JPH04284430A - Driving device for piezoelectric actuator - Google Patents

Abstract

PURPOSE:To obtain a large displacement quantity even with low power consumption by applying a voltage to the piezoelectric actuator reversely and then applying a forward voltage. CONSTITUTION:A machine means operates according to the displacement of the piezoelectric actuator 1 which causes the mechanical displacement by voltage application. Before main driving, transistors(TR) Q11 and Q12 are turned ON to apply the opposite-polarity potential from a TR Q7, and then the piezoelectric actuator 1 is driven reversely. Consequently, the piezoelectric actuator 1 is displaced in the reverse direction to contract. Then the main driving is performed through TRs Q5 and Q9 right after said contraction. The piezoelectric actuator 1 is displaced in the reverse direction from a stationary point, so the acceleration increases and the large displacement quantity is obtained, so that the force driving the machine means increases.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric actuator that is extremely effective for use in cameras.

0002

2. Description of the Related Art Piezoelectric elements called piezoelectric actuators have been used for converting electrical signals into mechanical displacement. This piezoelectric element has a multi-layered structure of thin ceramic substrates made of piezoelectric material with a piezoelectric effect. When a voltage of about 100 volts is applied between two electrodes, it expands and contracts depending on the polarity of the voltage. has the property of changing. Although the amount of displacement at this time is relatively small at several tens of microns, the piezoelectric element can generate a large force of several tens of kilograms considering its volume, so it is attracting attention as an electromechanical transducer in small devices such as cameras.

0003

[Problem to be Solved by the Invention] A piezoelectric actuator having the above-mentioned characteristics is capable of controlling a mechanical system with its displacement force by utilizing the expansion or contraction of the piezoelectric actuator when a rated voltage is applied from a state where no voltage is applied. However, there are limits to the amount of displacement and displacement acceleration that can be used, and this has not been sufficient for widespread use in driving mechanical systems. In addition, piezoelectric actuators require a certain amount of time from the time a voltage is applied until the end of displacement due to their mechanical inertia, resulting in a problem that the response is inevitably slow. Furthermore, since the piezoelectric actuator is a capacitor in terms of equivalent circuit, a large current flows when voltage is applied. However, if the applied voltage is increased in order to increase the amount of displacement of the piezoelectric actuator, this current also increases, leading to an increase in power consumption. do. When applying a piezoelectric actuator to a camera, the camera already has a built-in large-capacity electrical load for strobe light emission, backlight source for LCD display, etc., so if the electrical load is increased significantly, Since this would shorten the life of the battery, it has been desired to develop a piezoelectric actuator that consumes less power but has a larger amount of displacement.

0004

[Means for Solving the Problems] Mechanical means that operates according to the displacement of a piezoelectric actuator that generates mechanical displacement when a voltage is applied is provided, and forward voltage generating means that generates a voltage of a predetermined polarity; a reverse voltage generating means that generates a voltage of opposite polarity to the voltage of the voltage generating means; and a control means that applies the voltage generated by the forward voltage generating means to the piezoelectric actuator after applying the voltage generated by the reverse voltage generating means to the piezoelectric actuator. It has been established.

[0005]

[Operation] A reverse polarity voltage is applied to the piezoelectric actuator to displace the piezoelectric actuator in a direction opposite to the operating direction, and then a forward polarity voltage is applied to displace the piezoelectric actuator in the operating direction. Since the piezoelectric actuator is displaced from the opposite direction, the acceleration is large, and a larger displacement amount than before can be obtained.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram of an electric circuit including a piezoelectric actuator driving device of the present invention, and FIG. 2 is a perspective view illustrating a mechanical configuration when a piezoelectric actuator is used to drive a camera shutter. In order to understand the operation of the piezoelectric actuator, FIG. 2 will first be explained. In FIG. 2, the piezoelectric actuators 1 and 2 are the shutter front curtain 17,
It is used to control the opening start of the rear curtain 37,
The figure shows the state before the front curtain is opened. The actuator 1 is fixed to a fixed member 3, and a lever 4 is brought into contact with an end surface of the fixed member 3 by a spring 5. The lever 4 is rotatably supported around a rotating shaft 6 together with a pin 7 provided thereon. A lever 8 rotatable about a shaft 9 is biased by a spring 10, and one end of the lever 8 can come into contact with the pin 7.
Rotation of the other lever 11 is prohibited at the other end. Lever 1
1 is rotatable around a shaft 13, and is normally biased by a spring 12, but its rotation is restricted by the other end of the lever 8. A pin 14 on the lever 11 is a member that directly controls the operation of a shutter front curtain 17, and the front curtain 17 covers a film surface (not shown) using a known method. A lever 15 provided in the middle of the pin 14 is located at a position where a switch 16 can be turned on and off. In this case, switch 16 is in an off state.

