JPH0262249A - Drive for piezoelectric actuator - Google Patents

Abstract

PURPOSE:To obtain characteristics optimum for the conditions of the vibrations of the mechanical system of a section to be driven by conducting control in response to a set value read from the memory of the set value of the charging currents or discharging currents of a piezoelectric element driven by an excitation power supply. CONSTITUTION:The ideal displacement curves of the mechanical system of a piezoelectric actuator at the time of the charge and discharge of a previously used piezoelectric element 8 are acquired, the curves are stored successively in addresses in memories 14a, 14b in digital values, and read at every generation of pulses by a pulse signal from a memory reading mechanism 15. The digital output signals of the memories 14a, 14b are converted respectively into analog signals by D/A converters 16a, 16b, and applied separately to one input terminals of comparators 17a, 17b. Current limiting mechanisms are installed respectively to the charging circuit and discharging circuit of the piezoelectric element 8, a measuring signal from a measuring mechanism 19 for the mechanisms is transmitted separately to the other input terminals of the comparators 17a, 17b, and ON-OFF switches 18a, 18b are controlled by outputs from the input terminals.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a piezoelectric actuator drive device that drives a printer head using a piezoelectric element.

(Prior Art) This type of conventional piezoelectric actuator drive device is driven by the circuit shown in FIGS.
(Refer to Publication No. 198885). In FIGS. 3 and 4, 1 is a drive signal input terminal, 2.4.6 is a transistor,
3 and 12 are resistors, 11 and 13 are diodes, 7 is a coil, 8 is an electrostrictive element or piezoelectric element, 9 is an excitation mechanism, and 10 is an inverter. In the circuit shown in FIG. 3, a drive signal with a frequency of, for example, several kHz, which continues at a constant period as shown in FIG. , and this drive signal is inverted by the inverter 10 and applied to the transistor 6 at the same time, the transistor 6 becomes non-conductive, and the signal is transmitted from the excitation voltage input terminal 5 to the piezoelectric element 8 via the resistor 12 as shown in FIG. 5(b).
A current I as shown in FIG. 5 flows through the piezoelectric element 8 as shown in FIG.
A voltage {circle around (2)} as shown by C1 is applied to drive the piezoelectric element 8, and the tip of the enlarged frame of the excitation mechanism 9 connected to the piezoelectric element 8 is displaced by β as shown in FIG. 5fd).

Further, after the above-mentioned fixed period, the transistors 2 and 4 become non-conductive and the transistor 6 becomes conductive, so that the residual charge in the piezoelectric element 8 is discharged from the transistor 6 to the ground via the resistor 12.

The capacitor component of the piezoelectric element 8 is quite large, as shown in Figure 5 (
As shown in b), the current 1c becomes an excessive charging current at the rising edge of the drive signal. Similarly, the discharge current becomes excessive at the falling edge of the drive signal. On the other hand, the tip of the enlarged frame of the excitation mechanism 9 becomes as shown in FIG.

Similarly, when driving with the circuit shown in Fig. 4, the excitation voltage input terminal 5 is connected to the piezoelectric element 8 via the coil 7 as shown in Fig. 6(b).
A current as shown in■. flows into the piezoelectric element 8 as shown in Fig. 6 (
A voltage (2) as shown in cl is applied to drive the piezoelectric element 8, and the tip of the enlarged frame of the excitation mechanism 9 connected to the piezoelectric element 8 is displaced by l as shown in FIG. 6 (dl).

Further, after the above-mentioned fixed period, the transistors 2 and 4 become non-conductive and the transistor 6 becomes conductive, so that the residual charge in the piezoelectric element 8 is discharged from the transistor 6 to the ground via the resistor 12.

This charging/discharging current for the piezoelectric element 8 becomes a resonant current of a series resonant circuit formed by an inductance component of the coil 7 and a capacitor component of the piezoelectric element 8.

Therefore, the current 1c does not become excessive even if the drive signal is at a high (H) level. However, as a characteristic of the resonant circuit, the electric charges flowing into the piezoelectric element 8 are extracted from the piezoelectric element 8 and recovered to the power supply side via the diode 13 because the voltage of the coil 7 is reversed from positive to negative. However, the charge flowing into the piezoelectric element 8 is transferred to the coil 7, the piezoelectric element 8, and the transistor 4.
Since the resonance vibration is attenuated by the resistance component of the circuit and the resistance component of the circuit, not all of the vibration is recovered. The charge remaining in the piezoelectric element 8 is grounded via the coil 7 and the resistor 12 when the transistor 6 is turned on by setting the drive signal to a low (L) level.

In addition, FIGS. 7(a) and (b) show the printer head, and 2
0 is a frame body to which the piezoelectric element 8 is attached, 21a and 21b are first actuating rods, and 22.23 are first and second actuating rods, respectively.
24 is a second operating rod, and 25 is a printing wire.

