JPH0584935A - Driving method and driving circuit for piezoelectric element - Google Patents

Abstract

PURPOSE:To discharge a piezoelectric element actually down to zero volt in relation to a driving method and driving circuit for the piezoelectric element for making use of the piezoelectric element as an actuator by charging, discharging, expanding and contracting the piezoelectric element. CONSTITUTION:In a piezoelectric element driving circuit possessing an electric power source E, the first switch SW1 for charging a piezoelectric element Pz with positive potential of the electric power source E and the second switch SW2 for discharging the piezoelectric element Pz, the piezoelectric element Pz is discharged down to negative electric potential at the time of discharge.

Description

Detailed Description of the Invention

(Table of Contents) Industrial Application Field of the Prior Art (FIGS. 9 and 10) Problems to be Solved by the Invention Means for Solving the Problems (FIGS. 1 and 2) Working Example (a) First Example (FIG. 3 to FIG. 5) (b) Description of second embodiment (FIG. 6) (c) Description of third embodiment (FIG. 7) (d) Description of fourth embodiment (FIG. 8) (e) Description of another embodiment Effect of the invention

[0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric element driving method and a driving circuit for charging and discharging a piezoelectric element to expand and contract the piezoelectric element to use it as an actuator.
In recent years, piezoelectric elements have begun to be used as actuators for printing wires in wire dot printers, wire dot line printers, and the like.

In order to use this piezoelectric element in an actuator, it is necessary to charge the piezoelectric element, extend the piezoelectric element, and then discharge the piezoelectric element to shrink and restore the piezoelectric element. A drive circuit for charging and discharging is required. Charging this piezoelectric element is easy,
Due to the characteristics of the piezoelectric element, electric discharge may leave electric charge, and a technique for preventing this is required.

[0004]

9 and 10 are explanatory views of a conventional technique. The piezoelectric element drive circuit includes a transformer method, a totem pole method, and the like. Here, the boost-up method proposed by the present inventors will be described as an example.

As shown in FIG. 9A, in the boost-up type drive circuit, a power source E includes a charging switch (transistor) SW1, a coil L, a discharging switch (transistor) SW2, and a piezoelectric element Pz. The coils L and the piezoelectric elements Pz are connected in series to form an LC resonance circuit.

Then, diodes D1 and D2 are provided in parallel with the charging switch SW1 and the discharging switch SW2, and a grounded third switch (transistor) SW3 is provided at a connection point between the coil L and the discharging switch SW2. A clamping diode D3 whose anode side is grounded is provided.

As for the operation of this circuit, as shown in FIGS. 9B and 10, the switches SW1 and SW3 are turned on and the power source E is turned on.
-Switch SW1-coil L-Current 13 is passed through the route of switch SW3 to store electromagnetic energy in coil L, and then switch SW3 is turned off. Power supply E-Switch SW1-Coil L-Diode D2-Piezoelectric element Pz
A series resonance circuit of is formed, and the piezoelectric element Pz is charged by the accumulated electromagnetic energy and the power supply voltage.

At this time, since the piezoelectric element Pz is charged by the sum of the electromagnetic energy and the voltage of the power source E, the power source E is stepped up, and the low voltage power source E can charge the high voltage. Becomes

On the other hand, in discharging, when the switch SW2 is turned on, a series resonance circuit of the piezoelectric element Pz-switch SW2-coil L-diode D1-power source E is formed, and the charging voltage (for example, 130 V) of the piezoelectric element Pz and the power source are supplied. Due to the potential difference from the voltage (for example, 50 V), regenerative current flows to the power source side for the time of the resonance frequency according to the series resonance of LC, discharge is performed, and energy can be regenerated.

At this time, the connection point between the coil L and the switch SW2 is clamped to zero volt by the regenerative diode D3. Therefore, when the potential at the connection point becomes zero volt, the diode D3-coil L-diode D1-power supply. In the route of E, a regenerative current flows, the discharge of the piezoelectric element Pz is stopped, and the potential of the piezoelectric element Pz is set to 0 volt.

[0011]

In this way, if one end of the piezoelectric element Pz is connected to the zero volt potential, theoretically,
The piezoelectric element Pz should discharge to zero volts. However, due to the electric / mechanical energy conversion of the piezoelectric element Pz, the capacitance of the piezoelectric element Pz is unstable, and even if the charge is suddenly removed, the distortion of the piezoelectric element Pz cannot catch up, and even if the voltage is apparently zero volts, Distortion remains and the residual charge causes
As indicated by Vp in FIG. 10, a phenomenon in which a voltage (charge) remains even after discharging to a zero volt potential occurred.

For this reason, if the piezoelectric element Pz does not shrink to its original size and is used in an actuator, it will not return to its original position, which causes a problem in the wire dot printer.
There was a phenomenon that the wire was slightly left and the ink ribbon was caught.

Therefore, it is an object of the present invention to provide a driving method and a driving circuit for a piezoelectric element, which can actually discharge the piezoelectric element to zero volt. Further, the present invention is
It is an object of the present invention to provide a drive circuit of a piezoelectric element in a boost-up type drive circuit, which can actually discharge the piezoelectric element to zero volt.

[0014]

1 and 2 show the principle of the present invention. According to claim 1 of the present invention, as shown in FIG. 1A, a power source E, a first switch SW1 for charging the piezoelectric element Pz with a positive potential of the power source E, and the piezoelectric element Pz are discharged. In the piezoelectric element drive circuit having the second switch SW2 for discharging, the piezoelectric element Pz is discharged to a negative potential during the discharging.

According to a second aspect of the present invention, as shown in FIG. 1B, the power source E is provided with a first switch SW1 and a coil L.
, A second switch SW2 and a piezoelectric element Pz are connected in series, and a grounded third switch SW3 is provided at a connection point between the coil L and the second switch SW2, and the first switch SW1 and the second switch SW2
And diodes D1 and D2 in parallel, and the first switch SW1 and the third switch SW3 are closed to charge the piezoelectric element Pz and the second switch SW2.
And a resistor R is provided in series with the current regeneration diode D3 at the connection point between the coil L and the second switch SW2 in the drive circuit of the piezoelectric element that discharges the piezoelectric element Pz. The piezoelectric element Pz is discharged to a negative potential.

According to claim 3 of the present invention, as shown in FIG. 2A, a primary side circuit in which a power source E and a first switch SW1 are connected in series to a primary side winding T1 of a transformer T, and a transformer T.
The second switch SW2 and the piezoelectric element P on the secondary winding T2 of
and a secondary side circuit in which z is connected in series, the first switch SW1 is closed to charge the piezoelectric element Pz, the second switch SW2 is closed to discharge the piezoelectric element Pz. In the element drive circuit, the closing time of the second switch SW2 is lengthened to discharge the piezoelectric element Pz to a negative potential during the discharging.

According to a fourth aspect of the present invention, as shown in FIG. 2B, the first switch SW1 and the second switch SW2 are connected in series to the first power source E1, and the first switch SW1 and the second switch SW2 are connected in series. A piezoelectric element Pz is provided at the midpoint between SW1 and the second switch SW2.
In the drive circuit of the piezoelectric element, the first switch SW1 is closed to charge the piezoelectric element Pz, and the second switch SW2 is closed to discharge the piezoelectric element Pz.
A second power source E2 is provided in series with the first power source E1,
The second switch SW2 is connected to the second power source E2, and the piezoelectric element Pz is discharged to a negative potential during the discharging.

According to a fifth aspect of the present invention, as shown in FIG. 2C, the power source E is provided with a second switch SW1 and a coil L.
, A second switch SW2 and a piezoelectric element Pz are connected in series, and a grounded third switch SW3 is provided at a connection point between the coil L and the second switch SW2, and the first switch SW1 and the second switch SW2
And diodes D1 and D2 in parallel, and the first switch SW1 and the third switch SW3 are closed to charge the piezoelectric element Pz and the second switch SW2.
And a current limiting resistor R3 and a grounded fourth switch SW4 are provided at any point of the discharge route in the piezoelectric element drive circuit for discharging the piezoelectric element Pz.
At the time of the discharge, the fourth switch SW4 is closed to forcibly discharge the piezoelectric element Pz.

[0019]

According to the first to fourth aspects of the present invention, by discharging the piezoelectric element Pz to a negative potential, the piezoelectric element Pz is negatively charged, and the remaining electric charge is drawn to the negative side, and finally the piezoelectric element Pz is discharged. The potential of Pz is set to zero.

According to a second aspect of the present invention, when applied to a boost-up type drive circuit, a resistor R is provided in series with the regenerative diode D3, and the coil L and the second switch SW2 are provided.
Set the potential of the connection point with
z is discharged to a negative potential.

According to a third aspect of the present invention, when applied to a transformer type drive circuit, the second switch SW for discharging is used.
The closing time of 2 is lengthened to lengthen the discharge time by the counter electromotive voltage of the secondary side transformer T2 to discharge the piezoelectric element Pz to a negative potential.

According to a fourth aspect of the present invention, when applied to a totem pole type driving circuit, the second power source E2 is provided in series with the first power source E1, and the second power source E2 is connected to the second power source E2.
The switch SW2 is connected and the piezoelectric element Pz is connected to a negative power source to discharge the piezoelectric element Pz to a negative potential.

According to a fifth aspect of the present invention, in the boost-up type drive circuit, at any point of the discharge route,
The current limiting resistor R3 and the grounded fourth switch SW4
Is provided, the fourth switch SW4 is closed at the time of discharge, current is regenerated by the series resonance circuit, and the piezoelectric element Pz is discharged.
The electric charge that cannot be completely discharged by the regenerative current is extracted by the fourth switch SW4 so that the potential of the piezoelectric element Pz becomes zero.

[0024]

【Example】

(a) Description of First Embodiment FIG. 3 is an explanatory diagram of a printing element to which an embodiment of the present invention is applied. In FIG. 3, the print element 1 of the wire dot print head has a beam 6 supporting a print wire 7 and an armature 4 held on a base 3 by an expanding spring 5, and an actuator 2 is provided on the base 3 and the armature 4 to provide an actuator. 2, the armature 4 is rotated around the expansion spring 5 as a fulcrum to reciprocate the print wire 7 to perform dot printing.

In this actuator 2, the piezoelectric element 8 is provided between the pair of block members 9 and 10, and the compression spring member 11 is provided on the pair of block members 9 and 10 to pre-compress the piezoelectric element 8 and 8 is charged, the compressed piezoelectric element 8 is extended against the compression spring member 11, the print wire 7 is struck on the paper, the piezoelectric element 8 is discharged, the piezoelectric element 8 is contracted, and the compression hooping member 11 compresses it. Then, the printing wire 7 is returned.

FIG. 4 is a circuit diagram of the first embodiment of the present invention, showing a boost-up type drive circuit, and FIG.
FIG. 3 is a waveform diagram of essential parts of the first embodiment of the present invention. 4 is different from the circuit shown in FIG. 9 in that a resistor R is provided on the cathode side of the regenerative diode D3 whose anode side is grounded.

As for the operation of this circuit, as shown in FIG. 5, the switches SW1 and SW3 are turned on, and the power source E-switch SW is turned on.
1-Coil L-A current 13 is caused to flow through the route of the switch SW3 to store electromagnetic energy in the coil L, and then the switch SW3 is turned off. A power source E-switch SW1-coil L-diode D2-piezoelectric element Pz A resonance circuit is formed, and the piezoelectric element Pz is charged by the accumulated electromagnetic energy and the power supply voltage.

At this time, since the piezoelectric element Pz is charged by the sum of the electromagnetic energy and the voltage of the power source E, it means that the power source E is stepped up, and the low voltage power source E can charge the high voltage. Becomes

On the other hand, in discharging, when the switch SW2 is turned on, a series resonance circuit of the piezoelectric element Pz-the switch SW2-the coil L-the diode D1-the power source E is formed, and the charging voltage (for example, 130 V) of the piezoelectric element Pz and the power source are supplied. Due to the potential difference from the voltage (for example, 50 V), the regenerative current flows to the power source side for the resonance frequency for the time period in accordance with the series resonance of the LC, discharging is performed, and energy can be regenerated.

At this time, since the connection point a between the coil L and the switch SW2 is grounded by the regenerative diode D3 via the resistor R, when the potential at the connection point a becomes zero volt, the diode D3-resistor R-. A regenerative current flows through the route of coil L-diode D1-power source E, and connection point a shown in FIG.
Potential of the resistor R decreases in the minus direction by the voltage drop of the resistor R.

Therefore, the piezoelectric element Pz is further discharged, the remaining electric charge is drawn in, the residual electric charge is moved, and the voltage Vp of the piezoelectric element Pz becomes zero volt and then decreases to a negative value. Upon completion, the electric potential at the connection point a becomes 0 V, so that the discharge is completed and finally converges to zero.

In this way, with the regenerative current, the residual electric charges that cannot be extracted are discharged to the negative side of the piezoelectric element Pz (negatively charged) and forced to disappear, and the piezoelectric element P is removed.
The potential of z is zero.

(B) Description of Second Embodiment FIG. 6 is an explanatory view of a second embodiment of the present invention, which is applied to a transformer system. In FIG. 6A, the same components as those shown in FIG. 2 are designated by the same symbols. A power source E, a primary winding (coil) T1, a switch SW1 and a regenerative diode D3 are connected in series on the primary side of the transformer T, and a secondary winding (coil) T2 and a piezoelectric element P are connected on the secondary side.
Switches SW2 and SW3 connected in parallel with z are connected in series.

The operation of this circuit will be described with reference to FIG. 6B. The switch SW1 is turned on, the current I1 is passed through the primary winding T1, the switch SW1 is turned off, and the switch SW3.
When turned on, a clockwise current flows in the secondary winding T2,
The piezoelectric element Pz is charged during the ON time of the switch SW3.

Next, when the switch SW2 is turned on, the counter electromotive force of the secondary winding T2 causes a current to flow counterclockwise,
The piezoelectric element Pz is discharged. At this time, if the ON time of the switch SW2 is longer than the normal ON time shown by the dotted line in the figure and is set as shown by the solid line, the potential Vp of the piezoelectric element Pz becomes zero volt and then is pulled to the negative side, and the residual charge is reduced. Is pulled out, and when the switch SW2 is turned off, it finally converges to zero.

In this way, even if the piezoelectric element Pz is apparently at 0 volt, the residual electric charge that cannot be pulled out is discharged to the negative side of the piezoelectric element Pz (negatively charged) and is forcibly disappeared. The potential of the element Pz is set to zero.

(C) Description of Third Embodiment FIG. 7 is an explanatory view of a third embodiment of the present invention, showing a totem pole drive circuit. 2 in FIG. 7 (A)
The same parts as those shown in are indicated by the same symbols.

The second power source E2, the first power source E1, the switch SW1, the current limiting resistor R1, the current limiting resistor R2, and the switch SW2 are connected in series to form a loop.

One end of the piezoelectric element Pz is connected to the connection point between the current limiting resistance R1 and the current limiting resistance R2, and the other end is connected to the connection point between the second power source E2 and the first power source E1. There is.

The operation of this circuit will be described with reference to FIG. 7B. First, the switch SW1 is turned on, and the piezoelectric element Pz is charged by the first power source E1. Next, when the switch SW2 is turned on, the piezoelectric element Pz moves to the second power source E2.
It is connected to the negative side of and discharges.

Therefore, the potential Vp of the piezoelectric element Pz is
After reaching 0 volt, it is drawn to the minus side, the residual charge is extracted, and finally converges to zero when the switch SW2 is turned off.

In this way, even if the piezoelectric element Pz apparently becomes zero volt, the residual electric charge that cannot be pulled out is discharged to the negative side of the piezoelectric element Pz (negatively charged), and is forcibly disappeared. The potential of the element Pz is set to zero.

(D) Description of Fourth Embodiment FIG. 8 is an explanatory view of the fourth embodiment of the present invention, showing a boost-up type drive circuit. FIG. 2 in FIG.
The same parts as those shown in are indicated by the same symbols.

In FIG. 8A, the difference from the circuit shown in FIG. 9 is that a switch SW4 in which a current limiting resistor R3 and a diode D4 are connected in parallel is connected in series at the connection point between the switch SW1 and the coil L. And grounded.

As shown in FIG. 8B, the operation of this circuit is such that the switches SW1 and SW3 are turned on, and the current I is passed through the route of the power source E-switch SW1-coil L-switch SW3.
3 to store electromagnetic energy in the coil L, and then
When the switch SW3 is turned off, the power supply E-switch SW1
-Coil L-Diode D2-A series resonance circuit of the piezoelectric element Pz is formed, and the piezoelectric element Pz is charged by the accumulated electromagnetic energy and the power supply voltage.

At this time, since the piezoelectric element Pz is charged by the sum of the electromagnetic energy and the voltage of the power source E, the power source E is stepped up, and the low voltage power source E can be charged at a high voltage. Becomes

On the other hand, in discharging, when the switch SW2 is turned on, a series resonance circuit of the piezoelectric element Pz-the switch SW2-the coil L-the diode D1-the power source E is formed, and the charging voltage (for example, 130V) of the piezoelectric element Pz and the power source. Due to the potential difference from the voltage (for example, 50 V), the regenerative current flows to the power source side for the resonance frequency for the time period in accordance with the series resonance of the LC, discharging is performed, and energy can be regenerated.

At this time, the connection point between the coil L and the switch SW2 is clamped to zero volt by the regenerative diode D3. Therefore, when the potential at the connection point becomes zero volt, the diode D3-coil L-diode D1-power supply. A regenerative current flows along the route E and the discharge of the piezoelectric element Pz is stopped. However, when the switch SW4 is turned on at the end of the discharge, the residual charge of the piezoelectric element Pz is The piezoelectric element Pz-switch SW2-coil L-resistor R3-switch SW4 is forcibly discharged along the route.

In this way, even after the discharge due to resonance is completed, the switch SW4 continues the discharge and discharges the residual charge of the piezoelectric element Pz. In this method, regenerated electric charges are regenerated, and residual electric charges that cannot be regenerated are forcibly discharged, whereby the electric current can be regenerated and the residual electric charges can be eliminated.

At the connection point between the switch SW1 and the coil L, a current limiting resistor R3 and a diode D4 are connected in parallel, the switch SW4 is connected in series, and a discharge circuit is grounded. Therefore, a switch (transistor) is provided. The withstand voltage of SW4 may be the voltage of the power supply E (for example, 50V).

(E) Description of Other Embodiments In addition to the above embodiments, the present invention can be modified as follows. In the second embodiment, instead of the switch SW3,
A diode may be provided.

In the fourth embodiment, a switch SW4 in which a current limiting resistor R3 and a diode D4 are connected in parallel is provided.
A discharge circuit in which is connected in series and grounded may be provided at the connection point between the coil L and the switch SW2 or at the connection point between the switch SW2 and the piezoelectric element Pz.

In the fourth embodiment, the diode D3
May be deleted. Although the present invention has been described with reference to the embodiments, various modifications are possible within the scope of the gist of the present invention, and these modifications are not excluded from the scope of the present invention.

[0054]

As described above, according to the present invention,
It has the following effects. Residual charges due to the delay of strain at the time of energy conversion of the piezoelectric element can be removed, and ideal driving becomes possible.

In the boost-up method of claim 2, only a resistor is provided, in the transformer method of claim 3, the discharge time is simply lengthened, and in the totem pole method of claim 4, the power source is simply provided. The boost-up method of No. 5 can be easily realized simply by providing a discharge circuit.

[Brief description of drawings]

FIG. 1 is a principle diagram (1) of the present invention.

FIG. 2 is a principle diagram (2) of the present invention.

FIG. 3 is an explanatory diagram of a print element applied to an embodiment of the present invention.

FIG. 4 is a circuit diagram of a first embodiment of the present invention.

FIG. 5 is a waveform diagram of essential parts of the first embodiment of the present invention.

FIG. 6 is an explanatory diagram of a second embodiment of the present invention.

FIG. 7 is an explanatory diagram of a third embodiment of the present invention.

FIG. 8 is an explanatory diagram of the fourth embodiment of the present invention.

FIG. 9 is an explanatory diagram (1) of a conventional technique.

FIG. 10 is an explanatory view (No. 2) of the conventional technique.

[Explanation of symbols]

 E, E1, E2 Power supply SW1, SW3 Charge switch SW2, SW4 Discharge switch Pz Piezoelectric element L Coil D1, D2, D3 Diode R, R1, R2, R3 Resistance

Claims (5)

[Claims] 1. A power source (E) and a first switch (SW) for charging a piezoelectric element (Pz) with a positive potential of the power source (E).
In a piezoelectric element drive circuit having 1) and a second switch (SW2) for discharging the piezoelectric element (Pz), the piezoelectric element (Pz) is discharged to a negative potential during the discharging. And a method for driving a piezoelectric element. 2. The power source (E) is provided with a first switch (SW).
1), coil (L), and second switch (SW2)
And a piezoelectric element (Pz) are connected in series, and a grounded third switch (SW3) is provided at a connection point between the coil (L) and the second switch (SW2), and the first switch A diode (D1, D1) is provided in parallel with each of the switch (SW1) and the second switch (SW2).
2) is provided, and the first switch (SW1) and the third switch (SW1)
3) to close the piezoelectric element (Pz) to charge the piezoelectric element (Pz), and to close the second switch (SW2) to discharge the piezoelectric element (Pz) in the drive circuit of the piezoelectric element, the coil (L) and A resistor (R) is provided in series with the current regeneration diode (D3) at a connection point with the second switch (SW2), and the piezoelectric element (Pz) is discharged to a negative potential during the discharging. Drive circuit for piezoelectric element. 3. A primary side circuit in which a power source (E) and a first switch (SW1) are connected in series to a primary side winding (T1) of a transformer (T), and a secondary side winding (T) of the transformer (T). T2) has a secondary side circuit in which a second switch (SW2) and a piezoelectric element (Pz) are connected in series, and the first switch (SW1) is closed to close the piezoelectric element (P2).
z) and closing the second switch (SW2),
In the piezoelectric element drive circuit for discharging the piezoelectric element (Pz), the closing time of the second switch (SW2) is lengthened to discharge the piezoelectric element (Pz) to a negative potential during the discharging. Characteristic piezoelectric element drive circuit. 4. A first switch (SW1) and a second switch (SW2) are connected in series to a first power supply (E1), and the first switch (SW1) and the second switch (SW1) are connected in series. The piezoelectric element (Pz) is connected to the middle point of SW2), the first switch (SW1) is closed, and the piezoelectric element (Pz) is closed.
z) and closing the second switch (SW2),
In a piezoelectric element drive circuit for discharging the piezoelectric element (Pz), a second power source (E2) is provided in series with the first power source (E1), and the second power source (E2) is connected to the second power source (E2). A driving circuit for a piezoelectric element, comprising a second switch (SW2) connected to discharge the piezoelectric element (Pz) to a negative potential during the discharging. 5. The power source (E) is provided with a first switch (SW).
1), coil (L), and second switch (SW2)
And a piezoelectric element (Pz) are connected in series, and a grounded third switch (SW3) is provided at a connection point between the coil (L) and the second switch (SW2), and the first switch A diode (D1, D1) is provided in parallel with each of the switch (SW1) and the second switch (SW2).
2) is provided, and the first switch (SW1) and the third switch (SW1)
3) A piezoelectric element drive circuit for closing the piezoelectric element (Pz) and closing the second switch (SW2) to discharge the piezoelectric element (Pz) by closing any one of the discharge routes. At the point of,
3) and a grounded fourth switch (SW4) are provided, and at the time of the discharge, the fourth switch (SW4) is closed to forcibly discharge the piezoelectric element (Pz), which drives the piezoelectric element. circuit.