On the other hand, the other actuator 2 is a fixed member 2
3, and a lever 24 is abutted on the end surface by a spring 25. The lever 24 is rotatably supported around a rotating shaft 26 together with a pin 27 provided below. A lever 28 rotatable about a shaft 29 is biased by a spring 30, and one end of the lever 28 can come into contact with the pin 27, while the other end prohibits rotation of the other lever 31. The lever 31 is rotatable about a shaft 33 and is normally biased by a spring 32, but its rotation is restricted 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 trailing curtain 37 is retracted from the film surface (not shown) using a known method. A lever 35 provided at the end of the pin 34 is located at a position where a switch 36 can be turned on and off. In this case, switch 36 is in an off state.

The exposure operation for controlling the shutter rear curtain 17 and front shutter curtain 37 is performed as follows. First, when the actuator 1 is energized and operated, its length extends in the longitudinal direction (upper right), and the force of the displacement is transmitted to the lever 4. The lever 4 rotates clockwise around the rotation axis 6 against the spring 5 (
(clockwise), and the pin 7 causes the lever 8 to rotate to the left (counterclockwise) about the rotating shaft 9 against the spring 10. Then, the lever 11, whose rotation due to the restoring force of the spring 12 was previously prohibited by the other end of the lever 8, moves to the rotation shaft 13.
The pin 14 also rotates around the rotating shaft 13 and moves to the upper right. The front curtain 17 then travels in the upper right direction indicated by the arrow and starts exposure. At this time, the switch 16 is turned on by the lever 15 at the same time as the front curtain 17 is opened.

As described above, when the timing to close the shutter rear curtain 37 comes after a predetermined period of time after the front curtain 17 has been opened, the actuator 2 is first energized. Then, its length extends in the longitudinal direction (upper left), and the force due to the displacement is transmitted to the lever 24. The lever 24 is rotated to the left about the rotation shaft 26 against the spring 25, and the lever 28 is rotated to the right about the rotation shaft 29 by the pin 27 against the spring 30. Then, the lever 31, whose rotation due to the restoring force of the spring 32 was previously prohibited by the other end of the lever 28,
However, this prohibition is canceled and the pin 34 rotates to the left about the rotating shaft 33 and moves upward and to the right. With this, the second act 37
Similarly to the front curtain 17, it travels toward the upper right and ends the exposure. At this time, the switch 36 is turned on by the lever 35 at the same time as the trailing curtain 37 is opened. As described above, the film exposure operation by the shutter front curtain 17 and rear shutter curtain 37 is completed.
This is possible by monitoring the status of 6 and 36.

Next, an electric circuit for driving a piezoelectric actuator will be explained with reference to FIG. Battery 40 supplies power to power supply circuits P1, P2, and P3. Power supply circuit P
The power supply circuit P2 outputs a voltage of about 5V and is used as a voltage for the control circuit including the CPU, and the power supply circuit P2 outputs a voltage of about 100V and is used to drive the actuators 1 and 2 and the lamp 43 for illuminating the liquid crystal display during normal operation. , power supply circuit P3 is 2
An emergency actuator 1 that outputs a voltage of about 00V,
2 It is also used to drive the strobe light emitting tube 44. The operation of the power supply circuit P1 is controlled by a half-press switch 41 that is turned on in conjunction with a shutter button (not shown) of the camera, and a transistor Q1 that is driven by the CPU. Here, the on/off state of the switch 41 is also transmitted to the CPU so that its operating state can be grasped. Further, a diode D1 is inserted between the transistor Q1 and the switch 41 to determine whether the transistor Q1 is on or the switch 41 is on. With this configuration, you can take your hand off the shutter button and press the switch 41.
Even after the transistor Q1 is turned off, the transistor Q1 remains on for a certain period of time, extending the operation of the camera. The above configuration is publicly known. The operations of power supply circuits P2 and P3 are controlled by transistors Q2 and Q3 driven by the CPU, respectively.

