JPH02136245A - Piezoelectric element driving apparatus - Google Patents

Abstract

PURPOSE:To rapidly reduce residual charge by bringing the voltage between both terminals of a piezoelectric element by regenerating the charge of the piezoelectric element to a power supply at the predetermined point of time of the resonance cycle of a resonance circuit and discharging the charge of the piezoelectric element from the intermediate tap of a coil through a transistor. CONSTITUTION:The first switch means 1 consisting of the coil L in series to a piezoelectric element 2, transistors Tr1, Tr2, resistors R4, R5 and a diode D4 and supplying exciting voltage Eo to the aforementioned coil L and a means (diode 5) regenerating the charge of the piezoelectric element 2 to a power supply when the first switching means 1 is turned OFF are provided in parallel. Further, the second switch means equipped with the transistor Tr3 connected to the intermediate tap M of the coil L and turned ON by predetermined coil voltage and discharging the charge of the piezoelectric element 2 is connected. By this constitution, a part of the charge of the piezoelectric element 2 is regenerated to the power supply and a part thereof is discharged through a discharge circuit.

Description

[Detailed Description of the Invention] [Field of Application in Industry A] The present invention provides a piezoelectric element drive device, particularly a piezoelectric element connected to a predetermined mechanical drive system, which supplies power to the piezoelectric element to generate dimensional distortion in the piezoelectric element. The present invention relates to a piezoelectric element drive device that obtains driving force.

[Prior Art] Piezoelectric actuators have conventionally been used as elements that generate driving force for striking wires or ejecting ink in recording heads of wire dot printers and inkjet printers. As a drive circuit for such a piezoelectric actuator, a series circuit consisting of a piezoelectric element and a resistor is used. An excitation voltage is applied to this series circuit via a switch activated by a drive signal, and the piezoelectric element is instantaneously activated. Charge and pressure! Dimensional distortion is caused in the element. Subsequently, the series circuit is short-circuited via another switch, thereby discharging the charge accumulated in the piezoelectric element and restoring the distortion of the piezoelectric element.

In such a circuit, the current that flows through each switch when conductive is quite large, so there is a risk that the switches will be damaged by the excessive current, and there is a problem that their lifespan will be shortened. Furthermore, since the electric charge charged in the piezoelectric element is completely discharged each time the piezoelectric element is driven, there is a problem in that extra power is consumed accordingly.

[Problems to be solved by the invention] In order to solve these problems,
No. 8885 proposes a drive circuit as shown in FIG. In FIG. 4, a coil L is connected to a piezoelectric element 53, and an excitation voltage Eo is applied to this series circuit via a switch 51 activated by a drive signal. A series circuit consisting of a resistor R1 and a switch 52 operated by a braking signal is connected in parallel with this series circuit. In addition,
Reference numeral 54 denotes a mechanical drive system composed of a wire drive mechanism of a wire dot head or an ink discharge mechanism of an inkjet head, which is driven in response to mechanical dimensional distortion of the piezoelectric element 53.

The operation timing of the circuit of FIG. 4 is as shown in FIG.

As shown in lines 1 and 2 of FIG. 5, the braking signal is controlled to low level during the high level period of the drive signal. This pulse width is set to be equal to one cycle of the reciprocating motion of the piezoelectric element 53 due to its dimensional distortion. During the period 11 in which the drive signal is at a high level and the braking signal is at a low level, the switch 52 is open, so the coil and piezoelectric element 53 form a resonant circuit. This resonant waveform is the fifth
As shown in the waveform of the current 1a flowing through the piezoelectric element 53 in the figure, damped vibration occurs. This is because the piezoelectric element 53 has a relatively large resistance component.

On the other hand, the voltage waveform of the element is shifted by approximately half a cycle from the current waveform, as shown in the fourth row of FIG. 5, and the dimensional distortion of the piezoelectric element 53 in response to this voltage change is shown in the bottom row of FIG. It becomes like this.

