect the humidity of the environment where the actuator is placed. If the operation of the piezoelectric actuator 1 is dangerous due to excessive humidity, the circuit blocks 46 and 47 will be described later.
The dehumidifying operation is executed by appropriately driving the internal transistors. The dehumidifying operation can be performed by performing intermittent driving at a frequency that does not cause displacement of the actuator. More specifically, the operation of applying a voltage by driving the transistor Q5 and then discharging the accumulated charge by driving the transistor Q11 is repeated at a constant frequency, thereby generating heat inside and releasing accumulated moisture. Because.

Next, it is determined whether the actuator is normal. This can be done by turning on the transistor Q4, applying the voltage of the power supply circuit P1 to the actuator, dividing the voltage generated at its terminals by the resistors R2, R3, and comparing the voltage with the voltage source 45 by the comparator C. If the piezoelectric actuator 1 is normal, the insulation resistance of the actuator is considerably large, and the voltage of the power supply circuit P1 applied through the transistor Q4 is equal to the diode D2 and the resistors R1 and R2.
This is because the voltage is applied to the comparator C as a higher voltage divided output by R2 and R3. On the other hand, if the piezoelectric actuator 1 has been broken down due to driving in a humid condition, the upper terminal of the piezoelectric actuator 1 is equivalently grounded. Therefore, when the transistor Q4 is turned on, the middle point between the resistors R1 and R2. Is grounded, so that the voltage applied to the comparator C is considerably lower than in the normal state. Here, as described later, when driving the piezoelectric actuator 1, the high voltage from the power supply circuit P2 when the transistor Q5 is turned on is applied to the transistor D4 in the reverse direction to destroy the diode D2. This is to prevent the water from flowing back and destroying it. The resistor R1 is unnecessary in a normal state, but is provided to prevent the transistor Q4 and the diode D2 from being directly grounded when the actuator 1 is insulated, resulting in thermal damage.

The surge absorber 42 connected in parallel with the actuator 1 has a function of preventing a high voltage generated and output by the piezoelectric actuator 1 itself in normal operation from adversely affecting peripheral circuits. Surge absorber 4
No. 2 functions as an infinite resistance (impedance) when the voltage applied between the terminals is up to several hundred volts, and when a voltage higher than that is applied, the resistance (impedance) decreases and short-circuits. It is. Such a surge absorber 42 normally has no effect, but when the piezoelectric actuator 1 generates a spike voltage of tens of thousands of volts due to a shock applied to the camera, the voltage is short-circuited and absorbed by itself. As a result, it is possible to prevent each element such as the transistor Q4, which cannot expect a withstand voltage of tens of thousands V, from being destroyed by a high voltage.

Further, electric charges may be accumulated on both electrodes of the piezoelectric actuator 1 by a pyroelectric effect due to infrared rays due to heat or the like. The operation for absorbing the voltage generated by the pyroelectric effect is as follows. When it is detected that the release switch for instructing the start of exposure is operated in conjunction with the shutter button, first, both the transistors Q9 and Q11 are turned on. As a result, the charges due to the pyroelectric effect generated in the piezoelectric actuator 1 are transferred to the transistors Q9 and Q9.
It disappears within 11. Such a pyroelectric charge absorption routine is not necessary only during the release routine, and may be executed periodically, such as during film winding, immediately after the start of the operation of the power supply circuit P1, and immediately before the end of the operation. Also,
The base drive current of the transistors Q9 and Q11 is
If there is no problem in the wear of the piezoelectric actuator 1, short-circuiting may be continuously performed while the power supply circuit P1 is operating and the piezoelectric actuator 1 is not driven. Here, when the generated voltage is high, it is conceivable that an excessive current may flow into both transistors and cause thermal destruction when the transistors Q9 and Q11 are short-circuited.
A small resistor may be connected in series with the piezoelectric actuator 1 on the collector side. The normal operation of the actuator is performed as described below following the short-circuit operation by the transistors Q9 and Q11 as described above. The transistor Q8 is turned on, and the transistor Q5 turns on the power supply circuit P2.
Is applied to the terminal above the actuator. Here, the output voltage of the power supply circuit P2 needs to be an appropriate rated voltage in view of the operation specifications of the actuator. In this embodiment, the case where the rated voltage matches the driving voltage of the lamp 43 is taken as an example. Driving the piezoelectric actuator 1 via the resistor R4 is for preventing thermal destruction of the transistor Q5. Since the mechanical system uses acceleration as shown in FIG. 2, the ON time of the transistor as described above can be relatively short. By this driving, the piezoelectric actuator 1 momentarily extends in the longitudinal direction to generate a force, and the operation described with reference to FIG. 2 continues.

