JPH09201963A - Inkjet head drive - Google Patents

Abstract

(57) Abstract: In a drive device for an inkjet head using a piezoelectric vibrator, a rise time and a standby time fall time of a drive voltage waveform are constant regardless of changes in the voltage amplitude of the drive voltage waveform. To do so. SOLUTION: The operation time of a charge control signal and a discharge control signal is set in consideration of a difference between drive voltage waveforms before and after a power amplifier for each voltage setting value of a drive voltage.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving apparatus for an ink jet head using a piezoelectric vibrator.

[0002]

2. Description of the Related Art A conventional ink jet head driving device is disclosed in, for example, Japanese Unexamined Patent Publication No. 7-148920. FIG. 9 shows a circuit configuration of the driving device disclosed in Japanese Patent Application Laid-Open No. 7-148920.
By inputting the signals S1 and S2 shown in 0 (a) and (b), it is possible to change only the peak value (maximum voltage value) while keeping the rising time t1, the waiting time t2, and the falling time t3 constant. By generating the voltage signal Vs (FIG. 10D) and supplying the drive voltage signal Vs to the piezoelectric element of the inkjet head, stable ink ejection characteristics that are not affected by environmental temperature or the like are obtained. In addition, 10
(C) has shown the electric current waveform which flows into one piezoelectric element.

[0003]

However, the power amplifier 3
0 is the configuration shown in FIGS. 12A and 12B, and in detail, due to the influence of the base-emitter voltage of the transistor that constitutes the power amplifier 30, the input voltage waveform Vc of the power amplifier 30 and the output In the voltage waveform Vs, as shown in FIG. 11A, the voltage amplitude of Vs is reduced by VBE1 and VBE2. Here, VBE1 is the base-emitter drop voltage in the transistor TR20 shown in FIG. 12 or in the Darling-connected transistors TR20 and 22, and VBE2 is the transistor TR21 or the Darling-connected transistor TR21. 23
Is the base-emitter drop voltage at. In addition, FIG.
In the configuration of the power amplifier 30 shown in (a) to (d), VB
E1 is a base-emitter drop voltage of the transistor TR20, and VBE2 is a base-emitter drop voltage of the transistor TR21.

That is, the start of rising and the start of falling of the output voltage waveform Vs are delayed with respect to the input voltage waveform Vc. Input voltage waveform Vc depending on environmental temperature
If the voltage amplitude changes while the rising time t1, the waiting time t2, and the falling time t3 of the above are kept constant, the rising and falling slopes of the voltage change. Therefore, the output voltage waveform Vs
The delays of the rising start and the falling start of are not uniform. When the voltage amplitude of the input voltage waveform Vc is reduced, the output voltage waveform changes from Vs to Vs' as shown in FIG. 11 (b), the rising time t1 is t1 ', and the standby time t2 is t2'. t3 changes to t3 '. This fluctuation becomes more prominent as the rising and falling slopes of the voltage waveform are gentler and the voltage amplitude is smaller.

The signal S shown in FIGS. 14 (a) and 14 (b) is also used.
When S1 and S2 are input to the driving device of FIG. 9 to generate the output voltage waveform Vs shown in FIG. 14C to drive the piezoelectric element, the pressure chamber of the head is sufficiently expanded and ink is filled in the period I. Period II is a period for holding the volume of the pressure chamber and waiting for the return of the meniscus of the nozzle drawn in period I, period II
I is the period during which the pressure chamber is contracted to eject ink, period IV
And period V is a period in which the pressure chamber is expanded in accordance with the meniscus vibration period in order to suppress the generation of satellites due to the meniscus vibration after ink ejection. At this time, FIG.
When the head drive voltage is changed from Vs to Vs 'as shown in (d), the ratio of the voltage amplitude directly contributing to ink ejection becomes V1' / V1, but the period limited by the pulse length p1 of the S1 signal. Ratio V of the final sustain voltage (intermediate voltage) at V
2 '/ V2 becomes smaller than V1' / V1 and V2: V
1 and V2 ': V1' are not equal. Also, t6 'becomes shorter than t6, and t5' becomes longer than t5 by that amount.
Furthermore, since V2 '/ V1' is smaller than V2 / V1, the time to rise from V2 'to V1' becomes longer,
As a result, t4 'becomes shorter than t4.

The driving method shown in FIGS. 10 and 14 stabilizes the ink ejection characteristics in particular according to the behavior of the meniscus, but the above-mentioned fluctuations hinder the stable ink ejection characteristics. .

[0007]

In order to solve the above-mentioned problems,
In the inkjet head driving device of the present invention,
A constant voltage source whose output voltage is changeable, a charging constant current source for generating one or more constant currents proportional to the output voltage via the constant voltage source, and an operation of the charging constant current source A charging control signal for controlling the operation, a capacitor charged with a constant current from the charging constant current source, and a discharging constant current source for discharging the capacitor with one or more constant currents proportional to the output voltage. , A driving voltage generator configured by a discharge control signal for controlling the operation and non-operation of the discharging constant current source, and a driving voltage generated by the driving voltage generator for driving the piezoelectric vibrator. A power amplifier for amplifying the electric power, and using one or both of the charge control signal and the discharge control signal, the operating time of one or both of the charging constant current source and the discharging constant current source Output voltage of constant voltage source And setting according to.

The operating time pc of the charge control signal
The rising time of the driving voltage is tc, the charging time constant of the driving voltage at the output voltage of a certain constant voltage source is dV / dtc, and the voltage amplitude decrease in the power amplifier is Vc.
When BE, it is characterized in that it is set to a time equal to or longer than pc = tc + VBE / (dV / dtc).

The operating time pd of the discharge control signal
The falling time of the drive voltage is td, the discharge time constant of the drive voltage at the output voltage of the certain constant voltage source is dV / dtd, and the voltage amplitude decrease in the power amplifier is Vd.
When BE, it is characterized in that it is set to a time equal to or longer than pd = td + VBE / | dV / dtd |.

A time pchd between the operation start timing of the charge control signal and the operation start timing of the discharge control signal.
The drive voltage rise time is tc, the standby time between the drive voltage rise and fall is tchd, the charge time constant of the drive voltage at the output voltage of a certain constant voltage source is dV / dtc, and the discharge time constant is Is dV / dtd and the voltage amplitude decrease in the power amplifier is VBE, pchd = tc + tchd + VBE / (dV / dtc)
It is characterized in that it is set to −VBE / | dV / dtd |.

Also, a time pdhc between the operation start timing of the discharge control signal and the operation start timing of the charge control signal.
The falling time of the driving voltage is td, the waiting time between the falling and rising of the driving voltage is tdhc, the charging time constant of the driving voltage at the output voltage of the constant voltage source is dV / dtc, and the discharging time is When the constant is dV / dtd and the voltage amplitude decrease in the power amplifier is VBE, pdhc = td + tdhc + VBE / | dV / dtd |
It is characterized in that it is set to −VBE / (dV / dtc).

[0012]

Embodiments of the present invention will be described below.

FIG. 1 is a block diagram showing the configuration of the present invention.

The drive device of the present invention comprises a constant voltage source 11 for outputting a predetermined constant voltage Vk based on an input drive voltage setting signal, and a capacitor 14 with a constant current corresponding to the output voltage Vk of the constant voltage source 11. Constant current source 12 that charges the capacitor, a discharge constant current source 13 that discharges the capacitor 14 with a constant current according to the output voltage Vk of the constant voltage source 11, and a capacitor 14
The power amplifier 2 is connected to the terminal for current amplification and supplies the output voltage Vs of the power amplifier 2 to each piezoelectric element of the inkjet head 4. The inkjet head 4 has a temperature detection unit 41, and the detected temperature information is input to the control unit 3, and the control unit 3 outputs a drive voltage setting signal according to the input temperature information.
Further, the control unit 3 outputs charging control signals S1 and S2 for operating the charging constant current source 12 and the discharging constant current source 13.

FIG. 2 is a circuit diagram showing an example of the constant voltage source 11, and the IC 201 is a serial-parallel conversion IC.
8-bit transfer data S3-1 is input in synchronization with the transfer clock S3-2 and written by the strobe signal S3-3 at the timing shown in FIG.
The logic levels of ~ P7 are set. Incidentally, S3-4 is a clear signal for clearing the set data.

The resistors R206 to R221 are ladder resistors and are resistors R213 to R2 connected to the ports P1 to P7.
20 and the resistance R221 are set to twice the resistance values of the resistances R206 to R212.

A transistor Q2 is provided at one end of the resistor R212.
When the base terminal of 02 is connected and the logical levels of the ports P1 to P7 are set by the control unit 3, a predetermined base current flows to the transistor Q202 to conduct, and at the same time, a transistor complementary to the transistor Q202. Q2
03 becomes conductive, and the same voltage as the one end of the resistor R212 is generated in the resistor R201 connected between the transistor Q203 and GND. The voltage of the resistor R201 is input to the base terminal of the transistor Q204 that constitutes the differential amplifier circuit. The other transistor Q2 forming the differential amplifier circuit
A voltage obtained by dividing the output Vk by the resistors R204 and 205 is input to the base terminal of 05.
Therefore, assuming that the resistance value of the resistor R204 is r1 and the resistance value of the resistor R205 is r2, an output voltage Vk of Vk = VR201 (r1 + r2) / r2 is output. VR201 is resistor R2
01, that is, the voltage at one end of the resistor R212.

FIG. 4 is a circuit diagram showing an example of the charging constant current source 12 for charging and discharging the capacitor 14 and the discharging constant current source 13. In this example, S1-1 is used as the charge control signal.
And S1-2 as the discharge control signal.
Two types of 2-1 and S2-2 can be selected, and charging and discharging can be performed with two different types of constant current values. It is easy to select three or more constant current values with the same configuration.

The charging constant current source 12 charges the capacitor C401 from the output Vk of the constant voltage source through the transistor Q403, the resistor R404, and the transistor Q402 when the charging control signal S1-1 is set to the high level, for example. At this time, the emitter terminal voltage of the transistor Q402 changes the output voltage Vk of the constant voltage source 11 to the resistance R402 and the resistance R401.
The voltage value divided by is maintained. Therefore, the capacitor C
The current value Ichg of the charging constant current for charging 401 is R4
The resistance value of 01 is r3, the resistance value of R402 is r4, R40
Assuming that the resistance value of 4 is r5, Ichg = Vk × r3 / (r3 + r4) / r5 and a constant current proportional to the output voltage Vk. Therefore, the voltage Vc appearing across the capacitor C401 is a time constant dV.
Increases with a slope of / dtc. dV / dtc is the current value I
By chg and the capacitance c1 of the capacitor C401, dV / dtc = I chg / c1 = Vk × r3 / (r3 +
r4) / r5 / c1. Similarly, when the charge control signal S1-2 is used and the resistance value of the resistor R405 is r6, the constant current is Ichg = Vk × r3 / (r3 + r4) / r6, and the charging slope time constant dV / dtc is dV / dt = Ichg / c1 = Vk × r3 / (r3 + r
4) / r6 / c1.

The discharge constant current source 13 has the same operating principle as the charge constant current source 12, and when the discharge control signal S2-1 is set to a high level, for example, the transistor Q408, the resistor R417,
The electric charge of the capacitor C401 is discharged through the transistor Q409. At this time, similarly to the above, the transistor Q
The emitter terminal voltage of 408 is maintained at a voltage value obtained by dividing the output voltage Vk of the constant voltage source 11 by the resistors R414 and R415. Therefore, the current value Idis of the constant discharge current for discharging the capacitor C401 via the resistor R417 is R
The resistance value of 415 is r7, the resistance value of R414 is r8, R4
Assuming that the resistance value of 17 is r9, Idis = Vk × r7 / (r7 + r8) / r9 and a constant current proportional to the output voltage Vk is obtained. Therefore, the voltage Vc appearing across the capacitor C401 is a time constant dV.
It descends with a slope of / dtd. dV / dtd is the current value I
By dis and the capacitance c1 of the capacitor C401,
dV / dtd = Idis / c1 = Vk × r7 / (r
7 + r8) / r9 / c1. Similarly, the discharge control signal S
When 2-2 is used, the resistance value of the resistor R420 is set to r10.
Then, the constant current is Idis = Vk × r7 / (r7 + r8) / r10, and the discharge slope time constant dV / dtd is: dV / dtd = Idis / c1 = Vk × r7 / (r7 +
r8) / r10 / c1.

The power amplifier 2 is disclosed in Japanese Patent Application Laid-Open No. 7-148920.
Although either the configuration shown in FIG. 12 or the configuration shown in FIG. 13 can be used, the simplest configuration shown in FIG.
The case of using the circuit of 2 (a) will be described.

Next, the drive voltage Vs of the piezoelectric element when the charge control signal S1 and the discharge control signal S2 are output to the recording apparatus of the ink jet head having the above structure will be described.

As a first example, the control unit 3 outputs the charge control signal S1-1 and the discharge control signal S2-1 shown in FIG. 5 (the charge control signal S1-2 and the discharge control signal S2-2 are not used. ) Shows the case. Charge control signal S1-1
Then, the discharge control signal S2-1 is output for a sufficient time until the charge / discharge of the capacitor C401 is saturated.

The output voltage Vk of the constant voltage source 11 at this time is V
When k1 is set, the relationship between the input and output voltage waveforms of the power amplifier 2 is as shown in FIG. The thick solid line is the output voltage Vs, and the thin solid line is the input voltage Vc.

The output voltage (driving voltage) Vs rises by the voltage V1 at t1 time, holds the voltage for t2 time, and then reaches t3.
The voltage drops by V1 over time. Charge control signal S at this time
The operation time p1 of 1-1 is p1> t1 + (VBE1 + VBE2) / (dV / dt depending on the charging slope time constant dV / tc.
c) and the rising of the output voltage Vs is the charge control signal S
From the rising edge of 1-1, (VBE1 + VBE2) /
It is delayed by (dV / dtc) time.

The operating time p of the discharge control signal S2-1
Similarly, 2 is p2> t3 + (VBE1 + VBE2) / (dV / dt due to the discharge slope time constant dV / dtd.
d) and the fall of the output voltage Vs is the discharge control signal S
From the falling edge of 2-1 (VBE1 + VBE2) /
It is delayed by (dV / dtd) time.

Assuming that the standby time for holding the voltage amplitude V1 is t2, the time p3 from the rise of the charge control signal S1-1 signal to the rise of the discharge control signal S2-1 signal.
Is p3 = t1 + t2 + (VBE1 + VBE2) / (dV /
dtc)-(VBE1 + VBE2) / (dV / dtd).

Since the charging slope time constant dV / dtc and the discharging slope time constant dV / dtd increase / decrease in proportion to Vk by changing the output voltage Vk of the constant voltage source 11, when the output voltage Vk changes, the charging / discharging signal is changed. If the pulse times of S1-1 and S2-1 are constant, t1, t2, and t3 will change. However, the pulse time p3 is set to the charging slope time constant dV / t
As a function of c and the discharge slope time constant dV / td, the standby time t2 can be kept constant.

Specifically, the control unit 3 is provided with a table for p3 time corresponding to the voltage setting value of the drive voltage setting signal set in the constant voltage source 11, and at the same time when the output voltage Vs is changed, the charging control signal is set. This can be realized by changing the time p3 from the output start of the S1-1 signal to the output start of the discharge control signal S2-1 signal by referring to the table. When the table is actually created, if the pulse time p3 is set in consideration of the switching time of the transistor and the like, a more accurate output voltage Vs can be obtained.

Next, as a second example, FIG.
Charging control signal S1-1 and discharging control signal S2-1
Output (charge control signal S1-2, discharge control signal S2-2
Is not used). Discharge control signal S
2-1 outputs for a sufficient time until the discharge of the capacitor C401 is saturated, but the charge control signal S1-1
Is different from the first example in that the time width is such that the charging of the capacitor C401 does not reach saturation.

The output voltage Vk of the constant voltage source 11 at this time is V
When k1 is set, the relationship between the input and output voltage waveforms of the power amplifier 2 is as shown in FIG. The thick solid line is the output voltage Vs, and the thin solid line is the input voltage Vc.

In this case, since the p1 time is shorter than that in the first example, the output voltage Vs does not rise to the vicinity of Vk at the time t1 but rises by the voltage V2, and after the voltage is maintained for the time t2, the voltage is increased at the time t3. Decrease by V2. The operation time p1 of the charging control signal S1-1 at this time is the charging slope time constant dV.
/ Tc, p1 = t1 + (VBE1 + VBE2) / (dV / dt
c).

The operation time p of the discharge control signal S2-1
Similarly, 2 is p2> t3 + (VBE1 + VBE2) / (dV / dt due to the discharge slope time constant dV / dtd.
d).

Assuming that the standby time for holding the voltage amplitude V2 is t2, the time p3 from the rising of the charge control signal S1-1 signal to the rising of the discharge control signal S2-1 signal.
Is p3 = t1 + t2 + (VBE1 + VBE2) / (dV /
dtc)-(VBE1 + VBE2) / (dV / dtd).

Therefore, the pulse time p1 is a function of the charging slope time constant dV / tc, and the pulse time p3 is the charging slope time constant d.
If it is a function of V / tc and discharge slope time constant dV / td,
t1 and t2 can be kept constant. Further, since the voltage V2 is automatically adjusted by adjusting the pulse time p1, t3 is also maintained at a constant value. The pulse times p1 and p3 can be changed by the table provided in the control unit 3 as described above.

Next, as a third example, a case where the control section 3 outputs the charge control signals S1-1 and S1-2 and the discharge control signals S2-1 and S2-2 shown in FIG. 7 will be described. This corresponds to the conventional driving method shown in FIG.

The output voltage Vk of the constant voltage source 11 at this time is V
When k1 is set, the relationship between the input and output voltage waveforms of the power amplifier 2 is as shown in FIG. The thick solid line is the output voltage Vs, and the thin solid line is the input voltage Vc. Output voltage Vs
The second charging control signal S1 after rising by the voltage V2.
-2 is output and the voltage is raised to the voltage V1 by another constant current charging.

Here, the pulse time p1 is defined as p1 = t1 + (VBE1 + VBE2) / (dV / dt
c) is a function of the charging slope time constant dV / tc
The time can be made constant with respect to the fluctuation of Vk, and V2
Since the fluctuation of is also proportional to Vk, the ratio of V2 and V1 also approaches a constant value. Furthermore, since the ratio of V2 and V1 approaches a constant value, fluctuations in the waiting time t5 can be suppressed. Also, the discharge control signal S2
P4 time from the rise of the −1 signal to the rise of the charge control signal S1-1 signal is p4 = t3 + t4- (VBE1 + VBE2) / (dV /
By setting dtc) + (VBE1 + VBE2) / (dV / dtd), the standby time t4 also becomes constant with respect to the fluctuation of Vk.

In all of the above three examples, the output voltage V
It was a case where s rises from around 0 [V].
As an example, even if the output voltage Vs has the voltage waveforms shown in FIGS.
It is possible to perform correction such that the fall time, the standby time, and the rise time are constant by the same measure.

[0040]

As described above, in the ink jet head drive device of the present invention, the rise time, the standby time, and the fall time of the drive voltage waveform are kept constant with respect to variations in the voltage amplitude of the drive voltage. Therefore, an appropriate voltage waveform can be output at any drive voltage, ink droplet ejection is stabilized, and print quality is improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of the present invention.

FIG. 2 is a circuit diagram showing an example of a constant voltage source according to the present invention.

FIG. 3 is a diagram showing a voltage setting operation of the constant voltage source of the present invention.

FIG. 4 is a circuit diagram showing an example of a charge constant current circuit and a discharge constant current circuit of the present invention.

FIG. 5 is a timing chart showing a first operation example of the present invention.

FIG. 6 is a timing chart showing a second operation example of the present invention.

FIG. 7 is a timing chart showing a third operation example of the present invention.

FIG. 8 is a timing chart showing a fourth operation example of the present invention.

FIG. 9 is a block diagram showing a configuration of a conventional technique.

FIG. 10 is a diagram of input / output waveforms showing the operation of the conventional technique.

FIG. 11 is a diagram of input / output waveforms showing a problem of the conventional technique.

FIG. 12 is a circuit diagram of a power amplifier.

FIG. 13 is a circuit diagram of a power amplifier.

FIG. 14 is a diagram of input / output waveforms showing a problem of the conventional technique.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 drive voltage generator 2 power amplifier 3 control unit 4 inkjet head 11 constant voltage source 12 charge constant current source 13 discharge constant current source 14 capacitor 41 temperature detection unit

Claims (5)

[Claims] 1. A drive device for an inkjet head using a piezoelectric vibrator, wherein a constant voltage source whose output voltage is variable and one or more constant currents proportional to the output voltage are generated via the constant voltage source. A constant current source for charging, a charge control signal for controlling the operation and non-operation of the constant current source for charging, a capacitor charged with a constant current from the constant current source for charging, and the output voltage of the capacitor. A constant voltage source for discharging with a constant current of at least one kind proportional to the above, and a drive voltage generator configured with a discharge control signal for controlling the operation and non-operation of the constant current source for discharging, and the drive voltage A power amplifier for amplifying a drive voltage generated by a generator to a power required to drive the piezoelectric vibrator, and using one or both of the charge control signal and the discharge control signal, the charging constant Current source and front An ink jet head drive device, wherein one or both of the discharge constant current sources are set in operation time according to the output voltage of the constant voltage source. 2. The ink jet head drive device according to claim 1, wherein the operating time pc of the charge control signal is tc, the rising time of the drive voltage is tc, and the drive voltage at the output voltage of a certain constant voltage source is charged. Constant is dV /
dtc, when the voltage amplitude decrease in the power amplifier is VBE, it is set to a time equal to or longer than pc = tc + VBE / (dV / dtc). 3. The ink jet head drive device according to claim 1, wherein the discharge control signal has an operating time pd, a drive voltage falling time is td, and the drive voltage is discharged at the output voltage of a constant voltage source. Time constant is dV /
dtd, where VBE represents a voltage amplitude decrease amount in the power amplifier, an ink jet head drive device is set to a time equal to or longer than pd = td + VBE / | dV / dtd |. 4. The inkjet head driving device according to claim 1, wherein a time pchd between an operation start time of the charge control signal and an operation start time of the discharge control signal is set to:
The rising time of the driving voltage is tc, the waiting time between the rising and falling of the driving voltage is tchd, the charging time constant of the driving voltage at the output voltage of a certain constant voltage source is dV / dtc, and the discharging time constant is dV. / Dtd, where VBE is the voltage amplitude decrease in the power amplifier: pchd = tc + tchd + VBE / (dV / dtc)
A drive device for an inkjet head, which is set to −VBE / | dV / dtd |. 5. The inkjet head driving device according to claim 1, wherein a time pdhc between an operation start timing of the discharge control signal and an operation start timing of the charge control signal is
The falling time of the driving voltage is td, the waiting time between the falling and rising of the driving voltage is tdhc, the charging time constant of the driving voltage at the output voltage of a certain constant voltage source is dV / dtc, and the discharging time constant is dV / dtd, where VBE is the voltage amplitude decrease in the power amplifier: pdhc = td + tdhc + VBE / | dV / dtd |
An inkjet head driving device characterized by being set to −VBE / (dV / dtc).