In the circuit shown in Fig. 4, the inductance component of the coil L is inserted to prevent a large current peak value from occurring, and the terminal voltage of the piezoelectric element is In other words, the purpose is to reduce the residual charge to almost zero.

However, in reality, after the period 11 in FIG. The same driving operation cannot be performed in the next period unless the residual charges are discharged.

The discharge power at this time is consumed as Joule heat by the resistor R1, and does not contribute to driving. Another problem is that it is difficult to increase the drive frequency due to the presence of the discharge period. In other words, the closer the start of discharge is to 1/-2 cycle later in order to increase the speed, the larger the discharge current will be and the more heat will be generated. There is a problem that occurs.

On the other hand, regarding the above-mentioned charging/discharging problem of the piezoelectric element 53, a voltage greater than the power supply voltage generated at the power supply side terminal of the coil L due to resonance between the coil L and the piezoelectric element 53 during the period 11 causes the diode D1 to However, since the piezoelectric element 53 has a large resistance component, it is not possible to regenerate all of the charge to the power source.

Therefore, in order to reduce the charge remaining in the piezoelectric element 53 to zero and return it to its original shape from the deformed state, discharging by the switch 52 is absolutely necessary. During this discharging period, the charged charges are all consumed by the resistor R1 in the case of FIG. 4 and are wasted.

In particular, when driving the piezoelectric element 53 repeatedly at high speed, the period 11 is shortened as shown in FIG. 6, and the switch 52 is closed before one cycle of resonance of the piezoelectric element 53 has elapsed to stop the discharge. I will do it. Fig. 6 is a power supply chart similar to Fig. 5, but in this case, the period during which the charged charge is regenerated to the power supply by the diode D1 is shortened, which corresponds to the portion shown by the broken line in the fourth row of Fig. 6. There is a problem in that most of the charged charge is consumed by the resistor R1, further reducing the efficiency.

Furthermore, in the above circuit, a discharge circuit is formed by a resistor, a transistor, and a coil, and the electric charge is discharged through this resistor, so that a large amount of heat is generated in the resistor. Moreover, currents and voltages of several tens of volts and several amperes flow through this resistor, so a resistor with high power resistance and a large size resistor and heat dissipation member are required, which increases the size and weight of the drive circuit. It had the disadvantage of being heavy.

An object of the present invention is to solve the above problems and provide a piezoelectric element drive device that is small, durable, and capable of completely reducing the residual charge in the piezoelectric element to zero at the end of a drive pulse.

[Means for Solving the Problems] In order to solve the above problems, in the present invention, power is supplied to a piezoelectric element connected to a predetermined mechanical drive system to generate dimensional distortion in the piezoelectric element and drive the piezoelectric element. In a piezoelectric element driving device that obtains a force, a coil connected in series to the piezoelectric element, a first switch means for supplying an excitation voltage to the coil, and a first switch means connected in parallel with the first switch means for supplying an excitation voltage to the piezoelectric element. means for regenerating the electric charge to the power source and a second switch means for discharging the electric charge of the piezoelectric element;
The first switch means is constituted by a transistor connected to an intermediate tap of the coil and turned on by a predetermined coil voltage, and the first switch means is turned off at a predetermined point in the resonance period of a resonant circuit formed by the coil and the piezoelectric element. A configuration is adopted in which the electric charge of the piezoelectric element is regenerated to the power source by the coil, and the electric charge of the piezoelectric element is discharged from the intermediate tap of the coil via a transistor that is turned on at a predetermined coil voltage.

[Function] In such a configuration, part of the charge charged in the piezoelectric element via the coil is regenerated to the power supply side at a predetermined point in the resonance cycle at the end of driving, and part of the charge is regenerated by the coil and transistor. It is possible to reduce the residual charge of the piezoelectric element to 7 and reduce the voltage across the piezoelectric element to .

In this case, the electric charge is discharged via the coil and the transistor, so the energy consumption is done in the transistor. The entire drive device can be made smaller.

[Example] Hereinafter, the present invention will be described in detail according to an example shown in the drawings.

An embodiment of the present invention is illustrated in FIG. 1, and what is designated by reference numeral 1 in the same figure is a first switch means for supplying an excitation voltage Eo to a coil L, and a transistor operated by a drive pulse. It consists of a transistor Tr2, resistors R4 and R5, and a diode D4.

The excitation voltage EO is applied to the transistor Tr from a power supply (not shown).
When the drive pulse is input, the transistors Tri and Tr2 become conductive, and an excitation voltage is supplied to the coil via the diode D4.

A predetermined mechanical drive system (not shown) is connected in series with this coil L.
A piezoelectric element 2 coupled with is connected. Piezoelectric element 2
One end of the piezoelectric element 2 is grounded, and the connection point between the other end of the piezoelectric element 2 and the coil L is connected to the base of a transistor Tr3 via a capacitor C1. The emitter of the transistor Tr3 is connected to the center tap M of the coil L, and the collector is connected to the piezoelectric element 2. When the transistor Tr3 is conductive, a discharge circuit is formed with respect to the piezoelectric element 2 by the coil L and the transistor Tr3.

In addition, a resistor R6 is connected in parallel to the coil L and the piezoelectric element 2,
R7 is connected, and when the transistor Tr3 becomes conductive, a positive feedback circuit is formed in the transistor Tr3 by the resistor, the coil, and the capacitor C1.

Further, a diode D5 is connected in parallel to the transistor Tr2, and when the switch means 1 is turned off, the piezoelectric element 2
The electric charge charged in the diode D5 is regenerated to the power supply side via the diode D5.

Next, the operation of the device configured as described above will be explained.

First, as shown in the first row of Figure 2, when the drive pulse is set to H at the time of to and the transistor Tri is turned on, the transistor Tr2 is turned on by the current flowing between the collector and emitter of the transistor Tri, and the transistor Tr2 is connected in series. An excitation voltage Eo is applied to both ends of the coil L and the piezoelectric element 2. As a result, a resonant current begins to flow through the piezoelectric element 2 via the coil L. At this time, the voltage V1 across the coil L and the current flow 1 flowing through the coil are shown in the second and third rows of FIG. 2, respectively.

As the base current of the transistor Tr3 temporarily flows at the time of to, a temporary current Ie flows through the coil L and the emitter collector of the transistor Tr3 for a short time (several microseconds) until the capacitor C1 is charged. The transistor Tr3 remains off until time t2, which will be explained in . This state is illustrated as emitter current Ie in the fourth row of FIG.

The piezoelectric element 2 is charged by this resonant current, and the voltage Vp of the piezoelectric element increases as shown in the fifth row of FIG.
Further, as shown in the sixth stage, a current Ip flows through the piezoelectric element 2.

On the other hand, the voltage v1 across the coil L changes from positive to negative. The drive pulse increases the coil voltage VJ at the time of tl, that is, at the time of about half the period To / 2, where To is the resonance period determined by the total inductance value and the total capacitor value of the circuit.
Z becomes the negative maximum value, and the current value flowing through the coil becomes 0. Also, at this time, the voltage Vp of the piezoelectric element 2 is at its maximum.

Moreover, after the time tl, the resonant current flowing through the coil is reversed. Since the transistor Tr2 is off at the time tl, the charge charged in the piezoelectric element 2 is regenerated to the power supply side via the diode D5. This regenerative current causes the base voltage of the transistor Tr3 to decrease via the capacitor c1. Since the emitter of the transistor Tr3 is connected to the center tap M of the coil L, the transistor Tr3 is turned on at time t2 due to the phase difference between the voltage and current between the coil L and the capacitor C1.

