JPS63130358A - Piezoelectric element driving unit - Google Patents

Abstract

PURPOSE:To improve the power efficiency of a piezoelectric element, by providing a converter controller for controlling a DC-DC converter to apply a predetermined voltage between terminals when the piezoelectric element is charged, while turning a second switching element ON when the piezoelectric element is discharged, and turning said switching element OFF when the terminal voltage becomes approximately 0 volt. CONSTITUTION:When a high voltage is applied onto a piezoelectric element 2 so as to drive said element 2, a switching element 31 in a DC-DC converter A is driven and the terminal voltage of the piezoelectric element is controlled to a predetermined level. When the piezoelectric element 2 is discharged after driving, and recovered to the original state, a second switching element 32 in a bilateral DC-DC converter A for regenerating power from the piezoelectric element A to a DC power source is turned ON, and when the terminal voltage of the piezoelectric element A reaches to approximately 0 volt, the second switching element 32 is turned OFF. Consequently, electrostatic energy being charged in the piezoelectric element when it is driven is regenerated to the power source 1 through utilization of resonance.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a piezoelectric element drive device with improved power efficiency.

[Prior art]

Conventionally, it has been proposed to use a piezoelectric element to drive a wire in a dot matrix printer or to drive an ink droplet generating mechanism in an inkjet printer. The piezoelectric element is driven, for example, by a drive circuit shown in Figure 'M7. That is, the piezoelectric element 2 is the transistor 3
The voltage of the DC power supply 1 is applied to the piezoelectric element 2 when the transistor 3 becomes conductive in response to the print start signal S1. When a voltage is applied, the piezoelectric element 2 expands or contracts, and the displacement is magnified by a transmission mechanism to drive a printing mechanism, such as a wire. However, the piezoelectric element 2 acts as a capacitor, and even if the transistor 3 is turned off, the piezoelectric element 2 remains expanded or contracted because it is charged, and the displacement of the printing mechanism does not return to its original state. For this reason, a transistor 4 is connected to a resistor 1 in parallel to the piezoelectric element 2.
0 and outputs the print end signal S after the end of the print operation.
2 turns on the transistor 4 for a certain period of time to discharge the charge accumulated in the piezoelectric element 2 and reduce the applied voltage to zero,
The displacement of the printing mechanism is returned to its original state.

[Problems to be solved by the invention]

However, the charge accumulated in the piezoelectric element 2 is lost as resistance loss during discharge, and when the piezoelectric element 2 is driven again, it is charged again from the DC power source 1. For this reason, there is a problem in that the printing machine also suffers from a large power loss during driving, resulting in poor power efficiency.

[Purpose of the invention]

The present invention has been made in order to solve the above problems, and its purpose is to improve the power efficiency of the piezoelectric element by regenerating the charge charged in the piezoelectric element during driving to the power source. It's about improving.

[Means to solve the problem]

The structure of the invention to solve the above problems is such that the first switch cable is interposed between the piezoelectric element and the DC power source, and performs a switching operation to supply power from the DC power source to the piezoelectric element, and the piezoelectric element. a second switching element that performs a switching operation to regenerate the power stored in the DC power source into the DC power supply; When charging the piezoelectric element in response to the drive signal of the piezoelectric element, the DC-
The DC converter is controlled to set the voltage between the terminals of the piezoelectric element to a predetermined value, and when the piezoelectric element is to be discharged, the second switch element is turned on and the voltage between the terminals of the piezoelectric element reaches approximately 0V.
f! The present invention includes a converter control device that turns off the J2 switch element.

[Effect]

When applying a high voltage to the piezoelectric element to drive the piezoelectric element, a switching element of the DC-DC converter is driven to control the voltage between the terminals of the piezoelectric element to a predetermined voltage. Next, after driving the piezoelectric element, when discharging the electric charge charged in the piezoelectric element and returning the displacement of the piezoelectric element to the original position, a bidirectional DC-DC
After the second switching element of the converter that performs a switching operation for regenerating power from the piezoelectric element to the DC power source is turned on, the second switching element is turned off when the voltage between the terminals of the piezoelectric element becomes approximately 0V. As a result, the electrostatic energy charged in the piezoelectric element during driving is regenerated into the power source using resonance after driving.

【Example】

The present invention will be described below based on specific examples. FIG. 1 is a circuit diagram of a piezoelectric element drive circuit according to a specific embodiment of the present invention. The DC-DC converter shown in Fig. 1 that is capable of buck-boosting and capable of transmitting power in both directions uses the unidirectional buck-boost capable C-DC converter shown in Fig. 5 as its basic circuit, and has two The basic circuit of a DC-DC converter is connected in parallel with a common coil. The basic circuit shown in FIG. 5 consists of a DC power supply 1, a transistor 30 as a switching element, a coil '50, and a diode 40. The transistor 30 is duty-controlled by the control signal S1. When the transistor 30 is on, a current flows from the DC power supply 1 to the coil 50, and the power supplied from the DC power supply 1 is stored in the coil 50 as magnetic energy. Next, when the transistor 30 is off, the coil 50
The energy stored in the diode 40 flows through the load and the diode 40. By repeating this on-off cycle, an averaged DC current is supplied to the load. When the load is a resistive load, a constant load current flows, so if the transistor 30 is controlled with a constant duty ratio, the voltage between the terminals of the load will be a constant value. However, when the load is a capacitive load, there is no current consumption, so the voltage increases and cannot be controlled to a predetermined value. Moreover, if the charge charged in the piezoelectric element is regenerated to the DC power supply 1 after the piezoelectric element is brought into operation, energy loss will be reduced. Therefore, as shown in FIG. 1, a buck-boost DC-DC converter capable of bidirectional power transmission was constructed by connecting parallel-connected buck-boost C-DC converters capable of transmitting power in one direction. 2 is a piezoelectric element. A C-DC converter A in which the transistor 31, the coil 50, and the diode 41 are capable of unidirectional step-up and step-down voltage supply that supplies power from the DC power source 1 to the piezoelectric element 2.
The transistor 32, the coil 50, and the diode 42 constitute a unidirectional step-up/down C-DC converter B that regenerates power from the piezoelectric element 2 to the DC power supply 1. A first switching element that performs a switching operation to supply power from the DC power source to the piezoelectric element is composed of a transistor 31, and a second switching element that performs a switching operation to regenerate the power accumulated in the piezoelectric element to the DC power source. The switch element is composed of a transistor 32. Both these DCs
- The DC converters are connected in parallel with the coil 50 in common. However, since the input voltage E1 and the output voltage E2 of the DC-DC converter have opposite polarities, the diodes 41.42 and the transistors 31.32 are connected so that their conduction directions are opposite to each other. Further, a comparator 70 is provided as a voltage detection circuit for detecting the inter-terminal voltage E2 of the piezoelectric element 2. The terminal voltage -E2 of the piezoelectric element 2 is input to the non-inverting input terminal of the comparator 70, and the resistor 71 is input to the inverting input terminal.
(!: The reference voltage Et obtained by dividing the voltage with the resistor 72 is input. Then, the output of the comparator 70 becomes a low level when the voltage E2 between the terminals of the piezoelectric element 2 exceeds the absolute value of the reference voltage Et. In addition, as the converter control device E, a rectangular wave oscillator 80 is used.
, an AND gate 81 which inputs the output of the rectangular wave oscillator 80 and the drive signal ■1, a NAND gate 82 which inputs the output of the ANO gate 81 and the output of the comparator 70, and a NAND gate 82 which inputs the drive signal ■1 and generates a constant signal. It consists of a monostable multivibrator 84 that outputs a pulse signal with a pulse width, and an analog switch 85 that inputs the output of the monostable multivibrator 84 to a control terminal. One signal terminal of the analog switch 85 is grounded,
The other signal terminal is connected to the base of transistor 32. Next, the operation will be explained based on the timing chart of FIG. The drive signal Vl rises at time t1 and rises at time t3.
This is a signal that falls at The rising edge of the drive signal means the timing to charge the piezoelectric element 2 and drive the wire, and the falling edge of the drive signal causes the electric charge accumulated in the piezoelectric element 2 to be recovered as a power source and return the wire to its original position. It means the timing. Output v2 of AND gate 81
The square wave oscillator 80 is activated only during the period when the drive signal v1 is at a high level.
output, and is at a low level during other periods. Furthermore, since the output v3 of the comparator 70 is at a high level until time t2 when the terminal voltage -E2 of the piezoelectric element 2 exceeds the reference voltage Et in the negative direction, the output v4 of the NANO gate 82
is an inverted waveform of the output (2) of the AND gate 81 until time t2. Therefore, since the transistor 310 base voltage is at a high level until time tl, the transistor 310 base voltage is at a high level until time tl.
is off, but since the base voltage of the transistor 31 oscillates between time tl and time t2, the transistor 31 repeats on and off. Then, as mentioned above,
Due to the circuit of the coil 50", the piezoelectric element 2, and the diode 41, the voltage E2 between the terminals of the piezoelectric element 2 gradually increases, and the terminal voltage -E2 decreases toward the reference voltage Et. The terminal voltage -E2 becomes the reference voltage Et. After time t2, which exceeds 1Etl, Be-xWNl of the transistor 31 becomes high level, and the transistor 31 turns off.At this time, the voltage E2 between the terminals of the pressure i-element 2 is maintained at 1Etl.At time t3, Since the monostable multi-by break 84 is triggered by the falling edge of the drive signal, its output ■5
is a pulse with a constant width, that is, from time t3 to time t4
High level between. Therefore, analog switch 85
is in an on state during this period, the base potential of the transistor 320 becomes the ground potential, and the base and emitter thereof are forward biased, so that the transistor 32 is in an on state. Then, the charge charged in the piezoelectric element 2 in the direction is
The electrostatic energy of the piezoelectric element 2 flows through the circuit of the coil 50 and the transistor 32, and is stored in the coil 50 as magnetostatic energy. Then, the voltage between the base and emitter of the transistor 32 becomes zero at time t4 when the voltage E2 between the terminals of the piezoelectric element 2 becomes zero, so the transistor 32 is turned off, and the back electromotive force generated in the coil 50 causes the coil 5 to
The energy stored in the DC power supply 1 is regenerated to the DC power supply 1 via the diode 42. Due to such control, the voltage E2 between the terminals of the piezoelectric element 2 becomes a predetermined value during driving, and when the impact of the wire is completed, the transistor 31 is turned off, so that switching loss of the transistor 31 is suppressed. Further, during regeneration, the transistor 32 is turned on and off only once, so switching loss can be suppressed. Although the transistor 32 is indirectly controlled by the analog switch 85, is it possible to fix the base of the transistor 32 with a negative voltage? It may be controlled. Incidentally, the circuit configuration of the voltage detection circuit and converter control bag rME shown in FIG. 1 in the above embodiment is an example, and the present invention is not limited to this configuration. Further, FIG. 2 is a circuit diagram showing another configuration of the C-DC converter, which is capable of bidirectional power transmission and voltage step-up/down. The DC-DC converter shown in Figure 2 uses the unidirectional step-up/down capable C-DC converter shown in Figure 6 as its basic circuit, and the basic circuit of two DC-DC converters with different transmission directions using a common coil and capacitor. are connected in parallel. The basic circuit in Figure 6 is the DC power supply 1
, a transistor 33 which is a switching element, and a coil 51 .
52, a capacitor 60, and a diode 43. The duty of the transistor 33 is controlled by the control signal s2. When the transistor 33 is on, current flows from the DC power supply 1 to the coil 51, and the power supplied from the DC power supply 1 is stored as magnetic energy in the coil 51. Next, when the transistor 33 is off, current flows through the coil 51, capacitor 60, and diode 43, and the energy stored in the coil 51 is stored in the capacitor 60 as electrostatic energy. Next, when transistor 33 is turned on again, the charge accumulated in capacitor 60 flows through a closed circuit of transistor 33, load, coil 52, and capacitor 60, and current flows to the load. By repeating this on-off cycle, an average DC current is supplied to the load. When the load is a resistive load, a constant load current flows, so if the transistor 33 is controlled with a constant duty ratio, the voltage between the terminals of the load will be a constant value. However, when the load is a capacitive load, there is no current consumption, so the voltage increases and cannot be controlled to a predetermined value. Moreover, if the charge charged in the piezoelectric element is regenerated to the DC power supply 1 after the piezoelectric element is activated, energy loss will be reduced. Therefore, as shown in FIG. 2, a buck-boost DC-DC converter capable of transmitting power in both directions can be constructed by connecting parallel-connected C-DC converters capable of transmitting power in one direction. Transistor 34 and coil 51
．． 52, a capacitor 60, and a diode 44 constitute a C-DC converter A capable of unidirectional step-up and step-up supplying power from the DC power supply 1 to the piezoelectric element 2, and the transistor 35
and coil 51, 52, capacitor 60 and diode 45
constitutes a C-DC converter B capable of unidirectional voltage step-up and step-up regenerating power from the piezoelectric element 2 to the DC power source 1. A first switching element that performs a switching operation to supply power from the DC power source to the piezoelectric element is composed of a transistor 34, and a second switching element that performs a switching operation to regenerate the power accumulated in the piezoelectric element to the DC power source. The switch element is composed of a transistor 35. Both of these D
