JP3255298B2 - Piezo element drive circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving circuit for driving a piezoelectric element used for driving a print head of a wire dot printer.

[0002]

2. Description of the Related Art A reference potential of a control circuit of a piezoelectric element drive circuit is generally called 0V, which is called GND. Conventionally, a voltage difference to be applied to both electrodes of a piezoelectric element is defined as a potential which is a voltage difference to be applied to one of the two electrodes of the piezoelectric element with respect to the reference potential (GND) and the other of the two electrodes with respect to the reference potential (GND). Was obtained by doing. FIG. 4 shows a conventional circuit example, and FIG. 5 shows a time chart of the operation.

In FIG. 4, a piezoelectric element drive section 11 is a drive circuit for charging and discharging a piezoelectric element P. Power supply Vp and G
Between ND, the transistor Tr1, the coil L, and the piezoelectric element P
Are sequentially connected in series to form a charging circuit for the piezoelectric element P. In addition, a transistor Tr2 is connected in parallel with the circuit of the piezoelectric element P and the coil L to form a discharge circuit.

The forward direction of the transistor Tr1 is a direction from the positive electrode of the power supply Vp to the electrode of the piezoelectric element P that is to be the positive electrode. The forward direction of the transistor Tr2 is a direction from the connection point between the transistor Tr1 and the coil L to GND. Diodes D1 and D2 are connected in parallel to the transistors Tr1 and Tr2, respectively.

The power supply Vp is connected to the electrode of the piezoelectric element P which is to be a positive electrode by a diode D3, and the forward direction of the diode D3 is opposite to the forward direction of the circuit. Further, a diode D4 is connected in parallel with the piezoelectric element P, and the forward direction is a direction from the electrode side to be the negative electrode of the piezoelectric element P to the electrode side to be the positive electrode.

On the other hand, the drive control unit 12 includes a control device (CP
U) 13, and the CPU 13 is supplied with a power supply Vcc with respect to GND (reference potential). CPU 13
And the discharge from the piezoelectric element P is commanded to the piezoelectric element drive unit 11 by the inverted CHHG signal from the piezoelectric element driving unit 11. Inverters I1 and I2 for inverting an output signal are connected to the inverted CHG signal output side and the inverted DCHG signal output side of the CPU 13, respectively. The output of the inverter I1 is a transistor T
given to a transistor Tr3 for controlling the conduction of r1;
The output of the inverter I2 is given to the transistor Tr2.

In the piezoelectric element driving circuit having the above configuration, the potential is Vp (for example, 100 V)> GND (for example, 0 V)
And the potential of both electrodes to be applied to the piezoelectric element P is Vp
And GND, and the reference potential of the drive control unit 12 is GND (0 V). 5A shows the timing of the inverted CHG signal, FIG. 5B shows the timing of the inverted DCHG signal, and FIG. 5C shows the voltage Vcp ′ between the two electrodes of the piezoelectric element P.
Shows the change.

[0008]

However, in the piezoelectric element driving circuit having the above structure, the potential of the positive electrode to be applied to the piezoelectric element P is equal to the reference potential (GN) of the control circuit.
The potential becomes higher than D). For this reason, (1) the power supply becomes expensive, (2) the control circuit requires components with high withstand voltage, and it becomes expensive. (3) Depending on the product, the interlock is used to protect the circuit components by high voltage. There is a problem that a safety circuit such as a switch is required. The present invention
It was made in order to solve the above problems,
The potential difference applied to the piezoelectric element with respect to the reference potential of the control circuit can be reduced, eliminating the need for components with high withstand voltage in the circuit.
An object of the present invention is to provide a driving circuit for a piezoelectric element at low cost.

[0009]

According to the present invention, there is provided a piezoelectric element comprising: a piezoelectric element; a charge / discharge circuit for charging or discharging the piezoelectric element; and a control circuit for controlling the charge / discharge circuit. In the element driving circuit, positive and negative potentials are simultaneously applied to both poles of one piezoelectric element so that the reference potential of the control circuit is substantially intermediate between the potentials of both poles of one piezoelectric element, and a potential difference between the two poles is provided. Is applied to one piezoelectric element.

[0010]

According to the above arrangement, the reference potential of the control circuit is one.
As it will be substantially intermediate potential of both poles of the potential of pieces of piezoelectric elements, one of simultaneously giving positive and negative potential with respect to both poles of the piezoelectric elements, one of pressure charging voltage corresponding to potential difference between both electrodes <br / > Because it is applied to the electric element, one piezoelectric element
The potential to be applied to both poles of the control circuit is the reference potential of the control circuit
It becomes small in view of it.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram of a piezoelectric element drive circuit. The piezoelectric element drives, for example, a printing wire of a dot impact printer by utilizing the characteristics of the piezoelectric element that expands and contracts when a voltage is applied. The piezoelectric element driving unit 11
The transistor Tr1, the coil L, and the piezoelectric element P are connected in series between the power supplies VH and VL, forming a charging circuit for the piezoelectric element P. A transistor Tr2 is connected in parallel with the circuit of the piezoelectric element P and the coil L to form a discharge circuit. Drive control unit 1
2 has a control device (CPU) 13 similar to that described above.
The CPU 13 instructs the piezoelectric element driving unit 11 to charge the piezoelectric element P by the inverted CHG signal and discharge the piezoelectric element P by the inverted DCHG signal. An inverter I1 for inverting an output signal is connected to an inverted CHG signal output side of the CPU 13. The output of the inverter I1 is a transistor T1 for turning on the transistor Tr1.
r3. The inverted DCHG signal is output from the transistor Tr4 for turning on the transistor Tr2.
Has been given to. The magnitude relationship between the reference potential GND of the CPU 13 and the potentials of the power supplies VH and VL is VH (for example, 4
5V)> GND (0 V)> VL (for example, −55 V), and the voltages of both electrodes to be applied to the piezoelectric element P are VH and VL.