Next, the operation of the multi-stage driving which characterizes the present invention will be described. The above-described piezoelectric actuator 1
The circuit operation when the operation of the piezoelectric actuator 1 is not correctly transmitted to the mechanical system shown in FIG. 2 due to variations in its own characteristics, individual differences in the output of the power supply circuit P2, and even bad conditions such as the posture of the camera. State. When the piezoelectric actuator 1 operates only insufficiently even when the transistor Q5 applies the voltage from the power supply circuit P2, FIG.
The front curtain does not run as described in
Does not turn on. Since the switch 16 is in the switch group SW, the CPU itself can know that the driving by applying the voltage from the power supply circuit P2 has failed. In such a case, the voltage applied to the piezoelectric actuator 1 is slightly increased, and the piezoelectric actuator 1 is driven again. That is, the transistor Q10
To turn on the power supply circuit P via the transistor Q6.
3 is applied to the piezoelectric actuator 1. Here, a resistor R5 is used to prevent thermal destruction of the transistor Q6.
Are connected in series similarly to the transistor Q5. Here, the voltage used for re-driving is the maximum allowable voltage of the actuator or a voltage slightly lower than the maximum allowable voltage. That is, the voltage is applied so as not to exceed a voltage at which the actuator is destroyed when a voltage higher than that is applied. By driving with such a voltage value, it is possible to expect the maximum amount of the generated force and displacement of the actuator. In this embodiment, the voltage source is a strobe circuit S
Although an example is shown in which the power supply is shared with the power supply to B, it goes without saying that a separately prepared voltage source may be used. In the above embodiment, the maximum allowable voltage was used for the second drive, but it is sufficient that the second operation can be performed even if the same voltage as the previous drive is used, and this method is also practical. It is also conceivable to drive at the rated voltage several times and then drive at the maximum allowable voltage.

Next, the displacement amount from the piezoelectric actuator 1
The method of extracting the maximum acceleration may be as follows. That is, the transistors Q11 and Q11
When the transistor 12 is turned on to apply a potential of the opposite polarity from the transistor Q7, the piezoelectric actuator 1 is reversely driven. Thereby, the piezoelectric actuator 1 is displaced in the opposite direction and contracts. Even in this state, the lever 4 in FIG. 2 moves following the end face of the piezoelectric actuator 1 by the force of the spring 5, so that there is no gap. Then, immediately after this state, the main driving by the transistors Q5 and Q9 is performed. As a result, the displacement of the actuator 1 is equivalently nearly doubled, the generated acceleration is similarly increased, and the displacement can be increased. This operation state will be described later with reference to FIG. Here, a resistor R6 for preventing thermal destruction is also connected in series to the transistor Q7.