Further, circuit blocks having the following input/output functions are connected to the CPU. Photometric circuit LM
A subject brightness signal is input to the CPU. The display circuit DSP visually or audibly outputs shutter time information to be controlled and various warning signals in response to signals from the CPU so that the photographer can judge them. The aperture control circuit AP controls the aperture in the lens so that the aperture becomes an appropriate aperture based on a signal from the CPU. 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 inside the camera and transmits the signal to the CPU. In this case, the humidity sensor may be located at a position where the humidity of the piezoelectric actuator itself provided inside the camera can be determined, but ideally, if it is bonded to the actuator, the humidity can be detected with high accuracy. The switch group SW includes a release switch for issuing an exposure start command in conjunction with the shutter button, a switch for detecting the completion of film winding, the aforementioned trailing curtain/front curtain running completion detection switches 16 and 36, and the like. Although the wiring is omitted,
Each of the circuit blocks described above operates by being supplied with power from the power supply circuit P1.

On the other hand, power is also supplied from the power supply circuit P2 to the lighting circuit EL, and when the CPU turns on the transistor Q13, the lamp 43 serving as a backlight lights up, and the liquid crystal display in the liquid crystal display circuit DSP described above is lit. Illuminate the element. Here, since the lamp 43 is an electroluminescent lamp, the output voltage of the power supply circuit P2 is approximately 100V, and the same voltage output can be shared by the actuators 1 and 2 as described later. Furthermore, the output voltage from the power supply circuit P3 is supplied to the strobe circuit SB. Strobe light tube 44
The light emission can be made by the CPU turning on the transistor Q14 at the timing when the shutter is opened. This power output is also shared when used to drive the actuator when an abnormal situation occurs, as will be described later. The circuit blocks 46 and 47 are driving circuits for the actuators 1 and 2, respectively, but since the circuit contents are the same, the following explanation will be given only for the actuator 1, and the explanation for the actuator 2 will be omitted.

A voltage from the power supply circuit P2 is applied to the upper terminal of the actuator 1 through a transistor Q5, and a voltage from the power supply circuit P3 is applied through a transistor Q6. Also C
It is grounded through a transistor Q11 directly driven by the PU. Here, transistors Q5 and Q6 are respectively CPU
It is controlled by transistors Q8 and Q10 driven by. Further, the lower terminal of the actuator 1 is grounded by a transistor Q9 driven by the CPU, or a voltage from a power supply circuit P2 is applied via a transistor Q7. Here, the transistor Q7 is controlled by the transistor Q12 driven by the CPU. Furthermore, the voltage of the power supply circuit P1 is applied to the upper terminal of the actuator 1 via the transistor Q4, the diode D2, and the resistor R1, and is grounded via the resistors R2 and R3. Also, resistance R2
, R3 is applied to one input terminal of a comparator C, and compared with a 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 also prepared for the actuator 2 in the circuit 47.

The above circuit is driven as follows. First, when the power supply circuit P1 starts supplying power and the CPU starts operating, the photometry circuit LM and the film sensitivity detection circuit FM
The appropriate exposure conditions are calculated by calculating both input signals. The result is displayed on the display circuit DSP, or if the conditions are inappropriate, a warning is also issued in addition to the display. At the same time, the power supply circuits P2 and P3 are operated to generate two types of high voltages, and the illumination lamp 43 for the liquid crystal display element in the display circuit DSP to which the power supply circuit P2 is connected is started to be lit by turning on the transistor Q13. Further, the voltage of the power supply circuit P3 is stored in a capacitor (not shown) for operating the strobe circuit SB. Next, the humidity detection circuit HMD is activated to detect the humidity of the environment in which the actuator is placed. If the humidity is too high and operation of the piezoelectric actuator 1 is dangerous, the circuit blocks 46 and 47 may be removed as described below.
The internal transistors are driven appropriately to perform dehumidifying operation. The dehumidification operation can be performed by intermittent driving at a frequency that does not cause displacement of the actuator. Specifically, by driving the transistor Q5 to apply a voltage, and then driving the transistor Q11 to discharge the accumulated charge, this operation is repeated at a constant frequency to generate heat inside and release the accumulated moisture. It is from.