FIG. 8 is an explanatory diagram of the operating state of this printer head.

This operating condition also exists in the direction perpendicular to the plane of FIG.

(Problems to be Solved by the Invention) As described above, the tip of the enlarged frame of the excitation mechanism 9 is displaced as shown in FIG. 5(d) and FIG. 6(d). Such a displacement curve is usually different from the ideal displacement curve of the mechanical system of the piezoelectric actuator including the piezoelectric element, the excitation mechanism, etc., and it is also possible to change the resistance 12 and coil 7, etc. whose characteristics are electrically determined. It is extremely difficult to create an ideal curve in the mechanical system.

Therefore, energy transmission efficiency, impact force, stroke, and response speed cannot be maximized.

Furthermore, when the piezoelectric element 8 is discharged, an overshoot may occur in the mechanical system depending on the case, resulting in various drawbacks such as the print head performing a printing operation incorrectly.

An object of the present invention is to compensate for the above-mentioned drawbacks and to obtain characteristics that are optimal for the vibration conditions of the mechanical system of the driven part.

(Means for Solving the Problems) A piezoelectric actuator drive device of the present invention includes a piezoelectric element driven by an excitation power source, a memory for the charging current or discharging current setting value of the piezoelectric element, and a piezoelectric actuator drive device that is operated according to a drive signal. It is characterized by comprising a mechanism for reading out the set value from the memory, and a charging current or discharging current control mechanism for the piezoelectric element that is controlled according to the set value read by this mechanism.

Further, the piezoelectric actuator drive device of the present invention includes a piezoelectric element driven by an excitation power source, a memory for charging current and discharging current setting values of the piezoelectric element, and reading out the setting values from the memory when actuated in accordance with a drive signal. a mechanism, a mechanism for detecting the charging current of the piezoelectric element, a comparator for comparing a detection value from the detection mechanism with the charging current setting value, and a piezoelectric element controlled according to the comparison result of the comparator. a charging current control mechanism, a mechanism for detecting the discharging current of the piezoelectric element, a comparator for comparing the detected value from the detecting mechanism and the discharging current set value, and control according to the comparison result of the comparator. The invention is characterized by comprising a discharge current control mechanism for a piezoelectric element.

(Example) The present invention will be explained in detail below with reference to the drawings.

In the present invention, as shown in FIG. 1, ideal displacement curves of the mechanical system of the piezoelectric actuator during charging and discharging of the piezoelectric element 8 used are determined in advance using a simulator, and these curves are stored in memory. 14a, 14b
The memory 14a stores digital values sequentially at addresses within the memory 14a.

14b from the memory reading mechanism 15, for example in FIG.
The address is read out sequentially from address No. 1 every time a pulse is generated by a pulse signal of several 10 Mf (z) shown at a+.

This memory reading mechanism 15 generates a pulse signal in response to the rise of the drive signal shown in FIG. 2 (bl), continues until the fall of the drive signal, and repeats this cycle thereafter.

FIG. 2 (C1 shows the digital output signal thus read out from the memories 14a, 14b).

The digital output signals of the memories 14a and 14b are respectively D.
/A converters 16a and 16b convert the signals into analog signals, and comparators 17a, respectively.

17b to one input terminal.

The analog signals become curves shown by solid lines and dotted lines, for example, in FIG. 2 fd), which represent ideal displacement curves of the mechanical system.

In the present invention, a current limiting mechanism, for example, ON-OFF switches 18a and 18b, is further inserted in the charging circuit and discharging circuit of the piezoelectric element 8, respectively, and a charging/discharging current measuring mechanism 19 is provided in the charging/discharging circuit of the piezoelectric element 8, The measurement signals from this measurement mechanism 19 are applied to the other input terminals of the comparators 17a and 17b, respectively, and the outputs of the comparators 17a and 17b turn off the ON-OFF switches 18a and 1, respectively.
8b.

Since the piezoelectric actuator drive device of the present invention has the above configuration, it operates as follows.

When the piezoelectric element 8 is charged via the 0N-OFF switch 18a or discharged via the 0N-OFF switch 18b, the charging/discharging current of the piezoelectric actuator 8 changes with time, for example, as shown in FIG. ) as shown by the solid and dotted lines.

First, when the value from the measuring mechanism 19, that is, the charging/discharging current of the piezoelectric element 8 is zero, the D/A converter 16a.

The analog outputs from 16b are shown in FIG. 2(e).

As shown in <n, the values are set to be sufficiently lower and sufficiently higher than zero.