FIG. 3 et seq. Show an example of an operation program of the CPU. In FIG. 3, while the power supply circuit P1 is operating, CP
U repeatedly executes this routine. In step 50, the output of the photometric circuit LM and the output of the film sensitivity detection circuit FM are calculated, and an appropriate control condition is calculated. Step 5
At 1, the operation of the power supply circuit P2 is started, and at the same time, the transistor Q13 is turned on to turn on the lamp 43. In step 52, the appropriate control conditions in step 50 are displayed on the display circuit DSP. In step 53, a check routine of the insulation state of the piezoelectric actuators 1 and 2 is executed. This detailed operation will be described with reference to FIG. Next, at step 54, it is determined whether or not any of the actuators 1 and 2 has an insulation failure as a result of step 53. If an insulation failure has occurred, a warning is issued in step 55 that one of the piezoelectric actuators 1 and 2 is abnormal. A visual method and an audible warning method are performed by the display circuit DSP. In step 56, a prohibition state is set so that the release routine is not entered even if the shutter button is pressed. After this routine, the process returns to step 50 to continue displaying the calculation result and warning about an abnormal state of the actuators 1 and 2. If the insulation state is good, in step 57, the humidity detection circuit HMD detects the humidity state in the camera. If the humidity is good, step 5
At 8, the release is permitted. The permission is given here because it is necessary to reset the prohibited state so that the exposure operation can be performed when the state previously prohibited in step 55 is released. In step 59, the operation of the power supply circuit P3 is started. Thus, the flash circuit SB is ready for light emission. At step 60, it is determined whether or not the release switch has been turned on by the shutter button. If the release switch has not been turned on, the process returns to step 50. If the release switch has been turned on, at step 61, FIG.
A release sequence, which will be described in detail later, is executed. Step 5
If the humidity condition is not good in step 7, a warning is issued in the display circuit DSP in step 62 because the humidity in the camera is too high and it is dangerous to operate the actuators 1 and 2. In step 63, the release prohibited state is set. At step 64, a dehumidification routine is executed. The details will be described with reference to FIG. After the execution of this routine, the process returns to step 50 to repeat the above. When the dehumidification is completed, the process proceeds to the release routine of step 61 unless the insulation state is not bad.

FIG. 4 shows the details of the insulation state detection routine in step 53 of FIG. In step 70, the transistor Q9 is turned on, and in step 71, the transistor Q4
Turn on. Thus, the voltage of the power supply circuit P1 is applied to the piezoelectric actuator 1 via the diode D2 and the resistor R1. In step 72, the output of the comparator C is determined, and in step 73, it is determined whether the output of the comparator C has been reliably determined. This is to ensure a certain result by repeating a plurality of times instead of making a judgment by reading only once. Next, step 74
, The reading result is stored in the memory. In step 54 of FIG. 3, the contents of the memory stored in step 74 are confirmed. At step 75, the transistor Q4 is turned off. At step 76, the transistor Q9 is turned off.
Turn off. This completes the routine for applying the output of the power supply circuit P1 to the actuator 1. A similar routine is required for the piezoelectric actuator 2, but details thereof are omitted.

FIG. 5 shows a detailed example of the dehumidification routine of step 64 in FIG. In step 80, the number of repetitions n is set to 0 first. In step 81, it is determined whether or not the number of repetitions n exceeds a predetermined value N. At first, since the value N has not been reached, the process proceeds to step 82, where the transistor Q9 is turned on, and step 8
At 3, the transistor Q8 is turned on. Transistor Q
When transistor 8 is turned on, transistor Q5 is also turned on, and the output voltage from power supply circuit P2 is applied to actuator 1.
At step 84, a fixed delay time is provided, and the voltage application to the actuator 1 is maintained for a predetermined time. During this time, the actuator 1 is charged. This predetermined time is set in a range where the actuator 1 does not sufficiently displace and operate the load. After a lapse of a predetermined time, step 8
At 5, the transistor Q8 is turned off, and the transistor Q5 is also turned off, thereby terminating the output voltage application from the power supply circuit P2.
In step 86, the transistor Q11 is turned on, whereby the electric charge stored in the actuator 1 is discharged.
In step 87, a certain delay time is provided to ensure discharge. This time is set to a time at which a sufficient discharge for performing the next charge is performed. In step 88, since one cycle of charge / discharge has been completed, the number of repetitions n
Is added to. Next, in step 89, the process returns to step 81 after turning off the transistor Q11. Since then
This operation is repeated.