The C-DC converters are connected in parallel with the coils 51 and 52 and the capacitor 60 in common. However, since the input voltage E1 and output voltage E2 of the DC-DC converter have opposite polarities, the diode 44.45
and transistors 34 and 35 are connected so that their conducting directions are opposite to each other. Further, a diode 46 is connected between the terminals of the piezoelectric element 2 so that the regenerative current flowing in the opposite direction to the charging current during regeneration bypasses the piezoelectric element 2. In addition, a voltage detection circuit that detects the voltage E2 between the terminals of the piezoelectric element 2, the output of the voltage detection circuit and the drive signal 1 are inputted, and the transistors 34 and 35 are turned on and off.
A converter control device E is provided to control the converter. The voltage detection circuit and converter control device E can be constructed using a circuit almost similar to that described in connection with the circuit of FIG. 1, and operate in the same manner. That is, in synchronization with the rise of the drive signal Vl, when only the transistor 34 is controlled to turn on and off while the transistor 35 is off, the transistor 34 with the coil 51
Through the circuit including the capacitor 60, the diode 44, and the coil 52, the voltage E1 of the DC power supply 1 is boosted and applied to the piezoelectric element 2. Then, when the inter-terminal voltage E2 becomes larger than the absolute value of the reference voltage Et, the transistor 34 is turned off, and the piezoelectric element 2 is charged to the voltage Et. Next, in synchronization with the fall of the drive signal 1, when the transistor 34 is off and only the transistor 35 is turned on, a current flows through the circuit of the coil 52 and the transistor 35, and the charge in the piezoelectric element 2 is discharged. . Next, the voltage E between the terminals of the piezoelectric element 2
2 is approximately 0 volts, transistor 35 is turned off. When the transistor 35 is turned off, a current flows through the diode 45, the capacitor 60, the coil 53, and the diode 46 connected in parallel to the piezoelectric element 2 due to the back electromotive force generated in the coil 52, and the capacitor 60 is charged and the piezoelectric element 2 is charged. The charged electric charge is regenerated. FIGS. 3 and 4 show a drive circuit for a dot matrix printer. A DC-DC converter is shared by each piezoelectric element that drives each wire. The piezoelectric element 21 in the circuit CI is connected to the DC-DC converter CNV via a parallel circuit of a transistor 71 and a diode 81. And a circuit c2~ which is the same as the circuit C1 composed of the piezoelectric element 2I, the transistor 71, and the diode 81.
Cn are provided in the same number as each wire. transistor 7
1 is for selecting a piezoelectric element driven by a transistor that is turned on when a wire connected to the piezoelectric element 21 is driven. In addition, the diode 81 is connected after the impact of the wire is completed.
This is for bypassing the transistor 71 when regenerating the charge stored in the piezoelectric element 21 to the DC power supply l. The DC-DC converter CNV has a drive signal Vl
In synchronization with the rise of the drive signal Vl, only the transistor 31 or 34 is controlled on and off until the output voltage reaches a predetermined reference voltage, and then in synchronization with the fall of the drive signal Vl,
Only the transistor 32 or 35 is turned on until the voltage E2 between the terminals of the piezoelectric element 21 becomes approximately 0 volts. In this way, only the selected piezoelectric elements can be charged, and the charges charged in each piezoelectric element can be regenerated to the DC power supply 1 all at once. In any of the above embodiments, when charging the piezoelectric element 2, only the transistors 31 and 34, which are the switch elements of ml, are controlled on/off until the voltage Et at the terminal 17j'l of the piezoelectric element 2 reaches a predetermined reference value. However, transistor 3 is connected so that when one transistor is on, the other transistor is off, without providing a voltage detection circuit.
1 and the transistor 32 or the transistor 34 and the transistor 35 at a predetermined ratio. Alternatively, a predetermined inter-terminal voltage Et may be obtained by controlling the voltage Et. Further, as shown in FIG. 9, a coil 54 and a diode 43
．． 44 may be connected, and during regeneration (7) the DC-DC converter B may be configured with the transistor 32, the coils 53 and 54, and the diode 43. When charging the piezoelectric element 2, the duty of the transistor 31 is controlled at high frequency, so the smaller the inductance of the coil, the better.
During regeneration, the transistor 32 is made conductive once to perform regeneration during 1/4 cycle of LC resonance, so it is desirable that the inductance of the coil be large. In the four-channel configuration shown in FIG. 9, the coils 53 and 54 are connected in series during regeneration, so the inductance can be increased.

【Effect of the invention】

In the present invention, the piezoelectric element is driven using a DC-DC converter that can step up and down the voltage and transmit power bidirectionally, so the electric charge charged in the piezoelectric element during driving can be regenerated into the power source, and the electric power Increased efficiency. During regeneration, only the second switching element of the bidirectional DC-DC converter, which regenerates the power accumulated in the piezoelectric element into the DC power supply, is turned on once until the voltage between the terminals of the piezoelectric element becomes almost 0 volts. Therefore, switching loss during regeneration is suppressed.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a piezoelectric rope drive circuit according to a specific embodiment of the present invention. FIG. 2 is a circuit diagram of a Z piezoelectric element drive circuit according to another embodiment. 3 and 4 are circuit diagrams of a piezoelectric element drive circuit that selectively drives a plurality of piezoelectric elements. FIG. 5 is a circuit diagram of a DC-DC converter that is the basis of the drive circuit shown in FIG. m1. Figure 6 shows the basic driving circuit of Figure 2.
-Circuit diagram of DC converter. FIG. 7 is a circuit diagram of a conventional piezoelectric cable drive circuit. FIG. 8 is a timing chart illustrating the operation of the circuit shown in FIG. 1. FIG. 9 is a circuit diagram of a piezoelectric element drive circuit according to another embodiment. 1 DC power supply 2.21 Piezoelectric element 30.31.32
．． 33.34.35 ° Transistor 50.51.5
2 Coil 60-Capacitor 70 Comparator
81.83-AND gate 82-ND gate to N
84 Monostable multi-bi break 85 Analog switch C1 to Cn - Circuit patent applicant Brother Industries, Ltd. Figure 1 Figure 4 Figure 5 Figure 6 Figure 7

Claims (4)

[Claims] (1) A first switch element that is interposed between the piezoelectric element and the DC power source and performs a switching operation to supply power from the DC power source to the piezoelectric element, and regenerates the power accumulated in the piezoelectric element to the DC power source. a second switch element that performs a switching operation for the piezoelectric element, and that increases or decreases the voltage in response to a control signal and transmits power bidirectionally; When charging the piezoelectric element, the DC-DC converter is controlled to set the voltage between the terminals of the piezoelectric element to a predetermined value, and when discharging the piezoelectric element, the voltage between the terminals of the piezoelectric element is turned on after turning on the second switch element. a converter control device that turns off the second switch element when the voltage between the two switches reaches approximately 0V. (2) When charging the piezoelectric element, the converter control device controls the duty cycle of the first switching element and the second switching element so that the voltage between the terminals of the piezoelectric element becomes a predetermined value. A piezoelectric element driving device according to claim 1. (3) The converter control device includes a voltage detection circuit that detects a voltage between terminals of the piezoelectric element, and when charging the piezoelectric element, the voltage between the terminals detected by the voltage detection circuit reaches a predetermined value. 2. The piezoelectric element driving device according to claim 1, wherein only the first switching element is controlled to be turned on and off until the piezoelectric element is reached. (4) The piezoelectric element drive device according to claim 1, wherein the DC-DC converter is configured such that the inductance of the coil increases during regeneration.