When the transistor Tr3 is turned on, a discharge circuit is formed for the piezoelectric element 2 by the coil L and the transistor Tr3, so that the charge in the piezoelectric element 2 is discharged to the ground via the coil L1 and the transistor Tr3. At this time coil L1
Capacitor c1, transistor Tr3, resistors R6, R7
constitutes a positive feedback circuit for the transistor, so one end of the coil is A1, the other end is 81, the center tap is M, and the voltage at both ends A and B of the coil L is determined by the turns ratio of AM and B, and M
It is the product of the voltage applied between B, and the turns ratio and capacitor C1
, by adjusting the resistors R6 and R7, the voltage across the coil L can be made equal to the excitation voltage at the end of resonance t3, and therefore the voltage Vp across the piezoelectric element can be made equal to the excitation voltage.
O as shown in the fifth row of the figure.

Further, the above positive feedback circuit makes it possible to shorten the discharge time.

The charge charged to the piezoelectric element 2 through the coil L in this way is regenerated to the power supply side through the diode D5 at the end of the drive pulse, and a portion is grounded through the coil L and the transistor Tr3. By amplifying the voltage generated by the current flowing through the coil, it is possible to reduce the voltage across the piezoelectric element 2 to 0 and also to reduce the residual charge in the piezoelectric element 2 to 0.

Another embodiment of the invention is illustrated in FIG.
In this embodiment, the PNP type transistor Tr shown in FIG.
3 is replaced with an NPN type field, and the same operation and effect as the circuit of FIG. 1 can be obtained.

[Effects of the Invention] As explained above, according to the present invention, the switch means is turned off at a predetermined point in the resonance period of the resonant circuit formed by the coil and the piezoelectric element, and the electric charge of the piezoelectric element is regenerated into the power source. Since the electric charge of the piezoelectric element is discharged from the middle tap of the coil via a transistor that turns on at a predetermined coil voltage, a portion of the electric charge charged to the piezoelectric element via the coil is transferred to the power supply side at the end of driving. A portion of the piezoelectric element is regenerated, and a part of it is discharged through a discharge circuit made up of a coil and a transistor, reducing the voltage across the piezoelectric element to zero and quickly removing the residual charge in the piezoelectric element.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a first embodiment of the piezoelectric element driving device, FIG. 2 is an operation waveform diagram of the circuit in FIG. 1, and FIG. 3 is a circuit diagram showing another embodiment of the piezoelectric element driving device. FIG. 4 is a circuit diagram of a conventional drive device, and FIGS. 5 and 6 are waveform diagrams illustrating the operation of the circuit shown in FIG. 1...First switch means 2...Piezoelectric element L...Coil' Since the continuous discharge is performed via the coil and the transistor, energy consumption is performed by the transistor, and therefore the power resistance is large. Since there is no need to use a large resistor and heat dissipation member, the entire drive device can be made smaller. t + t2 system 10 hahi・) column to agency time A1 Fig. 1 4 对 乍三Antagonal μ and] Fig. 2 Eve j (Yomen, f column pu 已 藲藩 Δza wo E) 8 I+v
Iko a times y each σ Fn I 乍 Jsu I

Claims (1)

[Scope of Claims] 1) In a piezoelectric element drive device that supplies power to a piezoelectric element connected to a predetermined mechanical drive system to generate dimensional distortion in the piezoelectric element and obtain driving force, a connected coil; a first switch means for supplying an excitation voltage to the coil; a means connected in parallel with the first switch means for regenerating the electric charge of the piezoelectric element into a power source; and discharging the electric charge of the piezoelectric element. and a second switch means configured to set the resonant period of a resonant circuit formed by the coil and the piezoelectric element, the second switch means comprising a transistor connected to a center tap of the coil and turned on at a predetermined coil voltage. At a predetermined time point, the first switch means is turned off to regenerate the electric charge of the piezoelectric element to a power source, and at the same time, the electric charge of the piezoelectric element is discharged from the center tap of the coil via a transistor that is turned on at a predetermined coil voltage. A piezoelectric element drive device characterized by: 2) The piezoelectric element driving device according to claim 1, wherein positive feedback is applied to the transistor when the transistor is turned on.