The operation of the above charge / discharge cycle is executed until the number of repetitions n reaches the value N. When the value N is reached, after step 81, the process jumps to step 90,
Thus, at step 90, the transistor Q9 is turned off. Thereafter, the process returns to step 50 of FIG. 3 and the above-described processing is repeated. As described above, it is important to set the charging time to a time that does not cause the displacement of the actuator 1 to drive the load. Otherwise, the mechanical system shown in FIG. 2 is operated in spite of the dehumidification routine. In addition, the repetition frequency and the number of repetitions N need to be strictly obtained from experimental values based on the humidity resistance characteristics of the actuator to be used. However, it is generally sufficient to drive at several kHz and for several tens of milliseconds. Would. Note that the numerical value N may be variable depending on the humidity of the atmosphere.

In the above embodiment, the actuator 1 is driven in the forward direction, but may be driven in the reverse direction. In this case, the difference from the operation in FIG. 5 is that in step 82, the transistor Q11 is turned on, and in step 83, the transistor Q12 is turned on to turn on the transistor Q7, and a reverse voltage is applied to the actuator 1. . After a certain time delay in step 84, step 85
Then, the transistor Q12 is turned off and the transistor Q12 is turned off.
7 is turned off, and in step 86, the transistor Q9 is turned on to discharge the electric charge stored in the actuator 1. At step 87, a fixed delay time is provided, and at step 88, 1 is added to the number of repetitions n, and step 8
In step 9, after turning off the transistor Q9, step 81
Return to The operation of the above charge / discharge cycle is executed until the number of repetitions n reaches the numerical value N. When the numerical value N is reached, after step 81, the process jumps to step 90, in which the transistor Q11 is turned off in step 90, and thereafter, the process returns to step 50 in FIG. 3 and the above-described processing is repeated.
In this example of the application of the reverse voltage, the actuator 1 is displaced in the direction opposite to the direction in which the load is driven. Can be lengthened.
If this time is long, heating is sufficiently performed, so that the number N of repetitions can be reduced.

FIGS. 6 and 7 show details of the release routine shown in step 61 of FIG. At step 95, the transistor Q13 is turned off. As a result, the illumination lamp 43 is turned off, and the output voltage of the power supply circuit P2 in the future will be used only for the actuators 1 and 2. In step 96, the reflecting mirror of the camera is raised, and in step 97, the aperture control circuit AP is driven to set the aperture to a predetermined value. At step 98, the transistor Q8 is turned on, which turns on the transistor Q5. In step 99, the transistor Q9 is turned on. With the above operation, the actuator 1 is driven by the power supply circuit P2. In step 100, an operation for measuring a predetermined shutter time is started, and in step 101, it is confirmed whether or not the switch 16 is turned on. This is for detecting the result of whether the actuator 1 has correctly driven the mechanical system. If the switch 16 has not been turned on, that is, if the front curtain mechanical system has not operated, the process proceeds to step 106. When the switch 16 is turned on, step 102
It is determined whether or not the timing started in step 100 has been completed.

When the time measurement is completed, the process for controlling the second curtain is executed after step 103 since the time measurement time has reached the set value. First, in step 103, a transistor Q8 equivalent of the front curtain actuator 2 in the rear curtain control circuit block 47 is turned on. Thus, the transistor Q5 equivalent product is also turned on. In step 104, the transistor Q9 equivalent product is turned on, whereby the actuator 2 is energized. In step 105, it is confirmed that the switch 36 is turned on. If the switch 36 does not turn on, that is, if the rear curtain mechanical system does not operate properly,
Proceeding to step 111, if the switch 36 is turned on, proceeding to step 125 of FIG. At step 125,
All the transistors involved in the drive of the actuators 1 and 2 are turned off, the aperture is returned in step 126, the mirror is lowered in step 127, and the step 128 is performed.
Then, the transistor Q13 is turned on to restart the illumination by the lamp 43. In step 129, since the exposure of the film has been completed in the above routine, the winding routine is executed. With respect to the film feeding, only the above-described film feeding routine has been described. The rewind routine can be performed by a known method, and a description thereof will be omitted.