Next, it is determined whether the actuator is normal. This can be done by turning on the transistor Q4 and applying the voltage of the power supply circuit P1 to the actuator, dividing the voltage generated at its terminals by resistors R2 and R3, and comparing it with the voltage source 45 by a 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 applied to the diode D2 and the resistors R1 and R2.
, R3 is applied to the comparator C as a higher partial voltage output. On the other hand, if the piezoelectric actuator 1 has dielectric breakdown due to driving in a humid environment, the upper terminal of the piezoelectric actuator 1 is equivalently grounded, so when the transistor Q4 is turned on, the resistance R
Since the midpoint between R1 and R2 is grounded, the voltage applied to the comparator C becomes considerably lower than that in normal conditions. Here, when driving the piezoelectric actuator 1 as described later, the diode D2 may cause the high voltage from the power supply circuit P2 when the transistor Q5 is turned on to apply a voltage in the opposite direction to the transistor Q4 and destroy it, or cause the power supply circuit P1 to This is to prevent the water from flowing backwards and destroying it. Further, the resistor R1 is not required during normal operation, but is provided to prevent the transistor Q4 and the diode D2 from being directly grounded and causing thermal breakdown when the actuator 1 has dielectric breakdown.

By the way, the surge absorber 42 connected in parallel to the actuator 1 has the function of preventing the high voltage that the piezoelectric actuator 1 generates and outputs from having an adverse effect on the peripheral circuitry during normal operation. surge absorber 4
2 acts as an infinite resistance (impedance) until the voltage applied between the terminals is up to several hundred V, and when a voltage higher than that is applied, the resistance (impedance) decreases and causes a short circuit. It is. Such a surge absorber 42 does not normally have any 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, it short-circuits and absorbs the voltage. This can prevent elements such as the transistor Q4, which cannot be expected to withstand a voltage of tens of thousands of volts, from being destroyed by high voltage.

Furthermore, charges may be accumulated on both electrodes of the piezoelectric actuator 1 due to the pyroelectric effect due to infrared rays caused by heat. The operation for absorbing the voltage generated by this pyroelectric effect is as follows. When the release switch, which commands the start of exposure in conjunction with the shutter button, is detected to be on, both transistors Q9 and Q11 are first turned on. With this, the electric charge due to the pyroelectric effect generated in the piezoelectric actuator 1 is transferred to the transistors Q9 and Q.
It disappears within 11. Such a pyroelectric charge absorption routine is not necessary only during the release routine, but may be executed periodically, such as during film winding, immediately after the start of operation of the power supply circuit P1, and immediately before the end of operation. Also,
The base drive current of transistors Q9 and Q11 is
If there is no problem with consumption of the piezoelectric actuator 1, it may be kept short-circuited at all times during the time when the power supply circuit P1 is in operation and the piezoelectric actuator 1 is not driven. Here, when the generated voltage is high, it is possible that an excessive current flows into both transistors when short-circuited by transistors Q9 and Q11, resulting in thermal destruction.
A small resistor may be connected in series with the piezoelectric actuator 1 to the collector side of the piezoelectric actuator 1. The actuator is normally driven as follows following the short-circuiting operation by the transistors Q9 and Q11 as described above. transistor Q
8 is turned on and high voltage from the power supply circuit P2 is applied to the upper terminal of the actuator by the transistor Q5. Here, the output voltage of the power supply circuit P2 needs to be an appropriate rated voltage considering the operating specifications of the actuator. In this embodiment, a case where this rated voltage matches the driving voltage of the lamp 43 is taken as an example. Further, the reason why the piezoelectric actuator 1 is driven through the resistor R4 is to prevent thermal breakdown of the transistor Q5. Since the mechanical system uses acceleration as shown in FIG. 2, the ON time of the transistors described above can be relatively short. Due to this drive, the piezoelectric actuator 1 momentarily stretches in its longitudinal direction, generates force, and continues to operate as described in FIG. 2.

Next, due to a combination of adverse conditions such as the above-mentioned variations in the characteristics of the piezoelectric actuator 1 itself, individual differences in the output of the power supply circuit P2, and the posture of the camera, the operation of the piezoelectric actuator 1 is caused by the mechanical system shown in FIG. This section describes the circuit operation when the signal is not transmitted correctly. If the piezoelectric actuator 1 does not operate sufficiently even when the transistor Q5 applies the voltage from the power supply circuit P2, the front curtain does not run as explained in FIG. 2, and therefore the switch 16 does not turn on. . Since the switch 16 is included in the switch group SW, the CPU itself can know that driving by voltage application from the power supply circuit P2 has failed. In such a case, the voltage applied to the piezoelectric actuator 1 is slightly increased to drive it again. That is, the transistor Q10 is turned on and the output voltage of the power supply circuit P3 is applied to the piezoelectric actuator 1 via the transistor Q6. Similar to the transistor Q5, a resistor R5 is connected in series to prevent thermal breakdown of the transistor Q6. Here, the voltage used for re-driving is the maximum allowable voltage of the actuator or a voltage slightly lower than that. In other words, the voltage is applied so as not to exceed a voltage that would destroy the actuator if applied. By driving with such a voltage value, it is possible to expect the maximum amount of force and displacement of the actuator. Although this embodiment shows an example in which this voltage source is shared with the power supply for the strobe circuit SB, it goes without saying that a separately prepared voltage source may be used.