The forward direction of the transistor Tr1 is a direction from the positive electrode of the power supply VH to the electrode of the piezoelectric element P that is to be the positive electrode. The forward direction of the transistor Tr2 is a direction from the connection point between the transistor Tr1 and the coil L toward the power supply VL. Diodes D1 and D2 are connected in parallel to the transistors Tr1 and Tr2, respectively, and the forward direction of each diode D1 and D2 is opposite to the forward direction of each transistor Tr1 and Tr2.

The power supply VH is connected to the electrode of the piezoelectric element P which is to be a positive electrode by a diode D3, and the forward direction of the diode D3 is opposite to the forward direction of the circuit. Further, a diode D4 is connected in parallel with the piezoelectric element P, and the forward direction is a direction from the electrode side to be the negative electrode of the piezoelectric element P to the electrode side to be the positive electrode.

The operation of the piezoelectric element driving circuit having the above configuration will be described. The CPU 13 turns on the transistor Tr3 and turns on the transistor Tr1 in response to the output of the inverted CHG signal. Accordingly, a current flows into the piezoelectric element P via the transistor Tr1 and the coil L due to a potential difference between the power supply VH and the power supply VL, and the coil L and the piezoelectric element P are charged while resonating, and the piezoelectric element P is displaced (extended).

Thereafter, the CPU 13 outputs the inverted DCHG signal, turns on the transistor Tr4, and turns on the transistor Tr2. Thereby, the electric charge charged in the piezoelectric element P is discharged via the coil L and the transistor Tr2, and the displacement of the piezoelectric element P is returned to the initial position.
After that, the transistors Tr2 and Tr4 are turned off. By repeating the above charging and discharging, the piezoelectric element P can be driven.

FIG. 2 shows the state when the above operation is performed.
4 shows a time chart of the output signal and the bipolar voltage of the piezoelectric element P. In the figure, (a) shows the inverted CHG signal and (b)
Shows the timing of the inverted DCHG signal, and (c) shows the change in the voltage Vcp between both electrodes of the piezoelectric element P. As described above, the voltage for driving the piezoelectric element P can be set low by setting the reference potential GND of the drive control unit 12 to 0 V and varying the potential of both electrodes of the piezoelectric element P to ±. In this embodiment, the voltage of the power supply VH is set to 45 V and the voltage of the power supply VL is set to -55 V. Therefore, a member having a low withstand voltage can be used for the piezoelectric element drive circuit. Can be used.

Next, an example of a power supply circuit used in the present piezoelectric element drive circuit will be described with reference to FIG. This circuit includes a transformer 15, diodes D5 and D6 for rectifying and smoothing, capacitors C1 and C2, and transistors Tr5 and Tr for voltage adjustment.
6 and its regulator circuits 16 and 17, smoothing capacitors C3 and C4, and resistors R1 and R2. With this configuration, the respective voltages of the power supplies VH and VL of this embodiment are 45V,-
55V is obtained. The withstand voltages of the smoothing capacitors C3 and C4 and the resistors R1 and R2 can be lower than those of a conventional one. Thus, the potential to be applied to the piezoelectric element P as viewed from the reference potential can be made smaller than the conventional one.

[0018]

As described above, according to the present invention, a potential of ± with respect to the reference potential (0 V) of the control circuit is applied to one piezoelectric element, that is, the reference potential of the control circuit is so as to be substantially intermediate potential between both poles of the potential of one of the piezoelectric elements, simultaneously giving positive and negative potential with respect to both poles of one of <br/> piezoelectric elements, one of the charging voltage corresponding to potential difference between both electrodes Since the voltage is applied to the piezoelectric element, the two electrodes of one piezoelectric element
The potential to be applied becomes smaller than the reference potential of the control circuit . For this reason, (1) components with low withstand voltage can be used,
The cost of the piezoelectric element drive circuit can be reduced, (2) an inexpensive power supply can be used, and (3) depending on the circuit, the safety circuit such as an interlock switch is not required.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a piezoelectric element driving circuit according to an embodiment of the present invention.

FIG. 2 is a time chart of driving the piezoelectric element according to the embodiment.

FIG. 3 is a circuit diagram of a power supply circuit used in the present embodiment.

FIG. 4 is a circuit diagram of a conventional piezoelectric element drive circuit.

FIG. 5 is a time chart for driving a conventional piezoelectric element.

[Explanation of symbols]

 Tr1, Tr2 Transistor P Piezoelectric element 11 Piezoelectric element drive unit 12 Drive control unit 13 Control device VH power supply VL power supply GND Reference potential

Claims (1)

(57) [Claims] 1. A piezoelectric element drive circuit comprising a piezoelectric element, a charge / discharge circuit for charging or discharging the piezoelectric element, and a control circuit for controlling the charge / discharge circuit, wherein the reference potential of the control circuit is one piezoelectric element. The positive and negative potentials are simultaneously applied to both electrodes of one piezoelectric element so that the potential is substantially intermediate between the potentials of both electrodes of the element, and a charging voltage corresponding to the potential difference between the two electrodes is applied to one piezoelectric element. A piezoelectric element drive circuit, characterized in that: