JPH06127034A - Device for driving piezoelectric element - Google Patents

Abstract

PURPOSE:To reduce an instantaneous current and instantaneous power without being accompanied by the deterioration of printing quality by driving a large number of piezoelectric elements in a time sharing manner by a drive circuit having a simple constitution. CONSTITUTION:Piezoelectric element groups 11a, 11b, 11c, 11d are connected to arbitrary waveform generating means 10a, 10b for generating arbitrary waveforms having a predetermined phase difference and for driving respective groups. By driving the piezoelectric element groups 11a, 11b, 11c, 11d in a time sharing manner, an instantaneous current and instantaneous power can be suppressed low.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric drive device having an electrostrictive effect used in an actuator such as an ink jet or wire dot printer.

[0002]

2. Description of the Related Art In recent years, piezoelectric materials (those having an electrostrictive effect such as PZT) have been widely applied to actuators for print heads such as ink jet and wire dot printers. For example, JP-A-2-274554, JP-A-3-36036, and JP-A-3-133647 have been disclosed as examples in which the technique of driving a piezoelectric body is applied to an ink jet printer. Figure 9
Will be described with reference to FIG.

In FIG. 9, reference numeral 1 is a scanning voltage generating means for periodically generating a predetermined scanning voltage Vs with low impedance. Reference numeral 2 is a piezoelectric material, and 3 is a scanning voltage generating means 1 on the piezoelectric material 2.
Is a gate which is energized in both directions for applying the scanning voltage Vs. Reference numeral 4 is a drive signal generating means for applying a control signal to the gate 3 by the print data in synchronization with the scanning voltage generating means 1.

FIG. 10 is an operation waveform diagram for explaining the circuit operation of FIG. (a) is a waveform of the scanning voltage Vs generated by the scanning voltage generating means 1. The ink chamber is gradually expanded and ink is drawn in during the rising process of the scanning voltage Vs, and the ink chamber is rapidly compressed during the falling process of the scanning voltage Vs. In order to eject the ink, a predetermined waveform is generated in synchronization with the printing cycle. (c) shows the voltage applied to the piezoelectric body 2 when the conduction signal at the timing shown in (b) is input to the gate 3. (d) shows the charging / discharging current due to the parasitic capacitance of the piezoelectric body 2, the flowing current and the current direction depending on the change rate of the applied voltage,
It shows the difference in time. Although not described in detail, the polarity or waveform shape of the scanning voltage Vs is determined by the characteristics of the piezoelectric body.

[0005]

In an ink jet printer that discharges ink by using such a piezoelectric material, in the case of a piezoelectric material composed of a single layer, a scanning voltage of 100 V or more is required to obtain a necessary displacement. The parasitic capacitance is about 500 pF, and in the case of a piezoelectric body formed by stacking, the scanning voltage is 20 V or more and the parasitic capacitance is several tens nF. If the current flowing into one piezoelectric body is i, the parasitic capacitance of the piezoelectric body is C, and the time change rate of the scanning voltage is dV / dt, then i = C × dV / dt, so the power loss PL due to charge / discharge is If the repetitive frequency absorption coefficient of the scanning voltage is f, then PL = C × V ² × f. That is, the power loss PL increases as the repetition frequency f increases.

By the way, in recent years, there has been a demand for a printer capable of printing closer to the print type and recording closer to the original image in the graphic, and for this reason, it is necessary to increase the dot density to be formed. If the dot density is increased, the character / image forming speed will be reduced unless the response frequency of the actuator is increased. Therefore, the number of dots n formed at one time must be increased and the response frequency f must be improved. Therefore, the instantaneous current and the power loss increase as a whole. More specifically, when the piezoelectric bodies are driven at the same time, the instantaneous current becomes tens of amperes and the instantaneous power becomes hundreds of watts. However, the average power is only several tenths of watts or tens of watts.

In the prior art, when the number of piezoelectric bodies is increased or the driving frequency is increased, the instantaneous current or the power is increased to cause an excessive load on the power supply device, a switch element having a large capacity is required, and line drop is considered. Therefore, there is a problem that it is necessary to increase the wiring capacity. Further, due to these problems, the printing conditions vary, and the printing quality is impaired.

The present invention has been conceived in order to solve such a problem. An object of the present invention is to provide a plurality of arbitrary waveform generators having a simple adjusting means and to provide a large number of piezoelectric bodies. By providing multiple power supplies for each piezoelectric block to apply a predetermined waveform voltage to each piezoelectric block, and driving each piezoelectric block in a time-division manner, instantaneous power or current can be obtained. It is an object of the present invention to provide a piezoelectric body driving device having a reduced simple structure.

[0009]

In order to solve such a problem, a piezoelectric body driving apparatus of the present invention is a piezoelectric body driving apparatus that drives N × M piezoelectric bodies, and Arbitrary waveform generating means for generating M or M integers for generating different drive waveforms, and corresponding to these arbitrary waveform generating means, the N × M piezoelectric bodies in units of N Divide into groups and selectively apply the drive waveform of the M or M integer arbitrary waveform generating means to the N × M piezoelectric bodies.
× M switch means, a timing signal for giving a generation timing to the M or M integer arbitrary waveform generating means, and a printing data to the N × M switch means in synchronization with the timing signal. And a control means for giving a control signal by a computer.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram showing a concrete block configuration in an embodiment of the present invention. Piezoelectric body for illustration simplicity
11 illustrates a case where 11 is divided into 4 groups and driven by two waveform generators 10 that generate two scanning voltages (or common driving voltages).

As shown in FIGS. 2A and 2B, the waveform generators 10a and 10b generate scanning voltages Vsa and Vsb having two troughs and peaks in one printing cycle and having mutually different phases. The switches 12a, 12b, 12c, 12d are provided corresponding to the piezoelectric members 11a, 11b, 11c, 11d divided into groups, and one of which is capable of conducting current in both directions is connected to GND. The control unit 13 uses A1 and A2 that represent line or timing signals.
The waveform generators 10a and 10b generate scanning signals at a predetermined timing, and control signals are applied to the switches 12a, 12b, 12c, 12d by the print data placed on the print data lines 13a, 13b, 13c, 13d. . As a result, ink is ejected. Since the ejection timing differs among the four groups, although not shown, the ink ejection port of the print head is arranged so as to be displaced from the reference ejection port by 1/4 of the printing interval in the print head scanning direction.

FIG. 2 shows the operation or state of each part in FIG.
Is. 2 (c), (d), (e), and (f) show timings for controlling the switches 12a, 12b, 12c, 12d at timings different from each other. 2 (g), (h), (i), and (j) are piezoelectric bodies 11a, 11b, 11
It represents the current flowing into c and 11d, and since the phases are different, the instantaneous current and instantaneous power are reduced. However, the power consumption does not change.

2 (k) and 2 (l) show the current flowing into the piezoelectric body 11 and the current flowing out of the piezoelectric body 11 as a whole.

As a result, the power supply for supplying power to the waveform generator 10 needs to be able to supply a much smaller instantaneous current / instantaneous power than the power supply conventionally required, and thus has a feature that it can be constructed at a much lower cost than before.

Although FIG. 1 has explained four time division driving with two waveform generators, one printing cycle is, for example, 10 kHz to 20 k.
When it becomes Hz, the piezoelectric body driving time is 1/10 kHz
Since the driving time becomes 2 and the driving time becomes short, the phase is shifted by using 4 waveform generators and 4 scanning voltages are generated to 4
Execute time division drive.

In FIG. 1, the common terminal of the switch 12 is connected to GND.
Although the switch 12 and the piezoelectric body 11 may be interchanged, the common terminal of the switch 12 may be connected to the waveform generator 12. The configuration of the bidirectional switch 12 may be one in which the main poles of complementary transistor pairs are connected in parallel, or one in which a diode is added to the main poles of the transistors. This is the so-called transfer gate.

Next, a specific circuit configuration of the waveform generator 10 will be described with reference to FIG. In FIG. 3, the capacitor 21 is charged / discharged by the bidirectional constant current source 20, the voltage generated in the capacitor 21 is made into a predetermined scanning voltage waveform, and the power is amplified by the amplifier 22 of the emitter follower composed of complementary transistor pairs. The configuration is one waveform generator. Similarly, the other waveform generator is composed of a bidirectional constant current source 23, a capacitor 24, and an emitter follower amplifier 25 composed of complementary transistor pairs. OT1 and OT2 are the output terminals for the scanning voltages Vsa and Vsb, and A1 and A2 are the capacitors 21,
This is a signal terminal for switching the charging / discharging direction to 22.

The constant current source circuit for charging the capacitor 21 has a resistor 31a, a PNP type transistor 30a, a reference voltage and a feedback voltage from the resistor 31a, and an error to amplify the error.
Operational amplifier 3 applied to the base of transistor 30a via
4a and. The constant current source circuit that discharges the capacitor-21 is a resistor 31b, an NPN transistor 30b,
It is composed of an operational amplifier 34b which amplifies the error by comparing the reference voltage with the feedback voltage from the resistor 31b and gives it to the base of the transistor 30b via the resistor 33b. The constant current value can be determined by the reference voltage and the values of the resistors 31a and 41a. Since the current stopping circuit of the other waveform generator is exactly the same, its explanation is omitted.

If the constant current source is constructed in this way, the resistors 31a,
The voltage generated on 41a, 31b and 41b becomes the same as the reference voltage,
The currents flowing through the transistors 30a, 40a and 30b, 40b are constant. The direction switching of the bidirectional constant current sources 20 and 23 is performed by changing the signal logic input to the timing signals A1 and A2.

The reference voltage is generated by a variable resistor 50a, a resistor 51 and a variable resistor 50b connected in series between the power source VP and GND, and distributed to the operational amplifier of each constant current source by the signal lines 52a and 52b. In the present invention, even if the number of constant current sources is increased, one set of reference voltage power sources may be used, and the current accuracy of each constant current source is resistors 31a, 41a and 31b, 4.
It is determined by the accuracy of 1b, and there is no variation between constant current sources. Further, since the accuracy of the capacitors 21 and 24 can be adjusted to several percent or less, the inclination angles of the scanning voltages Vsa and Vsb can be set to several percent or less, and all the piezoelectric bodies are driven in substantially the same manner. If the variation is more than a predetermined value, the speed and timing of ink ejection will change and the print quality will deteriorate.

FIG. 4 shows operation waveforms or states of the respective parts of FIG. 4 (a) to 4 (e) are diagrams of the waveform generator 10a, and FIGS. 4 (f) to 4 (j) are diagrams of the waveform generator 10b. In FIG. 4, one printing cycle = (t1 + t2) × 2. (a) and (f) show the charging / discharging voltage of the capacitors 21 and 24 or the scanning voltages Vsa and Vsb. (b) and (g) are timing signals
In A1 and A2, (c) and (h) are time width τ2 and capacitors -21 and 24
Shows the discharge current for discharging the. (d) and (i) are signals A1
(E) and (j) are the anti-phase timing signals of A2 and A2, respectively, and show the charging current for charging the capacitors -21 and 24 in the time width τ1.

Next, another embodiment in which the constitution of the constant current source is easily integrated into an IC (integrated circuit) will be described with reference to FIG. Similarly to FIG. 3, FIG. 5 will be described in the case of forming two bidirectional constant current sources.
FIG. 5 shows a so-called current mirror configuration. P-type FET
(Field effect transistor) If the characteristics of 62, 65a, and 70a are made to be almost the same, FET62 in which the drain and the gate are directly connected
If the drain voltage of is connected to the gates of FETs 65a and 70a,
The drain currents of 65a and 70a are regulated by a current determined by the variable resistor 63 and the FET 62 with a variation of several% or less, and serve as a constant current source. Similarly, if the characteristics of the N-type FETs 64, 65b, and 70b are made to be almost the same, the FET 65 is generated by the current determined by the variable resistor 61 and the FET 61.
The drain currents of b and 70b are constant currents. The signals A1 and A2 are
Level conversion is performed by the level converters 67 and 72, and the signals are given to the control electrodes of the transfer gates 66a and 71a and the control electrodes of the transfer gates 66b and 71b directly via the inverters 68 and 73, respectively.
The constant current source for charging or discharging is activated by the logic of A1 and A2. In FIG. 5, the parts after the dotted frame 60, which is easy to integrate into an IC, are the same as those in FIG. It is easy to make the transistor characteristics uniform on the same silicon wafer.

Next, although there are few waveform generators using the constant current source shown in FIGS. 3 and 5, there are adjustment points.
~ 8 will be described.

FIG. 6 shows a basic unit 90 of the waveform generator, 91 is a clock, and 93 is a frequency divider for dividing the clock 91. Reference numeral 94 is an addition / subtraction counter that counts the output from the frequency divider 93. Data for changing the frequency division ratio of the frequency divider 93 and data for controlling the start and stop of counting of the counter 94 are placed on the data line 92, and the frequency divider 3 and the counter 94 are made to latch the data.

Reference numeral 95 is a level converter for converting the level of each bit data of the counter 94 into the power supply voltage Vp. A D / A converter 96 performs D / A (digital-analog) conversion on each bit data whose level has been converted. OT is an output or output terminal converted into analog. FIG. 7 shows the waveform of this output OT. The time width τ1 is an addition count and the time width τ2 is a subtraction count, and these time widths are changed by changing the division ratio of the frequency divider 93. The counting pause section is the maximum value and the minimum value of the counter 94, and the pause section is determined by another means although not shown.

The capacity of the counter 94 may be about 3 bits or more, and the stepped shape of the output OT may be smoothed by a capacitor before power amplification.

FIG. 8 shows an example in which two basic units 90 shown in FIG. 6 are used as the waveform forming section 100 to form a waveform generator. The capacitors 101a and 101b are smoothing capacitors. The controller 102 generates the clock 91 and the controller 13 of FIG.
It is the same except for the generation of the control signal on the data line 92. The waveform forming section 100 is not only easy to be integrated into an IC, but naturally has the effect that there is no variation between the basic units because it is digitally controlled.

[0028]

According to the above-described structure of the present invention, a large number of piezoelectric bodies are grouped and driven in synchronization with the phase-shifted scanning voltages of a plurality of waveform generators having a simple structure. Therefore, it is possible to reduce the instantaneous current and the instantaneous power. Also, there is little variation in the driving conditions so that the printing quality is not deteriorated even with a large number of nozzles. At the same time, the large-capacity element is not required and the cost is reduced. The effect is tremendous.

[Brief description of drawings]

FIG. 1 is a diagram showing a specific block configuration according to an embodiment of the present invention.

FIG. 2 is a diagram showing operation timings and operation waveforms of respective parts in FIG.

FIG. 3 is a diagram showing a specific circuit configuration of a waveform generator used in the present invention.

FIG. 4 is a diagram showing operation waveforms in FIG.

FIG. 5 is a diagram showing another specific circuit configuration of the waveform generator used in the present invention.

FIG. 6 is a diagram showing a configuration of a basic unit in which the configuration of the waveform generator used in the present invention is digitally executed.

FIG. 7 is a diagram showing an output waveform of the basic unit shown in FIG.

8 is a diagram showing an example in which a waveform generator is configured using the basic unit of FIG.

FIG. 9 is a diagram showing an example of a conventional technique.

FIG. 10 is a diagram showing operation waveforms in FIG. 9.

[Explanation of symbols]

 1 ... Scan voltage generating means 4 ... Drive signal generating means 2, 11a, 11b, 11c, 11d ... Piezoelectric bodies 10a, 10b ... Waveform generators 20, 23, 60 ... Constant current source 90 ... Basic unit 100 ... Waveform forming section 34a , 34b, 44a, 44b ... Operational amplifiers 66a, 66b, 71a, 71b ... Transfer gates 12a, 12b, 12c, 12d ... Bidirectional switches 13, 102 ... Control section 22, 25 ... Amplifiers 67, 72, 95 ... Level conversion Unit 93… Divider 94… Counter 96… D / A converter 21, 24… Capacitor − Vp… Power supply voltage GND… Ground Vs, Vsa, Vsb… Scan voltage OT, OT1, OT2… Output terminals A1, A2… Timing signal

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Reference number within the agency FI Technical display location B41J 2/30 H01L 41/09 9211-2C B41J 3/10 114 D 9274-4M H01L 41/08 K

Claims (3)

[Claims] 1. A piezoelectric body driving device for driving N × M piezoelectric bodies, wherein M or M arbitrary waveform generating means for generating driving waveforms having mutually different phases, Corresponding to these arbitrary waveform generating means, the N × M piezoelectric bodies are divided into M groups with N as a unit, and the M or M integer fractional arbitrary waveform generating means N × M switch means for selectively applying the drive waveform of the N × M piezoelectric body, and a timing signal for giving the generation timing to the M or M integer waveform division means And a control means for applying a control signal based on print data to the N × M switch means in synchronism with the timing signal. 2. The M or M integer-arbitrary arbitrary waveform generating means, a bidirectional constant current source pair, a capacitor for charging and discharging with a current from the bidirectional constant current source, and the capacitor. 2. The piezoelectric body drive device according to claim 1, further comprising a power amplification means for power-amplifying the charge / discharge voltage of −. 3. The M or M integer arbitrary waveform generating means, a counter, a modulating means for modulating an input clock of the counter, and digital-analog conversion of output data of the counter. 2. The piezoelectric body driving apparatus according to claim 1, further comprising: a D / A converter for performing power conversion, and power amplification means for power-amplifying an analog amount of the D / A converter.