The digital output signal just read out from the memory 15 is D/
It is converted into an analog signal by the A converter 16a and compared by the comparator 17a, and as a result, the 0N-0FF switch 1
8a turns on and a charging current flows through the piezoelectric element 8,
As shown in FIG. 2(d), if the output of the measuring mechanism 19 that measures the charging current of the piezoelectric element 8 increases and this value becomes higher than the value of the D/A converter 16a that indicates the ideal displacement curve, then An output is generated in the comparator 17.8, and this output causes the ON-OFF switch 1 to be turned on as shown in FIG.
8a is turned off, and charging of the piezoelectric element 8 is stopped. Therefore, in this state, the value of the measuring mechanism 19 remains unchanged. However, as time passes and the value from the D/A converter 16a exceeds the value from the measuring mechanism 19, the comparator 17a does not output an output, and the 0N-OF
The F switch 18a is turned on, the output value of the measuring mechanism 19 increases, and this operation is repeated to increase the output value of the measuring mechanism 1.
The output of 9 has a step change as shown in FIG. 2(d).

When the piezoelectric element 8 discharges, the same operation is repeated and the ON-OFF switch 18b is turned off as shown in FIG. 2(h).
is controlled, and as a result, the mechanical system of the piezoelectric actuator can be driven according to its ideal displacement curve.

In the piezoelectric actuator drive device of the present invention, the comparators 17a, 17b and the charging/discharging current measuring mechanism 19 may be omitted, and the charging/discharging circuit of the piezoelectric element 8 is directly controlled by the analog output of the D/A converters 16a, 16b. In this case, the 0N-OFF switch 18
For example, transistors are used as a and 18b, respectively,
The collector and emitter of this transistor may be inserted into the charging circuit and the discharging circuit, respectively, and the analog signals from the D/A converters 16a, 16b may be directly applied between the base and emitter of the transistor.

(Effects of the Invention) According to the piezoelectric actuator drive device of the present invention, charging and discharging of the piezoelectric element can be arbitrarily controlled so that the displacement of the mechanical system of the piezoelectric actuator follows an ideal displacement curve, and energy transfer efficiency is achieved. , impact force and stroke,
The response speed can be maximized.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a piezoelectric actuator drive device of the present invention, FIGS. 2(a) to (hl are waveform diagrams of each part thereof, and FIGS. 3 and 4 are circuit diagrams showing a conventional piezoelectric actuator drive device, respectively. , Fig. 5(a) to (d), Fig. 6(a) to
(d+ is the waveform diagram of each part, Fig. 7 fa), (
b) is a front view and a plan view of the printer head, respectively, and FIG. 8 is an explanatory diagram of its operating state. DESCRIPTION OF SYMBOLS 1... Drive signal input terminal, 2, 4.6... Transistor, 3, 12... Resistor, 5... Excitation voltage input terminal, 7... Coil, 8... Piezoelectric element, 9 . . . Excitation mechanism, 10 . 17b... Comparator, 18a, 18b... Current limiting mechanism (ON-OFF switch), 19... Measuring mechanism, 2
0... Frame body, 21a, 21b... First operating rod, 2
2.23... Leaf spring, 24... Second operating rod, 25
...Printing wire. Agent Patent Attorney Makoto Sawagi - O 1F■o1-C Neiro Ago

Claims (4)

[Claims] 1. a piezoelectric element driven by an excitation power source, a memory for a charging current setting value of the piezoelectric element, and a mechanism operated in response to a drive signal to read the setting value from the memory;
A piezoelectric actuator drive device comprising: a charging current control mechanism for a piezoelectric element that is controlled according to the set value read by the mechanism. 2. a piezoelectric element driven by an excitation power source; a memory for charging and discharging current settings of the piezoelectric element; a mechanism operated in response to a drive signal to read out the setting values from the memory; A piezoelectric actuator drive device comprising a piezoelectric element charging current and discharging current control mechanism that is controlled according to a set value. 3. a piezoelectric element driven by an excitation power source, a memory for a charging current setting value of the piezoelectric element, and a mechanism operated in response to a drive signal to read the setting value from the memory;
A mechanism for detecting the charging current of the piezoelectric element, a comparator for comparing the detection value from the detection mechanism with the set value, and a charging current control mechanism for the piezoelectric element that is controlled according to the comparison result of the comparator. A piezoelectric actuator drive device comprising: 4. A piezoelectric element driven by an excitation power supply, a memory for charging current and discharging current setting values of the piezoelectric element, a mechanism operated according to a drive signal to read the setting value from the memory, and a charging current for the piezoelectric element. a comparator that compares the detection value from the detection mechanism with the charging current set value; a charging current control mechanism for the piezoelectric element that is controlled according to the comparison result of the comparator; A mechanism for detecting the discharge current of the element, a comparator for comparing the detection value from the detection mechanism with the discharge current setting value, and a discharge current control mechanism for the piezoelectric element that is controlled according to the comparison result of the comparator. A piezoelectric actuator drive device comprising: