JPS6012523A - Driving circuit of piezoelectric action element - Google Patents

Abstract

PURPOSE:To simplify a constitution of a circuit by utilizing a residual displacement of a piezoelectric action element, and switching and setting it to two positions by a temporary voltage generated in the secondary side of a boosting transformer as a capacitor is charged and discharged. CONSTITUTION:An electrode terminal of a piezoelectric action element 3 is connected between both terminals of a secondary coil 2b of a boosting transformer 2, a capacitor 4 is connected in series to a primary coil 2a, a charge control of the capacitor 4 is executed by executing an off-on control of a feeding path 6 for connecting the series connecting part of the primary coil 2a and the capacitor 4, and a DC power source 5 by a charge controlling circuit 7, and on the other hand, a discharge control of the capacitor 4 is executed by other discharge controlling circuit part 8. In this way, when charging the capacitor 4, the piezoelectric action element 3 is displaced to the first direction by a voltage boosted to the secondary coil 2b, and when discharging the capacitor 4, said element is displaced to the opposite second direction.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a drive circuit for a piezoelectric element (trade name: Bimorph) used as an actuator that converts applied voltage into mechanical displacement.

Prior Art The piezoelectric element described above is a type of electrostrictive element that can utilize the deflection displacement generated by applying a voltage to a place where mechanical displacement is required. One use of this element is proposed in Japanese Patent Laid-Open No. 57-92321, in which it is used in a focusing control mechanism for a photographic lens of a camera.

The relationship between the applied voltage and the displacement of the piezoelectric element is as shown in FIG. The displacement at the end tiO is about 3 . Furthermore, if a DC voltage of 150 V is applied in the opposite direction, a displacement of about 0.3 volts will also occur in the opposite direction.

In this way, piezoelectric elements require a relatively high applied voltage of 150V to obtain a small displacement of about 0.3 m, making them difficult to apply to devices such as cameras that use small, low-voltage batteries as power sources. When this type of piezoelectric element is used, there is a risk that a drive circuit for obtaining a high voltage for driving the displacement of the piezoelectric element from a low voltage power source may become large.

Particularly in the case of a configuration with space constraints such as a small camera, it is essential to keep the drive circuit of the piezoelectric element small.

Purpose This invention aims to provide a piezoelectric element drive circuit suitable for using a piezoelectric element in a compact structure such as a camera.

Embodiment An embodiment of the piezoelectric element driving circuit of the present invention will be described below with reference to FIGS. 2 to 4.

This piezoelectric element driving circuit drives the piezoelectric element used in the photographing distance range switching mechanism of the camera, and is used to drive the piezoelectric element used in the photographing distance range switching mechanism of the camera. The electrode terminal of the piezoelectric element 3 is connected between both terminals of the coil 2b, and the capacitor 4 is connected in series with the primary coil 2a of the step-up transformer 2.
The charging control circuit section 7 controls the charging control of the capacitor 4 by controlling the power supply line 6 connecting the series connection section of the capacitor 4 and the DC power source 5 to the DC power source 5. This is designed to control the discharge of the capacitor 4. As a result, the charging voltage of the capacitor 4 is increased due to the charging current flowing through the secondary coil 2a, and this voltage causes the piezoelectric element 3 to be displaced in the first direction. . Conversely, when capacitor 4 is discharged,
A boost voltage in the opposite direction to that during charging is generated in the secondary coil 2b,
This reverse voltage causes the piezoelectric element 3 to be displaced in a second direction opposite to the first direction.

The charging control circuit section 7 consists of a transistor 9.10111 and a resistor 12+13+14, and a transistor 911.
The resistor 12, the transistor 11, and the resistor 13 constitute a base circuit of the transistor 90, while the resistor 14 constitutes the base circuit of the transistor 10.

The discharge control circuit section 8 includes a transistor 15 and a resistor 16 that constitute a discharge path connecting one end of the series connection between the capacitor 4 and the primary coil 2a and the ground, and another circuit that connects the other end of the series connection and the ground. Discharge -5 = transistor 17118 and resistor 19.
It consists of 20.

FIG. 3 shows a photographing distance range switching mechanism of a camera incorporating the piezoelectric element 3. By selectively overlapping another auxiliary lens 22 with the photographing lens 21, the closest distance that can be photographed is taken. The settings are changed to be shorter than when the lens 21 is used alone, so that photography can be performed at an even shorter distance.

The auxiliary lens 22 is attached to one end of the lever 23 so that the rotation range of the auxiliary lens 22 overlaps with the arrangement of the photographing lens 21. The lever 23 is rotatable about a shaft 24, is biased clockwise by a spring 25, and is provided with an engaging pawl 26 with which the tip 3a of the piezoelectric element 3 is engaged.

6- Separately, a holding lever 2B is provided on the rear side of the lever 23 and is rotatable around a shaft 27.
A locking pin 29 provided at 8 receives the rear end of the lever 23 to restrict clockwise rotation of the lever 23, while a concave curved portion 23& is formed at the rear of the lever 23, When the holding lever 28 rotates counterclockwise from the state shown in FIG. 3 in the counterclockwise direction indicated by the arrow P1 in the figure and the locking pin 29 comes to a position facing the recessed portion 23a, the locking pin 29 engages the lever. 23 is released from the clockwise rotation restriction. The lever 23 comes into contact with the pin 30 and stops at a predetermined rotational position where the auxiliary lens 22 is retracted in the direction indicated by arrow P2 from the position where it overlaps with the photographing lens 21. At the time of release, the lens is rotated counterclockwise by a mechanism (not shown) by a predetermined angle to come into contact with a pin 31 shown in FIG. 3, and after exposure is completed, it returns to the original position shown in the same drawing.

Next, the operation of this piezoelectric element drive circuit will be explained.

The voltage of the DC power supply 5 is set to 3V, and the turns ratio between the primary coil 2a and the secondary coil 2b of the step-up transformer 2 is -
It is determined that a secondary voltage of 150V can be taken out for a secondary voltage of 3.

When an H signal (high voltage, e.g., 3 cm below the power supply voltage) corresponding to a charging command is input from the control terminal 7a of the charging control circuit section 70, the base potential of the transistor 11 rises via the resistor 13, and the transistor 11 Conduction becomes possible. As the transistor 11 becomes conductive, the base potential of the transistor 9 drops, and the transistor 9 becomes conductive. On the other hand, the H signal input from the control terminal 7a is applied to the base of the transistor 10 via the resistor 14, and the transistor 10 also becomes conductive. As a result, a charging current flows from the DC power source 5 to the capacitor 4 and the primary coil 2a, and a step-up voltage of 150V is generated in the secondary coil 2'E, causing the piezoelectric element 3 to move in the first direction, that is, at its tip in FIG. When the shutter button is pressed in the above state in which the lever 23 is unlocked by the piezoelectric element 3, the holding lever 28
is rotated counterclockwise from the position shown in Fig. 3, and the locking pin 2 is
9 is released, the lever 239- is rotated clockwise by the bias of the spring 25, and the auxiliary lens 22 is moved from the photographing lens 2.
The camera moves away from the position where it overlaps with lens 1, and photography is performed using the photography lens 21 alone. When the exposure is completed, the holding lever 28
returns to the original position shown in FIG. A voltage (for example, the power supply voltage of 3V) is input.

This causes resistor 16' (through i7 to transistor 15).
The 0 base potential rises and the transistor 15 becomes conductive. At the same time, the base potential of the transistor 18 rises via the resistor 20, making the transistor 18 conductive, and the base potential of the transistor 17 drops via the resistor 19, so that the transistor 17 also becomes conductive. As a precaution, a discharge path is formed by the conduction of the transistors 15, 17, and 18, and the discharge of the capacitor 4 is started and the primary coil 2a is
A discharge current begins to flow. As a result, a boosted voltage of 150V is generated in the secondary coil 2b in the opposite direction to that during charging, and the piezoelectric element 3 is oriented in the second direction, that is, in the second direction, where the tip 3a is engaged with the engaging claw 26 of the lever 23. Displace to the locking position shown in Figure 3.

The boosted voltage applied to the piezoelectric element 3 by the charge control and discharge control of the capacitor 4 is temporary, but since the piezoelectric element 3 has hysteresis characteristics as shown in FIG. is maintained until the next applied voltage of opposite polarity is applied.

The hysteresis characteristic shown in Fig. 4 shows that the length of the vibrating piece is 20
This is a case where a DC voltage of about 150V is applied to a piezoelectric element with the polarity changed sequentially, and the applied voltage is E+15.
Under 0'V, the displacement of the piezoelectric element is +0.3 as shown by A in the figure. Even if the voltage applied to the piezoelectric element is removed from state A, the displacement does not return to 0, and B
As shown in , a residual displacement (hysteresis) dt of about +0.1 m occurs. From this state B, when the polarity is reversed from the previous case, that is, when the full DC voltage of -150V is applied, the displacement of the piezoelectric element becomes -0.3M, as shown by 0 in the figure. Even if the applied voltage is returned to O from this state 'ftT4a, the displacement does not return to O, and a residual displacement d2 of about -0.2 wn occurs as shown by D in the figure. If a DC voltage of +150V is further applied from the state, the displacement is +Q, 3m (returns to state A shown in i7).

As is clear from the above hysteresis characteristics, when a voltage is temporarily applied to the piezoelectric element 3 as the capacitor 4 is charged and discharged in the drive circuit described above, the residual displacement during charging is +0.
1 m, and the residual displacement during discharge is about -0.2 m. That is, the tip portion 3a of the piezoelectric element 3 can be switched between two positions with an interval of 0.3 cm by only temporarily applying the voltage without maintaining the applied voltage.

In the previous operation of the drive circuit, the control terminal 7a.

Inputting a charging command and a discharging command to 8a corresponds to the withdrawal of the auxiliary lens 22 from the position where it overlaps with the photographing lens 21 and the return to the overlapping position, but generation of such command signals may not be separately incorporated into the camera. Based on the detection result of the automatic distance measuring device, that is, based on the detection result of detecting whether the subject distance is greater than the closest distance of the photographing lens 21, automatic control is performed according to the subject distance. It is possible to perform a retracting operation of the auxiliary lens 22 at the same time. In this case, for example, at the first pressing stage of the shutter button, an automatic distance measuring device is operated to determine the distance, and if the subject distance is greater than a predetermined value, an H signal is applied to the control terminal 7a. Displaces the piezoelectric element 3 upward and engages the engaging claw 2.
After the exposure is completed, release the locking state with the holding lever 28.
When the piezoelectric element 3'Jfr returns to the state shown in FIG. 3, an H signal may be applied to the control terminal 8a to displace the piezoelectric element 3'Jfr to its original locking position. In this case, if the subject distance is determined to be smaller than the predetermined value,
The piezoelectric element 3 is not driven.

The above is an example in which a piezoelectric element is incorporated into the photographing distance range switching mechanism, but the piezoelectric element may also be applied to a mechanical part in which an electromagnet is normally used in a camera. The driving circuit described above can be similarly used for driving it.

Effects According to the piezoelectric element drive circuit of the present invention, a step-up transformer is connected to the secondary side of the piezoelectric element capable of obtaining mechanical displacement according to an applied voltage, and a charger is connected in series to the primary side of the step-up transformer. Since it has a discharging capacitor, a charging control means for supplying a charging current to the charging/discharging capacitor, and a discharging control means for discharging the charge of the charging/discharging capacitor, the voltage generated on the secondary side of the step-up transformer as the capacitor is charged and discharged is By applying a temporary voltage, it is possible to switch and set the piezoelectric element between two positions using the residual displacement of the piezoelectric element. The circuit configuration for driving the element is simplified, and it is possible to provide reliable displacement to the piezoelectric element, and it can be easily installed in structures that do not have much space, such as small cameras, and is inexpensive. It is also possible to reduce the

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing the characteristics of the piezoelectric element, Fig. 2 is a circuit diagram showing an embodiment of the present invention, and Fig. 3 is a perspective view of the photographing distance range switching mechanism of a camera incorporating the piezoelectric element. , FIG. 4 is an explanatory diagram showing the hysteresis characteristics of the piezoelectric element. 2...Step-up transformer, 2a...-secondary coil, 2b...
...Secondary coil, 3...Piezoelectric element, 4...Capacitor, 5-pin DC power supply, 6...Power supply path, 7...Charge control circuit section, 8...Discharge control circuit section application People Minolta Camera Co., Ltd. 17- Figure 1 JP-A-11FFGO-12523 (6) Figure 2 Figure 3

Claims (1)

[Claims] A step-up transformer has a piezoelectric element connected to its secondary side that can obtain mechanical displacement according to an applied voltage, a charge-discharge capacitor connected in series to the primary side of the step-up transformer, and a charging current to the charge-discharge capacitor. A piezoelectric element drive circuit having a charge control means for supplying charge and a discharge control means for discharging the charge charged in a charge/discharge capacitor.