JP2945093B2 - Piezo element drive circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] Piezoelectric element drive circuit An object of the present invention is to provide a piezoelectric element drive circuit which can simplify a check circuit and the like of a piezoelectric element. A first switching means for connecting a coil to the coil, supplying current from the DC power supply to the coil, and charging the piezoelectric element by a back electromotive force generated at the time, and charging the coil from the charged piezoelectric element to the coil. And a second switching means for regenerating electric energy in the DC power supply by a back electromotive force generated at that time. The first and second switching means are connected so that the terminal voltages of the elements have the same direction.

[Industrial applications]

 The present invention relates to a piezoelectric element driving circuit.

Since a piezoelectric element constitutes a capacitor in terms of a circuit, in order to repeatedly drive the piezoelectric element, it is necessary to not only apply a voltage to the piezoelectric element but also discharge the electric charge stored in the piezoelectric element. is there.

[Conventional technology]

If a resistor is connected in the driving circuit, electric energy is consumed by the resistor when charging and discharging the voltage element, and power consumption becomes extremely large.

Therefore, conventionally, as shown in FIG. 5, for example, a DC power supply 51, a coil 52, and a piezoelectric element 53 are connected in parallel, and the DC power supply 51 and the coil 52 and the coil 52 and the piezoelectric element 53 The switching elements 54 and 55 are connected in-between, and the piezoelectric element 53 is charged by the back electromotive force of the coil 52.
Electric energy is regenerated on the DC power supply 51 side (Japanese Patent Laid-Open No. 63-126285).

[Problems to be solved by the invention]

However, in the circuit as described above, the direction of the terminal voltage of the piezoelectric element 53 is opposite to the power supply voltage of the DC power supply 51.

Therefore, as shown in FIG. 5, a negative voltage is applied to the piezoelectric element 53 when viewed from the DC power supply 51 side,
If a check circuit or the like for checking the operation of 53 is to be configured, there is a disadvantage that the circuit configuration becomes extremely complicated.

In addition, for example, when driving the impact dot wire of the printer with the piezoelectric element 53, the greater the rise of the inter-terminal voltage when charging the piezoelectric element 53, the greater the printing pressure can be obtained, To do so, the current flowing through the switching element (transistor) must be increased, and there is a disadvantage that the configuration of the drive circuit becomes large.

SUMMARY OF THE INVENTION An object of the present invention is to provide a piezoelectric element drive circuit which can solve such a conventional drawback and can simplify a check circuit for a piezoelectric element and the like.

Still another object of the present invention is to provide a piezoelectric element drive circuit that can increase the voltage between terminals of a piezoelectric element quickly without increasing the circuit configuration.

[Means for solving the problem]

To achieve the above object, the piezoelectric element drive circuit of the present invention connects a coil between a DC power supply 1 and a piezoelectric element 2 as shown in FIG. A first switching means 4 for flowing a current from the DC power supply 1 to the coil 3 to charge the piezoelectric element 2 with a back electromotive force generated at that time, and a charge from the charged piezoelectric element 2 to the coil 3 A second switching means 5 for discharging and regenerating electric energy in the DC power supply 1 by the back electromotive force generated at that time.
In the piezoelectric element drive circuit provided with
The first and second switching means so that the direction of the terminal voltage of the piezoelectric element 2 becomes the same as the power supply voltage of
It is characterized by connecting 4,5.

The switching means 4 and 5 are connected in series.
Two switching elements TR1, TR2, TR3, TR4 are provided, and the coil 3 is connected between the intermediate points thereof, and one of the switching elements TR1, TR2 connected in series is connected.
May be connected in series to the DC power supply 1, and the piezoelectric element 2 may be connected in series to the other set of switching elements TR3 and TR4 connected in series. Further, the first and second switching means 4 and 5 are respectively provided with two switching elements TR1 and TR4 and TR2 and TR2 which are in an oblique positional relationship with the coil 3 interposed therebetween.
R3 may be configured.

Further, the first to fourth rectifying elements 11, 12, 13, and 14 are arranged so that a current flows in the opposite direction to the switching elements TR1, TR2, TR3, and TR4 in parallel with the switching elements TR1, TR2, TR3, and TR4. 1
4 may be connected, and the first to fourth rectifying elements 11,
One end of at least one of the rectifying elements 12, 13, and 14 may be connected in the middle of the coil 3.

The impact dot wire 50 of the printer may be driven forward and backward by the piezoelectric element 2.

[Action]

By switching the first switching means 4, a current from the DC power supply 1 flows through the coil 3,
The piezoelectric element 2 is charged by the back electromotive force generated at that time so that the direction of the terminal voltage of the piezoelectric element 2 becomes the same as the power supply voltage of the DC power supply 1.

Next, when the second switching means 5 is switched, the piezoelectric element 2 is discharged to the coil 3 and electric energy is regenerated to the DC power supply 1 by the back electromotive force generated at that time.

The current due to the back electromotive force is the switching elements TR1, TR2, TR
3, flows through rectifiers 11, 12, 13, 14 connected in parallel to TR4.

If at least one of the rectifying elements 11, 12, 13, and 14 is connected in the middle of the coil 3, the rising and falling speeds of the voltage between the terminals of the piezoelectric element 2 can be changed.

〔Example〕

 Embodiments will be described with reference to the drawings.

 The first shows a first embodiment of the present invention.

In the figure, 1 is a DC power supply, 2 is a piezoelectric element, and one end of each is grounded. The ground potential is, for example, 0 volt.

A coil 3 is connected between the DC power supply 1 and the piezoelectric element 2, and four switching transistors TR1, TR2, TR3, TR for turning on / off a current flowing through the coil 3
4 are provided.

These switching transistors TR1, TR2, TR3, TR4
Are connected in an H-shape with the coil 3 interposed therebetween. That is, the first and second switching transistors TR connected in series
1, TR2 and third and fourth switching transistors TR3, TR4 connected in series are provided, and a coil 3 is connected to an intermediate point between them. The DC power supply 1 is applied to one of the series-connected switching transistors TR1 and TR2.
Are connected in series, and the other set of switching transistors
The piezoelectric element 2 is connected in series to TR3 and TR4.

In addition, each switching transistor TR1, TR2, TR3, TR4
Are connected in parallel with diodes 11, 12, 13, and 14 for rectifying in the direction opposite to the current direction.

6 is each switching transistor TR1, TR2, TR3, TR4
Is a control unit for controlling the switching operation of the two switching transistors TR1 in an oblique positional relationship with the coil 3 interposed therebetween by an output signal from the control unit 6.
And the switching transistor TR4 (first switching means 4) are simultaneously turned on / off, and the switching transistor TR2 and the switching transistor TR3 (second switching means 5) are turned on / off simultaneously.

Next, the operation of the above embodiment will be described with reference to the time chart of FIG.

For example, in a case where the piezoelectric element 2 is used to drive an impact dot wire of a printer, for example, a print pulse is input to the control unit 6 from an upper circuit (not shown).

Thereby, first, the first and fourth switching transistors TR1 and TR4 (first switching means 4) are turned on for a time t. As a result, a current _IL flows through the coil 3, and the first and fourth switching transistors TR1, TR4
Immediately before turning off, I _L = t · V / L.

Of course, the first and fourth switching transistors TR
1, The same amount of current flows in TR4.

Here, V is the voltage of the DC power supply 1. L is the inductance of the coil 3.

In this manner, the electromagnetic energy is stored in the coil 3, and the first and fourth switching transistors TR1, TR4
Simultaneously with the (first switching means 4) off, the counter electromotive force generated in the coil 3, the current I _c toward the piezoelectric element 2 through the second and third diodes 12 and 13 flows The piezoelectric element 2 is charged by the electromagnetic energy stored in the coil 3.

At this time, the voltage V _c charged in the piezoelectric element 2 is And the startup time for charging is Here, C is the capacitance of the piezoelectric element 2.

At this time, the terminal voltage of the piezoelectric element 2 has the same direction as the power supply voltage of the DC power supply 1. That is, assuming that the ground potential is 0 volt, the non-grounded terminal has a positive voltage for both the DC power supply 1 and the piezoelectric element 2 (for example, +40 volts for the DC power supply 1 and +120 volts for the piezoelectric element 2).

Next, the second and third switching transistors TR
2. When TR3 (second switching means 5) is turned on,
The first and fourth coils are discharged from the piezoelectric element 2 to the coil 3 by the back electromotive force generated in the coil 3 simultaneously with turning off the second and third switching transistors TR2 and TR3.
A current flows from the coil 3 to the DC power supply 1 through the diodes 11 and 14, and electric energy is regenerated to the DC power supply 1. Thus, the electric energy stored in the piezoelectric element 2 is regenerated to the DC power supply 1 via the coil 3.

FIG. 3 shows a second embodiment of the present invention, in which one end of a second diode 12 is connected to the middle of the coil 3 using an intermediate tap, and the other parts are the same as those of the first embodiment. Same as the example.

According to this structure, the inductance L ₁ in the circuit for charging the piezoelectric element 2 is smaller than the inductance L of the coil 3 the full length, the rise time of the charging Is compared with the case of the first embodiment. Becomes

On the other hand, the first and fourth switching transistors TR1,
The magnitude of the current I _L flowing through TR4 is the same as that in the case of the first embodiment.

As described above, in the second embodiment, when charging the piezoelectric element 2, the first and fourth switching transistors are used.
The rise time of the voltage between the terminals of the piezoelectric element 2 can be reduced without increasing the value of the current flowing through TR1 and TR4.

However, one end of the third diode 13 may be connected in the middle of the coil 3 or the second and third diodes 12, 1
The same effect can be obtained by connecting both ends of the coil 3 in the middle of the coil. Similarly, if the first or fourth diode 11, 14 is connected in the middle of the coil 3, the piezoelectric element
The fall time of the terminal voltage can be changed.

Therefore, by changing the size of the coil 3 and the connection position of each of the diodes 11, 12, 13, 14 with respect to the coil 3, the charging time of the electromagnetic energy to the coil 3, the size of the current flowing through the switching transistor at that time, and the electromagnetic energy discharge The time and the magnitude of the discharge current, the charging time and the discharging time of the piezoelectric element, and the like can be arbitrarily changed.

The piezoelectric element 2 driven by the drive circuit of the present invention
For example, as shown in FIG. 4, it can be used to drive an impact dot wire 50 of a printer.

As the piezoelectric element 2 in such a case, a stacked type in which many piezoelectric elements 2 are stacked is used. Then, the end of the piezoelectric element 2 is connected to an intermediate portion of the movable arm 51 to which the wire 50 is connected at the tip. As a result, the amount of expansion / contraction e of the piezoelectric element 2 is increased, and the amount of advance / retreat f of the wire 50 is obtained.
Impact printing can be performed at the tip of the printer.

Although five wires 50 are shown in FIG. 4, generally, 24 wires 50 are incorporated in the print head, and each of them is driven by the piezoelectric element 2.

〔The invention's effect〕

According to the piezoelectric element drive circuit of the present invention, not only can the electric energy stored in the piezoelectric element by charging be efficiently regenerated to the DC power supply, but also the terminal voltage of the piezoelectric element with respect to the power supply voltage of the DC power supply The piezoelectric element can be charged in the same direction, so that a positive potential can be directly obtained from the terminal of the piezoelectric element, and a check circuit and the like for checking the state of the piezoelectric element can be easily configured. be able to.

If the rectifying element is connected in the middle of the coil, the rise time of the voltage between the terminals of the piezoelectric element can be shortened without increasing the current flowing through the switching element, and a small, high-performance piezoelectric element can be obtained. For example, various characteristics of the piezoelectric element drive circuit can be arbitrarily changed.

[Brief description of the drawings]

 FIG. 1 is a circuit diagram of the first embodiment, FIG. 2 is a time chart of the first embodiment, FIG. 3 is a circuit diagram of the second embodiment, and FIG. And FIG. 5 is a circuit diagram of a conventional example. In the figure, 1 ... DC current, 2 ... Piezoelectric element, 3 ... Coil, 4 ... First switching means, 5 ... Second switching means.

Claims (6)

(57) [Claims] 1. A coil (3) is connected between a DC power supply (1) and a piezoelectric element (2), and a current flows from the DC power supply (1) to the coil (3). First switching means (4) for charging the piezoelectric element (2) by a back electromotive force; and discharging the coil (3) from the charged piezoelectric element (2) to generate a reverse current generated at that time. A piezoelectric element driving circuit provided with a second switching means (5) for regenerating electric energy in the DC power supply (1) by an electromotive force, wherein the piezoelectric element is driven by a power supply voltage of the DC power supply (1). (2) The piezoelectric element drive circuit, wherein the first and second switching means (4, 5) are connected so that the terminal voltage directions are the same. 2. The switching means (4, 5) includes two switching elements (TR1, TR2), (TR3, TR2) connected in series.
4), the coil (3) is connected between the intermediate points thereof, and the DC power supply (1) is connected to one of the switching elements (TR1, TR2) connected in series.
2. The piezoelectric element drive circuit according to claim 1, wherein the piezoelectric elements are connected in series, and the piezoelectric elements are connected in series to the other set of switching elements connected in series. 3. The first and second switching means (4, 4).
5) are two switching elements (TR1, TR4), (TR2, TR4), which are in an oblique positional relationship with respect to the coil (3).
3. The piezoelectric element driving circuit according to claim 2, wherein the driving circuit comprises: 4. The switching element (TR1, TR2, TR3, TR
In parallel with 4), each switching element (TR1, TR2, TR3, TR4)
4. The piezoelectric element driving circuit according to claim 2, wherein the first to fourth rectifying elements (11, 12, 13, 14) are connected so that a current flows in a direction opposite to the direction in which the current flows. 5. The first to fourth rectifiers (11, 12, 1).
5. The piezoelectric element drive circuit according to claim 4, wherein one end of at least one of the rectifying elements of (3, 14) is connected in the middle of the coil (3). 6. An impact dot wire (50) of a printer is driven forward and backward by said piezoelectric element (2).
The piezoelectric element drive circuit according to 1, 2, 3, 4, or 5.