Further, a method for maximizing the amount of displacement and acceleration from the piezoelectric actuator 1, which is a technique that characterizes the present invention, may be carried out as follows. That is, just before main driving, the piezoelectric actuator 1 is reversely driven by turning on the transistors Q11 and Q12 and applying a potential of opposite polarity from the transistor Q7. As a result, the piezoelectric actuator 1 is displaced in the opposite direction and contracts. Even in this state, Figure 2
The lever 4 is actuated by the piezoelectric actuator 1 by the force of the spring 5.
Since it moves following the end face of , there is no gap. Immediately after this state, the aforementioned transistors Q5 and Q9
The main drive is performed by As a result, the amount of displacement of the actuator 1 is equivalently nearly doubled, and the generated acceleration is similarly increased, making it possible to increase the amount of displacement. This operating state will be explained later in FIG. 12 as well. Here, a thermal breakdown prevention resistor R6 is also connected in series with the transistor Q7.

FIG. 3 and subsequent figures show examples of operating programs for the CPU. In FIG. 3, while the power supply circuit P1 is operating, CP
U repeatedly executes this routine. At step 50, the output of the photometric circuit LM and the output of the film sensitivity detection circuit FM are calculated to calculate appropriate control conditions. Step 51
At this point, the power supply circuit P2 starts operating, and at the same time, the transistor Q13 is turned on to light the lamp 43. In step 52, the appropriate control conditions obtained in step 50 are displayed on the display circuit DSP. In step 53, a routine for checking the insulation state of the piezoelectric actuators 1 and 2 is executed. This detailed operation will be explained with reference to FIG. Then, in step 54, the actuator 1 as a result of step 53,
It is determined whether an insulation defect has occurred in either of the two. If an insulation failure has occurred, a warning is given in step 55 that either piezoelectric actuator 1 or 2 is abnormal. A visual method or an audible warning method using a display circuit DSP is performed. In step 56, a prohibition state is set so that the release routine does not start even if the shutter button is pressed. After this routine, the process returns to step 50 to continue displaying the calculation results and warning of abnormal conditions of the actuators 1 and 2. Also, if the insulation condition is good, step 5
At step 7, the humidity state inside the camera is detected by the humidity detection circuit HMD. If the humidity condition is good, release is permitted in step 58. The reason why permission is given here is that when the previously prohibited state at step 55 is canceled, it is necessary to reset the prohibited state to enable the exposure operation. At step 59, the power supply circuit P3 starts operating. In this way, the strobe circuit SB is prepared to emit light. In step 60, it is determined whether the release switch has been turned on using the shutter button, and if it has not been turned on, the process returns to step 50, and if the release switch has been turned on, then in step 61, the details are shown in FIG. Execute the release sequence described below. If the humidity condition is not good in step 57, the display circuit DSP issues a warning in step 62 because the humidity inside the camera is too high and it is dangerous to operate the actuators 1 and 2. At step 63, a release prohibition state is set. At step 64, a dehumidification routine is performed. The details are shown in Figure 5.
It will be explained in. After executing this routine, the process returns to step 50 and repeats the above steps. When the dehumidification is completed, the process moves to the release routine of step 61 unless the insulation condition is bad.

FIG. 4 shows details of the insulation state detection routine in step 53 of FIG. At step 70, transistor Q9 is turned on, and at step 71, transistor Q4 is turned on.
Turn on. As a result, 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 comparator C output is determined, and in step 73, it is determined whether the comparator C output has been determined reliably. This is to ensure that a certain result is obtained by repeating the process multiple times rather than making a judgment based on just one reading. Then, in step 74, the read results are stored in memory. Step 54 in FIG. 3 checks the contents of the memory stored in step 74. At step 75, transistor Q4 is turned off, and at step 76, transistor Q9 is turned off. This completes the routine for applying the output of the power supply circuit P1 to the actuator 1. Piezoelectric actuator 2
A similar routine is required for , but its details will be omitted.

FIG. 5 shows a detailed example of the dehumidification routine of step 64 of FIG. At step 80, the number of repetitions n is first set to zero. In step 81, it is determined whether the number of repetitions n exceeds a predetermined value N. At first, since the numerical value N has not been reached, the process proceeds to step 82, turns on the transistor Q9, and step 8
At step 3, transistor Q8 is turned on. transistor Q
8 also turns on the transistor Q5, and the output voltage from the power supply circuit P2 is applied to the actuator 1. In step 84, a certain delay time is provided, and voltage application to the actuator 1 is maintained for a predetermined period of time. During this time, the actuator 1 is charged with electric charge. This predetermined time is set within a range in which the actuator 1 does not make a sufficient displacement to operate the load. After the predetermined time has passed, step 8
At step 5, transistor Q8 is turned off, transistor Q5 is also turned off, and the application of the output voltage from power supply circuit P2 is completed. At step 86, transistor Q11 is turned on, thereby discharging the charge stored in actuator 1. At step 87, a certain delay time is provided to ensure discharge. This time is set to a time during which sufficient discharge is performed for the next charge. At step 88, one cycle of charging and discharging is completed, so 1 is added to the number of repetitions n. Next, in step 89, the transistor Q11 is turned off, and then the process returns to step 81. After this, repeat this operation.

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

In the above embodiment, the actuator 1 is driven in the forward direction, but it may be driven in the reverse direction. In this case, the difference from the operation in FIG. 5 is that in step 82, transistor Q11 is turned on, and in step 83, transistor Q12 is turned on and transistor Q7 is turned on.
A voltage in the opposite direction is applied to the actuator 1. After a certain time delay is performed in step 84, in step 85, transistor Q12 is turned off and transistor Q7 is turned off, and in step 86, transistor Q9 is turned on to discharge the charge stored in actuator 1. . At step 87, a certain delay time is provided, and at step 88
At step 89, 1 is added to the number of repetitions n, and at step 89, the transistor Q9 is turned off, and then the process returns to step 81. The above charge/discharge cycle operation is executed until the number of repetitions n reaches the numerical value N. When the numerical value N is reached, the process jumps to step 90 after step 81, and in step 90, the transistor Q11 is turned off, and after this, the process shown in FIG.
The process returns to step 50 and repeats the above-described process. In this example of reverse voltage application, the actuator 1 is displaced in the opposite direction to the direction in which it drives the load, so it never happens that the actuator 1 is displaced too much and drives the load, so the delay time in step 84 is can be made longer. If this time is long, sufficient heating can be achieved, so that the number of repetitions, N, can be made small.

FIGS. 6 and 7 show details of the release routine shown in step 61 of FIG. At step 95, 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 will be used only for the actuators 1 and 2 from now on. In step 96, the reflection 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, transistor Q8 is turned on, which turns on transistor Q5. At step 99, transistor Q9 is turned on. Through the above operations, 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 the switch 16 has been turned on. This is to detect whether the actuator 1 was able to correctly drive the mechanical system. If the switch 16 is not turned on, that is, if the front curtain mechanical system is not activated, the process moves to step 106. When the switch 16 is turned on, step 102
At step 100, it is determined whether or not the time measurement started at step 100 has ended.

If the time measurement has ended, from step 103 onwards, since the time measurement has reached the set value, processing for controlling the trailing curtain is executed. First, in step 103, the equivalent transistor Q8 of the leading curtain actuator 2 in the trailing curtain control circuit block 47 is turned on. This also turns on the equivalent of transistor Q5. At step 104, the transistor Q9 or equivalent is turned on, thereby energizing the actuator 2. At step 105, it is confirmed that the switch 36 is on. If the switch 36 is not turned on, that is, if the rear curtain mechanical system does not operate properly,
The process proceeds to step 111, and if the switch 36 is turned on, the process proceeds to step 125 in FIG. At step 125,
All transistors involved in driving actuators 1 and 2 are turned off, the aperture is restored in step 126, the mirror is lowered in step 127, and step 128
At , the transistor Q13 is turned on and the illumination by the lamp 43 is resumed. At step 129, since exposure of the film has been completed in the above routine, a winding routine is executed. Regarding film feeding, only the film feeding routine described above has been described. Since the rewind routine can be performed using a known method, the explanation will be omitted.

Operations in the case where the switch 16 is not turned on in step 101, that is, the front curtain mechanical system does not operate properly, are performed in steps 106 and thereafter. At step 106, transistor Q8 is turned off, transistor Q5 is also turned off, and voltage application from power supply circuit P2 is stopped. At step 107, transistor Q
10 is turned on, thereby turning on the transistor Q6 and applying the output voltage from the power supply circuit P3 to the actuator 1. As described above, the voltage application by the power supply circuit P3 is intended to maximize the amount of displacement of the actuator 1. Since the applied voltage is close to the maximum allowable rating, constant use may adversely affect the durability of the actuator, so it is used only in such emergencies. In step 108, the shutter time measurement is restarted. In step 109, it is confirmed whether the switch 16 is turned on. If the front curtain mechanical system operates correctly in the above emergency operation, the switch 16 is turned on, and the process returns to step 102 to continue the above-described process. In this case, there is no need to take any particular warning action. This is to prevent the photographer from becoming confused by giving a warning, since there may be cases where the camera does not operate accidentally due to the camera's posture or an external impact. On the other hand, if the front curtain mechanical system does not operate even with the above operations, the switch 16 does not turn on, so the process moves to step 110, where a warning that the front curtain mechanical system does not operate is issued on the display circuit DSP, and then, as shown in FIG. Proceed to step 120.

At step 120, actuator 1,
All transistors involved in drive 2 are turned off, the aperture is restored in step 121, the mirror is lowered in step 122, and the transistor Q is turned off in step 123.
13 to light up the illumination lamp 43, step 1
In step 24, in the above operation, since the front curtain is not operating, no exposure operation is performed and there is no need to carry out film feeding, so feeding is first prohibited. Then, the process returns to step 50 in FIG. 3 and a warning operation is performed.

If the trailing curtain mechanical system does not operate correctly in step 105, the process moves to the next step. Step 11
1, the transistor Q8 equivalent in the trailing curtain control circuit block 47 is turned off, thereby turning off the transistor Q5.
The corresponding product is also turned off and driving by the power supply circuit P2 is stopped. At step 112, the transistor Q10 or equivalent is turned on, which turns on the transistor Q6 or equivalent, and the output voltage from the power supply circuit P3 is applied. The reason for this is the same as the first curtain type. In step 113, it is confirmed whether the switch 36 has operated, and in step 114, it is determined that the switch 36 has been turned on, that is, although the rear curtain mechanical system has operated and exposure has been performed, steps 111, 112, and 113
Since the exposure completion timing was delayed, an operation is started to issue a warning to the effect that the shutter time has become longer and proper exposure has not been obtained. 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 issue a warning if a high-speed time is set. After this, the process moves to step 125 in FIG. 7, and the above-mentioned processing is executed. If the rear curtain mechanical system is not operated again in step 113, that is, there is an emergency situation in which the rear curtain does not close, a warning that the shutter curtain is in the open state is issued in step 115. 7, the routine described above following step 120 is executed.

FIG. 8 is an explanation of the operation characterizing the present invention. That is, this is an explanation of a method for obtaining a larger displacement amount and acceleration from the actuators 1 and 2. The steps from step 97 to step 98 in FIG. 6 are executed. In step 130, transistor Q11 is turned on, thereby grounding the upper terminal of actuator 1. In step 131, transistor Q12 is turned on, transistor Q7 is turned on, and the output voltage of power supply circuit P2 is applied to the lower terminal of actuator 1. The actuator 1 is now applied with a voltage in the opposite direction, contracts, and is displaced in the opposite direction. In step 132, this reverse voltage application state is maintained for a certain period of time. At step 133, transistor Q12 is turned off, thereby ending the application of the reverse voltage. At step 134, transistor Q11 is turned off. In the above routine, the actuator 1 is once contracted, and due to the synergistic effect with the expansion from step 98, a larger amount of displacement and acceleration can be obtained. A large amount of displacement and acceleration can be obtained for the actuator 2 by executing a similar reverse voltage application routine, but the details of that routine will be omitted.