The operation when the switch 16 is not turned on in step 101, that is, when the front curtain mechanical system does not operate properly, is performed after step 106. This operation characterizes the present invention. That is, in step 106, the transistor Q8 is turned off, thereby turning off the transistor Q5 and stopping the voltage application from the power supply circuit P2. In step 107, the transistor Q10 is turned on, whereby the transistor Q6 is turned on, and the output voltage from the power supply circuit P3 is applied to the actuator 1. As described above, the application of the voltage to the power supply circuit P3 seeks to obtain the maximum amount of displacement of the actuator 1. Since the applied voltage is close to the allowable maximum rating, if it is always used, the durability of the actuator may be adversely affected. Therefore, it is used only in such an emergency. At step 108, the shutter time measurement is started again. In step 109, it is confirmed whether the switch 16 has been turned on. If the front curtain mechanical system operates correctly in the emergency operation described above, the switch 16 is turned on, so the flow returns to step 102 again to continue the above-described processing. In this case, it is not necessary to perform a warning operation. This is because it is considered that it is difficult to operate the camera accidentally due to the posture of the camera or an externally applied impact, and a warning is issued to avoid confusion of the photographer. On the other hand, if the front curtain mechanical system does not operate even in the above operation, the switch 16 does not turn on, so the process proceeds to step 110, and a warning that the front curtain mechanical system does not operate is issued on the display circuit DSP, and thereafter, FIG. Proceeds to step 120.

In step 120, the actuator 1,
All the transistors involved in the 2 drive are turned off, the aperture is restored in step 121, the mirror is lowered in step 122, and the transistor Q
13 to turn on the illumination lamp 43, and
At 24, the exposure operation is not performed because the front curtain is not operated in the above operation, and it is not necessary to feed the film. Then, the process returns to step 50 in FIG. 3 to perform the warning operation.

If the rear curtain mechanical system does not operate properly in step 105, the process proceeds to the next step. Step 11
At 1, the transistor Q8 equivalent product in the rear curtain control circuit block 47 is turned off.
The corresponding product is also turned off, and the drive by the power supply circuit P2 stops.
At step 112, the transistor Q10 equivalent is turned on, whereby the transistor Q6 equivalent is turned on, and the output voltage from the power supply circuit P3 is applied. The reason is the same as that of the first-curtain system. In step 113, it is confirmed whether the switch 36 has been operated. In step 114, the switch 36 is turned on, that is, although the rear curtain mechanical system operates and exposure is performed, steps 111, 112, and 113 are performed.
Since the exposure completion timing is delayed, an operation for giving a warning that a proper exposure cannot be obtained due to a long shutter time is started. Of course, if the processing in steps 111, 112, and 113 is relatively short compared to the shutter time, such a warning is unnecessary. It is only necessary to warn when the high-speed time has been set. Thereafter, the flow shifts to step 125 in FIG. 7 to execute the above-described processing. If the operation of the rear curtain mechanical system has not been performed again in step 113, that is, if there is an emergency in which the rear curtain does not close,
At step 115, a warning that the shutter curtain is open is issued, and the above-described routine following step 120 of FIG. 7 is executed.

FIG. 8 is a diagram for explaining a method for obtaining a larger displacement and acceleration from the actuators 1 and 2. The processing is executed between step 97 and step 98 in FIG.
At step 130, the transistor Q11 is turned on, whereby the upper terminal of the actuator 1 is grounded.
In step 131, the transistor Q12 is turned on, the transistor Q7 is turned on, and the output voltage of the power supply circuit P2 is applied to the lower terminal of the actuator 1. As a result, the actuator 1 is contracted by applying a voltage in the reverse direction and displaced in the reverse direction. In step 132, the state is applied with a delay for a predetermined time, and this reverse voltage application state is maintained. In step 133, the transistor Q12 is turned off, thereby ending the application of the reverse voltage. At step 134, the transistor Q11 is turned off. In the above routine, the actuator 1 contracts once, and a larger displacement amount and acceleration can be obtained by a synergistic effect with the subsequent expansion from step 98. A large amount of displacement and acceleration can be obtained by executing the same reverse voltage application routine for the actuator 2, but details of the routine are omitted.