FIG. 9 is an illustration of an example routine for improving the actuation response of an actuator. The actuator is caused to vibrate slightly at a frequency near its mechanical resonance point, and the displacement operation by the subsequent main drive is performed quickly. This routine is similar to the dehumidification routine of FIG. 5, but its frequency and operating time are different. Further, this routine is also inserted between step 98 following step 97 and executed. At step 140, first set the number of repetitions n to 0,
In step 141, it is determined whether the number of repetitions n exceeds a predetermined value N. When the number of repetitions n has not reached the numerical value N, the transistor Q9 is turned on in step 142, and the transistor Q8 is turned on and the transistor Q5 is turned on in step 143, thereby causing the actuator 1 to receive power from the power supply circuit P2. Output voltage is applied. In step 144, a certain delay time is provided to provide a time for voltage application to the actuator 1. During this time, the actuator 1 is charged with electric charge. At step 145, transistor Q8 is turned off, transistor Q5 is also turned off, and the application of the output voltage from power supply circuit P2 is completed. When transistor Q11 is turned on in step 146, the charges stored in actuator 1 are discharged. At step 147, a certain delay time is provided to ensure discharge. At step 148, since one cycle of charging and discharging has been completed, 1 is added to the number of repetitions n. At step 149, transistor Q11 is turned off,
Return to step 141.

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 141, the process jumps to step 98, and the subsequent routine is executed to control the running of the leading curtain. Among the above processes, it is important to set the charging time to a time that does not cause displacement of the actuator 1. Otherwise, even though it is a preliminary operation routine, Figure 1
This is because it causes the mechanical system to operate. Further, the repetition frequency and the number of repetitions N must be determined strictly from the response characteristics based on the resonance characteristics of the actuator used, but generally it is sufficient to drive the actuator at several kHz for several milliseconds. The above processing is the same for the actuator 2, so detailed description will be omitted.

FIGS. 10, 11, and 12 are diagrams showing the expansion and contraction conditions of the actuator 1 during each of the above routines. FIG. 10 is a diagram showing an operating situation according to the normal driving method of FIG. 6. The actuator 1 in a resting state before step 98 has a length as shown in FIG. 10(a). Then, when the output voltage of the power supply circuit P2 is applied in step 99, a displacement of A1 in the forward direction as shown in FIG. 10(b) is obtained. In addition, if the displacement amount A1 is accidentally insufficient as described above, as shown in FIG. 10(c), the power supply circuit P
3 is applied, and the larger displacement amount A2 is utilized as in step 107. As mentioned above, the feature of the mechanical system according to the present invention is that this change in length and its acceleration are used.

FIG. 11 shows the amount of displacement during the dehumidification routine of FIG. The actuator 1 in a resting state before step 82 has a length as shown in FIG. 11(a). Then, when the output voltage of the power supply circuit P2 is applied in step 83, a displacement A3 as shown in FIG. 11(b) is obtained. Here, since intermittent driving is performed, the driving voltage is removed before the displacement is completely saturated, so the displacement amount is A3 at the time of step 83 from the length before step 82, but before this length approaches A1. Then, the process moves to step 85, and the original length is restored as shown in FIG. 11(c). FIG. 12 explains the operation characterizing the present invention described in FIG. 8, and is an explanation of the case where the amount of expansion after contraction is used. As shown in FIG. 12(a), the length before step 130 is the conventional length, but at step 13
A reverse voltage is applied at B1 as shown in FIG. 12(b).
It contracts by the amount of displacement. Then, by applying a voltage in step 99, the length is expanded by the displacement amount A1 from the original length as shown in FIG. 12(c). As a result, the mechanical system uses the displacement amount added by B1 and A1, and as described above, a larger displacement amount and acceleration can be obtained.

[0035]

As described above, the present invention provides a piezoelectric actuator that generates a mechanical displacement by applying a voltage, and a mechanical means that utilizes the displacement to perform an operation. After applying
By applying a forward voltage, a larger displacement can be achieved, increasing the force driving the mechanical means,
This has the excellent effect of improving the reliability of operation.

[Brief explanation of the drawing]

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

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

FIG. 3 is a flowchart for explaining the operation of the CPU in FIG. 2;

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

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

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

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

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

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

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

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

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

[Explanation of symbols]

1, 2 Piezoelectric actuator 1
7 Shutter front curtain 37
Shutter rear curtain 46, 47
Circuit blocks P1, P2, P3 power supply circuit

Claims (1)

[Claims] 1. A piezoelectric actuator that generates mechanical displacement when a voltage is applied, mechanical means that operates according to the displacement of the piezoelectric actuator, forward voltage generation means that generates a voltage of a predetermined polarity, and Reverse voltage generation means for generating a voltage of opposite polarity to the voltage of the voltage generation means, and after applying the voltage generated by the reverse voltage generation means to the piezoelectric actuator, apply the voltage generated by the forward voltage generation means. A piezoelectric actuator drive device having a control means for controlling a piezoelectric actuator.