FIG. 9 is an explanation of an example of a routine for improving the operation response of the actuator. The actuator is finely vibrated at a frequency near the mechanical resonance point, and the displacement operation by the main drive is performed quickly. This routine is the same as the dehumidification routine of FIG. 5, but its frequency and operating time are different. This routine is also inserted and executed between step 97 and step 98. In step 140, first, the number of repetitions n is set to 0,
In step 141, it is determined whether the number of repetitions n has exceeded a predetermined value N. If the number of repetitions n has not reached the numerical value N, the transistor Q9 is turned on in step 142, the transistor Q8 is turned on in step 143, and the transistor Q5 is turned on. Output voltage is applied. In step 144, a fixed delay time is set, and a voltage application time to the actuator 1 is set.
During this time, the actuator 1 is charged. In step 145, the transistor Q8 is turned off, and the transistor Q5 is also turned off, ending the output voltage application from the power supply circuit P2. When the transistor Q11 is turned on in step 146, the electric charge stored in the actuator 1 is discharged. At step 147, a certain delay time is provided to ensure discharge. At step 148, 1 is added to the number of repetitions n since one cycle of charge / discharge has been completed.
At step 149, the transistor Q11 is turned off.
It returns to step 141.

The above charge / discharge cycle is executed until the number of repetitions n reaches the value N. When the numerical value N is reached, after step 141, the routine jumps to step 98, where the subsequent routine is executed to control front curtain travel. It is important to set the charging time in the above processing to a time that does not cause displacement of the actuator 1. Otherwise, although it is a preliminary operation routine, FIG.
This is because the mechanical system is operated. In addition, the repetition frequency and the number of repetitions N need to be strictly determined from the response characteristics based on the resonance characteristics of the actuator to be used. In general, driving at several kHz and several milliseconds may be performed. The above processing is the same for the actuator 2 and will not be described in detail.

FIGS. 10, 11, and 12 show the expansion and contraction state of the actuator 1 during each of the above routines.
FIG. 10 is a diagram showing an operation state characterizing the present invention in the normal driving method of FIG. The actuator 1 in the stationary state before step 98 has a length as shown in FIG. When the output voltage of the power supply circuit P2 is applied in step 99, the displacement of A1 in the forward direction as shown in FIG. 10B is obtained. In addition, as described above, when the displacement amount A1 is insufficient by accident, FIG.
, The output voltage of the power supply circuit P3 is applied, and the larger displacement amount A2 is used as in step 107. The use of this change in length and its acceleration is a feature of the mechanical system according to the present invention, as described above.

FIG. 11 shows the displacement during the dehumidification routine of FIG. The actuator 1 in the stationary state before step 82 has a length as shown in FIG.
Then, when the output voltage of the power supply circuit P2 is applied in step 83, a displacement A3 as shown in FIG. 11B is obtained. Here, since the driving voltage is removed before the displacement completely saturates due to the intermittent driving, the displacement amount becomes A3 at the time of step 83 from the length before step 82, but before the length approaches A1. Then, the process goes to step 85 to return to the original length as shown in FIG. FIG. 12 illustrates the operation described with reference to FIG. 8 and illustrates a case where the amount of expansion once contracted is used. As shown in FIG. 12A, the length before step 130 is the conventional length. However, in step 131, a reverse voltage is applied, and the rod-shaped actuator 1 is displaced linearly, as shown in FIG. It contracts by the displacement amount of B1. Then, by applying the voltage in step 99, a rod-shaped actuation is performed.
The dispenser 1 is displaced linearly, and extends from the original length by the displacement A1 as shown in FIG. As a result, the mechanical system uses the displacement amount of the addition of B1 and A1,
As described above, a larger displacement and acceleration can be obtained.

[0035]

As described above, the present invention provides a piezoelectric actuator having a piezoelectric actuator which generates a mechanical displacement by applying a voltage and a mechanical means which operates using the displacement. To operate the mechanical means.If the operation is not completed within a predetermined time, a reverse polarity voltage is applied for a predetermined time, and then a forward polarity voltage is applied again to operate. It is possible to obtain more displacement and acceleration when a forward polarity voltage is applied, to increase the possibility of completing the operation of the mechanical means, and to improve the reliability of the operation of the mechanical means. Has an effect. Also, when applying the voltage again, make the voltage higher than the previous one,
The reliability of the operation can be further improved.

[Brief description of the drawings]

FIG. 1 is an electric circuit for driving a piezoelectric actuator according to one embodiment of the present invention.

FIG. 2 is a mechanical configuration diagram for driving a shutter of a camera driven by the piezoelectric actuator of FIG. 1;

FIG. 3 is a flowchart illustrating an operation of a CPU in FIG. 2;

FIG. 4 is a flowchart of an insulation state detection routine in step 53 of FIG. 3;

FIG. 5 is a flowchart of a dehumidification routine in step 64 of FIG. 3;

FIG. 6 is a flowchart of a release routine of step 61 in FIG. 3;

FIG. 7 is a flowchart of a release routine of step 61 in FIG. 3;

FIG. 8 is a flowchart of an operation routine for obtaining a large displacement and acceleration from a piezoelectric actuator.

FIG. 9 is a flowchart of an operation routine for improving the response of the piezoelectric actuator.

FIG. 10 is an explanatory diagram of a displacement amount during a normal operation of the piezoelectric actuator.

FIG. 11 is an explanatory diagram of a displacement amount during a dehumidification routine of the piezoelectric actuator.

FIG. 12 is an explanatory diagram of a displacement amount in an operation routine for obtaining a large displacement amount and acceleration of the piezoelectric actuator.

[Explanation of symbols]

 1, 2 Piezoelectric actuator 17 Shutter front curtain 37 Shutter rear curtain 46, 47 Circuit block P1, P2, P3 Power supply circuit EL Illumination circuit SB Strobe circuit

──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Masanori Hasuda 1-6-3 Nishioi, Shinagawa-ku, Tokyo Nikon Oi Works Co., Ltd. (56) References JP-A-63-237044 (JP, A) JP-A-60-108913 (JP, A) JP-A-2-246780 (JP, A) JP-A-2-290087 (JP, A) JP-A-63-2026 (JP, A) Japanese Utility Model Application Sho-63-199234 (JP) , U) Fully open sho 61-117263 (JP, U) Fully open sho 59-132659 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03B 9/08-9/54 H01L 41/08

Claims (3)

(57) [Claims] 1. A piezoelectric actuator that generates a mechanical displacement when a voltage is applied, mechanical means for performing an operation according to the displacement of the piezoelectric actuator, and end detecting means for detecting that the operation of the mechanical means has been completed. A voltage generating means for generating a forward-polarity voltage for causing the piezoelectric actuator to generate a mechanical displacement in a predetermined direction and a reverse-polarity voltage for generating a mechanical displacement in a direction opposite to the predetermined direction; If the end detecting means does not detect the operation end of the mechanical means within a predetermined time after applying a voltage of a polarity to the piezoelectric actuator, after applying the voltage of the opposite polarity to the piezoelectric actuator for a predetermined time, And a control unit for applying a voltage of a forward polarity. 2. The voltage generator according to claim 1, wherein the voltage generator generates a plurality of different forward-polarity voltages and the opposite-polarity voltages in the piezoelectric actuator; When the end detecting means does not detect the end of the operation of the mechanical means within a predetermined time after applying the voltage to the piezoelectric actuator, after applying the voltage of the opposite polarity to the piezoelectric actuator for a predetermined time, the predetermined voltage is applied. A driving device for a piezoelectric actuator, which applies a forward polarity voltage having a voltage value larger than a voltage value to the piezoelectric actuator. 3. The piezoelectric actuator according to claim 2, wherein the predetermined voltage value generated by the voltage generating means is a rated drive voltage value of the piezoelectric actuator, and a voltage value larger than the predetermined voltage value is a maximum allowable voltage of the piezoelectric actuator. A driving device for a piezoelectric actuator that is a driving voltage value.